BREN KARA (US)
CN111172068A | 2020-05-19 | |||
US10047443B2 | 2018-08-14 | |||
US10047443B2 | 2018-08-14 |
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What is claimed: 1. A composition for producing hydrogen, comprising: (a) a nanoparticle or plurality of nanoparticles; (b) an external source of electrons, wherein the external source of electrons is an electrogenic bacterium or a plurality of electrogenic bacteria and a carbon source; and (c) an aqueous medium; wherein the nanoparticle or the plurality of nanoparticles and the aqueous medium are combined in a mixture; upon exposure to electromagnetic radiation with a wavelength in the absorption profile of the nanoparticle or the plurality of nanoparticles, the nanoparticle or the plurality of nanoparticles is capable of generating an electron that can reduce a proton in the aqueous medium; and the source of electrons is capable of reducing the nanoparticle or the plurality of nanoparticles. 2. The composition of claim 1, wherein the nanoparticle or the plurality of nanoparticles are selected from the group consisting of: (1) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and Ge nanoparticles; (2) core-shell nanoparticles, including CdSe/CdS, CdSe/CdTe, CdTe/CdSe, and PbSe/PbS core-shell nanoparticles; (3) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and/or Ge nanorods; (4) dot-in rods, including CdSe/CdS, CdSe/CdTe, CdTe/CdS, and CdTe/CdSe dot-in rods; (5) Zn-based II-VI core QDs, (6) nanoplatelets including core-crown and core-shell nanoplatelets comprising CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, Ge, SnS, SnSe, SnTe, Ag2S, Ag2Se and/or Ag2Te; (7) SnS, SnSe, SnTe, Ag2S, Ag2Se and Ag2Te; and combinations thereof. 3. The composition of claim 2, wherein the nanoparticle or the plurality of nanoparticles comprise cadmium chalcogenide (CdSe or CdS). 4. The composition of claim 2, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots. 5. The composition of claim 1, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer. 6. The composition of claim 5, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 7. The composition of claim 6, wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 8. The composition of claim 6, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA. 9. The composition of claim 1, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots, and wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or a genetically-modified bacterium. 10. The composition of claim 1, wherein the electromagnetic radiation has a wavelength of between approximately 400 and 1100 nanometers (nm). 11. The composition of claim 10, wherein the electromagnetic radiation has a wavelength of approximately 530 nm. 12. The composition of claim 1, wherein the pH of the mixture is approximately 7. 13. The composition of claim 1, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots, the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or a genetically-modified bacterium, the electromagnetic radiation has a wavelength of approximately 530 nm and the pH of the mixture is approximately 7. 14. The composition of claim 13, wherein the wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 15. The composition of claim 14, wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 16. The composition of claim 14, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA. 17. The composition of claim 1, wherein the aqueous medium is wastewater. 18. The composition of claim 1, wherein the carbon source comprises lactate. 19. The composition of any of claims 9-16, wherein the carbon source comprises lactate. 20. A method for producing hydrogen comprising: (a) providing a source of electrons wherein the source of electrons is an electrogenic bacterium or a plurality of electrogenic bacteria and a carbon source; (b) contacting a nanoparticle or a plurality of nanoparticles in an aqueous medium to form a mixture in the presence of the source of electrons; and (c) exposing the mixture from (b) to electromagnetic radiation having at least a wavelength in the absorption profile of the nanoparticle or the plurality of nanoparticles, wherein: upon exposure to the electromagnetic radiation, the nanoparticle or the plurality of nanoparticles is capable of generating an electron that can reduce a proton in the aqueous medium, and the source of electrons is capable of reducing the nanoparticle or the plurality of nanoparticles, such that hydrogen is produced. 21. The method of claim 20, wherein the nanoparticle or the plurality of nanoparticles are selected from the group consisting of: (1) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and Ge nanoparticles; (2) core-shell nanoparticles, including CdSe/CdS, CdSe/CdTe, CdTe/CdSe, and PbSe/PbS core-shell nanoparticles; (3) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and/or Ge nanorods; (4) dot-in rods, including CdSe/CdS, CdSe/CdTe, CdTe/CdS, and CdTe/CdSe dot-in rods; (5) Zn-based II-VI core QDs, (6) nanoplatelets including core-crown and core-shell nanoplatelets comprising CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, Ge, SnS, SnSe, SnTe, Ag2S, Ag2Se and/or Ag2Te; (7) SnS, SnSe, SnTe, Ag2S, Ag2Se and Ag2Te; and combinations thereof. 22. The method of claim 21, wherein the nanoparticle or the plurality of nanoparticles comprise cadmium chalcogenide (CdSe or CdS). 23. The method of claim 21, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots. 24. The method of claim 20, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer. 25. The method of claim 24, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 26. The method of claim 25, wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 27. The method of claim 25, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA. 28. The method of claim 20, wherein the electromagnetic radiation has a wavelength of between approximately 400 and 1100 nanometers (nm). 29. The method of claim 28, wherein the electromagnetic radiation has a wavelength of approximately 530 nm. 30. The method of claim 20, wherein the pH of the mixture is approximately 7. 