Rapid detection of lethal pathogens is critical to abate the mortality rate of patients suffering from infectious diseases. Herein, we report a pH-sensitive detection of the pathogenic bacteria using multicolor emissive Nitrogen-doped Carbon Dots (NtCD) synthesized by a one-step hydrothermal method. The unique pH-sensitive interaction of NtCD with bacteria was best studied at pH 2. NtCD was competent to detect several pathogenic bacteria such as; Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Proteus vulgaris (P. vulgaris). The fluorescence spectral investigations of NtCD revealed the excitation dependent emission property with a red-shift. It shows an intense photoluminescent (PL) emission at λex/λem = 340/435 nm. The calculated quantum yield of NtCD was 27.2%. It also possesses multicolor emission at different excitation wavelengths. TEM analysis displayed the uniform spherical morphology of NtCD particles with an average hydrodynamic diameter of 3.11 ± 0.75 nm. The zeta potential of NtCD was measured as −8.4 mV at pH 2. The interaction between NtCD and bacteria was explained on the basis of their zeta potential values. The PL emission response of NtCD tagged bacteria was investigated at λex = 340 nm. It was potentially tagging to both E. coli and S. aureus but with a better response towards E. coli cells. The human squamous epithelial cells (SEC) were deployed as a fitting substitute for achieving NtCD-mammalian cell imaging. Both NtCD tagged bacterial cells and SEC exhibited multicolor emission as well. Mechanistic implications of pH-dependent PL emission property of NtCD and its bacterial interaction were discussed extensively.
A. Pathak, Venugopal, P., Dr. Bipin G. Nair, Suneesh, P. Vasu, and Babu, T. G. Satheesh, “Facile pH-sensitive optical detection of pathogenic bacteria and cell imaging using multi-emissive nitrogen-doped carbon dots”, Microchemical Journal, vol. 159, p. 105324, 2020.