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The Glory of Gold Gold possess many properties that make it an ideal material for biomedical purpose. It has been thoroughly established that gold is chemically inert for all biological processes. Gold nanoparticles are the metal of choice because gold remains unoxidized at the nanoparticulate size. Other metals typically oxide, lose their nanoparticle optical properties useful for imaging, and ultimately collect together to form macroparticles. Gold retains its nanoparticle property to produce great contrast in optical images.
Synthesis of Gold NanoparticlesGold nanoparticles are of great interest because of their remarkable optical and electronic properties. In fabrication several issues are particular importance: control of size, control of size dispersion, and control of particle-particle arrangement. Two advances in synthesis processes have developed a rational approach to the growth of soluble gold nanoparticles in a highly size-selective manner. This is possible via detailed control of the surface adsorbate as the nanoparticle grows. The adsorbate defines the equilibrium surface stress on the nanoparticle and hence the size. Secondly, researchers have managed to grow gold nanoparticles in the pores of the mesoporous a silicate. The result is arrays of nanoparticles (spheres, rods, wires) embedded in the silicate template. The silicate/gold composite can be used directly in measurements and applications or the gold nanostructures can be released by treating the silicate with thiols and hydrofluoric acid.
Cancer Imaging Optical illumination of the particles is promising as means to detect the presence of cancer in a tissue, but to tell if a person has cancer through a minimally-invasive procedure, a different type of imaging is necessary. Researchers at the University of Missouri-Columbia used a combination of gold nanoparticles and CAT scan technology to image early-stage cancer in the lungs of a pig. The researchers laced the nanoparticles with antibodies that would form bonds with proteins expressed by cancerous lung cells. The rods were injected into the pig through intravenous needles upon which their affinity for lung cancer caused them to localize at the lungs as markers to establish a contrast medium for lung imaging. A CAT scan is then performed on the pig which reveals the cancerous areas. Based on some very solid preliminary data, lung cancer detection and treatment is one area where nanoparticles show promise. Another advantage of using nanoparticles is that they clear out of the lungs safely. The fact that animals can be injected and imaged with minimal discomfort creates hope that physicians may one day use this technique to screen humans as part of a routine check-up. Tracking and Imaging Blood Flow Researchers at Purdue University have developed a technique that tracked the flow of blood throughout the ear of a mouse. They attached single gold nanoparticles to blood cells and used a method called two-photon luminescence (TPL) to produce an image. The image is produced by using a scanning confocal microscope with using a sapphire laser beam, and the nanoparticles remained detectable for half an hour before the mouse's kidneys finally filtered them out. [17] It has been proven that the formation of new blood vessels—angiogenesis—is a first step for tumor growth. The ability to detect cancer at this stage would greatly increase the chances for successful treatment and recovery. Targeting angiogenesis is extremely difficult using conventional methods due to the smaller size of new blood vessels, but nanoparticles, because of their size similarity, provide researchers with a tool to probe all cellular components as well as angiogenesis. By mapping the angiogenesis surround a tumor, a physician could cut-off the angiogenesis, the food chain of the tumor, and thus curtail the it's growth. The imaging of blood vessels with gold nanorods also highlights another advantage they offer over conventional methods of imaging: the ability to image in three dimensions. The scientists believe that plasmon resonance of the nanorods boosts the TPL signal. The longitudinal plasmon modes of gold nanorods are resonant at near-infrared wavelengths. These frequencies are ideal for biological imaging as water and biological molecules have relatively low absorption in the range. Experiments showed that the TPL excitation spectrum overlapped with the longitudinal plasmon band. Researchers explain that this indicated that the TPL intensity was governed by the local field enhancement from the plasmon resonance. This nonlinear dependence of TPL readings makes it possible to plot along an axial direction and create a resolution in 3-D. |
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Copyright © 2005
Nanogroup Beta: Jason Feng, Maryam Liaqat, Eric Shubo Ma |
Physics 87N: Prof. Hari Manoharan
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