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 (MnO2 NSs) and carbon dots (CDs) for the quantitative detection of ONOO-. Under acidic conditions, MnO2 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 excellent sensitivity for ONOO- detection. For the colorimetric mode based on TMB + MnO2 NSs, the detection limit (LOD) was 28.73 nM in the range 1-70 µM. In the fluorescence mode based on TMB + MnO2 NSs + CDs, the LOD was 40.17 nM in the range 0.3-45 µM. The LOD of the fluorescence mode based on CDs was 25.47 nM in the range 0.3-55 µM. 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 overcomes the limitations of single-mode detection and provided an economical, efficient, and convenient method for ONOO- detection.