Facile synthesis of long-wavelength fluorescent carbon dots: toward multifunctional applications in nitrite sensing and bioimaging.

Long-wavelength carbon dots (L-CDs) were fabricated via hydrothermal route using neutral red and p-aminobenzoic acid as precursors under hydrochloric acid conditions, and further explored for nitrite (NO2⁻) sensing. The L-CDs displayed outstanding optical characteristics and exhibited excellent selectivity toward NO2⁻. Upon exposure to NO2⁻, the fluorescence of L-CDs was remarkably quenched via a static quenching mechanism. A favorable linear correlation was achieved between 5 and 100 µM, yielding a calculated limit of detection of 2.89 µM. This method demonstrated satisfactory recoveries and minimal relative standard deviations when utilized for NO2⁻ determination analysis in actual samples. Moreover, the L-CDs proved effective for fluorescence imaging of NO2⁻ in living cells and zebrafish, revealing their promising application potential in the field of biosensing.