Utilizing a high fundamental frequency quartz crystal resonator as a biosensor in a digital microfluidic platform

Elastic compliance and adsorption profiles of Bovine serum albumin at fluid/solid interface in the presence of electrolytes

Non-trivial topology of proteins under shear suggests that even small structural changes in proteins result in dramatic variations in the mechanical properties and stability. In this study, we have analysed the elastic compliance of solvated bovine serum albumin (BSA) with NaCl,MgCl₂, FeCl₃ of concentration-ranging from 50 mM to 250 mM using Quartz crystal microbalance with dissipation. The compliance shows a reverse Hofmeister trend (Na + <Mg ²⁺ < Fe ³⁺) for high salt concentrations with a fine balance, between intra and intermolecular interactions for the cations. Radius of gyration of BSA with the electrolytes from small angle X-ray scattering (SAXS) is in agreement with this reverse Hofmeister trend. Depending on the valency and concentration of metal ion, the repulsive double layer screening provides sufficient energy to overcome the interactions between hydrophobic domains in the protein molecule resulting in protein assemblies. The long-range effect of high concentrations of divalent and trivalent ions in solution studied using UV-visible and fluorescence spectroscopy, zeta potential and circular dichroism, demonstrates spontaneous aggregated assemblies of BSA. These assemblies are dominated by the long-range distribution of the ions around the proteins, as described by Debye-Hückel theory, with the local salt structure near the protein surface playing a minor role.

Structural and rheological properties conferring fertilization competence to Xenopus egg-coating envelope

The extracellular egg-coating envelope that comprises a meshwork of filaments polymerized by glycoproteins plays a pivotal role in species-selective sperm recognition and subsequent fertilization; however, the structural and rheological properties conferring fertilization competence to the egg-coating envelope remain poorly unveiled. Here we show several nanoscale-structural and viscoelastic properties of the egg-coat using the transmission electron microscopy and the quartz crystal microbalance experiments, following clamp of the egg-coat at either fertilization-competent or -incompetent statuses by short-term pretreatment with synthetic peptides. Individual filament of approximately 4.8 nm diameter crossed one another, forming several types of intersections. Higher competence-inducing treatment changed the proportion of V-, Y-, and T-type intersections, and induced more randomly deflected angles at intersections. Incompetence-inducing treatment increased the median of a Gaussian distribution of filament lengths that had a peak of 10–20 nm under control conditions; furthermore, this treatment created bumps in the 30–40 and 50–60 nm windows. Quartz crystal microbalance study revealed that viscoelasticity of the competent VE suspension was lower than that of incompetent VE, indicating that viscoelastic property required for successful fertilization resides within a specific range. These findings indicated that the architecture of the egg-coat is capable of rapid and dynamic remodeling, which determines fertilization efficiency.

A Novel Slope Method for Measurement of Fluid Density with a Micro-cantilever under Flexural and Torsional Vibrations

A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration.

An experimental study on fabricating an inverted mesa-type quartz crystal resonator using a cheap wet etching process

In this study, a miniaturized high fundamental frequency quartz crystal microbalance (QCM) is fabricated for sensor applications using a wet etching technique. The vibration area is reduced in the fabrication of the high frequency QCM with an inverted mesa structure. To reduce the complexity of the side wall profile that results from anisotropic quartz etching, a rectangular vibration area is used instead of the conventional circular structure. QCMs with high Q values exceeding 25,000 at 47 MHz, 27,000 at 60 MHz, 24,000 at 73 MHz and 25,000 at 84 MHz are fabricated on 4 × 4 mm² chips with small vibration areas of 1.2 × 1.4 mm². A PMMA-based flow cell is designed and manufactured to characterize the behavior of the fabricated QCM chip in a liquid. Q values as high as 1,006 at 47 MHz, 904 at 62 MHz, 867 at 71 MHz and 747 at 84 MHz are obtained when one side of the chip is exposed to pure water. These results show that fabricated QCM chips can be used for bio- and chemical sensor applications in liquids.