At the University of Washington and Emory University, scientists have developed a new technique that allows for faster selective silencing of particular genes. At the heart of the method, which is designed for selective regulation of protein production, are specially engineered multifunctional nanoparticles composed of short-interfering RNA (siRNA) and semiconductor quantum dots (QDs), all enclosed by a proton-absorbing polymeric coating (aka proton sponge).
Each quantum dot was surrounded by a proton sponge that carried a positive charge. Without any quantum dots attached, the siRNA’s negative charge would prevent it from penetrating a cell’s wall. With the quantum-dot chaperone, the more weakly charged siRNA complex crosses the cellular wall, escapes from the endosome (a fatty bubble that surrounds incoming material) and accumulates in the cellular fluid, where it can do its work disrupting protein manufacture.
Key to the newly published approach is that researchers can adjust the chemical makeup of the quantum dot’s proton-sponge coating, allowing the scientists to precisely control how tightly the dots attach to the siRNA.
Quantum dots were dramatically better than existing techniques at stopping gene activity. In experiments, a cell’s production of a test protein dropped to 2 percent when siRNA was delivered with quantum dots. By contrast, the test protein was produced at 13 percent to 51 percent of normal levels when the siRNA was delivered with one of three commercial reagents, or reaction-causing substances, now commonly used in laboratories.
Central to the finding is that fluorescent quantum dots allow scientists to watch the siRNA’s movements. Previous siRNA trackers gave off light for less than a minute, while quantum dots, developed for imaging, emit light for hours at a time. In the experiments the authors were able to watch the process for many hours to track the gene-silencer’s path.
The new approach is also five to 10 times less toxic to the cell than existing chemicals, meaning the quantum dot chaperones are less likely to harm cells. The ideal delivery vehicle would have no effect; the only biological change would be siRNA blocking cells’ production of an unwanted protein.
The exact reason that the quantum dots were more effective than previous techniques is, however, still a mystery.
University of Washington press release: Gene silencer and quantum dots reduce protein production to a whisper …
Abstract: Proton-Sponge Coated Quantum Dots for siRNA Delivery and Intracellular Imaging J. Am. Chem. Soc., ASAP Article, 10.1021/ja800086u
