Kit and method for simultaneous electrochemical determination of at least two protein analytes Field of Art The present invention relates to a kit and method for simultaneous determination of two or three protein analytes, using an electrochemical technique. Background Art The composition of body fluids, such as blood, plasma, cerebrospinal fluid, lymph, effusion or amniotic fluid during pregnancy, is always a reflection of the current state of the body. The presence or concentration of specific analytes, referred to in clinical practice as biomarkers, is measured and evaluated as an indicator of physiological and/or pathological processes (inflammation, infection, tumor growth, tissue damage etc.) or response to therapeutic intervention. The presence of, or change in the concentration of such analytes in body fluids becomes an effective tool for early diagnosis, monitoring the course of a disease or evaluating the effectiveness of therapy. In some diseases, the determination of a single analyte is sufficient for the diagnosis. However, in many cases, it is advisable to monitor several analytes at the same time, as this increases the diagnostic relevance. A method enabling simultaneous determination of more than one biomarker significantly increases the correctness of the diagnosis. A careful selection of the analytes to be determined, or a combination thereof, also provides more detailed information in terms of clinical interpretation. The vast majority of the methods which are suitable for simultaneous detection and quantification of analytes are immunoanalytical methods. They are based on a highly specific and sensitive reaction between the analytes to be determined and specific antibodies, leading to the formation of an immunocomplex. In the next step, the so-called detection conjugate, ie the secondary antibody linked with the detection tag (also called “indicator”), binds to the formed immunocomplex. This tag is responsible for generating the resulting signal, which is proportional to the concentration of the analyte to be determined in the analysed sample. The tag is typically an enzyme, a fluorescent substance or a radioisotope. These methods are commonly used in routine laboratory analysis of a number of substances. However, all traditional colorimetric (ELISA), fluorescence (FIA) or chemiluminescence (CLIA) immunoassay methods have their limits in the classical arrangement. The possibility of simultaneous detection of various analytes is very limited due to the physico-chemical nature of the generated signals. Electrochemical biosensors represent an alternative to immunoanalytical methods. The electrochemical biosensors exploit the advantages of immunoassay methods, in combination with electrochemical detection. An electrochemical immunosensor consists of a biorecognition part and a physico-chemical converter providing a measurable signal. The biorecognition part contains a carrier with covalently bound specific antibody for capturing the analyte molecules. In order to detect the formation of an immunocomplex, a secondary antibody is added to the reaction medium, which carries a tag yielding an electrochemical signal. A physico-chemical converter is a device that converts information from a chemical reaction to a measurable signal recorded by an electronic unit. Electrochemical detection offers many advantages, such as the ability to detect an analyte in nano-, pico- or even femtomolar quantities, the measurement being robust, easily miniaturizable and automatizable. Summary of the Invention The present invention aims to provide a system suitable for simultaneous detection of two to three protein or protein-type analytes (ie analytes of a proteinaceous nature). The system should be sufficiently specific and robust, with zero interference of up to three signals and achieving the required sensitivity. Thus, the present invention provides a kit and a method for the detection and quantification of protein analytes, the presence or concentration of which in body fluids change as a result of the development of inflammation, tumor growth or infection. An essential feature of the invention is the combination of two or three types of detection conjugates containing detection particles suitable for simultaneous electrochemical detection without mutual interference and for quantification of two or three different analytes in one sample in one analysis, while providing a sufficiently strong and robust signal to detect very low levels of analytes. The present invention, therefore, provides a kit for simultaneous detection and/or quantification of two to three target protein analytes, comprising one or more types of separation conjugate(s) for each target analyte and at least two types of detection conjugates, wherein each type of the detection conjugate is destined for one analyte, wherein - each type of separation conjugate contains a primary antibody against the target analyte, said primary antibody being bound to the surface of a magnetic particle; - each detection conjugate contains a secondary antibody for binding to the target analyte, wherein each type of the detection conjugate contains a conjugation particle which is covalently bound to the secondary antibody, and wherein a plurality of detection particles of one type, selected from CdTe quantum dots, PbS quantum dots and gold nanoparticles, are bound to the surface of the conjugation particle, wherein each type of the detection conjugate comprises a different type of detection particles; wherein the said at least two types of detection conjugates are: - the detection conjugate containing CdTe quantum dots and the detection conjugate containing gold nanoparticles, or - the detection conjugate containing PbS quantum dots and the detection conjugate containing gold nanoparticles, or - the detection conjugate containing CdTe quantum dots, the detection conjugate containing PbS quantum dots and the detection conjugate containing gold nanoparticles. The kit may further comprise disposable (single-use) sensors for detecting the electrochemical signal from the detection particles. Particularly preferred are printed sensors comprising a ceramic or plastic plate, a working electrode and a reference electrode, and optionally also an auxiliary electrode. The material of the electrodes and the surface treatment of the electrodes may be selected based on the reaction conditions, the type of analyte to be determined (detected and/or quantified) and the detection method used. Preferably, the disposable sensor may be a three-electrode SPCE (C-C-Ag) sensor with a carbon working electrode, a carbon auxiliary electrode and a silver reference electrode. A physico-chemical converter is used to measure the electrochemical signal. A physico-chemical converter is a device which converts information from the chemical reaction to a measurable signal. An electrochemical voltammetric converter is preferably used as the physico-chemical converter. The detection method in this preferred embodiment is square-wave anodic / cathodic stripping voltammetry (SWASV / SWCSV). The kit of the present invention together with the