Sensing humidity using virus-nanoparticle assembly

A virus-gold nanoparticle (AuNP) composite film was prepared through the layer-by-layer assembly of cationic filamentous virus (M13 phage) particles (displaying a positively charged peptide on the major coat) and anionic spherical AuNPs. The surface plasmon resonance (SPR) for AuNPs in the virus-nanoparticle nanocomposite films was found to be sensitive to the environmental humidity. In air, both ¿_max and peak absorbance of the SPR spectra of the nanocomposite films are linearly dependent on the environmental humidity. We believe that when the environmental humidity is reduced, the height of the phage particles in the nanocomposite films is reduced, leading to the shortening of the spacing between neighboring gold nanoparticles in the films. Therefore, the SPR band systematically redshifts with the decrease in humidity. Furthermore, the response of the virus-nanoparticle film to the humidity is rapid and reversible, which favors in it for humidity sensing application.