Biosensing by WGM Microspherical Resonators

Abstract

Whispering gallery mode (WGM) microresonators, thanks to their unique properties, have allowed researchers to achieve important results in both fundamental research and engineering applications. Among the various geometries, microspheres are the simplest 3D WGM resonators; the total optical loss in such resonators can be extremely low, and the resulting extraordinarily high Q values of 108–109 lead to high energy density, narrow resonant-wavelength lines and a lengthy cavity ringdown. They can also be coated in order to better control their properties or to increase their functionality. Their very high sensitivity to changes in the surrounding medium has been exploited for several sensing applications: protein adsorption, trace gas detection, impurity detection in liquids, structural health monitoring of composite materials, detection of electric fields, pressure sensing, and so on. In the present paper, after a general introduction to WGM resonators, attention is focused on spherical microresonators, either in bulk or in bubble format, to their fabrication, characterization and functionalization. The state of the art in the area of biosensing is presented, and the perspectives of further developments are discussed.

Single Nanoparticle Detection Using Optical Microcavities

“…[13][14][15][16][17][18][19][20] Over the past few years, optical sensing methods, featuring low cost, miniature fingerprint, non-invasiveness, fast response, and high sensitivity have been developed. [47][48][49][50][51][52][53] The rapid progress in microcavity sensing has led to several recent reviews, [54][55][56][57][58][59][60][61][62][63] but none of them focus mainly on single nanoparticle detection. [30][31][32][33][34][35][36][37] Microcavity sensing has seen tremendous progress and the sensing performance has been demonstrated by detecting single nanoparticles and single biological molecules.…”

Whispering Gallery Mode Optical Microresonators: Structures and Sensing Applications

“…The benefits of this method are a small loss, uniform surface, easy to control the diameter of the microsphere cavity, low cost, and so on. However, the shortcoming is that glass exists in rod form, and only one microsphere cavity can be produced at a time …”

“…As the simplest 3D resonator, the microsphere resonator not only has extremely low optical loss and high energy density but also can be surface functionalized to improve sensing performance. Due to the ultra‐high sensitivity of the microsphere resonators, the devices have been widely used in the fields of physics, biology, and chemistry …”

“…However, the shortcoming is that glass exists in rod form, and only one microsphere cavity can be produced at a time. [20][21][22] Hydrogen-oxygen flame method: the top of the fiber is placed in a hydrogen-oxygen/nitrogen-butane microflame for about 1 min, and the fiber head melted into a ball under the action of surface tension. When the tip of the optical fiber melts, the fiber needs to rotate around the axis to minimize the bending of the microcavity.…”

Droplet lasers: a review of current progress

“…The focus of work on WGMs has been on sensing, and they have been used to examine the detection of biomolecules, viruses and other small particles [37]. As an example, Vollmer, Arnold and King [38] made use of a microsphere to detect the real time presence, in a label free manner, of a single Influenza A virus.…”