Results are visible colorimetric signals and ARTs are also more affordable than RT-PCR, making ARTs a prime candidate to fulfil current point-of-care testing needs. On the other hand, antigen rapid tests (ARTs) can function at the point-of-care, provide results in minutes and do not require specialised equipment or labour. Point-of-care molecular detection techniques such as reverse transcription loop-mediated isothermal amplification (RT-LAMP), though simpler to perform than RT-PCR with adequate assay performance, still require skilled technologists to carry out the test. Rapid serological tests, which detect SARS-CoV-2 antibodies from a drop of blood, have not been proven useful for acuteВ diagnosis, as these antibodies can remain detectable in patients who had undergone vaccination or have recovered from a SARS-CoV-2 infection for up to 13В months. Point-of-care tests that use easily accessible samples with high sensitivity are urgently needed. However, though labour for sample collection is reduced, laboratory support is still needed for sample extraction and analyses, thus limiting their usefulness for rapid testing. Another emerging approach is the detection of SARS-CoV-2 from exhaled breath, using RT-PCR or mass spectroscopy, with reported sensitivity ranging from 68 to 93.5% and 80 to 97.3%, respectively. While urine and stool RT-PCR, which do not require labour for sample collection, had also been investigated, a meta-analysis showed that results using either sample type were inconsistent. These challenges make widespread implementation of RT-PCR challenging. It is also costly, with the reagent cost alone estimated at USD17.22 per test. This is especially since reverse transcription-polymerase chain reaction (RT-PCR) testing from nasopharyngeal swab samples, which is the current gold standard, would require suitably equipped laboratories and trained personnel to conduct the assay. A highly sensitive, affordable and easy-to-use test to diagnose COVID-19 rapidly for case management remains an unmet need. Furthermore, the emergence of new variants of concern such as the more transmissible delta variant is fuelling new waves of outbreaks.

Low- to middle-income countries (LMICs) are most severely impacted with limited access to vaccines, leaving majority of their population vulnerable to the devastating effects of COVID-19. Despite the unprecedented pace of vaccine deployment, demand for vaccines far outstrips supply. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the aetiological agent responsible for coronavirus disease 2019 (COVID-19), has negatively affected global health and economy. Thus, AP-ART has the potential to be developed for point-of-care testing, which may be particularly important in resource-limited settings, and for early diagnosis to initiate newly approved therapies to reduce COVID-19 severity. Compared to the gold standard reverse transcription-polymerase chain reaction testing on nasopharyngeal samples, non-fasting saliva tested on AP-ART showed a sensitivity of 97.0% (95% CI: 84.7вЂ“99.8) without amplification, the sensitivity was 72.7% (95% CI: 83.7вЂ“94.8). Unlike commercially available ARTs, the sensitivity of AP-ART was maintained even when non-fasting saliva was used. AP-ART performance in detecting SARS-CoV-2 in saliva of COVID-19 patients was investigated using a caseвЂ“control study (139 participants enrolled and 162 saliva samples tested). Compared to existing dual gold amplification techniques, a limit of detection of one order of magnitude lower was achieved (0.0064 ng The second contained signal amplifying nanoparticles that complex with the former and amplify the signal without any linker. The first contained spike protein binding gold nanoparticles which produced a visible red line upon encountering the virus. It also featured two parallel flow channels. The virus was captured multimodally, using both anti-spike protein antibodies and Angiotensin Converting Enzyme 2 (ACE2) protein. Herein, we report an Amplified Parallel ART (AP-ART) with sensitivity above 90%, even with non-fasted samples.

Saliva-based antigen rapid tests (ARTs) can fulfil this need, but these tests requireВ overnight-fasted samples without which independent studies have demonstrated sensitivities of only 11.7 to 23.1%. The ongoing COVID-19 pandemic, simple, rapid, point-of-care tests not requiring trained personnel for primary care testing are essential.

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