Plasmonic enhancement of a whispering-gallery-mode biosensor for single nanoparticle detection

Abstract

We describe and demonstrate a physical mechanism that substantially enhances the label-free sensitivity of a whispering-gallery-mode biosensor for the detection of individual nanoparticles in aqueous solution. It involves the interaction of dielectric nanoparticle in an equatorial carousel orbit with a plasmonic nanoparticle bound at the microparticle's equator. As the dielectric particle parks to hot spots on the plasmonic particle we observe frequency shifts that are enhanced by a factor of 4, consistent with a simple reactive model. Once optimized the enhancement by this mechanism should exceed several orders of magnitude, putting individual protein within reach.

Ultrasensitive detection of a protein by optical trapping in a photonic‐plasmonic microcavity

“…Several approaches have been investigated recently, and specific examples for enhancement mechanisms include the use of multiplexed sensor arrays [27], self-referenced mode-splitting techniques [25,26] as well as hybrid photonicplasmonic WGMs [29,30]. In the latter approach, a WGM is tuned close to the plasmon resonance of a surface bound gold (Au) nanoparticle (NP) 'antenna' so that a hotspot of high field intensity is created at the NP site -without significant loss of Q-factor.…”

Detection of nanoparticles with a frequency locked whispering gallery mode microresonator

“…Recently, however, several theoretical studies have emphasized that the predicted detection limit of current devices is well above that which is required for single molecule sensitivity 3 . For this reason many efforts have been made to improve the signal-to-noise ratio (SNR) and thereby reach the single molecule limit, including interferometry 4,5 , plasmonic enhancement 3,6,8,9 and frequency stabilization 10-12 . In this letter we build on these works, demonstrating real-time detection of gold (Au) nanorods with a silica microtoroid stabilized using the Pound-Drever-Hall (PDH) technique 13 .…”

Detection limits in whispering gallery biosensors with plasmonic enhancement

“…Recently, it was shown experimentally that a localized surface plasmon resonance (LSPR) in a large metallic nanoshell can enhance single nanoparticle optical frequency shifts in a microsphere resonator by a factor of four. 9 The enhancement was predicted to be as much as 200 for BSA. A similar effect was shown in Ref.…”

“…(1), the frequency shift is found by numerically integrating the field intensity associated with polarizing the BSA molecule. 9 The enhancement in dx is the ratio of the polarization energies with and without the nanorod…”