Chiral Upconversion Heterodimers for Quantitative Analysis and Bioimaging of Antibiotic‐Resistant Bacteria In Vivo

Heterodimers of upconversion nanoparticles (UCNPs) and gold yolk-shell nanoparticles are fabricated for the quantification of polymyxin-B-resistant Escherichia coli. They produce two signals, circular dichroism (CD) and upconversion luminescence (UCL). Interestingly, due to the different affinity of polymyxin B for sensitive and resistant strain, as the concentration of polymyxin B increases, the amount of UCNPs in sensitive bacteria increases sharply, increasing the intracellular UCL signal at a low polymyxin B concentration immobilized on the UCNP. The CD intensity is correspondingly reduced as the amount of UCNPs in solution decreased. Meanwhile, for polymyxin-B-resistant strain, the intracellular UCL increases slowly even in a high polymyxin B concentration, and the CD intensity in solution is also enhanced because of the inefficient entering of UCNP. Therefore, based on the concentration of polymyxin B coupled to the UCNPs, the levels of polymyxin-B-resistant bacteria can be detected with dual signals. Importantly, with 980 nm irradiation, both polymyxin-B-sensitive strains and polymyxin-resistant bacteria used to induce infection in mice are detected with UCL imaging in vivo and treated well with photodynamic therapy. This novel dual-mode heterodimer has potential utility for the advanced surveillance and control of drug-resistant bacteria.