For decades, lateral flow assays (LFAs) have served as tools for rapid diagnostic testing. Clinical professionals use LFAs regularly, and the public routinely uses OTC versions of the devices (e.g., pregnancy and rapid COVID-19 tests). This wide-spread use is a testament to the speed, simplicity, and low cost of LFAs.
Despite being well established in the market, these diagnostic tools continue to evolve. Recent advances have seen increased sensitivity, expanded capability, and growing integration with smart devices. As a result, LFAs have substantial potential to grow in existing applications and extend into new areas.
Precision Diagnostics
Lateral flow assays provide a simple and reliable method for detecting specific biomarkers above their tested detection threshold. However, clinical professionals have a persisting need for increased sensitivity to identify these biomarkers at earlier and earlier stages of disease progression.
A key factor in assay sensitivity is the readout method. Commonly, LFAs display results using colorimetric detection as colored lines, often using gold or latex nanoparticles for test and control lines (1). 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. Labs commonly use these markers, which have been adapted for use in LFAs, including in roadside tests for tetrahydrocannabinol (THC) (2).
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 (3, 4).
Each detection approach has unique challenges. For example, fluorescent markers can be susceptible to bleaching or have limited shelf life, while electrochemical detection requires additional steps compared to colorimetric detection (1). Over time, however, its likely assay developers will overcome many of these challenges.
Improved sensitivity and the 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
Multiplexing is another area in which significant growth of LFAs is possible. The 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 (5). 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 increase the chances of false positives. This challenge was highlighted by a recent example in which cross-reactivity prevented multiplexed detection of similar viral infections, dengue and zika (6).
The more complex readout of multiplex assays is another potential challenge. Digital readouts could address this challenge, especially for those assays that might otherwise require expertise for interpretation. Several OTC LFAs already use such digital readouts (1).
Remote Healthcare
Recent decades have seen a general trend toward the public taking a more proactive role in accessing and addressing their own healthcare, including the use of OTC tests.
A multitude of LFAs are available over the counter, including tests for pregnancy, allergies, drugs, diabetes, and other diseases. Improving LFAs through increased sensitivity and simpler, easier-to-understand readouts will likely lead to an expansion of OTC 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 that LFAs will increasingly integrate with mobile devices. These devices could play a key role in the capture and interpretation of test results at home and in 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. These devices would also enable patients to share this information with healthcare providers (1, 5).
This type of electronic analysis would complement an increase in the complexity of assays. Smart assays could provide standardized readouts, simplified interpretation, reduced risk of misinterpretation, and greater reliability than current assays.
The Future of Lateral Flow Assays
The simplicity, ease-of-use, and low cost of LFAs, as well as the potential for remote healthcare, will be primary drivers for the market’s continued growth. 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 OTC 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.
References
- Mak WC, Beni V, Turner APF. Lateral-flow technology: From visual to instrumental. Trends Analyt Chem. 2016;79:297-305. doi:10.1016/j.trac.2015.10.017
- Plouffe BD, Murthy SK. Fluorescence‐based lateral flow assays for rapid oral fluid roadside detection of cannabis use. Electrophoresis. 2016;38(3-4):501-506. doi:10.1002/elps.201600075
- Ruiz‐Vega G, Kitsara M, Pellitero MA, Baldrich E, del Campo FJ. Electrochemical lateral flow devices: Towards rapid immunomagnetic assays. ChemElectroChem. 2017;4(4):880-889. doi:10.1002/celc.201600902
- Akanda MdR, Joung H-A, Tamilavan V, et al. An interference-free and rapid electrochemical lateral-flow immunoassay for one-step ultrasensitive detection with serum. Analyst. 2014;139(6):1420-1425. doi:10.1039/c3an02328a
- Eltzov E, Guttel S, Low Yuen Kei A, Sinawang PD, Ionescu RE, Marks RS. Lateral flow immunoassays – from paper strip to smartphone technology. Electroanalysis. 2015;27(9):2116-2130. doi:10.1002/elan.201500237
- Mohd Hanafiah K, Arifin N, Bustami Y, Noordin R, Garcia M, Anderson D. Development of multiplexed infectious disease lateral flow assays: Challenges and opportunities. Diagnostics. 2017;7(3):51. doi:10.3390/diagnostics7030051
