Label-Free Quartz Crystal Microbalance Biosensor Based on Aptamer-Capped Gold Nanocages Loaded with Polyamidoamine for Thrombin Detection

Thrombin is an important biomarker, and its detection is of great significance for diagnosis and prevention of related diseases. Conventional methods such as enzyme-linked immunosorbent assay are sensitive but require multiple steps. In this work, a label-free biosensor that only required one step of incubation was developed based on target-triggered release of the cargo molecules from gold nanocages, which achieved highly sensitive and specific detection of thrombin. The proposed biosensor consists of an array of gold nanocages loaded with molecules in their interiors and the DNA probes immobilized on their surface for hybridization with thrombin-specific aptamers to seal their pores. Upon interaction with thrombin, the surface aptamers were lifted off the gold nanocages, resulting in release of the cargo molecules. The loss of cargo molecules was detected by quartz crystal microbalance (QCM). The signal could be amplified by the choice of cargo molecules. The use of polyamidoamine as cargo molecules allowed us to achieve a label-free biosensor with a linear detection range of 0.0086–86 nM and a limit of detection of 7.7 pM. The biosensor was also tested with spiked human serum samples with a limit of detection of 1.2 nM. The detection could be carried out within 1.5 h with only one incubation step of 45 min. The specificity of the biosensor was confirmed by testing against bovine serum albumin and lysozyme at 1 μM.