Our previous studies have led to a novel "nonrelease" approach to making materials bactericidal by covalently attaching certain moderately hydrophobic polycations to their surfaces. In the present work, this strategy is extended beyond the heretofore-used nonporous materials to include common woven textiles (cotton, wool, nylon, and polyester). Pieces of such cloths derivatized with N-hexylated+methylated high-molecular-weight polyethylenimine (PEI) are strongly bactericidal against several airborne Gram-positive and Gram-negative bacteria. In contrast, the immobilized and N-alkylated PEIs of low molecular weight have only a weak, if any, bactericidal activity. These findings support a mechanism of the antibacterial action whereby high-molecular-weight and hydrophobic polycationic chains penetrate bacterial cell membranes/walls and fatally damage them. The bactericidal textiles prepared herein are lethal not only to pathogenic bacteria but to fungi as well.

We previously discovered that covalently coating glass and plastic slides with certain long poly(vinyl-N-alkylpyridinium) chains enables the resultant surfaces to kill a variety of airborne and waterborne bacteria on contact. In the present study, these findings have been extended to an unrelated polymer class, polyethylenimines (PEIs). Alkylated PEIs attached to flat macroscopic surfaces and to those of nanoparticles make these materials highly bactericidal toward both Gram-positive and Gram-negative pathogenic bacteria. Systematic chemical modifications of the immobilized PEI conducted herein shed light on the relationship between the structure of the polymer and the antibacterial efficiency of the resultant coating.

A novel colorimetric aptamer sensor (aptasensor) for the detection of streptomycin (STR) is developed based on the peroxidase-like activity of gold nanoparticles (AuNPs) and their interaction with STRaptamer complex. It is known that AuNPs can easily oxidize substrates in the presence of hydrogen peroxide in a manner identical to peroxidase and 2,2 0 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) is a commonly used peroxidase substrate with green oxidation product and a characteristic absorption peak at 733 nm. In the absence of STR, STR1 aptamer is adsorbed on the surface of AuNPs, and restrains its catalytic activity due to shield effect of ssDNA sequence against substrates. STR first binds with STR1 aptamer to form an STR-aptamer complex; thus, aptamer sequences do not get absorbed on the surface of the nanoparticles and their peroxidase activity is further greatly enhanced by the STR-aptamer complex, which enables AuNPs to catalyse the oxidation of the substrates. To achieve a higher level of sensitivity, several key parameters of the proposed aptasensor such as pH, concentrations of STR1 aptamer and AuNPs, and incubation and reaction temperature have been investigated. Under optimal conditions, the proposed aptasensor can detect STR in a linear range from 0.1 mM to 0.5 mM with a limit of detection (LOD) as low as 86 nM and exhibits good selectivity. Moreover, further studies also validate the applicability of the proposed aptasensor in milk samples, revealing that it may have enormous potential utility for practical STR detection in food products in the future.