Lateral Flow Overview
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.
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 application remains the most widespread and well-known function of lateral flow technology.
BLOG: An ‘old’ technology with plenty of potential
Lateral Flow Functionality
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.
SONACAST: Lateral flow R&D
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