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Title:
ELECTROPHORETIC MOLECULAR COMMUNICATION
Document Type and Number:
WIPO Patent Application WO/2019/097204
Kind Code:
A1
Abstract:
Molecular communication is established in a medium, and is managed by an electrical field to urge a signalling molecule from a source to a point at which the molecule can be detected.

Inventors:
COON JUSTIN (GB)
Application Number:
PCT/GB2018/053194
Publication Date:
May 23, 2019
Filing Date:
November 02, 2018
Export Citation:
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Assignee:
UNIV OXFORD INNOVATION LTD (GB)
International Classes:
H04B13/00
Domestic Patent References:
WO2011007139A22011-01-20
WO2004051247A22004-06-17
WO2017015468A12017-01-26
Foreign References:
US20080087546A12008-04-17
Other References:
MANOCHA PUNEET ET AL: "Dielectrophoretic Relay Assisted Molecular Communication for In-Sequence Molecule Delivery", IEEE TRANSACTIONS ON NANOBIOSCIENCE, IEEE SERVICE CENTER, PISCATAWAY, NY, US, vol. 15, no. 7, 1 October 2016 (2016-10-01), pages 781 - 791, XP011638133, ISSN: 1536-1241, [retrieved on 20161220], DOI: 10.1109/TNB.2016.2618904
NARIMAN FARSAD ET AL: "A Comprehensive Survey of Recent Advancements in Molecular Communication", IEEE COMMUNICATIONS SURVEYS & TUTORIALS, 1 January 2016 (2016-01-01), pages 1887 - 1919, XP055552600, Retrieved from the Internet DOI: 10.1109/COMST.2016.2527741
NARIMAN FARSAD ET AL: "On the capacity of diffusion-based molecular timing channels with diversity", 2016 50TH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 1 November 2016 (2016-11-01), pages 1117 - 1121, XP055552530, DOI: 10.1109/ACSSC.2016.7869544
None
Attorney, Agent or Firm:
ROUND, Edward (15 Fetter Lane, London EC4A 1BW, GB)
Download PDF:
Claims:
CLAIMS:

1. A communication device comprising a housing for containing a fluid chemical communication medium, the housing having at least two ports, a fluid chemical communication medium within the housing, the medium extending between the ports, an information modulator located at one of the ports, the information modulator being operable to impart, to the medium, a substance comprising a compound with a non-uniform molecular charge density, a detector located at another of the ports, configured to detect a concentration of the compound in the medium at that port, and a field generator for generating a substantially uniform electrical field through the medium, the field being oriented to urge a molecule, in the medium, having a non-uniform charge density, in a direction from the information modulator towards the detector.

2. A communication device in accordance with claim 1 wherein the field generator is operable to generate a field which varies in strength with respect to time.

3. A communication device in accordance with claim 1 or claim 2 wherein the information modulator is operable to impart the substance to the medium responsive to an information input, wherein the information input can assume one of at least two states, a first state corresponding to imparting of the substance to the medium at a first delivery rate, a second state corresponding to an imparting of the substance to the medium at a second delivery rate.

4. A communication device in accordance with claim 3 wherein the information input can assume a third state, corresponding to an imparting of the substance to the medium at a delivery rate different from the delivery rate associated with the second state.

5. A communication device in accordance with claim 3 or claim 4 wherein the information input is operable to receive an input signal, the input signal bearing information encoding one or more symbols, each symbol corresponding to one of the available states of the information input.

6. A communication device in accordance with any one of the preceding claims, comprising a controller for controlling the field generator, the controller being selectively operable in first and second operational modes, wherein, in a first mode, the controller is operable to control the field generator not to generate an electrical field, wherein, in a second mode, the controller is operable to control the field generator to generate a substantially time invariant electrical field.

7. A communication device in accordance with claim 6 wherein, in the second mode, the controller is operable to cause the field generator to generate an electrical field for a specified period, and then to revert to the first mode of operation.

8. A communication device in accordance with claim 6 or claim 7 and wherein the controller is operable in a third operational mode, in which the controller is operable to cause the field generator to generate an electrical field whose field strength is variable with respect to time.

9. A communication device in accordance with claim 8 wherein, in the third mode, the controller is operable to cause the field generator to generate an electrical field whose field strength varies substantially without discontinuity.

10. A communication device in accordance with claim 8 or claim 9 wherein, in the third mode, the controller is operable to cause the field generator to generate an electrical field for a specified period, and then to revert to the first mode of operation.

