Antibacterial mechanism for inactivation of E. Coli by AgNPs@polydoamine/titania nanotubes via speciation analysis of silver ions and silver nanoparticles by cation exchange reaction

Abstract In this method, silver nanoparticles (AgNPs) were anchored on titania nanotubes (TNT) surface by chelation of polydopamine (PD) to generate an AgNPs@polydopamine/titania nanotubes (TPAS). To reveal the antibacterial mechanism of TPAS, a speciation analysis of silver ion (Ag+) and AgNPs was developed based on cation exchange reaction (CER). Owing to only the Ag+ can exchange the Cd2+ in the CdTe quantum dots (QDs), the speciation of Ag+ and AgNPs was realized via detecting the Cd2+ for the indirect but ultrasensitive detection of Ag+ by hydride generation (HG)-atomic fluorescence spectrometer (AFS). The limit of detections (LODs) of Ag+ and AgNPs were 0.0001 ng mL−1. Relative standard deviations (n=7) are better than 2.2% at a concentration of 0.02 ng mL-1 Ag+. Due to this strategy, the trace AgNPs and Ag+ in antibacterial assay were accurately detected. The results show AgNPs anchored on TPAS predominantly contributed to bactericidal action by contact-killing. Ag+, released from TPAS, synergistically increased the antibacterial activity by release-killing. The proposed method has been successfully utilized for inactivation of E. Coli to explore the antibacterial mechanisms of AgNPs.