physico-chemical converter forms an electrochemical immunosensor. The biorecognition part of the immunosensor are the separation and detection conjugates. The specific primary antibodies bound to the surface of the magnetic particles (separation conjugate) bind the target analytes from the aqueous medium of the sample to form immunocomplexes, and then the resulting immunocomplexes are labeled with specific secondary antibodies carrying the signal generating particles (detection conjugate). The kit of the present invention may further comprise a magnetic separator, e.g. a stand for reaction tubes or microtubes provided with an NdFeB magnet. The kit of the present invention may further contain an agent for acidic hydrolysis of the detection particles. The agent may be, for example, an inorganic acid such as hydrochloric acid. The invention also provides a process for preparing the kit according to the present invention, wherein to prepare the detection conjugates, carboxyl groups on the surface of the detection particles are activated with N-ethyl-N´-(2-dimethylaminopropyl)carbodiimide hydrochloride (EDAC) to form detection particles with o-acylisourea ester reactive groups on the surface. The o-acylisourea ester reactive groups further react with amino groups on the surface of the conjugate particles to form signal generating particles. Subsequently, hydroxyl functional groups of monosaccharide units present in the structure of the secondary antibody are oxidized to form reactive aldehyde groups, which are then reacted with amino groups on the surface of the conjugate particles to form the detection conjugate. To prepare the separation conjugates, carboxyl groups on the surface of the magnetic particles are activated with N-ethyl-N´-(2-dimethylaminopropyl)carbodiimide hydrochloride (EDAC) to form activated magnetic particles with reactive o-acylisourea ester groups on the surface and then the activated magnetic particles are reacted with amino groups present in the structure of the primary antibody molecule. Preferably, the unreacted detection particles are separated from the signal generating particles by a gravity-based separation method or centrifugal separation method, for example by centrifugation. Preferably, the unreacted activated functional groups of the detection conjugate or the signal generating particles, respectively, are subjected to a blocking reaction, preferably with a mixture of 2-(N- morpholino)ethanesulfonic acid (MES, MES buffer), tris(hydroxymethyl)aminomethane (Tris buffer) and EDAC for activated carboxyl groups, or with NaCNBH ₃ in NaOH solution for reactive aldehyde groups. Another aspect of the invention is a method for simultaneous electrochemical detection and/or quantification of two to three protein analytes in a sample, using the kit described above. This method includes the following steps: a) contacting the sample (in which the analytes should be detected and/or quantified) with the separation conjugates in order to form immunocomplexes by binding the target analytes to the corresponding separation conjugates; b) subjecting the sample to magnetic field separation to separate the separation conjugates and/or the immunocomplexes; c) contacting the separated separation conjugates and/or immunocomplexes with the detection conjugates to bind the detection conjugates to the immunocomplexes; d) eluting unbound detection conjugates; e) subjecting the immunocomplexes with the bound detection conjugates to acidic hydrolysis; and f) determining metal ions released from the detection particles of the detection conjugates in the acidic hydrolysis product by the SWASV / SWCSV method. Metal ions released from the nucleus of quantum dots and gold nanoparticles are determined electrochemically using SWASV / SWCSV. Preferably, disposable screen-printed three-electrode sensors are used for the measurement, enabling the reduction of the analysed volume to the necessary minimum (eg 50 to 100 µl, depending on the size of the electrode). The resulting signal is directly proportional to the amount of metal ions released, and thus the concentration of the analyte to be determined in the sample. Detailed Description and Definitions The separation conjugate contains magnetic particles with a covalently bound primary antibody. A primary antibody is an antibody that specifically binds to the corresponding target analyte. Magnetic particles are particles having a size within the range of 0.7 to 3 μm, having a magnetic core exhibiting superparamagnetic properties. The superparamagnetic properties of the particles enable fast and efficient separation of particles from the liquid sample and from contaminants, and the subsequent washing of the magnetic particles. The magnetic particles are surface-modified with functional groups via which the primary antibodies are covalently bound. Such magnetic particles are known in the art, and are commercially available. Commercially available magnetic particles usually contain functional groups on the surface, which may be first subjected to activation and then the primary antibodies are bound to the (activated) functional groups. Typically, these reactions follow the manufacturer's / supplier's instructions. In some embodiments, the magnetic particles contain carboxyl groups as functional groups on the surface. The primary antibodies may be monoclonal or polyclonal, preferably monoclonal antibodies. Preferably, the primary antibodies are IgG class antibodies. The detection conjugate contains a secondary antibody to which a signal generating particle is covalently bound. The signal generating particle is a conjugation particle to which detection particles are covalently bound. As part of the biorecognition portion of the immunosensor, the detection conjugate forms a specific complex with the analyte trapped/bound on the surface of the separation conjugate (ie in an immunocomplex). This step yields an amount of detection particles which is proportional to the amount of the analyte trapped/bound in the immunocomplex. This is a non-competitive arrangement, wherein an equilibrium state must be reached in the liquid environment between the individual steps. The secondary antibodies may be monoclonal or polyclonal antibodies, preferably polyclonal antibodies. Preferably, the secondary antibodies are IgG class antibodies. The IgG antibodies used to prepare the separation and detection conjugates for a particular analyte may be of mono- or polyclonal origin. Antibodies differing in specificity as well as in the composition of the antigenic determinants against which they are directed are typically used for these two types of conjugates. However, the antigenic determinants must be sterically accessible to allow the binding of the antibody to the analyte. IgG antibodies to many protein analytes are commercially available or can be prepared by known methods, such as the animal immunization method or the hybridoma method. The conjugation particle is covalently bound to the antibody, preferably it is bound to the carbohydrate portion of the antibody by an amide bond. One or more conjugation particles may be bound to a