1 1. A method of communication on a communication channel defined in a housing for containing a fluid chemical communication medium, the housing having at least two ports, and a fluid chemical communication medium within the housing extending between the ports, the method comprising:

modulating information at one of the ports, by imparting, to the medium, a substance comprising a compound with a non-uniform molecular charge density,

detecting a concentration of the compound in the medium at another of the ports, and generating a substantially uniform electrical field through the medium, the field being oriented to urge a molecule, in the medium, having a non-uniform charge density, in a direction from the information modulator towards the detector.

Description:
Electrophoretic Molecular Communication

FIELD

The present disclosure is in the field of molecular communication.

BACKGROUND

Molecular communication is a communications technique whereby molecules are used as signal carriers. The presence or absence (or, in certain circumstances, relative concentrations) of a molecule in a fluid medium can be used to encode information. Suitable communications media include gaseous or liquid substances, such as air or water.

Molecular communication is known to occur naturally, as various plants and animals emit and detect chemicals for the purpose of communicating information.

At present, the technical harnessing of molecular signalling from one point to another in a fluid medium can be achieved in an engineered manner by exploiting the diffusion of information carrying molecules. Various techniques can be employed within this context. For instance, diffusion-plus-drift (fluid flow) processes, provide description of expected propagation of molecules within a transport medium, without intervention. Active transport techniques can be envisaged that use molecular motors or cytoskeletal filaments. Other means of propagation may be contemplated, using bacteria. Further, the well-understood transport of kinesin proteins over microtubule tracks can be explored.

The first two methods noted above are the simplest techniques since they do not rely on particular chemical reactions or biological processes. Flowever, diffusion is a slow process, which limits the maximum achievable rate of information transfer. Exploiting diffusion and fluid flow can improve the potential rate of flow of information, but flow is typically limited by the microfluidic mechanical nature of the system. DESCRIPTION OF DRAWINGS

Figure 1 is a schematic side view of an electrophoretic molecular communication system in accordance with a described embodiment;

Figure 2 is a sequence of diagrams showing use of the system in accordance with a background mode;

Figure 3 is a sequence of diagrams showing use of the system in accordance with an embodiment; and

Figure 4 is a graph showing, at instances in time, concentration of a signalling substance over a length of a signalling medium.

DESCRIPTION OF EMBODIMENTS

In general terms, certain embodiments disclosed herein implement molecular communication in a medium, managed by an electrical field to urge a signalling molecule from a source to a point at which the molecule can be detected.

In general terms, certain embodiments described herein intend to implement drift in a static fluid medium using electric fields along with natural surface charge distributions present in potential information carrying molecules. The use of electric fields offers a degree of freedom that is inherently separate from the molecular system. High field strengths can be used to propagate information very quickly (low delay) and localise “packets” of molecules. It is contemplated that this could provide a desirable communication performance. Furthermore, embodiments described herein envisage the variation, over time, of an applied electrical field in order to achieve enhanced performance in a single direction of propagation or to achieve bidirectional communication.

Embodiments described herein employ electrophoresis for molecular communication. Embodiments described herein implement electrophoresis using smoothly time-varying fields, to enable certain desirable levels of performance and, specifically, bidirectional communication.

The physical effect of electrophoresis takes advantage of the observation that many molecular structures (e.g., many colloids) exhibit non-uniform charge densities. When placed in the presence of an electric field (spatially constant or otherwise), these particles will diffuse and drift according to their electrochemical properties. In the context of communication systems, information can be encoded at the molecular level by modulating the concentration of a chemical injected into a fluid medium over time, or by attaching other biochemical substances to molecular carriers as they propagate from the transmitter to the receiver. At the receiver, information is decoded by measuring the particle concentration observed in prescribed time windows (or“symbol periods”), or by logging the outcome of a particular chemical reaction. The exact nature of detection depends on the type of modulation employed at the transmitter.

It can be desirable to ensure signalling molecules, and thus the information they represent, propagate through the medium as quickly as possible. Applying an electric field across the medium will induce drift in the information-bearing molecules, thus achieving data transfer with a low delay. Due to the diffusion process, however, some carriers will arrive outside of their prescribed symbol period. This dispersion, which is inherent to all diffusion-based systems, can affect the performance of the communication system.

In essence, this has parallels with other forms of communication, in which information rate can be dependent on the length of the communication channel, and long distance communication can be hampered by the deterioration in quality of the encoded information as it progresses along the communication path. For instance, a square voltage pulse transmitted in an electrical conductor will, over the length of the conductor, lose its definition as higher frequency components of the signal attenuate. Similarly, fibre optic communication is subject to the fact that light entering an optical fibre normal to the end surface will take less time to propagate along a given length of the fibre, than light entering the fibre at a more oblique angle. This leads to dispersion which, for long fibres, can be significant and must be mitigated. By appropriately varying the electric field strength over time, it is possible to stem the effects of diffusion, thus better localising sets of carriers and improving communication system performance. Furthermore, a time-varying field can be used to cause information carriers to propagate in the reverse direction as well, thus facilitating bidirectional communication.

