Human exposure to nanoparticles is inevitable as nanoparticles become more widely used and, as a result, nanotoxicology research is now gaining attention. However, while the number of nanoparticle types and applications continues to increase, studies to characterize their effects after exposure and to address their potential toxicity are few in comparison. In the medical field in particular, nanoparticles are being utilized in diagnostic and therapeutic tools to better understand, detect, and treat human diseases. Exposure to nanoparticles for medical purposes involves intentional contact or administration; therefore, understanding the properties of nanoparticles and their effect on the body is crucial before clinical use can occur. This Review presents a summary of the in vitro cytotoxicity data currently available on three classes of nanoparticles. With each of these nanoparticles, different data has been published about their cytotoxicity due to varying experimental conditions as well as differing nanoparticle physiochemical properties. For nanoparticles to move into the clinical arena, it is important that nanotoxicology research uncovers and understands how these multiple factors influence the toxicity of nanoparticles so that their undesirable properties can be avoided.

Nanotechnology-based cancer treatment approaches potentially provide localized, targeted therapies that aim to enhance efficacy, reduce side effects, and improve patient quality of life. Gold-nanoparticle-mediated hyperthermia shows particular promise in animal studies, and early clinical testing is currently underway. In this article, the rapidly evolving field of gold nanoparticle thermal therapy is reviewed, highlighting recent literature and describing current challenges to clinical translation of the technology.

We are developing a novel treatment for high-grade gliomas using near infrared-absorbing silica–gold nanoshells that are thermally activated upon exposure to a near infrared laser, thereby irreversibly damaging cancerous cells. The goal of this work was to determine the efficacy of nanoshell-mediated photothermal therapy in vivo in murine xenograft models. Tumors were induced in male Icr-Tac:ICR-PrkdcSCID mice by subcutaneous implantation of Firefly Luciferase-labeled U373 human glioma cells and biodistribution and survival studies were performed. To evaluate nanoparticle biodistribution, nanoshells were delivered intravenously to tumor-bearing mice and after 6, 24, or 48 h the tumor, liver, spleen, brain, muscle, and blood were assessed for gold content by inductively coupled plasma-mass spectrometry (ICP-MS) and histology. Nanoshell concentrations in the tumor increased for the first 24 h and stabilized thereafter. Treatment efficacy was evaluated by delivering saline or nanoshells intravenously and externally irradiating tumors with a near infrared laser 24 h post-injection. Success of treatment was assessed by monitoring tumor size, tumor luminescence, and survival time of the mice following laser irradiation. There was a significant improvement in survival for the nanoshell treatment group versus the control (P < 0.02) and 57% of the mice in the nanoshell treatment group remained tumor free at the end of the 90-day study period. By comparison, none of the mice in the control group survived beyond 24 days and mean survival was only 13.3 days. The results of these studies suggest that nanoshell-mediated photothermal therapy represents a promising novel treatment strategy for malignant glioma.

Many optical diagnostic approaches rely on changes in scattering and absorption properties to generate optical contrast between normal and diseased tissue. Recently, there has been increasing interest in using exogenous agents to enhance this intrinsic contrast with particular emphasis on the development for targeting specific molecular features of disease. Gold nanoshells are a class of core-shell nanoparticles with an extremely tunable peak optical resonance ranging from the near-UV to the mid-IR wavelengths. Using current chemistries, nanoshells of a wide variety of core and shell sizes can easily be fabricated to scatter and/or absorb light with optical cross sections often several times larger than the geometric cross section. Using gold nanoshells of different size and optical parameters, we employ Monte Carlo models to predict the effect of varying concentrations of nanoshells on tissue reflectance. The models demonstrate the importance of absorption from the nanoshells on remitted signals even when the optical extinction is dominated by scattering. Furthermore, because of the strong optical response of nanoshells, a considerable change in reflectance is observed with only a very small concentration of nanoshells. Characterizing the optical behavior of gold nanoshells in tissue will aid in developing nanoshells as contrast agents for optical diagnostics.