single antibody. Anchoring the conjugation particle with detection quantum dots or gold nanoparticles to the carbohydrate portion of the antibody ensures that the detection portion will not interfere with the binding portions of the antibody, the so-called Fab fragments, and the antibody can thus effectively bind to the target analyte. This also ensures steric access to the detection particles (quantum dots or gold nanoparticles) during acidic hydrolysis, and thus a quantitative release of metals for the electrochemical detection. The conjugation particle is preferably a mesoporous nanoparticle based on SiO ₂ , surface-modified with functional groups via which the detection particles are covalently bound. (In some embodiments, the conjugation particle is surface-modified with amino groups.) The nanoparticle has a size in the range of 10 to 900 nm, preferably 50 to 500 nm, more preferably 100 to 300 nm. The size of the mesopores of the particle is preferably in the range of 2 to 50 nm, more preferably up to 10 nm. The conjugation particles are commercially available. The conjugation particles in the complex with the detection particles represent a suitable tag for the preparation of the detection conjugate. Due to the large surface area of the conjugation particles, a plurality of detection particles are bound to one conjugation particle, and thus the signal generated per analyte molecule is amplified. Another indisputable advantage is the possibility of using traditional separation methods (centrifugation, membrane filtration) in the preparation of the detection conjugates and thus achieving high yields and purity. The problem of separating the analyte-bound detection particles from the unbound detection particles was very limiting in the prior art, especially in the case of quantum dots. Because of the typical size of the quantum dots and/or of the gold nanoparticles, there is no effective process for separating the analyte-bound detection particles from unbound detection particles. Thus, the degree of contamination of the final product with free quantum dots, free gold nanoparticles and reactive reagents is considerable in the procedures of the prior art. By forming signal-generating particles (composites of detection particles with conjugation particles), the present invention allows to obtain a product which can be easily separated from the mixture and obtain a highly pure product. This product is then easily conjugated with the secondary antibody. The binding of the detection quantum dots or gold nanoparticles by means of the conjugation particle to the secondary antibody allows to significantly amplify the signal even with a small amount of the target analyte. The detection particles are metal ion-based particles and have a size in the range of 1 to 160 nm. They are surface-modified by functional groups through which they covalently bind to the conjugation particle. Such particles are commercially available. In some embodiments, the detection particles are surface-modified with carboxyl groups. Commercially available detection particles and conjugation particles usually contain functional groups on the surface (i.e. are surface-modified with functional groups), which are first activated and then subjected to reactions leading to covalent bonding, always following the manufacturer's / supplier's instructions. Different detection conjugate types contain different detection particles. The detection particles are CdTe quantum dots, PbS quantum dots, and gold nanoparticles. In the present invention, it has been found that their electrochemical signals do not overlap, and at the same time, they can be used in the same system simultaneously. The CdTe quantum dots have a particle size typically ranging from 5 to 20 nm, preferably 6 to 10 nm; PbS quantum dots have a particle size typically ranging from 60 to 90 nm. The gold nanoparticles preferably have a size in the range of 1 nm to 100 nm, more preferably 10 to 30 nm. All three types of detection particles can thus be classified as nanoparticles. Thus, three analytes can be detected by a combination of three types of detection particles. These three types of detection particles are CdTe quantum dots for first analyte detection, PbS quantum dots for second analyte detection, and gold nanoparticles for third analyte detection. It is a unique combination of detection particles usable for simultaneous determination in a single measurement. These three detection particles can be detected in a single electrochemical assay because they provide an electrochemical signal after acidic hydrolysis (so-called dissolution). The signals obtained from these three labels do not overlap and thus provide measurable values for the quantification of the target analytes. If only two analytes need to be detected, only two of these types of detection particles can be used, as listed above. The analytes determined by this method may generally be substances of protein nature (protein analytes), preferably of clinical significance, whose presence or concentration in body fluids varies depending on the presence of inflammation, infection or tumor growth. The protein analytes include proteins, glycoproteins, phosphoproteins, nucleoproteins or lipoproteins. The protein analytes are analytes for which specific antibodies can be prepared. Thus, in this text, an analyte is understood to mean in particular a clinically important molecule of a protein type, the levels of which in body fluids change in connection with inflammation, infection, tumor growth or other pathological conditions. In some embodiments, the analytes may be determined in an aqueous environment, in body fluids such as serum, plasma, cerebrospinal fluid, cervical mucus, effusion, or amniotic fluid (in the event of pregnancy). In one preferred embodiment, the analytes are pentraxin 3 (PTX3), calreticulin (CALR) and interleukin 6 (IL-6). These analytes play an important role in the pathophysiology of specific pregnancy complications such as inflammation and infection in the amniotic cavity (the cavity inside the pregnant uterus, filled with amniotic fluid, in which the fetus is connected to the placenta). These analytes are determined in an aqueous buffered medium and in a suitably diluted amniotic fluid sample. The primary and secondary antibodies used in the kit of the present invention are then anti-PTX3 antibodies, anti- CALR antibodies and anti-IL-6 antibodies, in particular IgG class antibodies. In the present invention, PTX3, CALR and IL-6 in amniotic fluid have been found to be an optimal combination of analytes to determine and predict inflammation and infection in the amniotic cavity in patients with premature amniotic fluid outflow before delivery. The levels of pentraxin 3 (PTX3), calreticulin (CALR) and interleukin 6 (IL-6) in the amniotic fluid taken from a patient to be diagnosed are indicative of inflammation and/or infection in the amniotic cavity. Inflammation and infection in the amniotic cavity represent a risk during childbirth and may result in a decision to speed-up the childbirth or perform a Cesarean section. The levels of the markers are