1.1 Bio-detection application
In recent years, bio-detection techniques have been widely used for diagnosis of disease and environment analysis. Researchers have used nanotechnology and nano-approaches to explore new alternative bio-imaging and bio-labeling strategies based on fluorescent nanomaterials in both biological and medicinal field 1.
Fluorescent materials are generally used in combination with fluorescent microscopy. Fluorescent nanomaterials are targeted at cells or objects in order to display the target cells on microscopic or camera images. Specific excitation light irradiates the specimen, which is treated by fluorescent agents. A digital camera detects the fluorescent emission wavelength only and shows a bright area against a dark background. The high contrast between the fluorescent target and non-fluorescent materials enhances the efficiency of microscopy. The use of fluorescent materials makes it possible to identify specific cell targets or sub-cellular components. This technique can be applied to both in vitro and in vivo targets 1,2.
One of the most important techniques in bio-labeling based on fluorescent materials is immunofluorescence. Immunofluorescence takes advantage of the conjunction property innumerable antibodies and antigens. In one work the relation between antibodies and antigens was specific and strong 2. Selected antibodies were treated chemically to attach the fluorescent agents. If the antigen presented in the target sample, the labeling antibody conjugates bound to the antigens. After the sample was washed, fluorescent antibody-antigen combinations still remained. The result was that emission was visible by eye or detected by camera when the sample was exposed to light at its excitation peaks2.
Another important development technique based on fluorescent materials is cancer tracing and cancer cell imaging for diagnosis and analysis. Cancer is the leading cause of death in developed countries, so its treatment has long been the goal of scientists and physicians. The first stage in cancer treatment is malignancy detection. However, most tumors are only detectable after growing larger than 1 centimeter. At that point, millions of tumor cells may already be metastasized and could cause serious damage to the body. Fluorescent imaging and labeling techniques are powerful and fast tools for cancer diagnosis and analysis. Since the fluorescent agents range from molecules to nano-size, agents are able to label cell components, such as mutant DNA, protein or cell membrane. Moreover, a labeling technique helps pathologists classify tumor cell types to make appropriate treatment recommendations to promote the success rate of surgery or chemotherapy. Therefore, fluorescent detection technologies dramatically raise the accuracy of diagnosis and analysis in medical detection1.