Abstract
Combining the high sensitivity properties of surface plasmon resonance refractive index sensing with a tunable external cavity laser, we demonstrate a plasmonic external cavity laser (ECL) for high resolution refractometric sensing. The plasmonic ECL utilizes a plasmonic crystal with extraordinary optical transmission (EOT) as the wavelength-selective element, and achieves single mode lasing at the transmission peak of the EOT resonance. The plasmonic ECL refractometric sensor maintains the high sensitivity of a plasmonic crystal sensor, while simultaneously providing a narrow spectral linewidth through lasing emission, resulting in a record high figure of merit for refractometric sensing with an active or passive optical resonator. We demonstrate single-mode and continuous-wave operation of the electrically-pumped laser system, and show the ability to measure refractive index changes with a 3σ detection limit of 1.79 × 10(-6) RIU. The demonstrated approach is a promising path towards label-free optical biosensing with enhanced signal-to-noise ratios for challenging applications in small molecule drug discovery and pathogen sensing.
Highlights
Surface plasmon resonance (SPR) biosensors that measure changes in surface-adsorbed refractive index as biomolecules adsorb onto metal surfaces have been used effectively to analyze biomolecular interactions since the first demonstration in 1991 [1, 2]
Several types of high-Q dielectric resonators achieve detection figure of merit (FOM) metrics that far exceed that of SPR, where the FOM is defined as FOM = Sb/Γ, in order to simultaneously capture the effects of the magnitude of the refractive index induced resonant shift and the ability to measure small wavelength shifts
We experimentally demonstrate a plasmonic external cavity laser (ECL) refractometric sensor, which achieves sharp resonant linewidth associated with external cavity laser emission, while at the same time maintaining the high Sb associated with SPR
Summary
Surface plasmon resonance (SPR) biosensors that measure changes in surface-adsorbed refractive index as biomolecules adsorb onto metal surfaces have been used effectively to analyze biomolecular interactions since the first demonstration in 1991 [1, 2]. The extraordinary optical transmission (EOT) effect [9], arising from plasmon interactions between periodic arrays of metallic elements, leads to large field enhancement and high sensitivity to surface-localized refractive index changes. Extensive effort has been devoted to further enhancing the performance of plasmonic nanostructured sensors for the most challenging biosensing applications, where plasmonic devices with both narrow resonant linewidth and high refractive index sensitivity are required to detect extremely small resonance shifts. Novel designs for plasmonic nanostructures that redistribute the plasmon-enhanced electric fields have been demonstrated with the goal of making the resonant field accessible to the surrounding environment [12, 13], so as to achieve greater sensitivity (Sb, as measured by the bulk refractive index sensitivity Sb = Δλ/Δn, where Δλ is the shift in resonant wavelength induced by a change in refractive index of liquid on the sensor surface of Δn). Because increased Q for an optical resonator has generally resulted in reduced Sb [18], there has been a great deal of research focused on development of active optical resonators that achieve narrow resonant linewidth without sacrificing sensitivity through the process of stimulated emission [18,19,20,21]
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