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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 DeltaSigma modulator (DeltaSigmaM) and a frequency-shift-keyed (FSK) voltage-controlled oscillator (VCO) operating near 433 MHz. It is fabricated using the AMI 0.5 mum double-poly triple-metal n -well CMOS process, and requires only one off-chip component for operation. Measured dc current resolutions of ~ 250 fA, ~ 1.5 pA, ~ 4.5 pA, and ~ 17 pA were achieved for input currents in the range of plusmn5, plusmn37, plusmn150, and plusmn600 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 muM wirelessly over a transmission distance of ~ 0.5 m in flow injection analysis experiments.