Tight spatial distribution control of the bacteriophage-mediated incorporation of gold nanoparticles. A. XPS depth profiling analysis of the gold distribution as a function of the film depth, converted to nanoparticle to phage ratio for different film architectures. The top panel shows the distribution for nanoparticles infiltrated post-assembly, while the bottom panel shows films that were assembled with phage-nanoparticle complexes. B. SEM image of a phage film infiltrated with AuNPs, and coated with titania. The bright circles are the AuNPs dispersed within the nanowire mesh. C. Comparison of optical properties of AuNPs under different conditions; freely suspended in water, complexed to bacteriophages in solution, and incorporated into 59% porous dried bacteriophage films during LbL, or dropcast onto a film post-assembly. The theoretical prediction for each peak is shown with a dotted vertical line corresponding to the color of the experimental data. D. Shift in AuNPs absorption peak observed upon coating of the bacteriophage film with titania, before and after crystallization.