Multimodal sensing platform based on MnO2 nanozyme and carbon dots for colorimetric and fluorescent detection of peroxynitrite

Peroxynitrite (ONOO ^- ), as a crucial bioactive molecule, is closely associated with various diseases when present at abnormal levels, making reliable and accurate detection urgently needed. This study developed a colorimetric and fluorometric multi-mode sensing platform based on manganese dioxide nanosheets (MnO ₂ NSs) and carbon dots (CDs) for the quantitative detection of ONOO ^- . Under acidic conditions, MnO ₂ NSs oxidized 3,3’,5,5’-tetramethylbenzidine (TMB) to a blue oxidized product (TMB ⁺ ), which was subsequently further oxidized by ONOO ^- to the diimine form (oxTMB). The resulting oxTMB effectively quenched the fluorescence of CDs via a fluorescence resonance energy transfer (FRET) mechanism. Additionally, ONOO ^- can directly quench the fluorescence of CDs through a FRET effect. The developed multi-mode sensing strategy exhibited good linear relationships in the ranges of 1–70 µM, 0.3–45 µM, and 0.3–55 µM, with corresponding detection limits (LODs) of 28.73 nM, 40.17 nM, and 25.47 nM, respectively. By integrating a portable smartphone with a color recognition application, visual and on-site detection of ONOO ^- was achieved. The proposed method was successfully applied to detect ONOO ^- in human serum samples, yielding satisfactory recoveries ranging from 95.5% to 104.7%. Furthermore, CDs were successfully utilized for fluorescence imaging of ONOO ^- in living cells. This multimodal sensing platform overcomed the limitations of single-mode detection and provided an economical, efficient, and convenient method for ONOO ^- detection.