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High Load StrongZyme™ Streptavidin-(Poly)HRP #HL-SZ-SA novel conjugate ideal for High Sensitivity detection in (pseudo)-1-step ELISA tests with concentrated serum and plasma samples. Recently some ELISA assemblers offer so-called pseudo-1-step assay test kits. The distinguishing feature of these assay systems is a sequential addition of all reagents with no wash between sample, biotinylated detector antibody/antigen and Streptavidin-HRP (SA-HRP). Despite the tricky pipeting associated with the risk of cross-contamination and imprecision these systems are obviously accepted by certain customers in the blood donor screening marketplace. Abandoning one or two washing steps shortens assay time. Complementary advertised advantage is the smaller consumption of wash buffer. Another, probably true, advantage is that human serum/plasma matrix itself (as a rule applied in e.g. HBsAg and HIV-1/2 4G test kits undiluted) works as an effective blocker reducing non-specific binding of all detection system components. On the other hand false positives or false negatives may occur through diverse "irrelevant circuits" (essentially specific interactions apart of the assay components specificity) associated with possible presence in the blood sample of antibodies against biotinylated proteins, streptavidin and peroxidase. Moreover, serum of the healthy adults contains from 0,1 to 0,4 nmol/L of the endogenous biotin. Biotin weakens detection power of SA-HRP through competing for the biotin-binding sites in conjugate that would otherwise effectively react with the biotin label on the tracer antibody and/or antigen. When using SA-PolyHRP conjugates inhibition through endogenous biotin is much stronger compared to the conventional SA-HRP. The reason is that in the SA-PolyHRP a molar SA/HRP ratio is heavily shifted towards HRP. This means that the same working strength concentration of SA-PolyHRP contains essentially smaller concentration of streptavidin and respectively smaller concentration of the biotin-binding sites than conventional SA-HRP. As a result SA-PolyHRP is basically less effective in pseudo-1-step ELISAs. Otherwise presence of endogenous biotin in the clinical specimens necessitates increase of the working strength conjugate concentrations to the levels that make application of the SA-PolyHRP in pseudo-1-step ELISA test kits unlikely economical. Above problem is addressed now. Currently we offer novel High-Load Streptavidin-HRP conjugate, item #HL-SZ-SA, that is especially designed for the cost-effective applications in High Sensitivity ELISA test kits made in pseudo-1-step format. Based on the advanced StrongZyme™ conjugation chemistry #HL-SZ-SA has available an increased number of the biotin-binding sites per mol of the bound HRP. Respectively, larger number of the biotin-binding sites creates an extra "buffering" capacity against irrelevant biotin present in the assay sample matrix making such conjugate less sensitive to the endogenous biotin burden in serum and plasma specimens. |