Abstract
This paper describes the development and application of microfluidic cord-based analytical devices (µCADs) in two enzyme-linked immunosorbent assays (ELISAs) and glucose assay. In this study, biotinylated goat anti-mouse immunoglobulin (IgG) antibody, rabbit IgG antibody, and glucose are quantitatively detected. In the ELISA systems, the antibody is spotted on the cord at the detection site and a series of washes, followed by streptavidin-alkaline phosphatase (Strep-ALP) or alkaline phosphatase (ALP)-conjugated secondary antibody and colorimetric substrate, completing the experiment. The devices are subsequently scanned and analyzed yielding a correlation between inverse yellow or inverse blue intensity and antibody concentration. For the first ELISA, a linear range of detection was observed at lower concentrations (2.50 × 10−4–1.75 × 10−3 mg/mL) of Strep-ALP with saturation of the enzyme achieved at higher concentrations (>2.50 × 10−4). For the second ELISA, the L50 was demonstrated to be 167.6 fmol/zone. The glucose assay consisted of spotting increasing concentrations of glucose on the analysis sites and transporting, via capillary action, a solution containing glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) to the detection sites realizing a yellow-brown color indicating oxidation of iodide to iodine. The device was then dried, scanned, and analyzed to show the correlation between yellow inverse intensity and glucose. Glucose in artificial urine showed good correlation using the devices.
Highlights
Since the development of the first microfluidic devices (MDs) in the early 1990s, microfluidic technologies have evolved to incorporate a wide range of applications including biomedical analysis, environmental, and agricultural testing, food safety control, medical diagnosis, and drug testing [1]
Tween-20 viscous liquid, alkaline phosphatase yellow (p-NPP) Liquid Substrate System for enzyme-linked immunosorbent assays (ELISAs), albumin from bovine serum (BSA), a mix-n-stain biotin antibody labeling kit, immunoglobulin G (IgG) from rabbit serum, 5-bromo-4-chloro-3-indolyl phosphate disodium (BCIP), nitrotetrazolium blue chloride (NBT), magnesium chloride, sodium chloride, potassium chloride, sodium dihydrogen phosphate, and disodium phosphate were all purchased from Sigma-Aldrich
The colorimetric solution for alkaline phosphatase (ALP) was prepared by preparing a substrate buffer (5 mM MgCl2, 100 mM NaCl, 0.05% (v/v) Tween-20 in 100 mM Tris), the substrate buffer was used as the dilution buffer when preparing 5.36 mM BCIP and 3.6 mM of NBT Prior to spotting on the detection site, equal volumes of BCIP and NBT were mixed to create a final concentration of 2.7 mM BCIP and 1.8 mM NBT
Summary
Since the development of the first microfluidic devices (MDs) in the early 1990s, microfluidic technologies have evolved to incorporate a wide range of applications including biomedical analysis, environmental, and agricultural testing, food safety control, medical diagnosis, and drug testing [1]. The resultant microfluidic paper-based analytical devices (μPADs) are well documented as platforms for point-of-care (POC) applications and especially in resource-limited settings [19,20,21,22,23,24,25,26,27]. Thread is a useful material to fabricate POC diagnostic devices. Typical cord fabrics exist as twisted or rotated yarn woven and fitted with either one or several layers of substrate thereby creating adhesion to rubber mixtures. It can be fabricated from nylon, cotton, polyester, and other materials. It was found that glucose in artificial urine was correlated to the μCAD
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