Fluorescent/SERS dual-sensing and imaging of intracellular Zn2+

A fluorescent and surface-enhanced Raman spectroscopy (SERS) dual-mode probe is developed for imaging of intracellular Zn2+ based on N-(2-(bis(pyridine-2-ylmethyl)amino)ethyl)-2-mercaptoacetamide (MDPA) modified gold nanoparticles (MDPA-GNPs). Benefiting from the chelation-enhanced fluorescence (CHEF) between MDPA-GNPs and Zn2+, the fluorescent intensities of MDPA-GNPs are substantially enhanced with the increment of Zn2+ concentrations, which can be clearly observed by the naked eye. Under physiological conditions, the probe exhibits a stable response for Zn2+ from 1 μM to 120 μM, with a detection limit of 0.32 μM in aqueous solutions. The resultant MDPA-GNPs can be used for ultrasensitive SERS detection of Zn2+ because of the strong inter-particle plasmonic coupling generated in the process of Zn2+-triggered MDPA-GNPs self-aggregation, with a low detection limit of 0.28 pM, which is eight order of magnitude lower than the United States Environmental Protection Agency (US EPA)-defined limit (76 μM) in drinkable water. More importantly, the proposed probe can be applied for efficient detection of intracellular Zn2+ with excellent biocompatibility and cellular imaging capability. Therefore, a highly sensitive and selective nanosensor has been demonstrated for both reliable quantitative detection of Zn2+ in aqueous solution and real-time imaging of intracellular Zn2+, suggesting its significant potential utility in bioanalysis and biomedical detection in the future.