Detecting rare microRNAs with gold nanoparticles

Over the past three years, numerous studies have shown that short pieces of single-stranded RNA, known as microRNAs, play a central role in the development of at least some cancers.

Now, cancer researchers have a nanoparticle-based tool for more quickly and accurately detecting the presence of specific microRNAs, a development that could lead to new diagnostic tests for cancer.

Robert Corn, Ph.D., of the University of California-Irvine, led the team of investigators that has developed a novel assay for microRNAs. This new assay, which is about 50 times more sensitive than the methods used currently to detect miRNAs, uses gold nanoparticles and surface plasmon resonance imaging to detect attomole amounts of microRNAs. This sensitivity is sufficient to detect microRNAs in biological samples, even those containing large amounts of other RNA molecules. This investigators report this work in the Journal of the American Chemical Society.

The assay relies on the ability of commercially available, DNA-like molecules known as locked nucleic acids to bind with incredible strength to microRNAs. The investigators first create an array of locked nucleic acids immobilized onto a solid substrate. They then add the microRNAs-containing sample to this array and allow hybridization to take place between the locked nucleic acids and any microRNAs.

Next, the investigators use an enzyme known as poly(A) polymerase to add a long tail of adenine (A) to the end of any bound microRNAs molecules. Finally, they add gold nanoparticles coated with strands of thymine (T) – thymine and adenine are complementary nucleic acid, so the poly(T) strands bind strongly to any poly(A) tails extended from microRNAs. The attached gold nanoparticles are easily detected and quantified using surface plasmon resonance imaging.

To demonstrate the utility of this assay, the investigators used it to detect three specific microRNAs in total RNA samples from mouse liver. The assay was able to detect microRNA concentrations as low as 20 femtomolar. The investigators are now creating a larger array capable of profiling all microRNAs in biological samples.

This work is detailed in a paper titled, “Attomole microarray detection of microRNAs by nanoparticle-amplified SPR imaging measurements of surface polyadenylation reactions.” This paper was published online in advance of print publication. An abstract is available at the journal’s website. View abstract.