February 13, 2006
Nanoparticles Enable Rapid and Sensitive Detection of MicroRNAs
Over the past three years, a variety of technically difficult studies have shown that small RNA molecules, known as microRNAs or miRNAs, play a previously unappreciated but critical role in regulating gene expression, including the expression of cancer-related genes. Now, researchers attempting to better understand the precise role that miRNAs play in human diseases have a new tool – a nanoparticle-based assay that can detect the trace amounts of miRNAs found in cells. A paper in the journal Analytical Chemistry describes this new assay.
Zhiqiang Gao, Ph.D., and Zichao Yang, B. Eng., both at Nanyang Technological University in Singapore, developed the new assay using reactive nanoparticles made of osmium oxide. These nanoparticles will oxidize a chemical known as hydrazine, and if the nanoparticles are bound to an electrode, the oxidation of hydrazine generates a sharp, sensitive electrical signal registered by the electrode.
To construct the assay device, the researchers attached short RNA probes to the surfaces of electrodes made of indium tin oxide that were grown as an array on a glass slide. Each RNA probe is designed to bind to, or capture, a specific miRNA that might be found among all the RNA molecules extracted from a tissue sample. The investigators also created osmium oxide nanoparticles and coated them with isoniazid, a molecule that forms a chemical bond with the chemical functionality found at the end of miRNAs.
The assay itself involves adding a biological sample to the electrodes, and after an hour at room temperature, washing off any RNA molecules that have not bound to the capture probes. Osmium nanoparticles are then added and allowed to react with the captured miRNAs. After another washing to remove excess osmium nanoparticles, hydrazine is added and the electrical signals from the electrodes are recorded.
Results obtained using this method duplicated those obtained using more laborious and time-consuming assays involving the use of electrophoresis gels and fluorescence measurements. The investigators note that their nanoparticle-enabled assay is sensitive and accurate enough to detect changes in miRNA levels corresponding to less than a doubling in expression level, an important finding given that miRNA levels do not change dramatically when cellular conditions are altered.
This work is detailed in a paper titled, “Detection of microRNAs using electrocatalytic nanoparticle tags.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.