After having reviewed some aspects of microfluidic system preparation in the first part (1), in this second part of the review we will cover a number of standard operations (namely: sample preparation, sample injection, sample manipulation, reaction, separation, and detection) as well as some biological applications of micro total analysis systems (namely: cell culture, polymerase chain reaction, DNA separation, DNA sequencing, and clinical diagnostics). As previously, we will include papers issued from different scientific journals as well as useful abstracts from three conference proceedings: MEMS, Transducers, and μTAS. In this second part, we do not include the period covered by the history section (1975-1997) from part 1 but try to cover the relevant examples of the literature published between January 1998 and March 2002. We briefly describe articles that struck us as needing special attention, while more “standard” papers are dutifully reported in groups of interest. An article might be included in more than one section, depending on the ideas developed in it.

Micro total analysis systems. 2. Analytical standard operations and applications.

Data Acquisition- Sensor Characteristics- Physical Principles of Sensing- Optical Components of Sensors- Interface Electronic Circuits- Occupancy and Motion Detectors- Position, Displacement, and Level- Velocity and Accleration- Force, Strain and Tactile Sensors- Pressure Sensors- Flow Sensors- Acoustic Sensors- Humidity and Moisture Sensors- Light Detectors- Radiation Detectors- Temperature Sensors- Chemical Sensors- Sensor Technologies- Appendix

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Handbook of modern sensors

Micro total analysis systems. Recent developments.

This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO3) substrates or SAW resonator structures on quartz or LiTaO3 with periodic mass gratings. The latter are termed “surface transverse waves” (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes.

Surface acoustic wave biosensors: a review

Research activity in chemical gas sensing is currently directed towards the search for highly selective (bio)chemical layer materials, and to the design of arrays consisting of different partially selective sensors that permit subsequent pattern recognition and multi-component analysis. Simultaneous use of various transduction platforms has been demonstrated, and the rapid development of integrated-circuit technology has facilitated the fabrication of planar chemical sensors and sensors based on three-dimensional microelectromechanical systems. Complementary metal-oxide silicon processes have previously been used to develop gas sensors based on metal oxides and acoustic-wave-based sensor devices. Here we combine several of these developments to fabricate a smart single-chip chemical microsensor system that incorporates three different transducers (mass-sensitive, capacitive and calorimetric), all of which rely on sensitive polymeric layers to detect airborne volatile organic compounds. Full integration of the microelectronic and micromechanical components on one chip permits control and monitoring of the sensor functions, and enables on-chip signal amplification and conditioning that notably improves the overall sensor performance. The circuitry also includes analog-to-digital converters, and an on-chip interface to transmit the data to off-chip recording units. We expect that our approach will provide a basis for the further development and optimization of gas microsystems.

Smart single-chip gas sensor microsystem.

It has been shown recently that a properly designed Love wave sensor is very promising for (bio)chemical sensing because of its high sensitivity. Furthermore, it is well known that a Love wave has a pure shear horizontal polarization and therefore no elastic interaction with an ideal liquid. This property makes it particularly interesting for (bio)chemical sensing in a liquid environment. However, interaction with a viscous fluid can never be avoided. It causes a small frequency shift which slightly distorts the sensor response and increases the insertion loss of the device. A theoretical and experimental study of this viscous fluid loading is presented here.

A love wave sensor for (bio)chemical sensing in liquids

It has been shown that a properly designed Love wave sensor is very promising for (bio)chemical sensing in liquids. Some fundamental properties of a Love wave delay line, such as dispersion relation, electromechanical coupling factor, and, in particular, sensitivity to mass loading on its surface are discussed. Theoretical predictions are compared with experimental data obtained from measurements on eight different devices built in ST-quartz with a sputtered SiO/sub 2/-layer. >

Love waves for (bio)-chemical sensing in liquids

A combination of different technologies is used for the realization of smart acoustic-wave-based microsensors, where electronic circuitry and an acoustic delay line are integrated on a single silicon chip. For a monolithic Lamb wave oscillator, the three required technologies are described: bipolar IC technology, thin-film piezoelectric zinc oxide technology, and micromachining technology. The last two technologies have to be IC compatible and are not allowed to affect the IC processing in order to prevent malfunction of the electronic circuitry. The realized monolithic Lamb wave sensor has several applications. Examples are the determination of the density, viscosity and sound speed of liquids, and (bio)chemical applications, where mass adsorption at the sensor surface is monitored. The sensor described in this paper demonstrates the determination of the weight percentage of water in water—ethanol solutions.

Integrated-circuit-compatible design and technology of acoustic-wave-based microsensors

In this paper, we present an electronic interface dedicated to capacitively coupled four-electrode liquid conductivity detection in micro capillary electrophoresis devices. Due to the small dimensions of the detector ( 106 μm ×170  μm), it is necessary to adapt the read-out interface. Our study focuses on two major aspects of the four-electrode setup: First, the current which flows between the two outer electrodes must be known. Second, the two inner electrodes must be connected to a high input impedance and high common mode rejection ratio (CMRR) differential amplifier. The results obtained in a miniaturized CE channel show a linear response with liquid impedances within a range of 250 kΩ to 3.45 MΩ (for a MES/His buffer, this compares to a concentration range of 0.2–20 mM).

Design of an electronic interface for capacitively coupled four-electrode conductivity detection in capillary electrophoresis microchip

We are presenting the experimental results of capacitively coupled 2- and 4-electrode conductivity detector fabricated as a glass dip-stick. These results are used as a starting point for investigating the consequences of downscaling the device for on-chip capillary electrophoresis (CE) applications, where the detector is located in a separation microchannel. Our studies show that, it is possible to do accurate and sensitive conductivity sensing in a 150 μm wide channel, by making use of 4-electrode set-up with silicon carbide (SiC) thin insulating layers on top of the electrodes.

G.W. Lubking

Papers

A love wave sensor for (bio)chemical sensing in liquids

Love waves for (bio)-chemical sensing in liquids

Integrated-circuit-compatible design and technology of acoustic-wave-based microsensors

Design of an electronic interface for capacitively coupled four-electrode conductivity detection in capillary electrophoresis microchip

Downscaling aspects of a conductivity detector for application in on-chip capillary electrophoresis