Analytical and biosensing platforms for insulin: A review

Human insulin regulates carbohydrate metabolism to maintain the blood glucose level and this peptide hormone has been considered an important biomarker in diabetic management. Several fast-acting and long-acting insulin analogs have also emerged to improve insulin dose regimes for chronic diabetic patients. The administration of insulin is currently based on some glucose-insulin models; however, simultaneous measurement of glucose and insulin enables better glucose control and circumvents abnormal levels of blood insulin. Reliable quantification of glucose is well served by glucose meters, which have become less invasive and more powerful, and even non-invasive devices for continuous monitoring of glucose have emerged. However, the measurement of insulin and its analogs is more difficult and complicated due to their large size (> MW 5.8 kDa) and picomolar levels in the blood as well as the presence of endogenous interfering molecules. In clinical and hospital settings, insulin detection is performed by fully automated immunoassay platforms with high throughput and reliability. Chromatographic techniques equipped with tandem mass spectrometry perform the separation of insulin from its analogs. Albeit insulin can be electrochemically oxidized, electroanalysis still lacks detection sensitivity and selectivity without sample pre-treatment. Biosensing based on aptamers and molecular imprinted polymers (MIP) shows great promise to overcome these two key drawbacks. Future developments will focus on robust antibodies, aptamers, and insulin selective biorecognition elements with high selectivity, stability, and capacity. Such robust aptamers might open the possibility for the development of Point-of-Care (POC) devices to measure ultra-low levels of insulin in blood with high selectivity and reliability.