Conspectus Plasmons, collective oscillations of conduction band electrons in nanoscale metals, are well-known phenomena in colloidal gold and silver nanocrystals that produce brilliant visible colors in these materials that depend on nanocrystal size and shape. Under illumination at or near the plasmon bands, gold and silver nanocrystals exhibit properties that enable fascinating biological applications: (i) the nanocrystals elastically scatter light, providing a straightforward way to image them in complex aqueous environments; (ii) the nanocrystals produce local electric fields that enable various surface-enhanced spectroscopies for sensing, molecular diagnostics, and boosting bound fluorophore performance; (iii) the nanocrystals produce heat, which can lead to chemical transformations at or near the nanocrystal surface, and can photothermally destroy nearby cells. While all the above-mentioned applications have already been well-demonstrated in the literature, this Account focuses on several other aspects of these nanomaterials, in particular gold nanorods that are approximately the size of viruses (diameters ~10 nm, lengths up to 100 nm). Absolute extinction, scattering, and absorption properties are compared for gold nanorods of various absolute dimensions, and references for how to synthesize gold nanorods of four different absolute dimensions are provided. Surface chemistry strategies are detailed that coat nanocrystals with smooth or rough shells; specific examples include mesoporous silica and metal-organic framework shells for porous (rough) coatings, and polyelectrolyte layer-by-layer wrapping for “smooth” shells. For self-assembled monolayer molecular coating ligands, the smoothest shells of all, a wide range of ligand densities have been reported from many experiments, yielding values from less than 1 to nearly 10 molecules/nm2 depending on nanocrystal size and ligand nature. Systematic studies of ligand density for one particular ligand with a bulky headgroup are highlighted, showing that the largest ligand density occurs for the smallest nanocrystals, even though these ligand headgroups are the most mobile as judged by NMR relaxation studies. Biomolecular coronas form around spherical and rod-shaped nanocrystals upon immersion into biological fluids; these proteins, and lipids, can be quantified, and their degree of adsorption depends on nanocrystal surface chemistry as well as biophysical characteristics of the adsorbing biomolecule. Photothermal adsorption and desorption of proteins on nanocrystals depend on the enthalpy of protein-nanocrystal surface interactions, leading to light-triggered alteration in protein concentrations near the nanocrystals. At the cellular scale, gold nanocrystals exert genetic changes at the mRNA level, with a variety of likely mechanisms that include alteration of local biomolecular concentration gradients, changing mechanical properties of the extracellular matrix, and physical interruption of key cellular processes - even without plasmonic effects. Microbiomes, both...

Upon exposure to a biological environment, nanoparticles (NPs) acquire biomolecular coatings, the most studied of which is the protein corona. This protein corona gives NPs a new biological identity that will determine various biological responses including cellular uptake, biodistribution, and toxicity. The standard method to isolate NPs from a biological matrix in order to study their coronas is centrifugation, but more gentle means of retrieval may enable deeper understanding of both irreversibly bound hard coronas and more loosely bound soft coronas. In this study, magnetic gold-coated iron oxide NPs were incubated with rainbow trout gill cell total protein extracts and mass spectrometric proteomic analysis was conducted to determine the composition of the protein coronas isolated by either centrifugation or magnetic retrieval. The number of washes were varied to strip away the soft coronas and isolate the hard corona. Hundreds of proteins were adsorbed to the NPs. Some proteins were common to all isolation methods and many others were particular to the isolation method. Some qualitative trends in protein character were discerned from quantitative proteomic analyses, but more importantly, a new kind of protein corona was identified, mixed corona, in which the labile or inert nature of the protein−NP interaction is dependent upon sample history.

The wide applications of lithium intercalating complex metal oxides in energy storage devices call for a better understanding of their environmental impact at the end of their life cycle. In this study, we examine the biological impact of a panel of nanoscale lithium nickel manganese cobalt oxides (LixNiyMnzCo1−y−zO2, 0 < x, y, z < 1, abbreviated to NMCs) to a model Gram-positive bacterium, Bacillus subtilis, in terms of cellular respiration and growth. A highly sensitive single-cell gel electrophoresis method is also applied for the first time to understand the genotoxicity of these nanomaterials to bacterial cells. Results from these assays indicate that the free Ni and Co ions released from the incongruent dissolution of the NMC material in B. subtilis growth medium induced both hindered growth and cellular respiration. More remarkably, the DNA damage induced by the combination of the two ions in solution is comparable to that induced by the NMC material, which suggests that the free Ni and Co ions are responsible for the toxicity observed. A material redesign by enriching Mn is also presented. The combined approaches of evaluating their impact on bacterial growth, respiration, and DNA damage at a single-cell level, as well as other phenotypical changes allows us to probe the nanomaterials and bacterial cells from a mechanistic prospective, and provides a useful means to an understanding of bacterial response to new potential environmental stressors.