Tunable persistent luminescence nanoparticles for profiling bacterial extracellular azoreductase activity and...

Persistent luminescence nanoparticles (PLNPs) have attracted significant attention in biosensing and bioimaging. However, the variety of PLNPs that can be directly synthesized via bottom-up approaches remains largely limited to ZnGa₂O₄:Cr, Zn₂GeO₄:Mn, and their analogs. Herein, we report new spinel-structured CaSc₂O₄:Tb (CSO) PLNPs synthesized via a straightforward one-step hydrothermal method. The morphology of CSO PLNPs can be precisely tuned from spindle-like to bipyramidal and rod-like structures by adjusting the pH values of the synthesis solution, which in turn directly modulates their persistent luminescence intensity and decay duration. The CSO PLNPs were further functionalized with an azo-bond-containing BHQ-1 quencher to construct CSO-BHQ nanoprobes for profiling bacterial extracellular metabolism by targeting azoreductase (AzoR) activity. As a key enzyme in extracellular bacterial metabolism, AzoR participates in critical processes including azo-antibiotic degradation and bacterial communication, and its secretion level serves as an indicator of metabolic activity. Detecting AzoR secretion across different bacterial growth phases shows that enzyme production peaked during the exponential growth phase, reflecting the most active stage of extracellular metabolism. Moreover, by assessing extracellular metabolic activity with the CSO-BHQ nanoprobes, we can also determine bacterial antibiotic susceptibility. For instance, S. aureus was found to be insensitive to ampicillin but highly susceptible to vancomycin, while E. coli showed the opposite sensitivity profile. This work not only introduces a new class of easily synthesized PLNPs but also highlights their promising utility in tracking bacterial metabolism and rapidly identifying antibiotic susceptibility.