GetWiki

{{short description|Immunochromatographic testing devices}}(File:Lateral Flow Assay.jpg|thumb|300x300px|A NASA illustration of a lateral flow assay)A lateral flow test (LFT),WEB,weblink Concurrent engineering for lateral-flow diagnostics, IVD Technology, 1 November 1999, 1 October 2022, Alan, Weiss,weblink" title="web.archive.org/web/20140415073429weblink">weblink 2014-04-15, is an assay also known as a lateral flow device (LFD), lateral flow immunochromatographic assay, or rapid test. It is a simple device intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment. LFTs are widely used in medical diagnostics in the home, at the point of care, and in the laboratory. For instance, the home pregnancy test is an LFT that detects a specific hormone. These tests are simple and economical and generally show results in around five to thirty minutes. Many lab-based applications increase the sensitivity of simple LFTs by employing additional dedicated equipment.JOURNAL, Yetisen AK, Akram MS, Lowe CR, Paper-based microfluidic point-of-care diagnostic devices, Lab on a Chip, 13, 12, 2210–51, June 2013, 23652632, 10.1039/C3LC50169H, 17745196, Because the target substance is often a biological antigen, many lateral flow tests are rapid antigen tests (RAT or ART).LFTs operate on the same principles of affinity chromatography as the enzyme-linked immunosorbent assays (ELISA). In essence, these tests run the liquid sample along the surface of a pad with reactive molecules that show a visual positive or negative result. The pads are based on a series of capillary beds, such as pieces of porous paper,WEB,weblink Lateral Flow Introduction, khufash.com, 27 July 2012, dead,weblink" title="web.archive.org/web/20120728025400weblink">weblink 28 July 2012, microstructured polymer,JOURNAL, Hansson J, Yasuga H, Haraldsson T, van der Wijngaart W, Synthetic microfluidic paper: high surface area and high porosity polymer micropillar arrays, Lab on a Chip, 16, 2, 298–304, January 2016, 26646057, 10.1039/C5LC01318F,weblink JOURNAL, Weijin Guo, Jonas Hansson, Wouter van der Wijngaart, 2016, Viscosity Independent Paper Microfluidic Imbibition,weblink MicroTAS 2016, Dublin, Ireland, or sintered polymer.JOURNAL, Crozier, Alex, Rajan, Selina, Buchan, Iain, McKee, Martin, Put to the test: Use of rapid testing technologies for Covid-19, BMJ, 3 February 2021, 372,weblink Appendix p. 6, 10.1136/bmj.n208, 33536228, 231775752, Appendix Table 1, p. 6, free, Each of these pads has the capacity to transport fluid (e.g., urine, blood, saliva) spontaneously.WEB, Antibodies, Proteins, ELISA kits,weblink Abbexa, 12 January 2022, en, Lateral Flow Assays, also known as Lateral Flow Immunochromatographic Assays [...] The technology is based on a series of capillary beds; such as pieces of porous paper, micro-structured polymer, or sintered polymer. Each of these elements has the capacity to transport fluid (e.g., urine), spontaneously., The sample pad acts as a sponge and holds an excess of sample fluid. Once soaked, the fluid flows to the second conjugate pad in which the manufacturer has stored freeze dried bio-active particles called conjugates (see below) in a salt–sugar matrix. The conjugate pad contains all the reagents required for an optimized chemical reaction between the target molecule (e.g., an antigen) and its chemical partner (e.g., antibody) that has been immobilized on the particle's surface. This marks target particles as they pass through the pad and continue across to the test and control lines. The test line shows a signal, often a color as in pregnancy tests. The control line contains affinity ligands which show whether the sample has flowed through and the bio-molecules in the conjugate pad are active. After passing these reaction zones, the fluid enters the final porous material, the wick, that simply acts as a waste container.LFTs can operate as either competitive or sandwich assays.

