Wireless electrochemical and luminescent detection of bacteria based on surface-coated CsWO₃-immobilized fluorescent carbon dots with photothermal ablation of bacteria

Simple and rapid simultaneous detection and killing of bacteria is crucial for addressing health issues related to pathogenic bacteria. Here, we describe the design of a wireless electrochemical and luminescent sensor for bacteria detection using surface-coatable electrochemically generated fluorescent carbon dots (FCDs), which were synthesized from a cationic polymer. The FCDs were further integrated with near-infrared (NIR)-responsive cesium tungsten oxide (CsWO₃) by utilizing catechol moieties on the FCD surface for photothermal-based antibacterial activity. The CsWO₃–FCD nanohybrids showed strong fluorescence emission, which was quenched due to interaction between the cationic FCD surface and the anionic bacterial cell wall. This interaction could also be observed electrochemically according to the change in resistance values before and after binding with bacteria. In this study, the limit of detection (LOD) was determined at 70 CFU/mL for Escherichia coli and 131 CFU/mL for Staphylococcus aureus using the luminescent method and <10 CFU/mL for both bacterial strains using the electrochemical method, indicating the electrochemical approach as the more sensitive method. Additionally, the electrochemical-based bacterial detection assay can be developed into a wireless bacteria-sensing system, which can be easily monitored in real-time via a smartphone. Furthermore, this nanohybrid was able to cause photothermolysis of bacteria upon NIR exposure owing to the photothermal conversion of CsWO₃, which killed almost 100% of E. coli and S. aureus using only 1 mg/mL of CsWO₃–FCD. Thus, this nanohybrid offers a novel approach for dual electrochemical- and luminescent-based detection of bacteria along with high antibacterial activity.