Aptamer-enhanced laser desorption/ionization for affinity mass spectrometry.

The thrombin-binding DNA aptamer was used for affinity capture of thrombin in MALDI-TOF-MS. The aptamer was covalently attached to the surface of a glass slide that served as the MALDI surface. Results show that thrombin is retained at the aptamer-modified surface while nonspecific proteins, such as albumin, are removed by rinsing with buffer. Upon application of the low-pH MALDI matrix, the G-quartet structure of the aptamer unfolds, releasing the captured thrombin. Following TOF-MS analysis, residual matrix and protein can be washed from the surface, and buffer can be applied to refold the aptamers, allowing the surface to be reused. Selective capture of thrombin from mixtures of thrombin and albumin and of thrombin and prothrombin from human plasma was demonstrated. This simple approach to affinity capture, isolation, and detection holds potential for analysis, sensing, purification, and preconcentration of proteins in biological fluids.