Ultrasensitive enzyme-free fluorescent detection of VEGF based on target-triggered hybridization chain reaction amplification.

Sensitive detection of vascular endothelial growth factor (VEGF) is important for early cancer disease diagnosis in the clinic. A sensitive fluorescent sensing platform for VEGF detection is developed in this work. It is based on a target-triggered hybridization chain reaction (HCR) and graphene oxide (GO) selective fluorescence quenching. In this assay, in the presence of the VEGF, the hairpin structure of Hp opens up and the initiation sequence will be exposed to Hp1 to open its hairpin structure. Then the opened Hp1 hybridizes with Hp2 to expose the complementary sequence of Hp1 which hybridizes with Hp1 again by HCR. Thus HCR would be initiated, generating super-long dsDNA. After the HCR, the double strands of the HCR product cannot be adsorbed on the GO surface. As a result, the HCR product gives a strong fluorescence signal which is dependent on the concentration of VEGF. By using VEGF as a model analyte, the assay provides a highly sensitive fluorescence detection method for VEGF with a detection limit down to 20 pg mL. The proposed aptasensing strategy based on target-triggered HCR amplification can thus be realized. It was successfully applied to the determination of VEGF in spiked human serum, urine and saliva. Therefore, it can easily have wide applications in the diagnosis of vital diseases.