In-Column Electrochemical Detection for Liquid Chromatography

This research focuses on the development of whole column detection (WCD) for liquid chromatography (LC). The WCD uses electrochemical techniques for detecting the analytes passing through the separation column. Electrode array for in-column electrochemical detection (ICED) is fabricated along the separation column to enable whole column separation monitoring and allow better understanding on the affinity of particular analyte to the stationary and mobile phases. Numerical models were built to understand the feasibility and differences of electrochemical detection within an unpacked and packed column. From the simulated results, the surface area of the electrode was not hindered by the presence of the particles in flow condition. An electrochemical microfluidic device has been successfully fabricated on PET (polyethylene terephthalate) substrate using the reverse imprinting technique. The photolithographically produced gold metal electrode lines were imprinted into the PET substrate using a blank mould and produced an inlaid electrode array with overall step residue within 40 nm. The semi-cured thermoset polyester channel was irreversibly thermal bonded on the PET substrate. The devices were able to tolerate pressure in excess of 90 bars. The PET column was packed with 5 μm C18 silica beads to perform reverse phase chromatography separation. The array was electrochemically characterised using standard redox probes in both stagnant conditions and under flow. Both numerical modelling and experimental data show improved sensitivity under flow and a limiting current which scaled linearly with cubic root of volume flow rate. Isocratic and gradient mode chromatographic separations of neurotransmitters and metabolites: serotonin, dopamine, adrenaline, 5- HIAA and DOPAC were conducted in the fabricated device. Separation progress was electrochemically detected at multiple locations along the column. Whole column assessment on separation efficiency and column packing efficiency monitoring were conducted using the ICED

Planar Imaging of Stagnant and Hydrodynamic Fluid using Miniaturized ECT Device

This paper discusses the development of an on chip planar capacitance tomography (ECT) for stagnant and hydrodynamic multiphase fluid monitoring. The 8-electrode planar ECT device is developed based on Lab-on-chip (LOC) or microfluidic device concept. The ECT with LOC application is an improved design to allow ECT to be portable and small scaled measurement. To reconstruct images, ECT measures the permittivity variation within the sensing area. Eight-planar electrodes with dimension of 5.00 mm × 2.08 mm (length × width) are fabricated on printed circuit board (PCB). These electrodes are aligned to circulate 16 mm diameter of sensing area. For stagnant sample, the design of the chamber is simpler from the hydrodynamic flow. The hydrodynamic flow consists with two inlets to allow multiphase flow testing. Fan beam projection technique is utilized with Linear Back Projection (LBP) algorithm to reconstruct images of the substance within the chamber. Time is an important item for hydrodynamic flow compared to stagnant sample to ensure that the data taken is useful to the user. For stagnant experiment, the ECT system able to produce image reconstruction for water – air, oil – water and yeast – glucose samples. For hydrodynamic flow, the test conducted for immiscible water – oil sample, and miscible water – glucose solution is done. The results show the system produce the best result when one liquid is dominating the sensing area. Â

Characterization of Electromagnetic Valveless Micropump

This paper presents an electromagnetically-actuated micropump for microfluidic application. The system comprises two modules; an electromagnetic actuator module and a diffuser module. Fabrication of the diffuser module can be achieved using photolithography process with a master template and a PDMS prepolymer as the structural material. The actuator module consists of two power inductors and two NdFeB permanent magnets placed between the diffuser elements. The choice of this actuation principle merits from low operating voltage (1.5 Vdc) and the flow direction can be controlled by changing the orientation of the magnet vibration. Maximum volumetric flow rate of the fabricated device at zero backpressure is 0.9756 µLs-1 and 0.4659 µLs-1 at the hydrostatic backpressure of 10 mmH2O at 9 Hz of switching speed

Nano lab-on-chip systems for biomedical and environmental monitoring

In recent years, nano lab-on-chip (NLOC) has emerged as a powerful tool for biosensing and an active area of research particularly in DNA genetic and genetic related investigations. Compared with conventional sensing techniques, distinctive advantages of using NLOC for biomedicine and other related area include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize recent  advancements in two major types of NLOC sensing approaches, label and labelled free NLOC, as well as their biomedical applications. The state-of-the-art on how these sensors interface with nano/microfluidics is then presented and the latest papers in the area summarized and also proposal to develop compact NLOC with four different sensing elements with two different mechanisms, common and separate padding is prospected.Keywords: Nano lab-on-chip, in-situ, nano/microfluidics, sensors, DNA African Journal of Biotechnology Vol. 12(36), pp. 5486-549

autotuned electrical muscle stimulator with electromyogram biofeedback

This paper discusses on the implementation of electromyogram sensor as the biofeedback of the improvised electrical muscle stimulation technology to improve the muscle strength. The paper explains some fundamental of muscle behavior followed by the muscle weakness issues. The techniques of muscle stimulation and the innovative solutions to overcome the problems encountered by the current muscle stimulation techniques are discussed. The project methodology is explained with proper circuit configurations and programming technique. Preliminary works and validation process on the wrist extensor muscle are presented. Finally, the project functionality is examined based on the simulation results that show the system behavior with respect to the muscle contraction reading

