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Establishing a sensitive and selective method to measure tryptophan in situ with good spatiotemporal resolution is invaluable to understanding its biological role and activity in nutrition, health, brain disorders, and the gut-brain axis. Here, we report on a sensitive and selective method to measure tryptophan over its main interfering species tyrosine. Specifically, we achieve this using fast scan cyclic voltammetry at carbon fiber microelectrodes via the application of an optimized multi-scan rate sawhorse waveform. We report over four-fold increase in sensitivity over previously reported methods and a six-fold selectivity of tryptophan quantitation over that of tyrosine. We demonstrate the utility of our method via measuring extracellular Trp in cultured PC-12 cells and PC-12 cells with overexpressed tryptophan hydroxylase 2.

Despite the fact that tryptophan is an essential amino acid that humans typically obtain through diet, there are several interesting tryptophan dynamics at play in the body. Quantifying and understanding these dynamics are crucial in studies of depression, autism spectrum disorder, and other disorders that involve neurotransmitters directly synthesized from tryptophan. Here we detail the optimization of waveform parameters in fast scan cyclic voltammetry at carbon fiber microelectrodes to yield four-fold higher sensitivity and six-fold higher selectivity compared to previously reported methods. We demonstrate the utility of our method in measuring tryptophan dynamics in two cell model systems.