History

LFTs derive from paper chromatography, which was developed in 1943 by Martin and Synge, and elaborated in 1944 by Consden, Gordon and Martin.JOURNAL, Consden R, Gordon AH, Martin AJ, Qualitative analysis of proteins: a partition chromatographic method using paper, The Biochemical Journal, 38, 3, 224–32, 1944, 16747784, 1258072, 10.1042/bj0380224, NEWS,weblink Paper chromatography {{!, chemistry|work=Encyclopedia Britannica|access-date=2018-06-01|language=en}} There was an explosion of activity in this field after 1945.JOURNAL, Haslam E, Vegetable tannins - lessons of a phytochemical lifetime, Phytochemistry, 68, 22–24, 2713–21, 2007, 18037145, 10.1016/j.phytochem.2007.09.009, 2007PChem..68.2713H, Edwin Haslam, The ELISA technology was developed in 1971.JOURNAL, Engvall, E, 1972-11-22, Enzyme-linked immunosorbent assay, Elisa,weblink The Journal of Immunology, 109, 1, 129–135, 10.4049/jimmunol.109.1.129, 0022-1767, 4113792, free, A set of LFT patents, including the litigated US 6,485,982 described below, were filed by Armkel LLC starting in 1988.

Synopsis

Colored particles

In principle, any colored particle can be used, but latex (blue color) or nanometer-sized particlesJOURNAL, Quesada-González D, Merkoçi A, Nanoparticle-based lateral flow biosensors, Biosensors & Bioelectronics, 73, special, 47–63, November 2015, 26043315, 10.1016/j.bios.2015.05.050, 10261/131760,weblink of gold (red color) are most commonly used. The gold particles are red in color due to localized surface plasmon resonance.WEB,weblink Gold Nanoparticle Labels Custom Designed for Lateral Flow Assays, NanoHybrids, NanoHybrids, en, 29 September 2020, 11 September 2021,weblink dead, FluorescentJOURNAL, Faulstich K, Gruler R, Eberhard M, Haberstroh K, Developing rapid mobile POC systems. Part 1: Devices and applications for lateral-flow immunodiagnostics., IVD Technology, July 2007, 13, 6, 47–53,weblink 2007-11-22, 2009-03-02,weblink" title="web.archive.org/web/20090302094532weblink">weblink dead, or magneticJOURNAL, LaBorde RT, O'Farrell B, Paramagnetic-particle detection in lateral-flow assays., IVD Technol, April 2002, 8, 3, 36–41,weblink 2007-11-22, 2010-03-01,weblink" title="web.archive.org/web/20100301171711weblink">weblink dead, WEB,weblink Magnetic immunoassays: A new paradigm in POCT (IVDT archive, Jul/Aug 2008), 2008-10-23,weblink" title="web.archive.org/web/20131028183523weblink">weblink 28 October 2013, dead, labelled particles can also be used, but these require the use of an electronic reader to assess the test result.

Sandwich assays

(File:ELISA or Lateral flow formats.svg|thumb|upright=1.3|Difference between sandwich assay and competitive assay formats of lateral flow tests{{clarify|date=December 2021}})Sandwich assays are generally used for larger analytes because they tend to have multiple binding sites. As the sample migrates through the assay it first encounters a conjugate, which is an antibody specific to the target analyte labelled with a visual tag, usually colloidal gold. The antibodies bind to the target analyte within the sample and migrate together until they reach the test line. The test line also contains immobilized antibodies specific to the target analyte, which bind to the migrated analyte bound conjugate molecules. The test line then presents a visual change due to the concentrated visual tag, hence confirming the presence of the target molecules. The majority of sandwich assays also have a control line which will appear whether or not the target analyte is present to ensure proper function of the lateral flow pad.The rapid, low-cost sandwich-based assay is commonly used for home pregnancy tests which detect human chorionic gonadotropin, hCG, in the urine of pregnant women.

