New nanoimmunoassay can detect anti–SARS-CoV-2 antibodies in ultralow-volume blood samples

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The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been the largest global public health crisis in recent memory. To date, it has been responsible for over 158.3 million infections and over 3.3 million deaths the world over.

Managing this crisis, mitigating viral spread, and planning to prepare for the next phase of the pandemic involves numerous testing and analysis regimes. Continuous monitoring of the virus spread to control the disease, the efficacy of vaccines in trials, current infection fatality rates and the health status post-vaccination, call for a large sampling of blood and tests to detect the seroprevalence of SARS-CoV-2.

In a recent study, researchers developed and validated a nanoimmunoassay (NIA) that analyzes 1,024 samples in parallel on a single microfluidic device the size of a USB stick. They detected anti-SARS-CoV-2 IgG antibodies, achieving a sensitivity of 98% and specificity of 100% based on an analysis of 134 pre-pandemic sera (collected in 2013/2014 and 2018) and 155 sera from reverse transcription-polymerase chain reaction (RT-PCR) confirmed COVID-19 positive individuals. The study is published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

The results from the study indicated that an accurate binary classification of serum samples could be achieved with NIA. The study involves a detailed development and validation of the NIA method and a rigorous analysis and testing of ultralow-volume whole blood collection.

In this study, the researchers analyzed samples obtained more than 20-day post-onset of symptoms, and also for samples obtained less than 20-day past onset of symptoms – in both cases, the NIA results performed excellently. They demonstrated that NIA could be used to detect anti–SARS-CoV-2 antibodies in ultra low-volume dried whole blood samples (eliminating the need for venipuncture blood collection).

The platform capabilities can be expanded to include multiplexed analysis, allowing four or more biomarkers – multiple antigens, cytokines, or inflammatory markers – to be tested for each sample to gain insights into the viral infection and response.

Consumables, reagent consumption, and associated costs are negligible with NIA, which is an important consideration when compared to the high reagent cost of ELISAs and when considering potential reagent shortages that may be encountered during critical phases in a global pandemic.”

The current testing methods, such as ELISA, chemiluminescent immunoassays (CLIA), or Lateral flow assays (LFAs), require venipuncture for blood collection, followed by sample pretreatment, and involve costly reagents and testing procedures; all of which precludes comprehensive testing and contributes to high healthcare costs. The main advantages presented here are that this assay relies on a repurposed blood from a glucose test strip (finger prick) and other low-cost blood sampling methods to eliminate the need for venipuncture, and is capable of analyzing up to 1,024 samples per device. Also, the NIA reagent consumption and corresponding costs are roughly 1,000 times lower than standard enzyme-linked immunosorbent assays (ELISA).

To implement this method, the researchers explained that laboratories require a commercially available contact microarrayer, and the ability to fabricate masks, molds, and PDMS microfluidic devices, which can be fabricated easily using a spin coater, 80°C ovens, and stereomicroscope. The device readout is performed on a standard epifluorescence microscope equipped with an automated stage.

The researchers tested two commercial blood collection devices: Neoteryx’s Mitra® and DBS System SA’s HemaXisTM DB10, to show the possibility to repurpose low-cost and widely available blood glucose test strips for sample collection and shipment. Samples could be stored up to 6 d at room temperature with minimal sample degradation. The researcher demonstrated that all three methods combined with NIA identified more positive samples than a standard ELISA performed on serum samples collected from the same individuals.

The researchers foresee that an individual can purchase a simple blood sampling kit containing a lancet, a blood sampling device, and a return mail envelope at a local pharmacy or supermarket. Then, the individual can collect the blood with a simple finger prick, and send the device with the blood sample to a laboratory which will analyze for one or more biomarkers, interpret the data, and return the test results to the individual via electronic communication.

The method in this study can be used to analyze large samples collected as part of epidemiological studies, identifying donors for plasma therapy as well as offering vaccine trial support. During a global pandemic, such technologies could enable the collection of critical epidemiological data, providing instrumental data for vaccine development and vaccine rollout, the researchers write.

The combination of a high-throughput, highly specific and sensitive NIA and the ability to analyze minute volumes of dried blood samples have enormous potential for SARS-CoV-2 serology, epidemiological studies, vaccine trial, and therapeutic development support.”

Journal reference:
  • Zoe Swank, Grégoire Michielin, Hon Ming Yip, Patrick Cohen, Diego O. Andrey, Nicolas Vuilleumier, Laurent Kaiser, Isabella Eckerle, Benjamin Meyer, Sebastian J. Maerkl. A high-throughput microfluidic nanoimmunoassay for detecting anti–SARS-CoV-2 antibodies in serum or ultralow-volume blood samples. Proceedings of the National Academy of Sciences. May 2021, 118 (18) e2025289118; DOI:,
Dr. Ramya Dwivedi

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.


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