31. The method of claim 20, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots, the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer, the electromagnetic radiation has a wavelength of approximately 530 nm and the pH of the mixture is approximately 7. 32. The method of claim 31, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 33. The method of claim 32, wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 34. The method of claim 32, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, CymA. 35. The method of claim 20, wherein the aqueous solution is wastewater. 36. The method of claim 20, wherein the carbon source comprises lactate. 37. The method of any of claims 24-34, wherein the carbon source comprises lactate. 38. A composition for producing hydrogen, comprising: (a) a nanoparticle or plurality of nanoparticles; (b) an external source of electrons, wherein the external source of electrons is an electrogenic bacterium or a plurality of electrogenic bacteria and a carbon source; (c) a surface; and (d) an aqueous medium; wherein the nanoparticle or the plurality of nanoparticles adhere to the surface and the surface is in contact with the aqueous medium; upon exposure to electromagnetic radiation with a wavelength in the absorption profile of the nanoparticle or the plurality of nanoparticles, the nanoparticle or the plurality of nanoparticles is capable of generating an electron that can reduce a proton in the aqueous medium; and the source of electrons is capable of reducing the nanoparticle or the plurality of nanoparticles. 39. The composition of claim 38, wherein the surface is an electrode or is comprised of quantum dots and wherein at least one electrogenic bacterium adheres to the surface. 40. The composition of claim 39, wherein electrogenic bacteria form a biofilm. 41. The composition of claims 38, 39 or 40 wherein the nanoparticle or the plurality of nanoparticles are selected from the group consisting of: (1) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and Ge nanoparticles; (2) core-shell nanoparticles, including CdSe/CdS, CdSe/CdTe, CdTe/CdSe, and PbSe/PbS core-shell nanoparticles; (3) CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and/or Ge nanorods; (4) dot-in rods, including CdSe/CdS, CdSe/CdTe, CdTe/CdS, and CdTe/CdSe dot-in rods; (5) Zn-based II-VI core QDs, (6) nanoplatelets including core-crown and core-shell nanoplatelets comprising CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, Ge, SnS, SnSe, SnTe, Ag2S, Ag2Se and/or Ag2Te; (7) SnS, SnSe, SnTe, Ag2S, Ag2Se and Ag2Te; and combinations thereof. 42. The composition of claim 41, wherein the nanoparticle or the plurality of nanoparticles comprise cadmium chalcogenide (CdSe or CdS). 41. The composition of claim 41, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots. 42. The composition of claims 38, 39 or 40, wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer. 43. The composition of claims 38, 39 or 40, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots, and wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer. 44. The composition of claim 43, wherein the wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 45. The composition of claim 44, wherein the wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 46. The composition of claim 44, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA. 47. The composition of claims 38, 39 or 40, wherein the electromagnetic radiation has a wavelength of between approximately 400 and 1100 nanometers (nm). 48. The composition of claim 47, wherein the electromagnetic radiation has a wavelength of approximately 530 nm. 49. The composition of claims 38, 39 or 40 wherein the pH of the mixture is approximately 7. 50. The composition of claims 38, 39 or 40, wherein the nanoparticle or the plurality of nanoparticles comprise water-soluble cadmium chalcogenide (CdSe or CdS) quantum dots, the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis, a Geobacter species or any bacterium capable of extracellular electron transfer, the electromagnetic radiation has a wavelength of approximately 530 nm and the pH of the mixture is approximately 7. 51. The composition of claim 50, wherein the wherein the electrogenic bacterium or plurality of electrogenic bacteria comprise Shewanella oneidensis and has at least one mutation selected from the group consisting of (1) deletion of the genes HydA and/or HyaB, encoding hydrogenases; (2) deletion of any of the hydrogenase-related genes, or any combination of HydA, HydB, HydE, HydF, and/or HydG; (3) deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA; (4) deletion or overexpression of any of the genes associated with extracellular electron transfer mediated by flavins and/or flavin biosynthesis, including RibF, RibDBAE, and/or OprF; (5) deletion or overexpression of any of the genes associated with biofilm formation including RibF and/or YdeH; and (6) display of surface peptides containing amino acids that may bind to nanoparticles, including histidine and cysteine. 52. The composition of claim 51, wherein the mutation is deletion of the genes HydA and/or HyaB, encoding hydrogenases. 53. The composition of claim 51, wherein the mutation is deletion or overexpression of any of the genes associated with extracellular electron transfer, including OmcA, MtrA, MtrB, MtrC, and/or CymA. 54. The composition of claims 38, 39 or 40, wherein the aqueous medium is wastewater. 55. The composition of claims 38, 39 or 40, wherein the carbon source comprises lactate. 56. The composition of any of claims 43-53, wherein the carbon source comprises lactate. |
Attorney Docket No.1625_028PCT PATENT C hemical description FW g/100mL Formula Vendor/Cat # Final conc. in (10000X) MM nM medium (Table 1) was prepared according to the recipe shown in Table 2.
Attorney Docket No.1625_028PCT PATENT C hemical description FW g/L Formula Vendor/Cat # Final conc. in (100X) MM µM abe S. nera souton 00 . e mnera souton used n te mnma medum (Table 1) was prepared according to the recipe shown in Table 3.