Competitive assays

Competitive assays are generally used for smaller analytes since smaller analytes have fewer binding sites.WEB,weblink Introduction to Lateral Flow Rapid Test Diagnostics, nanoComposix, nanoComposix, en, 4 November 2019, The sample first encounters antibodies to the target analyte labelled with a visual tag (colored particles). The test line contains the target analyte fixed to the surface. When the target analyte is absent from the sample, unbound antibody will bind to these fixed analyte molecules, meaning that a visual marker will show. Conversely, when the target analyte is present in the sample, it binds to the antibodies to prevent them binding to the fixed analyte in the test line, and thus no visual marker shows. This differs from sandwich assays in that no band means the analyte is present.JOURNAL, Koczula, Katarzyna M., Gallotta, Andrea, Lateral flow assays, Essays in Biochemistry, 30 June 2016, 27365041, 4986465, 60, 1, 111–120, 10.1042/EBC20150012,

Quantitative tests

Most LFTs are intended to operate on a purely qualitative basis. However, it is possible to measure the intensity of the test line to determine the quantity of analyte in the sample. Handheld diagnostic devices known as lateral flow readers are used by several companies to provide a fully quantitative assay result. By utilizing unique wavelengths of light for illumination in conjunction with either CMOS or CCD detection technology, a signal rich image can be produced of the actual test lines. Using image processing algorithms specifically designed for a particular test type and medium, line intensities can then be correlated with analyte concentrations. One such handheld lateral flow device platform is made by Detekt Biomedical L.L.C.WEB,weblink Detekt Biomedical L.L.C.- Lateral Flow Readers for Rapid Test Strip Detection and Immunoassays, idetekt.com, en-US, 6 July 2017, Alternative non-optical techniques are also able to report quantitative assays results. One such example is a magnetic immunoassay (MIA) in the LFT form also allows for getting a quantified result. Reducing variations in the capillary pumping of the sample fluid is another approach to move from qualitative to quantitative results. Recent work has, for example, demonstrated capillary pumping with a constant flow rate independent from the liquid viscosity and surface energy.JOURNAL, 10.1021/acs.langmuir.6b03488, Capillary Pumping Independent of Liquid Sample Viscosity, 2016, Guo, Weijin, Hansson, Jonas, Van Der Wijngaart, Wouter, Langmuir, 32, 48, 12650–12655, 27798835, 24662688,weblink BOOK, 10.1109/MEMSYS.2017.7863410, Capillary pumping with a constant flow rate independent of the liquid sample viscosity and surface energy, 2017 IEEE 30th International Conference on Micro Electro Mechanical Systems (MEMS), 2017, Guo, Weijin, Hansson, Jonas, Van Der Wijngaart, Wouter, 339–341, 978-1-5090-5078-9, 13219735,weblink JOURNAL, Guo W, Hansson J, van der Wijngaart W, Capillary pumping independent of the liquid surface energy and viscosity, Microsystems & Nanoengineering, 4, 1, 2, 2018, 31057892, 6220164, 10.1038/s41378-018-0002-9, 2018MicNa...4....2G,

Control line

(File:Negative_Pregnancy_Test.JPG|thumb|200x200px|The control line of this pregnancy test is blank, making the test invalid.)Most tests will incorporate a second line which contains a further antibody (one which is not specific to the analyte) that binds some of the remaining colored particles which did not bind to the test line. This confirms that fluid has passed successfully from the sample-application pad, past the test line. By giving confirmation that the sample has had a chance to interact with the test line, this increases confidence that a visibly-unchanged test line can be interpreted as a negative result (or that a changed test line can be interpreted as a negative result in a competitive assay).

