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Lateral flow

An introduction to lateral flow

What is lateral flow?

Lateral flow is, at its core, a simple technology; a paper-based diagnostic test used to confirm the presence or absence of a target analyte in a sample without the need for specialist lab equipment.

Low cost, easy to use and easy to interpret, lateral flow tests, also known as lateral flow immunochromatographic assays, lateral flow immunoassays or dipstick tests, are ideal for home and point-of-care testing.

The most well-known type of lateral flow test is the home pregnancy test.


SONACAST: Lateral flow basics


What is the history of lateral flow?

The origins of lateral flow technology go all the way back to the 1960s and the discovery of the antibody-antigen immunoassay reaction combined with thin layer chromatography (TLC).

But the technology as we know it today was first properly developed in the late 1980s when three researchers filed separate patents within months of each other for what is now considered the basis of the lateral flow platform. 

All three patents were looking for a way to develop an over-the-counter home pregnancy test, and today that remains the most widespread and well-known application of lateral flow technology.


BLOG: An ‘old’ technology with plenty of potential


Where are the tests used?

Lateral flow tests have most commonly been used in human health diagnostics, but today lateral flow tests have a wide range of uses across various sectors. These include:

  •          Animal and veterinary health
  •          Food and drink
  •          Environmental testing
  •          Agricultural testing
  •          Drugs of abuse
  •          Health, wellbeing and sport

They can be used in labs or in the field by professionals and by non-professionals alike.


BLOG: How digitized lateral flow tests will transform healthcare

BLOG: Home testing is the future – one day it might even replace your doctor


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How does lateral flow technology work?

Let’s take the home pregnancy test as an example. The sample, in this case urine, is introduced to the sample pad, which holds the fluid like a sponge. The fluid then moves to the conjugate pad, which stores the conjugated antibodies and labels used to detect the analyte. There are many different labels but in most tests the label is gold, which is red in colour. In pregnancy tests it tends to be latex, which is blue.

In a pregnancy test the analyte being detected is human chorionic gonadotropin (hCG), a hormone produced by the placenta. If this target analyte is present, the conjugated antibodies and labels will bind to it and continue to move along the test. A coloured line will form at the test line, giving a simple visual confirmation that the analyte has been detected. An independent control line contains an antibody that captures the free labels to confirm the test is working properly.


SONACAST: Lateral flow R&D

What labels are available?

The most popular labels are gold nanoparticles and latex nanobeads, but today a range of label options are available. These include:

  •         Fluorescent dyes or proteins
  •         Quantum dots
  •         Cellulose nanobeads
  •         Polystyrene nanobeads
  •         Paramagnetic nanoparticles
  •         Enzymatic reagents

Sona Nanotech’s unique gold nanorods are powering the next generation of lateral flow tests. As they can be produced in multiple different lengths they produce different colours, making them perfect for multiplexing (having more than one line in a test). They offer clear visual readings, distinct colour patterns and greater sensitivity and can be read quantitatively by a reader.


BLOG: Entering the golden era of lateral flow diagnostics


SONACAST: Colloidal gold and gold nanorods

What is the market for lateral flow?

The lateral flow diagnostic test market is huge and growing. It was worth an estimated US$6 bn in 2018, and is predicted to be worth US$8.7 bn in 2023. More than 2 billion lateral flow assays are produced each year, including more than 400 million a year each for malaria and HIV tests. 


BLOG: The lateral flow market in 2020


SONACAST: The rapid point of care diagnostic test market