(20−22) The Centers for Disease Control and Prevention estimates that 9–45 million influenza infections occur in the United States each year, leading to 140,000–810,000 hospitalizations and 12,000–61,000 deaths per year. Some important examples of LFAs are those used for the rapid diagnosis of influenza, (16,17) Streptococcus, (18,19) and many other viral and bacterial infections. (12) In biomedical diagnosis, an important advantage of this technology is that it enables the decentralization of laboratory testing to POC sites. In addition to the detection of SARS-CoV-2, LFAs have also been widely applied in biomedicine, food contaminant and toxic chemical detection, and environmental monitoring. These costs can be expected to drop further because other commercialized LFAs, such as human chorionic gonadotropin (pregnancy) LFAs, are <$1 per test.īecause LFAs are arguably the cheapest, fastest, and easiest to use paper-based POC tests, (11−15) they exhibit promise as a tool for achieving global pandemic control by enabling the rapid screening of infections. (6−8) In addition, the long turnaround time (hours to days) and high cost of RT-PCR (100–200 USD per COVID-19 swab test) compared to other rapid (<15 min) diagnostic tools, such as lateral flow assays (LFAs <$50 per COVID-19 swab test), (9,10) restrict its deployment in POC settings. Although RT-PCR has excellent sensitivity and specificity, it cannot be used as a POC test because this method requires trained staff in laboratories equipped with specialized thermal cycling equipment and strict environmental conditions to prevent contamination. (1−5) Unfortunately, this need cannot be met using the current primary diagnostic tools, such as reverse transcription polymerase chain reaction (RT-PCR). (1−5) In an ideal situation, at-risk individuals would be tested regularly ( i.e., weekly or daily) to enable timely isolation and to minimize virus transmission among the community. As a single serological antibody or antigen test can only indicate past or recent exposure to SARS-CoV-2, multiple and broad testing throughout the population will be needed to identify “hot spots” and to control the disease effectively. In summary, with continuing improvements, LFAs may soon offer performance at the POC that is competitive with laboratory techniques while retaining a rapid format.Īlthough infectious diseases have always posed global threats, there is no clearer current example of the need for inexpensive and high-performing ( i.e., low rates of false negatives (FNs) and positives (FPs)) point-of-care (POC) diagnostics than with the global pandemic of SARS-CoV-2 ( i.e., COVID-19). Furthermore, novel highly specific molecules, such as CRISPR/Cas systems, can be integrated into diagnosis with LFAs to produce not only ultrasensitive but also highly specific POC diagnostics. In the case of LFA specificity, recent research efforts have focused on high-affinity molecules and assay optimization to reduce nonspecific binding.
Perspectives to achieve future rapid (<30 min), ultrasensitive (PCR-level), and “sample-to-answer” POC diagnostics are also provided. However, these amplification strategies also increase the detection time and assay complexity, which inhibits the large-scale POC use of LFAs.
In addition, sample preamplification can be applied to both nucleic acids (direct amplification) and other analytes (indirect amplification) prior to LFA testing, which can lead to PCR-level (aM) sensitivity. Together, these efforts have produced LFAs with ELISA-level sensitivities (pM–fM). Recent work to improve the sensitivity through assay improvement includes optimization of the assay kinetics and signal amplification by either reader systems or additional reagents. In this Perspective, we review the evolving efforts to increase the sensitivity and specificity of LFAs. Unfortunately, traditional commercial LFAs have significantly poorer sensitivities (μM) and specificities than standard laboratory tests (enzyme-linked immunosorbent assay, ELISA: pM–fM polymerase chain reaction, PCR: aM), thus limiting their impact in disease control. Lateral flow assays (LFAs) are paper-based point-of-care (POC) diagnostic tools that are widely used because of their low cost, ease of use, and rapid format.
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