Strategy to enhance the wettability of bioacive paper-based sensors

This paper reports a potential method that can restore the wettability of bioactive paper-based sensors while maintaining their bioactivity. This study is driven by the need to increase the wettability of the antibody-loaded blood typing paper devices in order to increase the blood typing assaying speed using such paper devices. Plasma treatment is used to improve the wettability of bioactive paper; the protective effect of bovine serum albumin (BSA) to biomolecules against plasma deactivation is investigated. In the first stage, horseradish peroxidase (HRP) was used as a model biomolecule, because of the convenience of its quantifiable colorimetric reaction with a substrate. By using this protection approach, the inactivation of biomolecules on paper during the plasma treatment is significantly slowed down. This approach enables plasma treatment to be used for fabricating paper-based bioactive sensors to achieve strong wettability for rapid penetration of liquid samples or reagents. Finally, we demonstrate the use of plasma treatment to increase the wettability of antibody treated blood typing paper. After the treatment, the blood typing paper becomes highly wettable; it allows much faster penetration of blood samples into the plasma treated testing paper. Antibodies on the paper are still sufficiently active for blood typing and can report patients' blood type accurately.

Blood separation on microfluidic paper-based analytical devices

A microfluidic paper-based analytical device (μPAD) for the separation of blood plasma from whole blood is described. The device can separate plasma from whole blood and quantify plasma proteins in a single step. The μPAD was fabricated using the wax dipping method, and the final device was composed of a blood separation membrane combined with patterned Whatman No.1 paper. Blood separation membranes, LF1, MF1, VF1 and VF2 were tested for blood separation on the μPAD. The LF1 membrane was found to be the most suitable for blood separations when fabricating the μPAD by wax dipping. For blood separation, the blood cells (both red and white) were trapped on blood separation membrane allowing pure plasma to flow to the detection zone by capillary force. The LF1-μPAD was shown to be functional with human whole blood of 24-55% hematocrit without dilution, and effectively separated blood cells from plasma within 2 min when blood volumes of between 15-22 μL were added to the device. Microscopy was used to confirm that the device isolated plasma with high purity with no blood cells or cell hemolysis in the detection zone. The efficiency of blood separation on the μPAD was studied by plasma protein detection using the bromocresol green (BCG) colorimetric assay. The results revealed that protein detection on the μPAD was not significantly different from the conventional method (p > 0.05, pair t-test). The colorimetric measurement reproducibility on the μPAD was 2.62% (n = 10) and 5.84% (n = 30) for within-day and between day precision, respectively. Our proposed blood separation on μPAD has the potential for reducing turnaround time, sample volume, sample preparation and detection processes for clinical diagnosis and point-of care testing.