Why has no one tried this before now?
Actually, this testing technique has been tried for heroin and morphine prior to now, but the exact chemistry was not optimized, and could not compete with other assays. In fact, the concentrations of the reagents proved critical to the overall performance of the assay. It was found that both heroin esterase and morphine dehydrogenase exhibit poor thermal stability at temperatures above 30oC, and impaired activity at temperatures below 25oC. Therefore, all luminescence assays were conducted at 30oC. Each component in the assay was varied in turn, and the response of each measured, so the optimum concentrations could be determined.
Click here to see these optimum concentrations
It was determined that the heroin esterase step was rate-limiting in that assay, so excess esterase was required. For the assay with 0.5 unit of morphine dehydrogenase, the minimum amount of heroin esterase required to give a fast response to 0.1mM heroin was 2.0 units of the enzyme (7.8 units/mg).