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Lateral Flow Immunoassay

Lateral flow immunoassays, also known as immunochromatographic assays or strip tests, are unidirectional assays which are used to quickly and easily establish whether a target analyte is present in a test sample. The advantages of the lateral flow immunoassay system are well-known:

  • High sensitivity and specificity
  • Requires only a low sample volume
  • Applicable to a wide range of settings
  • One-step assay, no wash steps, short time to result
  • Possibility of multiplexing
  • Low cost
  • Simple, user-friendly operation
  • High potential for commercialization

A typical lateral flow immunoassay consists of four key components: a sample application pad, a conjugate release pad, a nitrocellulose membrane, and a wicking pad.

Schematic representation of a typical lateral flow immunoassay

The sample is added to the sample application pad. From here it flows to the conjugate release pad, into which the detection reagent has been dried. The sample then migrates along the nitrocellulose membrane, upon which antibodies have been immobilized as a test line and a control line; a signal at the test line is indicative of a positive result, while a signal at the control line demonstrates the lateral flow immunoassay to be performing correctly. The role of the wicking pad is to increase the volume of sample which enters the test strip and to prevent backflow.

For a more detailed overview of lateral flow assays, why not download our free Guide?

Alternatively, take a look at our webinar: “A Guide to Lateral Flow Immunoassay Development”

Lateral flow immunoassays rely on the use of antibodies which have been conjugated to colored detection moieties such as gold nanoparticles or latex beads, or to fluorescent labels such as fluorescent dyes, fluorescent proteins or Europium particles. Expedeon offers a wide range of products to help you simplify the development of your own lateral flow immunoassay.

Particles for lateral flow immunoassays

Colloidal gold

Gold nanoparticles are ideally suited to lateral flow immunoassays due to their intense ruby red color, which makes them easy to visualize on the test strip. Expedeon’ colloidal gold has been developed using specialized techniques which enable the production of extremely uniform nanoparticles with a narrow size distribution, thereby minimizing assay variability.

  • Uniform spherical shape and narrow size distribution
  • Different nanoparticle sizes and concentrations available
  • Stringently QC tested

Our colloidal gold can be produced at high concentrations (>20OD) and large volumes (liters) without compromising on quality. Why not get in touch for more information on bulk ordering?

InnovaCoat® GOLD Conjugation Kits

The use of colloidal gold for lateral flow immunoassays requires passive adsorption of the antibody to the surface of the nanoparticle, a process which can be challenging and which necessitates specialist knowledge. To overcome this, we have developed InnovaCoat® GOLD conjugation kits.

Lateral Flow Assay process using 40nm InnovaCoat GOLD

Figure 3. Lateral flow assay using our 40nm InnovaCoat® GOLD. The nanoparticles were conjugated to a goat anti-rabbit antibody and used to quantify a titration of rabbit IgG. The signal intensity of the test line clearly changes in proportion to the antigen concentration and can be quantified using a lateral flow strip reader.

  • Quick and easy to use – the conjugate is ready to use in just 20 minutes
  • Covalent conjugation –highly stable conjugates formed
  • Proprietary surface coating prevents metal-protein interactions

Conjugation to InnovaCoat® GOLD nanoparticles uses significantly less antibody when compared to traditional passive conjugation methods. And with different nanoparticle sizes, concentrations and chemistries available, our InnovaCoat® GOLD product range provides excellent levels of flexibility in your lateral flow immunoassay.

Lateral Flow Strip Reader showing different readings at various antigen concentrationsResults of a lateral flow strip reader quantified to show signal intensity changes in proportion to the antigen concentration

 

Lateral flow assay using our 40nm InnovaCoat® GOLD. The nanoparticles were conjugated to a goat anti-rabbit antibody and used to quantify a titration of rabbit IgG. The signal intensity of the test line clearly changes in proportion to the antigen concentration and can be quantified using a lateral flow strip reader.

Gold nanoparticle conjugates

On some occasions, it may be preferable to use pre-conjugated gold nanoparticles in a lateral flow immunoassay. We offer a range of suitable products which have been manufactured using our InnovaCoat® GOLD technology. Like all our products, these highly stable conjugates have been stringently QC tested, minimizing assay variability and making them ideal for lateral flow.