typically compared with the levels obtained for healthy pregnant women not suffering from inflammation or infection in the amniotic cavity. Thus, the present invention provides the possibility of simultaneous, i.e. parallel, detection of two or three analytes. The ability to simultaneously detect multiple analytes in a single sample in a single analytical procedure offers a number of advantages, including lower reagent consumption, smaller sample volume, shorter time to result, less labor for laboratory workers and final lower costs as the most significant benefits. The development and validation of such an electrochemical immunosensor for clinical practice are challenging. The system must be sufficiently reliable, robust and must allow the detection and quantification of up to three analytes simultaneously, without mutual interference, even if their concentrations differ significantly. The quality of the method for simultaneous detection of analytes using an electrochemical sensor is fundamentally based on the choice of electrochemical indicators, which must provide a sufficiently strong signal and at the same time, there must be no overlap of detection potentials. Another condition is that the generated signals must not interfere with each other in any way. Another parameter that must be taken into account is the sensitivity of the assay. If it is necessary to detect analytes present in biological material in nano- to picogram quantities, then detection particles with appropriate properties and parameters must be used. The intensity of the generated signal per mole of test substance must meet the requirements of clinical practice for the minimum detection limit (MDL) and the limit for quantification (LOQ) for each of the analytes to be determined. The above requirements are fully met by the kit and method of the present invention. The present invention eliminates the limitations of immunoanalytical methods which are currently used for the simultaneous detection of analytes in body fluids or other samples. The invention, in contrast to conventional ELISA methods, offers the possibility of simultaneous detection of up to three analytes in one assayed sample. The method according to the invention is robust. Due to the simultaneous detection and the small amount of reagents required (detection conjugates and separation conjugates), the cost per analysis is relatively low. Using the invention, high sensitivity of the method and a low limit of detection for analytes in nano to picogram amounts (ng-pg / mL of analysed sample) can be achieved. The design of the detection conjugate, where the secondary antibody is labelled with signal-generating particles, offers the ability to amplify a measurable signal and increase measurement sensitivity. Due to the specific surface area of the conjugation nanoparticles, a larger number of detection nanoparticles are bound within one detection conjugate, and thus the signal generated per analyte molecule is amplified. Another indisputable advantage is the possibility to use simple and inexpensive separation techniques (centrifugation, membrane filtration) in the preparation of the detection conjugates and thus achieve high yields and purity with minimal losses during the preparation. Another advantage is the gentle way of labelling the secondary antibody even under the conditions of signal amplification. Due to the conjugation of the detection particles with the conjugation particles in the first preparation step without the participation of specific antibodies, neither the binding activity nor the specificity of these molecules is affected. The present invention allows to use electrochemical methods which do not require expensive equipment, automatic analysers, an equipped laboratory nor specifically educated personnel. The method and the kit according to the invention are versatile. Adaptation for individual analytes is ensured by antibody selection, and antibodies to various analytes are often commercially available or can be prepared by generally known methods. The method of simultaneous detection of analytes according to the invention provides a more sensitive diagnosis or prediction of a given pathological condition (so-called receiver operating characteristic curve; ROC, sensitivity and specificity of the determination and the so-called separation criterion). The method in this arrangement meets the requirements of point of care testing (POCT), ie it allows the determination of selected analytes outside standard diagnostic laboratories. The only instrumentation required is an easily transportable potentiostat for measuring the electrochemical signal on the surface of the screen-printed three-electrode sensor. In a preferred embodiment, the present invention provides the possibility to simultaneously detect and quantify two or three analytes related to the pathophysiology of inflammation and infection in the amniotic cavity, namely PTX3, CALR and IL-6. Reliable and timely acquisition of information about the presence of inflammation and infection in the amniotic cavity, by assaying a sample of amniotic fluid, is very important to determine the optimal therapeutic management in patients with premature amniotic fluid outflow before delivery. Optimal therapeutic management is the only way to minimize short- and long-term neonatal morbidity and mortality, but also maternal morbidity. The timeliness of obtaining information about the condition of the amniotic cavity is crucial from a clinical point of view. There is currently no suitable POCT method allowing the simultaneous detection/quantification of more than one analyte in amniotic fluid to determine and predict inflammation and infection in amniotic fluid. For optimal use directly at the patient's bedside or in the delivery room, it is absolutely necessary that the test must be in the form of a POCT which is a form that can be performed anywhere, with minimal and cheap instrumental equipment, and with low demands on the technical education of the staff. The use of the kit according to the present invention meets these conditions. The following examples illustrate the invention, but should not be construed as limiting the scope of the invention. Brief description of drawings Figure 1. Schematic representation of the principle of the signal generating particles preparation. Reaction between amino groups (-NH ₂ ) of SiO ₂ -based conjugation particles and carboxyl groups (- COOH) of detection quantum dots or gold nanoparticles activated by EDAC. Figure 2. Schematic representation of the principle of preparation of the detection conjugate. The signal generating particles (1) react with specific antibodies oxidized by NaIO ₄ (2) to form a detection conjugate (3). Residual aldehyde groups are blocked by NaCNBH ₃ (4). Figure 3. Voltammogram (dependence of the current on the applied potential) for testing the effect of the conjugation particles. 