Dry reagent chemistries

As stated above, the beginning of optical pH sensor technology remains hidden. What is nowadays refered to as a sensor layer was formerly mostly refered to as a test strip, a dry reagent chemistry, or an immobilized reagent. 

Numerous other FOCS schemes have been described for heavy metals in the past 20 years (for reviews, see 113-115). In looking at the more recent literature one may state, however, that some of the newly described "chemistries" perform hardly better than the rather old commercial systems based on the use of dry reagent chemistries, with the additional advantage that they are compatible with a single instrument for read-out. In fact, some of the newer systems involve rather extensive chemistry and - worst of all -seem to strongly differ in terms of spectroscopy and analytical wavelengths so that they all require their own opto-electronic platform. On the other hand, there is substantial need for (low-cost) sensors for less common... 

Most dry reagent chemistries are designed to be self-contained analytical devices. Each element may have several functional zones that are introduced as single layers or combined into one layer during construction. Regardless of the number of layers present, all dry reagent elements have a support function, a reflectance function, and an analytical function (Fig. I). Some elements may also contain a sample-spreading function. 

CONSTRUCTION OF DRY REAGENT CHEMISTRY ELEMENTS 4.1. Layer Construction... 

A dry reagent chemistry is designed to simplify what otherwise is a complex multistep analytical procedure for the user. The sole function of the element is to convert an analyte in a sample to a specific qucuitifiable material. To accomplish this, all physical and chemical functions needed for an tinalysis must be integrated into one element. 

Fig. 6. Comparison of multiple layering and multiple saturation strategies in dry reagent chemistry construction.

Shelf-life estimation involves developing a thermodynamic model of the dry reagent chemistry. This model is used to make projections of the shelf-life and the estimates are continuously compared with real time data to substantiate the validity of the model or to revise it. A typical study to create a database for shelf-life estimation may consist of subjecting a dry reagent chemistry, in its final packaging format, to continuous thermal stress for 2-3 years in the temperature range of 0-70 °C. An example of a schedule for such a study is shown in Fig. la. At each check point, dry reagent chemistries are removed from each of the stress conditions, allowed to come to thermal equilibrium, and analyzed, and the per-... 

Dry reagent chemistries have been described for the analysis of a variety of blood constituents. These include metabolites, enzymes, electrolytes, hormones, and therapeutic drugs. A partial list is presented in Table 3. With the exception of electrolytes, nearly all analyses depend on enzyme-mediated chemistries and that includes immunochemical assays. A brief survey of element structures will illustrate how physical functions and chemical reactions used in conventional multistep procedures are integrated in the construction of dry reagent test devices. These examples will illustrate how reactions in dry reagent elements can be compartmentalized and how end produas are shunted to other compartments for further reaction. In its final form, each element provides a complete analytical procedure. 

The oldest example of an integrated dry reagent chemistry for quantitative analysis of a metabolite is the Dextrostix reagent strip (Miles Dia ostics) for whole blood glucose analysis. The cross section of the element is illustrated in Fig. 8a. The detection chemistry is the well-known glucose oxidase-peroxidase procedure. Approximately 50 pL of whole blood is applied to the surface of the... 

Analyses for Which Dry Reagent Chemistries Have Been Reported... 

Constructing dry reagent chemistries for blood enzyme analysis presents new levels of complexity, since enzymes are too large to readily diffuse through most conventional matrices. In addition, many enzyme analyses require coupling multistep reactions which are frequendy catalyzed by other enzymes. Some dry reagent matrices have a large, open lattice that allows free diffusion of macro-... 

The success of any new technology depends on its correlation to established methodologies. Table 4 summarizes comparisons between dry reagent chemistries made by several manufacturers (44, 46, 56, 57) and conventional solution chemistries. In most cases, the correlation coefficients are greater than 0.95, with the slopes of the correlations close to unity. 

Comparison of Dry Reagent Chemistries With Reference Methods... 

Dry Reagent Chemistries, Fundamentals of The Role of Enzymes (Walter). 36... 

Walter, B. (1983). Dry reagent chemistries in clinical analysis. Anal. Chem. 55, 498 A-514 A. 

Okuda, K. (1990). A compact, automated, dry-reagent chemistry analyzer. J. IFCC 2, 39-43. 

S30 Zipp, A. (1981). Development of dry reagent chemistry for the clinical laboratory. J. Automat. Chem. 3, 71-75. 

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