Thus, an implementation of this approach will now be described with the aid of the accompanying drawings.

As shown in figure 1 , an example is provided of an electrophoretic communication system in accordance with an embodiment. The system 10 comprises a signal generator 20 operable to generate an information signal, on an electrical communication medium, to an injector 30.

Embodiments contemplate that the injector can be implemented by way of a controllable pump or a micropipette. Such a device can be controlled by a microcontroller. This microcontroller can read input information, such as electrical signals, which may be in digital form, and convert that information into a control signal for the pump or pipette, as the case may be.

The injector 30 is, under the control of the information signal, operable to inject a signalling substance into a fluid communication medium borne in a capillary tube 40. The injector 30 is positioned at one end of the capillary tube 40, a detector 50 is positioned at the other end, operable to detect presence and/or concentration of the signalling substance in the fluid communication medium. The detector 50 can, in certain embodiments, be implemented as a chemical sensor, capable of converting a chemical detection into an electrical signal. Examples exist for detection of ethanol (alcohol) in this way. The detector 50 is operable to output a detection signal, on the basis of detection, to a signal processor 60 which is capable of interpreting the resultant data.

A transmission driver 70 has two outputs, between which it is operable to develop an electrical potential difference. These outputs are applied, respectively, to two annular electrodes 72A and 72B, positioned at opposite ends of the capillary tube 40. Thus, an electrical field is developed between the electrodes, and this is imparted on the medium contained in the tube 40. The transmission driver 70 is operable to coordinate with the injector 30 such that an injection of signalling substance is synchronised with a smoothly varying function governing the magnitude of the electric field strength between the two electrodes 72A and 72B.

In this particular embodiment, the function driving the electrical field is smoothly periodic. Examples of suitable functions include sinusoidal functions and their variants, including raised sines (i.e. sines raised to a power). It is, for example, desirable to avoid functions which are not smooth. This is because discontinuities in any derivative of the function can produce unpredictable, undeterminable effects. For instance, a large non-smooth change in the electrical field may result in discharge of medium from the tube 40, which would result in a modification to the channel itself and thus information loss.

Given that a signal may comprise the injection, for a finite period, of the signalling substance into the communication medium, this is in effect a pulse imparted to the medium. The function governing the electrical field is attuned to the natural rate of drift and diffusion of the signalling medium, so as to reduce the tendency of the signalling substance to disperse into the medium and thus lose definition as a signal.

This can be considered further by inspection of examples in figures 2 and 3. Figure 2 comprises three instances (i), (ii) and (iii) of the capillary tube 40 according to a background example. Figure 3 comprises three instances (i), (ii) and (iii) of the capillary tube 40 according to an embodiment.

In figure 2, instance (i), a scenario is depicted wherein a quantity of the signalling substance has recently been injected into the capillary tube 40. This is depicted as a generally elliptical region of the contained medium. A uniform electric field of constant strength is applied between the electrodes 72. This urges the signalling substance towards the detector 50. As time progresses, the substance travels along the capillary tube, by drift and diffusion. In instance (ii), the substance is shown as having extended to around half way along the tube. While the injection remains discernible as a formation in the tube, it has less definition than at the point of injection. It will be understood that a certain concentration of the substance will remain at the injection end of the tube despite the effect of the electrical field. While the pulse of injected signalling substance remains defined, the boundaries thereof are increasingly blurred. The‘tail’ of the injection spreads behind it. Of course, beyond a certain point away from the injector, there will be no signalling substance, because the rate of electrophoretic diffusion dictates that no substance can have reached that point in time. The reader will also appreciate that line drawings cannot provide a depiction of variation of concentration of the substance over the length of the tube as a whole. To account for this, figure 4 is a graph illustrating how the density of information carrying chemical changes as time progresses. In this figure, concentration of the signalling chemical is shown on the y-axis, while distance from the point of injection is shown on the x-axis. The darkest shaded line shows a localised concentration near the transmitter (injector), the other curves are at later times. The reader will see that, as time progresses, drift moves the centre of concentration of the signalling chemical to the right (away from the transmitter), whereas the maximum concentration of the signalling chemical reduces, as the chemical disperses throughout the medium by the effect of diffusion.

In instance (iii), sufficient time has elapsed to allow diffusion of the substance completely to the other end of the tube. Thus, depending on the sensitivity of the detector, the presence of the signalling substance can be detected. However, the definition of the information content, represented by the finite period over which the substance was injected, has been completely lost. The leading and trailing edges of the injection are now entirely without definition at the detector end. The concentration of the substance across the whole tube becomes increasingly uniform, with the progress of time, and this therefore loses informational value.

