Poly(N,N-dimethylacrylamide)-stabilized gold nanoparticles as nanozymes with enhancement of catalytic activity for detection of lomefloxacin.

Recently, polymer-protected gold nanoparticles (AuNPs) have attracted extensive attention due to their good catalytic activities. However, how to regulate their catalytic activities by changing the polymer chain morphologies or the interactions between the ligands and the analytes through external stimuli is still a great challenge. This study describes a simple synthesis of AuNPs capped by thermo-responsive poly(N,N-dimethylacrylamide) (PDMAM). In comparison with three kinds of PDMAMs@AuNPs, PDMAM-2@AuNPs exhibited better peroxidase-mimic ability via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) to generate oxidized TMB (oxTMB). Interestingly, its catalytic activity could be regulated by changing environmental temperature. Importantly, the addition of the antibiotic lomefloxacin endowed the PDMAM-2@AuNPs with enhancement in catalytic efficiency due to electrostatic interactions and the increased levels of reactive oxygen species. Based on this principle, a protocol for highly selective and sensitive monitoring of lomefloxacin has been constructed with the color change from pale blue to deep blue. The ultraviolet-visible absorbance of oxTMB at the wavelength of 650 nm showed a good linear relationship with antibiotic concentration in the range of 0.25-10.0 µM (R2 = 0.990). The limit of detection was 0.1 µM. The practical application of the proposed protocol with the promoted peroxidase-mimic activity for the measurement of lomefloxacin in capsules was realized.