Wireless Amperometric Neurochemical Monitoring Using an Integrated Telemetry Circuit

An integrated circuit for wireless real-time monitoring of neurochemical activity in the nervous system is described. The chip is capable of conducting high-resolution amperometric measurements in four settings of the input current. The chip architecture includes a first-order $\Delta$ $\Sigma$ modulator ($\Delta$ $\Sigma$M) and a frequency-shift-keyed (FSK) voltage-controlled oscillator (VCO) operating near 433 MHz. It is fabricated using the AMI 0.5 $\mu$m double-poly triple-metal n -well CMOS process, and requires only one off-chip component for operation. Measured dc current resolutions of $\sim$250 fA, $\sim$ 1.5 pA, $\sim$4.5 pA, and $\sim$17 pA were achieved for input currents in the range of $\pm$5, $\pm$37, $\pm$150, and $\pm$600 nA, respectively. The chip has been interfaced with a diamond-coated, quartz-insulated, microneedle, tungsten electrode, and successfully recorded dopamine concentration levels as low as 0.5 $\mu$M wirelessly over a transmission distance of $\sim$0.5 m in flow injection analysis experiments.