Polymer based whispering gallery mode laser for biosensing applications

Abstract

Whispering gallery mode lasers are of interest for a wide range of applications and especially biological sensing, exploiting the dependence of the resonance wavelengths on the surrounding refractive index. Upon lasing, the Q factors of the resonances are greatly improved, enabling measurements of wavelength shifts with increased accuracy. A way forward to improve the performance of the refractive index sensing mechanism is to reduce the size of the optical resonator, as the refractive index sensitivity is inversely proportional to the resonator dimensions. However, as the lasing threshold is believed to depend on the Q factor among other parameters, and the reduction of the microresonator size results in lower Q, this poses additional challenges for reaching the lasing threshold. In this letter, we demonstrate lasing in 10 μm diameter dye doped polystyrene microspheres in aqueous solution, the smallest polystyrene microsphere lasers ever reported in these conditions. We also investigate the dependence of the lasing threshold on the Q factor by changing the refractive index surrounding the sphere, highlighting a much stronger dependency than initially reported.

Q-factor limits for far-field detection of whispering gallery modes in active microspheres

“…Whispering gallery modes (WGMs), otherwise referred to as morphology dependent resonances, are optical modes propagating in resonators having at least one axis of revolution such as capillaries, disks or toroids, spheres and shells [1][2][3][4]. Light that is trapped by total internal reflection circulates inside the cavity close to the surface, and when returning in phase gives rise to resonance features.…”

Dynamic Self-Referencing Approach to Whispering Gallery Mode Biosensing and Its Application to Measurement within Undiluted Serum

“…A schematic of the optical setup is shown in Fig. 1 (B), where a frequency doubled YAG laser (λ = 532 nm, ~ 800 ps pulse duration, 10 kHz repetition rate) was used for the excitation of the active microspheres beyond their lasing thresholds, enabling higher Q-factors as previously shown 32 . The light from the YAG was spatially filtered using a tapered single mode fiber (SMF28 Øcore = 4 µm) before being coupled into the 4-hole silica MOF (Øcore = 7 µm, Øhole ~ 15 μm), Fig.…”

“…Experimental setup, materials and method. The polystyrene microspheres (nominal diameter of 15.00 ± 1.43 μm from Polyscience Inc) were doped with the fluorescent dye Nile Red (λex = 532 nm, λem = 590 nm) 31 using a liquid two-phase system 32 . Following this process, the microspheres were annealed and rinsed thoroughly to remove any trace of the organic solvent (xylene) used during the doping process, eliminating any drift of the resonance positions over time.…”

Optical Tracking of Anomalous Diffusion Kinetics in Polymer Microspheres

“…While the high Q factors of these surface-type modes provide a sensitive method of studying diffusion kinetics or sensing of volatiles, this work also provides a, hitherto lacking, quantitative description of the degradation and swelling processes affecting polymer biosensors, which are invariably used in aqueous environments [5,7]. We primarily concern ourselves with polymer-penetrant systems suffering relatively small physical changes from penetrant diffusion, as may result from, for example, low penetrant solubility, slow dissolution rates, and small molar volume.…”

“…Diffusion in polymers is a complex process, the understanding of which can bring great benefit to, for example, design of polymer membranes, microfluidics, fuel cells, controlled drug delivery systems, and sensors [1][2][3][4][5][6][7]. Fundamentally, many physical principles can influence the diffusion kinetics, such that differing diffusion regimes have been observed ranging from so-called Fickian (case I) diffusion, in which the rate of penetrant diffusion dominates the kinetics, through anomalous diffusion, to non-Fickian (case II) diffusion governed by polymer relaxation [8,9].…”