Attorney Docket No.1625_028PCT PATENT C hemical description g/100mL (100X) Vendor/Cat # Final conc. in MM, mg/mL medium (Table 1) was prepared according to the recipe shown in Table S4. [00113] Synthesis of CdSe-MPA [00114] Inside a nitrogen filled glovebox, 0.79 g of Selenium was dissolved in 10 mL of 97% trioctylphosphine in a scintillation vial and allowed to stir at 50° C until all solid had dissolved. In a separate vial, 0.747 g of anhydrous Cadmium Acetate was dissolved in 12 ml of 97% trioctylphosphine and stirred at 50 °C until all solid had dissolved. Outside of the glovebox, to a 100 mL three neck flask was added 7.8 g of trioctylphosphine oxide, 2.3 g of 98% hexadecylamine, and 0.171 g of 97% tetradecylphosphonic acid. The flask was purged with N 2 three times and heated to 100 °C below 0.1 Torr with stirring for 30 minutes. After returning to N 2 , 2.5 mL of the TOP/Se solution was injected, and the reaction was heated to 310 °C, where 2.5 mL of the TOP/Cd solution was injected very quickly with a syringe. The flask was transferred to a heating mantle set to 260° C, and the reaction was allowed to stir for 7 minutes. The solution was cooled using a heat gun (set to low) and placed into a water bath.15 mL of hexanes was injected into the reaction to prevent solidification of TOPO. The mixture was separated into 250-mL centrifuge tubes, where 10 ml of methanol and 25 mL of acetone was added. The product was centrifuged for 15 minutes at 8000 RPM. The clear supernatant was discarded, and the solid pellet was allowed to air dry. The solid was dispersed in 10 mL hexanes and placed in the centrifuge again for 15 minutes at 8000 RPM (repeated as needed). The final product was dissolved in hexanes. [00115] To exchange the native ligands with mercaptopropionic acid (MPA), 0.2401 g of tetrame-thylammonium hydroxide pentahydrate was dissolved in 13.3 mL of Attorney Docket No.1625_028PCT PATENT methanol along with 82.7 μL of MPA.100 nmol of TOPO-CdSe QDs in hexanes was added to 7.33 mL of the methanol solution in a 100 mL round bottom flask. The flask was put under N2 gas and refluxed at 65 C for 45 minutes. The solution was then dived into 2 centrifuge tubes, where 35 mL of ethyl ether and 10 mL of ethyl acetate were added. The tubes were placed into a centrifuge and spun at 8000 RPM for 15 minutes. The supernatant was disposed of, and the pallet was allowed to air dry. The results solid was dispersed in water. [00116] Photochemical Experiments [00117] Prior to beginning photochemical experiments, 41-mL scintillation vials (Sigma-Aldrich) and custom gas-tight caps containing GC septa (Restek) were autoclaved. Each experimental solution was a total of 5.0 mL in modified minimal medium (MM, pH 7). After bacterial cultures were grown to an OD600 of 0.4 - 0.5, approximately 500 µL of the cultures were transferred to MM (no fumarate) to reach an OD 600 of 0.05 in photochemical vials. CdSe- MPA were added to a final concentration of 1 µM, typically requiring about 230 µL from a CdSe-MPA stock solution. Each 5-mL solution in a 41-mL vial was sealed with a gas-tight cap and a septum and deoxygenated by purging the solution for 20 min and headspace for 10 min with a 79.31%/20.69% N 2 /CH 4 (Airgas) mixture using sterile needles. CH 4 is present as a reference for product quantification. [00118] Irradiation in the photochemical experiments was performed in a custom- built 16-sample apparatus where 41-mL scintillation vials were placed. The samples are temperature controlled at 25 °C with a circulating water bath, and maintain constant shaking at 100 rpm throughout the experiment. Samples are illuminated from below by a light-emitting diode (Philips LumiLED Luxeon Star Hex green 700 mA LEDs) at 530 nm (±10 nm). At the beginning of each experiment, the power of each LED was set to 25 mW ± 5 mW, as measured with a Nova II power meter (Ophir-Spiricon LLC) placed over each of the 16-wells. The amount of H2 produced was determined by sampling the headspace via gas chromatography (GC). To monitor H 2 evolution, 25 μL of headspace gas was withdrawn from each vial through a septum with a 50 μL gas-tight syringe (Hamilton). Headspace gas samples were analyzed on a Shimadzu GC-2014AT gas chromatograph (GC) with a thermal conductivity detector and Carboxen 1010 Attorney Docket No.1625_028PCT PATENT PLOT column (30 m × 0.53 mm, Supelco) to quantify the H 2 evolved with reference to CH 4 (in the purging gas mixture) as the internal standard. [00119] Preparation of Samples for Microscopy [00120] A glass coverslip (Fisherbrand 18x18-1, cat.12542A) was cut in half and inserted into the bottom of 41 mL experimental vials and autoclaved prior to experimental setup. The glass coverslip was used to remove the bacteria:QD aggregates without disturbing their architecture post-experiment. As described above, experiments combining WT and ΔhyaA MR-1 with CdSe-MPA were carried out for one week, and MR-1:CdSe-MPA aggregate formation was observed. After a week-long experiment, the supernatant was carefully removed from around the aggregates, which adhered to the coverslip as liquid was removed. To ease the process of removing the coverslip from the bottom of the vial without disturbing the aggregate, a low flow of nitrogen through a sterile air filter was used to dry the coverslip while it remained in the bottom of the vial. After drying for 45 minutes, a sterile inoculation loop was used to displace the coverslip, and the coverslip was then removed with sterile tweezers and placed onto clean slides. To prepare slides of the WT and ΔhyaA MR-1 in the absence of QDs (no aggregate formation), planktonic cells were transferred from media by placing two drops of media onto a clean microscope slide. They were then left to dry in sterile petri dishes under a low flow of sterile nitrogen for approximately one hour. [00121] Slides were washed with a few drops of PBS, pH 7.4, prior to fixation. Fixation of cells was carried out using 