Gold nanoparticle-mediated photothermal therapy (PTT) has shown great potential for the treatment of cancer in mouse studies and is now being evaluated in clinical trials. For this therapy, gold nanoparticles (AuNPs) are injected intravenously and are allowed to accumulate within the tumor via the enhanced permeability and retention (EPR) effect. The tumor is then irradiated with a near infrared laser, whose energy is absorbed by the AuNPs and translated into heat. While reliance on the EPR effect for tumor targeting has proven adequate for vascularized tumors in small animal models, the efficiency and specificity of tumor delivery in vivo, particularly in tumors with poor blood supply, has proven challenging. In this study, we examine whether human T cells can be used as cellular delivery vehicles for AuNP transport into tumors. We first demonstrate that T cells can be efficiently loaded with 45 nm gold colloid nanoparticles without affecting viability or function (e.g. migration and cytokine production). Using a human tumor xenograft mouse model, we next demonstrate that AuNP-loaded T cells retain their capacity to migrate to tumor sites in vivo. In addition, the efficiency of AuNP delivery to tumors in vivo is increased by more than four-fold compared to injection of free PEGylated AuNPs and the use of the T cell delivery system also dramatically alters the overall nanoparticle biodistribution. Thus, the use of T cell chaperones for AuNP delivery could enhance the efficacy of nanoparticle-based therapies and imaging applications by increasing AuNP tumor accumulation.

We demonstrate the capability of using immunotargeted gold nanoshells as contrast agents for in vitro two-photon microscopy. The two-photon luminescence properties of different-sized gold nanoshells are first validated using near-infrared excitation at 780 nm. The utility of two-photon microscopy as a tool for imaging live HER2-overexpressing breast cancer cells labeled with anti-HER2-conjugated nanoshells is then explored and imaging results are compared to normal breast cells. Five different imaging channels are simultaneously examined within the emission wavelength range of 451-644 nm. Our results indicate that under near-infrared excitation, superior contrast of SK-BR-3 cancer cells labeled with immunotargeted nanoshells occurs at an emission wavelength ranging from 590 to 644 nm. Luminescence from labeled normal breast cells and autofluorescence from unlabeled cancer and normal cells remain imperceptible under the same conditions.

The relative transparency of Daphnia magna (daphnia) and the unique optical properties of quantum dots (QDs) were paired to study the accumulation potential and surface coating effects on uptake of amphiphilic polymer coated CdSe/ZnS QDs. Fluorescence confocal laser scanning microscopy was used to visualize and spectrally distinguish QDs from competing autofluorescent signals arising from the daphnia themselves and their food sources. QDs were found to accumulate within the digestive tracts of daphnia, as well as, in some cases, adhere to the carapace, antennae, and thoracic appendages. After 48 h of gut clearance with and without feeding, QD fluorescence signal was still apparent in the digestive tracts of daphnia, and inductively coupled plasma mass spectrometry (ICP-MS) measurements confirmed that 36-53% of the initial uptake was retained. As surface charge and pegylation can influence the uptake of nanoparticles, uptake of QDs coated with two different amphililic polymers and their polyethylene glycol (PEG) coated counterparts was also examined. Fluorescence microscopy and ICP-MS measurements revealed differences in uptake after 24 h of exposure which were attributed to particle surface coating and stability.

An in depth analysis of gold nanoparticle (AuNP) synthesis and size tuning, utilizing carbon monoxide (CO) gas as a reducing agent, is presented for the first time. The sizes of the AuNPs are tunable from ~4 to 100 nm by altering the concentration of HAuCl4 and inlet CO gas-injection flow rate. It is also found that speciation of aqueous HAuCl4, prior to reduction, influences the size, morphology, and properties of AuNPs when reduced with CO gas. Ensemble extinction spectra and TEM images provide clear evidence that CO reduction offers a high level of monodispersity with standard deviations as low as 3%. Upon synthesis, no excess reducing agent remains in solution eliminating the need for purification. The time necessary to synthesize AuNPs, using CO, is less than 2 min.