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AIP Adv ; 8(6): 065214, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29938122


A whispering gallery mode resonator based magnetometer using chip-scale glass microspherical shells is described. A neodynium micro-magnet is elastically coupled and integrated on top of the microspherical shell structure that enables transduction of the magnetic force experienced by the magnet in external magnetic fields into an optical resonance frequency shift. High quality factor optical microspherical shell resonators with ultra-smooth surfaces have been successfully fabricated and integrated with magnets to achieve Q-factors of greater than 1.1 × 107 and have shown a resonance shift of 1.43 GHz/mT (or 4.0 pm/mT) at 760 nm wavelength. The main mode of action is mechanical deformation of the microbubble with a minor contribution from the photoelastic effect. An experimental limit of detection of 60 nT Hz-1/2 at 100 Hz is demonstrated. A theoretical thermorefractive limited detection limit of 52 pT Hz-1/2 at 100 Hz is calculated from the experimentally derived sensitivity. The paper describes the mode of action, sensitivity and limit of detection is evaluated for the chip-scale whispering gallery mode magnetometer.

Sci Rep ; 7(1): 14965, 2017 11 02.
Artigo em Inglês | MEDLINE | ID: mdl-29097682


Arrays of on-chip spherical glass shells of hundreds of micrometers in diameter with ultra-smooth surfaces and sub-micrometer wall thicknesses have been fabricated and have been shown to sustain optical resonance modes with high Q-factors of greater than 50 million. The resonators exhibit temperature sensitivity of -1.8 GHz K-1 and can be configured as ultra-high sensitivity thermal sensors for a broad range of applications. By virtue of the geometry's strong light-matter interaction, the inner surface provides an excellent on-chip sensing platform that truly opens up the possibility for reproducible, chip scale, ultra-high sensitivity microfluidic sensor arrays. As a proof of concept we demonstrate the sensitivity of the resonance frequency as water is filled inside the microspherical shell and is allowed to evaporate. By COMSOL modeling, the dependence of this interaction on glass shell thickness is elucidated and the experimentally measured sensitivities for two different shell thicknesses are explained.

Langmuir ; 33(29): 7215-7224, 2017 07 25.
Artigo em Inglês | MEDLINE | ID: mdl-28655276


In this Article, we experimentally measure the adsorption kinetics of human serum albumin (HSA) on a hydrophobic hexadecanethiolated gold surface. We use micromachined quartz crystal resonators with fundamental frequency of 83 MHz to accomplish these measurements in real time. In this work, we focus on two key results: (i) asymptotic behavior of the sensor responses upon HSA adsorption and (ii) the jamming limit of adsorbed layer formed by both single-injection and multi-injection experiments with the same value of final concentration. We develop a new interface-depletion modified random sequential adsorption (RSA) model to elucidate the adsorption kinetics and the transport properties of the protein molecules. Analysis of the experimentally measured data shows that the results can be explained on the basis of the exponentially depleting interfacial layer RSA model. To better understand the origin of the formation of the interfacial depletion region where the supply of protein molecules is dramatically reduced, we performed a series of molecular dynamics (MD) simulations using the ReaxFF method. These simulations predict that the resulting adsorption of the protein molecules on the thiolated surface results in a specific orientation at the interface and the diffusion constant of the protein molecules in this layer is significantly reduced. This interplay between the surface adsorption rate and the reduced diffusion coefficient leads to the depletion of the protein molecules in the interfacial layer where the concentration of the protein molecules is much less than the bulk concentration and explains the observed slowdown of the HSA adsorption characteristics on a hydrophobic surface.

Proteínas/química , Adsorção , Difusão , Interações Hidrofóbicas e Hidrofílicas , Cinética , Transição de Fase , Propriedades de Superfície
Proc IEEE Sens ; 20162016.
Artigo em Inglês | MEDLINE | ID: mdl-30906488


Via optimization of the mechanical coupling, alignment of Metglas® magnetic domains, relief of residual stress, and operation of the PZT-5A under a DC electric field of 2 kV/cm an unprecedented magnetoelectric voltage coefficient of 9.52 V/cm-Oe is achieved; resulting to a magnetic field sensitivity of 150 pT at 20 Hz for a d31 Metglas®/PZT-5A laminate. Mechanical coupling is improved by reducing the thickness and porosity of the epoxy. The Metglas® residual stress reduction and easy axis alignment is accomplished by a 30 minute 400 °C anneal under a 1600 Oe magnetic field in vacuum. Finally, a DC electric field bias is applied to increase the d 31 coefficient of the PZT-5A piezoelectric.

Nano Lett ; 14(11): 6115-20, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25268467


We locally investigate the electronic transport through individual tunnel junctions containing a 10 nm thin film of vanadium dioxide (VO2) across its thermally induced phase transition. The insulator-to-metal phase transition in the VO2 film collapses the Hubbard gap (experimentally determined to be 0.4 ± 0.07 V), leading to several orders of magnitude change in tunnel conductance. We quantitatively evaluate underlying transport mechanisms via theoretical quantum mechanical transport calculations which show excellent agreement with the experimental results.