10% formalin (equivalent 4% paraformaldehyde) in PBS at pH 7.4 for 10 min at room temperature. After fixation, cells were gently washed with PBS. For membrane permeabilization to allow entry of DAPI, Triton X-100 was used. A 0.05% v/v Triton solution was prepared, and cells were incubated with Triton for 3 min at room temperature. Cells were rinsed with PBS immediately after permeabilization to remove the detergent. A DAPI stock solution was prepared at 20 mg/mL in DI H2O from lyophilized DAPI powder. A diluted stock of 0.5 µg/mL was prepared in PBS for staining the cells.500 µL of DAPI (0.5 µg/mL) were added to each slide, which incubated for 5 minutes at room temperature in the dark. After staining, cells were rinsed with PBS. For slides containing a coverslip and aggregate, they were Attorney Docket No.1625_028PCT PATENT secured to the microscope with a minimal amount of adhesive on the slide corners, which was allowed to harden to keep the coverslip in place. Slides were mounted for fluorescence microscopy using ProlongTM Diamond Antifade Mounting Media (Invitrogen; cat. P36961), sealed with a rectangular #1.5 coverslip, and cured overnight before imaging. [00122] Collection of Microscopy Data [00123] The slides as prepared above were imaged on an Olympus BX51 microscope connected to a Hamatsu ORCA-ER detector and illuminated with a Prior Lumen 200 source with a Hg lamp (Prior; cat LM200B1-A). Excitation lines and band pass (BP) or long pass (LP) emission filter pairs are as follows (excitation/BP or LP) – 350 nm / 450 nm BP; 405 nm / 532 nm LP; 405 nm/610 nm LP. These pairs were used to capture PL from DAPI stained bacteria, CdSe-MPA QDs, and neither DAPI or CdSe-MPA QDs, respectively. The emission was collected through an infinity-corrected 60x PlanApo 1.4NA oil objective with a 0.17mm working distance (Olympus). The emission is then passed through an OptiGrid structured illumination element to form a “grid” confocal image on the detector. For each sample, 12 images were taken at z-stack intervals of 0.5μm for a total depth of 6μm and compressed into the extended focus view presented in Figure S13. The exposure time for each channel was optimized and kept the same between each sample.Collection of Lactate Consumption Data. [00125] Time course lactate consumption was measured using a Colorimetric Lactate Assay Kit (Sigma Aldrich). Samples were prepared in a single well on a 96-well clear bottom plate using 2 mL of Lactate Enzyme Mix, 2 µL of Colorimetric Lactate Probe and 46 mL of Lactate Assay Buffer. The remaining 50 mL contained a lactic acid standard or minimal medium sample diluted with Lactate Assay Buffer. The samples were incubated for 30 min at room temperature. The samples were quantified using a Tecan Infinite 1000 multi-well plate reader using the absorbance at 570 nm. Samples (50 mL) were extracted from experimental vials at specific timepoints using a long sterile needle and aliquoted for quantification. Various dilutions of the minimal medium samples were used to ensure reproducibility of the absorbance readings. The external calibration was run with each assay to ensure accurate quantification. Attorney Docket No.1625_028PCT PATENT [00126] Collection of Colony Forming Unit Data. [00127] Colony forming unit (CFU) data on the QD-bacteria aggregate was obtained by transferring the aggregate with a minimal amount of MM solution from the photochemical vial to a centrifuge tube and centrifuging at 1300 rpm for 2 min. The supernatant was removed, and the cell pellet was resuspended in 500 mL of 1X sterile PBS (pH 7.4). A series of 2-fold dilutions was performed to yield six total solutions.100 mL of the solution was plated on an LB agar plate and incubated at 35 ⁰C for 24 hrs. Plates with between 30 and 300 colonies were counted to yield CFU/mL quantities. [00128] Electron Microscopy Experiments. [00129] For electron microscopy experiments, after a week-long hydrogen production experiment, aggregates comprised of MR-1 WT and CdSe-MPA were prepared for transmission electron microscopy imaging via fixation with a 2.5% glutaraldehyde/0.1 M sodium cacodylate solution. Images were taken on a Hitachi 7650 Transmission Electron Microscope with EDS (IF Instruments). [00130] Quantum Yield Measurements [00131] The quantum yield for hydrogen generation was calculated according to the equation below: ^ Φ ^^ = 2 [00132] Quantum yield to the amount of H2 produced relative to photons absorbed. Two photons are required to produce one mole of H2. k is the rate of H2 production, defined as: ^ = ^^ ^^^^^ Attorney Docket No.1625_028PCT PATENT [00133] q p is the photon flux, which measures of photons per second, and is defined as: ^ ^ = ^ ^^^^^ ^ ^^^ = ^ ^^ ! " # ! $ ! % [00134] The photon flux can be calculated using the power absorbed at a particular wavelength used during the experiment: & '(^ = & ) − & +, [00135] In this case, Pabs (W), power absorbed, was calculated by subtracting the power when quantum dots were present, PQD, from the initial power of the LED, P0, measured by a Newport power meter (Model 1918-C). For CdSe-MPA, the average Pabs is equal to 0.008 W at a wavelength (λ) of 525 nm. qp is calculated using the rest of the constants, where c is the speed of light (m/s), h is Planck’s constant (J s), and A is Avogadro’s constant (mol -1 ). [00136] Sample Calculation. [00137] H2 Generated in 168 Hours: 20.8 µmol = 2.1 x 10 -5 mol Time 168 hours = 10,080 min = 604,800 seconds - = ./ ^012^ = ^/.565789 012 = ^ = >.9657855 012/= U ./ = 7. /%
