Paper-based microfluidic devices provide interesting applications including clinical "point-of-care" diagnostic, food quality control, biochemical analysis and environmental monitoring. Paper as a matrix for microfluidic devices offers many advantages compared to other materials. Particularly, its capability to transport liquid by capillary forces without external pumps is an important feature for the development of low-instrumented "lab-on-paper" devices.<br/>One issue in the successful development of "lab-on paper" devices is the limitation of sensitivity and specificity for analyte detection. To overcome these limitations, at first a detailed understanding of analyte-cellulose surface interactions is required to efficiently design an analytic devices. Thus, we investigated the influence of fluid (concentration, pH and conductivity) and substrate (grammage and pulp type) characteristics on analyte retention on cellulose fibers. Secondly, we introduced a novel lithographic process for site-specific modification of cellulose fibers in paper-sheets using photo-reactive, functional polymers. Lab-made, chemically microstructured paper-sheets were prepared by covalent attachment of photo-reactive, hydrophobic polymers, defining hydrophilic channels in between hydrophobic coats. In a second step copolymers based on arbitrary bulk polymers and 4-methacryloyloxybenzophenone (MABP) can be localized, and bound at specific regions (patches) within the channel. Depending on the bulk polymer characteristics these patches may serve as filtration, reaction, dwell time control or detection sites. In one example, positive polyelectrolyte patches were site-specifically, covalently fixed in channels and their capacity to retain oppositely-charged molecules from solution is studied. These devices realize an increasing detection limit for enhanced sensitivity, as well as specific filtration to improve specificity.

Understanding and designing the retention of model compounds in microfluidic paper devices

251st National Meeting (2016)

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