Protein-Encapsulated DNA Metal Nanocluster as a Fluorescent Nanoprobe for Detecting Insulin

The exploration of insulin detection is of great significance for achieving diabetes monitoring and treatment. In this study, a protamine-encapsulated DNA copper nanocluster (Prot@DNACuNC) was synthesized as a novel fluorescent nanoprobe for detecting insulin, a unique biomarker of diabetes. Prot@DNACuNC was found to be highly sensitive toward glucose-responsive insulin releasing pancreatic β-cells, TC6, and MIN-6. Here, the system leverages the specific interaction between insulin and protamine, leading to a strong fluorescence change that correlates with the insulin concentration. The sensor platform achieved a 0.016 ng/mL (2.8 pM) limit of detection (LOD) that was well within physiological insulin levels and showed minimal interference from other biologically relevant proteins. The system demonstrated good batch-to-batch reproducibility. Here, the protamine serves a dual role: it stabilizes the nanocluster structure while enhancing its fluorescence and also functions as the recognition element for the insulin. Upon contact with insulin, Prot@DNACuNC firmly binds to it, leading to fluorescence quenching. The quenching mechanism involves (i) morphological changes in the nanoprobe and (ii) a conformational transition of insulin from α-helical to β-sheet structures, an indicator of its aggregation. With their small size, photostability, and biocompatibility, Prot@DNACuNCs act as effective insulin sensors. This protein-based encapsulation approach has the potential to offer a promising route to develop future nanoprobes for detecting other targets.