Gold nanoparticles have favorable characteristics for their use as the basis for multifunctional microorganism simulants [18] . Nanoparticle size, shape, and capacity for surface modifications, based on chemical characteristics and environments, make the use of nanoparticles advantageous for detection, discovery, and diagnosis [7, 19] . Previous studies have shown that nanoparticles are capable of accepting a wide array of functional molecules via the Au-thiol bonds at the interface of the ligand and particle [20] . Since the physical and chemical properties of nanoparticles are dependent upon size [6] , the gold nanoparticles can be customized to simulate the variability in pathogen size. MPCs in this work had an average diameter of 2.6± 0.6 nm. Influenza virions vary in size, normally around 100 nm in diameter, but smaller nanoparticles were chosen in this study since they have a larger surface area to volume ratio and therefore increase the ratio of possible antigen presentation to gold core [21] . These nanoparticles were polyfunctionalized to increase the presentation of the nanoparticle epitope to the antibody. Previous studies have found multivalent ligand attachment to gold nanoparticles enhances the affinity measured in binding studies [22, 23] . The selectivity of antibody sensors for functionalized MPCs has been examined using two orthogonal epitopes: FLAG and HA. The FLAG epitope is a biological peptide sequence commonly used for identification of proteins in biological samples [24] . HA-and FLAG-functionalized MPCs can be used as a synthetic simulant and negative control for the HA epitope of the influenza virus [25, 26] . The binding of these nanoparticles was also compared with binding of negative-control Au-tiopronin nanoparticles and an authentic sample of H5 HA proteins from influenza virus (H5N1). The simulants work as safe controls whose application could be extended to address various pathological threats, in which using attenuated controls is problematic.