Single Upconversion Nanoparticle–Bacterium Cotrapping for Single‐Bacterium Labeling and Analysis

Detecting and analyzing pathogenic bacteria in an effective and reliable manner is crucial for the diagnosis of acute bacterial infection and initial antibiotic therapy. However, the precise labeling and analysis of bacteria at the single‐bacterium level are a technical challenge but very important to reveal important details about the heterogeneity of cells and responds to environment. This study demonstrates an optical strategy for single‐bacterium labeling and analysis by the cotrapping of single upconversion nanoparticles (UCNPs) and bacteria together. A single UCNP with an average size of ≈120 nm is first optically trapped. Both ends of a single bacterium are then trapped and labeled with single UCNPs emitting green light. The labeled bacterium can be flexibly moved to designated locations for further analysis. Signals from bacteria of different sizes are detected in real time for single‐bacterium analysis. This cotrapping method provides a new approach for single‐pathogenic‐bacterium labeling, detection, and real‐time analysis at the single‐particle and single‐bacterium level.