Dual functional highly luminescence B, N Co-doped carbon nanodots as nanothermometer and Fe³⁺/Fe²⁺ sensor

Dual functional fluorescence nanosensors have many potential applications in biology and medicine. Monitoring temperature with higher precision at localized small length scales or in a nanocavity is a necessity in various applications. As well as the detection of biologically interesting metal ions using low-cost and sensitive approach is of great importance in bioanalysis. In this paper, we describe the preparation of dual-function highly fluorescent B, N-co-doped carbon nanodots (CDs) that work as chemical and thermal sensors. The CDs emit blue fluorescence peaked at 450 nm and exhibit up to 70% photoluminescence quantum yield with showing excitation-independent fluorescence. We also show that water-soluble CDs display temperature-dependent fluorescence and can serve as highly sensitive and reliable nanothermometers with a thermo-sensitivity 1.8% °C^-1, and wide range thermo-sensing between 0-90 °C with excellent recovery. Moreover, the fluorescence emission of CDs are selectively quenched after the addition of Fe²⁺ and Fe³⁺ ions while show no quenching with adding other common metal cations and anions. The fluorescence emission shows a good linear correlation with concentration of Fe²⁺ and Fe³⁺ (R² = 0.9908 for Fe²⁺ and R² = 0.9892 for Fe³⁺) with a detection limit of of 80.0 ± 0.5 nM for Fe²⁺ and 110.0 ± 0.5 nM for Fe³⁺. Considering the high quantum yield and selectivity, CDs are exploited to design a nanoprobe towards iron detection in a biological sample. The fluorimetric assay is used to detect Fe²⁺ in iron capsules and total iron in serum samples successfully.