1 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots CdTe QDs; 2 - detection conjugate using only detection quantum dots CdTe QDs; 3 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots PbS QDs; 4 - detection conjugate using only PbS QDs quantum dots. Figure 4. Voltammogram (dependence of the current on the applied potential) to test the effect of blocking the residual reactive groups of the detection conjugates. A separate analysis of detection conjugates without blocking. 1 - detection conjugate using signal generating particles composed of conjugation particles and detection gold nanoparticles AuNPs; 2 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots PbS QDs; 3 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots CdTe QDs. Figure 5. Voltammogram (dependence of the current on the applied potential) to test the effect of blocking the residual reactive groups of the detection conjugates. A separate analysis of detection conjugates with blocking. 1 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots CdTe QDs; 2 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots PbS QDs; 3 - detection conjugate using signal generating particles composed of conjugation particles and detection gold nanoparticles AuNPs. Figure 6. Calibration curves of detection conjugates using signal generating particles composed of conjugation particles and detection quantum dots CdTe QDs without blocking (top) and with blocking (bottom) of residual reactive groups measured separately (curve 1) and simultaneously (curve 2). Figure 7. Calibration curves of detection conjugates using signal generating particles composed of conjugation particles and detection quantum dots PbS QDs without blocking (top) and with blocking (bottom) of residual reactive groups measured separately (curve 1) and simultaneously (curve 2). Figure 8. Calibration curves of detection conjugates using signal generating particles composed of conjugation particles and detection gold nanoparticles AuNPs without blocking (top) and with blocking (bottom) of residual reactive groups measured separately (curve 1) and simultaneously (curve 2). Figure 9. Voltammograms (dependence of current on applied potential) for comparison of separate and simultaneous analysis of detection conjugates with blocking of residual reactive groups of the detection conjugates. Separate analysis of blocking detection conjugates (top), simultaneous analysis (bottom).1 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots CdTe QDs; 2 - detection conjugate using signal generating particles composed of conjugation particles and detection quantum dots PbS QDs; 3 - detection conjugate using signal generating particles composed of conjugation particles and detection gold nanoparticles AuNPs. Figure 10. Calibration curve as a dependence of the measured signal on the amount of detection conjugate, where two types of separation conjugates were used, specifically for the determination of IL- 6. 1 - separation conjugate with monoclonal antibodies; 2 - separation conjugate with polyclonal antibodies. Figure 11. Voltammogram (top) and calibration curve (bottom) for IL-6 protein analyte determination. 1 - IL-6 concentration 0 µg mL ^-1 ; 2 - IL-6 concentration 0.015 µg mL ^-1 ; 3 - IL-6 concentration 0.03 µg mL ^-1 . Figure 12. Voltammogram (top) and calibration curve (bottom) for determination of protein analyte PTX 3.1 - PTX 3 concentration 0 µg mL ^-1 ; 2 - PTX 3 concentration 0.01 µg mL ^-1 ; 3 - PTX concentration 30.02 µg mL ^-1 . Figure 13. Voltammogram (top) and calibration curve (bottom) for CALR protein analyte determination. 1 - CALR concentration 0 µg mL ^-1 ; 2 - CALR concentration 0.075 µg mL ^-1 ; 3 - CALR concentration 0.15 µg mL ^-1 . Figure 14. Voltammogram for determination of IL-6 protein analyte to verify the effect of a real sample matrix - amniotic fluid. 1 - IL-6 at a concentration of 0 µg mL ^-1 in 0.2 M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20; 2 - IL-6 at a concentration of 0 µg mL ^-1 in a sample of amniotic fluid diluted 1:1; 3 - IL-6 at a concentration of 0.015 µg mL ^-1 in a sample of amniotic fluid diluted 1:1; 4 - IL-6 at a concentration of 0.015 µg mL ^-1 in 0.2 M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. Figure 15. Voltammogram of simultaneous detection of PTX 3, IL-6 and CALR protein analytes. PTX 3 - detection conjugate using signal generating particles containing quantum dots CdTe QDs; IL-6 - detection conjugate using signal generating particles containing PbS QDs quantum dots; CALR - detection conjugate using signal generating particles containing gold nanoparticles AuNPs. Protein analyte concentrations: PTX 3 - 0.02 µg mL ^-1 , IL-6 - 0.03 µg mL ^-1 , CALR - 0.15 µg mL ^-1 in reaction medium 0.2 M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. Figure 16. Calibration curves of detection conjugates for verification of reactivity with target analyte (antigen) as a dependence of the current response on the amount of antigen immobilized on magnetic particles in the range from 1 to 8.3 µg.1 – PTX 3 antigen; 2 – IL-6 antigen; 3 – CALR antigen Figure 17. Verification of the level of non-specific sorption of detection conjugates using inert protein. Dependence of the current response on the amount of BSA (inert protein) immobilized on magnetic particles in the range from 1 to 10 µg.1 – PTX 3 antigen; 2 – IL-6 antigen. Figure 18. Calibration curves of simultaneous detection of three biomarkers. PTX 3 – 0 to 100 ng mL ^-1 , IL-6 – 0 to 100 ng mL ^-1 , CALR – 0 to 300 ng mL ^-1 in reaction medium of 0.2 M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. Figure 19. Calibration curves of simultaneous detection of three biomarkers. PTX 3 – 0 to 100 ng mL ^-1 , IL-6 – 0 to 100 ng mL ^-1 , CALR – 0 to 300 ng mL ^-1 in amniotic fluid diluted 1:4 with 0.2 M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. Examples of carrying out the invention Example 1: Preparation of a detection conjugate Chemical reactions between the functional groups (in this example -NH ₂ , -COOH, -CHO groups) present on the individual components of the detection conjugate are used to prepare the detection conjugate. Commercially available starting materials: - conjugation particles: SiO ₂ -based nanoparticles (SiNPs): commercially available (Sigma-Aldrich, St. Louis, MO, USA) - surface modification - NH ₂ , mesoporous, particle size 200 nm, pore size 4 nm. - CdTe quantum dots (CdTe QDs) - commercially available (Sigma-Aldrich, St. Louis, MO, USA) - surface modification - COOH, particle size 6-7 nm, λ _em 570 nm - PbS quantum dots (PbS QDs) - commercially available (Suzhou Xingshuo Nanotech, China) - surface modification - COOH, particle size 80 nm, λ _em 1100 nm - gold nanoparticles (AuNPs) - commercially available (Sigma-Aldrich, St. Louis, MO, USA) - surface modification - COOH, particle size 20 nm - antibodies against Pentraxin 3 (anti-PTX3 IgG), Calreticulin (anti-CALR IgG), Interleukin 6 (anti-IL- 6 IgG), –monoclonal anti-PTX3 IgG (clone 7.1, Moravian Biotechnology, Brno, Czech Republic), monoclonal anti-CALR IgG (clone 5.1, Moravian Biotechnology, Brno, Czech Republic), polyclonal anti-IL-6 IgG (LS Bio, USA) Procedure: 1. Preparation of signal generating particles: the formation of covalent bonds between detection quantum dots and SiO ₂ -based nanoparticles is carried out by one-step carbodiimide method