A Conjugated Polymer‐Based Portable Smartphone Platform for Sensitive and Point‐Of‐Care Detection of Monoamine Neurotransmitter

The precise and effective detection of neurotransmitters (NTs) is crucial for clinical investigation of neuronal processes, and timely monitoring of NT‐related chronic diseases. However, sensitive detection of specific NT with unprecedented selectivity is highly challenging due to similarities in chemical and electronic structures of various interfering neurochemicals. Herein, an anionic conjugated polyelectrolyte Poly[(9,9‐bis(4’‐sulfonatobutyl)fluorene‐co‐alt‐1,4‐phenylene) sodium], PFPS was rationally designed and synthesized for amplified detection and point‐of‐care (PoC) determination of monoamine neurotransmitter, serotonin (5‐Hydroxy tryptamine or 5‐HT, also diagnostic biomarker of carcinoid tumor) in human blood plasma. The PFPS displayed a remarkable sensing response with an exceptionally high fluorescence quenching constant of 1.14×105 M−1 and an ultralow detection limit of 0.67 μM or 0.142 ppm, much below the clinical range. Furthermore, a smartphone‐enabled portable platform was constructed for real‐time onsite detection of 5‐HT by quantification of visual fluorescence response of PFPS into RGB values using a color recognizer android application. The smartphone platform could be readily applied for convenient, non‐invasive PoC testing of 5‐HT levels in complex biological fluids accurately and is expected to revolutionize clinical diagnosis and personalized health care devices. A convenient and highly sensitive biosensor is constructed for the selective detection of neurotransmitters (5‐hydroxytryptamine, 5‐HT) using rationally designed anionic conjugated polyelectrolyte PFPS. The polyelectrolyte displayed a fluorescence turn‐off response on successive addition of 5‐HT with obvious visual color fading under 365 nm UV light, resulting in the onsite visual detection with a limit of detection in part per million.