Integrated microfluidic devices

Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.

https://iopscience.iop.org/article/10.1088/0960-1317/17/5/R01/pdf

Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem : a review

This review article describes recent developments in microfluidics, with special emphasis on disposable plastic devices. Included is an overview of the common methods used in the fabrication of pol...

https://www.future-science.com/doi/pdf/10.2144/05383RV02

Disposable microfluidic devices: fabrication, function, and application

Significant progress in the development of miniaturized microfluidic systems has occurred since their inception over a decade ago. This is primarily due to the numerous advantages of microchip analysis, including the ability to analyze minute samples, speed of analysis, reduced cost and waste, and portability. This review focuses on recent developments in integrating electrochemical (EC) detection with microchip capillary electrophoresis (CE). These detection modes include amperometry, conductimetry, and potentiometry. EC detection is ideal for use with microchip CE systems because it can be easily miniaturized with no diminution in analytical performance. Advances in microchip format, electrode material and design, decoupling of the detector from the separation field, and integration of sample preparation, separation, and detection on-chip are discussed. Microchip CEEC applications for enzyme/immunoassays, clinical and environmental assays, as well as the detection of neurotransmitters are also described.

Recent developments in electrochemical detection for microchip capillary electrophoresis

Capacitively coupled contactless conductivity detection (C4D) is presented in a progressively detailed approach. Through different levels of theoretical and practical complexity, several aspects related to this kind of detection are addressed, which should be helpful to understand the results as well as to design a detector or plan experiments. Simulations and experimental results suggest that sensitivity depends on: 1) the electrolyte co-ion and counter-ion; 2) cell geometry and its positioning; 3) operating frequency. Undesirable stray capacitance formed due to the close placement of the electrodes is of great importance to the optimization of the operating frequency and must be minimized.

Understanding Capacitively Coupled Contactless Conductivity Detection in Capillary and Microchip Electrophoresis. Part 1. Fundamentals

Contactless conductivity detection was carried out on a planar electrophoresis device by capacitive coupling using an ac excitation voltage of 500 V(p-p) and a frequency of 100 kHz. It was possible to carry out detection in this way through a cover plate of 1 mm thickness. Better sensitivity is obtained, however, by placing the electrodes into troughs that allow tighter coupling to the separation channel. The 3 x S/N detection limits are 0.49, 0.41, and 0.35 microM for the small inorganic ions K+, Na+, and Mg2+. The detection of heavy metals is demonstrated with the example of Mn2+, Zn2+, and Cr3+ with detection limits of 2.1, 2.8, and 6.8 microM, respectively. The universal nature of the method is further illustrated by the detection of citric and lactic acids, which are of interest in food and beverage analysis, and detection of three antiinflammatory nonsteroid drugs, 4-acetamidophenol, ibuprofen, and salicylic acid, as examples of species of pharmaceutical interest.

High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis.

The new features of the capacitively coupled contactless conductivity detector for capillary electrophoresis described are higher peak-to-peak excitation voltages for the detector cell of up to 250 V, a pick-up amplifier in close proximity to the electrode and synchronous detection. The electrical performance of the cell was characterized and found to follow readily predictable patterns. The alterations led to a higher signal strength, a better signal-to-noise ratio (S/N) and improved stability. The 3 × S/N detection limits obtained for inorganic cations and anions are in the range 0.1–0.2 μM. For the indirect detection of model compounds of organic cations and anions (aliphatic amines and sulfonates), detection limits of typically 1 μM were achieved.

Improved capacitively coupled conductivity detector for capillary electrophoresis

The detection of alkali, alkaline earth and heavy metal ions with a high-voltage capacitively coupled contactless conductivity detector (HV-C(4)D) was investigated. Eight alkali, alkaline earth metal ions and ammonium could be separated in less than 4 min with detection limits in the order of 5 x 10(-8) M. The heavy metals Mn2+, Pb2+, Cd2+ Fe2+, Zn2+, Co2+, Cu2+ and Ni2+ could also be successfully resolved with a 10 mM 2-(N-morpholino)ethanesulfonic acid/DL-histidine (MES/His)-buffer. Zn2+, Co2+, Cu2+ and Ni2+ showed an indirect response. The detection limits for the heavy metals were determined to range from about 1 to 5 microM.

High-voltage contactless conductivity detection of metal ions in capillary electrophoresis.

Microfluidic lab-on-a-chip systems based on polymers - fabrication and application

Potentiometric detection is rarely used in separation methods but is promising for certain classes of analytes which can only with difficulty be quantified by more standard methods. Conductimetric detection of ions is very versatile and has recently received renewed interest spurned by the introduction of the capacitively coupled contactless configuration. Both are useful and complementary alternatives to the established optical detection methods, and to the more widely known electrochemical method of amperometry. The simplicity of the electrochemical methods makes them particularly attractive for microfabricated devices, but relatively little work has to date been carried out with regard to potentiometric and conductimetric detection.

Jatisai Tanyanyiwa

Papers

High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis.

Improved capacitively coupled conductivity detector for capillary electrophoresis

High-voltage contactless conductivity detection of metal ions in capillary electrophoresis.

Microfluidic lab-on-a-chip systems based on polymers - fabrication and application

Conductimetric and potentiometric detection in conventional and microchip capillary electrophoresis.