Fabrication of ZIF-8 capsule with commodious microenvironment and synergistic effect for CBX@ZIF-8: Facilitating the detection of protamine

We previously reported an organic fluorescent probe CBX for protamine detection. However, the detection limit, biocompatibility and stability can be further optimized. Considering the excellent performance of the current mesoporous materials, we tried to further prepare the nanocomposite probe based on 2-methylimidazole zinc salt (ZIF-8) using CBX for the purpose of improving the detection performance of CBX. Excitingly, this method has indeed provided a new type of metal-organic frameworks (MOFs) probe with excellent detection performance. In this work, three ZIF-8 materials with different morphologies by adjusting the ratio of zinc ion and ligand (2-methylimidazole) were prepared, and three nanocomposite probes including CBX@ZIF-8 (1:2), CBX@ZIF-8 (1:4) and CBX@ZIF-8 (1:16) were synthesized. Experimental results showed that CBX@ZIF-8 (1:16) has the lowest detection limit for protamine. Also, the signal-to-noise ratio of these nanocomposite probes are much higher than that of free probe CBX. Differential charge data analysis suggests that the N atom on the imidazole of the ZIF-8 materials can effectively increase the electronegativity of the carboxyl group, enhance the electrostatic interaction with protamine, and improve the detection sensitivity. This work can inspire the researchers to develop novel nanocomposite probes for sensitive detecting biomolecules.