Ratiometric detection of dopamine using NIR carbon dots and Alizarin red S-boronic acid complex: A competitive displacement approach.

Dopamine, a critical neurotransmitter regulating motor control, cognition, and reward pathways, requires sensitive and selective detection methods for neurological disorder diagnosis and therapeutic monitoring. We developed a novel dual-emission ratiometric fluorescence sensor comprising near-infrared carbon dots NIR-CDs, λ = 730 nm and the alizarin red S-3-nitrophenylboronic acid complex ARS-3-NPBA, λ = 550 nm under single 450 nm excitation for dopamine quantification based on competitive boronate affinity displacement, wherein dopamine's catechol moiety displaces ARS from 3-NPBA, simultaneously decreasing ARS-3-NPBA fluorescence at 550 nm while recovering inner-filter-quenched NIR-CD fluorescence at 730 nm. The self-calibrating fluorescence ratio (F/F) exhibits excellent linear correlation with dopamine concentration over 0.1-65.0 μM R = 0.9946 with a limit of detection of 0.035 μM. The sensor demonstrates superior selectivity, showing negligible interference from common biological species. Spike-and-recovery experiments in human plasma yielded recovery percentages of 97.0 % to 98.3 % with RSD values of 2.53 %-4.23 %. The ratiometric readout inherently corrects for instrumental variations, photobleaching, and matrix effects, positioning this platform as a robust, cost-effective alternative to conventional chromatographic methods for dopamine quantification in clinical diagnostics and potential real-time in vivo monitoring applications.