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We have encapsulated self-organized protein superstructures containing cytochrome c into a mesoporous silica-based nanoarchitecture. The protein superstructure, nucleated by colloidal gold in buffered medium and nanoglued with silica sol, remains intact upon supercritical drying of the wet composite gel and exhibits rapid gas-phase recognition of NO. We posit that specific adsorption of the heme edge at nanoparticulate Au creates a high radius-of-curvature nanoscale hybrid that induces protein−protein self-directed assembly. We also have evidence that an outer “skin” of protein is damaged upon experiencing the chemical and physical denaturants necessary to create an aerogel but that this sacrificial layer shields the proteins within the superstructure. Transmission electron microscopy verifies that objects on the order of 102 nm are present in the biocomposite silica aerogel. The temperature−pressure stability exhibited by the protein in the biocomposite nanoarchitecture may provide an experimental, sea-level analogy to prebiotic hypotheses, which propose that cellular evolution occurred in hydrothermal vents within porous minerals that stabilized precellular progenitors.

We recently discovered that self-organized superstructures of the heme protein cytochrome c (cyt. c) are nucleated in buffer by gold nanoparticles. The protein molecules within the superstructure survive both silica sol-gel encapsulation and drying from supercritical carbon dioxide to form air-filled biocomposite aerogels that exhibit gas-phase binding activity for nitric oxide. In this investigation, we report that viable proteins are present in biocomposite aerogels when the nucleating metal nanoparticle is silver rather than gold. Silver colloids were synthesized via reduction of an aqueous solution of Ag+ using either citrate or borohydride reductants. As determined by transmission electron microscopy and UV-visible absorption spectroscopy, the silver nanoparticles vary in size and shape depending on the synthetic route, which affects the fraction of cyt. c that survives the processing necessary to form a biocomposite aerogel. Silver colloids synthesized via the citrate preparation are polydisperse, with sizes ranging from 1 to 100 nm, and lead to low cyt. c viability in the dried bioaerogels (approximately 15%). Protein superstructures nucleated at approximately 10-nm Ag colloids prepared via the borohydride route, including citrate stabilization of the borohydride-reduced metal, retain significant protein viability within the bioaerogels (approximately 45%).