Filtration & fl uid control


gonadotropin (hCG) hormone detected in the urine of pregnant women, the viral load present in a Covid-19 swab can vary significantly. Without an amplification method, such tests are always going to be less sensitive to lower viral loads than RT-PCR. The lack of amplification means that paper lateral flow tests typically have low sensitivity – the ability of the test to correctly identify those patients with the disease – so, a large amount of antigen is required to trigger a positive band. Another challenge is lateral flow tests typically only detect a single biomarker, so they can only be used to rule out one disease at a time. More sophisticated microfluidic tests typically use miniscule channels encased in glass or silicon.


For decades, point-of-care diagnostics have been heralded as the answer to global healthcare challenges. LOC technology could perhaps have the most impact in detecting infectious diseases in developing countries, where healthcare facilities and diagnostic laboratories are in short supply. However, most low-income countries are still yet to see meaningful adoption of LOC tests despite the years of research investment.


Making microfluidics One reason for the lack of uptake is that the technology required to manufacture sophisticated microfluidic tests is very expensive, points out Robert Hughes from the department of mechanical engineering at the University of Bristol, who studies the mechanics behind point-of-care diagnosis. “The researchers in the developing world often don’t have the agency and the tools to make use of these technologies,” he says.


LOC tests contain micro-scale channels that are often around the width of a human hair. Fluid is controlled, manipulated, and analysed within these channels. But manufacturing the tiny passageways is costly. The most common method involves a process called photolithography, which uses a beam of photons to etch channels into silicon wafers. This technique produces a master mould of the microfluidic system. Next, a biocompatible polymer such as polydimethylsiloxane (PDMS) is poured


Medical Device Developments / www.nsmedicaldevices.com 95


over the mould, peeled free and then bound to glass. Photolithography can even produce high- resolution channels at the nanometre scale. But the method is time-consuming – and the cost is considerable. This makes the widespread research and development of LOC technology near impossible for all but the wealthiest of research institutes, says Hughes.


“The researchers in the developing world often don’t have the agency and the tools to make use of these technologies.”


Robert Hughes


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