A colorimetric probe based on peroxidase-like activity of CuAl-LDH/agarose nanocomposite hydrogel for determination of vancomycin in exhaled breath condensate

<i>Background</i>: Vancomycin is a glycopeptide antibiotic used to treat certain bacterial infections. It works by interfering with RNA synthesis, altering cell membrane permeability, and inhibiting peptidoglycan synthesis in the cell wall. The recommended therapeutic concentration of vancomycin in plasma and serum is 5.0-40 μg mL^-1, reflecting a narrow therapeutic window that can lead to toxic side effects and bacterial resistance if the concentration is too high or too low. Monitoring vancomycin in a low-cost and convenient way is significant in administering accurate dosages of vancomycin to prevent the development of bacterial resistance. <i>Results</i>: Herein, a colorimetric nanoprobe was established to detect vancomycin in exhaled breath condensate samples. This platform incorporated agarose hydrogels with nanozymes to initiate specific reactions and produce colorimetric signals. CuAl-layered double hydroxide was used as nanozyme, which exhibits peroxidase-like activity accelerating the oxidation of the colorless compound 3,3',5,5'-tetramethylbenzidine (TMB) to the blue product oxTMB in the presence of hydrogen peroxide. The detection mechanism of vancomycin was its interaction with Cu in CuAl-LDH/agarose, inhibiting the oxidation process of TMB. The inhibiting effect of vancomycin led to a significant decrease in the analytical response across a concentration range of 0.04-0.3 μg mL^-1. The inter- and intra-day relative standard deviations of the nanoprobe were recorded at 1.2% and 4.4%, respectively. This proposed system was effectively employed to quantify vancomycin levels in patients receiving the medication, with samples collected from the expiratory circuit of a mechanical ventilator. <i>Significant</i>: As a result, LDH/agarose nanocomposite catalyzed H₂O₂ : TMB system's benefits of simplicity, versatility, and cost-effectiveness make this platform a promising tool for colorimetric detection of vancomycin in clinical settings. Notably, this sensing platform can be customized for optical assays targeting different molecules by altering the encapsulated substances within the hydrogel.