In the frist study, A simple and ultrasensitive method was developed for the detection of insulin in plasma samples, utilizing an aptamer as a molecular recognition probe and real-time PCR (RT-PCR) amplification of its complementary DNA as signal generators. Under the optimized conditions, the cycle threshold (Ct) increased linearly with 10-fold serial dilutions of insulin from 5×10 ?3 to 50 ng mL ?1 , with a limit of detection (LOD) of 0.002 ng/ml. The same linear range was found in spike human plasma samples with a detection limit of 0.003 ng/ml. The specificity of this aptasensor was considered to be excellent, as when tested against two other protein it produced no obvious Ct value change. Furthermore, a satisfactory analyte concentration recovery was obtained from a series of concentrations of insulin spiked into plasma samples.this aptasensor is credible and has enormous potential to analysis trace amounts of harmful target objects. In the final study, fluorescence resonance energy transfer (FRET) was introduced for the analysis of insulin in plasma samples. Under the optimum conditions, a linear range from 0.09 nM to 7.92 nM was obtained with a detection limit of 0.04nM. The same linear range was found in spike human plasma samples with a detection limit of 0.05 nM.
