Surface-active agent enhanced FRET effect Cu-doped NH₂-MIL-88(Fe) for highly sensitive detection of...

In this study, Cu-doped NH₂-MIL-88(Fe) metal-organic frameworks (MOF) were synthesized via a one-step method. Characterization techniques such as XPS, XRD and FTIR confirmed the successful incorporation of Cu²⁺ into NH₂-MIL-88(Fe), naming this MOF as NH₂-MIL-88(Fe)@Cu²⁺. This MOF was employed to develop a highly sensitive fluorescence sensing platform for detecting 3-nitro-L-tyrosine(3-NT). The potential for fluorescence resonance energy transfer (FRET) was suggested by the spectral overlap between NH₂-MIL-88(Fe)@Cu²⁺'s emission and 3-NT's UV absorption. To augment this effect, cationic surfactant hexadecyltrimethylammonium bromide (CTAB), which self-assembled into nanostructured microspheres above its critical micelle concentration, was utilized. The charged surface of these microspheres, formed by the self-assembly of CTAB, is bound to the MOF surface through electrostatic force and simultaneously attracts 3-NT. Adjusting the solution's pH strengthened the interaction between NH₂-MIL-88(Fe)@Cu²⁺ and 3-NT, thereby enhancing their mutual FRET interaction. Experimental results indicated that CTAB's introduction markedly improved the FRET effects, potentially converting a weak FRET into a strong one and enhancing detection sensitivity and accuracy. Under optimal conditions, NH₂-MIL-88(Fe)@Cu²⁺ detected 3-NT within 0-30 μM range, with a limit of detection (LOD, S/N = 3) of 41.1 nM. Finally, the applicability of the sensor is tested by calibrating measurements in fetal bovine serum samples, achieving good performance in terms of sensitivity, selectivity and reproducibility. This research provides a method for efficient and highly sensitive 3-NT detection and insights into the FRET effect between MOF and target molecules, likely advancing related fields and inspiring future fluorescence sensor designs.