Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements of cell stimulation. Although indium-based colloidal quantum dots with type-I band alignment have attracted significant attention as a nontoxic alternative to cadmium-based ones, little attention has been paid to their photovoltaic potential as type-II heterostructures. Herein, we demonstrate type-II indium phosphide/zinc oxide core/shell quantum dots that are incorporated into a photoelectrode structure for neural photostimulation. This induces a hyperpolarizing bioelectrical current that triggers the firing of a single neural cell at 4 μW mm–2, 26-fold lower than the ocular safety limit for continuous exposure to visible light. These findings show that nanomaterials can induce a biocompatible and effective biological junction and can introduce a route in the use of quantum dots in photoelectrode architectures for artificial retinal prostheses.

Photovoltaic substrates have attracted significant attention for neural photostimulation. The control of the Faradaic and capacitive (non-Faradaic) charge transfer mechanisms by these substrates are critical for safe and effective neural photostimulation. We demonstrate that the intermediate layer can directly control the strength of the capacitive and Faradaic processes under physiological conditions. To resolve the Faradaic and capacitive stimulations, we enhance photogenerated charge density levels by incorporating PbS quantum dots into a poly(3-hexylthiophene-2,5-diyl):([6,6]-Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend. This enhancement stems from the simultaneous increase of absorption, well matched band alignment of PbS quantum dots with P3HT:PCBM, and smaller intermixed phase-separated domains with better homogeneity and roughness of the blend. These improvements lead to the photostimulation of neurons at a low light intensity level of 1 mW cm −2 , which is within the retinal irradiance level. These findings open up an alternative approach toward superior neural prosthesis.

Light is crucial for many biological activities of most organisms, including vision, resetting of circadian rhythm, photosynthesis, and DNA repair. The cryptochrome/photolyase family (CPF) represents an ancient group of UV-A/blue light sensitive proteins that perform different functions such as DNA repair, circadian photoreception, and transcriptional regulation. The CPF is widely distributed throughout all organisms, including marine prokaryotes. The bacterium Vibrio cholerae was previously shown to have a CPD photolyase that repairs UVinduced thymine dimers and two CRY-DASHs that repair UV-induced single-stranded DNA damage. Here, we characterize a hypothetical gene Vca0809 encoding a new member of CPF in this organism. The spectroscopic analysis of the purified protein indicated that this enzyme possessed a catalytic cofactor, FAD, and photoantenna chromophore 6,7-dimethyl 8-ribityllumazin. With a slot blot-based DNA repair assay, we showed that it possessed (6−4) photolyase activity. Further phylogenetic and computational analyses enabled us to classify this gene as a member of the family of iron−sulfur bacterial cryptochromes and photolyases (FeS-BCP). Therefore, we named this gene Vc(6−4) FeS-BCP.

Neural photostimulation has high potential to understand the working principles of complex neural networks and develop novel therapeutic methods for neurological disorders. A key issue in the light-induced cell stimulation is the efficient conversion of light to bioelectrical stimuli. In photosynthetic systems developed in millions of years by nature, the absorbed energy by the photoabsorbers is transported via nonradiative energy transfer to the reaction centers. Inspired by these systems, neural interfaces based on biocompatible quantum funnels are developed that direct the photogenerated charge carriers toward the bionanojunction for effective photostimulation. Funnels are constructed with indium-based rainbow quantum dots that are assembled in a graded energy profile. Implementation of a quantum funnel enhances the generated photoelectrochemical current 215% per unit absorbance in comparison with ungraded energy profile in a wireless and free-standing mode and facilitates optical neuromodulation of a single cell. This study indicates that the control of charge transport at nanoscale can lead to unconventional and effective neural interfaces.

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