A novel ratiometric fluorescent nanosensor based-on UiO-66-NH2 capped carbon dots for nitrite determination.

Nitrite is a commonly used food preservative and a water contaminant that has garnered significant attention due to its harmful effects on human health. Developing a simple and sensitive method for determining nitrite levels is crucial for safeguarding public health. In this paper, we present a novel ratiometric fluorescent nanosensor (CDs@UiO-66-NH₂), created by combining orange-red-emitting CDs with blue-emitting UiO-66-NH₂. This ratiometric probe detects nitrite ions (NO₂^-) based on the diazotization reaction between the amino group in UiO-66-NH₂ and the target NO₂^-, where the blue emission of UiO-66-NH₂ is quenched but the orange-red emission of CDs remains stable. The probe demonstrated a detection range of 0.5-20 μM with a limit of detection (LOD) of 0.157 μM for NO₂^-. Due to the probe's distinct color changes in response to NO₂^-, RGB values can be easily read using a smartphone, enabling ultrasensitive visual detection of NO₂^- with an LOD of 0.76 μM. This sensor was successfully applied to detect NO₂^- in environmental water samples. Finally, a smartphone-based RGB reading method using CDs@UiO-66-NH₂ for visual quantitative detection of NO₂^- was proposed, broadening the application of CDs@UiO-66-NH₂ in environmental protection.