The technology behind the Talis One molecular point-of-care test
The COVID-19 pandemic has highlighted the power of molecular diagnostics, with the rapid development of sensitive and specific SARS-CoV-2 tests within weeks of the first reports of widespread infection in China.1 However, the pandemic has also emphasized one of the biggest weaknesses of many molecular diagnostic assays—that their complexity often requires that the tests be performed by highly trained personnel in a central lab environment. This requirement sometimes can result in delays of 24-hours or more between collecting a patient specimen and when the results are available. In the case of infectious disease testing, this delay can increase risks to public health if a positive individual does not quarantine while waiting for test results, or unnecessary loss of work hours if a negative individual does quarantine.
A new paradigm for infectious diseases
At Talis, we are pioneering a new paradigm for infectious diseases molecular testing, bringing the accuracy of a central lab molecular test to a variety of care settings. With the Talis One COVID-19 Test System, healthcare professionals can run a molecular point-of-care test with minimal training, delivering results to patients within 30 minutes of obtaining a sample. Our system is able to deliver accurate, sensitive results quickly due to the unique engineering and design of our nucleic acid amplification test (NAAT) chemistry.
What an ideal molecular point-of-care test should look like
When developing the Talis One Test System, our goal was to maximize the system’s utility for healthcare professionals by focusing on the following features:
Speed—Any test that is used at the point of care should have a fast turnaround time, typically during the normal course of a patient’s visit to a physician’s office. Many healthcare professionals prefer point-of-care tests that provide results within 30 minutes.
Ease-of-use—Point-of-care test adoption should go from setup to routinely producing reliable results without extensive user training, since the focus of the medical professionals prescribing the tests is care giving, not assay implementation.
Accuracy—Point-of-care tests need to be sensitive and specific in order to be effective. The risks of delivering a false negative result is calculated to be high with tests that have moderate sensitivity (70%) if the disease is widespread.2 Thus, tests need to be both sensitive and specific to achieve healthcare goals, although less sensitive tests can be useful for surveillance testing if they can be used frequently enough.3
To ensure that we achieved these goals, we carefully selected and optimized the technology used in the Talis One Test System.
Leveraging LAMP for speed and accuracy
Why isothermal NAAT is better than conventional PCR for molecular point of care testing
While there are many different kinds of nucleic acid amplification technologies, many are not suited to point-of-care applications. Conventional PCR-based methods like qPCR need to cycle between multiple temperatures 20 or more times, which results in turnaround times of ~4 hours.4 Isothermal NAAT avoids this issue with biochemistry that operates at a single temperature, giving most isothermal NAAT methods the potential to deliver results on a much faster timeline.
Why LAMP is an excellent choice for molecular point of care testing
There are also many ways to implement isothermal NAAT, many of which are reviewed in Khan, et al.4 The Talis One Test System relies on real-time loop-mediated isothermal amplification (rtLAMP) for DNA targets and real-time reverse transcription loop-mediated isothermal amplification (rtRT-LAMP) for RNA targets (Figure 1).
LAMP is a well-studied technique known for sensitivity and specificity, especially when nucleic acid is first extracted from the sample.4 LAMP is also fairly resistant to inhibitors in the sample4, making it a good technique for diagnostic applications.
How we’ve made LAMP more sensitive by using on-cartridge sample extraction
We also improve the sensitivity of LAMP by including an on-cartridge sample extraction step. Our sample extraction method is a solid matrix column-based approach which maximizes nucleic acid recovery, and the fully enclosed design of the Talis One cartridge ensures that all fluids remain contained within the cartridge.
Why Talis achieves high performance with our proprietary molecular point-of-care testing
Compared to other isothermal NAAT methods such as the nicking and extension amplification reaction (NEAR) used in another point of care SARS-CoV-2 test, the proprietary NAAT technology used in Talis One’s COVID-19 Test System delivers orders of magnitude higher sensitivity, achieving an LOD of 500 copies/mL (Figure 2).6,7
Figure 2. LOD determined using the FDA SARS-CoV-2 Reference Panel.
