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Lateral Flow Assay Technology Evolves as POC Testing Demands Higher Performance

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NEW YORK (360Dx) – Mainly because of its affordability and clinical utility in point-of-care applications, lateral-flow assay technology continues to evolve, and diagnostic test developers are finding new ways to improve its performance.

Speaking on improving the performance and connectivity of lateral flow assays for diagnostic applications at the Next Generation Dx Summit held in Washington, DC last week, David Fraser, product manager of lateral flow and detection at BBI Group, which does assay development and manufacturing for diagnostic organizations, described a range of innovative initiatives that are pushing the technology beyond the capabilities of existing products.

Lateral flow assay technology — consisting of a nitrocellulose membrane over which blood passes allowing antibodies to detect analytes — is mature and well understood. However, technology designs are evolving, Fraser said, as are methods of blood collection; methods of conjugation leading to sensitivity and speed improvements; and innovations in reader technology that enable use of different types of smartphone readers with different tests.

In the context of lateral flow assays, there are many important aspects to consider during blood collection and sample pretreatment where the user must ensure that the correct volume of blood is delivered safely to the device. In his talk, Fraser highlighted a technology developed by Ceres Nanosciences as noteworthy for the way that it improves the sensitivity of assays to which it's connected.

The firm's Nanotrap particle technology enables biomarker capture and biofluid sample processing for a range of diagnostic technologies, applications, and sample handling needs. Invented at George Mason University and developed with funding from the National Institutes of Health, Nanotrap technology uses hydrogel nanoparticles functionalized with internal affinity baits to enrich target analytes for downstream analysis. The system uses chemical dyes to bind the analytes of interest, concentrating them inside the nanoparticles and protecting them from enzymatic degradation, thereby improving the sensitivity of the ultimate clinical detection method, which could, for instance, be an ELISA, mass spectrometer, or lateral flow immunoassay.

Just as sample collection is important to high quality lateral flow assays, so too is proper conjugation, Fraser said, adding, "Without a robust and consistent conjugation process, you will never achieve the assay requirements that you need."

To that end, BBI has developed the Morffi signal enhancement technology, which Fraser said provides increased assay sensitivity, signal intensity, and faster time to result over assays developed using existing gold conjugation methods.

Morffi achieves this by increasing the availability of the binding partner on the label surface, thereby increasing the opportunity for binding with the target analyte, according to BBI.

In its lateral flow assay development work, BBI is also working with companies to incorporate improvements to the device design. For example, they are applying aptamers — single-stranded DNA or RNA oligonucleotides that bind with high affinity and high specificity to various targets, including ions, small organic compounds, large proteins, and live cells — as alternatives to antibodies to detect analytes.

Among their potential advantages over antibodies, aptamers can be used to detect small molecules directly, potentially improving sensitivity, Fraser said, and once optimal aptamer sequences have been selected, production of new batches of material is fast and inexpensive compared to antibodies. Further, aptamers are chemically synthesized, simplifying scale-up and enabling a high degree of manufacturing control from batch to batch.

In a recent review of aptamers in therapeutics and diagnostics pipelines, published in the journal Theranostics, the authors noted that few companies have so far translated their research into viable commercial diagnostic products or commercial reagents. Among the commercially successful aptamer companies are Neo Ventures Biotechnology, SomaLogic, Aptamer Sciences, and BasePair Biotechnologies, the paper said.

William Clarke, associate professor of pathology at Johns Hopkins University School of Medicine, said in a separate presentation at the conference that few POC devices can presently do more than one type of test. "Having devices that have some flexibility to increase menu is a challenge that needs to be met," he said.

However, quantitative, multiplexed, and highly sensitivity lateral flow tests are emerging, Fraser said.

One company, Sartorius Stedim Biotech, is altering the structure of nitrocellulose, a key material in lateral flow assays over the years, to enhance lateral flow assay performance. Fraser noted that the Göttingen-Grone, Germany-based firm has developed a method of engraving patterns into a nitrocellulose membrane, leading to hydrophobic barrier delineating membrane zones and enabling the membrane to function like a microfluidic device. The firm said its technology could be used to transform nitrocellulose membranes into multiplex platforms.

Further, Fraser said, Nanjing, China-based researchers are developing a lateral flow assay based on core-shell surface enhanced Raman scattering nanotags for multiplex and quantitative detection of cardiac biomarkers used in the early diagnosis of acute myocardial infarction.

This method could make it possible to conduct lateral flow assay testing at the point of care with performance comparable to chemiluminescence immunoassays used in labs, the researchers said in their paper.

Lateral flow assays will need to compete with several devices in development that can test multiple analytes using a single drop of blood.

James Nichols, medical director of clinical chemistry and point-of-care testing at Vanderbilt University School of Medicine, noted in a separate presentation that Genalyte's Maverick analyzer, for example, is being developed to complete a battery of blood tests in 15 minutes. The company aims to eventually place analyzers in physician’s offices. The system uses microfluidics in applying blood across a multiplex silicon chip-based platform that consists of 128 photonic sensors that trap light of a specific wavelength. When an analyte binds to a sensor, it generates a change in resonance proportional to the amount of the bound analyte.

Fraser noted that researchers are also looking at design elements that will improve lateral flow assay performance. He said that researchers at the University of Southampton, UK, recently reported use of a laser-direct write technique that allows the fabrication of lateral flow devices with enhanced sensitivity and limit of detection. This manufacturing technique comprises the dispensing of a liquid photopolymer at specific regions of a nitrocellulose membrane and its subsequent photopolymerization to create impermeable walls inside the volume of the membrane. The researchers tested a C-reactive protein sandwich assay that they said demonstrated a sixty-twofold improvement in sensitivity and thirtyfold improvement in limit of detection compared to a standard lateral flow CRP device.

Smartphones are being increasingly used as readers in association with point-of-care tests. Novarum DX, a subsidiary of BBI, has developed smartphone software and image-capture technology that enables different versions of smartphones to read and share results of diagnostic tests, including those based on lateral flow technology.

The Novarum software enables users to share test results securely through an online portal to healthcare professionals operating in a connected mobile eco-system.

Clarke said in his presentation that protecting health information transmitted over Wi-Fi or cellular networks is among the important challenges to adoption for point-of-care testing in general. Along with the associated need for reliable electric power sources for test systems, robust connectivity is among the challenges associated with the mobility of these types of tests, he said.