Self-reporting fluorescence deciphers the antibacterial nature of cationic amphiphiles:Monomer or aggregate?

Cationic amphiphile aggregates exhibit superior antibacterial activity than monomers.However,the antimicrobial mechanism of aggregates has not been well understood because it is difficult to distinguish and monitor aggregate and monomer in antimicrobial process.Herein,three bola-type cationic amphiphiles with aggregation-induced emission property have been developed to show distinguishable fluorescence in their monomer and aggregate.The hydrophilicity of monomer and the stability of aggregate are finely tuned by tailoring the linkers between two quaternary ammonium end groups and tetraphenylethylene skeleton.The sensitive fluorescence switching of monomer and aggregate achieves the quantitative monitoring of dynamic interaction of three amphiphiles with bacteria.The aggregates with cationic charges first attach to bacterial surface,and the monomers subsequently dissociate from aggregates to penetrate bacterial membrane.Further,our results reveal the vital role of stability of aggregates during antimicrobial process,shedding light on the rational design of high-efficient antimicrobials.