Rapid visual detection of histidine in biological systems by a naphthalimide-based fluorescent probe.

Histidine (His), an essential amino acid involved in diverse physiological and metabolic pathways, serves as a vital biomarker for metabolic disorders, nutritional status, and disease progression. Here, we report a naphthalimide-dipicolylamine-based fluorescent probe (DPA-BID-Cu2+) capable of rapid, selective, and visual detection of histidine. The probe is a non-emissive complex with Cu2+, in which fluorescence from the naphthalimide core is efficiently quenched. Upon His introduction, competitive coordination displaces Cu2+, restoring strong fluorescence through a displacement-induced "turn-on" mechanism. This system enables real-time detection within 20 s and exhibits a large Stokes shift of 110 nm, providing excellent signal clarity and minimal background interference. The probe displays outstanding selectivity, and sensitivity across diverse biological matrices-including urine, live cells, onion epidermis, and Arabidopsis thaliana-allowing for direct visualization without sample pretreatment. Furthermore, a portable dual-tube detection device was developed based on this system, enabling simple, on-site His sensing through instant mixing and fluorescence readout under UV illumination. Collectively, this work introduces a highly efficient, fast-response, and field-deployable fluorescent platform that bridges molecular sensing and practical application, offering significant promise for point-of-care diagnostics, nutritional monitoring, and in situ bioanalysis in both clinical and agricultural settings.