A Wireless IC for Time-Share Chemical and Electrical Neural Recording

A 1.1-mW 4-channel integrated circuit for wireless time-share monitoring of chemical and electrical neural activity in the brain is described. The chip architecture can be configured to perform neurochemical monitoring using 300-V/s fast-scan cyclic voltammetry (FSCV) and neuroelectrical recording using extracellular electrophysiology. The 5-mm(2) IC is fabricated in AMI 0.5 mu m double-poly triple-metal n-well CMOS process and uses a 76-mu W, third-order, continuous-time, Delta Sigma modulator (CT-Delta Sigma M) per channel that achieves an input-referred noise of 56.7 pA(rms) (dc-5 kHz) and 3.5 mu V-rms (1.1-5 kHz) for chemical and electrical neuromonitoring, respectively. The chip architecture also incorporates monolithic circuitry for generating FSCV and biphasic constant-current stimulus waveforms. The chip has been externally interfaced with carbon-fiber microelectrodes (CFMs) implanted acutely in the caudate-putamen of an anesthetized rat, and enables chemically resolved monitoring of electrically evoked dopamine release and its postsynaptic bioelectrical response at the same recording site. The dopamine limit of detection (LOD) corresponding to a signal-to-rms noise ratio of three is estimated to be 16.7 nM based on the measured noise performance of the device and its sensitivity to dopamine determined empirically via flow injection analysis. This detection limit compares favorably with the amplitude of phasic dopamine transients that varies in the range of 40 nM-1 mu M.