Enhanced sensitivity of localized surface plasmon resonance biosensor by phase interrogation

We proposed an innovative phase interrogation method for localized surface plasmon resonance (LSPR) detection. To our knowledge, this is the first demonstration of LSPR biosensor by phase interrogation. LSPR is realized as the plasmonic resonance within confined metal nanoparticle. Nanoparticle couples the light by means of a non-radiative inter-band absorption, and a scattering from surface plasmon oscillation, the total contribution is the optical extinction of nanoparticles. Due to the variety of resonance types, LSPR is extensively studied in the field of biological sensing, imaging, and medical therapeutics. Generally, LSPR is probed by optical intensity variation of continuous wavelength, in other words, wavelength interrogation. LSPR sensitivity probed by this method is ranged from several tens nm/RIU to less than 1000nm/RIU depending on the nanostructure and metal species, which at least an order of magnitude less than conventional SPR biosensor in wavelength interrogation. In this work, an innovative common-path phase interrogation system is applied for LSPR detection. Phase difference in our home-made system is simply extracted through the correlation of optical intensity under different polarization without any heterodyne optical modulator or piezoelectric transducer, and thus low down the cost and complexity in optical setup. In addition, signal-to-noise ratio is substantially reduced since the signal wave and reference wave share the common path. In our preliminary results, LSPR resolution of Au nanodisk array is 1.74 x 10(-4) RIU by wavelength interrogation; on the other side, LSPR resolution of Au nanodisk array is 2.02x10(-6) RIU in phase interrogation. LSPR sensitivity is around one order of magnitude enhanced. In conclusion, we demonstrated that LSPR sensitivity can be further enhanced by phase interrogation.