Coherent Optical Transduction of Suspended Microcapillary Resonators for Multi-Parameter Sensing Applications

Abstract

Characterization of micro and nanoparticle mass has become increasingly relevant in a wide range of fields, from materials science to drug development. The real-time analysis of complex mixtures in liquids demands very high mass sensitivity and high throughput. One of the most promising approaches for real-time measurements in liquid, with an excellent mass sensitivity, is the use of suspended microchannel resonators, where a carrier liquid containing the analytes flows through a nanomechanical resonator while tracking its resonance frequency shift. To this end, an extremely sensitive mechanical displacement technique is necessary. Here, we have developed an optomechanical transduction technique to enhance the mechanical displacement sensitivity of optically transparent hollow nanomechanical resonators. The capillaries have been fabricated by using a thermal stretching technique, which allows to accurately control the final dimensions of the device. We have experimentally demonstrated the light coupling into the fused silica capillary walls and how the evanescent light coming out from the silica interferes with the surrounding electromagnetic field distribution, a standing wave sustained by the incident laser and the reflected power from the substrate, modulating the reflectivity. The enhancement of the displacement sensitivity due to this interferometric modulation (two orders of magnitude better than compared with previous accomplishments) has been theoretically predicted and experimentally demonstrated.

Hydrodynamic assisted multiparametric particle spectrometry

“…1a, in which the hollow microchannel can mechanically oscillate in a guitar-string mode. The fabrication of the device is based on a thermal stretching technique described elsewhere 24 . The mechanical modes of the capillary are excited by means of a piezoelectric actuator, while its resonance frequency is tracked in real-time by means of a home-made interferometric readout system and a lock-in amplifier (Fig.…”

“…1b). This interferometric system also allows tracking the reflected light power by the fused silica resonator to obtain information about the optical properties of the flowing analytes by analyzing in real-time the scattered light 24,25 . Moreover, the device is pressurized by means of a nitrogen pressure pump (Fluigent INC, MFCS-EZ-07000001), which allows flow control by setting a pressure difference.…”

Hydrodynamic Assisted Multiparametric Particle Spectrometry

“…1.b). This interferometric system also allows tracking the reflected light power by the fused silica resonator to obtain information about the optical properties of the flowing analytes by analyzing in real-time the scattered light 24,25 . Moreover, the device is pressurized by means of a nitrogen pressure pump (Fluigent INC, MFCS-EZ-07000001), which allows flow control by setting a pressure difference.…”

“…Among the SMR devices, transparent microcapillary resonators (TMR) not only combine a nanomechanical resonator with a microfluidic channel but also allow the optical probing of the flowing particles. These devices have been demonstrated in previous works as an interesting alternative to cantilever-type SMRs for mass sensing [18][19][20][21][22][23] , introducing a new source of information about the particle based on its optical characterization 24,25 . This double mechanooptical particle detection technique has been proved in recent work as a highly reliable technique for particle discerning, even in cases of particles of similar masses.…”

Nanomechanical Molecular Mass Sensing Using Suspended Microchannel Resonators

“…This problem becomes even more dramatic for gases, as their density is not as well defined as in liquids due to their compressibility. To overcome this problem, transparent microcapillary resonators (TMR) have been developed to combine the highly sensitive mass density sensing, measured from its mechanical frequency signal [ 25 , 26 , 27 , 28 ], with refractive index measurements, obtained from its reflectivity signal with detection limit of 10 −5 [ 7 , 29 ].…”