HST’s latest products are C•spec® particles encapsulating Tetramethylrhodamine (TRITC) dye with different sizes conjugated to streptavidin (SA).

C•spec® streptavidin conjugates consist of streptavidin covalently bonded to C•spec® particles. Dye-labeled conjugates of SA are used with a conjugate of biotin (vitamin B7) to achieve highly specific detection of a variety of biomolecules.

Biotinylated primary antibodies or peptides bound to a protein target can be detected with fluorescently labeled streptavidin. Biotin is often chemically linked to biomolecules because its small size (molecular weight 244) reduces the likelihood that their biological activity is affected.

The binding of biotin to streptavidin is one of the strongest non-covalent interactions known in nature. Streptavidin's high affinity for biotin has made it a widely used labeling tool.

When the target analytes are abundant (e.g., human chorionic gonadotropin (hCG), which pregnancy tests detect in urine), a dye-labeled antibody is adequate for detection. However, many researchers are seeking to identify or quantify biomolecules whose concentrations may be orders of magnitude lower.

For rare analytes the use of enhanced fluorescent labels has emerged as a strategy to achieve the sensitivity needed. Quantum dots represent one class of such labels. Unlike quantum dots, C•spec® particles have an emission that depends on the characteristics of the encapsulated fluorescent dye molecules, not the size of the nanoparticle.

C•spec® particles are nearly as bright as quantum dots on an equal size basis, and can be made even brighter by incorporating more fluorescent dyes in a larger nanoparticle. At larger sizes, however, steric hindrance may become a factor, so there is likely an optimum size C•spec® particle for a given application/assay. 

To help researchers evaluate the impact of fluorophore size for a particular assay, HST provides a sampler kit with three differently sized C•spec® particles. Each of the three conjugates in the C•spec® Streptavidin Sampler Kit is supplied in lyophilized form.