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Although H5N1 avian influenza has not yet acquired the capacity to readily infect humans, should it do so, this viral pathogen would present an increasing threat to the immunologically naive human population. Subunit vaccines based on the viral glycoprotein hemagglutinin (HA) can provide protective immunity against influenza. Polyanhydride nanoparticles have been shown to enhance efficacy of subunit vaccines, providing the dual advantages of adjuvanticity and sustained delivery resulting in enhanced protein stability and immunogenicity. In this work, a recombinant trimer of H5 (H53 ) was encapsulated and released from polyanhydride nanoparticles. Release kinetics of the encapsulated H53 were found to be dependent on polymer chemistry (i.e., hydrophobicity and molecular weight). Polyanhydride nanoparticles composed of sebacic anhydride and 1,6-bis(p-carboxyphenoxy)hexane (CPH; that degrade into more acidic monomers) released structurally stable HA H53 , while H53 released from formulations composed of CPH and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) (that are amphiphilic and whose degradation products are less acidic) displayed unfolding of tertiary structure. However, the antigenicity of the H53 based on binding of a H5-specific monoclonal antibody was preserved upon release from all the formulations studied, demonstrating the value of polyanhydride nanoparticles as a viable platform for HA-based influenza vaccines.

This minireview highlights recent advances of research dedicated to photoswitchable fluorescent nanoparticles and their applications. Recently, several strategies have been developed to synthesize nanoparticles with optically switchable emission properties: either fluorescence on/off or dual-alternating-color fluorescence photoswitching. The underlying mechanisms of fluorescence photoswitching enable many different types of photoswitchable fluorescent nanoparticles to change fluorescence colors, thus validating the basis of the initial photoswitching design. Among all possible applications, the usage of photoswitchable fluorescent nanoparticles to empower super-resolution fluorescence imaging and to label biological targets was subsequently reviewed. Finally, we summarize the important areas regarding future research and development on photoswitchable fluorescent nanoparticles.