A novel fluorescent sensor based on rambutan peel-derived carbon quantum dots for sensitive detection of carmine in food matrices

Today, the food industry is highly dependent on food additives, especially colorants, to increase the visual appeal and attractiveness of foods. Food industry uses Carmine as a food additive. Carmine is cheap, has a very strong coloring power, is very soluble in water, and is durable. The World Health Organization has suggested a daily dosage limit of 5.0 mg/kg based on body mass. Therefore, a regulation is required to protect the consumer health despite the hazards of excessive consumption. Traditional detection methods such as chromatography, spectrophotometry, extraction and precipitation are not suitable for routine food safety monitoring because of their expensive, time-consuming and complex sample preparation. Carbon quantum dots (CQDs), sometimes called fluorescent carbon nanoparticles, are a new type of carbon nanoparticles with the size smaller than 10 nm and many applications. CQDs have some remarkable properties, including photostability, low toxicity, biocompatibility, environmental sustainability, and great water solubility. Food waste is carbon-rich. In addition, proper use of food waste benefits environmental sustainability and commercial interest. In this study, rambutan ( Nephelium lappaceum ) peel, a sustainable and abundant biomass resource, was used to prepare carbon quantum dots (CQDs) using hydrothermal technique. The CQDs were characterized for optical and morphological properties by UV–visible spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The fluorescence of CQDs may be tuned, with maximum intensity at the excitation wavelength of 340 nm and emission wavelength of about 441.5 nm. The CQDs showed the highest photoluminescence (PL) intensity at pH 3. The fluorescence quantum yield was about 9.14% under the above synthetic conditions. These CQDs showed excellent fluorescence capabilities and can be used for sensing applications. The synthesized CQDs were applied for the detection of carmine in food samples and the limit of detection (LOD) and linearity were also demonstrated. The method provides an efficient way for rapid and accurate detection of food deterioration and adulterants.