Gold nanorods: multifunctional agents for cancer imaging and therapy

Synthesis of gold nanorods and their performance in the field of cancer cell imaging and photothermal therapy

Cancer is one of the most common incident in the world, with malignant tumors having a death rate of up to 19%. A new method of treating cancer cells effectively with minimal cytotoxicity is needed. In the field of biomedicine with unique shape-dependent optical properties, gold nanorods (GNRs) have attracted worldwide interest. These nanorods have two distinct plasmon bands. One is transverse plasmon band in the area of visible light, and the other is longitudinal band of plasmons in near infrared region. These specific characters provide promise for the design of new optically active reagents that simultaneously perform light-mediated imaging and photothermal cancer treatment. We begin our review by summarizing the latest developments in gold nanorods synthesis with a focus on seed-mediated growth method. Nanorods spontaneous self-assembly, polymer-based alignment and its applications as a novel agent for simultaneous bioimaging and photothermal cancer therapy are listed in particular.

Wavelength-Tunable Optical Fiber Localized Surface Plasmon Resonance Biosensor via a Diblock Copolymer-Templated Nanorod Monolayer

Well-dispersed and dense layers of gold nanorods (AuNRs) on optical fibers are shown to regulate the longitudinal peak wavelength and enhance the sensing performances of localized surface plasmon resonance (LSPR) biosensors. A simple self-assembly method relying on a brush-like monolayer of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer was used to immobilize AuNRs with various aspect ratios from 2.33 to 4.60 on optical fibers. Both the experimental and simulation results illustrated that the particle aspect ratio, deposition time (related to the coverage of AuNRs), and interparticle gap significantly affected the optical properties of the fiber-based LSPR biosensors. The highest refractive index (RI) sensitivity of the sensor was 753 nm/RIU, while the limit of detection for human IgG was as low as 0.8 nM. Compared with standard nanoparticle deposition methods of polyelectrolytes or alkoxysilanes, the RI sensitivity of the PS-b-PAA dip-coating method was approximately 3-fold better, a consequence of the higher particle coverage and fewer AuNR aggregates. The presented AuNR-based LSPR sensors could regulate the detection range by tuning the aspect ratios of AuNRs. Applicability is demonstrated via quantitative analysis of antigen-antibody interactions, DNA sensing, and surface-enhanced Raman scattering.

Activatable ultrasmall gold nanorods for “off–on” fluorescence imaging-guided photothermal therapy

We developed activatable ultrasmall gold nanorods (AUGNRs) to realize “off–on” switched fluorescence imaging-guided efficient PTT.

Citrate-stabilized gold nanorods

Stable aqueous dispersions of citrate-stabilized gold nanorods (cit-GNRs) have been prepared in scalable fashion by surfactant exchange from cetyltrimethylammonium bromide (CTAB)-stabilized GNRs, using polystyrenesulfonate (PSS) as a detergent. The surfactant exchange process was monitored by infrared spectroscopy, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopy (XPS). The latter established the quantitative displacement of CTAB (by PSS) and of PSS (by citrate). The Cit-GNRs are indefinitely stable at low ionic strength, and are conducive to further ligand exchange without loss of dispersion stability. The reliability of the surface exchange process supports the systematic analysis of ligand structure on the hydrodynamic size of GNRs, as described in a companion paper.

Gold nanorods based platforms for light-mediated theranostics

Due to their tunable surface plasmon and photothermal effects, gold nanorods (AuNRs) have proved to be promising in a wide range of biomedical applications such as imaging, hyperthermia therapy and drug delivery. All these applications can be remotely controlled by near infrared (NIR) light which can penetrate deep into human tissues with minimal lateral invasion. AuNRs thus hold the potential to combine both imaging diagnosis and therapeutic treatment into one single system and function as a NIR light-mediated theranostic platform. Herein we review recent progress in diagnostic and therapeutic applications of AuNRs with a highlight on combined applications for theranostic purposes.

Challenges and opportunities in the advancement of nanomedicines

Nanomedicine-based approaches to cancer treatment face several challenges that differ from those encountered by conventional medicines during clinical development. A systematic exploration of these issues has led us to identify the following needs and opportunities for further development: (1) robust and general methods for the accurate characterization of nanoparticle size, shape, and composition; (2) scalable approaches for producing nanomedicines with optimized bioavailability and excretion profiles; (3) particle engineering for maintaining low levels of nonspecific cytotoxicity and sufficient stability during storage; (4) optimization of surface chemistries for maximum targeted delivery and minimum nonspecific adsorption; (5) practical methods for quantifying ligand density and distributions on multivalent nanocarriers; and (6) the design of multifunctional nanomedicines for novel combination therapies with supportable levels of bioaccumulation.

