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Issue 4, 2015
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Metal-Amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA)

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Abstract

This paper reports the development of Metal-amplified Density Assays, or MADAs – a method of conducting quantitative or multiplexed assays, including immunoassays, by using Magnetic Levitation (MagLev) to measure metal-amplified changes in the density of beads labeled with biomolecules. The binding of target analytes (i.e. proteins, antibodies, antigens) to complementary ligands immobilized on the surface of the beads, followed by a chemical amplification of the binding in a form that results in a change in the density of the beads (achieved by using gold nanoparticle-labeled biomolecules, and electroless deposition of gold or silver), translates analyte binding events into changes in density measureable using MagLev. A minimal model based on diffusion-limited growth of hemispherical nuclei on a surface reproduces the dynamics of the assay. A MADA – when performed with antigens and antibodies – is called a Density-Linked Immunosorbent Assay, or DeLISA. Two immunoassays provided a proof of principle: a competitive quantification of the concentration of neomycin in whole milk, and a multiplexed detection of antibodies against Hepatitis C virus NS3 protein and syphilis T. pallidum p47 protein in serum. MADAs, including DeLISAs, require, besides the requisite biomolecules and amplification reagents, minimal specialized equipment (two permanent magnets, a ruler or a capillary with calibrated length markings) and no electrical power to obtain a quantitative readout of analyte concentration. With further development, the method may be useful in resource-limited or point-of-care settings.

Graphical abstract: Metal-Amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA)

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Publication details

The article was received on 02 Oct 2014, accepted on 27 Nov 2014 and first published on 04 Dec 2014


Article type: Paper
DOI: 10.1039/C4LC01161A
Citation: Lab Chip, 2015,15, 1009-1022
  • Open access: Creative Commons BY license
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    Metal-Amplified Density Assays, (MADAs), including a Density-Linked Immunosorbent Assay (DeLISA)

    A. B. Subramaniam, M. Gonidec, N. D. Shapiro, K. M. Kresse and G. M. Whitesides, Lab Chip, 2015, 15, 1009
    DOI: 10.1039/C4LC01161A

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