Attorney Docket No.1625_028PCT PATENT [00138] Results of QY Calculations. Bacteria [CdSe-MPA] (µM) Total H2 (µmol) TONNC QY (%) WT MR-1 0 6.2 ± 3.2 N/A N/A 5 5 6 tabulation of average hydrogen evolved and the corresponding TONs and QYs are shown in Table 5. [00139] The nanoparticle may be any nanoparticle that is a semiconductor. Without intending to be bound by any particular theory, it is considered that, upon illumination by electromagnetic radiation, H 2 evolves from the nanoparticles, which are eplenished by the bacteria through EET. [00140] “Nanoparticle” (NP) as used herein includes nanocrystals, quantum dots (QDs), magic size clusters (MSCs), quantum rods, dot-in-rod nanocrystals, quantum wires, dendritic inorganic nanostructures, tetrapods, cubes, core-shell and alloy structures of any of the preceding, and the like. Nanoparticles also include any 3-D geometry whereby one or more dimensions are in nanoscale size (<100 nm). The nanocrystals include quantum dots such as, for example, cores, core-shells, alloyed cores, alloyed core-shells, and the like. Type I and Type II nanocrystals (e.g., Type II core-shell nanocrystals) can be used. [00141] The nanoparticles can have a narrow size distribution. In an embodiment, a plurality of nanoparticles having a narrow size distribution (e.g., the nanoparticles are Attorney Docket No.1625_028PCT PATENT substantially monodisperse) is used. In an embodiment, the nanoparticles are substantially monodisperse. The term "substantially monodisperse" when describing nanoparticles denotes a population of nanoparticles of which a major portion, typically at least about 60%, in other embodiments from 75% to 90%, fall within a specified particle size range. A population of substantially monodisperse nanoparticles deviates 15% rms (root-mean-square) or less in diameter and typically less than 5% rms. In addition, upon exposure to a primary light source, a substantially monodisperse population of nanoparticles is capable of emitting energy in narrow spectral linewidths, as narrow as 12 nm to 60 nm full width of emissions at half maximum peak height (FWHM), and with a symmetric, nearly Gaussian line shape. The formulator will recognize, the linewidths are dependent on, among other things, the size heterogeneity (i.e., monodispersity) of the nanoparticles in each preparation. [00142] The absorption profile and, thus, the reduction potential of the nanoparticles are determined, at least in part, by the size of the nanoparticles. A selected size (or size distribution) of nanoparticles can be used. In one embodiment, smaller nanoparticles are used. For example, in the case of CdSe nanoparticles, nanoparticles having a size of 1.5 nm to 30 nm, including all nm values and ranges there between, are used. In one example, CdSe QDs were synthesized with a diameter of 2.6 nm as defined by the wavelength of the peak in their lowest energy excitonic absorption feature (525 nm, FIG.4). Quantum dots with varied sizes (between 2-10 nm) can be used. Changing the quantum dot size changes the wavelength of light absorbed and the energies of the conduction and valence bands. A higher conduction band may yield more active catalysis, and a lower valence band may enhance EET from bacteria. [00143] The surface of the nanoparticles can be controlled. A desired surface composition (e.g., surface concentration of anions or cations) can be obtained using known methods. For example, known post-particle-formation reactions can be used. As another example, a desired surface composition can be obtained without using post particle formation reactions. [00144] In an embodiment, the nanoparticles are capped (i.e., surface functionalized) with a ligand. The ligand can make the nanoparticles soluble in a convenient Attorney Docket No.1625_028PCT PATENT solvent (e.g., water). Such ligands are known in the art. Examples of suitable ligands include dihydrolipoic acid (DHLA), 3-mercapmercaptopropionic acid (e.g., MPA), and/or cysteine. Such capping ligands can be used with CdSe nanoparticles or other nanoparticles. In an embodiment, depending on the composition and/or structure of the nanoparticles, ligands are used that have one or more sulfur atoms. In another embodiment, ligands are used that have at least 2 sulfur atoms. Other ligands that can be used, particularly with CDSe QDs, are acids, amines and phosphines. [00145] The nanoparticles can be doped with isovalent ions and/or aliovalent metal ions. The isovalent ions may be magnetic. Suitable metal ions include Mn 2+ , Cu 2+ , Co 2+ , Group I cations, Group III cations, Au + , Ag + , Al 3+ , and the like. Charged nanoparticles can be obtained using known nanoparticle formation reactions. [00146] The nanoparticles can be obtained commercially or produced using methods known in the art. The nanoparticles can be soluble (or form a colloidal suspension) in an aqueous medium (e.g., water). For example, CdSe nanoparticles at a concentration of 0.5 µM to 10 µM are used. Some portion of the nanoparticles can precipitate from the mixture and the mixture continues to produce hydrogen. [00147] Examples of suitable nanoparticles include CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and/or Ge nanoparticles. Suitable nanoparticles also include core- shell nanoparticles, including CdSe/CdS, CdSe/CdTe, CdTe/CdSe, and/or PbSe/PbS core-shell nanoparticles. Nanorods such as CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, and/or Ge nanorods may be used. Also suitable are dot-in rods, including CdSe/CdS, CdSe/CdTe, CdTe/CdS, and CdTe/CdSe dot-in rods. Zn-based II-VI core QDs are also suitable. Other examples include nanoplatelets such core-crown and core-shell nanoplatelets comprising CdSe, CdS, CdTe, PbS, PbTe, PbSe, GaAs, InP, InAs, Si, Ge, SnS, SnSe, SnTe, Ag2S, Ag2Se and/or Ag2Te. Suitable nanoparticles also include SnS, SnSe, SnTe, Ag2S, Ag2Se or Ag2Te. Combinations of any of the foregoing may also be suitable. Attorney Docket No.1625_028PCT PATENT [00148] The nanoparticles may also be ternary or quaternary compounds. Cu- based ternary or quaternary quantum dots (QDs), or semiconductor nanocrystals (NCs) have unique optical properties regarding their emission mechanism, high photoluminescent quantum yields (PLQYs), size-dependent bandgap, composition-dependent bandgap, broad emission range, large Stokes’ shift, and long photoluminescent (PL) lifetimes. Various types of Cu-based ternary or