Introduction to metallic nanoparticles

Abstract

Metallic nanoparticles have fascinated scientist for over a century and are now heavily utilized in biomedical sciences and engineering. They are a focus of interest because of their huge potential in nanotechnology. Today these materials can be synthesized and modified with various chemical functional groups which allow them to be conjugated with antibodies, ligands, and drugs of interest and thus opening a wide range of potential applications in biotechnology, magnetic separation, and preconcentration of target analytes, targeted drug delivery, and vehicles for gene and drug delivery and more importantly diagnostic imaging. Moreover, various imaging modalities have been developed over the period of time such as MRI, CT, PET, ultrasound, SERS, and optical imaging as an aid to image various disease states. These imaging modalities differ in both techniques and instrumentation and more importantly require a contrast agent with unique physiochemical properties. This led to the invention of various nanoparticulated contrast agent such as magnetic nanoparticles (Fe(3)O(4)), gold, and silver nanoparticles for their application in these imaging modalities. In addition, to use various imaging techniques in tandem newer multifunctional nanoshells and nanocages have been developed. Thus in this review article, we aim to provide an introduction to magnetic nanoparticles (Fe(3)O(4)), gold nanoparticles, nanoshells and nanocages, and silver nanoparticles followed by their synthesis, physiochemical properties, and citing some recent applications in the diagnostic imaging and therapy of cancer.

Keywords: Fe3O4; gold nanoparticles; iron oxide nanoparticles; metallic nanoparticles; nanocages; nanoshells; silver nanoparticles.

Figure 1

Schematic diagram representing the fucntionalization of magnetic nanoparticles with bioresponsive peptide, PEG linker, chemotherapeutic agent, antibody, and cell-penetrating peptide.[11]

Figure 2

Photographs of aqueous solutions of gold nanospheres (upper panels) and gold nanorods (lower panels) as a function of increasing dimensions. Corresponding transmission electron microscopy images of the nanoparticles are shown (all scale bars 100 nm). The difference in color of the particle solutions is more dramatic for rods than for spheres. This is due to the nature of plasmon bands (one for spheres and two for rods) that are more sensitive to size for rods compared with spheres. For spheres, the size varies from 4 to 40 nm (TEMs a-e), whereas for rods, the aspect ratio varies from 1.3 to 5 for short rods (TEMs f-j) and 20 (TEM k) for long rods[50]

Figure 3

Gold nanorods (NRs) with tunable optical absorptions at visible and near-infrared wavelengths; a) Optical absorption spectra of gold NRs with different aspect ratios (a–e); b) Color wheel, with reference to gold NRs labeled a–e. TR, transverse resonance[51]

Figure 4

Dark field light scattering images of cytoplasm and nuclear targeting AuNPs. a) RGD-AuNPs located in the cytoplasm of cancer cells. b) RGD/NLS-AuNPs located at the nucleus of cancer cells. c) RGD-AuNPs located in the cytoplasm of normal cells. d) RGD/NLS-AuNPs located at the nucleus of normal cells. The cancer and normal cells were incubated in the presence of these AuNPs at a concentration of 0.4 nM for 24 hours and these images clearly display the efficient uptake of AuNPs in cancer cells compared with normal cells. Scale bar 10 μm[72]

Figure 5

Gold nanoshell plasmon resonances for a 120-nm core with indicated shell thickness[81]

Figure 6

Formation of nanoshell dimer with the interaction of antibodies immobilized on the surface of the nanoshells[82]