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Cytochrome P450 (CYP) is a superfamily of enzymes in charge of elimination of the majority of clinically used drugs and other xenobiotics.This study focuses on the development of a rapid microfluidic lateral flow assay to study human phase I metabolism reactions mediated by CYP2A6 isoenzyme, the major detoxification route for many known carcinogens and drugs, with coumarin 7-hydroxylation, as the prototype model reaction. Assay fabrication utilizes custom-designed porous functionalized calcium carbonate (FCC) coatings and inkjet-printed fluid barriers. All materials used are novel and carefully chosen to preserve biocompatibility. The design comprises separate zones for reaction, separation and detection, and an absorbent pad to keep the assay wet for extended periods (up to 10 min) even when heated to physiological temperature. The concept enables CYP assays to be made at lower cost than conventional well-plate assays, while providing increased selectivity at equally high speed, owing to the possibility for simultaneous chromatographic separation of the reaction products from the reactants on the FCC coating. The developed concept provides a viable rapid prediction of the interaction risks related to metabolic clearance of drugs and other xenobiotics, and exemplifies a novel coating technology illustrating the opportunity to broaden application functionality.

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Devising controlled microfluidic liquid transfer in porous diagnostic devices presents challenges in respect to differentiation between surface/film flow and wicking within the bulk of the substrate. Rapid liquid translation is predominantly driven by film flow mechanisms in such devices. However, the more complex needs of in-pore reactivity between test fluids and reactive agents, followed typically by the need to perform chromatographic separation of eluents, demands the often contradictory facility of rapid spatial transport whilst allowing exposure to high internal surface area, i.e. by the mechanism of internal bulk wicking. The key parameters are permeability to saturated flow relatively far behind the wetting front, limiting the delivery rate of liquid to the wetting front, and capillarity within an ideally parallel high surface area pore network. We demonstrate a way to balance these properties using a coating with a discretely bimodal pore structure, whereby bulk flow is controlled by interparticle connectivity and interpore throat size, and capillarity and surface reactivity by ultrafine intraparticle pores. The distance travelled at time t by the wetting front is expressed as a power law function, tp . Evaluating p  provides a measure as to the closeness of dependence on viscous-controlled bulk flow permeability as p  tends to 0.5, i.e.  √t. Deviation from bulk flow dependence indicates the presence of pore wall film flow or inertial plug flow, possibly combined with evaporation and/or material sorption onto the pore wall surface or into the binder matrix. In this context, a variety of coating formulations are evaluated, and wicking rate is shown to vary strongly as a function of the binder impact on interparticle pore connectivity and on the absorption behaviour of the binder itself. Microfibrillated cellulose is shown to be a highly suitable binder for microfluidic diagnostic coatings. Reactivity within the coating is illustrated using charge-driven chromatographic colorant separation.

Printed, self-contained sensor designs based on capillary transport and microfluidic principles form a major part of current research in printed functionality. Previous work into such designs has mainly focused on cellulosic papers as base substrates. In this study, novel findings are presented employing alternative customdesigned functional pigment coated substrates, locally functionalised by inkjet printed polyelectrolytes, to separate or transport anionic or cationic molecules by surface chemistry tailoring. Both anionised and cationised coatings are tested and found to transport similarly charged model colorants successfully, while separating those of opposite charge, with the extent of separation depending on colorant concentration. Furthermore, surface chemistry reversal by cationic (polyethyleneimine, polyDADMAC) and anionic (carboxymethyl cellulose) polyelectrolyte inks is demonstrated as a complementary method for analyte separation or concentration. However, the deposition of the polyelectrolyte ink itself was found to affect the cationised coating by solubilising and re-depositing coating components, while the printed polyethyleneimine was found to be partially dissolved and transported by water elution, suggesting limited adsorption under tested conditions.