quaternary QDs (including anisotropic NCs, polytypic NCs, and spherical, nanorod and tetrapod core/shell heterostructures) may be used. For example, ternary Cu-In-Se (CISe) and Cu-In-S (CIS) compounds may be used, such as CuInS2 and CuInSe2, or Cu-Sn-Se (CTSe) and Cu-Sn-S (CTS) compounds may be used. [00149] Additionally, metal halide perovskite NCs have attractive optical and electronic properties along with low cost and solution processability. Halide perovskites have a general formula of ABX3, where A and B are monovalent and divalent cations, respectively, and X is a monovalent halide (Cl, Br, I) anion. Lead halide perovskites, classified into either organic–inorganic (hybrid) or all-inorganic, depending on whether the A cation is an organic molecule. Most commonly used is methylammonium (MA, CH 3 NH 3+ ) for a hybrid compound, or an inorganic cation (commonly Cs+), may be used for the inorganic compound. Examples are MAPbX 3 nanoparticles and caesium lead halide perovskite NCs (CsPbX 3 ) where X=Cl, Br or I. [00150] In an embodiment, the nanoparticles are capped with a plurality of organic molecules (or mixture of organic molecules) and the catalyst has ligands formed from the same organic molecules. DHLA is an example of such an organic molecule. [00151] Mixtures of nanoparticles can be used. The mixture can include, but is not limited to, nanoparticles having different sizes (e.g., average diameters) and/or different compositions. For example, in one embodiment, mixtures of two or more nanoparticles having different absorbance profiles are used. In another embodiment, mixtures of at least two nanoparticles having different absorbance profiles are used. [00152] In an embodiment, the mixture of nanoparticles has a different absorption profile such that a greater portion of the solar spectrum is absorbed than is by one of the types of Attorney Docket No.1625_028PCT PATENT nanoparticles alone. For example, CdSe QDs can be used with QDs that absorb in the near infrared (e.g., CdTe, PbS, or PbSe) providing a nanoparticle mixture that absorbs in a greater portion of the solar spectrum than CdSe QDs alone. [00153] The mixture of nanoparticles can be present in a variety of configurations. In an embodiment, two or more types (i.e., at least two types) of nanoparticles are mixed together in the aqueous medium. In another embodiment, multiple aqueous media (each having a different type of nanoparticle) are used. The multiple aqueous media are exposed to electromagnetic radiation (e.g., solar flux) in a desired sequence. For example, wider band gap particles absorb first letting the unabsorbed energy (e.g., infrared (IR) wavelengths) through to be absorbed by subsequent a narrower band gap particles (e.g., in a separate container). [00154] A wide range of nanoparticle concentrations can be used. In one embodiment, to increase the production of hydrogen, the concentration(s) of the nanoparticle(s) is selected. [00155] The source of electrons reduces the photoexcited nanoparticle. In one embodiment, the source of electrons is inexpensive. Internal sacrificial electron donors can be used. Such sacrificial electron donors can be present in the mixture. A fixed amount of a source of electrons can be used. For example, in one embodiment, a fixed amount of a source of electrons is an amount equal to the concentration of the nanoparticles up to the saturated amount the solution can hold. In another embodiment, a fixed amount of a source of electrons means an amount not continually added. Additional source(s) of electrons can be added to the mixture to provide a continuous hydrogen production. Hydrogen production can be continued as long as sufficient source of electrons is added or is available to the mixture. For example, the sacrificial electron donor (e.g., ascorbic acid) is present at concentrations of 0.1 M to 1 M, including all values to 0.1 M and ranges there between. [00156] In an embodiment, the source of electrons is a biological system. Any biological system that can generate electrons can be used. In an embodiment, the biological system comprises prokaryotes that exhibit extracellular electron transfer (EET) such as, for Attorney Docket No.1625_028PCT PATENT example, electrogenic bacteria. The bacteria can be naturally-occurring bacteria or modified bacteria (e.g., genetically modified bacteria). [00157] In an embodiment, the organisms consume a carbon source that the organisms then convert to electrons that are transferred extracellularly. The “carbon source” may include adenosine, L-arabinose, D-arabitol, D-galacturonic acid, inosine, D-psicose, uridine, 2’- deoxyadenosine, dihydroxyacetone, L-alanine, α-keto-valeric acid, L-lactic acid, D-lactic acid methyl ester, methylpyruvate, propionic acid, pyruvic acid, L-serine, acetic acid, acetoacetic acid, butyric acid, 2-amonoethanol, caproic acid, L-leucine, L-threonine, Tween 20, Tween 40, Tween 80, D-cellobiose, chondroitine sulfate C, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, dulcitol, D-fructose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, D-glucosamine, α-D- glucose, glycogen, laminarin, maltose, maltotriose, D-mannose, pectin, sucrose, Gly-Glu, Gly- Pro, Gly-Asp, Ala-Gly, gelatin, L-asparagine, bromosuccinic acid, citric acid, fumaric acid, L- glutamic acid, L-glutamine, L-isoleucine, α-ketobutyric acid, L-malic acid, D,L-malic acid, mono-methylsuccinate, phenylethylamine, putrescine, and/or succinic acid. These carbon sources are described in Rodrigues, J. L., Serres, M. H. & Tiedje, J. M. Large-scale comparative phenotypic and genomic analyses reveal ecological preferences of Shewanella species and identify metabolic pathways conserved at the genus level. Applied and Environmental Microbiology 77, 5352–5360 (2011). Preferably, the carbon source may be adenosine, 2’- deoxyadenosine, L-lactic acid, methylpyruvate, pyruvic acid, Tween 20, Tween 40, Tween 80, N-acetyl-D-glucosamine, Gly-Glu, Gly-Pro, Gly-Asp and/or