PRINTING AND CHARACTERIZATION OF INKS FOR PAPER-BASED BIOSENSORS

Abstract

<p>This thesis describes solutions to many of the challenges in the development of paper-based biosensors. Coupling techniques in analytical biochemistry with knowledge of paper science and technology, advances are described in the areas of: the influence of paper surface chemistry on bioactivity; optimizing bioactive ink formulation; the printing of paper supported microfluidic channels; and, the characterization of complex sensors based on printed sol-gel material layers.</p> <p>The stability of paper-immobilized antibodies under various conditions was first studied using both untreated filter paper and PAE-treated paper. Antibody stability decreased with increasing temperature and relative humidity. Paper treated with PAE had no significant influence on antibody stability under the experimental conditions. The experimental result was also encapsulated in an empirical equation to predict the impact of printing and coating operations on antibody activity.</p> <p>The influence of paper sizing agent (AKD) on the adsorption and inactivation of antibody was also investigated. The preliminary study showed that the small amount of AKD improved the antibody adsorption on paper and also did not interfere antibody activity. Therefore, packaging papers containing sizing agents can be used as a substrate for antibody immobilization.</p> <p>Two strategies to fabricate hydrophobic barriers were developed, based on sol-gel derived MSQ material. The first method is based on ink-jet printing a highly basic solution onto MSQ-impregnated filter paper to re-exposing the cellulose and producing a hydrophilic patterned region. The second method is direct ink-jet printing of MSQ onto paper to outline the hydrophobic walls bordering the hydrophilic channels. The resistance of the barriers to surfactants and organic solvents was tested. The functionality of MSQ-based devices was further demonstrated by using a colorimetric assay for <em>E. coli </em>detection.</p> <p>Multiple-stage inkjet printing of sol-gel based bioink onto porous filter paper for enzyme immobilization was characterized by various methods. Confocal microscope and SEM/TEM images confirmed the formation of sol-gel and enzyme composite material on the paper fibers without cracking. The protease assay proved that the entrapment of enzyme molecules improved with the increasing amount of the sol-gel derived material printed on paper. The top layer of sol-gel ink was found to play a major role in protection against enzyme proteolysis, while the bottom layer of sol-gel ink was found to be necessary to prevent the potential inhibition of enzyme by the cationic polymer.</p>