New methods for easy, rapid enzymatic assays in very small (sub-microliter) sample volumes will greatly benefit the prognosis, diagnosis, and detection of cancer, in that many cancer markers are enzymes. Currently, the blood sample must be transported to a clinical laboratory for assay, requiring enzyme storage stability, a problem for some enzymes including prostatic acid phosphatase (PAP). Although assay of prostatic specific antigen has largely replaced PAP for initial diagnosis, PAP is still used for staging, and can be used in the developing world for point-of-care diagnosis by unskilled personnel with the proposed technique. Phase I demonstrated the feasibility of adapting silicon microsampling and assay devices, originally developed for diabetic blood glucose monitoring, to enzyme activity measurement, using PAP as the example enzyme. This work is significant because the novel technique employed, diffusive enzyme activity measurement, is a general method adaptable to assaying a wide range of medically important enzymes. Phase II will develop a complete system for PAP assay and will perform simulations to assess its extension to other enzymes having different kinetic constants. The product emerging from this work will be a hand-held instrument capable of accepting single-use disposables to measure the enzymatic activity of PAP. The disposable has a silicon microneedle chip that draws the very small sample easily and reliably, and performs an on-chip assay without further liquid transfer. This system has no on-chip biologicals, and thus can be stored for long periods at ambient temperature.
