Researchers from North Carolina State University (NCSU, Raleigh, USA) used a laser-based rapid prototyping approach to create microneedles of varying lengths and shapes, based on two-photon polymerization of an acrylate-based polymer, which enabled the fabrication of hollow, plastic, microneedles with specific design characteristics. These were then used to deliver the quantum dots, nanoscale sized semiconductor crystal dyes with unique properties in terms of light emission that hold promise as a powerful tool in medical diagnosis and theranostics-based clinical applications.

The researchers then tested the plastic microneedle delivery system using pig skin, which has characteristics closely resembling human skin. Using a water-based solution containing the quantum dots, the researchers were able to capture images of the dots entering the skin using multiphoton microscopy. The images allowed the researchers to verify the effectiveness of the microneedles as a delivery mechanism. The study was published in the September 2010 issue of Faraday Discussions.

"Our use of this fabrication technology highlights its potential for other small-scale medical device applications," said lead author Professor Roger Narayan, Ph.D., of the department of biomedical engineering. "Our findings are significant, in part, because this technology will potentially enable researchers to deliver quantum dots, suspended in solution, to deeper layers of skin. That could be useful for the diagnosis and treatment of skin cancers, among other conditions."

Quantum dots have been found to be superior to traditional organic dyes on several counts, one of the most immediately obvious being brightness; it has been estimated that quantum dots are 20 times brighter and 100 times more stable than traditional fluorescent dyes. The use of quantum dots for highly sensitive cellular imaging has seen major advances over the past decade, allowing the acquisition of many consecutive focal-plane images that can be reconstructed into a high-resolution three-dimensional image. Another application that takes advantage of the extraordinary photostability of quantum dot probes is the real-time tracking of molecules and cells over extended periods of time; researchers were able to observe quantum dots in lymph nodes of mice for more than 4 months.

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