Background-free luminescent and chromatic assay for strong visual detection of creatinine

Creatinine is an essential biomarker for the clinical diagnosis and treatment of renal insufficiency. Although fluorescent methods are powerful tools for creatinine detection, almost all reported fluorescent probes rely on short-wavelength excitation and a single fluorescent signal, making them susceptible to environmental and operational conditions. In this study, a near-infrared excited, highly sensitive, and multi-output signal sensing system was established using upconversion nanoparticles and 3,5-dinitrobenzoic acid (DNBA) for synergistic luminescent and colorimetric assay for strong visual detection of creatinine. DNBA undergoes a specific colorimetric reaction with creatinine, quenching the green upconversion luminescence (UCL) while leaving the red UCL unaffected, thus constructing the luminescent and colorimetric sensing modes for creatinine. The designed near-infrared excited sensing system eliminates auto-fluorescence with a multi-output signal, thereby enhancing the sensitivity and convenience of creatinine detection. Under optimal conditions, the detection limit in the colorimetric mode is 26 nM, while the detection limit in the luminescent mode is 2 nM. Moreover, a portable sensing platform is further developed, demonstrating sensitive sensing performance and paving a new way for point-of-care testing (POCT) of human body fluid biomarkers.