Sulfonate-functionalized tetraphenylethylenes for selective detection and wash-free imaging of Gram-positive bacteria (Staphylococcus aureus)
Two sulfonate functionalized tetraphenylethylene (TPE) derivatives were synthesized and used as probes for the detection and imaging of Gram-positive bacteria (e.g. Staphylococcus aureus). The strategy is based on AIE-based turn-on fluorescence resulting from simple electrostatic interactions between the negatively charged probe and positively charged functionalities of lipoteichoic acid (LTA) which is a major component of the outer cell wall of Gram-positive bacteria. TPE-mono-sulfonate (1) and TPE-di-sulfonate (2) both exhibited fast detection ability but the latter, owing to its high-water solubility and higher sensitivity, is the preferred probe for fluorimetric studies and wash-free bacterial imaging. Probe 2 efficiently interacts with the cell-wall of Gram-positive bacteria (S. aureus or B. subtilis) and the bacteria fluoresce blue, whereas, it showed negligible response to both Gram-negative and acid-fast bacteria. Up to 43 fold increase in fluorescence intensity was observed for probe 2 within the bacterial concentration of 0–12 × 108 CFU mL−1. Interestingly, probe 2 showed significant antibacterial activity against S. aureus with an MIC of 23.4 μg mL−1. This simple strategy is advantageous in many ways such as cost-effectiveness and easy synthesis, high water solubility of the probe, fast response, etc. and can be applicable for real sample analysis which is demonstrated by artificially contaminating apple juice with S. aureus.