Blood plasma extraction

Because the intense red color of hemoglobin interferes with the readout of colorimetric or optical detection-based diagnostic tests, blood plasma separation is a common first step to increase diagnostic test accuracy. Plasma can be extracted from whole blood via integrated filtersJOURNAL, Tripathi S, Kumar V, Prabhakar A, Joshi S , Agrawal A, 2015, Passive blood plasma separation at the microscale: a review of design principles and microdevices, J. Micromech. Microeng., 25, 8, 083001, 10.1088/0960-1317/25/8/083001, 2015JMiMi..25h3001T, 138153068, or via agglutination.JOURNAL, Guo W, Hansson J, van der Wijngaart W, Synthetic Paper Separates Plasma from Whole Blood with Low Protein Loss, Analytical Chemistry, 92, 9, 6194–6199, May 2020, 32323979, 10.1021/acs.analchem.0c01474, free,

Speed and simplicity

Time to obtain the test result is a key driver for these products. Tests results can be available in as little as a few minutes. Generally there is a trade off between time and sensitivity: more sensitive tests may take longer to develop. The other key advantage of this format of test compared to other immunoassays is the simplicity of the test, by typically requiring little or no sample or reagent preparation.JOURNAL, Liu, Yilin, Zhan, Li, Qin, Zhenpeng, Sackrison, James, Bischof, John C., Ultrasensitive and Highly Specific Lateral Flow Assays for Point-of-Care Diagnosis, ACS Nano, 23 March 2021, 15, 3, 3593–3611, 10.1021/acsnano.0c10035, 33607867, 231969545,weblink 1936-0851,

Patents

This is a highly competitive area and a number of people claim patents in the field, most notably Alere (formerly Inverness Medical Innovations, now owned by Abbott) who own patentsPATENT, US, 6485982, patent, Test device and method for colored particle immunoassay, November 26, 2002, David E. Charlton, Church & Dwight,weblink originally filed by Unipath. The US 6,485,982 patent, that has been litigated, expired in 2019. A number of other companies also hold patents in this arena. A group of competitors are challenging the validity of the patents.WEB,weblink Grassroots Web group challenging lateral-flow patents, Medical DeviceLink, November 2000,weblink" title="web.archive.org/web/20010708181513weblink">weblink 8 July 2001, The original patent is apparently from 1988.WEB, Lateral Flow Sensors,weblink 2024-04-18, www.sensor100.com, PATENT, US6485982B1, Test device and method for colored particle immunoassay, 2002-11-26, Charlton, David E.,weblink

Applications

Lateral flow assays have a wide array of applications and can test a variety of samples like urine, blood, saliva, sweat, serum, and other fluids. They are currently used by clinical laboratories, hospitals, and physicians for quick and accurate tests for specific target molecules and gene expression. Other uses for lateral flow assays are food and environmental safety and veterinary medicine for chemicals such as diseases and toxins. LFTs are also commonly used for disease identification such as ebola, but the most common LFT are the home pregnancy and SARS-CoV-2 tests.

