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Lateral Flow

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, simple to administer 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.

FURTHER LISTENING:
SONACAST: Lateral flow basics

 

The history of lateral flow technology

The origins of lateral flow technology originated in the 1960s with the discovery of the antibody-antigen immunoassay reaction combined with thin layer chromatography (TLC). However, the technology as we know it today was first properly developed in the late 1980s. Three researchers filed separate patents within months of one another, creating what is now considered the basis of the lateral flow platform. The goal of all three aforementioned patents was to develop an over-the-counter home pregnancy test. Today, this appication remains the most widespread and well-known function of lateral flow technology.

FURTHER READING:
BLOG: An ‘old’ technology with plenty of potential

How is lateral flow technology applied?

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

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

Lateral flow tests can be used in labs or in the field by professionals and by non-professionals alike.

FURTHER READING:
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?

Using 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 (flows) to the conjugate pad, which stores the conjugated antibodies and labels used to detect the analyte. There are several different labels but in most tests the label is gold, which presents as red in colour. In pregnancy tests the analyte 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.

FURTHER LISTENING:
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.

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BLOG: Entering the golden era of lateral flow diagnostics

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SONACAST: Colloidal gold and gold nanorods

The market for lateral flow tests

The lateral flow diagnostic test market continued to expand. in 2018, this sector was valued at an estimated US$6 billion. It is predicted that this market will grow to be worth US$8.7 billion 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. 

FURTHER READING:  
BLOG: The lateral flow market in 2020

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SONACAST: The rapid point of care diagnostic test market