Multiplexed, waveguide approach to magnetically assisted transport evanescent field fluoroassays

This paper, expanding upon the recently developed magnetically assisted transport evanescent field fluoroassays (MATEFFs), takes advantage of several innovations in order to successfully integrate a microfluidic platform and planar waveguide technology for exploitation of multiplexing advantages. In the current adaptation of MATEFFs, a multiple internal reflection element (waveguide) is created using a simple microscope slide and PDMS microfluidic architecture, allowing simultaneous detection of multiple samples. Furthermore, the magnetic beads are manipulated using a passive pumping technique and a simple external permanent magnet, thereby circumventing the need for electromagnetic fabrication or complicated architectures and equipment. Initial testing, optimization, and calibration were performed using a model sandwich immunoassay system for the detection of rabbit IgG, with which we demonstrate a linear dynamic range of 3 orders of magnitude and physiologically relevant detection limits of nanograms per milliliter. Further work employed a sandwich immunoassay for the detection of interleukin-4, a cytokine that promotes proliferation and differentiation of B cells, to demonstrate technique reproducibility with RSD values of 5% and reported LOD of 10 ng/mL. The use of harvesting magnetic beads resulted in assays with mass-sensing behavior. Using IgG as a model cross-reactant with the interleukin-4 system, we additionally illustrate technique selectivity and multiplexing capability. A DNA hybridization assay is carried out using magnetic bead-immobilized single-stranded DNA with hybridization detected via ethidium bromide intercalation, further establishing technique versatility.