N-Doped carbon quantum dot-based ratiometric fluorescent nanosensor platforms for detection of gastric cancer-associated Helicobacter pylori genes.

Carbon quantum dot (CQD)-based fluorescent nanosensor platforms were developed using gastric cancer-associated Heliobacter pylori (H. pylori) genes. N-doped CQDs were synthesized using two different organic acids (citric acid and malic acid) and ethylenediamine by the microwave method. The photophysical and photochemical properties of the synthesized CQDs were investigated by ultraviolet-visible, fluorescence, and Fourier-transform infrared spectra. The surface of the synthesized N-doped CQDs was conjugated with single-stranded DNA (ssDNA), which is specific for gastric cancer. Ethidium bromide, a selective dye, shows enhanced fluorescence intensity upon intercalating with DNA. In the blue-emissive CQD-ssDNA nanoprobe system, the fluorescence intensity was quenched by ethidium bromide due to Förster resonance energy transfer (FRET) processes. When complementary ssDNA was introduced, the ethidium bromide strongly intercalated with the newly formed double-stranded DNA, shifting to a red emission. Using this ratiometric system, the detection method was improved for gastric cancer-associated genes, achieving a limit of detection (LOD) of 0.098 µM, within a concentration range 1.30 to 11.49 µM. Spike and recovery tests were also conducted to evaluate the precision of the presented method in synthetic saliva solutions, with recoveries ranging from 93.06% to 101.85% The performance of the nanosensors was compared using two different synthesized CQDs.