Wirelessly Driven and Battery-Free Love Wave Biosensor Based on Dinitrophenyl Immobilization

Abstract

A Love wave-based wireless immunosensor with a 440 MHz operating frequency was developed on a 41° YX LiNbO3 piezoelectric substrate. The developed sensor was composed of a shear horizontal surface acoustic wave (SH SAW) reflective delay line, a poly(methyl methacrylate) (PMMA) waveguide layer, and a 2,4-dinitrophenyl (DNP) receptor layer that specifically responds to an anti-DNP immunoglobulin G (IgG). Fabricated devices were wirelessly tested using a network analyzer. Four reflection peaks with large signal/noise (S/N) ratios and sharp reflection peaks were observed in the time domain, and are attributed to three shorted grating reflectors and DNP-bound gold film. With 10 mW radio frequency (RF) power from the network analyzer, a readout distance of ∼1 m was observed. The binding of IgG to DNP receptor molecules induced a change in the Love wave velocity owing to a mass loading effect, resulting in phase shifts of the original reflection peaks. The phase shifts increased linearly with increasing IgG concentration. Fast response time and long-term stability of the developed sensor in a liquid environment were observed. The phase shifts depending on different PMMA thicknesses were also investigated to identify the optimal PMMA waveguide thickness.