Heterogeneous Immunoassay Using Channels and Droplets in a Digital Microfluidic Platform

Abstract

This work presents a heterogeneous immunoassay using the integrated functionalities of a channel and droplets in a digital microfluidic (DMF) platform. Droplet functionality in DMF allows for the programmable manipulation of discrete sample and reagent droplets in the range of nanoliters. Pressure-driven channels become advantageous over droplets when sample must be washed, as the supernatant can be thoroughly removed in a convenient and rapid manner while the sample is immobilized. Herein, we demonstrate a magnetic bead-based, enzyme-linked immunosorbent assay (ELISA) using ~60 nL of human interleukin-6 (IL-6) sample. The wash buffer was introduced in the form of a wall-less virtual electrowetting channel by a syringe pump at the flow rate of 10 μL/min with ~100% bead retention rate. Critical parameters such as sample wash flow rate and bead retention rate were optimized for reliable assay results. A colorimetric readout was analyzed in the International Commission on Illumination (CIE) color space without the need for costly equipment. The concepts presented in this work are potentially applicable in rapid neonatal disease screening using a finger prick blood sample in a DMF platform.

Magnetic nanoparticles in microfluidic and sensing: From transport to detection

“…A digital microfluidic (DMF) platform based on the manipulation of magnetic beads was used to perform heterogeneous sandwich immunoassays [163]. Individual drops of samples and reagents using electrowetting were free to move without channels and did not get clogged.…”

Role of Digital Microfluidics in Enabling Access to Laboratory Automation and Making Biology Programmable

“…An additional commonly cited benefit of using DMF is the absence of blockages, a consistent challenge found in flow-based microfluidics devices. 20,21 In addition to this, integration with different detector modules, 22,23 and support for purification, 24 DMF can allow a convergence of all steps in an experimental workflow on a single device. Workflows like running heterogeneous immunoassays (enzyme-linked immunosorbent assay [ELISA]) 24,25 and enzymatic assays 26 for diagnostics, sample preparation for proteomics, 27 gene editing, 28 and drug screening via MS 29 all give an indication of the breadth of workflows that can be automated using DMF.…”

A fucosyltransferase inhibition assay using image-analysis and digital microfluidics

“…For example, DMF is already successful as a miniature and cost-effective platform for enzymatic assays. 11,16 Generally, this application involves dispensing droplets from reservoirs primed with the different assay solutions and then follows with merging and mixing operations such that each droplet is a single bioreactor. Their low volume improves their mass and heat transfer rates, which increases the speed of temperature-variable assays and enzymatic reactions.…”