Dimension icon scan asyst atomic force microscope

All fluorescence spectra were acquired using a Shimatzu RF-5301PC fluorescence spectrophotometer (Kyoto, Japan). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images were performed on a JEOL 2100F field emission transmission electron microscope (Tokyo, Japan). The thickness of CQDs was characterized using a Dimension Icon Scan Asyst atomic force microscope (AFM, Bruker Co., Karlsruhe, Germany). Elemental and functional group analyses were performed using an ESCALAB Xi⁺ X-ray photoelectron spectrometer (XPS, Thermo Fisher Scientific Inc., Waltham, MA, USA) and a Nicolet iS5 Fourier Transform Infrared spectrometer (FTIR, Thermo Fisher Scientific Inc., Waltham, MA, USA). The Raman spectrum obtained on the Ag substrate (excited by a 532 nm laser) was recorded with a DXR 2xi Raman microscope (Thermo Fisher Scientific Inc., Waltham, MA, USA). The C9920-02G fluorescence spectrophotometer (Hamamatsu Photonics KK, Tokyo, Japan) was used to measure the fluorescence lifetime. Zeta potentials of CQDs were obtained with a Zetasizer Nano ZS90 System (Malvern, UK). The concentration of bacteria was determined by measuring the optical density at 600 nm (OD₆₀₀) via UV–vis spectroscopy. The morphology of bacteria was observed under a Hitachi S-3400N scanning electron microscope (SEM, Tokyo, Japan).