Red-emitting carbon dots as luminescent agent in wide-range water detection in organic solvents and polarity-selective zebrafish imaging

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Heteroatom-doped carbon dots with promising luminescent properties are excellent candidates for sensing and imaging applications. Herein, we reported a facile one-step hydrothermal synthesis of highly-fluorescent red-emitting carbon dots (R-CDs) with quantum yield of 37.2 %. R-CDs exhibit a maximum emission band at 640 nm under the excitation wavelength of 500 nm. Furthermore, R-CDs show excitation-dependent and solvent-engineered fluorescent characteristics that the luminescent properties could be greatly affected by polarity. Due to the sensitivity to polarity, a quick and precise approach for wide-range water detection in organic solvents has been developed. Because of the low autofluorescence background, R-CDs were applied to the zebrafish larvae imaging. Polarity-selective bright red light from R-CDs is seen in the low-polarity organs like yolk sac and eyes, which contain abundant lipids and lipoprotein. Our results demonstrate that R-CDs could be used as bio-imaging agents and fluorescent sensors for quantitative and visual water detection in various organic solvents. • High-fluorescent red-emitting carbon dots are synthesized from hydrothermal treatment of DMAB and boric acid. • Bright red emission at 640 nm (λ ex = 500 nm) and high QY of 37.2 % are achieved. • The variation of the emission intensity of R-CDs is highly dependent on solvent polarity. • Polarity-selective bright red light from R-CDs is seen in the low-polarity organs like yolk sac and eyes.