COVID-19 testing

(File:Test de antígenos Covid 3.jpg|thumb|COVID-19 rapid antigen lateral flow test showing a negative result)Lateral flow assays have played a critical role in COVID-19 testing as they have the benefit of delivering a result in 15–30 minutes.JOURNAL, Guglielmi G, Fast coronavirus tests: what they can and can't do, Nature, 585, 7826, 496–498, September 2020, 32939084, 10.1038/d41586-020-02661-2, 2020Natur.585..496G, 221768935, The systematic evaluation of lateral flow assays during the COVID-19 pandemicWEB, Guidance: First wave of non-machine based lateral flow technology (LFT) assessment,weblink 11 January 2021, 20 January 2021, GOV.UK, en, was initiated at Oxford University as part of a UK collaboration with Public Health England. A study that started in June 2020 in the United Kingdom, FALCON-C19, confirmed the sensitivity of some lateral flow devices (LFDs) in this setting.WEB, Oxford University and PHE confirm high-sensitivity of lateral flow tests,weblink 11 November 2020, GOV.UK, en, WEB, FALCON — CONDOR Platform,weblink 25 November 2020, www.condor-platform.org, JOURNAL, Peto T, COVID-19: Rapid antigen detection for SARS-CoV-2 by lateral flow assay: A national systematic evaluation of sensitivity and specificity for mass-testing, eClinicalMedicine, 36, 100924, June 2021, 34101770, 10.1016/j.eclinm.2021.100924, 8164528, 231609922, Four out of 64 LFDs tested had desirable performance characteristics according to these early tests; the Innova SARS-CoV-2 Antigen Rapid Qualitative Test performed moderately in viral antigen detection/sensitivity with excellent specificity, although kit failure rates and the impact of training were potential issues. The Innova test's specificity is more widely publicised, but sensitivity in phase 4 trials was 50.1%.WEB, Wolf A, Hulmes J, Hopkins H, 10 March 2021, Lateral flow device specificity in phase 4 (post marketing) surveillance,weblink live, gov.uk,weblink 2022-08-14, This describes a device for which one out of every two patients infected with COVID-19 and tested in real-world conditions would receive a false-negative result. After closure of schools in January 2021, biweekly LFTs were introduced in England for teachers, pupils, and households of pupils when schools re-opened on March 8, 2021 for asymptomatic testing.WEB, Coronavirus (COVID-19) asymptomatic testing in schools and colleges,weblink 2021-05-27, GOV.UK, en, Biweekly LFT were made universally available to everyone in England on April 9, 2021.WEB, Twice weekly rapid testing to be available to everyone in England,weblink 2021-04-05, 2021-05-27, GOV.UK, en, LFTs have been used for mass testing for COVID-19 globallyNEWS, Agence France-Presse, 2 November 2020, Slovakia carries out Covid mass testing of two-thirds of population, en-GB, The Guardian,weblink 0261-3077, WEB, 6 November 2020, The UK is trialling lateral flow testing for Covid-19 – how does it work?, Peter Littlejohns,weblink NS Medical Devices, WEB, Merthyr Tydfil County Borough to be first whole area testing pilot in Wales,weblink 18 November 2020, GOV.WALES, en, and complement other public health measures for COVID-19.WEB, 19 August 2020, Population-wide testing of SARS-CoV-2: country experiences and potential approaches in the EU/EEA and the United Kingdom,weblink European Centre for Disease Prevention and Control, en, Some scientists outside government expressed serious misgivings in late 2020 about the use of Innova LFDs for screening for Covid. According to Jon Deeks, a professor of biostatistics at the University of Birmingham, England, the Innova test is "entirely unsuitable" for community testing: "as the test may miss up to half of cases, a negative test result indicates a reduced risk of Covid, but does not exclude Covid".WEB, Scientists urge caution on use of lateral flow tests to screen for Covid-19, Burke M, Chemistry World, 18 November 2020,weblink Criticism of LFDs for Covid testing by several experts, with detailed numerical discussion.WEB, Covid-19: government must urgently rethink lateral flow test roll out, Deeks J, Raffle A, Gill M, The BMJ Opinion, 12 January 2021,weblink Sensitivity of tests used in 2022 was around 70%.JOURNAL, Tapari A, Braliou GG, Papaefthimiou M, Mavriki H, Kontou PI, Nikolopoulos GK, Bagos PG, Performance of Antigen Detection Tests for SARS-CoV-2: A Systematic Review and Meta-Analysis, Diagnostics, 4 June 2022, 12, 6, 1388, 35741198, 10.3390/diagnostics12061388, 9221910, free,

See also

• {{section link|Luteinizing hormonePredicting ovulation}}: LFT test for ovulation

References

{{Reflist}}

Further reading

• BOOK, Hassan, Muntaha M., Rapid Immunochrotographic Techniques, University of Anbar, Ramadi, Al Anbar, Iraq, Didactic presentation (lab notes for students),weblink 12 January 2022,
• Porex Clinical Sciences (manufacturer) WEB,weblink Sample Collection & Transport &124; Sample Preparation &124; Sample Analysis,