Biomedical Imaging of Cells using Quantum Dots

A joint research team, working at the National Institute of Standards and Technology (NIST) and the National Institute of Allergy and Infectious Diseases (NIAID), has discovered a method of using nanoparticles to illuminate the cellular interior to reveal these slow processes. Nanoparticles, thousands of times smaller than a cell, have a variety of applications. One type of nanoparticle called a quantum dot glows when exposed to light. These semiconductor particles can be coated with organic materials, which are tailored to be attracted to specific proteins within the part of a cell a scientist wishes to examine.

These quantum dots last longer than most of the organic dyes and fluorescent proteins that we previously used to illuminate the interiors of cells. They also have the advantage of monitoring changes in cellular processes while most high-resolution techniques like electron microscopy only provide images of cellular processes frozen at one moment. Using quantum dots, cellular processes involving the dynamic motions of proteins can be elucidated.

In the recent study, the research team focused primarily on characterizing quantum dot properties, contrasting them with other imaging techniques. In one example, they employed quantum dots designed to target a specific type of human red blood cell protein that forms part of a network structure in the cell's inner membrane. When these proteins cluster together in a healthy cell, the network provides mechanical flexibility to the cell so it can squeeze through narrow capillaries and other tight spaces. But when the cell gets infected with the malaria parasite, the structure of the network protein changes.

Since the clustering mechanism is not well understood, it was examined with the dots. Researchers believed that if they could develop a technique to visualize the clustering, they could learn something about the progress of a malaria infection, which has several distinct developmental stage.

fig : Human red blood cells, in which membrane proteins are targeted and labeled with quantum dots, reveal the clustering behavior of the proteins. The number of purple features, which indicate the nuclei of malaria parasites, increases as malaria development progresses. The NIST logo at bottom was made by a photo lithography technique on a thin film of quantum dots, taking advantage of the property that clustered dots exhibit increased photoluminescence. (White bars: 1 micrometer; red: 10 micrometer)

The team's efforts revealed that as the membrane proteins bunch up, the quantum dots attached to them are induced to cluster themselves and glow more brightly, permitting scientists to watch as the clustering of proteins progresses. More broadly, the team found that when quantum dots attach themselves to other nanomaterials, the dots' optical properties change in unique ways in each case. They also found evidence that quantum dot optical properties are altered as the nanoscale environment changes, offering greater possibility of using quantum dots to sense the local biochemical environment inside cells. about the progress of a malaria infection, which has several distinct developmental stages.