using N-ethyl-N'-(3- dimethylaminopropyl)carbodiimide hydrochloride (EDAC) as a crosslinking agent. The carboxyl groups of the detection quantum dots or gold nanoparticles are activated by EDAC to form an active intermediate (QDs/AuNPs-o-acylisourea), which immediately reacts with the amino groups on the surface of the SiO ₂ -based nanoparticles to form an amide bond (see Fig.1). The pore size (4 nm) of the mesoporous SiO ₂ -based nanoparticles sterically prevents quantum dots from penetrating the porous surface and negatively affecting their release necessary for the final electrochemical detection. Due to the high density of the signal generating particles, they are easily separated from the solution containing the reagents and free unconjugated detection quantum dots or gold nanoparticles. Unconjugated detection quantum dots or gold nanoparticles can be easily separated by centrifugation, thus avoiding the lengthy dialysis step that would reduce preparation yield. More specifically, the procedure for preparing signal-generating particles is as follows: Conjugation particles (SiNPs, 3 mg) are washed 5 times with 0.1M phosphate buffer pH 7.3 (1 mL). The particles are separated from the solution by centrifugation for 5 minutes at 5000 rpm. Subsequently, 0.5 mg mL- ¹ EDAC solution, CdTe QDs solution (50 µL, 1 mg mL ^-1 ), PbS QDs (4 µL stock solution) or AuNPs (10 µL, 1 mg mL ^-1 ) are added. After making up the reaction volume to 1 mL, incubation for 1 hour at room temperature in the dark with gentle rotation followed. After incubation, the detection particles are washed 3x with 0.1M phosphate buffer pH 7.3 with 1M NaCl and 2x with 0.1M phosphate buffer pH 7.3 (1 mL). Excess activated -COOH groups of the quantum dots or gold nanoparticles are blocked with a solution of 0.1M 2-(N-morpholino)ethanesulfonic acid hydrate (MES buffer) pH 4.7 with 0.1M Tris with the addition of 10 mg EDAC (total reaction volume 1 mL). The blocking step was performed for 2 hours at room temperature in the dark with gentle rotation. After incubation, the detection particles are washed 3x with 0.1M phosphate buffer pH 7.3 with 1M NaCl and 2x with 0.1 M phosphate buffer pH 7.3 (1 mL each). 2. Preparation of the detection conjugate: in the preparation of the signal generating particles, the ratio of both components, i.e. SiNPs and QDs/AuNPs, is set with respect to an excess of SiO ₂ -based nanoparticles with free amino functional groups. These are then used to bind specific antibodies to form a detection conjugate. Antibodies are conjugated by the site-specific covalent binding method. The hydroxyl functional groups of the monosaccharides present in the structure of antibody molecule and localized at the end of the glycosidic chain are first oxidized with sodium periodate to form reactive aldehydes that react spontaneously with the amino groups of the signal generating particles. The reaction leads to a formation of a stable amide bond (see Fig. 2). The final stabilization step is the blocking of the remaining reactive functional groups. Blocking substantially reduces the non-specific sorption of the detection conjugate to the surface of the separation conjugate. More specifically, the detection conjugate was prepared as follows: Detection antibodies (20 µg) were oxidized with a solution of NaIO ₄ (0.02 M) in a reaction volume of 250 µL for 30 minutes at room temperature in the dark with gentle rotation. After stopping the oxidation by adding 1.5 µL of ethylene glycol and removing the NaIO ₄ by desalting using silica gel centrifugal columns, the oxidized antibodies were added to the prepared detection particles. After making up the reaction volume to 1 mL with 0.1M phosphate buffer pH 7.3, incubation followed overnight at 2-8 °C in the dark with gentle rotation. After washing 4 times with 0.1M phosphate buffer pH 7.3 (1 mL each), the remaining reactive aldehyde groups of the antibodies were blocked with 1M NaOH solution containing 10 μL of 5M NaCNBH ₃ . Blocking is performed for 15 minutes at room temperature with gentle rotation. This is followed by a final washing: 3x 0.1M phosphate buffer pH 7.3 with 1M NaCl and 2x 0.1M phosphate buffer pH 7.3 (1 mL each). Detection conjugates are stored at 2-8 ° C. Example 2: Preparation of a separation conjugate Chemical reactions between the functional groups present on the surface of the magnetic particles (-COOH) and on the molecules of specific IgG antibodies (-NH ₂ ) are used to prepare the separation conjugate. Commercially available starting materials: - antibodies against Pentraxin 3 (anti-PTX3 IgG), Calreticulin (anti-CALR IgG), Interleukin 6 (anti-IL- 6 IgG), monoclonal - anti-PTX3 IgG (clone 1.1, Moravian Biotechnology, Brno, Czech Republic), anti- CALR IgG (clone 4.1, Moravian Biotechnology, Brno, Czech Republic), monoclonal anti-IL-6 IgG (LS Bio, USA) - Magnetic microparticles: Dynal MyOne carboxylic, particle size 1 µm, functional groups -COOH (ThermoFisher Scientific, USA) Procedure: Magnetic microparticles (1 mg) were washed 5 times with 0.1M MES solution (MES buffer pH 5.0; 0.1 mL). The particles were separated from the solution by means of a magnetic separator. Subsequently, a 7.5 mg/0.5 mL EDAC solution was added. After making up the reaction volume to 1 mL with 0.1M MES solution (MES buffer pH 5.0), incubation followed for 1 hour at room temperature with gentle rotation. After incubation, the magnetic microparticles were washed twice with 0.1M MES pH 5.0 (1 mL). Subsequently, specific IgG antibodies were added at a concentration of 50 μg mL ^-1 of 0.1M MES pH 5.0. This was followed by incubation for 16 hours at 4 °C with gentle rotation. The separation conjugate was washed 3x with 0.1M MES pH 5.0, 2x 0.1M PBS buffer pH 7.4 and 3x 0.1M MES pH 5.0 (1 mL each). The separation conjugates were stored at 4 °C. Example 3: Procedure for analyte determination (immunocomplex formation and subsequent electrochemical detection) The individual steps take place in a total reaction volume of 100 µl. In general, these conditions are suitable for various analytes. 1. Binding of the target analyte with the separation conjugate: the binding is proceeded in a reaction solution of 0.2M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. An amount of the separation conjugate corresponding to 2.5 µg of specific antibodies against the target analyte is used for binding. Incubation of the separation conjugate with the analyte takes place for 10 minutes at room temperature with gentle rotation. This is followed by washing of the formed immunocomplex 3x with 0.1M phosphate buffer pH 7.3 with 1M NaCl and 2x 0.1M phosphate buffer pH 7.3 (100 µL each). 2. Binding of the detection conjugate: the binding takes place in a reaction medium containing 0.2M Tris-HCl buffer pH 8.0 with 1% BSA and 0.1% Tween 20. An amount of the suspension corresponding to 0.5 (0.75) µg antibodies is used for binding. Incubation with the detection conjugate takes place for 10 minutes at room temperature with gentle rotation and is followed by washing of the formed immunocomplex 3x with 0.1M phosphate buffer pH 7.3 with 1M NaCl and 2x 0.1M phosphate buffer pH 7.3 (100 µL each). 