Fe3+ and intracellular pH determination based on orange fluorescence carbon dots co-doped with boron, nitrogen and sulfur

Highlights: • Fabrication of fluorescent BNSCDs by one-step hydrothermal carbonization method. • Lable-free detection of Fe³⁺ with linear range of 1.5–692 μM and LOD of 87 nM. • Detection of Fe³⁺ in tap water, coal wastes and food samples with satisfying results. • Intracellular pH determination by BNSCDs, possessing fast and real-time response. The fluorescent boron, nitrogen and sulfur co-doped carbon dots (BNSCDs) were prepared by simple hydrothermal reaction of 4-carboxyphenylboronic acid and 2,5-diaminobenzenesulfonic acid at 200 °C for 8 h. The fluorescence of the BNSCDs could be quenched by Fe³⁺ based on the electron transfer between Fe³⁺ and BNSCDs, so a label-free, good selectivity and high sensitivity method for Fe³⁺determination was established with linear range and LOD of 1.5–692 μmol/L and 87 nmol/L, respectively. And then the fluorescent probe was employed for detection of Fe³⁺ in tap water, coal gangue, fly ash and food samples successfully. Moreover, the as-prepared BNSCDs could serve as a novel pH fluorescent probe in the range of pH 1.60–7.00, which could be attributed to the proton transfer of carboxyl groups on the surface of BNSCDs. More importantly, the pH fluorescent probe possesses fast, real-time and low toxicity, applying for intracellular pH fluorescence imaging in HIC, HIEC, LO2 and SMMC7721 cells. In view of its simplicity, timely response and outstanding compatibility, the as-fabricated BNSCDs show the potential applications in water quality and solid waste monitoring, food detection, real-time measuring of intracellular pH change in vitro.