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      Electrochemical Capillary-Flow Immunoassay for Detecting Anti-SARS-CoV-2 Nucleocapsid Protein Antibodies at the Point of Care

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          Abstract

          Rapid and inexpensive serological tests for SARS-CoV-2 antibodies are needed to conduct population-level seroprevalence surveillance studies and can improve diagnostic reliability when used in combination with viral tests. Here, we report a novel low-cost electrochemical capillary-flow device to quantify IgG antibodies targeting SARS-CoV-2 nucleocapsid proteins (anti-N antibody) down to 5 ng/mL in low-volume (10 μL) human whole blood samples in under 20 min. No sample preparation is needed as the device integrates a blood-filtration membrane for on-board plasma extraction. The device is made of stacked layers of a hydrophilic polyester and double-sided adhesive films, which create a passive microfluidic circuit that automates the steps of an enzyme-linked immunosorbent assay (ELISA). The sample and reagents are sequentially delivered to a nitrocellulose membrane that is modified with a recombinant SARS-CoV-2 nucleocapsid protein. When present in the sample, anti-N antibodies are captured on the nitrocellulose membrane and detected via chronoamperometry performed on a screen-printed carbon electrode. As a result of this quantitative electrochemical readout, no result interpretation is required, making the device ideal for point-of-care (POC) use by non-trained users. Moreover, we show that the device can be coupled to a near-field communication potentiostat operated from a smartphone, confirming its true POC potential. The novelty of this work resides in the integration of sensitive electrochemical detection with capillary-flow immunoassay, providing accuracy at the point of care. This novel electrochemical capillary-flow device has the potential to aid the diagnosis of infectious diseases at the point of care.

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          Fair Allocation of Scarce Medical Resources in the Time of Covid-19

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            Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study

            Summary Background Spain is one of the European countries most affected by the COVID-19 pandemic. Serological surveys are a valuable tool to assess the extent of the epidemic, given the existence of asymptomatic cases and little access to diagnostic tests. This nationwide population-based study aims to estimate the seroprevalence of SARS-CoV-2 infection in Spain at national and regional level. Methods 35 883 households were selected from municipal rolls using two-stage random sampling stratified by province and municipality size, with all residents invited to participate. From April 27 to May 11, 2020, 61 075 participants (75·1% of all contacted individuals within selected households) answered a questionnaire on history of symptoms compatible with COVID-19 and risk factors, received a point-of-care antibody test, and, if agreed, donated a blood sample for additional testing with a chemiluminescent microparticle immunoassay. Prevalences of IgG antibodies were adjusted using sampling weights and post-stratification to allow for differences in non-response rates based on age group, sex, and census-tract income. Using results for both tests, we calculated a seroprevalence range maximising either specificity (positive for both tests) or sensitivity (positive for either test). Findings Seroprevalence was 5·0% (95% CI 4·7–5·4) by the point-of-care test and 4·6% (4·3–5·0) by immunoassay, with a specificity–sensitivity range of 3·7% (3·3–4·0; both tests positive) to 6·2% (5·8–6·6; either test positive), with no differences by sex and lower seroprevalence in children younger than 10 years ( 10%) and lower in coastal areas (<3%). Seroprevalence among 195 participants with positive PCR more than 14 days before the study visit ranged from 87·6% (81·1–92·1; both tests positive) to 91·8% (86·3–95·3; either test positive). In 7273 individuals with anosmia or at least three symptoms, seroprevalence ranged from 15·3% (13·8–16·8) to 19·3% (17·7–21·0). Around a third of seropositive participants were asymptomatic, ranging from 21·9% (19·1–24·9) to 35·8% (33·1–38·5). Only 19·5% (16·3–23·2) of symptomatic participants who were seropositive by both the point-of-care test and immunoassay reported a previous PCR test. Interpretation The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas. Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic. These results emphasise the need for maintaining public health measures to avoid a new epidemic wave. Funding Spanish Ministry of Health, Institute of Health Carlos III, and Spanish National Health System.
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              Immune response to SARS‐CoV‐2 and mechanisms of immunopathological changes in COVID‐19

