A microfluidic-based spectrophotometer for neurotransmitters sensing is presented in this paper. In addition, a neurotransmitter photo-fingerprint is analyzed to evaluate the feasibility of selective neurotransmitter detection using optical techniques. The aim of this work is to detect major neurotransmitters (NTs) using a compact, portable and cost effective optical system for selective and real time NT concentration monitoring. Micro-spectroscopic detection of NTs is challenging because most of them are transparent to visible light. Nevertheless, they interfere with the absorption spectrum of gold nanoparticles (Au-NP), which exhibit maximum absorbance in the range of 520 nm. We observed an Au-NP maximum absorbance shift of up to 4nm in presence of NTs. Based on this shift, it is possible to detect NTs using visible ligh by using vertical-cavity surface-emitting laser (VCSEL) as light sources and an integrated system-on-chip (SoC) spectrophotometer.