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Usage of Lateral Flow Assays in Point-of-Care Diagnosis

The usage of Ultrasensitive and Highly Specific Lateral Flow Assays for the purpose of POC (Point-of-Care Diagnosis)

The lateral flow assay (LFA) is regarded as a paper-based platform for the adequate detection & quantification of analytes inside the complex mixtures, where the sample is properly placed on a test device & the final results are displayed within a time span of around (5–30) min. The Lateral Flow Assay Market size piled up to an amount of around USD 8.4 billion in 2020. The world Market forecast suggests that by the year 2030, the market value is likely to reach USD 12.85 billion, accompanied by a growth rate of 4.34%.


Improving the range of Sensitivity by Assay Improvisation 

The overall sensitivity rate of the LFAs can be substantially improvised via either sample enrichment or assay improvement. Assay improvement inculcates the overall optimization of the fundamental assay kinetics & signal amplification methods by means of either chemical enhancement & reader use. The overall perspectives on their future improvisations were also discussed in detail.


The overall optimization process of the Assay Kinetics 

Exploring the assay kinetics (i.e., the transport & reaction kinetics) is regarded as a fundamental step in the LFA development & is very much essential for the enhancement of the LFA sensitivity. These sorts of kinetics ultimately impact the overall specific binding (SB) & nonspecific binding (NSB) events, which, in turn, determines the sensitivity & specificity of the assay.

Therefore, the goals of optimization of the assay kinetics are basically to (a) maximize SB & (b) minimize NSB. The quantitative assay optimization can be easily achieved by the maximization of the signal-to-noise ratio (SB/NSB). As a result, the overall reaction rate gets highly boosted by increasing the rate of reaction kinetics.

There are several kinds of reports on increasing the overall reaction kinetics that is readily associated with forming the antigen/conjugation/capture antibody ternary (sandwich ternary). A person named Liang found out that the sandwich ternary forms at a slower rate when the antigen first binds with a conjugated label & then it captures the antibody in a premixing flow than when it first binds with a captured antibody & then a conjugated label in the process of a sequential flow. Hence, the limit of detection (LoD) in the case of a malarial protein from a sequential flow was reported to be like 4- to 10-fold lower as compared to that obtained from a premixing flow.


Increasing the rate of Reaction Time 

Increasing the overall rate of the reaction time can also augment the total number of captured labels in the test region. For example, putting the cotton threads into the membrane can easily display the rate of flow & improve the overall rate of detection sensitivity by 4-fold. Adding a stacking pad in-between the conjugation pad & membrane can also increase the duration of reaction time, thereby leading to 1.1- to 2-fold decreases in the LoD.

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Designing of Labels

Label design adequately replaces the traditional small (ca. 20–40 nm) GNSS that are employed in LFAs, along with the other labels that have a stronger colorimetric contrast during the maintenance of the traditional LFA format. An even stronger contrast is achievable by modifying the overall structure & size of the GNPs or by the replacement of the GNPs with particle clusters or particles that are composed of another metal, organic material, or metal oxide.

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