Boosting the Figure-Of-Merit of LSPR-Based Refractive Index Sensing by Phase-Sensitive Measurements

Abstract

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications, only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost 1 order of magnitude smaller than those for intensity based measurements. As this phase change is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure-of-merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles.

Phase‐sensitive surface plasmon resonance biosensors: methodology, instrumentation and applications

“…The improvement of contour sharpness resulted in phase sensitivity of 5 × 10 5 deg./RIU that was 5-10 times better compared to classical gold film SPR geometry. Similar phase-sensitive concept was recently applied to different configurations of uncoupled localized plasmons, including randomly distributed glass-supported gold nanorings or nanodiscs [123]. Here, the phase jump feature appeared to be much narrower than the intensity dip associated with the excitation of localized plasmons.…”

Immunosensing platform based on gallium nanoparticle arrays on silicon substrates

“… is the difference between the phase shifts for both polarization components. This parameter seems to have a relevant role for arrays of plasmonic nanostructures because of its large variation in resonant conditions, which makes it very sensitive to changes in the surrounding medium (Lodewijks et al 2012). In air ambient   1  n , the pseudodielectric function     is related to those parameters through: …”

“…One interesting feature of LSPRs is the possibility to enhance the sensitivity in optical sensing systems (Lodewijks et al 2012;Michieli et al 2015). GaNPs present two oscillatory modes at different energies due to the hemispherical geometry of the NPs (Tonova et al 1999).…”

Refractometric biosensing based on optical phase flips in sparse and short-range-ordered nanoplasmonic layers

“…However, it has recently been proposed that the phase information contained in light scattered or reflected from nanoparticles excited at resonance could be used to implement alternative and even more effective LSPR sensing schemes. [6][7][8][9][10][11] Indeed, phase interrogation techniques have significantly decreased the limits of detection in the case of classical surface plasmon resonance sensors based on planar gold films. 7,[12][13][14] In this case, the sensitivity enhancement is primarily due to the rapid phase flip that occurs when the reflectance approaches zero close to the resonance wavelength.…”