A new study from Vall d'Hebron has analyzed the use of synthetic erythrocytes versus fresh animal erythrocytes in hemagglutination (HA) and hemagglutination inhibition (HAI) assays used for the control of influenza viruses. Preliminary results show that the synthetic reagent works properly, as well as being faster and more stable. This research is led by the CIBBIM Nanomedicine -Diagnostic Nanotools group of the Vall d'Hebron Research Institute (VHIR), in collaboration with the Respiratory Virus Unit of the Microbiology Service of the Vall d'Hebron Hospital, and the VHIR Molecular Medical Imaging Group. The study was published in the journal https://pubs.acs.org/doi/10.1021/acssensors.0c01830 ACS Sensors.Hemagglutination (HA) and hemagglutination inhibition (HAI) assays are reference serological tests that have been used since the 1960s to analyze different parameters. For example, these techniques are used to determine which influenza viruses are circulating at any given time and to study the level of immunity of the population against these viruses. This task, which is carried out by an international network of laboratories under the coordination of the World Health Organization (WHO), provides the information needed to annually recommend the composition of the influenza vaccine, and is also crucial to anticipate in time the appearance of especially dangerous viruses. Both HA and HAI are simple and inexpensive techniques, do not require sophisticated equipment and generate results in hours. The problem is that the technique must be performed using erythrocytes of animal origin, which have a short half-life (Syntrocytes, a synthetic reagent that mimics erythrocytes in the HA and HAI assays, have been developed in the study, without having to alter the methodology currently used by laboratories around the world. Syntrocytes are produced by chemically modifying existing microparticles using a simple procedure developed by the Diagnostic Nanotools group. Ana Sánchez-Cano, predoctoral researcher in this group and first author of the publication, emphasizes: "These syntrocytes recognize influenza A and B viruses faster than native erythrocytes -5 minutes compared to 30-60 that take animal erythrocytes- and are more stable. Therefore, they could be a good alternative as a synthetic agent".The interaction between synchrocytes and influenza viruses can be inhibited with a specific antibody against that virus, which allows HAI-like assays for antigenic characterization of the virus and population serological studies.The results show that it is possible to replace erythrocytes with a synthetic reagent that generates results more quickly and can be adapted to the laboratory to adjust its specificity to different viruses. "The mass production of syntrocytes would allow their global distribution, which would facilitate the standardization of HA and HAI methods worldwide, providing improved tools for the monitoring of pathogens and the control of vaccine production", says Dr. Eva Baldrich, head of the Nanotools Diagnostic group.