Wasif Khan

A Flexible, Micro-Lens-Coupled LED Stimulator for Optical Neuromodulation

Optogenetics is a fast growing neuromodulation method, which can remotely manipulate the specific activities of genetically-targeted neural cells and associated biological behaviors with millisecond temporal precision through light illumination. Application of optogenetics in neuroscience studies has created an increased need for the development of light sources and the instruments for light delivery. This paper presents a micro-lens-coupled LED neural stimulator which includes a backside reflector and a frontside microlens for light collection and collimation. The device structure has been optimized using optical simulation and the optimized device is able to increase the volume of excitable tissues by 70.4%. Device prototypes have been fabricated and integrated based on an optimization of the device structure. The measurement results show that the light power increases by 99% at an effective penetration depth of 5 000

Wireless opto-electro neural interface for experiments with small freely behaving animals

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Characteristics of PEDOT:PSS thin films spin-coated on ITO

by the fabricated device under various voltages of 2.4-3.2 V.

Towards a free-floating wireless implantable optogenetic stimulating system

This paper presents a wireless opto-electro neural interface system that combines ECoG recording and optogenetic stimulation for closed-loop neuromodulation on small freely behaving animals, such as rodents. The prototype opto-electro neural interface array includes 4 μLEDs for optical stimulation and 2 microelectrodes for ECoG recording, all on a flexible polyimide substrate. The detachable headstage, connected to a custom-designed USB dongle via Bluetooth low energy (BLE), is capable of wirelessly receiving user commands to selectively drive the μLEDs, and transmitting the recorded ECoG data, to enable bidirectional data communication. A proof-of-concept in vivo experiment was conducted on a freely behaving rat, while successfully applying optical stimulation to synchronize the wirelessly recorded ECoG signals.

Neuronal excitability and network formation on optically transparent electrode materials

This paper reports on flexible, transparent, conductive films, which consist of poly-(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) spun onto indium-tin-oxide (ITO) substrates for potential applications in biomedical optoelectronic devices. The properties of the combined films are characterized using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), and ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy. Compared to bare ITO electrodes, the ITO-PEDOT:PSS multilayer electrodes show significantly enhanced electrochemical conductance, charge storage capacity, and mechanical flexibility while preserving excellent optical transparency.

Wafer level fabrication method of hemispherical reflector coupled micro-led array stimulator for optogenetics

This paper presents a wirelessly-powered and free-floating implantable optogenetic stimulating (FF-WIOS) implant with negligible footprint and high power transfer efficiency (PTE). FF-WIOS ASIC with embedded μLED and reflective lens is expected to stimulate the target cortical neuronal ensembles at high temporal and spatial resolution with minimal damage and no tethering effects. To improve the PTE, and stay below the SAR limit, a flexible planar transmitter (Tx) resonator, L2, will be implanted under the scalp, but over the skull. The Tx coil, L1, embedded in a headstage, L2 resonator, and a wire-bond receiver (Rx) coil, L3, wound around the FF-WIOS device, form a 3-coil inductive link operating at 135 MHz, which directly charges a surface-mount storage capacitor. At the onset of stimulation, the storage capacitor discharges into the μLED, while the stimulation parameters are sent to FF-WIOS by amplitude modulating of the power carrier. Post-layout simulation results show functionality of the storage capacitor charging, forward data transmission, and optogenetic stimulation with adjustable parameters.

A mm-sized free-floating wirelessly powered implantable optical stimulating system-on-a-chip

With the advent of genetically-encoded optical tools to trigger or report neuronal activity, new designs for multielectrode arrays (MEAs) used in neural interfacing incorporate both optical and electrical modes of stimulating or recording neural activity. Likewise, the need to improve upon the biocompatibility of implanted MEAs has moved the field towards the use of softer, more compliant materials in device fabrication. However, there is limited available information on the impact of the materials used in MEAs on the function of interfaced individual neurons and neuronal networks. We assessed the responses of rat cortical neurons on optically transparent materials commonly used in the construction of “next-generation” devices: indium tin oxide (ITO), parylene-C, and polydimethylsiloxane (PDMS). We found that neuronal network formation and spiking responses to electrical stimulation were enhanced in neurons cultured on ITO. We observed reduced excitability and synaptic connectivity between neurons cultured on PDMS. We hypothesize that the superior conductivity of ITO and suboptimal neuronal attachment to PDMS contributed to our results.

A miniaturized, wirelessly-powered, reflector-coupled single channel opto neurostimulator

We report a monolithic wafer-level fabrication method for a hemispherical reflector coupled light-emitting-diode (LED) array using isotropic etching of silicon. These neural stimulators collect the backside as well as the front side emission of the μ-LEDs and thus provide higher intensity, which is imperative for opsin expressions in optogenetics experiments. Aluminum was used as the reflective layer and the planarization of polymer on the reflector cavity was done using polydimethylsiloxane (PDMS). The lateral and vertical profiles of silicon etching were measured and the light intensity increase due to the reflector was investigated. It was found that the intensity increases by a minimum of 49% and maximum of 65% when coupling a reflector with the μ-LEDs.