No abstract

We report on the selective and sensitive colorimetric detection of Ag+ in a dimethylformamide (DMF) solution in the presence of graphene oxide based on the surface plasmon resonance absorption of Ag nanoparticles (NPs).

A novel ratiometric fluorescent probe BCB was reported for the first time for the sensitive and selective analysis of Ag based on two Boradiazaindacene (BODIPY) as both the reference fluorophore and recognition part. Upon the addition of Ag ions, a strong fluorescence emission at 570 nm from recognition BODIPY would be appeared, whereas the fluorescence of the other BODIPY at 535 nm would be a constant reference fluorescence signal. As a result, the ratio of fluorescence intensity (λ570/λ535) was changed from 0.16 to 1.0. And the selectivity of BCB towards Ag over other metal ion was excellent. Other metal ions, such as Cd, Cu, Fe, Hg, Mg, Ni, Pb and Zn showed negligible changes in the both absorption and fluorescence spectra of BCB.

An increase in the number of infections caused by resistant bacteria worldwide necessitates the development of alternatives to antibiotics. Human defensin (HD) 5 is an innate immune peptide with broad-spectrum antibacterial activity, but its complicated structure makes its preparation difficult. Herein, we truncated the HD5 structure by extracting the highly conserved γ-core motif. A structure-activity study showed that this motif was ineffective in killing bacteria in the absence of specific spatial conformation. Notably, after the introduction of two intramolecular disulfide bonds, its antibacterial activity was markedly improved. Glu and Ser residues were then replaced with Arg to create the derivative RC18, which exhibited stronger potency than HD5, particularly against methicillin-resistant S. aureus (MRSA). Mechanistically, RC18 bound to lipid A and lipoteichoic acid at higher affinities than HD5. Furthermore, RC18 was more efficient than HD5 in penetrating the bacterial membranes. Molecular dynamics simulation revealed that five Arg residues, Arg1, Arg7, Arg9, Arg15, and Arg18, mediated most of the polar interactions of RC18 with the phospholipid head groups during membrane penetration. In vivo experiments indicated that RC18 decreased MRSA colonization and dramatically improved the survival of infected mice, thus demonstrating that RC18 is a promising drug candidate to treat MRSA infections.