Development of microfluidic concentrator using ion concentration polarization mechanism to assist trapping magnetic nanoparticle-bound miRNA to detect with Raman tags.

MicroRNAs (miRNAs) are small noncoding single-stranded ribonucleic acid molecules. This type of endogenous oligonucleotide could be secreted into the circulation and exist stably. The detection of specific miRNAs released by cancer cells potentially provides a noninvasive means to achieve early diagnosis and prognosis of cancers. However, the typical concentration of miRNAs in blood is below the ultratrace level. This study uses a simple thermoplastic microfluidic concentration device based on an ion concentration polarization mechanism to perform enrichment and cleanup and Raman sensing beads to determine miRNA quantitatively. One sample solution containing target miRNA molecules having been hybridized with two nucleotide probes, where one probe is on a Raman tag of a nanoaggregate embedded bead (NAEB) and the other probe is on a magnetic nanoparticle (MNP), is first filled into the device. When an external field is applied across a cation exchange membrane stationed in the middle conduit of the device, the MNP-miRNA-NAEB complexed particles are enriched near the membrane edge of the cathode side. The concentrated complexed particles are further trapped using an external magnet to perform washing steps to remove excess noncomplexed NAEBs. When cleanup steps are accomplished, the remaining complexed particles are loaded into one detection capillary to acquire Raman signals from the sensing beads. Compared with that using a conventional magnetic trapping device, the cleanup time is shortened from nearly an hour to less than 10 min. Sample loss during the washing steps becomes more controllable, resulting in adequate standard curve linearity (R > 0.99) ranging from 1 to 100 pM.