A study of the transport and immobilisation mechanisms of human red blood cells in a paper-based blood typing device using confocal microscopy.

Recent research on the use of bioactive paper for human blood typing has led to the discovery of a new method for identifying the haemagglutination of red blood cells (RBCs). When a blood sample is introduced onto paper treated with the grouping antibodies, RBCs undergo haemagglutination with the corresponding grouping antibodies, forming agglutinated cell aggregates in the paper. A subsequent washing of the paper with saline buffer could not remove these aggregates from the paper; this phenomenon provides a new method for rapid, visual identification of the antibody-specific haemagglutination reactions and thus the determination of the blood type. This study aims to understand the mechanism of RBC immobilization inside the paper which follows haemagglutination reactions. Confocal microscopy is used to observe the morphology of the free and agglutinated RBCs that are labelled with FITC. Chromatographic elution patterns of both agglutinated and non-agglutinated RBCs are studied to gain insight into the transport behaviour of free RBCs and agglutinated aggregates. This work provides new information about RBC haemagglutination inside the fibre network of paper on a microscopic level, which is important for the future design of paper-based blood typing devices with high sensitivity and assaying speed.

Electrogenerated chemiluminescence detection in paper-based microfluidic sensors.

This paper describes the first approach at combining paper microfluidics with electrochemiluminescent (ECL) detection. Inkjet printing is used to produce paper microfluidic substrates which are combined with screen-printed electrodes (SPEs) to create simple, cheap, disposable sensors which can be read without a traditional photodetector. The sensing mechanism is based on the orange luminescence due to the ECL reaction of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) with certain analytes. Using a conventional photodetector, 2-(dibutylamino)ethanol (DBAE) and nicotinamide adenine dinucleotide (NADH) could be detected to levels of 0.9 µM and 72 µM, respectively. Significantly, a mobile camera phone can also be used to detect the luminescence from the sensors. By analyzing the red pixel intensity in digital images of the ECL emission, a calibration curve was constructed demonstrating that DBAE could be detected to levels of 250 µM using the phone.

Capillary driven low-cost V-groove microfluidic device with high sample transport efficiency.

In this study we investigate the liquid sample delivery speed and the efficiency of microfluidic channels for low-cost and low-volume diagnostic devices driven only by capillary forces. We select open, non-porous surface grooves with a V-shaped cross section for modeling study and for sensor design. Our experimental data of liquid wicking in V-grooves show an excellent agreement with the theoretical data from the V-groove model of Rye et al. This agreement allows us to quantitatively analyze the liquid wicking speed in V-grooves. This analysis is used to generate data for the design of sensors. By combining V-groove channels and printable paper-like porous detection zones, microfluidic diagnostic sensors can be formed. Non-porous V-grooves can be fabricated easily on polymer film. Suitably long surface V-grooves allow short liquid transport time (<500 ms), thus reducing the evaporation loss of the sample during transport. Non-porous V-grooves also significantly reduce chromatographic loss of the sample during transport, therefore increasing the sample delivering efficiency. Sensors of such design are capable of conducting semi-quantitative chemical and biochemical analysis (i.e. with a calibration curve) with less than 1000 nL of sample and indicator solution in total.

Thread as a versatile material for low-cost microfluidic diagnostics.

This paper describes a new and simple concept for fabricating low-cost, low-volume, easy-to-use microfluidic devices using threads. A thread can transport liquid via capillary wicking without the need of a barrier; as it is stainable, it is also a desirable material for displaying colorimetric results. When used in sewing, threads have 3D passageways in sewed materials. The wicking property and flexibility of thread make it particularly suitable to fabricate 3D microfluidic devices. Threads can also be used with other materials (e.g., paper) to make microfluidic devices for rapid qualitative or semiquantitative analysis. These thread-based and thread-paper-based devices have potential applications in human health diagnostics, environmental monitoring, and food safety analysis, and are particularly appropriate for the developing world or remote areas, because of their relatively low fabrication costs.

Quantitative biomarker assay with microfluidic paper-based analytical devices.

This article describes the use of microfluidic paper-based analytical devices (muPADs) to perform quantitative chemical assays with internal standards. MicroPADs are well-suited for colorimetric biochemical assays; however, errors can be introduced from the background color of the paper due to batch difference and age, and from color measurement devices. To reduce errors from these sources, a series of standard analyte solutions and the sample solution are assayed on a single device with multiple detection zones simultaneously; an analyte concentration calibration curve can thus be established from the standards. Since the muPAD design allows the colorimetric measurements of the standards and the sample to be conducted simultaneously and under the same condition, errors from the above sources can be minimized. The analytical approach reported in this work shows that muPADs can perform quantitative chemical analysis at very low cost.