MOESM1 of Polylysine as a functional biopolymer to couple gold nanorods to tumor-tropic cells

Additional file 1. Additional figures

Partial Decoupling in Aggregates of Silanized Gold Nanorods

The introduction of gold nanorods as contrast agents for applications in biomedical optics is receiving significant interest. However, particle aggregation in endocytic vesicles may jeopardize their great potential of photothermal or photoacoustic conversion because the multitude of couplings in tight clusters of plasmonic particles deteriorates their functional fingerprints of optical extinction. Here, we investigate the benefit of silanization on self-aggregated gold nanorods as a function of their shell width. We have increased this parameter from zero up to a value similar to the particle diameters, that is, about 12 nm in our case. With this shell width, we have recovered two distinct peaks in the green and near-infrared sides of the experimental spectrum, with the latter about 2-fold higher than its uncapped counterpart. This result points to a significant decoupling between neighboring particles. We interpret our experimental results in terms of the residual couplings in building blocks that yield the greatest optical response, which are pairs of particles in a so-called end-to-end configuration. Our simulations account for the coexistence of particles with different shapes and orientations and reproduce well both their longitudinal and transverse modes of plasmonic oscillations

Controlled Veiling of Silver Nanocubes with Graphene Oxide for Improved Surface-Enhanced Raman Scattering Detection

Hybrid graphene oxide (GO)/metal nanocomposites have been recently proposed as novel surface-enhanced Raman scattering (SERS) substrates. Despite an increasing interest in these systems, standardization in their fabrication process is still lacking but urgently required to support their use for real-life applications. In this work we investigate how the assembly of GO should be conducted to control adsorption geometry and optical properties at the interface with plasmonic nanostructures as monolayer assemblies of silver nanocubes, by tuning main experimental parameters including GO concentration and self-assembly time. We finally identified the experimental conditions for building up a close-fitting soft dressing of the plasmonic surface, which shows optimal characteristics for flexible and reliable SERS detection

SERS Detection of Amyloid Oligomers on Metallorganic-Decorated Plasmonic Beads

Protein misfolded proteins are among the most toxic endogenous species of macromolecules. These chemical entities are responsible for neurodegenerative disorders such as Alzheimer’s, Parkinson’s, Creutzfeldt–Jakob’s and different non-neurophatic amyloidosis. Notably, these oligomers show a combination of marked heterogeneity and low abundance in body fluids, which have prevented a reliable detection by immunological methods so far. Herein we exploit the selectivity of proteins to react with metallic ions and the sensitivity of surface-enhanced Raman spectroscopy (SERS) toward small electronic changes in coordination compounds to design and engineer a reliable optical sensor for protein misfolded oligomers. Our strategy relies on the functionalization of Au nanoparticle-decorated polystyrene beads with an effective metallorganic Raman chemoreceptor, composed by Al³⁺ ions coordinated to 4-mercaptobenzoic acid (MBA) with high Raman cross-section, that selectively binds aberrant protein oligomers. The mechanical deformations of the MBA phenyl ring upon complexation with the oligomeric species are registered in its SERS spectrum and can be quantitatively correlated with the concentration of the target biomolecule. The SERS platform used here appears promising for future implementation of diagnostic tools of aberrant species associated with protein deposition diseases, including those with a strong social and economic impact, such as Alzheimer’s and Parkinson’s diseases

Size Affects the Stability of the Photoacoustic Conversion of Gold Nanorods

Gold nanorods exhibit intense optical absorption bands in the near-infrared region of principal interest for applications in biomedical optics, which originate from sharp plasmon resonances. This high absorbance, combined with the biochemical inertness and targetability of gold nanoparticles, makes these materials excellent candidates to provide contrast in photoacoustic imaging and for other applications such as the selective hyperthermia of cancer. One issue demoting the potential of gold nanorods as contrast agents in photoacoustic applications is their limited photostability, which falls below relevant permissible exposure limits. In particular, when gold nanorods are resonantly excited by laser pulses in the nanosecond duration regime, there may occur phenomena like reshaping into rounder nanoparticles as well as fragmentation and sublimation, which modify their optical absorption bands and hinder their efficiency of photoacoustic conversion. Here we investigate the influence of nanoparticle size on the photostability and reproducibility of photoacoustic conversion of gold nanorods embedded in biomimetic phantoms. We compare samples containing gold nanorods with different sizes but the same shapes and overall optical densities. We demonstrate clear size effects as the thresholds of optical fluences for nanoparticle deformation improve from below 2 to above 6 mJ/cm² with nanoparticle miniaturization from 22 to 5 nm effective radii. We interpret these results in terms of a better thermal coupling and faster heat dissipation from smaller nanoparticles to their environment, originating from their larger specific surface area

Photostability of Gold Nanorods upon Endosomal Confinement in Cultured Cells

The photoinstability of plasmonic particles remains one remarkable obstacle before their clinical penetration as powerful contrast agents, for instance, in photoacoustic imaging. In particular, gold nanorods easily revert to nanospheres and so lose their best optical features under exposure to few-nanoseconds-long laser pulses. While this issue is attracting much attention and stimulating ad hoc solutions, such as the addition of rigid shells, the biological environment may cause even more instability. For instance, a frequent outcome of the interaction between this type of particles and malignant or immune cells is their tight confinement into endocytic vesicles. In this study, we assess whether this configuration may make an adverse impact on the photostability of gold nanorods, due to the effect of heat confinement. We compare experimental measurements from a limited set of representative samples and verify their relevance by the use of numerical simulations. Under conditions that are typical for photoacoustic microscopy, we estimate the threshold fluence for the onset of photoinstability to remain around 7 mJ·cm^–2, independent of the distance among neighboring particles, within accessible limits. Then, we simulate the effect of pulse duration in our model of endocytic confinement. Only in a μs regime of lesser potential for biomedical optics do we predict this configuration to destabilize the gold nanorods, still by as little as 15–20%. Our results span from the femtosecond up to the continuous wave regimes of irradiation and suggest that the biological interface does not pose a major threat on the photostability of plasmonic particles for most biomedical applications, including the photoacoustic imaging and photothermal ablation of cancer