Detection of Sub-Nanomolar Concentration of Trypsin by Thicken-Shear Mode (TSM) Acoustic Wave Biosensor

The determination of protease activity is very important for disease diagnosis, drug development, and quality and safety assurance for dairy products. Therefore, the development of low-cost methods for assessing protease activity is critical. Here, we demonstrate that an acoustic wave-based biosensor operated in the thickness-shear mode (TSM) enables the low-cost detection of protease activity in real time. The TSM sensor was based on a protein substrate (PS) β-casein immobilized on a piezoelectric quartz crystal electrode. The β-casein layer was immobilized onto a gold surface by a carboxylate terminated self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (MUA). The carboxylic acid terminal was activated by the reaction of a mixture of water- soluble N-(3-Dimethylaminopropyl)-N0-ethylcarbodiimide (EDC) and N–Hydroxysuccinimide (NHS) on the electrode surfaces. We demonstrated that β-casein can form a stable assembly on a piezoelectric quartz crystal electrode. After an enzymatic reaction with trypsin, it cleaved the surface-bound β-casein substrate, which increased the frequency of the crystal in a sigmoidal manner. Trypsin was detected in the range of concentrations from 1 to 50 nM. The limit of detection was 0.2 nM. Initial reaction rates measured at different enzyme concentrations have been used to construct a calibration curve. Considering the results obtained, we believe that the TSM biosensor is a useful tool for protease analysis.

Pengukuran solubilitas n-amylalkohol dalam poly (n-butyl methacrylate) dan polyisobutylene menggunakan metode piezoelectric-quartz crystal microbalance sorption

The Piezoelectric Quartz Crystal Microbalance (QCM) method was used to measure the solubilities of n-amylalcohol in poly (n-butyl methac1ylate) and polyisobutylene at temperatures of 333.15 K, 353.15 K and 353.15 K. The crystals used were 5 MHz, AT-Cut, 5.5 mm in diameter and 0.3 mm in thick. Reliability of the measurements was comfirmed by comparing the present data with the literature data for the system of benzene-polyisobutylene at temperature 338.15K. The solubilities n-amyl alcohol in polyisobutylene were undectedable in the range of temperature experiments by the present apparatus because of the low solubility. For the solubilities of n-amyl alcohol in ploy (n-butyl methacryalate) the higher temperature, the lower solubility and the experimental data could be correlated by the UNIQUAC equation with average absolute deviation between experimental and calculated solvent activities of 3.8%. Keywords: Solubility, Quartz Crystal Microbalance, Solvent, Polymer AbstrakDalam penelitian ini, metode Piezoelectric Quartz Crystal Microbalance (QCM) digunakan untuk mengukur kelarutan pelarut n-amylalkohol dalam polimer poly (n-butyl methacrylate) dan polyisobutylene pada temperatur 333,15 K, 343,15 K dan 353,15 K. Kristal yang digunakan adalah jenis AT-Cut 5 MHz, diameter 5,5 mm dan ketebalan 0,3 mm. Reliabilitas dari pengukuran di tes dengan membandingkan hasil pengukuran dengan data literatur untuk sistem benzene­polyisobutylene pada temperatur 338, I 5K. Kelarutan n-amyl alkohol dalam polyisobutylene tidak dapat terdeteksi pada range temperatur eksperimen dengan peralatan yang ada karena kelarutannya rendah. Untuk kelarutan n-amylalkohol dalam poly(n-butyl methacrylate), semakin besar suhu, kelarutannya semakin rendah dan data eksperimen dapat dikorelasikan menggunakan persamaan UNIQUAC dengan rata-rata deviasi ahsolut sebesar 3,8%.Kata Kunci: Kelarutan, Quartz Crystal Microbalance, Pelarut, Polimer

Performance Enhancement of Interdigital Electrode-Piezoelectric Quartz Crystal (IDE-PQC) Salt Concentration Sensor by Increasing the Electrode Area of Piezoelectric Quartz Crystal (PQC)

In this paper, a new approach to enhance the performance of the interdigital electrode-piezoelectric quartz crystal (IDE-PQC) salt solution concentration sensor by modifying the electrode area of PQC was proposed. Equivalent circuit analysis showed that the static capacitor (C0) which is related to the electrode area of PQC directly affected the response sensitivity of the IDE-PQC sensor. Further, the sensing responses of IDE-PQC sensors to various concentrations of salt solution were measured. Three kinds of salt solution, including NaCl, KCl, and Na2SO4, were adpoted to evaluate the sensing performances of the IDE-PQC sensors. The experimental results also indicated that increasing the electrode area of PQC can enhance the sensitivity response of the IDE-PQC sensors to the change of salt solution concentration. For example, the detection sensitivity of the IDE-PQC sensor with an electrode diameter of 5 mm was about three times larger than that of the sensor with an electrode diameter of 3 mm. Meanwhile, we found that the frequency stability of the IDE-PQC sensor was also improved by increasing the electrode area of PQC. In addition, the influence of the electrode area of PQC on the repeatability and the transient response of IDE-PQC salt solution concentration sensor were also studied. This work demonstrates simple and cost-effective method to achieve the performance enhancement of IDE-PQC salt solution concentration sensor by modifying the electrode area of PQC.