Customer requirements - increasing sensitivity

The construction of complicated three-dimensional structures on a sub-micrometer scale requires increasingly sensitive and sophisticated methods amenable to both custom and mass production. Electrochemical machining is increasingly important (in addition to lithography, direct writing, molecular assembly) to achieve the construction of micro- and nanodevices. 

Finally, there are custom two-step quantitation methods such as chromatography or ELISA that require a capture step for isolating the protein and then a quantitation step based on a standard curve of the purified target protein. The preliminary capture step may also concentrate the protein for increased sensitivity. These techniques are typically not available in a commercial kit form and may require extensive method development. They are more labor intensive and complex than the colorimetric or absorbance-based assays. In addition, recovery of the protein from and reproducibility of the capture step complicate validation. Despite these disadvantages, the custom two-step quantitation methods are essential in situations requiring protein specificity. 

Some examples of hydrolases are listed in Table 7.3 according to the industrial sector in which they are used. Most of these hydrolases operate in the hydrolytic mode, since only a few processes are currently known that make use of the synthetic power of hydrolases. Increasingly, however, these enzymes are being tailored by genetic tools such as random or site-directed mutagenesis and overexpression to lower the operational costs of the biocatalyst and to obtain enzymes of high purity, as well as to meet specific customer requirements such as stability, substrate specificity, and optimal pH and temperature of operation. A typical example is the protease subtilisin from Bacillus subtilus, which was made bleach-resistant by replacing one bleach-sensitive amino acid (cysteine) by the chemically inert alanine [12]. 

As the acceptance specifications imposed by the container manufaaurer s customers become stricter, the sensitivity of the pack rate to disturbances increases. It can be seen that to reverse this trend, and improve or restore profitability, some form of corrective action is required to reduce the impact of the disturbances on the process. Closed loop control, in which key process variables are measured, and compensating adjustments are automatically applied, provides an approach for achieving the desired reduction in variability and ultimately increasing profitability of the operation. 

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