Insulin Detection Enabled by Sensors Employing Fluorescence Signal Amplification Strategy

We present the development of a fluorescent aptamer sensor for insulin detection, which is based on single-walled carbon nanohorns (SWCNHs). This sensor capitalizes on the high affinity and strong specificity of a FAM-labeled aptamer for insulin. In the absence of insulin, the aptamer is adsorbed onto SWCNHs. This adsorption triggers fluorescence resonance energy transfer (FRET), leading to fluorescence quenching and a low fluorescence intensity. When insulin is present, the FAM-aptamer binds to insulin to form a complex. As a result, the aptamer detaches from the SWCNHs, preventing the SWCNHs from fully quenching the aptamer's fluorescence. The addition of the Cryonase enzyme initiates the hydrolysis of the complex. This process releases both the fluorescent molecules and insulin, allowing them to enter the next cycle. Through multiple hydrolysis cycles, a substantial number of FAM-labeled small oligonucleotide fragments are set free, thereby amplifying the fluorescence signal. The sensor shows a linear detection range from 5 to 250 ng/mL and a detection limit as low as 3.98 ng/mL. This method is simple, sensitive, and exhibits high specificity for insulin detection.