During the last decade oncological diseases have spread enormously. According to the statistics of World Health Organization, cancer takes second place in the list of leading lethal diseases. The first place goes to cardiovascular diseases. Only in 2008 more than 7.6 million people died from cancer worldwide. In order to improve survival factors, early diagnostics and effective therapy is a necessity.
Fluorescence imaging is a sensitive and quantitative method that is widely used for observing cells and cell processes in vivo, also for noninvasive tissue imaging, which is a promising tool for cancer diagnostics. Unfortunately, the sensitivity of fluorescence imaging is limited due to characteristics of fluorescent agents applied. In biological studies most commonly used fluorophores are organic dyes and semiconductor quantum dots. Currently another type of imaging agents has been shown to have a particularly great promise in bioimaging – fluorescent gold nanoclusters. Being composed of non-toxic elements and having surface that could be easily modified with antibodies, biomarkers or functional molecules, they also possess properties such as high fluorescence yield and good biocompatibility.
Gold nanoparticles typically have very tiny dimensions between 1 and 500 nanometers. This means that if you divide a meter in one-billion parts, the biggest of these particles would have a length comprised by 500 parts. These nanoparticles also possess features that differ from bulk gold. For example when the particle diameter becomes smaller than some characteristic size, particles display size dependent surface plasmon resonance absorption. Surface plasmon resonance is a coherent oscillation of the surface conduction electrons excited by electromagnetic radiation which gives rise to a sharp and intense absorption band in the visible part of a spectrum. Very early appearance of this phenomenom (even though not understood at that time) can be seen in medieval windows of churches across Europe and even in 4th-century Roman glass.
The optical response for these particles varies with shape, size, dielectric environment and surface coatings and these are the properties that make them of great interest for applications. It has also already been demonstrated that functionalized gold nanoparticles can be used for drug delivery. The effectiveness of employing gold nanoparticles has already been demonstrated in pre-clinical studies using small animal models. A few clinical trials are already taking place looking at gold nanoparticles effectiveness in tumor targeting and tumor toxicity. What is more, gold itself has also a property of attenuating X-rays, which makes it a good contrast agent for radiology.
However in order to employ all possible effects mentioned above several goals have to be reached. Firstly it is important to investigate photophysical, optical and structure related properties of synthesized gold nanoparticles as well as accumulation of gold nanoparticles in cells. There is still a lot of research going on dedicated for increasing gold nanoparticles properties as drug carriers, imaging agents and reducing chances of side effects. Due to their set of unique physical, chemical and biological properties there is a number of areas where those particles can be used in a near future and the amount of scientific literature appearing each year demonstrating progress in perfection of gold nanoparticles suited for applications suggest that we will not have to wait for too long.
Marius Stalnionis is a PhD student and as a Medical Physicist at the National Cancer Institute in Lithuania. His thesis involves investigation of gold nanoparticles as diagnostic multifunctional imaging tracers for cancer. He has graduated from Nuclear Medicine Imaging programme at the University of Salford, UK.
Deividas Sabonis did his undergraduate studies in Physics jointly in Vilnius University and University of Copenhagen, Niels Bohr Institute. He was awarded a graduate studies fellowship by the German Academic Exchange Service or DAAD for the period of 2014-2016 at TU Munich.