Protocol abstract

Nature Protocols 2, 1438 - 1444 (2007)
Published online: 31 May 2007 | doi:10.1038/nprot.2007.201

Subject Categories: Nanotechnology | Chemical modification | Biochemistry and protein analysis

Detection of proteins using a colorimetric bio-barcode assay

Jwa-Min Nam1,2, Kyung-Jin Jang2 & Jay T Groves3

The colorimetric bio-barcode assay is a red-to-blue color change-based protein detection method with ultrahigh sensitivity. This assay is based on both the bio-barcode amplification method that allows for detecting miniscule amount of targets with attomolar sensitivity and gold nanoparticle-based colorimetric DNA detection method that allows for a simple and straightforward detection of biomolecules of interest (here we detect interleukin-2, an important biomarker (cytokine) for many immunodeficiency-related diseases and cancers). The protocol is composed of the following steps: (i) conjugation of target capture molecules and barcode DNA strands onto silica microparticles, (ii) target capture with probes, (iii) separation and release of barcode DNA strands from the separated probes, (iv) detection of released barcode DNA using DNA-modified gold nanoparticle probes and (v) red-to-blue color change analysis with a graphic software. Actual target detection and quantification steps with premade probes take approx3 h (whole protocol including probe preparations takes approx3 days).

  1. Department of Chemistry, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-747, South Korea.
  2. Interdisciplinary Program in Nano-Science and Technology, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-747, South Korea.
  3. Department of Chemistry, University of California, Berkeley and Physical Biosciences Division, Lawrence Berkeley National Laboratory, California 94720, USA.

Correspondence to: Jwa-Min Nam1,2 e-mail:

Correspondence to: Jay T Groves3 e-mail:


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