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Bactericidal filter papers offer the simplicity of gravity filtration to simultaneously eradicate microbial contaminants and particulates. We previously detailed the development of biocidal block copolymer micelles that could be immobilized on a filter paper to actively eradicate bacteria. Despite the many advantages offered by this system, its widespread use is hindered by its unknown mechanism of action which can result in non-reproducible outcomes. In this work, we sought to investigate the mechanism by which a certain percentage of Escherichia coli cells survived when passing through the bactericidal filter paper. Through the process of elimination, the possibility that the bacterial survival probability was controlled by the initial bacterial load or the existence of resistant sub-populations of E. coli was dismissed. It was observed that increasing the thickness or the number of layers of the filter significantly decreased bacterial survival probability for the biocidal filter paper but did not affect the efficiency of the blank filter paper (no biocide). The survival probability of bacteria passing through the antibacterial filter paper appeared to depend strongly on the number of collision between each bacterium and the biocide-loaded micelles. It was thus hypothesized that during each collision a certain number of biocide molecules were directly transferred from the hydrophobic core of the micelle to the bacterial lipid bilayer membrane. Therefore, each bacterium must encounter a certain number of collisions to take up enough biocide to kill the cell and cells that do not undergo the threshold number of collisions are expected to survive., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The surface-modification of paper substrates with functional layers is gaining increasing interest, both from academic and industrial research. In this case, the cellulosic paper (CP) surface was functionalized with zwitterionic poly-(3-dimethyl(methacryloyloxyethyl) ammoniumpropane sulfonate) (CP-g-P(DMAPS) via surface-initiated atom transfer radical polymerization (ATRP) technique for enhancing blood compatibility. An obvious increase in graft yield of the functional P(DMAPS) with polymerization time was observed. The new CP-g-P(DMAPS) produced was investigated for its hemocompatibility. The hemocompatibility studied including platelet and whole blood ceels adhesion tests, hemolysis assay, morphological changes of red blood cells (RBCs), coagulation time tests, and complement activation, platelet activation at the molecular level. Most assays had remarkable differences in the presence of the new zwitterionic CP, indicated the importance of the zwitterion for hemocompatibility of CP., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Paper-based biosensors represent a disruptive technology by providing instantaneous and low-cost diagnostics for health and environmental applications. The lack of sensitivity can be an obstacle for this technology to compete with traditional analytical instrumentations. Aiming to improve the sensitivity of a paper-based colorimetric biosensor, we have applied colloids engineering in combination with filtration to lower the paper substrate backgrounds and optimize the immobilization of bio-molecules on paper. A model system consisting of an enzyme, alkaline phosphatase (ALP), and an inorganic colloid, calcium carbonate (CC), flocculated by a cationic dimethylamino-ethyl-methacrylate polyacrylamide (CPAM), demonstrated that the optimized CC flocs are best for enhancing the detecting sensitivity of ALP. The CC floc structure on paper was optimized by modulating its structure in suspension. Subsequently, the filtration process and the wicking ability of paper enabled to freeze the deposited CC structure inherited from the suspension. The incorporation of biomolecules into the CC before immobilizing on paper through filtration provided not only a better microenvironment, but also a higher surface density of immobilized biomolecules. The ALP detection limit of 117 fmol per zone (5mm circle) in the current study was fifty times lower than that of the common soaking method for biomolecule immobilization. The minimum amount of biomolecules per unit substrate area required for detection was lowered by over an order of magnitude, compared with spotting methods (i.e. inkjet printing). The improvement was also demonstrated by the steepest slope of standard curve, the lowest background, and the highest activity of the bioactive paper probed with the diluted BCIP/NBT liquid substrates., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The effect of polymer on the retention and the thermal stability of bioactive enzymatic papers was measured using a colorimetric technique quantifying the intensity of the enzyme-substrate product complex. Alkaline phosphatase (ALP) was used as model enzyme. Three water soluble polymers: a cationic polyacrylamide (CPAM), an anionic polyacrylic acid (PAA) and a neutral polyethylene oxide (PEO) were selected as retention aids. The model polymers increased the enzyme adsorption on paper by around 50% and prevented enzyme desorption upon rewetting of the papers. The thermal deactivation of ALP retained on paper with polymers follows two sequential first order reactions. This was also observed for ALP simply physisorbed on paper. The retention aid polymers instigated a rapid initial deactivation which significantly decreased the longevity of the enzymatic papers. This suggests some enzyme-polymer interaction probably affecting the enzyme tertiary structure. A deactivation mathematical model predicting the enzymatic paper half-life was developed., (Crown Copyright 2010. Published by Elsevier B.V. All rights reserved.)

A novel method for the fabrication of paper-based microfluidic diagnostic devices is reported; it consists of selectively hydrophobizing paper using cellulose reactive hydrophobization agents. The hydrophilic-hydrophobic contrast of patterns so created has excellent ability to control capillary penetration of aqueous liquids in paper channels. Incorporating this idea with digital ink jet printing techniques, a new fabrication method of paper-based microfluidic devices is established. Ink jet printing can deliver biomolecules and indicator reagents with precision into the microfluidic patterns to form bio-chemical sensing zones within the device. This method thus allows the complete sensor, i.e. channel patterns and the detecting chemistries, to be fabricated only by two printing steps. This fabrication method can be scaled up and adapted to use high speed, high volume and low cost commercial printing technology. Sensors can be fabricated for specific tests, or they can be made as general devices to perform on-demand quantitative analytical tasks by incorporating the required detection chemistries for the required tasks., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

The thermal stability of two enzymes adsorbed on paper, alkaline phosphatase (ALP) and horseradish peroxidase (HRP), was measured using a colorimetric technique quantifying the intensity of the product complex. The enzymes adsorbed on paper retained their functionality and selectivity. Adsorption on paper increased the enzyme thermal stability by 2-3 orders of magnitude compared to the same enzyme in solution. ALP and HRP enzymatic papers had half-lives of 533 h and 239 h at 23 degrees C, respectively. The thermal degradation of adsorbed enzyme was found to follow two sequential first-order reactions, indication of a reaction system. A complex pattern of enzyme was printed on paper using a thermal inkjet printer. Paper and inkjet printing are ideal material and process to manufacture low-cost-high volume bioactive surfaces.