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

Light-activated biointerfaces provide a non-genetic route for effective control of neural activity. InP quantum dots (QDs) have a high potential for such biomedical applications due to their uniquely tunable electronic properties, photostability, toxic-heavy-metal-free content, heterostructuring, and solution-processing ability. However, the effect of QD nanostructure and biointerface architecture on the photoelectrical cellular interfacing remained unexplored. Here, we unravel the control of the photoelectrical response of InP QD-based biointerfaces via nanoengineering from QD to device-level. At QD level, thin ZnS shell growth (∼0.65 nm) enhances the current level of biointerfaces over an order of magnitude with respect to only InP core QDs. At device-level, band alignment engineering allows for the bidirectional photoelectrochemical current generation, which enables light-induced temporally precise and rapidly reversible action potential generation and hyperpolarization on primary hippocampal neurons. Our findings show that nanoengineering QD-based biointerfaces hold great promise for next-generation neurostimulation devices.

Bidirectional optical neuromodulation using capacitive charge-transfer.

Artificial control of neural activity allows for understanding complex neural networks and improving therapy of neurological disorders. Here, we demonstrate that utilization of photovoltaic biointerfaces combined with light waveform shaping can generate safe capacitive currents for bidirectional modulation of neurons. The differential photoresponse of the biointerface due to double layer capacitance facilitates the direction control of capacitive currents depending on the slope of light intensity. Moreover, the strength of capacitive currents is controlled by changing the rise and fall time slope of light intensity. This approach allows for high-level control of the hyperpolarization and depolarization of membrane potential at single-cell level. Our results pave the way toward advanced bioelectronic functionalities for wireless and safe control of neural activity.

Efficient photocapacitors via ternary hybrid photovoltaic optimization for photostimulation of neurons.

Optoelectronic photoelectrodes based on capacitive charge-transfer offer an attractive route to develop safe and effective neuromodulators. Here, we demonstrate efficient optoelectronic photoelectrodes that are based on the incorporation of quantum dots (QDs) into poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. We control the performance of the photoelectrode by the blend ratio, thickness, and nanomorphology of the ternary bulk heterojunction. The optimization led to a photocapacitor that has a photovoltage of 450 mV under a light intensity level of 20 mW.cm-2 and a responsivity of 99 mA/W corresponding to the most light-sensitive organic photoelectrode reported to date. The photocapacitor can facilitate action potential generation by hippocampal neurons via burst waveforms at an intensity level of 20 mW.cm-2. Therefore, the results point to an alternative direction in the engineering of safe and ultra-light-sensitive neural interfaces.

Organic Photovoltaic Pseudocapacitors for Neurostimulation.

Neural interfaces are the fundamental tools to understand the brain and cure many nervous-system diseases. For proper interfacing, seamless integration, efficient and safe digital-to-biological signal transduction, and long operational lifetime are required. Here, we devised a wireless optoelectronic pseudocapacitor converting the optical energy to safe capacitive currents by dissociating the photogenerated excitons in the photovoltaic unit and effectively routing the holes to the supercapacitor electrode and the pseudocapacitive electrode-electrolyte interfacial layer of PEDOT:PSS for reversible faradic reactions. The biointerface showed high peak capacitive currents of ∼3 mA·cm-2 with total charge injection of ∼1 µC·cm-2 at responsivity of 30 mA·W-1, generating high photovoltages over 400 mV for the main eye photoreception colors of blue, green, and red. Moreover, modification of PEDOT:PSS controls the charging/discharging phases leading to rapid capacitive photoresponse of 50 µs and effective membrane depolarization at the single-cell level. The neural interface has a device lifetime of over 1.5 years in the aqueous environment and showed stability without significant performance decrease after sterilization steps. Our results demonstrate that adopting the pseudocapacitance phenomenon on organic photovoltaics paves an ultraefficient, safe, and robust way toward communicating with biological systems.

Plasmon-Coupled Photocapacitor Neuromodulators.

Efficient transduction of optical energy to bioelectrical stimuli is an important goal for effective communication with biological systems. For that, plasmonics has a significant potential via boosting the light-matter interactions. However, plasmonics has been primarily used for heat-induced cell stimulation due to membrane capacitance change (i.e., optocapacitance). Instead, here, we demonstrate that plasmonic coupling to photocapacitor biointerfaces improves safe and efficacious neuromodulating displacement charges for an average of 185% in the entire visible spectrum while maintaining the faradic currents below 1%. Hot-electron injection dominantly leads the enhancement of displacement current in the blue spectral window, and the nanoantenna effect is mainly responsible for the improvement in the red spectral region. The plasmonic photocapacitor facilitates wireless modulation of single cells at three orders of magnitude below the maximum retinal intensity levels, corresponding to one of the most sensitive optoelectronic neural interfaces. This study introduces a new way of using plasmonics for safe and effective photostimulation of neurons and paves the way toward ultrasensitive plasmon-assisted neurostimulation devices.

High-Performance, Large-Area, and Ecofriendly Luminescent Solar Concentrators Using Copper-Doped InP Quantum Dots.

Colloidal quantum dots (QDs) are promising building blocks for luminescent solar concentrators (LSCs). For their widespread use, they need to simultaneously satisfy non-toxic material content, low reabsorption, high photoluminescence quantum yield, and large-scale production. Here, copper doping of zinc carboxylate-passivated InP core and nano-engineering of ZnSe shell facilitated high in-device quantum efficiency of QDs over 80%, having well-matched spectral emission profile with the photo-response of silicon solar cells. The optimized QD-LSCs showed an optical quantum efficiency of 37% and an internal concentration factor of 4.7 for a 10 × 10-cm2 device area under solar illumination, which is comparable with the state-of-the-art LSCs based on cadmium-containing QDs and lead-containing perovskites. Synthesis of the copper-doped InP/ZnSe QDs in gram-scale and large-area deposition (3,000 cm2) onto commercial window glasses via doctor-blade technique showed their scalability for mass production. These results position InP-based QDs as a promising alternative for efficient solar energy harvesting.

Ecofriendly and Efficient Luminescent Solar Concentrators Based on Fluorescent Proteins.

In recent years, luminescent solar concentrators (LSCs) have received renewed attention as a versatile platform for large-area, high-efficiency, and low-cost solar energy harvesting. So far, artificial or engineered optical materials, such as rare-earth ions, organic dyes, and colloidal quantum dots (QDs) have been incorporated into LSCs. Incorporation of nontoxic materials into efficient device architectures is critical for environmental sustainability and clean energy production. Here, we demonstrated LSCs based on fluorescent proteins, which are biologically produced, ecofriendly, and edible luminescent biomaterials along with exceptional optical properties. We synthesized mScarlet fluorescent proteins in Escherichia coli expression system, which is the brightest protein with a quantum yield of 61% in red spectral region that matches well with the spectral response of silicon solar cells. Moreover, we integrated fluorescent proteins in an aqueous medium into solar concentrators, which preserved their quantum efficiency in LSCs and separated luminescence and wave-guiding regions due to refractive index contrast for efficient energy harvesting. Solar concentrators based on mScarlet fluorescent proteins achieved an external LSC efficiency of 2.58%, and the integration at high concentrations increased their efficiency approaching to 5%, which may facilitate their use as "luminescent solar curtains" for in-house applications. The liquid-state integration of proteins paves a way toward efficient and "green" solar energy harvesting.