Fig. 1

The Physicochemical characterization of N-GQDs and A-GQDs. a, b TEM imaging and size distribution of N-GQDs and A-GQDs, respectively; c, d UV-vis absorption spectra of N-GQDs and A-GQDs in deionized (DI) water and culture medium; e, f Fluorescence spectra of N-GQDs and A-GQDs in DI water and culture medium, emission spectrum of N-GQDs at λ_ex = 350 nm for DI water and λ_ex = 380 nm for medium, and excitation spectrum of N-GQDs at λ_em = 420 nm for DI water and λ_em = 480 nm for medium, while emission spectrum of A-GQDs at λ_ex = 380 nm for both DI water and medium, and excitation spectrum of A-GQDs at λ_em = 460 nm for both DI water and medium, respectively. Insert: Photographs of N-GQDs and A-GQDs in DI water or culture medium under the radiation of white light (Up) and 365 nm UV lamp (Down); Hydrous particle diameter of N-GQDs (g, h) and A-GQDs (i, j) in DI water and culture medium, respectively; Zeta potential of N-GQDs (k, l) and A-GQDs (m, n) in DI water and culture medium, respectively