For advice on working with our pre-conjugated gold nanoparticles please don’t hesitate to contact us.

Target Group by Nanoparticle Size

Latex Conjugation Kits

Latex beads are another hugely popular choice as the detection moiety for lateral flow immunoassays since they are available in a range of vibrant colors, making them easily visible and providing the opportunity for multiplexing. Traditional methods of conjugating antibodies to latex beads are technically complex and can waste a lot of precious material. Latex conjugation kits from Expedeon have been designed to greatly simplify the process.

  • Quick and easy to use – the conjugate is ready to use in just 35 minutes
  • Specially treated particles are resistant to aggregation and require no extensive pH optimization
  • Different colors available – ideal for multiplexing

Multiplexed lateral flow assay using latex beads from Expedeon

Our latex conjugation kits are fully scalable, providing easy transfer from R&D to manufacturing.

Contact us to discuss bulk purchasing, or for technical support with your lateral flow immunoassay.

Europium Conjugation Kits

For lateral flow immunoassays that require higher levels of sensitivity, we offer our europium conjugation kits. Our specially-treated 200nm europium beads, a unique product to Expedeon, become covalently bound to the antibody or protein to form highly stable conjugates. Accumulation of the beads on the nitrocellulose membrane can be visualized using a specialized strip reader to provide a quantitative readout.

  • Quick and easy to use – the conjugate is ready to use in just 35 minutes
  • 15-fold higher sensitivity compared with other common particles
  • Specially treated particles are resistant to aggregation and require no extensive pH optimization

 

Titration of CRP Quantified by Lateral Flow Assay with InnovaCoat Gold

Lateral flow assay using our specially-treated europium beads. The europium beads were conjugated to a monoclonal anti-CRP antibody and used to quantify a titration of CRP. The conjugate is easily able to detect as little as 63pg/ml CRP, in part due to the low background and lack of aggregation.

Fluorescently-labeled antibodies for lateral flow immunoassays

An alternative to particle-based detection is to use an antibody which has been labeled with a fluorescent dye or a fluorescent protein. Our Lightning-Link® antibody conjugation kits enable the quick and easy conjugation of antibodies, proteins, peptides, or any other biomolecule which contains free amine groups, to a wide range of fluorescent detection moieties.

  • Quick and easy to use – the conjugate is ready to use in just 15 minutes
  • Wide range of labels available
  • Reliable – cited in over 300 publications

The use of fluorescently-labeled antibodies provides the opportunity for multiplexing in a lateral flow immunoassay. A specialized strip reader allows the readout to be quantified, although it is possible to visualize many fluorescently-labeled antibody conjugates by eye provided the antibody conjugate is present at a suitable concentration.

Lightning-Link Conjugation Process

The Lightning-Link® conjugation process. The conjugation reaction is initiated simply by adding the antibody to a vial of a lyophilized mixture which contains the label of interest. Following a short incubation, the conjugate is ready to use

How can I confirm that my antibody conjugation has been successful?

Although all of our products have been designed to guarantee first-time success provided that the protocol is followed correctly, we offer our Conjugate Check&Go! kit for extra peace of mind. This kit is a dipstick lateral flow assay for confirming the successful conjugation of an IgG antibody to a colored label. It is compatible with antibody conjugates produced using colloidal gold, InnovaCoat® GOLD, latex conjugation kits, and Lightning-Link®, as well as with any other conjugation technology which uses colored labels. The Conjugate Check&Go! kit is compatible with IgG antibodies from multiple species, provided that they have an affinity for either Protein A or G, which are immobilized on the T-line of the half strip.

 

Schematic representation of the Conjugate Check&Go! process

Schematic representation of the Conjugate Check&Go! process. The antibody conjugate flows along the nitrocellulose membrane and binds to the Protein A and Protein G which are concentrated at the test line. When the antibody is successfully conjugated to a colored label, a visible line appears on the strip.

  • Quick and easy to use – just 10 minutes to confirm successful conjugation
  • Requires only a small volume of diluted conjugate
  • No specialist equipment required

For more information about any of our products, for technical support, or to discuss custom services or bulk purchasing, please contact us.

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Fluorescent detection in lateral flow

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Videos

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