EIA Kits

Quantitative, Competitive ELISA for Detection of Soluble Factors in a Variety of Species


RayBio® kits utilize the principle of Competitive Enzyme Immunoassay (EIA), in which the target protein and a biotin-conjugated peptide bind competitively to a capture antibody. This assay requires only a single antibody, generating signal output by interaction of the biotinylated competitor with streptavidin-HRP. Thus, the EIA kits are particularly useful for detecting peptide hormones and other molecules for which no antibody pair exists, or for which antibody pairs cannot be developed.

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Blue Ribbon Seal ELISA

Another important advantage of the EIA format is broad-species reactivity. For each kit, a peptide derived from a high-homology region of the target protein sequence serves as both the standard and the biotin-labeled competitor. RayBio® EIA kits are validated for rat, mouse, and human samples and have expected reactivity with many other species.


  • Excellent for follow up/confirmation of E-Series Array data
  • Broad species reactivity
  • Strip plate format minimizes waste
  • Complete kit includes all necessary reagents
  • Highly sensitive and specific
  • Reproducible and reliable
  • Optimized for serum, plasma, and cell culture medium

Contents of Kit

  • 96-well strip plate (12x8)
  • Wash Buffer Concentrate (20x)
  • Standard Peptide 
  • Capture antibody
  • Positive control
  • Diluent Buffers
  • Biotin-labeled peptide
  • HRP-Streptavidin concentrate
  • TMB One-Step Substrate Reagent
  • Stop Solution

How It Works

Competition-based ELISA: How It Works

The samples and standards, which are spiked with biotinylated peptide, are pipetted into the assay plate; the target protein and the labeled peptide interact competitively with the capture antibody.  After washing, the bound biotin-peptide then interacts with streptavidin-HRP, producing a color development reaction. The intensity of colorimetric signal is directly proportional to the amount of biotin-peptide and inversely proportional to the amount of target protein in the samples.

Research Applications

  • Detection of quantitative protein levels in biological fluids
  • Validation of array results
  • Validation of biomarker discovery studies

Representative Data

Competition-based ELISA (EIA) Standard Curves

Reference List

  1. Plum L, Lin HV, Dutia R, Tanaka J, Aizawa KS, et al. The Obesity Susceptibility Gene Carboxypeptidase E Links FoxO1 Signaling in Hypothalamic Pro–opiomelanocortin Neurons with Regulation of Food Intake. Nature Med. 2009;15(10):1195-1201. (Ghrelin EIA, EIA-GHR-1) | Full Text

  2. Hug C, Lodish HF. Visfatin: a new adipokine. Science. 2005; 307(5708):366-7.

  3. Kim MK. Crystal structure of visfatin/pre-B cell colony-enhancing factor 1/nicotinamide phosphoribosyltransferase, free and in complex with the anti-cancer agent FK-866. J Mol Biol. 2006; 362(1):66-77.

  4. Revollo, J.R., et al. The NAD biosynthesis pathway mediated by nicotinamide phosphoribosyltransferase regulates Sir2 activity in mammalian cells. J. Biol. Chem. 2004; 279: 50754-50763.

  5. Oh-I S, Shimizu H, Satoh T, et al. Identification of nesfatin-1 as a satiety molecule in the hypothalamus". Nature 2006; 443 (7112): 709-12.

  6. Zhang J, Ren P, Avsian-Kretchmer O, Luo C, Rauch R, Klein C, Hsueh A. Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake. Science 2005; 310 (5750): 996-9.

  7. Cummings D, Weigle D, Frayo R, Breen P, Ma M, Dellinger E, Purnell J. Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery. N Engl J Med 2002; 346 (21): 1623-30.

  8. Tschöp M, Smiley DL, Heiman ML. Ghrelin induces adiposity in rodents. Nature 2002; 407 (6806): 908-913.9. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature 1999; 402 (6762): 656-60.