3. Acid hydrolysis: metal ions are released from the detection conjugates by treatment with 0.1M HCl for 3 minutes at room temperature, with gentle rotation. The reaction volume is 100 µl. The hydrochloric acid dissolves the detection quantum dots and releases the metal ions forming the nucleus of QDs, namely Cd (II) and Pb (II), whose electrochemical signal is monitored. In the case of detection gold nanoparticles, the action of hydrochloric acid produces the intermetallic compound Au(III), the signal of which is electrochemically measured. After separation, the electrochemical determination is carried out in the solution after magnetic separation under the conditions listed in Table 1. Metal ions released from the nucleus of the quantum dots and the gold nanoparticles, which are components of the detection conjugates, are measured electrochemically using square-wave stripping voltammetry in the negative and positive potential area (SWASV / SWCSV). Disposable screen-printed three-electrode sensors can be used for measurement, enabling the reduction of the analysed volume to the necessary minimum (eg 50 to 100 µL, depending on the size of the electrode). The resulting signal is directly proportional to the amount of the metal ions released, and thus the concentration of the assayed protein analyte in the sample. The electrochemical detection in the examples was performed using a portable MultiEmStat 3 electrochemical device with four independent potentiostats controlled by MultiTrace 4 software (PalmSens, The Netherlands), and printed three-electrode sensors containing a carbon working electrode, carbon auxiliary electrode and silver reference electrode (C-110; W/A-C, R-Ag; Metrohm, Switzerland). Table 1. Experimental parameters for electrochemical determination by square wave dissolution voltammetry in the anodic (SWASV) and cathodic (SWCSV) areas Example 4: Verification of the signal increase due to the construction of the detection conjugates Using the detection conjugates prepared in Example 1, the effect of SiO ₂ -based conjugation particles on increasing the resulting signal was confirmed. Two types of detection conjugates were compared, without and with the conjugation particles. Detection conjugates with CdTe QDs and PbS QDs were tested. Both types of detection conjugates were analysed electrochemically under the experimental conditions listed in Table 1. The result of the analysis is shown in Fig. 3. For the detection conjugates with CdTe QDs, a very significant increase in the signal level can be observed when using conjugation particles (Fig. 3, curve 1) compared to the detection conjugate without conjugation particles (Fig. 3, curve 2). For the detection conjugate with PbS QDs, the signal of both types of detection conjugates is comparable (Fig. 3, curves 3 and 4), which can be explained by the size of the PbS QDs which are 12 times bigger compared to CdTe QDs, so binding of a significantly higher number of QDs to the conjugation particles cannot be expected. Nevertheless, the use of the conjugate particles brings the benefit of easy preparation of detection conjugates and the possibility of easy separation of the product from contaminants, such as unbound detection quantum dots. Example 5: Effect of a blocking step in the preparation of the detection conjugate on the signal intensity For the quality of the detection conjugates, their functionality, and the resulting sensitivity of the whole system, the key parameter is the low signal level of negative controls. Any sorption of the detection conjugate to the surface of the separation conjugate without the participation of the analyte (so-called non-specific sorption rate) is undesirable. Appropriate experimental conditions for the preparation of the detection conjugate and the binding of the detection conjugate to the antigen must ensure zero non- specific sorption. The degree of non-specific sorption affects the sensitivity of the assay. In the case of detection conjugates, the remaining reactive groups of all reagents used for their preparation are mainly responsible for the non-specific sorption. Therefore, a blocking step is preferably included in the detection conjugate preparation protocol. The procedure is described in Example 1. The signals of detection conjugates prepared without blocking the remaining reactive groups (i.e., omitting the blocking step) and with blocking (i.e., all steps of the procedure of Example 1) were compared. They were also compared from the view point of the detection method, where the individual detection conjugates were measured electrochemically as well as their mixture. The measuring of the mixture involved simultaneous measurement of the signals generated by the three detection conjugates in parallel. The electrochemical measurement was performed under the conditions shown in Table 1. The results are shown in Figures 4 to 8. In Figures 4 and 5, the results of the analysis of the individual detection conjugates are shown separately. Figure 4 shows the result of measuring detection conjugates with CdTe QDs detection quantum dots (curve 3) and PbS QDs detection quantum dots (curve 2) without blocking residual reactive groups. For the detection conjugate with detection gold nanoparticles AuNPs (curve 1), the step of blocking reactive groups is always used, because without the blocking step they did not provide any measurable signal. Figure 5 shows the result of measuring detection conjugates with CdTe QDs detection quantum dots (curve 3) and PbS QDs detection quantum dots (curve 2) with blocking of the residual reactive groups. The blocking of the residual reactive groups led to a decrease in non-specific sorption, ie. in the signal corresponding to the negative control, but at the same time, it led to an increase in the resulting signal. The blocking did not in any way affect the resulting peak shape nor the potential at which the peaks of the individual detection conjugates are recorded. Figures 6 to 8 show a comparison of calibration curves for individual and simultaneous analyses for the detection conjugates as well as a comparison of the preparation method, ie without blocking (top) and with blocking (bottom). As the number of detection conjugates increases, the current values for all three analysed detection conjugates also increase. However, there is a noticeable difference in the measured current values, especially for the detection conjugates with the detection quantum dots CdTe QDs, where the resulting signal is suppressed during simultaneous analysis. The results clearly show that it is very advantageous to use detection conjugates after blocking for simultaneous analysis. For detection conjugates without blocking, the current response intensity is higher in some cases, but under simultaneous analysis conditions the signal is significantly suppressed. Figure 9 is a record of a measurement comparing the current response intensities of the detection conjugates measured separately (top) and simultaneously (bottom). In simultaneous measurements, the signal for PTX3 was significantly suppressed, when the detection conjugate was labelled