Real-Time 5-Hydroxyindoleacetic Acid Monitoring in Guinea Pig Brain Using a Molecular Imprinted Polymer-Based Galvanic Redox Potentiometric Sensor

5-Hydroxyindoleacetic acid (5-HIAA), a vital metabolite of serotonin (5-HT), is crucial for understanding metabolic pathways and is implicated in various mental disorders. In situ monitoring of 5-HIAA is challenging due to the lack of affinity ligands and issues with electrochemical fouling. We present an advanced sensing approach that integrates customizable molecular imprinting polymer (MIP) with self-driven galvanic redox potentiometry (GRP) for precise, real-time in vivo monitoring of 5-HIAA. The sensor, featuring pyrrole as the functional monomer in the MIP on the micrometer-sized bipolar carbon fiber electrodes, exhibited nanomolar sensitivity and superior selectivity for 5-HIAA over biosynthetic pathway analogs like 5-hydroxytryptophan (5-HTP) and serotonin. The MIPGRP sensor demonstrated excellent reversibility and resistance to fouling, enabling continuous monitoring in live guinea pig brains. We observed that intraperitoneal 5-HTP injection increases brain 5-HIAA levels, which is amplified up to 8-fold with Carbidopa pretreatment, providing deeper insights into the serotonergic signaling pathway. This work underscores the MIPGRP sensor’s potential as a versatile and reliable tool for advancing neuroscience research.