The present invention relates to molecular constructs and methods of their use in detecting biochemical reactions. In particular, the invention relates to a molecular construct having a capture portion and a substrate portion, where the capture portion isolates the construct from a sample medium, and the substrate portion enables the construct to be acted upon and undergo a physical change which can be detected and measured. These molecular constructs may be used in diagnostic assays, genetic screening for potential risks of certain diseases in individuals, and drug discovery and toxicogenomics, using high throughput screening of compounds.