Photoelectrodes with Polydopamine Thin Films Incorporating a Bacterial Photoenzyme

Abstract

A fabrication strategy of photoactive biohybrid electrodes based on the immobilization of the bacterial reaction center (RC) onto indium tin oxide (ITO) is proposed. The RC is an integral photoenzyme that converts photons into stable charge‐separated states with a quantum yield close to one. The photogenerated electron–hole pair can be eventually exploited, with suitable redox mediators, to produce photocurrents. To this purpose, RC must be effectively anchored on the electrode surface and simple strategies for its stable immobilization ensuring prolonged enzyme photoactivity are strongly desired. In this work, polydopamine (PDA), a polymer reminiscent of the natural melanin, is used to anchor the RC on the electrode surface. PDA is easily prepared in situ by spontaneous polymerization of dopamine in slightly alkaline aerated buffered RC solution. This reaction, carried out in the presence of an ITO substrate dipped into the solution, directly leads to a stable RC‐PDA/ITO photoelectrode with 20 nm film thickness and 50% of fully functional RC occupancy. Photocurrents densities recorded using this photoelectrode are comparable to those obtained with far more sophisticated immobilization techniques. The RC‐PDA films are fully characterized by visible–near‐infrared absorption spectroscopy, ellipsometry, atomic force, and scanning electron microscopies.

Bio-Inspired Redox-Adhesive Polydopamine Matrix for Intact Bacteria Biohybrid Photoanodes

“…For instance, PDA prepared exclusively by electrochemical means is insulating, 39 a characteristic absent if obtained by oxygenic polymerization. 40 Dopamine monomers have been recently utilized to modify electrode materials, such as carbon nanotubes providing adhesive properties for the deposition of thylakoids composites for biophotocurrent generation, 41 and silk fibroin electrodes in microbial fuel cells. 42 The entrapment of isolated photosynthetic reaction centers from purple bacteria in PDA films or nanoaggregates for biophotoanode preparation has also been reported, 40,43 where diffusible exogenous redox mediators were required to obtain PDA−enzyme biohybrid systems for energy purposes.…”

“…On the basis of the polymerization conditions of dopamine (i.e., time, pH, temperature, ionic strength, medium), polymers with different characteristics can be obtained. For instance, PDA prepared exclusively by electrochemical means is insulating, a characteristic absent if obtained by oxygenic polymerization …”

Activity of photosynthetic Reaction Centers coated with polydopamine

“…The final solution results in a slow sedimenting colloidal suspension of PDA nanoaggregates stable for hour or days; moreover, PDA nanoaggregates adhere to the surface of the reaction vessel or to any substrate dipped in solution. The PDA films are largely studied in literature as surface coating material able to entrap active enzymes [10] and amenable to further functionalization exploiting their versatile chemical reactivity of the exposed catechol groups [11]. In this work, rather than to the adhesive PDA films, we focus our attention on the above mentioned PDA colloidal suspensions.…”

Polydopamine/Ethylenediamine Nanoparticles Embedding a Photosynthetic Bacterial Reaction Center for Efficient Photocurrent Generation

“…[13] Among the systems for embedding functional RC molecules, we have explored polydopamine (PDA) for its many attracting features. [14] Polydopamine (PDA) is a melanin-like adhesive material deriving from the spontaneous oxidative polymerization of dopamine (DA) in mild basic oxygenated aqueous solutions. [15] PDA is based on 5,6-dihydroxy-indole repeating units and π-π stacking of dopamine monomers, but its chemical structure is very complex and not yet fully elucidated.…”

“…Furthermore, PDA:EDA nanoparticles retain the biocompatibility of PDA, and remain suitable to interface biological components. [21] In our recent work, [14] we reported a straightforward strategy to embed the photosynthetic reaction center (RC) from R. sphaeroides in PDA films deposited onto ITO electrode. By simultaneous one pot PDA polymerization and encapsulation of fully active protein, we reported a photoelectrode based on the bacterial RC immobilized in a much easier and effective way than most of the previously reported methods.…”