Hybrid CMOS-Graphene Sensor Array for Sub-Second Dopamine Detection

• Published in: IEEE transactions on biomedical circuits and systems Vol. 11; no. 6; pp. 1192 - 1203
• Main Authors: Nasri, Bayan, Wu, Ting, Alharbi, Abdullah, You, Kae-Dyi, Gupta, Mayank, Sebastian, Sunit P, Kiani, Roozbeh, Shahrjerdi, Davood
• Format: Journal Article
• Language: English
• Published: 01.12.2017
• ISSN: 1932-4545; 1940-9990
• DOI: 10.1109/TBCAS.2017.2778048

We introduce a hybrid CMOS-graphene sensor array for sub-second measurement of dopamine via fast-scan cyclic voltammetry (FSCV). The prototype chip has four independent CMOS readout channels, fabricated in a 65 nm process. Using planar multilayer graphene as biologically compatible sensing material enables integration of miniaturized sensing electrodes directly above the readout channels. Taking advantage of the chemical specificity of FSCV, we introduce a region of interest technique, which subtracts a large portion of the background current using a programmable low-noise constant current at about the redox potentials. We demonstrate the utility of this feature for enhancing the sensitivity by measuring the sensor response to a known dopamine concentration in vitro at three different scan rates. This strategy further allows us to significantly reduce the dynamic range requirements of the analog-to-digital converter (ADC) without compromising the measurement accuracy. We show that an integrating dual-slope ADC is adequate for digitizing the background-subtracted current. The ADC operates at a sampling frequency of 5-10 kHz and has an effective resolution of about 60 pA, which corresponds to a theoretical dopamine detection limit of about 6 nM. Our hybrid sensing platform offers an effective solution for implementing next-generation FSCV devices that can enable precise recording of dopamine signaling in vivo on a large scale.