The Detection Of Amyloidogenic Protein Based On Quantum Dots

With the research and development of nanotechonology, nanomaterials have been recognized as the most promising material in this century. Quantum dots (QDs) as a new kind of efficient and stable fluorescent nanomaterial appeared. Compared with the traditional fluorescent materials, QDs have superior properties, including high fluorescence quantum yield, better photostability, narrow and symmetric emission spectra, broader absorption spectra, excellent biocompatibility. Therefore, they were widely applied in biochemical detection, clinic diagnosis, molecular labeling, bioimaging and high throughput screening.Alzheimer’s disease, prion disease, diabetes and other diseases are amyloidosis disease. The main reason to cause of these diseases is molecular conformation of the protein misfolding and abnormal aggregation. According to reports, there are nearly30kinds of diseases related to amyloid aggregation. For example, Alzheimer’s disease is a neurodegenerative disease related to aggregation of β-amyloid peptide. As a nervous system degenerative disease, the prion disease related to deposition of prion protein. Simultaneously, Parkinson’s disease and a-synuclein fibrosis also has a close relationship. Research shows that it can achieve early diagnosis of amyloidosis diseases by detecting amyloid proteins associated with diseases.Prion protein is the pathogen of neurodegenerative prion disease. It is a non-viral virulence factors not only the lack of nucleic acid also has a contagious. Prion diseases have many characteristics including fatal, infectious and genetic. Prion disease patient’s condition is sexual development which will lead to the patient death. The mortality rate of patient is about99.2%. far higher than cancer. Therefore, the development of a simple, sensitive, fast speed, low cost detection method which can detect prion protein in the actual biological samples is of great significance for preventing the spread of prion disease and early diagnosis of prion disease.The β-amyloid peptide in Alzheimer’s disease is generally considered the most likely system disease substances. Alzheimer’s disease is also called senile dementia, is a neurodegenerative disease, which have progressive and fatal. Patients with severe may also have the thoughts to suicidal. The consequences will be very serious If not to diagnosis and treatment, and control of the disease timely. Currently, the disease has affected35million people worldwide. To reduce the development of the disease, the most important is to achieve early detection and treatment of Alzheimer’s disease. The β-amyloid peptide as a causative agent of the Alzheimer’s disease, has attracted widespread attention. Currently, there are a lots of methods for detecting β-amyloid peptide, but the most of them are related to the antibodies which operation cumbersome and expensive. Therefore, we need to develop some detection methods which are simple, inexpensive to label-free detection of β-amyloid peptide associated with Alzheimer’s disease. The main works of this thesis are summarized as follows:(1) A novel colorimetric method on basis of the color complementarity principle has been well-established to detect easy fibrosis prion protein (rPrP). Two mutually complementary colors solution are mixed together at a certain amount, the color of mixture solution will change to gray or colorless is called color complementarity principle. Based on this principle, we mixed orange-red CdTe quantum dots (CdTe QDs, the absorption of480nm) with a certain amount of blue-green malachite green (MG, absorption of617nm) together, the solution is presented colorless. After the addition of rPrP into the mixed solution, the color changed from colorless to green-blue. And it could be observed by naked eyes. With the increase of rPrP concentration, the green-blue color from MG became deeper and the absorption at617nm increased. This phenomenon reminded us that the QDs-MG color complement system can be applied to rPrP detection. TEM was used to illustrate the rPrP-induced aggregation of QDs. The aggregations of QDs appeared after the addition of rPrP. And this aggregation will cause a decrease in QDs concentration in thesolution. Thus, rPrP can reduce the concentration of QDs in the QDs-MG color complement system, and as a result, green-blue color from MG appeared. We investigated the selectivity and interferences of coexisting substances by testing the response of the QDs-MG color complement system to interfere substances commonly found in biological samples. We found this method has a good selectivity. We used the reaction system to detect the actual content of the prion protein in a biological sample. We found that the original rPrP concentration in serum is relatively close to the actual sample. This showed that the method not only detects rPrP in biological sample, but also has potential for preventing spreading of prion diseases.(2) Using graphite oxide carbon quantum dots (CQDs) as a fluorescence probe lable-free detect Aβ1-42. CQDs as a probe intereacted with Aβ1-42, leading to the CQDs fluorescence decrease linear with the increase of Aβ1-42concentration, which could be used to quantitatively detect Aβ1-42. In order to improve the detection sensitivity, we optimized detection conditions, including pH, incubation temperature. Although the sensitivity of this method is not high, it provides a new method for detection the content of Aβ1-42in solution.