Quantum Dots used to diagnose cancer



Quantum Dots used to diagnose cancer

EE453 Project Report submitted by

Christopher McElhone MCELHON2@unlv.nevada.edu , Fall 2008

Introduction:

Cancer is a growing concern in America. With more than half a million people dying each year from advanced cancer early detection is vital. Many lives could be saved with early detection. However many diagnostic techniques such as medical imaging, tissue biopsy and bioanalytical assay of body fluids by enzyme linked immunosorbent assay (ELISA) are inadequate when detecting the early stages of cancer. Most cancers are not detectable until they reach a certain size. This creates huge problems when trying to detect cancer early on when survival rates are the highest and treatments are readily available. Once a cancer goes into the advance stages survival rate drastically drops and patients can die within a year of diagnoses. A reliable method for early cancer detection as well as an effective way to track cancer development is essential to the treatment of cancer. Quantum Dots are a new emerging technology that can be used as an economical and effective way to detect cancer early on as well as track its development in the body.

Project Description:

Quantum dots are very small particles, sometimes as small as 5 to 10 nanometers. These Quantum dots are then injected into tissue or cancer cells. Then by using near infrared or ultraviolet light these quantum dots can then be imaged to see a mapping of where they are in the blood stream. This is illustrated in (figure 1 and figure 3) shown below. The time between injection and detection is very fast and could allow for quick check ups for cancer as opposed to other techniques which can be very time consuming and expensive. By using various antibodies researchers can attach these quantum dots to cancer cells in the body which allows them to be imaged. This would allow doctors to diagnose cancer early on and save many lives. With this new technology doctors can then easily track cancer and how it develops through the body. Doctors will be able to tell if cancer has spread to other parts of the body or if it has been eliminated through various forms of treatment.

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Figure 1

Quantum Dots have many unique properties that allow them to be used as a means of detecting cancer. One of the main problems of current methods used is a materials fluorescence stability and time. Most dyes and inks lose their fluorescence quickly which makes tracking cancer difficult. Also Quantum Dots resists photo bleaching, have highly sensitive detection due to their ability to absorb and emit light very efficiently, and have large molar extinction coefficients. Quantum dots also have a major advantage over fluorophores. Many fluorophores under go an effect called photo bleaching where they go through photoxidation and become non-fluorescent. This causes them to lose their ability to be seen. (Figure 2) shows immuno-fluorescent images of human cancer cells labeled with green quantum dots.

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Figure 2

Most quantum dots used for these procedures are made from a semiconductor core of either CdSe or CdTe. Also an additional shell such as ZnS used for the CdSe. Hydrophilic coating is also used to overcome water soluble issues. Finally biomolucles or antibodies are used that are complementary to the target cancer markers at the tumour sites. [1]

The safety of quantum dots used in these procedures to treat cancer is still in question. Quantum dots are very toxic due to the CdSe in them. However various polymers and coatings have been used successfully to keep toxicity from spreading. A group of researchers has been studying a group of animals injected with quantum dots for two years know. None of these animals have shown any ill affects caused by the quantum dots even though they can still be seen inside the animals.

Many universities have successfully shown that quantum dots can be effectively used in diagnosing cancer. Carnegie Mellon University has been able to take images of sentinel lymph nodes in animals using quantum dots and near infrared light. Byron Ballou, Ph.D and his team have been able to map the lymph nodes that drain tumors in mouse models of human cancer. By injecting quantum dots into the tumors they were then able to track the quantum dots through the skin by using near-infrared fluorescence microscopy. Byron’s team was able to see the quantum dots move out of the tumors and into the lymph system. The team reported being able to see the quantum dots almost immediately after injection. [2]

Dr. Phelan and her team used quantum dots to help detect prostate cancer in African American Men. Dr. Phelan addressed that there was two main advantages over measuring blood proteins using quantum dots versus normal methods. The first was “the optical properties of quantum dots allow protein detection at much lower levels when the tumor is in its earliest stages.” Second was “the technology enables detection of multiple biomarkers simultaneously, thus increasing the specificity for detecting cancer versus non-cancer.” Dr. Phelan and her colleagues are working to enhance the detection of prostate cancer biomarkers at extremely low serum levels. This would allow for screening and help with early detection of the disease. [3]

Hideo Higuchi, Ph.D., and colleagues at Tohoku University in Japan were able to attach antibodies to quantum dots that bind them to a protein found on the surface of certain breast cancer and other tumors. Using a high-sensitivity fluorescence microscope Hideo was able to make 30 second movies of the quantum dots as they moved through the blood stream to tumors in mice. [4]

Paras Prasad, Ph.D and his colleagues at the State University in Buffalo New York have been able to create quantum rods which can then be used as quantum dots but offer a distinct advantage. These Quantum rods have a larger dimension than the usual quantum dots which makes them much easier to see when exposed to near infrared light. Thus low intensity near infrared light can be used which helps keep the integrity of the cells being exposed to the infrared light. Paras and his colleagues then attached a protein known as transferrin to the outside of these quantum dots. Transferrin then caused the quantum rods to attach to a receptor that is found in cancer cells. Paras and his team were then able to attach the quantum rods to only the cancer cells. Then by using low intensity near infrared light they were able to image the cancer cells. [4]

Hisataka Kobayashi, M.D., Ph.D. and his colleagues have developed a new method for determining if cancer has spread to the lymphatic system, particularly when it is necessary to assess lymphatic drainage from two separate drainage basins. This new method for accurately mapping lymphatic flow from more than one drainage basin is done by using two colors of quantum dots. They were the able to track lymphatic flow by using a two color near infrared lymphangiography. Researchers found that the size of the quantum dot was important when choosing what they wanted to image. For example they found that when imaging lymphatic flow from the upper extremities quantum dots of 12 nanometers proved to be the best size. However when imaging lymphatic drainage from mammary glands, they found 6 nanometers was the best size. [5]

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A tiny quantum dot laced in cancer-detecting peptides [6]

Figure 3

Quantum dots are the future of cancer diagnoses. There are many promising new development made each year. Within the next few years it might be possible for this new technology to become the new standard for cancer detection. Quantum dots will allow doctors to properly track cancer and see how it develops within the human body. No longer will doctors have to make educated guesses on whether a cancer has spread to other parts of the body. Further development is vital to the success of this new technology as new advancements could save thousands of peoples of lives every year including your own. More research and studies need to be conducted on the longer term effects of quantum dots in the human body before wide spread use can be adapted. Proving that quantum dots are safe and reliable is vital to the long term research and development of quantum dots being used as a means of detecting cancer. Without proper funding for research from universities and governmental institutions this new technology would not exist. We need to invest in our own future and ensure that this promising new technology reaches its full potential.

References:

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