Lateral flow assays (LFAs) have been on the market as a tool for performing fast diagnostic tests for several decades. Clinical professionals use LFAs routinely, and the public have gained familiarity outside the healthcare environment through over-the-counter devices, such as pregnancy tests.
In 2010, it was estimated that around 100 companies worldwide were involved in the production and sale of LFAs in a market worth over 3.36 billion USD [Eltzov]. This success came as a result of their speed, simplicity, and low cost; key benefits over ELISAs and other alternative diagnostic tests.
Now well established, these diagnostic tools continue to evolve, increasing in sensitivity, expanding capability, and beginning to integrate with smart devices. As a result, LFAs have substantial potential to both grow in existing applications and extend into new areas.
This article explores the potential for LFAs in precision diagnostics, multiplexed assays, and remote healthcare.
Precision diagnostics
LFAs provide a simple and reliable assay for detecting specific biomarkers above their tested detection threshold. However, clinical professionals have a persisting need for increased sensitivity as they aim to identify these biomarkers at earlier and earlier stages of disease progression.
A key factor in assay sensitivity is the method of readout. Commonly, LFAs will display results using colorimetric detection as colored lines, often using gold or latex nanoparticles for test and control line [Mak]. However, these visual readouts are often unreliable at the lower threshold of detection and provide limited potential for quantitation.
One of many approaches for improving sensitivity and quantitation is the use of fluorescent markers. These markers are common at the laboratory bench and were recently repurposed in LFAs for the roadside testing for tetrahydrocannabinol [Plouffe].
Other options that can facilitate quantitation include electrochemical detection. Electrochemical LFAs use enzyme-conjugated magnetic beads to catalyze a reaction that leads to a measurable change in current between two electrodes [Ruiz-Vega, Akanda].
Each detection approach has its unique challenges. For example, fluorescent markers can be susceptible to bleaching or have limited shelf life, while electrochemical detection required additional steps compared to colorimetric detection [Mak]. Over time, however, its likely assay developers will overcome many of these challenges.
Improved sensitivity and ability to accurately quantitate LFAs opens a host of new applications. Most commercially available LFAs only show a positive/negative result. In precision diagnostics, sensitivity over a range of analyte concentrations could allow the detection of the progression and severity of a condition while retaining the simplicity of an LFA.
Multiplexing assays
Typically, each LFA can identify a single biomarker. Multiplexing is another area where significant growth of LFAs is possible. Detection of multiple analytes in a single sample addresses a need by healthcare providers to gain more information per test and to detect increasingly complex conditions.
Multiplexing has the additional benefit of potentially reducing the number and volume of samples required, improving test times, and reducing costs for a set of assays [Eltzov]. To give multiplex assays the same lasting commercial success as single-analyte assays, scientists are working to overcome the challenges of multiplexing.
One of the key technical challenges is cross-reactivity. Multiple biomarkers and antibodies increases the chances of false positives. A recent example where cross-reactivity prevented multiplexed detection of similar viral infections, dengue and zika, highlights this challenge [Hanafiah].
The more complex readout of multiplex assays compared to single-analyte assays is another potential challenge for its introduction. Digital readouts could address this challenge, especially for those assays that might otherwise need some expertise for interpretation. Several over-the-counter LFAs already use such digital readouts [Mak].
Remote healthcare
Recent decades have seen a general trend towards the public taking a more proactive role in accessing and addressing their own healthcare, including the use of over-the-counter tests.
There are already a multitude of LFAs available over the counter, including tests for pregnancy, diabetes and other diseases, allergies, and drugs. Improving LFAs through increased sensitivity and simpler, easier-to-understand readouts will likely lead to an expansion of over-the-counter assays.
As these assays continue to evolve, primary healthcare providers will be able to take advantage of this trend for remote healthcare. Patients supplying LFA results will supplement prescribed tests, expanding the available pool of information.
The adoption of electrochemical detection and similar strategies also makes it likely LFAs will increasingly integrate with mobile devices. These devices would play a key role in the capture and interpretation of test results at home and other settings outside the clinical laboratory.
Even with standard detection methods, high-resolution smartphone cameras, combined with easy-to-use image analysis software, could help patients interpret LFA results more reliably than just by eye. These devices would also enable patients to share this information with healthcare providers [Mak, Eltzov].
This type of electronic analysis would complement an increase in complexity of assays. Smart assays could provide standardized readouts, simplified interpretation, reduced risk of misinterpretation, and greater reliability than current assays.
The future for lateral flow assays
The simplicity, ease-of-use, and low cost of LFAs, as well as the potential for remote healthcare, will be the drivers for continued growth of the market. There are, and will continue to be, considerable challenges. However, ongoing technical developments are likely to overcome many of these challenges, improving sensitivity and expanding opportunities for multiplexing and quantitation.
From the end-user’s perspective, there is a clear potential for testing a wider range of conditions through over-the-counter LFAs. Combined with smart devices, primary healthcare providers will benefit from a larger pool of reliable information. Patients will benefit from simpler tests, and the ability to obtain, record, and communicate results with their healthcare provider regardless of location.
Cytiva provides a range of components that are well suited for use in LFAs, as well as custom services and expertise to help develop new assays. To find out more about membrane materials and custom services, contact Cytiva Support or your local representative.
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References
Akanda M. R. et al. An interference-free and rapid electrochemical lateral-flow immunoassay for one-step ultrasensitive detection with serum. Analyst 139, 1420–1425 (2014).
Eltzov E. et al. Lateral Flow Immunoassays – from Paper Strip to Smartphone Technology. Electroanalysis 27, 2116–2130 (2015).
Hanafiah K. M. et al. Development of Multiplexed Infectious Disease Lateral Flow Assays: Challenges and Opportunities. Diagnostics 7(3), :51(2017).
Mak W. et al. Lateral-flow technology: From visual to instrumental. Trends in Analytical Chemistry 79, 297-305 (2016).
Plouffe B. D. and Murthy S. K. Fluorescence-based lateral flow assays for rapid oral fluid roadside detection of cannabis use. Electrophoresis 38, 501-506 (2017).
Ruiz-Vega G. et al. Electrochemical Lateral Flow Devices: Towards Rapid Immunomagnetic Assays. ChemElectroChem 4(4), 880–889 (2017).