Glycated hemoglobin (HbA1c) affinity biosensors with ring-shaped interdigital electrodes on impedance measurement.

Glycated hemoglobin (HbA1c) is one of the most important diagnostic assays for the long-term mark of glycaemic control in diabetes. This study presents an affinity biosensor for HbA1c detection which is label-free based on the impedance measurement, and it features low cost, low sample volume, and requires no additional reagent in experiments. The ring-shaped interdigital electrodes (RSIDEs) are designed to promote the distribution uniformity and immobilization efficiency of HbA1c, and are further employed to characterize the impedance change and identify various concentrations of HbA1c. The self-assembled monolayer (SAM) of thiophene-3-boronic acid (T3BA) is provided to modify the gold electrode surface. Afterwards, the esterification reaction between HbA1c and T3BA produces a relative change of electrical property on the electrode surface. The RSIDEs with SAM of T3BA exhibit a wide range from 100 to 10 ng/µL producing an approximate logarithmic decrease of impedance, a low detection limit of 1 ng/µL, a good selectivity and short-term stability for HbA1c determination. The remarkable advantages (miniaturization and low-cost) fill the bill of point-care diagnostics for portable sensor development.

Adjustable trapping position for single cells using voltage phase-controlled method.

We present an advanced technique improving upon the micron-sized particle trap integrated in biochip systems using a planar structure to generate an adjustable trapping position by utilizing voltage phase-controlled (VPC) method and negative dielectrophoresis (nDEP) theory in high conductivity physiological media. The designed planar and split structure is composed of independent components of measuring and trapping micro-electrodes. Through different voltage configurations on the device, the trapped position of single particles/cells was selected and adjusted in vertical and horizontal directions. The numerical simulations verify our theoretical predictions of the effects at the various voltages. It shows that the trapped position can be adjusted in the vertical (0 to 26 µm) and horizontal (0 to 74 µm) directions. In experiments, the single particles/cells is captured, measured, and then released, with the same process being repeated twice to demonstrate the precision of the positioning. The measurement results determined that particles at various heights result in different magnitude values, while the impedance error is less than 5% for the proposed electrode layout. Finally, the experiments are performed to verify that a particle/cell can be precisely trapped on the selected site in both the vertical and horizontal directions.

Integration of single-cell trapping and impedance measurement utilizing microwell electrodes.

The ability to research individual cells has been seen as important in many kinds of biological studies. In the present study, cell impedance analysis is integrated into a single-cell trapping structure. For the purpose of precise positioning, a cell manipulation and measurement microchip, which uses an alternating current electrothermal effect (ACET) and a negative dielectrophoresis (nDEP) force to move a particle and cell on measurement electrodes, is developed. An ACET and an nDEP can be easily combined with subsequent analyses based on electric fields. A microwell presented in a previous study is separated into two parts, which are regarded as the measurement electrodes. The original structure is modified for precise positioning. Numerical simulations and analyses are conducted to compute and analyze the effects of the structural parameters. The results of simulations and analyses are used to obtain the optimum structure for the cell. The capture range of the microwell can be designed for cells of various sizes. In order to demonstrate the precision of the positioning, a particle is captured, measured, and released twice. The results show that the impedance error of the particle is about 3%. Finally, the developed structure is applied to trap and measure the impedance of a HeLa cell.

Single-cell trapping utilizing negative dielectrophoretic quadrupole and microwell electrodes.

The handling of individual cells, which has attracted increasing attention, is a key technique in cell engineering such as gene introduction, drug injection, and cloning technology. Alternating current (AC) electrokinetics has shown great potential for microfluidic functions such as pumping, mixing, and concentrating particles. The non-uniform electric field gives rise to Joule heating and dielectrophoresis (DEP). The motion of particles suspended in the medium can be influenced directly, by means of dielectrophoretic effects, and indirectly, via fluid flow through a viscous drag force that affects the particles. Thus alternating current electrothermal effect (ACET) induced flow and DEP force can be combined to manipulate and trap single particles and cells. This study presents a microfluidic device which is capable of specifically guiding and capturing single particles and cells by ACET fluid flow and the negative dielectrophoretic (nDEP) trap, respectively. The experiment was operated at high frequencies (5-12 MHz) and in a culture medium whose high conductivity (sigma=1.25S/m) is of interest to biochemical analysis and environmental monitoring, which are both prone to producing ACET and nDEP. Manipulation of particle motion using ACET-induced fluid flow to the target trap is modeled numerically and is in good agreement with the experimental results.