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- Smith et al. https://doi.org/10.1101/2021.03.19.21253964
- Basu et al. J Clin Microbiol August 2020; 58(8): e01136-20
Leveraging a fully enclosed cartridge-based system for ease of use
We’ve designed the Talis One System for ease of use, enabling use by a wide range of healthcare professionals in a variety of care settings. The single-use test cartridge is a critical part of the system, and where all the rtLAMP/rtRT-LAMP reactions take place. One of the key advantages of how we implement the testing workflow is the inclusion of a solid phase sample extraction step, which maximizes the sensitivity of our system.
Excellent performance at the point of care
The Talis One COVID-19 Test System, was granted an Emergency Use Authorization (EUA) and demonstrates the excellent performance of our system.
Demonstrating the accuracy of the Talis One COVID-19 Test
We evaluated the accuracy of the Talis One COVID-19 Test System on a total of 77 residual clinical specimens (Figure 3).
In the clinical study, a series of analytical tests were conducted on 77 residual clinical samples to characterize the performance of the Talis One COVID-19 Test System. The Talis One COVID-19 Test System had positive and negative percent agreements (PPA, NPA) of 100% respectively.7
Diluted Specimen Testing
To obtain an adequate number of representative low titer specimens, testing was supplemented with eight additional positive samples that were diluted in individual negative nasal samples and randomized with an equivalent number (8) of negative samples.
Two-fold serial dilutions were carried out at the reference laboratory for samples that previously tested positive by the comparator test. Dilutions ranged from 4-fold to 131,072-fold. Combining diluted specimens with neat clinical specimens demonstrated a PPA of 95.7% (95% CI: 85.5%-98.8%) and NPA of 100% (95% CI: 92.4%-100%).
Demonstrating inclusivity of the Talis One COVID-19 Test
The analytical reactivity (inclusivity) study determined the Talis One COVID-19 Test System is expected to amplify 99.41% of published SARS-CoV-2 sequences.7
Demonstrating the sensitivity of the Talis One COVID-19 Test
We performed an analytical sensitivity (LOD) study using the BEI Resources SARS-Related Coronavirus 2, Isolate USAWA1/2020 (gamma-irradiated), which was titered into Talis One Inactivation Media to create the LOD samples. The LOD of the Talis One COVID-19 Test was determined to be 500 copies/mL.7
During the COVID-19 pandemic, molecular testing, with its many benefits as well as challenges, has become a ‘top of mind’ topic for most healthcare professionals and some well-informed patients. Talis is developing and implementing new technology to address molecular diagnostics challenges, transforming this powerful but complex technology into an accurate and reliable molecular point-of-care test.
- Corman VM, Landt O, Kaiser M, et al. Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR. Eurosurveillance. 2020;25(3):2000045. doi:10.2807/1560-7917.ES.2020.25.3.2000045
- Woloshin S, Patel N, Kesselheim AS. False Negative Tests for SARS-CoV-2 Infection — Challenges and Implications. N Engl J Med. 2020;383(6):e38. doi:10.1056/NEJMp2015897
- Larremore DB, Wilder B, Lester E, et al. Test Sensitivity Is Secondary to Frequency and Turnaround Time for COVID-19 Surveillance.; 2020:2020.06.22.20136309. doi:10.1101/2020.06.22.20136309
- Khan P, Aufdembrink LM, Engelhart AE. Isothermal SARS-CoV-2 Diagnostics: Tools for Enabling Distributed Pandemic Testing as a Means of Supporting Safe Reopenings. ACS Synth Biol. Published online September 23, 2020:acssynbio.0c00359. doi:10.1021/acssynbio.0c00359
- Gadkar VJ, Goldfarb DM, Gantt S, Tilley PAG. Real-time Detection and Monitoring of Loop Mediated Amplification (LAMP) Reaction Using Self-quenching and De-quenching Fluorogenic Probes. Sci Rep. 2018;8(1):5548. doi:10.1038/s41598-018-23930-1
- Evaluation Of The Talis One™ Covid-19 Test System For The Rapid Detection (< 30 Minutes) Of Sars-cov-2 From Nasal Swab Specimens. Accessed August 31, 2021.
- Talis One COVID-19 Test System Instructions For Use 152-0028851 REV.01