SURFACE MIP OF BIOSPECIES: POSSIBLE ASSAY FORMATS IN HEALTCARE

Surface molecular imprinting has developed to a very attractive technique for sensing biological species, including several proteins, bacteria, viruses and cell species. Those MIP-based sensors have in common that they detect the respective target species directly and hence represent a somewhat straightforward – yet important and successful – analytical approach. The possibilities in applying surface MIP, however, go beyond that: their binding sites are not restricted to a specific epitope on the target analyte, but usually interact with a larger part of the surface. This allows for not only deriving quantitative data from the respective sensors, but also for assessing functionality of the respective species including their behavior in binding assays.

Surface MIP of the dopaminergic receptor D1R are an example for the latter approach: D1R surface MIP indeed lead to concentration-dependent sensor responses on a quartz crystal microbalance (QCM). More interestingly, it is known that D1R binds dopamine – its target – in a binding pocket within the molecule, whereas several antagonists, for instance haloperidol – bind on the outer surface and thus change its morphology. This should lead to different sensor signals on the MIP. Indeed, both desorption and inhibition studies revealed such behavior: incubating D1R with haloperidol (binding to 10% of the D1R molecules) for instance reduces the sensor responses by almost 30%. This makes it possible to calculate binding constants and thus use the material for receptor-ligand binding assays.

Thrombocyte detection is a similar, yet different approach: first of all, the stamping procedures need to be thoroughly optimized to achieve imprinting of non-activated thrombocytes. That procedure indeed leads to MIPs that are useful for quantifying platelets in both serum samples and buffered solutions. More interestingly, MIP QCM sensor responses are reduced when exposing them to platelets incubated with acetyl salicylic acid and ibuprofen, respectively. Though the exact molecular mechanism is unclear, it is known that both drugs change surface morphology/chemistry of thrombocytes. This phenomenon again is accessible to the MIP and therefore allows for platelet functionality assay within 5-10 minutes. This is of interest both scientifically and clinically: scientifically, because thrombocyte sensor responses depend on antagonist concentration; clinically, because such sensors need not wait until aggregation and thus yield rapid responses.