              Abstract As a zoonotic disease that has already spread globally to several million human beings and possibly to domestic and wild animals, eradication of coronavirus disease 2019 (COVID‐19) appears practically impossible. There is a pressing need to improve our understanding of the immunology of this disease to contain the pandemic by developing vaccines and medicines for the prevention and treatment of patients. In this review, we aim to improve our understanding on the immune response and immunopathological changes in patients linked to detoriating clinical conditions such as, cytokine storm, acute respiratory distress syndrome, autopsy findings and changes in acute phase reactants and serum biochemistry in COVID‐19. Similar to many other viral infections, asymptomatic disease is present in a significant but currently unknown fraction of the affected individuals.In the majority of the patients, a one‐week, self‐limiting viral respiratory disease typically occurs, which ends with the development of neutralizing anti‐viral T cell and antibody immunity. The IgM, IgA and IgG type virus‐specific antibodies levels are important measurements to predict population immunity against this disease and whether cross‐reactivity with other coronaviruses is taking place.High viral‐load during the first infection and repeated exposure to virus especially in healthcare workers can be an important factor for severity of disease. It should be noted that many aspects of severe patients are unique to COVID‐19 and are rarely observed in other respiratory viral infections, such as severe lymphopenia and eosinopenia, extensive pneumonia and lung tissue damage, a cytokine storm leading to acute respiratory distress syndrome and multiorgan failure. Lymphopenia causes a defect in antiviral and immune regulatory immunity. At the same time, a cytokine storm starts with extensive activation of cytokine‐secreting cells with innate and adaptive immune mechanisms both of with contribute to a poor prognosis. Elevated levels of acute phase reactants and lymphopenia are early predictors of high disease severity. Prevention of development to severe disease, cytokine storm, acute respiratory distress syndrome and novel approachs to prevent their development will be main routes for future research areas. As we learn to live amidst the virus, understanding the immunology of the disease can assist in containing the pandemic and in developing vaccines and medicines to prevent and treat individual patients.
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                Author and article information

                Journal
                ACS Sens
                ACS Sens
                se
                ascefj
                ACS Sensors
                American Chemical Society
                2379-3694
                25 October 2021
                : acssensors.1c01527
                Affiliations
                []Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523, United States
                []Department of Chemical and Biological Engineering, Colorado State University , Fort Collins, Colorado 80523, United States
                [§ ]Diagnostic Nanotools Group, Institut de Recerca , Vall d’Hebron Barcelona Hospital Campus, Barcelona 08035, Spain
                []Universitat Autónoma de Barcelona , Barcelona 08193, Spain
                []Department of Chemistry, Faculty of Science, Srinakharinwirot University , Bangkok 10110, Thailand
                [# ]Institute of Nano Science and Technology, Hanyang University , Seoul 04763, South Korea
                []Department of Microbiology, Immunology, and Pathology, Colorado State University , Fort Collins, Colorado 80523, United States
                []School of Biomedical Engineering, Colorado State University , Fort Collins, Colorado 80523, United States
                Author notes
                Author information
                https://orcid.org/0000-0003-1393-215X
                https://orcid.org/0000-0003-3254-0717
                https://orcid.org/0000-0002-8671-7728
                Article
                10.1021/acssensors.1c01527
                8565458
                34694794
                0da83450-ee73-4392-8aa0-ce2df80e4254
                © 2021 American Chemical Society

                This article is made available via the PMC Open Access Subset for unrestricted RESEARCH re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

                History
                : 19 July 2021
                : 12 October 2021
                Funding
                Funded by: National Institutes of Health, doi 10.13039/100000002;
                Award ID: R01 AI132668
                Funded by: Science Achievement Scholarship of Thailand, doi NA;
                Award ID: NA
                Funded by: Balanced Biotech Inc., doi NA;
                Award ID: NA
                Funded by: European Regional Development Fund, doi 10.13039/501100008530;
                Award ID: MV19/00036
                Funded by: European Regional Development Fund, doi 10.13039/501100008530;
                Award ID: IFI18/00020
                Funded by: European Regional Development Fund, doi 10.13039/501100008530;
                Award ID: CPII18/00025
                Funded by: Colorado State University, doi 10.13039/100007235;
                Award ID: NA
                Categories
                Article
                Custom metadata
                se1c01527
                se1c01527

                point-of-care (poc) diagnostics,capillary-flow device,electrochemistry,sars-cov-2,serology

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