Nitrogen sulfur co doped carbon quantum dots as fluorescent probe for quantitative determination of monosodium glutamate in food samples

A validated, simple, and ecofriendly spectrofluorometric method has been developed for the determination of monosodium glutamate (MSG) in food matrices utilizing novel nitrogen and sulfur co doped carbon quantum dots (NS-CQDs) as fluorescent probes. MSG is one of the most commonly used food additives that has distinct taste. The proposed method is based on the finding that MSG can effectively enhance the fluorescence intensity of NS-CQDs as a result of the formation of CQDS-MSG complex via electrostatic interaction and electron transfer from the excited CQDs to MSG. NS-CQDs have been synthesized using citric acid and D, L- methionine as precursors and the formed quantum dots were characterized by FTIR spectroscopy and transmission electron microscopy (TEM). NS-CQDs display bright blue fluorescence at emission wavelength 440 nm after excitation wavelength 330 nm with a quantum yield of 38.68% and a production yield of 88.75%. The fluorescence intensity of CQDs was found to be stable over a wide range of pH value (4.0–10). Under optimal experimental conditions, there was a linear relationship between the increased fluorescence and MSG concentration over the range of 25–250 µg/mL with limit of detection and limit of quantification 6.20 and 18.79 µg/mL respectively. NS-CQDs show excellent selectivity to MSG and the proposed method has been applied for MSG determination in two food products with satisfactory recoveries achieved by standard addition method.