10 most popular questions from the LFA webinar

1. What’s the best size of gold nanoparticle to use for a lateral flow immunoassay?

40nm is the most widely used, however it’s definitely possible to use other sizes of nanoparticle for lateral flow.

2. How many lateral flow immunoassay strips can I prepare from a vial of Expedeon’ latex beads?

This varies from one assay to another, however one of our mini vials of latex beads provides sufficient conjugate for approximately 50 lateral flow tests, while one of our midi vials provides sufficient conjugate for approximately 500 lateral flow tests.

3. InnovaCoat® GOLD and colloidal gold nanoparticles are sold at different OD values – what is meant by OD?

The Optical Density (OD) is an absorbance value which reflects the concentration of the gold nanoparticles when they’re in a liquid suspension. 1ml of a 10 OD suspension corresponds to 9×1011 nanoparticles.

4. I’m new to working with gold nanoparticles. Which InnovaCoat® GOLD product would you recommend that I use?

Our original InnovaCoat® GOLD, which targets amine groups, is ideal for newcomers to gold conjugation. The kits are incredibly easy to use – you simply add your antibody to the vial of freeze-dried product, incubate, and your conjugate is ready to use within just 20 minutes.

5. I’ve just started to develop a lateral flow assay and I need to screen several different antibody-conjugates to find the best one. What is the fastest way to proceed?

We’d suggest that you begin by running your liquid conjugates on a dipstick assay, then grow the assay in complexity by adding in the other components, such as the conjugate and sample pads.

6. How do you guarantee that your colloidal gold nanoparticles are of the right size?

Each batch is analyzed by Transmission Electron Microscopy (TEM) to determine the mean particle size and standard deviation. When you purchase our colloidal gold we provide you with a certificate of analysis that gives you all of the QC data relevant to the specific batch.

7. I’m developing a different sort of lateral flow assay for which I need to label a protein, are your conjugation kits suitable for this?

Although our InnovaCoat® GOLD and Latex conjugation kits have been optimized for use with IgG antibodies, they can also be used with proteins or any other biomolecules which have primary amine groups. When working with other proteins, you may need to adjust the amount of molecule that you add to the vial of lyophilized label, without changing the reaction volume. Please get in touch with our technical support team for more information and help.

8. How do I measure the particles that are bound to the T line and C line?

This depends on what you want to achieve from the lateral flow assay, and the resources that you have available.

A qualitative readout is cost-effective, requiring only a visual assessment, and for this we suggest that you simply assign a number (e.g. 0 = no signal, through to 5) to the line/spot based on its color intensity. You can create your own standard line/spot intensities for consistency.

A quantitative readout is more expensive, requiring the use of an LFA strip reader. There are plenty of these devices on the market, with the price reflecting the level of sophistication. An LFA strip reader will allow you to create a calibration curve, and will provide reproducible and accurate measurements.

9. I am experiencing false positive results in my LFA. What do I need to change?

False positive results can be caused by multiple factors, including the antibodies, the conjugate, how the strips are made, the pads, the buffer, or the sample itself. It’s wise to optimize one assay component at a time to establish the cause of any non-specific binding. We recommend blocking the strips and/or pads, and adding blocking agents and a small amount of detergent to the buffers.

10. How should the LFA strips should be stored, and at what temperature?

The strips should be stored in sealed airtight containers, such as a foil pouches/pots containing silica gel or a molecular sieve to keep the relative humidity below 20%. The strips are stable at room temperature or stored in the fridge.