with cadmium- based quantum dots (CdTe QDs). Example 6: Effect of the antibody type on the preparation of a separation conjugate The effect of the antibody type was tested using an anti-IL-6 antibody. The method of preparation of the separation conjugate and the type of specific antibodies used from the point of view of clonality (monoclonal vs. polyclonal) are also relevant for the resulting functionality and sensitivity of the system. The effect of the type of antibodies against the IL-6 analyte is given as an example. Both monoclonal and polyclonal antibodies were used and tested to prepare the separation conjugate. Polyclonal antibodies were always used to prepare the detection conjugate (wider variability in polyclonal antibody specificity leads to a higher reactivity with the analyte). It was experimentally confirmed that the use of monoclonal antibodies is more advantageous for the preparation of the separation conjugate (see Figure 10). The procedure for preparing the separation conjugate is described in Example 2. Electrochemical detection was performed under the conditions listed in Table 1. Example 7: Analysis of analytes Standard commercially available proteins were used for separate analysis of analytes and preparation of calibration curves. PTX 3, IL-6 and CALR protein analyses are provided in this example. Monoclonal antibodies were used for PTX 3, CALR and IL-6for the preparation of the separation conjugate (preparation procedure according to Example 2). Monoclonal antibodies were used for PTX3 and CALR and polyclonal antibodies were used for IL-6 to prepare detection conjugates (preparation procedure according to Example 1). The analysis procedure is described in Example 3. The electrochemical detection was performed under the conditions shown in Table 1. The resulting voltammograms and calibration curves are shown in Figures 11-13 and 18-19. Example 8. Effect of a matrix (amniotic fluid) on the results of the analysis For a preferred embodiment which is the analysis of analytes in amniotic fluid samples, the effect of the matrix was tested. An example is the analysis of IL-6 protein, which was performed by measuring the standard in a model reaction medium in which the optimization steps took place, i.e. in a solution of 0.2M Tris-HCl buffer, pH 8.0 with 1% BSA and 0.1% Tween 20. Furthermore, a sample of physiological amniotic fluid (diluted 1:1) was prepared with a standard addition of 0.015 µg mL ^-1 protein analyte IL- 6. Immunocomplex formation was carried out according to the procedure described in Example 3, the conditions of electrochemical detection are shown in Table 1. The resulting voltammogram (Figure 14) demonstrates the usability of the system for real samples. The measured current response value for the amniotic fluid sample (diluted 1:1) with standard IL-6 analyte addition (curve 3) is comparable to the current response pattern of the sample containing the analyte (IL-6) in a buffer with defined molarity and pH (curve 4). The current response curve is partially different for negative controls in amniotic fluid (curve 2) and buffer (curve 1), but the absolute difference is the same for both environments and the measured analyte concentrations in the amniotic fluid sample fully correspond to the expected IL-6 levels. Example 9: Simultaneous analysis of three analytes Commercially available protein standards were used for simultaneous analysis of the analytes. Examples for PTX 3, IL-6 and CALR are provided. The immunocomplex formation procedure is described in Example 3. Electrochemical detection was performed under the conditions shown in Table 1. The resulting voltammogram is shown in Figure 15. Example 10: Verification of the reactivity of the detection conjugates Magnetic particles with immobilized target analytes (PTX3, IL-6, CALR) were used to confirm the reactivity of detection conjugates corresponding to the amount of the analyte. Aliquots of magnetic particles modified by target analytes differing in amount of analyte (1, 2.5, 5 and 8.3 µg) were incubated with constant amount of detection conjugates (125 µL corresponding to 2.5 µg of antibodies for each). Reaction was carried out in a solution of 0.2M Tris-HCl buffer, pH 8.0 with 1% BSA and 0.1% Tween 20 for 1 hour at room temperature upon gentle mixing. The reactivity was confirmed, signal increased with increasing amount of antigen in the reaction. In case of IL-6 the signal increase was limited by the binding capacity of the immunosorbent, due to the bigger size of detection quantum dots PbS QDs and due to the levels of IL-6 being higher than the levels of PTX3 and CALR. The resulting calibrations are shown in figure 16, wherein curve 1 corresponds to PTX3, curve 2 to IL-6 and curve 3 to CALR. Example 11: Verification of non-specific sorption of prepared detection bioconjugates For verification of non-specific sorption, inert protein represented by bovine serum albumin (BSA) was used. An increasing amount of protein was used for reaction with the constant amount of detection conjugates (125 µL corresponding to 2.5 µg of antibodies for each). Reaction was proceeded in a solution of 0.2M Tris-HCl buffer, pH 8.0 with 1% BSA and 0.1% Tween 20 for 1 hour at room temperature upon gentle mixing. Results shown in figure 17 showed a slight occurrence of non-specific sorption, but compared to specific target analytes (figure 16), current responses are significantly lower. The resulting calibrations are shown in figure 17, where curve 1 corresponds to PTX3, curve 2 to IL-6 and curve 3 to CALR. Example 12: Simultaneous analysis of two analytes in amniotic fluid Samples of amniotic fluid diluted 1 : 4 (0.2M Tris-HCl buffer, pH 8.0 with 1% BSA and 0.1% Tween 20) were used for simultaneous analysis of the two analytes. Examples for PTX 3 and CALR are provided. The immunocomplex formation procedure is described in Example 3. Electrochemical detection was performed under the conditions shown in table 1. The measured PTX3 and CALR levels for amniotic fluid of women with different clinical findings are shown in the below table. Clinical definitions *Intra-amniotic infection was defined as the concomitant presence of microbial invasion of the amniotic cavity and intra-amniotic inflammation. **Sterile intra-amniotic inflammation was defined as the presence of intra-amniotic inflammation without microbial invasion of the amniotic cavity. ***Colonization of the amniotic cavity was defined as the presence of microbial invasion of the amniotic cavity without intra-amniotic inflammation. ****Absence of microorganisms and inflammation was defined as the absence of both microbial invasion of the amniotic cavity and intra-amniotic inflammation. Microbial invasion of the amniotic cavity was defined as the presence of microorganisms and/or microbial nucleic acids in the amniotic fluid .Intra-amniotic inflammation was defined as a concentration of IL-6 in amniotic fluid ≥3,000 pg/mL using an automated electrochemiluminescence immunoassay method (described in: Musilova I, Andrys C, Holeckova M, Kolarova V, Pliskova L, Drahosova M, et al. J Matern Fetal Neonatal Med.2020;33(11):1919-26).