Biocompatible Quantum Funnels for Neural Photostimulation

Abstract

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.

Nanoengineering InP Quantum Dot-Based Photoactive Biointerfaces for Optical Control of Neurons

“…Capacitive biointerfaces have fast charging dynamics with rise times on the order of tens or hundreds of microseconds ( Ciocca et al, 2020 ; Han et al, 2020 ), whereas the decay times might be in milliseconds range ( Jakešová et al, 2019 ). On the other hand, faradaic devices have typically longer rise/fall times due to the slower charging–discharging kinetics governed by electron transfer rate and availability of ions at the reaction site ( Merrill et al, 2005 ; Bahmani Jalali et al, 2018b , 2019a ). In this context, the photocurrents in Figures 2B,C rise to their maximum levels and falls back to their steady-state levels in less than 3 ms (insets of Figures 2B,C ), which presents suitable charging/discharging dynamics for typical neuromodulation frequencies varying from few Hz to tens of Hz ( Cogan, 2008 ) (the photoresponses of the biointerfaces for 5 ms and 1 ms pulses can be seen in Supplementary Figure 3 ).…”

“…InP-based QDs show a promising nontoxic alternative to be used for neural interfaces owing to the composition of III-V elements with covalent bonds in their structure and not containing highly toxic elemental compounds (Bharali et al, 2005). In addition to the previous reports showing the biocompatibility of InP-based QDs for both in vitro and in vivo (Yong et al, 2009;Lin et al, 2015;Bahmani Jalali et al, 2019a), our study showed the biocompatibility of InP QDbased type I and type II biointerfaces on primary hippocampal neurons in vitro, which are commonly used neural cell type to observe neurotoxicity. Moreover, the Bohr exciton radius of InP (∼9 nm) is larger than CdSe (∼5 nm), which gives a high-level controlling ability of electron and hole energy levels.…”

“…We demonstrated that shell growth facilitates substantial enhancement of photoelectrochemical current levels. In addition to the QD level control, their optoelectronic engineering offers the ability to demonstrate unconventional biointerfaces using non-radiative energy transfer, like in photosynthesis processes of plants ( Bahmani Jalali et al, 2019a ).…”

“…Previously, our group showed successful operation of neural stimulation devices based on a biocompatible photoactive layer of InP/ZnO core/shell QDs ( Bahmani Jalali et al, 2018b ). More recently, we demonstrated a quantum funnel structure based on InP-based QDs, which can enhance the photocurrent production of QD-based biointerfaces through the non-radiative energy transfer mechanism ( Bahmani Jalali et al, 2019a ). Different from those studies, this report presents device- and nanostructure-level engineering to control the direction and strength of the neural modulation, leading to temporally precise, and rapidly reversible photostimulation of neurons.…”

Quantum dot and electron acceptor nano-heterojunction for photo-induced capacitive charge-transfer

“…Colloidal 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 . 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] . These devices, however, either contain toxic-heavy-metals or operate photoelectrochemically, both of which might harm the tissues in the long-term use.…”