Dual-colored carbon dot encapsulated metal-organic framework for ratiometric detection of glutathione

A dual-emissive metal−organic frameworks was prepared by encapsulating yellow emitting and blue emitting carbon dots into the zeolitic imidazolate framework (BYCDs@ZIF-8) which acted as a ratiometric probe for Glutathione. The composite shows dual-emissions which are centered at 565 and 440 nm under a single excitation wavelength of 365 nm. In the presence of Cu²⁺, the fluorescence of yellow emitting carbon dots in the nanocomposite was selectively enhanced, while the fluorescence of the blue emitting carbon dots was quenched. Upon addition of glutathione on Cu²⁺- BYCDs@ZIF-8 system, the fluorescence of both carbon dots gradually restored to their original amounts due to the strong interaction between glutathione and Cu²⁺. Detection progress can be observed by unaided eyes with a visual color change from yellow to blue under ultraviolet irradiation. Under the optimal conditions, glutathione determined in the range of 3–25 nM with a limit of detection of 0.90 nM (Signal/Noise = 3). The employed composite with distinct size-selectivity not only decreases the background interference from large molecule but it is also able to strongly accumulate the target analytes and thus greatly amplifies the sensing signal and specificity. Also, the ratiometric strategy provided built-in self-calibration for signal correction and improved precision and accuracy. This method was applied for the detection of glutathione in fruit samples and showed satisfactory results.