Planar Hall magnetoresistive aptasensor for thrombin detection.

The use of aptamer-based assays is an emerging and attractive approach in disease research and clinical diagnostics. A sensitive aptamer-based sandwich-type sensor is presented to detect human thrombin using a planar Hall magnetoresistive (PHR) sensor in cooperation with superparamagnetic labels. A PHR sensor has the great advantages of a high signal-to-noise ratio, a small offset voltage and linear response in the low-field region, allowing it to act as a high-resolution biosensor. In the system presented here, the sensor has an active area of 50 µm × 50 µm with a 10-nm gold layer deposited onto the sensor surface prior to the binding of thiolated DNA primary aptamer. A polydimethylsiloxane well of 600-µm radius and 1-mm height was prepared around the sensor surface to maintain the same specific area and volume for each sensor. The sensor response was traced in real time upon the addition of streptavidin-functionalized magnetic labels on the sensor. A linear response to the thrombin concentration in the range of 86 pM-8.6 µM and a lower detection limit down to 86 pM was achieved by the proposed present method with a sample volume consumption of 2 µl. The proposed aptasensor has a strong potential for application in clinical diagnosis.

Nanowires array modified electrode for enhanced electrochemical detection of nucleic acid.

The gold nanowires array electrode (AuNWsA) was synthesized by two step electrodeposition, which provided well oriented vertically aligned nanowires. The dimensions of the nanowires were determined by scanning electron micrograph and found to be around 1.5 µm in length with 200 nm diameter. Each nanowire was separated by a distance of 2-3 times the diameter of the nanowire itself. The electrochemical performance of the AuNWsA electrode was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Using these analytical tools, this AuNWsA electrode was shown to have a high effective surface area and excellent electron transfer surfaces compared with flat bare Au electrode. The AuNWsA electrode was then used as an electrochemical biosensor electrode by immobilizing probe DNA and analyzed by CV, EIS and Fourier transform infrared measurements. The results of this analysis suggested that the AuNWsA electrode provides good surfaces for the immobilization and hybridization of DNA. The selectivity of the probe DNA immobilized AuNWsA electrode was tested using non-complementary and one base pair mismatching DNA. The detection limit of the AuNWsA electrode was determined to be 6.78×10(-9) M, which is two times smaller than the bare Au electrode.

Ultrasonic alignment of bio-functionalized magnetic beads and live cells in PDMS micro-fluidic channel.

In this work, we demonstrated the alignment of polystyrene latex microspheres (diameter of 1 ~45 µm), bio-functionalized superparamagnetic beads (diameter 2.8 µm), and live cells (average diameter 1 ~2 µm) using an ultrasonic standing wave (USW) in a PDMS microfluidic channel (330 µm width) attached on a Si substrate for bio-medical applications. To generate a standing wave inside the channel, ultrasound of 2.25 MHz resonance frequency (for the channel width) was applied by two ultrasound transducers installed at both sides of the channel which caused the radiation force to concentrate the micro-particles at the single pressure nodal plane of USW. By increasing the frequency to the next resonance condition of the channel, the particles were concentrated in dual nodal planes. Migration time of the micro-particles towards the single nodal plane was recorded as 108 s, 17 s, and 115 s for polystyrene particles of 2 µm diameter, bio-functionalized magnetic beads, and live cells, respectively. These successful alignments of the bio-functionalized magnetic beads along the desired part of the channel can enhance the performance of a sensor which is applicable for the bio-hybrid system and the alignment of live cells without any damage can be used for sample pre-treatment for the application of lab-on-a-chip type bioassays.

Removal of Cr(VI) by thermally activated weed Salvinia cucullata in a fixed-bed column.

The present study evaluates the feasibility of using a thermally activated fresh water weed in removing Cr(VI) from wastewater through column studies. The effect of flow rate, bed height and Cr(VI) concentration of the feed solution on the adsorption capacity of the activated weed was investigated. The adsorption capacity increased with decrease in both flow rate and bed height but increased with an increase in initial adsorbate concentration. Four different kinetic models, such as. Adams-Bohart, Bed Depth Service Time (BDST), Thomas and Yoon-Nelson models were first applied to the experimental data to predict the breakthrough curve and to determine the characteristic parameters of the column useful for designing large-scale column studies. Different statistical methods such as Sum of the Square of the Error (SSE), Sum of the Absolute Error (SAE), Average Relative Error (ARE), Average Relative Standard Error (ARS) and regression coefficient, were applied to evaluate the prominent and unique characteristic features of the experimental and predicted parameters under the respective models to find out the best fit. The performance stability of the adsorbent was tested by continuous adsorption-desorption studies.