An overview: effectiveness of different arrangement for electrode guard in electrical capacitance tomography

Electrical capacitance tomography (ECT) system is useful to obtain information about the spatial distribution of a dielectric materials mixture inside a vessel. It has been suggested by many researchers previously to use guard electrode in ECT sensors. This paper describes various types of design for guard electrode in Electrical Capacitance Tomography (ECT) sensor. The design of these electrode guards is vital to reduce crosstalk (undesired signals) between the adjacent electrodes (positioned at the outside of the measured pipe) since the crucial signals are only inside the pipe. There are three types of electrode guards designed by various researchers which are radial guard, axial guard with end guard and driven guard. The configuration and the effectiveness of each designed electrode are discussed. Other than that this paper introduced new design of electrode guards which are embedded on electrode sensor instead of placing separately between or around adjacent measuring electrodes as the previous design

Characteristic of Thin Sheet Membrane for a Mechanical Driven Micropump System

This paper demonstrates the characteristic of thin sheet membrane for a mechanical driven micropump system by using a spin coater machine. The moving diaphragm material is made from a PDMS prepolymer material. A 100 mm diameter petri dish is used as the mold template for the membrane fabrication. There are three variables that influence the membrane thickness formation during the spin coating process, which are the prepolymer weight, spin coater spinning rate speed and the spinning time. Based on the study, the optimum parameters to fabricate a 300 µm thin sheet membrane by using a 100 mm diameter of petri dish are 2.5 g of prepolymer, 500 rpm of spin coater speed and 180 s of spin time. These parameters yield a thin sheet membrane for the micropump application with 314.82 ± 3.6556 µm thickness

Smart sensors for structural health monitoring (SHM)

Structural health monitoring (SHM) is a technique to diagnose an accurate and reliable condition of civil infrastructure by collecting and analyzing responses from distributed sensors. In recent years, aging civil structures have been increasing and they require further developed SHM technology for development of sustainable society. Wireless smart sensor and network technology, which is one of the recently emerging SHM techniques, enables more effective and economic SHM system in comparison to the existing wired systems. Researchers continue on development of the capability and extension of wireless smart sensors, and implement performance validation in various in laboratory and outdoor full-scale experiments.[1] the uses of wireless smart sensors has been contributing to the progress of SHM these past years. But the uses of it are still being investigated by the researchers to utilize it to its possible fullest capability

Segmented capacitance tomography electrodes: a design and experimental verifications

A segmented capacitance tomography system for real-time imaging of multiphase flows is developed and pre-sented in this work. The earlier research shows that the electrical tomography (ECT) system is applicable in flow visualization (image reconstruction). The acquired concentration profile ob-tained from capacitance measurements able to imaged liquid and gas mixture in pipelines meanwhile the system development is designed to attach on a vessel. The electrode plates which act as the sensor previously has been assembled and fixed on the pipeline, thus it causes obscurity for the production to have any new process installation in the future. Therefore, a segmented electrode sensor offers a new design and idea on ECT system which is portable to be assembled in different diameter sizes of pipeline, and it is flexible to apply in any number due to different size of pipeline without the need of redesigning the sensing module. The new ap-proach of this sensing module contains the integration intelligent electrode sensing circuit on every each of electrode sensors. A microcontroller unit and data acquisition (DAQ) system has been integrated on the electrode sensing circuit and USB technology was applied into the data acquisition system making the sensor able to work independently. Other than that the driven guard that usually placed between adjacent measuring electrodes and earth screen has been embedded on the segmented electrode sensor plates. This eliminates the cable noise and the electrode, so the signal conditioning board can be expanded according to pipe diameter

Sharp edges schottky contact electric field simulation

This paper reports investigation on effect of adding sharp edges to Schottky contact. Few studies suggested that sharp edge nanostructures produces high electric field which subsequently improve gas sensing performance on reversed biased mode. Three different shapes: circular-, hexagon- and star-shape were modeled by using COMSOL Multiphysics. The study on effects of different sizes sharp edges Schottky contact also reported. Electric field was observed and it shows that star-shape yields highest summation of electric field 2.79 x 109 V/m and lowest electric field observed at circular-shape 7 x 107 V/m. The results also revealed that distance of sharp edges from substrate edge affects the magnitude of electric field