Photoelectric properties of a detector based on dried bacteriorhodopsin film

A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of -669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

An Electronic and Optically Controlled Bifunctional Transistor Based on a Bio-Nano Hybrid Complex

We report an electronically and optically controlled bioelectronic field-effect transistor (FET) based on the hybrid film of photoactive bacteriorhodopsin and electronically conducting single-walled carbon nanotubes (SWNTs). Two-dimensional (2D) crystals of bacteriorhodopsin form the photoactive center of the bio-nano complex, whereas one-dimensional (1D) pure SWNTs provide the required electronic support. The redshift in the Raman spectra indicates the electronic doping with an estimated charge density of 3 × 10⁶ cm^-2. The hybrid structure shows a conductivity of 19 μS/m and semiconducting characteristics due to preferential binding with selective diameters of semiconducting SWNTs. The bioelectronic transistor fabricated using direct laser lithography shows both optical and electronic gating with a significant on/off switch ratio of 8.5 and a photoconductivity of 13.15 μS/m. An n-type FET shows complementary p-type characteristics under light due to optically controlled, electronic doping by the "proton-pumping" bacteriorhodopsin. The fabricated bioelectronic transistor exhibits both electronically and optically well-controlled bifunctionality based on the functionalized hybrid electronic material.

A Review on Bacteriorhodopsin-Based Bioelectronic Devices

Bacteriorhodopsin protein extracted from Halobacterium salinarum is widely used in many biohybrid electronic devices and forms a research subject known as bioelectronics, which merges biology with electronic technique. The specific molecule structure and components of bR lead to its unique photocycle characteristic, which consists of several intermediates (bR, K, L, M, N, and O) and results in proton pump function. In this review, working principles and properties of bacteriorhodopsin are briefly introduced, as well as bR layer preparation method. After that, different bR-based devices divided into photochemical and photoelectric applications are shown. Finally, outlook and conclusions are drawn to inspire new design of high-performance bR-based biohybrid electronic devices.

Bacteriorhodopsin-ZnO hybrid as a potential sensing element for low-temperature detection of ethanol vapour

Zinc oxide (ZnO) and bacteriorhodopsin (bR) hybrid nanostructures were fabricated by immobilizing bR on ZnO thin films and ZnO nanorods. The morphological and spectroscopic analysis of the hybrid structures confirmed the ZnO thin film/nanorod growth and functional properties of bR. The photoactivity results of the bR protein further corroborated the sustainability of its charge transport property and biological activity. When exposed to ethanol vapour (reducing gas) at low temperature (70 °C), the fabricated sensing elements showed a significant increase in resistivity, as opposed to the conventional n-type behaviour of bare ZnO nanostructures. This work opens up avenues towards the fabrication of low temperature, photoactivated, nanomaterial-biomolecule hybrid gas sensors.

Deposition of bacteriorhodopsin protein in a purple membrane form on nitrocellulose membranes for enhanced photoelectric response

Bacteriorhodopsin protein (bR)-based systems are one of the simplest known biological energy converters. The robust chemical, thermal and electrochemical properties of bR have made it an attractive material for photoelectric devices. This study demonstrates the photoelectric response of a dry bR layer deposited on a nitrocellulose membrane with indium tin oxide (ITO) electrodes. Light-induced electrical current as well as potential and impedance changes of dried bR film were recorded as the function of illumination. We have also tested bR in solution and found that the electrical properties are strongly dependent on light intensity changing locally proton concentration and thus pH of the solution. Experimental data support the assumption that bR protein on a positively charged nitrocellulose membrane (PNM) can be used as highly sensitive photo- and pH detector. Here the bR layer facilitates proton translocation and acts as an ultrafast optoelectric signal transducer. It is therefore useful in applications related to bioelectronics, biosensors, bio-optics devices and current carrying junction devices.

Potential applications of bacteriorhodopsin mutants

Bacteriorhodopsin (BR), a model system in biotechnology, is a G-protein dependent trans membrane protein which serves as a light driven proton pump in the cell membrane of Halobacterium salinarum. Due to the linkage of retinal to the protein, it seems colored and has numbers of versatile properties. As in vitro culture of the Halobacteria is very difficult, and isolation is time consuming and usually inefficient, production of genetically modified constructs of the protein is essential. There are three important characteristics based on protein catalytic cycle and molecular functions of photo-electric, photochromic and proton transporting, which makes this protein as a strategic molecule with potential applications in biotechnology. Such applications include protein films, used in artificial retinal implants, light modulators, three-dimensional optical memories, color photochromic sensors, photochromic and electrochromic papers and ink, biological camouflage and photo detectors for biodefense and non-defense purposes.

Förster Resonance Energy Transfer between Core/Shell Quantum Dots and Bacteriorhodopsin

An energy transfer relationship between core-shell CdSe/ZnS quantum dots (QDs) and the optical protein bacteriorhodopsin (bR) is shown, demonstrating a distance-dependent energy transfer with 88.2% and 51.1% of the QD energy being transferred to the bR monomer at separation distances of 3.5 nm and 8.5 nm, respectively. Fluorescence lifetime measurements isolate nonradiative energy transfer, other than optical absorptive mechanisms, with the effective QD excited state lifetime reducing from 18.0 ns to 13.3 ns with bR integration, demonstrating the Förster resonance energy transfer contributes to 26.1% of the transferred QD energy at the 3.5 nm separation distance. The established direct energy transfer mechanism holds the potential to enhance the bR spectral range and sensitivity of energies that the protein can utilize, increasing its subsequent photocurrent generation, a significant potential expansion of the applicability of bR in solar cell, biosensing, biocomputing, optoelectronic, and imaging technologies.

Fabrication and characterization of a radiation sensor based on bacteriorhodopsin

Available techniques of X-ray detection have been under development due to specific shortcomings such as finite lifetime, low sensitivity, and post-processing requirements. Here we report on the fabrication of an X-ray sensor based on bacteriorhodopsin (BR) with a radius of r=3mm as the sensing area on a flexible substrate. The flexible X-ray detector can be placed on the targeted area for real-time monitoring of radiation dosage. We show that BR sensor is a potential candidate for such a powerful sensing device. For this purpose, we measure the electrical current generated by the BR sensor under different radiation dosages, energies and dose rates. This averaged current is in the range of nanoampere and is proportional to the dose rate of the received X-ray. The current also increases with the increase of radiation energy. BR radiation sensor can be readily miniaturized and is relatively easy to fabricate. The capability for real-time data collection and reusability are other advantages of this radiation sensor.