"Surface plasmon resonance (SPR) can be used for sensing. What material property is being sensed<br /> (analysed) with this technique?", "Local refraction index, through the measure of the critical angle of the absorption ( in a monochromatics setup)" "Why is citrate often used in the formation of gold nanoparticles (two reasons)?", "Firstly sodium citrate acts as a reducing agent, reducing Au3´to its zero oxidation state allowing it to nucleate and grow into a spherical form.<br /> Secondly, sodium citrate acs as a stabilizing agent, given it net negative charge, surrounding the gold nanoparticles, making them repel each other, thus preventing unwanted aggregation." "Describe why gold nanoparticles have colour and how this property can be used to treat cancer? In the cancer application is it preferable to use nanorods instead of spheres, why?", "Gold nanoparticles present a color different than their bulk material and this color varies with the size of the nanoparticle(for sheres, the bigger the radius, the smaller the wavelength)<br /> This effect, localized surface plasmon resonance, is a collective oscillation of the conduction electrons induced by an EMW in a metallic material. Metallically bonded materials have their metalicions dispersed in a “sea” of electrons donated by themselves. These, also called the free electron gas, are free to move around, interacting with incoming EMW as predicted by Maxwell’sequations and further explained by the Mie solution.<br /> The size and shape of the nanoparticles determines the resonant frequency of the electrons, hence determining the EMW frequency with which they interact.<br /> Their application for cancer therapy arises when one is able to functionalize the gold nanoparticles so that they can preferably bind to cancer cells in the human system and the one irradiates them with the corresponding resonant frequency. These free electron gas get excited, subsequently when plasmon relaxation occurs, a photon of the corresponding frequency is emitted. Hence, gold nanoparticles can be used to absorb surrounding radiation and convert it into localized heat to kill cancer cells.<br /> Nanorods are preferred because they have a higher absorbance in the infrared spectrum. Infrared radiation is the prefered in this application given that it can harmlessly be irradiated to the human body and is great at converting to heat. Additionally, nanorods are easy to grow without unwanted aggregation and are harmless to the human body"
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