Label-acquired magnetorotation as a signal transduction method for protein detection: aptamer-based detection of thrombin

This paper presents a new signal transduction method, called label-acquired magnetorotation (LAM), for the measurement of the concentration of proteins in solution. We demonstrate the use of LAM to detect the protein thrombin using aptamers, with a limit of detection of 300 pM. LAM is modeled after a sandwich assay, with a 10 μm nonmagnetic "mother" sphere as the capture component and with 1 μm magnetic "daughter" beads as the labels. The protein-mediated attachment of daughter beads to the mother sphere forms a rotating sandwich complex. In a rotating magnetic field, the rotational frequency of a sandwich complex scales with the number of attached magnetic beads, which scales with the concentration of the protein present in solution. This paper represents the first instance of the detection of a protein using LAM.