Microfluidic chemical sensors

Several techniques for miniaturization of simple chemical and medical analysis systems are described. Miniaturization of total analysis systems realizes a small sample volume, a fast response and reduction of reagents. These features are useful in chemical and medical analysis. During the last decade many micro flow control devices, as well as the micro chemical sensors fabricated by three dimensional microfabrication technologies based on photofabrication, termed micromachining, have been developed. Miniaturized total analysis systems (pTAS) have been studied and some prototypes developed. In microfabricated systems, microfluidics , which represent the behavior of fluids in small sized channels, are considered and are very important in the design of micro elements used in pTAS. In this chapter microfluidics applied flow devices, micro flow control devices of active and passive microvalves, mechanical and non-mechanical micropumps and micro flow sensors fabricated by micromachining are reviewed. 

In conclusion, the advantages of microfluidic devices, parallel synthesis, and combinatorial approaches can be merged to integrate a fluorescent chemical sensor array in a microfluidic chip. Fluorescent microchannel array can be produced by parallel synthesis of fluorescent monolayers covalent attached to the walls of glass microchannels. 

Microfabrication technology used to manufacture microreactors also introduces many advantages, most notably the ability to rapidly and cheaply mass-produce devices. The low cost of microfabricated devices makes it possible for these devices to be disposable, a characteristic desirable for many medical applications. Rapid scale-up of production by operating many microreactors in parallel can also be accomplished. Microfabrication also presents the opportunity for complete systems in a single monolithic device or systems on a chip as microreactors are incorporated with chemical sensors and analysis devices, microseparation systems, microfluidic components, and/or microelectronics. 

Chapters 17 and 18 look at the importance of sampling technologies and the design of the microfluidic systems. In particular, the use of preconcentrators and solid phase micro extractors to boost the vapour concentration before it is introduced to the chemical sensor or electronic nose. 

Another relevant issue for sensors is packaging. In particular, for chemical sensors designed for working in solution, it is necessary to prevent the solution from any contact with the semiconductor layer (if this is not the sensitive layer of the device). Microfluidic systems [35,36] coupled with the sensor s active areas offer a valid solution to this problem because they allow the flow of the solution to the active area to be controlled and channeled, without compromising the semiconductor layer. For pressure/strain sensors the packaging should not compromise the mechanical flexibility of the whole structure. 

Grover, W.H., Skelley, A.M., Liu, C.N., Lagally, E.T., and Mathies, R.A. Monolithic membrane valves and diaphragm pumps for practical large-scale integration into glass microfluidic devices. Sensors and Actuators B—Chemical, 2003, 89, 315-323. 

Optofluidic detection techniques based on SERS can be used as a highly sensitive biomedical and chemical sensor. Combining a microfluidic device with Raman spectroscopy provides an opportunity to analyze target molecules in real time without labeling at the single molecular level. There are several methods for combining... 

For the fabrication of M/NEMS and chemical sensors, often thicker layers of resist are needed to buUd up channels or to define fluid reservoirs. In these cases SU-8 [15] or polyimide resist layers can be used [1]. Thicker layers are frequently used for molding or for microfluidic devices [16] for stereolithography [11], the desired pattern is defined in resin by scanning a laser through a thin layer of the material in a sequential fashion. 

Hervas, M., L6pez, M.A., and Escarpa, A. (2012) Microfluidic chips as new platforms for electrochemical sensing, in Chemical Sensors. Comprehensive Sensor Technologies, Electrochemical and Optical Sensors, vol. 5 (ed G. Korotcenkov), Momentum Press, pp. 275-310. 

The history of miniaturizing bio/chemical sensors is over 30 years old, as is represented by the development of ion-sensitive field-effect transistors (ISFETs). Stimulated by the current trend of pTAS and lab-on-a-chip technologies, they are currently being incorporated in microfluidic systems for the... 

Miniaturisation of various devices and systems has become a popular trend in many areas of modern nanotechnology such as microelectronics, optics, etc. In particular, this is very important in creating chemical or electrochemical sensors where the amount of sample required for the analysis is a critical parameter and must be minimized. In this work we will focus on a micrometric channel flow system. We will call such miniaturised flow cells microfluidic systems , i.e. cells with one or more dimensions being of the order of a few microns. Such microfluidic channels have kinetic and analytical properties which can be finely tuned as a function of the hydrodynamic flow. However, presently, there is no simple and direct method to monitor the corresponding flows in. situ. 

---