Smilax China-derived yellow-fluorescent carbon dots for temperature sensing, Cu²⁺ detection and cell imaging

Here, we report an environmentally friendly fabrication strategy of bright yellow fluorescent carbon dots (y-CDs) and construct a rapid and accurate multifunctional sensing platform for the effective detection of temperature and Cu2+. The y-CDs were favorably obtained through a one-step hydrothermal treatment of natural Smilax China for the first time and exhibit long-wavelength emission at 542 nm under an excitation wavelength of 470 nm. Additionally, the obtained y-CDs exhibit superior biocompatibility and distinguished stability under different conditions, and display a respectable fluorescence quantum yield of up to 22.37%. Appealingly, the as-prepared y-CDs were implemented as temperature probes within ranges of 25 °C-40 °C and 45 °C-80 °C. Significantly, based on the static quenching effect, the as-prepared y-CDs were developed as an effective platform for fluorescence sensing of Cu2+, with linear ranges of 0.5 μM-10 μM, 75 μM-225 μM and 250 μM-350 μM, achieving a detection limit of 28 nM. Furthermore, confocal fluorescence imaging of PC12 cells was achieved successfully, which indicated that the as-synthesized y-CDs could visualize Cu2+ fluctuations in living cells.