gelatin. The L-lactic acid may be in the form of lactate. The carbon source may be found in, for example, bacterial growth media such as Luria-Bertani medium, organic matter, organic waste, or waste water from a natural or industrial source. [00158] The biological system can be an internal source of electrons or an external source of electrons. For example, in an embodiment in which bacteria are the internal source of electrons, the bacteria make electrons and “spit” them out to the bacterial surface. These electrons then “bump” into nanoparticles to reduce them. In an embodiment in which bacteria Attorney Docket No.1625_028PCT PATENT are the external source of electrons, the bacteria reduce molecules in solution (e.g., flavins) that then reduce the nanoparticles. [00159] Examples of suitable electrogenic bacteria include members of the Shewanella genus (e.g., Shewanella oneidensis and Shewanella putrefaciens), Aeromonas hydrophila, and genetically modified Escherichia coli (e.g., E. coli-MtrC), Shewanella oneidensis (e.g., Shewanella oneidensis MR-1) and Bacillus subtilis (e.g., Bacillus subtilis-Omc expressed and -T. potens EET-mediating proteins expressed). Other examples of suitable electrogenic bacteria include Gram-positive bacteria such as Gram-positive dissimilatory metal- reducing bacteria. Examples of such bacteria include Thermincola potens. Other examples are bacteria that excrete flavins, for example, Bacillus subtilis, and Bacillus megatarium. Another embodiment may use a Geobacter species. Mixtures of bacteria can be used. Shewanella oneidensis MR-1 in which genes for both hydrogenase enzymes are knocked out (ΔhydA/ΔhyaB) can be used, with the advantage that without their own functional hydrogenases, these strains will not consume hydrogen produced by the system. [00160] Shewanella oneidensis in which genes expressing proteins that perform extracellular electron transfer are overexpressed will be used, with the advantage that these are expected to yield a greater flux of electrons to the quantum dots. The genes to be overexpressed include CymA, MtrA, MtrB, OmcA, MtrC. [00161] There are two routes for electrons to get from bacteria to the NPs. One route is "direct" EET from the bacteria to the NP. The second route is the excretion of electron shuttles such as flavins that are then capable of reducing the oxidized NP. In both cases, the original source of electrons is whatever medium serves as nutrients for the bacteria. [00162] In an embodiment, the source of electronic is electrogenic bacteria in the aqueous medium. In this embodiment, the electrogenic bacteria can be physically isolated from the QDs in the aqueous medium, but electrically connected to the QDs by a porous membrane (e.g., semi-permeable cellulose membranes, porous nanocrystalline silicon membranes, and Attorney Docket No.1625_028PCT PATENT porous carbon nanotube membranes) and a small molecule mediator (e.g., methyl viologen) added to facilitate electron transfer. [00163] In another embodiment, the electron source is electrogenic bacteria disposed (e.g., as a biofilm comprising the bacteria) on an electrode. The electrode can be external or internal to the aqueous medium. The electrogenic bacteria may also adhere to an electrode or nanoparticles but not form a film. [00164] The aqueous medium can have a variety of compositions. In an embodiment, the aqueous medium is water or wastewater. In an embodiment, the aqueous medium comprises water and/or wastewater. In another embodiment, the aqueous medium further comprises an organic solvent (or mixture of organic solvents). The organic solvent can be a protic solvent, an aprotic solvent, or a combination thereof. Examples of suitable organic solvents include alcohols such as ethanol, methanol, and ethylene glycol. For example, the aqueous medium is a 1:1 EtOH:water mixture by volume. [00165] The pH of the medium can be from 2.0 to 11.0, including all pH values to 0.1 pH unit and ranges therebetween (i.e., the tolerance is to 0.1 pH unit). In one embodiment, to increase the production of hydrogen, the pH of the medium is selected. H 2 evolution may occur between pH 2.2 and 4.5. It may also occur at approximately pH 7 (method described in Figs.3A and 3B). “Approximately” means within +/- 0.5 pH. [00166] Any wavelength (or wavelength range) of electromagnetic radiation that forms a photoexcited nanoparticle can be used and can be easily determined by one skilled in the art. Depending on the nanoparticle, wavelengths in the ultraviolet, visible, and near infrared can be used. Wavelengths in the solar spectrum can be used. Wavelengths greater than the energy of the lowest unoccupied molecular orbital (LUMO) of the nanoparticle(s) can be used. Wavelengths greater than the bandgap energy of the nanoparticle(s) can be used. [00167] The electromagnetic radiation can be provided in a variety of ways. Any radiation source providing the desired electromagnetic energy wavelength(s) can be used. For example, the electromagnetic radiation can be provided by a lamp (e.g., xenon lamp), arc lamp, Attorney Docket No.1625_028PCT PATENT black body radiation source, light emitting diode (LED), laser, or sunlight. The electromagnetic radiation can be provided in a continuous manner or intermittently as desired to control hydrogen production. Any range of wavelengths can be used as long as the nanoparticle absorbs the radiation. Preferably, the radiation comprises the visible and near-infrared (VNIR) portion of the electromagnetic spectrum, with wavelengths between approximately 400 and 1100 nanometers (nm). Most preferably, the radiation has a wavelength of 530 nm. [00168] The nanoparticles, source of electrons, and aqueous medium mixture can be present in a vessel. The vessel allows exposure of the mixture to the desired electromagnetic radiation. The size of the vessel can be scaled to the desired rate of hydrogen production. Examples of suitable vessels include flasks, vials, and