Label-free and reusable antibody-functionalized gold nanorod arrays for the rapid detection of Escherichia coli cells in a water dispersion

The growing spread of pathogens, caused by anthropogenic activities, pushes the interest of the scientific community towards developing biosensors with improved performance for rapid, simple, and on-site pathogen detection. In this study, we present and discuss a label-free gold nanorod (Au NR) array for the rapid detection of Escherichia coli cells in water, resulting in an effective optical transducer, based on the phenomenon of localized surface plasmon resonance (LSPR). Au NRs with different aspect ratios are functionalized with a suitable antibody by an electrostatic-linking method, resulting in two different Au NR-based bioconjugates. We investigate the ability of the two bioconjugates to detect and spectroscopically recognize E. coli cells dispersed in water by specific antigen-antibody interaction. The results allow selecting the Au NR morphology more suited for preparing the Au NR bioactive array on a glass substrate with excellent optical and morphological properties. The antibody-functionalized Au NR array can detect E. coli cells with high sensitivity and a limit of detection of 8.4 CFU mL⁻¹, resulting in an excellent label-free spectroscopic biosensor. In addition, the multicolor thermoplasmonic properties of the Au NR array, triggered by appropriate light sources, are suited to enable on-demand photothermal disinfection, thus providing an extraordinary capacity for the biosensor to be both disinfected and, more importantly, reutilized.