Search

Despite the high quantum efficiency of solar energy conversion by photosynthesis, practical development of photosynthetic solar energy has been limited so far. One of the main challenges is the relatively poor absorption of photons by photosystems due to narrow absorption spectra, reflection, and respiration. Although most studies focused on increasing the harvesting of photosynthetic electrons (PEs), engineering photon absorption in photosynthesis is another important pathway to pursue for enhancement of photosynthetic solar energy harvesting. Here, plasmonic resonance energy transfer (PRET) from plasmonic nanoparticles to thylakoid membranes (TMs) is proposed to stimulate photosynthesis and increase production of PEs. Gold nanorods (AuNRs), which have a plasmon resonance peak close to 680 nm, are selected to increase the production of high energy PEs by PRET. With AuNR conjugation to spinach TMs, light-triggered PE currents increase to the magnitude 4 fold larger than the currents without the plasmonic AuNRs. Biophotovoltaic (BPV) cells were prepared with the plasmon-enhanced spinach TMs, and they were connected in series and with a capacitor for charge accumulation. The spinach BPVs were charged to achieve high OCP enough to power an LED lamp, demonstrating the feasibility to operate low-power electronics.

For extraction of photosynthetic electrons (PEs) from plant cells and algal cells, there have been many approaches using living algal cells or isolated photosynthetic apparatus such as photosystem II, photosystem I, and thylakoid membranes (TMs). Among these, bio-photoanodes coated with TMs demonstrated stable performance and the possibility for their practical applications. When a TM photoanode is prepared, TMs are deposited on the surface of a metal electrode. However, since the thickness of TM films determines the light absorption and electron transfer processes, the performance of a TM bio-photoanode is significantly affected by the TM film quality. Thus, in this study, electrospraying was employed to deposit TMs with enhanced control of the thickness and uniformity of TM coating on metal electrodes. In particular, we investigated how both the quality of TM films and the magnitude of PE currents were influenced by electrospraying time, substrate motion, solution feed rates, TM concentration, and addition of graphene oxide (GO) nanosheets. Finally, to assess the feasibility of TM electrospraying as a scalable fabrication method, TMs were electrosprayed on 5 × 5 cm2 size films of indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) (ITO-PEN). The coating uniformity was assessed by measuring PE currents from different locations of the TM-deposited ITO-PEN films.

Harvesting solar energy in the form of electricity from the photosynthesis of plants, algal cells, and bacteria has been researched as the most environment-friendly renewable energy technology in the last decade. The primary challenge has been the engineering of electrochemical interfacing with photosynthetic apparatuses, organelles, or whole cells. However, with the aid of low-dimensional nanomaterials, there have been many advances, including enhanced photon absorption, increased generation of photosynthetic electrons (PEs), and more efficient transfer of PEs to electrodes. These advances have demonstrated the possibility for the technology to advance to a new level. In this article, the fundamentals of photosynthesis are introduced. How PE harvesting systems have improved concerning solar energy absorption, PE production, and PE collection by electrodes is discussed. The review focuses on how different kinds of nanomaterials are applied and function in interfacing with photosynthetic materials for enhanced PE harvesting. Finally, the review analyzes how the performance of PE harvesting and stand-alone systems have evolved so far and its future prospects.

Direct extraction of photosynthetic electrons from the whole photosynthetic cells such as plant cells or algal cells can be highly efficient and sustainable compared to other approaches based on isolated photosynthetic apparatus such as photosystems I, II, and thylakoid membranes. However, insertion of nanoelectrodes (NEs) into individual cells are time-consuming and unsuitable for scale-up processes. We propose simple and efficient insertion of massively-populated NEs into cell films in which algal cells are densely packed in a monolayer. After stacking the cell film over an NE array, gentle pressing of the stack allows a large number of NEs to be inserted into the cells in the cell film. The NE array was fabricated by metal-assisted chemical etching (MAC-etching) followed by additional steps of wet oxidation and oxide etching. The cell film was prepared by mixing highly concentrated algal cells with alginate hydrogel. Photosynthetic currents of up to 106 nA/cm2 was achieved without aid of mediators, and the photosynthetic function was maintained for 6 days after NE array insertion into algal cells.

