Power-free microchip could speed up disease diagnosis

The new microfluidic chip, developed by researchers at Japan’s RIKEN Advanced Science Institute (ASI), is claimed to enable the detection of microRNA (miRNA) from extremely small samples in 20 minutes.

By reducing the time and quantity of sample required for detection, the chip is claimed to lay the groundwork for the early-stage point-of-care diagnosis of diseases such as cancer and Alzheimer’s.

According to RIKEN, miRNAs are small, non-coding RNA molecules that regulate gene expression in a range of biological processes, including development, cell proliferation, differentiation and cell death (apoptosis).

Concentration of certain miRNA in body fluids increases with the progression of diseases such as cancer and Alzheimer’s, generating hope that these short RNA may hold the key to faster, more accurate diagnoses.

Currently available techniques for sensitive miRNA detection, however, require days to reach a diagnosis and involve equipment operated only by trained personnel.

According to a statement, the research team set out to overcome these obstacles by developing a device that enables fast, easy-to-use point-of-care diagnosis from only a very small sample.

In earlier research, the team developed a device in the form of a microchip that uses polydimethylsiloxane (PDMS), a silicone compound known for its air absorption properties, to pull reagents into a capture probe for analysis.

This pumping technique simplified design by eliminating the need for external power sources, but the device required a quantity of sample too large for practical applications.

The new device also uses PDMS as an air pump, but improves the method’s sensitivity through a signal amplification technique called laminar flow-assisted dendritic amplification (LFDA).

First, DNA fragments that bond to specific miRNA sequences are fixed to a glass surface along with the miRNA sample to be analysed and are then sandwiched under a layer of PDMS with channels in it.

Emptied of air in a vacuum, the PDMS layer induces a pump effect that pulls amplification reagents, inserted at the channel inlets, into the channels and into contact with the miRNA, creating fluorescence-labelled dendritic structures that grow over time and can be quickly detected.

The sensitivity of this technique is said to reduce the sample quantity required for diagnosis to 0.25 attomoles (10–18 mole), a 1,000-fold improvement over the team’s earlier model.

Together with its detection time of only 20 minutes, these properties make the self-powered device ideal for use in resource-poor environments, promising portable point-of-care diagnosis in developing countries.