We synergistically integrated bottom-up controlled nanotube synthesis with top-down microfabrication. Here, we developed a reliable, scalable CNT size-tunable enrichment microdevice (CNT-STEM) technology that provides size-based, label-free, viable enrichment of viruses from field samples. Although CNTs have been used as biochemical sensors ( 28), imaging probes ( 29), drug delivery vehicles ( 30), x-ray sources ( 31), neuron protection ( 32), treatment of drug addiction ( 33), and substrates for immunological capture of mammalian cells and bacteria ( 34), they have not been integrated into tunable devices able to isolate viruses of different sizes. In this context, robust arrays of aligned carbon nanotubes (CNTs) with controlled intertube distance could be used to effectively trap/concentrate viruses within a three-dimensional (3D) porous system. Although ultrafiltration membranes are widely used as an essential viral clearance step in the biopharmaceutical production from human or animal origin ( 21, 27), their usage for virus detection is rare, primarily because of their low porosity, high operation pressure, poor virus viability, and difficulty in virus access for further analysis. It is normally used as one of the steps in the whole sample preparation protocol for virus analysis however, it neither removes contaminants of small size (for example, nucleic acids and proteins) nor concentrates the sample ( 24– 26). Microfiltration membranes can remove large particles within samples while keeping the virus particles in the supernatant. Unfortunately, it involves bulky equipment, intensive labor, and lengthy sample preparation, and has limitations for concentrating small amounts of viruses in minute volumes ( 15, 22, 23). Ultracentrifugation is the most commonly used physical method for virus enrichment and concentration. Unfortunately, immunological capture requires previous knowledge of the targets thus, it is not appropriate for virus discovery and can lead to technical difficulties in identifying new or emerging virus strains. In addition, the most conventional virus sample preparation protocols use immunological capture, physical separation, or a combination of both ( 21, 22). However, additional advancements in the sample preparation techniques are urgently needed to enrich and concentrate viruses ( 16– 20). Our unique method demonstrates the early detection of emerging viruses and the discovery of new viruses directly from field samples, thus creating a universal platform for effectively remediating viral infectious diseases.īecause the high mutation rate and the genetic diversity of viruses warrant extensive surveillance ( 9), various virus detection approaches have been established: (i) enzyme-linked immunosorbent assay (ELISA) ( 10), (ii) polymerase chain reaction (PCR) ( 11, 12), (iii) virus isolation ( 13, 14), and (iv) next-generation sequencing (NGS) ( 5, 15). Using this device, we successfully identified an emerging avian influenza virus strain and a novel virus strain (IBDV/turkey/PA/00924/14). The CNT-STEM significantly improves detection limits and virus isolation rates by at least 100 times. The channel sidewall in the microdevice was made by growing arrays of vertically aligned nitrogen-doped multiwalled CNTs, where the intertubular distance between CNTs could be engineered in the range of 17 to 325 nm to accurately match the size of different viruses. We report a unique carbon nanotube size-tunable enrichment microdevice (CNT-STEM) that efficiently enriches and concentrates viruses collected from field samples. Although established methods, such as polymerase chain reaction, virus isolation, and next-generation sequencing have been used to detect viruses, field samples with low virus count pose major challenges in virus surveillance and discovery. Viral infectious diseases can erupt unpredictably, spread rapidly, and ravage mass populations.
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