A Multifunctional and Flexible Implantable Electrooptic Neural Probe With Embedded Micropump and Precise Flowmeter

Abstract

In this study, we introduce a multifunctional and flexible neural probe that includes a microlight-emitting diode ( $\mu $ -LED) for fluorescence excitation and optogenetics sensing, a micropump for drug delivery, and microelectrodes for electrophysiological recording. The microprobe has dimensions of 0.7 mm (W), 0.1 mm (H), and 10 mm (L). It integrates a polydimethylsiloxane (PDMS)-based micropump that operates through an electrolysis reaction at room temperature, a precise flowmeter for drug delivery, a $\mu $ -LED for neural stimulation, and four electrodes for recording action potentials. In addition, the probe includes a flexible printed circuit board (Flex-PCB) equipped with a bio-amplifier, LED driver, RF transceiver, and a microcontroller (MCU) to control the LED, capture and digitize brain activity, and to transmit neural data to a computer nearby. The MCU includes a proportional–integral–derivative (PID) controller and an analog-to-digital converter (ADC) for recording electrophysiological signals and measuring flow rate during experiments. The PDMS-based micropump contains a potassium hydroxide (KOH) reservoir for water electrolysis, a flexible membrane, a drug reservoir, and microfluidic channels for drug delivery, each with a capacity of $20~\mu $ L. This capacity allows for a duration of 1 h of continuous flow at the highest rate of 250 nL/min. Parallel gold-plated electrodes are integrated to function as a capacitance-based flowmeter, accurately measuring flow rates from 30 to 250 nL/min with an error margin of about 5% and a resolution of 20 pF per 100 pL/min. The PID controller maintains the desired flow rate by adjusting the pulsewidth modulation (PWM) duty cycle of the micropump driver. The probe also features four gold-plated square electrodes ( $125~\mu $ m in diameter) for capturing electrophysiological signals and a blue $\mu $ -LED for optogenetic stimulation or fluorescence excitation. It was tested in vitro to evaluate its performance in realistic experimental conditions. The probe, weighing just 1.5 g, is suitable for various neuroscience applications.