Capillary enzyme reactors

This chapter presents an approach to perform enzyme linked immunosorbent assays (ELISA) in a microfluidic format with electrochemical detection. This field of analytical chemistry has shown a strong activity in recent years, and many reports have presented the use of capillary-sized reactors for running immunoassays either in homogeneous format (where the antigen-antibody complex and the labelled revelation reagents are separated prior to detection, as for instance by capillary electrophoresis [1-3]) or in heterogeneous format (where the antibody is immobilised on the inner surface of the microsensor device [4] or on microbeads [5,6]). 

Figure 3. Flow sheet of laboratory experimental plant. REM, capillary enzyme membrane reactor SS,substrate reservoir, SP, permeate reservoir.

Sakai-Kato K, Kato M, Toyo oka T (2002) On-line trypsin-encapsulated enzyme reactor by the sol-gel method integrated into capillary electrophoresis. Anal Chem 74 2943-2949... 

Whole cells or enzymes immobilized in capillary membrane reactors... 

To fulfill such requirements, attempts have been made in the past decade by researchers working on peptide mapping and proteomics through development of immobilized microfluidic enzymatic reactors. Microfluidic enzymatic microreactors are an alternative to in-solution method employing immobilization of proteases on microchaimels of chip-based reactors or surfaces of capillaries. The microreactors that enable proteolytic digestion by enzymes immobilized on solid supports are also referred to as immobilized enzyme reactors, IMERs. The great potential of IMERS for proteomic applications comprise rapid and enhance... 

Table 10.2 Immobilized enzyme reactors (IMERs) in capillary and their applications in proteolysis.

HOLLOW-FIBER MEMBRANES. A hollow-fiher membrane is a capillary having an inside diameter of - inn and an outside diameter < I mm and whose wall functions as a semipermeahlc membrane. The fibers can he employed singly or grouped into a bundle which may contain tens of thousands of fibers and up to several million libers as in reverse osmosis (Fig. 11. In most eases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across (heir walls. However, they can also he used as containers to effect the controlled release of a specific material, or as reactors to chemically modify a permeate as il diffuses through a chemically activated hollow-liher wall. e g., loaded with immobilized enzyme. 

The basic hydrodynamic equations are the Navier-Stokes equations [51]. These equations are listed in their general form in Appendix C. The combination of these equations, for example, with Darcy s law, the fluid flow in crossflow filtration in tubular or capillary membranes can be described [52]. In most cases of enzyme or microbial membrane reactors where enzymes are immobilized within the membrane matrix or in a thin layer at the matrix/shell interface or the live cells are inoculated into the shell, a cake layer is not formed on the membrane surface. The concentration-polarization layer can exist but this layer does not alter the value of the convective velocity. Several studies have modeled the convective-flow profiles in a hollow-fiber and/or flat-sheet membranes [11, 35, 44, 53-56]. Bruining [44] gives a general description of flows and pressures for enzyme membrane reactor. Three main modes... 

Highly efficient enzyme membrane reactors can be also produced by immobilizing enzymes in membranes or in hollow fibers. For example, enzymes can be confined in the porous support matrix of an asymmetric capillary membrane, while substrate-containing solution flows through the fiber lumen. The dense skin layer at the lumen wall should be impermeable to the enzyme molecules. The latter diffuse through the inner wall of the fiber to the enzyme into the spongy part, where the conversion takes place. Applied transmembrane pressure and axial flow rate are parameters that contribute to control of the reactor performance. 

From the point of view of mechanical properties, performances of capillary membranes charged with cells are almost comparable to those of bacteria-free ones. The interesting conversions observed in lactose hydrolysis and the remarkable stability of immobilized bacterial fl-galac-tosidase encourage further studies for the development of an enzyme membrane reactor oriented to possible industrial applications. 

Overall enzyme amount in the reactor, M Number of capillary membranes in a bundle Product concentration, M L 3 Peclet number... 

We used capillary zone electrophoresis (CZE) [5] to measure accurately the concentrations of most of the small molecular species that are passed through the membrane. Because the enzymes are not present, the concentrations in aliquots taken from the reactor outflow just before the end of each sampling period reflect the concentrations inside the reactor. The set of perturbing input species concentrations and system responses form an ordered time series suitable for analysis by CMC. 

Edwards et al. (1999a) reported that during removal of polyphenols in an enzyme-immobilized membrane reactor, in order to remove the colored quinone-type by-products, which passed through the membrane, a chitosan-packed post-adsorption column was required to be integrated into the system. In another study Edwards et al. (1999b) utilized chito-san gel as an immobilization matrix for polyphenol oxidase on polysul-fone capillary membranes. They reported that during the treatment of... 

H. Nakamura, X. li, H. Wang, M. Uehara, M. MiyazakL A simple method of self assembled nano-particles deposition on the micro-capillary inner walls and the reactor application for photocatalytic and enzyme reactions, Chem EngJ., 2004, 101, 261-268. 

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