Understanding dopamine (DA) signaling in the brain is essential for advancing our knowledge of pathological disorders such as drug addiction, Parkinson's disease, and schizophrenia. Currently, fast-scan cyclic voltammetry (FSCV) with carbon microfiber (CMF) electrodes is the method of choice in neuroscience labs for monitoring the concentration of phasic (transient) DA release. This method offers sub-second temporal resolution and high specificity because the signal of interest occurs at a known potential. However, existing CMF electrodes are bulky, limiting the spatial resolution to single-site measurements. Further, they are produced through manual processes (e.g. cutting CMFs under optical microscope), thus introducing significant device variability . Lastly, when long probes (3-to-5cm) are used to monitor DA release in deep brain structures of large animals, environmental noise severely diminishes the detection limit . To address these problems, we combine advances in nanofabrication with silicon chip manufacturing to create a heterogeneous integrated CMOS-graphene sensor for accurate measurement of DA with high spatiotemporal resolution (Fig. 15.7.1).