Common techniques for Trp monitoring in foods, bodily fluids, and tissue is chromatography . For free Trp measurements, researchers often rely on colorimetric methods, near-infrared reflectance spectroscopy, optimized high performance liquid chromatography with mass spectrometry detection, and isotopic labelling (reviewed in ). These, however, do not provide any spatially-or time-resolved information. Moreover, in some of these methods, only total Trp content (rather than free Trp) in tissues were quantified and these do not usually change much. There have been efforts to measure free Trp using microdialysis coupled to high performance liquid chromatography and UV-Vis detection. The studies described above investigating the effects of i.p. administration of Trp and exercise on endogenous Trp dynamics are some examples that utilized this technique. While it is quantitative and provides time-resolved and spatially-resolved free Trp levels, it does have some limitations. Firstly, the time resolution of microdialysis-HPLC-UV-Vis is limited by the collection and separation times. While separations as fast as under a min has been reported for catecholamines, all of the previous free Trp data has been reported with 20 min time resolutions . Interestingly, these time-resolved data show an immediate change in free Trp within the first 20 min but these dynamics were too rapid to be resolved by conventional methods. Secondly, the large size of the microdialysis probe relative to the intercapillary distance of the vasculature has been shown by others to cause foreign body response in the surrounding tissue . While these are all powerful methods that have provided a plethora of valuable information, these methods are either offline (meaning ex situ), require a specialist to operate the instrumentation, necessitate the removal of interfering signals from other aromatic amino acids such as tyrosine (Tyr), involve sample treatment protocols before the analytes can be quantified, lacks spatiotemporal information, and/or causes foreign body response (and therefore may result in signal artifacts). Thus, there is still a need for a sensitive and selective Trp quantitation technique for in situ monitoring in cells, tissues, and in vivo. Moreover, release dynamics of Trp metabolites in the brain occur on the order of subseconds , so it is possible Trp dynamics occurs on comparable scales as well. Furthermore, Trp concentrations are hypothesized to vary between different cell types and brain regions so micron-scale spatial resolution would be advantageous. One of the techniques capable of making measurements at the appropriate spatiotemporal scale is fast scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes (CFMs). The Venton lab first demonstrated the utility of using FSCV at CFMs to measure gonadotropin-releasing hormone, which contains Trp and Tyr . The Ross lab demonstrated the utility of FSCV at CFMs (via the application of the dopamine waveform) to measure electroactive free amino acids, including Trp, with 100 ms timescale and micron spatial resolution . However, their paper did not demonstrate selective measurement of Trp over dominant interfering species such as Tyr, which has overlapping oxidation peaks. This is an important issue to address as there are significant amounts of dipeptides containing Tyr such as Tyr-Tyr, Tyr-Gly, Tyr-Glu in the brain and there are significant dynamics in these dipeptide levels . One of these regions is the hippocampus, a primary area of interest for studying depression and autism spectrum disorder. Since these dipeptides also contain Tyr, they also have overlapping oxidation peaks as Trp.