Ce-doped ZnO upconversion nanoparticles for optical thermometry, antibacterial therapy, and cardiac biomarker detection.

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) due to their unique optical properties are promising for applications ranging from bioimaging to biosensing. However, their practical implementation remains challenging owing to relatively low luminescence efficiency. Herein, we synthesize a series of Ce-doped Yb/Eu/ZnO, Yb/Er/ZnO and Yb/Tm/ZnO UCNPs via a hydrothermal method. Ce ions incorporation promotes anisotropic growth, which increases surface roughness and modulates the local coordination environment. Electrochemical impedance spectroscopy and Tafel plot analyses reveal that Ce doping significantly enhances charge separation and transfer kinetics. Ce ion doping markedly increases the emission intensities of Eu³⁺, Er³⁺ and Tm³⁺, attributed to the formation of Yb³⁺ dimers and efficient energy transfer under 980 nm excitation. Benefiting from these improvements, the Ce-doped ZnO UCNPs exhibit three distinct bio-applications: (i) superior low-temperature optical thermometry with a maximum relative sensitivity of 4.81% K^-1 at 80 K; (ii) excellent antibacterial activity against S. aureus and E. coli (up to 82.16% and 87.64% inhibition at 8 mol% Ce); and (iii) successful employment as luminescent probes in a multiplex immunoassay for the cardiac markers BNP (detection range 10-100 pg/mL) and ST2 (5-25 ng/mL), with high specificity and sensitivity. These findings underscore the potential of Ce-doped ZnO UCNPs as multifunctional platforms for optical thermometry, antibacterial therapy and biomedical diagnostics.