For that we nanoengineer toxic-heavy-metal-free InP-based QDs and QD-fullerene nano-heterojunctions. In this study, we demonstrate QD-fullerene donor–acceptor nano-heterojunction photoelectrodes that produce capacitive-dominant photoresponse. Heavy-metal-free QD-based neural interfaces that have dominant capacitive charge injection have not been reported in the literature yet. These devices, however, either contain toxic-heavy-metals or operate photoelectrochemically, both of which might harm the tissues in the long-term use. Photostimulation devices based on HgTe, CdSe and InP QDs were previously reported in the literature that can efficiently stimulate neurons and evoke action potentials 15, 16, 17, 18. Moreover, silicon, organic semiconductors and carbon nanotubes have been used for capacitive photostimulation of neurons 9, 10, 11, 12, 13.Ĭolloidal quantum dots (QDs) are promising nanomaterials for neural interfaces due to their advantageous structural and optoelectronic properties such as tunable bandgap, high absorption in the visible spectrum, solution processability and stability 14. The capacity of such electrodes charging and discharging the double layer can be improved by additional dielectric coatings of tantalum/tantalum oxide (Ta/Ta 2O 5). For example, titanium nitride (TiN)-based capacitive electrodes for electrical stimulation inject charges through the electrode–electrolyte double layer 8. Hence, both electrical and optical neurostimulators are material- and device-wise engineered to induce capacitive currents. In that regard, capacitive stimulation is accepted as a safe method that modulates the cell membrane by inducing transient displacement currents without any direct charge transfer from the electrode to the biological medium 6, 7. The safe modulation of neural activity requires the avoidance of irreversible faradaic reactions, which might be harmful to the biological tissues 6, 7. The charge injection mechanism at the device/tissue interface is an important parameter that affects the efficiency and safety of neuromodulating devices. Light-activated interfaces provide a wireless and non-genetic way to modulate neurons with high spatiotemporal resolution, which make them a promising alternative to wired and surgically more invasive electrical stimulation electrodes 4, 5. Proper design and engineering of such biointerfaces enables the extracellular modulation of the neural activity, which leads to possible treatments of neurological diseases like retinal degeneration, hearing loss, diabetes, Parkinson and Alzheimer 1, 2, 3. Neural interfaces that can supply electrical current to the cells and tissues play a central role in the understanding of the nervous system. This study paves the way toward safe and efficient nanoengineered quantum dot-based next-generation photostimulation devices. The reduced electron–hole wavefunction overlap of 0.52 due to type-II band alignment of the quantum dot and the passivation of the trap states indicated by the high photoluminescence quantum yield of 70% led to the domination of photoinduced capacitive charge transfer at an optimum donor–acceptor ratio. For that, we formed a novel form of nano-heterojunctions using type-II InP/ZnO/ZnS core/shell/shell quantum dot as the donor and a fullerene derivative of PCBM as the electron acceptor. In this study, we demonstrate heavy-metal-free quantum dot-based nano-heterojunction devices that generate capacitive photoresponse. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy-metal content in such architectures hinders their safe use. Capacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons.
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