Posted: March 22, 2008

A one-step homogeneous immunoassay for cancer biomarker detection using gold nanoparticle probes

(Nanowerk News) Millions of people around the world face the risk of cancer, which has been one of the leading causes of mortality. The early detection of cancer can significantly improve the treatment and survival rate of cancer patients. As tumors develop, the cells, tissues and organs can increase or decrease the release of certain chemicals in the circulatory system. These specific chemicals are called biomarkers. Some of these biomarkers have been approved by FDA for the in-vitro diagnosis of different types of cancer. A well known example is the test of PSA (prostate specific antigen) level for prostate cancer detection. A total PSA level of 4 ng/mL is generally considered as a normal threshold, and when this value exceeds 10 ng/mL, the chance of prostate malignancy is increased substantially.
In order to use the cancer biomarkers more effectively for the early detection and diagnosis of cancer, it is now generally recognized by scientists and medical practitioners that the cancer marker level should be tested frequently and accurately. Cancer markers not only exist in cancer patients, but also can be found in normal and healthy people, however, they exist in these populations at different levels of concentration. A biomarker concentration varies by gender, race, and age, and the concentration fluctuates depending on other non-cancerous physical conditions. A biomarker level which is normal for one person could be an indicator of cancer occurrence for another person. Without knowing the biomarker level history of a person, doctors could easily arrive at a false-positive or negative conclusion based on a one-time test or using only a limited amount of biomarker level testing.
However, in reality, it is difficult to require an overall healthy person to conduct a blood test several times or more per year to test cancer biomarker levels, unless enough evidence has arisen to make such a frequent blood testing necessary. The reason is that currently these tests can only be done in appropriately equipped medical testing labs by highly trained professionals. We currently have over-the-counter devices to measure blood pressure, cholesterol level, and blood sugar level in the market. However, we do not have an over-the-counter product in the market that allows us to measure the level of cancer markers accurately and conveniently. There have been many technical challenges towards the development of such a product due to the extremely low levels of cancer biomarkers in our blood stream and their small concentration variations at an early stage of cancer development.
A research group led by Professor Qun Huo at the University of Central Florida (Orlando, Florida) and her two key researchers, Xiong (Shawn) Liu and Qiu Dai, has developed a highly sensitive homogeneous one-step immunoassay, nanoDLSA, for cancer marker detection, according to their report in a most recent issue of J. Am. Chem. Soc. ("A One-Step Homogeneous Immunoassay for Cancer Biomarker Detection Using Gold Nanoparticle Probes Coupled with Dynamic Light Scattering"). To prepare the immunoassay, a pair of monocolonal antibodies that can specifically bind with a cancer marker antigen, are conjugated with two gold nanoparticle probes. To conduct the assay, one simply mixes the two nanoprobes with a sample solution. The antigen-antibody binding will introduce a nanoparticle aggregation. By measuring the degree of nanoparticle aggregation in the assay solution using dynamic light scattering (DLS), the concentration of cancer marker antigen in the sample can be quantitatively determined. In a recent study (results to be submitted and published soon), this research group has analyzed the free-PSA level of a few human serum samples collected from prostate cancer patients using both nanoDLSA and ELISA. The preliminary results revealed an excellent correlation between nanoDLSA and ELISA.
The nanoDLSA immunoassay is fast, highly sensitive, accurate, and extremely easy to conduct. It requires a much smaller amount (at least 100 times less) of blood samples and antibody probes to conduct the assay compared to ELISA. The cost reduction of nanoDLSA compared to other immunoassays is tremendous. Because of the minute amount of sample that is required by nanoDLSA, it is possible to conduct the detection and measurement of one or multiple cancer markers from a single drop of human blood sample using this new immunoassay technology. The goal of this research group is to develop a fully automated system that can be placed in supermarkets, pharmacy stores, hospitals, and clinics for the general public to test their cancer marker levels as frequently as necessary at affordable prices. The biomarker level history obtained from each individual will provide invaluable information to medical doctors for the early screening and diagnosis of cancer. Equally important, such frequent testing is also critical for cancer patients whose cancer marker levels need to be analyzed constantly to monitor the treatment effect and the recurrence of cancer.
Written by Qun Huo, Ph.D, Xiong Liu and Qiu Dai as part of Beyond the Abstract on This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations, etc., of their research by referencing the published abstract.
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