A planar split-ring resonator-based microwave biosensor for label-free detection of biomolecules

In this study, a planar split-ring resonator (SRR)-based RF biosensor was developed for label-free detection of biomolecules such as the prostate cancer marker, prostate specific antigen (PSA), and cortisol stress hormone. The biosensor has a resonance-assisted transducer and is excited by a time-varying magnetic field component of a local high-impedance microstrip line. The resulting device exhibits an intrinsic S-21 resonance with a quality-factor (or Q-factor) of 50. For the biomolecular interaction, anti-PSA and anti-cortisol were immobilized on the gold surface of the resonator by a protein-G mediated bioconjugation process and corresponding frequency shifts of Delta f(1)(p) = 30 +/- 2 MHz (for anti-PSA) and Delta f(1)(c) = 20 +/- 3 MHz (for anti-cortisol) were observed. The additional frequency shift of each PSA and cortisol antigen with a 100 pg/ml concentration was about 5 +/- 1.5 MHz and 3 +/- 1 MHz, respectively. From the experimental results, we confirmed that our device is very effective RF biosensor with a limit of detection (LOD) of 100 pg/ml and has sufficiently feasibility as a label-free biosensing scheme. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.