Time-Resolved Phosphorescence and Colorimetric Assays of Diabetes Biomarkers: Simultaneous Detection of 3-Nitro-l-Tyrosine and Total Antioxidant Capacity via Zeolite-Confined Carbon Dots

Chronic hyperglycemia in diabetes induces oxidative stress through excessive production of reactive oxygen/nitrogen species (ROS/RNS), leading to elevated 3-nitro-l-tyrosine (3-NT) concentration and depletion of endogenous antioxidants. This study presents a dual-mode sensing platform for simultaneous quantification of 3-NT and total antioxidant capacity (TAC) based on nitrogen- and boron-codoped carbon dots confined within AlPO-5 zeolite (N,B-CDs@AlPO-5). The composite exhibits robust room-temperature phosphorescence (RTP) with a quantum yield of 31.29% and a lifetime of 1.56 and 6 s aqueous afterglow. Leveraging these properties, time-resolved phosphorescence detection of 3-NT (10–1000 μM) with a detection limit of 2.19 μM is achieved due to the synergistic inner filter effect and static quenching. Concurrently, the composite’s excited triplet state-induced generation of superoxide radicals (O2.–) and Mn2+ → Mn3+ redox cycling collaboratively mediate 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to form blue ox-TMB, enabling colorimetric analysis of antioxidants and achieving ascorbic acid determination (5–50 μM) with a detection limit of 1.47 μM. Crucially, the RTP platform demonstrates clinical utility through reliable simultaneous detection of 3-NT and TAC in urine samples. This dual-mode sensing strategy establishes a novel paradigm for diabetes screening through rapid and noninvasive urinalysis through multidimensional biomarker verification.