Techniques for the delivery foreign materials into living cells as well as for sensing have undeniable worth in cell biology research. A major barrier for intracellular delivery is to cross the cell membrane with little or no damage. Among the various intracellular delivery methods, one-dimensional nanoneedles are one of the promising methods for insertion with minimal invasiveness to a cell. Most of the previous studies have been conducted using vertical nanoneedle. Here, we synthesized new inclined nanoneedles and demonstrated a novel platform using inclined-gallium nitride nanoneedles (iGaN NNs) to facilitate efficient intracellular delivery. In our system, foreign molecules were successfully delivered into cytoplasm of a cell through the penetration of the cell membrane by the iGaN NNs.

Harvesting photosynthetic electrons (PEs) from plant or algal cells can be a highly efficient and environmentally friendly way of generating renewable energy. Recent work on nanoelectrode insertion into algal cells has demonstrated the possibility to directly extract PEs from living algal cells with high efficiencies. However, the instability of the inserted cells limits the practicality of this technology. Here, the impact of nanoelectrode insertion on intracellular extraction of PEs is characterized with the goal of stabilizing algal cells after nanoelectrode insertion. Using nanoelectrodes

An electrochemically active nanowire system is fabricated using wet-tapped nanosphere lithography and a single photolithography step. The patterned nanowire/nanoelectrode is inserted into live algal cells, enabling the potential harvesting of photosynthetic electrons from multiple cells simultaneously. Light-dependent extraction of electrons from cells is observed; these electrons are derived from the photosynthetic electron transport chain based on a light intensity-dependence of the reaction coupled with the finding that electron extraction is inhibited in the presence of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a reagent that specifically blocks electron flow out of photosystem II. Insertion of nanoelectrodes into multiple algal cells is achieved, and sequential insertion of cells with the nanoelectrode, followed by subsequent removal of the electrode, yields a corresponding increase and then decrease in light-driven currents. Controlling the intensity of the illumination avoids nearly all photodamage and enables direct extraction of more photosynthetic electrons from multiple cells in parallel, which is sustained for an extended period of time.

Photosynthesis converts solar energy to electricity in a highly efficient manner. Since only water is needed as fuel for energy conversion, this highly efficient energy conversion process has been rigorously investigated. In particular, photosynthetic apparatus, such as photosystem II (PSII), photosystem I (PSI), or thylakoids, have been isolated from various plants to construct bio-hybrid anodes. Although PSII or PSI decorated anodes have shown potentials, there still remain challenges, such as poor stability of PSII-based systems or need for electron donors other than water molecules of PSI-based systems. Thylakoid membranes are relatively stable after isolation and they contain all the necessary photosynthetic apparatus including the PSII and PSI. To increase electrical connections between thylakoids and anodes, nanomaterials such as carbon nanotubes, nanowires, nanoparticles, or graphene have been employed. However, since they rely on the secondary electrical connections between thylakoids and anodes; it is desired to achieve larger direct contacts between them. Here, we aimed to develop micro-pillar (MP) array anodes to maximize direct contact with thylakoids. The thylakoid morphology was analyzed and the MP array was designed to maximize direct contact with thylakoids. The performance of MP anodes and a photosynthetic fuel cell based on MP electrodes was demonstrated and analyzed.

Effective insertion of vertically aligned nanowires (NWs) into cells is critical for bioelectrical and biochemical devices, biological delivery systems, and photosynthetic bioenergy harvesting. However, accurate insertion of NWs into living cells using scalable processes has not yet been achieved. Here, NWs are inserted into living Chlamydomonas reinhardtii cells (Chlamy cells) via inkjet printing of the Chlamy cells, representing a low-cost and large-scale method for inserting NWs into living cells. Jetting conditions and printable bioink composed of living Chlamy cells are optimized to achieve stable jetting and precise ink deposition of bioink for indentation of NWs into Chlamy cells. Fluorescence confocal microscopy is used to verify the viability of Chlamy cells after inkjet printing. Simple mechanical considerations of the cell membrane and droplet kinetics are developed to control the jetting force to allow penetration of the NWs into cells. The results suggest that inkjet printing is an effective, controllable tool for stable insertion of NWs into cells with economic and scale-related advantages.