A microfluidic-assisted microarray for ultrasensitive detection of miRNA under an optical microscope

In this article, we report on direct detection of microRNAs (miRNAs) on a microarray by differential interference contrast (DIC) imaging technique. While the best resolution achieved with a fluorescence scanner is similar to 1 mu m, the DIC imaging technique adopted in our study offers the possibility of imaging individual reporting gold nanoparticles, or, in other words, individual miRNA strands. Due to its unrivalled resolution, the present technique could detect as low as 300 copies of target miRNAs in a sample volume of 1.0 mu l. With the greatly improved sensitivity, the amount of total RNA needed in the assay is reduced to only a few nanograms, offering an excellent opportunity for fast and direct miRNA profiling without engaging any labeling and amplification procedure. Expression patterns of hsa-let-7 family members in healthy versus cancer cells analyzed on our microarray, are found to be consistent with the patterns obtained on a commercial microarray and those reported in the literature.