reactors. In the case where two or more (i.e., at least two) different nanoparticles are used, the vessel can be configured such that the different nanoparticles are physically separated from each other. [00169] The mixture can be present in an inert atmosphere. For example, the mixture can be present in a nitrogen or argon atmosphere. The atmosphere can be a mixture of inert gases. [00170] The methods can be carried out at a wide range of temperatures. The mixture can be at ambient temperature or elevated temperature. The method can be performed at ambient temperature or elevated temperature. By ambient temperature, it is meant a temperature of 15 °C (59 °F) to 25 °C (77 °F), though differences in climate may acclimate people to higher or lower temperatures. The mixture can be present at an elevated temperature of, for example, 25 °C to 40 °C. The mixture can be present at approximately 25 °C. The method can be performed at approximately 25 °C. The generation of hydrogen can occur at approximately 25 °C, at ambient temperature or elevated temperature. [00171] In an embodiment, the composition and/or method produces hydrogen continuously for at least 164 hours without external voltage. Replenishing the carbon source allows catalysis to continue for a second week. In various embodiments, the method produces hydrogen for at least 100, 200, 300, or 400 hours without external voltage. Attorney Docket No.1625_028PCT PATENT [00172] Nano-bio H2-evolving assembly designs. Three distinct assemblies can be used. [00173] The first approach is direct combination of QDs and bacteria in solution (FIG.11A). In this system, the sacrificial electron donor is replaced by electrogenic bacteria, and the system is run in an appropriate bacterial medium. As bacteria respire, they engage in EET. The electrons are then available for H2 production which occurs through respiration of the QDs through EET. This assembly can be constructed with and without soluble redox mediators. Because electrogenic bacteria typically donate electrons directly to solid metals, and have been shown to donate electrons to nanoparticles, direct electron transfer from bacteria to QDs is expected. The electrons produced by electrogenic bacteria are expected to have sufficient reducing power to serve as donors to oxidized QDs. Indeed, typical reduction potentials of OMCs (~ −0.3 V) are significantly lower than that of ascorbate (~ 0.06 V). A number of bacterial strains may be used in this assembly including S. oneidensis MR-1, which is frequently used in biofuel cells and has well-understood EET function, and engineered E. coli-MTR, expressing EET-mediating proteins of S. oneidensis MR-1. [00174] In addition, Gram-positive dissimilatory metal-reducing bacteria can be used. Such bacteria are attractive microbes because of their resistance to QD-mediated toxicity. An example is Thermincola potens, which undergoes EET via OMCs. It is expected that B. subtilis can be engineered to express the T. potens EET-mediating proteins. An advantage of using B. subtilis is that it already shows wide use for protein expression not only in research laboratories but also for a range of industrial applications, and is capable of excreting recombinant proteins. [00175] The second approach that can be used is separating the electrogenic bacteria and QDs by a porous membrane (FIG.11B) that allows the passage of small molecules and ions but not bacteria and QDs. In this scheme, QDs and bacteria do not come into direct contact with each other. Charge is transferred using a small-molecule mediator added to the system; some bacteria such as Shewanella or Bacillus also excrete mediators such as flavins. The advantage of this approach is that any damage to bacteria that may result from direct contact with Attorney Docket No.1625_028PCT PATENT QDs will be mitigated, although the cost may be lower efficiency owing to the use of electron mediators. Nevertheless, small-molecule electron shuttles are routinely used in MFCs and MECs with success, although a direct electron-transfer approach can be used when feasible. [00176] The third approach is to construct a photo-bioelectrochemical cell (FIG. 11C) in which electrogenic bacteria deliver electrons to the anode, and QDs receive electrons from the cathode to catalyze H2 evolution. The electrons are generated in situ from the bacteria, as opposed to coming external to the system such as from an applied potential. Irradiation of the QDs, putting them into the excited state, provides sufficient energy needed to drive the reaction, as has already been established. The QDs and bacteria can be separated by a cation-exchange membrane; Nafion TM is commonly used in BECs. This setup parallels that of MECs, except that no external voltage need be applied, because the needed energy is supplied photochemically. An advantage of this system is that the separation of the QDs and bacteria mitigates concerns about QD toxicity. Furthermore, biofilm-forming bacteria can be grown directly on the anode for direct electron transfer, which increases efficiency relative to use of mediators. [00177] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. [00178] While embodiments of the present disclosure have been particularly shown and described with reference to certain examples and features, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the present disclosure as defined by claims that can be supported by the written description and drawings. Further, where exemplary embodiments are described with reference to a certain number of elements it will be understood that the exemplary embodiments can be practiced utilizing either less than or more than the certain number of elements. Attorney Docket No.1625_028PCT PATENT [00179] All references cited herein are incorporated herein by reference in their entirety and for all purposes to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes. [00180] The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.