By contrast, figure 3 demonstrates the effect of a smooth periodic function on the electric field driving electrophoresis in the tube.

Again, in instance (i), a quantity of the signalling substance, recently injected into the capillary tube 40, is depicted as a generally elliptical region of the contained medium. As before, an electric field is generated down the tube 40, but this time the field is generated by way of a potential difference between the electrodes 72 governed by a smooth periodic function. The period of the function is selected on the basis of the implementation. Consideration needs to be taken of the dimensions of the tube, and thus natural constraints on flow. It is also appropriate to account for the combination of the signalling substance and the medium. That is, account should be taken for the effect of the field on the particular combination of signalling substance and medium, and thus the effect it will have on the ability to control the integrity of the injected amount as a signal form.

The amplitude of the periodically varying field also needs to be considered. In this case, depending on the implementation, there will be a range of amplitudes which will provide benefit. Below a certain level, the impact of the field on diffusion and drift will be negligible. Above a certain amplitude, the impact of the field will hit a physical limit; that is, there is a maximum speed at which the signalling substance can be made to travel through the medium by electrophoresis. This maximum speed is the“saturation velocity” of the signalling substance through the medium.

The desired impact of the varying electric field is that it synchronises with the injection as to apply electrophoresis to a greater extent to the trailing end of the injected signalling substance than to the leading edge. This means that the integrity of the injection, as a signal, is maintained to a greater degree. More distinct boundaries between presence and absence of the signalling substance can be determined.

Thus, in instance (ii), the injected amount is shown with a much greater maintenance of the high concentration region, than in the case shown in Figure 2. Even in instance (iii), when the bulk of the injected amount has been urged, by electrophoresis, to the detection end of the tube, the definition between the injected amount, and the medium behind the injected amount, remains discernible.

This is achieved by selecting the period of the field applied across the tube so that it accords with the speed at which the signalling substance can be made to travel by electrophoresis, given a particular amplitude of the field strength. The actual physical quantities concerned will depend on a number of factors, such as material selection.

The actual implementation of an embodiment is subject to many application-specific factors. However, to provide an example, the medium can be a liquid, such as water, or a gel, such as polyacrylamide. Polyacrylamide is a suitable medium for use with a protein information carrier.

A buffer can be employed, to ensure an ionic concentration sufficiently high to enable current flow. This could aid propagation of information carriers in some circumstances. Some examples of buffers which may provide characteristics of use in implementations include acetic acid, boric acid, citric acid, glycine, taurine, tricine and tris(hydroxymethyl)aminomethane (commonly abbreviated to tris). The selection of an appropriate buffer will depend on numerous factors, including the desired pH of the system, toxicity, solubility, ultraviolet light (UV) absorption qualities, and any expectations as to chemical interaction with other substances in the medium.

Likewise, the signalling substance to be employed in an actual embodiment will depend on a variety of factors. In particular, the choice of medium, buffer (if used) and signalling substance will, in many embodiments, be inter-dependent. Some examples, for the aid of the reader, include carbohydrates, proteins, nucleic acids, amino acids, and small organic compounds.

The selection of chemical substances to be used in a system, in accordance with an embodiment, should take into account any chemical processes or other interactions which may occur in the medium and that might limit carrier lifetime. An important example is that enzymatic reactions may remove protein carriers from the medium prematurely. Of course, the same reactions might be useful for removing “slow” proteins from the medium so as not to create too much dispersion in the information signal.

In an embodiment, the injection of a signalling substance into the provided medium can be accomplished in at least two ways. Hydrodynamic injection involves applying a pressure differential between the two ends of the capillary (e.g., by using a micropipette). Electrokinetic injection involves inducing a potential difference in the medium.

Hydrodynamic injection is useful when the medium lacks viscosity, but it can be difficult to attain an appropriate pressure differential in viscous media (e.g., gels). In this case, it may be more appropriate to use electrokinetic injection. In contemplated embodiments, detection of the signalling substance depends on the nature of the signalling substance (also known as the analyte). Typical capillary electrophoresis detectors utilise high performance liquid chromatography. Various modes exist. Examples include methods based on absorption, florescence, mass spectrometry, and conductivity.

While the above embodiments have been described with regard to a uni-directional communications channel, it will be evident that embodiments can be derived that enable bi-directional communication. By enabling injection of signalling substance at either end of the tube, and providing detection at both ends of the channel, an electrophoretic driving field can be made to urge the injected signalling substance in either direction. In effect, the signalling substance“rides” the wave of the electric field as it progresses along the tube. The effect is entirely reversible.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed the novel methods and devices described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of methods and devices described herein may be made. The accompanying claims and their equivalents are intended to cover such forms of modifications as would fall within the scope of the inventions.