Modeling the cellular impact of nanoshell-based biosensors using mouse alveolar macrophage cultures

In this study, the relative toxicity of native gold-silica nanoshells (NS) has been compared to nanoshells modified with poly(ethylene glycol)-thiol (PEG-SH) and a Raman-active PEG, p-mercaptoaniline-poly(ethylene glycol) (pMA-PEG), in mouse alveolar macrophage cell cultures (RAW 264.7). The results from toxicity profiling using an MTT assay demonstrate that cell viability post-particle exposure is a function of three factors: nanoshell concentration, surface functionalization, and incubation time. By minimizing particle concentrations and incubation times, cell cultures are able to recover within 24 h of nanoshell removal, indicative of nanoshells having more of a cytostatic versus cytotoxic effect on macrophage cells. The mechanism of the cytostatic effect has been investigated by imaging the presence of reactive oxygen species (ROS) using a fluorescence assay kit (Image-iT™ LIVE) after the introduction of NS to the cell cultures. Elevated ROS signals are seen in the cells containing higher concentration of NS, and indicate that the major reason of toxicity may due to the oxidative stress caused by excess NS particles. Raman imaging experiments with pMA-PEG coated nanoshells showed that cells exposed for even short exposure times (∼2 h) retained those particles up to 24 h after exposure, while migration experiments suggest that surviving cells retain their nanoshells and may reallocate them to progeny cells upon cell division.

SERS biodetection using gold-silica nanoshells and nitrocellulose membranes

We have developed a rapid, reproducible, easy to execute, surface enhanced Raman scattering (SERS) method for detection of low volumes and total amounts of biological antigens using an analyte capture system derived from methods commonly used in Western blotting. Our method is a "half-sandwich" assay with an antigen detection scheme that employs a nitrocellulose (NC) membrane with 200 nm pore size to capture subnanograms of analyte and concentrate them in a small area from applied volumes as low as one microliter. The SERS probes used for detection consist of gold-silica nanoshells modified with a two-component mixed monolayer system. One component consists of a poly(ethylene glycol) (PEG)-modified Raman-active chromophore bound to the gold surface which allows for SERS detection and imparts particle stability. The second component uses (ortho-pyridyl) disulfide-PEG-succinimidyl ester to couple the recognition antibody to the particle surface. By controlling the reaction time and concentration of thiols, a mixed monolayer is prepared on the nanoshell surface with the ability to recognize low concentrations of analyte and generate reproducible SERS signals. Using this strategy, we have achieved SERS signals that are proportional to antigen present on the membrane allowing detection of total antigen amounts as low as 1.25 ng for some cases. The performance of this new SERS bioassay has been tested with a variety of potential antigens, demonstrating the potential for multiplexed detection of analytes.

Rapid Raman imaging of stable, functionalized nanoshells in mammalian cell cultures

Two Raman-active poly(ethylene glycol) (PEG) molecules, one linear (MW 5000) and the other branched (MW 2420), are synthesized to stabilize gold-silica nanoshells in cell culture media and track nanoparticles in mammalian cell cultures. The linear PEG provides greater nanoshell stability in saline solution compared to commercially available PEG-thiol or the branched PEG. Surface enhanced Raman scattering rapidly tracks the probes and provides semiquantitative information regarding particle localization within mouse macrophage (RAW 264.7) and human breast cancer (MCF 7) cell cultures.

Determining the conformation of thiolated poly(ethylene glycol) on Au nanoshells by surface-enhanced Raman scattering spectroscopic assay

The packing density of thiolated poly(ethylene glycol) (PEG) adsorbates on Au nanoshells is determined by exploiting the surface-enhanced Raman scattering response of individual nanoshell substrates. By incorporating the linker molecule p-mercaptoaniline (pMA), the number of 2000 MW and 5000 MW PEG molecules on each nanoparticle is determined by interpolation of the Langmuir isotherm for pMA. We conclude that both PEG adsorbates maintain a compact "brush" rather than an extended "mushroom" configuration on nanoshell surfaces.