Abstract
A novel polarimetry methodology for phase-sensitive measurements in single reflection geometry is proposed for applications in optical transduction-based biological sensing. The methodology uses altering step-like chopper-based mechanical phase modulation for orthogonal s- and p- polarizations of light reflected from the sensing interface and the extraction of phase information at different harmonics of the modulation. We show that even under a relatively simple experimental arrangement, the methodology provides the resolution of phase measurements as low as 0.007 deg. We also examine the proposed approach using Total Internal Reflection (TIR) and Surface Plasmon Resonance (SPR) geometries. For TIR geometry, the response appears to be strongly dependent on the prism material with the best values for high refractive index Si. The detection limit for Si-based TIR is estimated as 10(-5) in terms Refractive Index Units (RIU) change. SPR geometry offers much stronger phase response due to a much sharper phase characteristics. With the detection limit of 3.2*10(-7) RIU, the proposed methodology provides one of best sensitivities for phase-sensitive SPR devices. Advantages of the proposed method include high sensitivity, simplicity of experimental setup and noise immunity as a result of a high stability modulation.
Highlights
Phase characteristics of light reflected or transmitted from a solid/air or solid/liquid interface can provide important information on properties of the interface, as well as to serve as an extremely sensitive parameter in gas- or biological sensing [1,2]
In the Total Internal Reflection (TIR) geometry, light is directed through the prism and reflected from its inner edge connected to the sensing interface
In the TIR geometry, we measured AC and DC responses for two prism materials: BK7 and SF11. As it was predicted by our theoretical modeling, the DC signal amplitude was constant while the AC output sharply rose immediately after the angle of total internal reflection (Fig. 7(a))
Summary
Phase characteristics of light reflected or transmitted from (through) a solid/air or solid/liquid interface can provide important information on properties of the interface, as well as to serve as an extremely sensitive parameter in gas- or biological sensing [1,2]. Employing phase characteristics of light under Surface Plasmon Resonance (SPR) and examining them by interferometry or polarimetry methods, one can achieve 1-2 order of magnitude gain in sensitivity of biosensors compared to conventional amplitude-sensitive devices [1,2,3,4,5,6,7,8,9,10,11,12,13]. Very promising results have been achieved in polarimetry or interferometry schemes using a liquid crystal [15], an acousto-optic [12] or piezoelectric modulators [6]. The implementation of these schemes often increases the cost and complexity of measurement methodology, which is not always consistent with potential applications of SPR technology
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