Gold nanorods for ovarian cancer detection with photoacoustic imaging and resection guidance via Raman imaging in living mice

Improved imaging approaches are needed for ovarian cancer screening, diagnosis, staging, and resection guidance. Here, we propose a combined photoacoustic (PA)/Raman approach using gold nanorods (GNRs) as a passively targeted molecular imaging agent. GNRs with three different aspect ratios were studied. Those with an aspect ratio of 3.5 were selected for their highest ex vivo and in vivo PA signal and used to image subcutaneous xenografts of the 2008, HEY, and SKOV3 ovarian cancer cell lines in living mice. Maximum PA signal was observed within 3 h for all three lines tested and increased signal persisted for at least two days postadministration. There was a linear relationship (R(2) = 0.95) between the PA signal and the concentration of injected molecular imaging agent with a calculated limit of detection of 0.40 nM GNRs in the 2008 cell line. The same molecular imaging agent could be used for clear visualization of the margin between tumor and normal tissue and tumor debulking via surface-enhanced Raman spectroscopy (SERS) imaging. Finally, we validated the imaging findings with biodistribution data and elemental analysis. To the best of our knowledge, this is the first report of in vivo imaging of ovarian cancer tumors with a photoacoustic and Raman imaging agent.

Photoacoustic imaging of mesenchymal stem cells in living mice via silica-coated gold nanorods

Improved imaging modalities are critically needed for optimizing stem cell therapy. Techniques with real-time content to guide and quantitate cell implantation are especially important in applications such as musculoskeletal regenerative medicine. Here, we report the use of silica-coated gold nanorods as a contrast agent for photoacoustic imaging and quantitation of mesenchymal stem cells in rodent muscle tissue. The silica coating increased the uptake of gold into the cell more than 5-fold, yet no toxicity or proliferation changes were observed in cells loaded with this contrast agent. Pluripotency of the cells was retained, and secretome analysis indicated that only IL-6 was disregulated more than 2-fold from a pool of 26 cytokines. The low background of the technique allowed imaging of down to 100,000 cells in vivo. The spatial resolution is 340 μm, and the temporal resolution is 0.2 s, which is at least an order of magnitude below existing cell imaging approaches. This approach has significant advantages over traditional cell imaging techniques like positron emission tomography and magnetic resonance imaging including real time monitoring of stem cell therapy.

Using matrix summation method for three dimensional dose calculation in brachytherapy

AIM

The purpose of this study is to calculate radiation dose around a brachytherapy source in a water phantom for different seed locations or rotation the sources by the matrix summation method.

BACKGROUND

Monte Carlo based codes like MCNP are widely used for performing radiation transport calculations and dose evaluation in brachytherapy. But for complicated situations, like using more than one source, moving or rotating the source, the routine Monte Carlo method for dose calculation needs a long time running.

MATERIALS AND METHODS

The MCNPX code has been used to calculate radiation dose around a (192)Ir brachytherapy source and saved in a 3D matrix. Then, we used this matrix to evaluate the absorbed dose in any point due to some sources or a source which shifted or rotated in some places by the matrix summation method.

RESULTS

Three dimensional (3D) dose results and isodose curves were presented for (192)Ir source in a water cube phantom shifted for 10 steps and rotated for 45 and 90° based on the matrix summation method. Also, we applied this method for some arrays of sources.

CONCLUSION

The matrix summation method can be used for 3D dose calculations for any brachytherapy source which has moved or rotated. This simple method is very fast compared to routine Monte Carlo based methods. In addition, it can be applied for dose optimization study.

Imaging and drug delivery using theranostic nanoparticles

Nanoparticle technologies are significantly impacting the development of both therapeutic and diagnostic agents. At the intersection between treatment and diagnosis, interest has grown in combining both paradigms into clinically effective formulations. This concept, recently coined as theranostics, is highly relevant to agents that target molecular biomarkers of disease and is expected to contribute to personalized medicine. Here we review state-of-the-art nanoparticles from a therapeutic and a diagnostic perspective and discuss challenges in bringing these fields together. Major classes of nanoparticles include, drug conjugates and complexes, dendrimers, vesicles, micelles, core-shell particles, microbubbles, and carbon nanotubes. Most of these formulations have been described as carriers of either drugs or contrast agents. To observe these formulations and their interactions with disease, a variety of contrast agents have been used, including optically active small molecules, metals and metal oxides, ultrasonic contrast agents, and radionuclides. The opportunity to rapidly assess and adjust treatment to the needs of the individual offers potential advantages that will spur the development of theranostic agents.