A Fluorescent Probe Based on Biological Matrix Carbon Dots for the Detection of Nitrite in Cured Meat Products

In order to establish a rapid method for detecting the content of nitrite in food, green carbon quantum dots (CQDs) originating from chicken paw skin were synthesized by the one-step hydrothermal method. The morphology, structure and optical properties of CQDs were characterized systematically by high resolution transmission electron microscopy (HRTEM), UV-Vis absorption spectroscopy (UV-Vis), Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy (FS) technologies. The prepared CQDs were distributed uniformly with a regular size, and the surface of the CQDs was rich in functional groups including hydroxyl, carboxyl, and carbonyl, et al. In addition, the CQDs emitted intense blue fluorescence under the excitation of a 365 nm UV light lamp. And the excitation spectrum and emission spectrum of CQDs were narrow and symmetrical, indicating CQDs had good luminescence properties. In the presence of Fe³⁺, the fluorescence of CQDs was quenched due to the formation of coordination bonds between Fe³⁺ and the oxygen-containing functional groups on the surface of CQDs. Based on that, a simple fluorescent probe was designed to detect indirectly nitrite (NO₂⁻) by CQDs for nitrite possesses strong oxidation in acidic solution and was capable to transform iron (II) into iron (III) ions. The parameters including the excitation wavelength of CQDs, buffer pH value and reaction time were studied. Under the optimized conditions, the fluorescence quenching intensity of CQDs-Fe²⁺ fluorescent probe increased linearly with the NO₂⁻ concentration in the range of 1~500 μmol/L (R²=0.9979) with a low detection limit of 0.61 μmol/L, and the probe had a good anti-interference ability. The method was applied to the determination of NO₂⁻ in three marinate meat and satisfactory recoveries of 98.61%~100.95% and consistent data compared with ion chromatography were obtained. The results indicated that the CQDs-Fe²⁺ fluorescent probe could be used for the detection of NO₂⁻ in real samples. In summary, the fluorescent probe constructed based on the carbon dots of the biological matrix is green and safe, simple to prepare, can detect the content of nitrite in cured meat products, indicating a good practical application prospect.