Adsorption and Unfolding of a Single Protein Triggers Nanoparticle Aggregation.

The response of living systems to nanoparticles is thought to depend on the protein corona, which forms shortly after exposure to physiological fluids and which is linked to a wide array of pathophysiologies. A mechanistic understanding of the dynamic interaction between proteins and nanoparticles and thus the biological fate of nanoparticles and associated proteins is, however, often missing mainly due to the inadequacies in current ensemble experimental approaches. Through the application of a variety of single molecule and single particle spectroscopic techniques in combination with ensemble level characterization tools, we identified different interaction pathways between gold nanorods and bovine serum albumin depending on the protein concentration. Overall, we found that local changes in protein concentration influence everything from cancer cell uptake to nanoparticle stability and even protein secondary structure. We envision that our findings and methods will lead to strategies to control the associated pathophysiology of nanoparticle exposure in vivo.

Plasmonic properties of regiospecific core-satellite assemblies of gold nanostars and nanospheres.

Solution-based molecularly-mediated bottom-up assembly of gold nanostars and nanospheres in regiospecific core-satellite nanoarchitectures is reported. The controlled assembly is driven by coupling reactions in solution between small, rigid, Raman-active organic molecules bound to the surface of the nanoparticles, and leads to much narrower interparticle gaps than achievable with DNA-based assembly methods. In the described system, gold nanostars with multiple sharp spikes, ideal for electromagnetic field enhancement, are used as the core particle onto which spherical satellites are assembled. Transmission electron micrographs show that the core-satellite structures assemble with <2 nm interparticle gaps and regiospecific binding of only one sphere per spike, and the process can be followed by monitoring changes in the surface enhanced Raman scattering (SERS) spectra of the Raman active linkers. The assembled structures give rise on average to two orders of magnitude SERS signal enhancement per nanoparticle in comparison to their constituents, which can be attributed to the creation of SERS "hot spots" between the nanostar tip and the satellite sphere. Two dimensional finite element electromagnetic models show strongly confined electromagnetic field intensity in the narrow interparticle gaps of core-satellite assemblies, which is significantly enhanced in comparison to the constituent nanoparticles, thus corroborating the experimental findings. Thus, the assemblies reported here can be envisioned as SERS-tags for imaging purposes as well as a model system for SERS-based chemical sensing with improved sensitivity.

Dimeric gold nanoparticle assemblies as tags for SERS-based cancer detection.

Herein, a new class of multifunctional materials combining a clustered nanoparticle-based probe is presented for surface enhanced Raman scattering (SERS)-based microscopy and surface functionalization for tissue targeting. Controlled assembly of spherical gold nanoparticles into dimers (DNP-REP) is engineered using a small, rigid Raman-active dithiolated linking reporter (REP) to yield narrow internanoparticle gaps and to strategically generate the "hot spot" while concurrently placing the reporter within the region of highest SERS enhancement. Peptide functionalized DNP-REP materials are highly stable even upon incubation with living cells and show controlled levels of binding and intracellular endocytosis. To demonstrate the functionality of such probes for disease detection, differentially targeted DNP-REPs are incubated over various time points with cultured human glioblastoma cells. Using human glioblastoma cells, the SERS maps of targeted tumor cells show the markedly enhanced signals of the DNP-REP, compared to conventional confocal fluorescence based approaches, especially at low incubation times. Even with as few as 40 internalized DNP-REP, a relatively intense SERS signal is measured, demonstrating the high signal to noise ratio and inherent biocompatibility of the materials. Thus, these Raman reporter-based nanoparticle cluster probes present a promising and versatile optical imaging tool for fast, reliable, selective, and ultrasensitive tissue targeting and disease detection and screening.