Bridging biological and food monitoring: A colorimetric and fluorescent dual-mode sensor based on N-doped carbon dots for detection of pH and histamine

Rapid and sensitive monitoring of pH and histamine is crucial for bridging biological and food systems and identifying corresponding abnormal situations. Herein, N-doped carbon dots (CDs) are fabricated by a hydrothermal method employing dipicolinic acid and o-phenylenediamine as precursors. The CDs exhibit colorimetric and fluorescent dual-mode responses to track pH and histamine variations in living cells and food freshness, respectively. The aggregation-induced emission enhancement and intramolecular charge transfer result in a decrease in absorbance and an increase in fluorescence, which become readily apparent as the pH changes from acidic to neutral. This property enables precise differentiation between normal and cancerous cells. Furthermore, given the intrinsic basicity of histamine, pH-responsive CDs are advantageous for additional colorimetric and fluorescent monitoring of histamine in food freshness, achieving linearities of 25-1000 µM and 30-1000 µM, respectively, which are broader than those of alternative nanoprobes. Interestingly, smartphone-integrated sensing platform can portably and visually evaluate pH and histamine changes due to sensitive color changes. Therefore, the sensor not only establishes a dynamic connection between pH and histamine for the purposes of biological and food monitoring, but also presents a novel approach for developing a multifunctional biosensor that can accomplish environmental monitoring and biosensing simultaneously. High amounts of histamine, hazardous substances produced by spoiled food, pose adverse effects for food poisoning and human health including vomiting, head-aches and death. Based on their harmfulness, the threshold histamine should be strictly controlled. So rapid and accurate histamine evaluation is crucial. This work employs a colorimetric and fluorescent CDs for pH and histamine dual-mode monitoring, achieving dynamic bridges of hazardous histamine between biological and food monitoring. Interestingly, sensitive color changes make smartphone-integrated sensor more portable and visual than other probes. This enables CDs a multifunctional biosensor for monitoring histamines with realistically detecting ranges to meet practical needs.