Miniaturized systems

There has been interest in miniaturizing and automating electrophoresis of proteins. Ruchel (1997) reported a miniaturized system where proteins are first separated by isoelectric focusing in millimeter diameter tubes. The tube s contents are transferred to a slab gel that is a few centimeters on a side. This technology was used to separate the proteins from a single giant neuron from Aplasia califomicus. More recently, native fluorescence has been used to resolve 200 proteins from a similar miniaturized electrophoresis system (Sluszny and Yeung, 2004). 

Laurell T, Nilsson J, Jensen K, Harrison DJ, Kutter JP (eds) (2004) 8th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2004). Malmo, Sweden, September 26-30 Manz A, Becker H (eds) (1998) Microsystem technology in chemistry and life sciences. Springer, Berlin Heidelberg New York Metaxas AC, Meredith RJ (1983) Industrial microwave heating. Peter Peregri-nus, London... 

In recent years, the search for superlubric materials has become a subject of practical importance, which may be most evident in the development of miniaturized systems, where nanoscopic surfaces slide past one another. In many cases, friction and wear are the main impediments to miniaturizing such devices even further. Identifying or designing superlubric materials may... 

Research has been done showing that rapid pressnre-driven LC analysis can be done with little solvent consumption, demonstrating this as a viable process analytical tool. Using electrokinetic nanoflow pumps LC can be miniaturized to the point of being a sensor system. Developments in terms of sampling to enable sampling directly from a process stream, to the separation channel on a chip are critical for the application of miniaturized process LC. The components (valves and pumps) required for hydrodynamic flow systems appear to be a current limitation to the fnll miniatnrization of LC separations. Detection systems have also evolved with electrochemical detection and refractive index detection systems providing increased sensitivity in miniaturized systems when compared to standard UV-vis detection or fluorescence, which may require precolumn derivatization. 

The use of miniaturized systems might provide a feasible approach for speeding up the separations (given that smaller column dimensions, in terms of both the inner diameter and the length, decrease the dilution). However, miniaturization is not necessarily synonymous with fast separations, since problems often arise with dead volumes, caused by the connections. Nano-LC has been used with UV or MS detection for the analysis of atenolol in urine [143]. A homemade column with an internal diameter of 75 jm containing diol silica modified with teicoplanin was used as the CSR... 

The analysis time for chiral HPLC separations will probably remain relatively long until CSPs with higher efficiency than the present ones become available. But monolithic columns, columns with a smaller particle size (i.e., UPLC ), and miniaturized systems would increase the efficiency and speed up the enantioseparation of existing types of CSPs. 

Miwa M, Douoka K, Yoneyama S, Tuchitani S, Kaneko YK (2005) Young s module control of the micro cantilever made by micro-stereolithography. In El-FatatryA (ed) MOEMS and miniaturized systems V. SPIE, Bellingham, pp 6-13. doi 10.1117/12.589197... 

Miniaturized systems for performing chemical/biochemical reactions and analysis require cavities, channels, pumps, valves, storage containers, couplers, electrodes, windows and bridges [53]. The typical dimensions of these components are in the range of a few micrometers to several millimeters in length or width, and between 100 nm and 100 pm in depth and height. An extensive set of techniques for fabricating these microstructures is discussed in Sect. 3. 

For air monitoring a complete miniaturized system made by silicon micromachining has been proposed [86]. Valves,gas fluidics, filters, thin film sensors and pumps are integrated in silicon and mounted on a printed circuit board (Fig. 3). The application of such systems will become apparent in the future. 

For developing miniaturized chromatographic systems, one possibility is to use a conventional pump with a split-flow device. Although such pumps are enough to ran miniaturized chromatographic systems, their size is very large compared to the system itself. Based on the size of such miniaturized systems, the size of the mini pump should be 25 cm3 or less. However, such small pumps are unavailable presently. 

The separation columns are fabricated from standard type 316 stainless steel tubing that is either 0.22 or 0.62 cm ID (depending upon whether it is an advanced miniaturized system or an earlier model) and 150 cm long. A 1 in. OD stainless steel heating jacket surrounds the column. The ion exchange resin is packed into the column as a thick slurry using a dynamic loading technique which provides reproducible... 

Samples are introduced by a six-port injection valve, and analytical results are presented graphically as a chromatogram showing the UV absorbance of the eluate stream versus run time, each molecular constituent being represented by a chromatographic peak (Fig. 9). The required sample size is 0.1-0.5 ml, and the total separation time is 40 hours for the larger system and 24 hours for the miniaturized system. Sensitivity is a few nanograms for many constituents (Fig. 10). 

The nanoscale dimensions of the biorecognition receptor allow for miniaturized systems with decreased reagent and power consiunption and with the concomitant increase of spatial and temporal information per unit area of device enabling simultaneous multiparametric information. 

There are hundreds if not thousands of miniaturized biosensors published in literature today. Thus, a selection of only a few of them for a brief description is a difficult task. While the biosensors described here are exceptional examples of miniaturized systems, there are many others that would have deserved a description as well, if the space had been available. A selection has been made to give an overview of interesting biosensors such as DNA microarrays, biosensors coupled with capillary electrophoresis (CE), cantilever-based biosensors, electrochemical systems, optical biosensors, and visions of a p.TAS. The examples are described only briefly, for a complete understanding of the work published, the reader is advised to refer to the original publication. Hopefully, this overview gives a grasp of the interesting biosensors developed in the new miniature world. 

The simple and inexpensive electrochemical detection systems are easier to miniaturize and included within the biosensor chip than their optical counterparts. They will thus lead to truly miniaturized systems in the near future. However, improvements in the optoelectronic technology will allow... 

Use Thin coatings of high purity and uniformity on almost any substrate that will resist a high vacuum, as paper, fabric, polyethylene and polystyrene film, ceramics, metals, many solid chemicals electronic miniaturization systems capacitors thin film circuits. 

In many cases, however, the costs arising from sample preparation will become decisive, which favors x-ray spectrometric methods, provided the earlier mentioned limitations are not encountered. Future progress will certainly depend on the avail-abilty of on-line sample treatment using, for example, flow injection and eventually on-line sample dissolution as is possible in some cases with microwave-assisted heating. Also the realization of separations in miniaturized systems and with minute amounts of reagents is very promising. In each instance the question of which method should be selected will have to be discussed for each type of analytical task to be solved. 

Microfluidics is the manipulation of fluids in channels, with at least two dimensions at the micrometer or submicrometer scale. This is a core technology in a number of miniaturized systems developed for chemical, biological, and medical applications. Both gases and liquids are used in micro-/nanofluidic applications, ° and generally, low-Reynolds-number hydrodynamics is relevant to bioMEMS applications. Typical Reynolds numbers for biofluids flowing in microchannels with linear velocity up to 10 cm/s are less than Therefore, viscous forces dominate the response and the flow remains laminar. 

Miniaturized systems where the transport processes occur across a length scale of 100-0.1 pm (or less) not only provide a reduced diffusion/conduction path length, but can also offer process selectivity. When the enhanced transfer rates are solely caused by reduction in length scale or enhanced surface area. 

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