Card-sized device can detect diseases from tiny samples in minutes
22 November 2012
A hand-held device that needs no power can detect the
molecular signature of diseases in minutes. By drastically reducing the
time and quantity of sample required for detection, the chip lays the
groundwork for early-stage point-of-care diagnosis of diseases such as
cancers and Alzheimer's.
The card-sized microfluidic chip developed by researchers at the
RIKEN Advanced Science Institute (ASI) in Japan can detect microRNA
from extremely small samples in only 20 minutes.
MicroRNAs (miRNAs) are small, non-coding RNA molecules that
regulate gene expression in a wide range of biological processes
including development, cell proliferation, differentiation and cell
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
diagnosis. Currently available techniques for sensitive miRNA
detection, however, require days to reach a diagnosis and involve
equipment operated only by trained personnel, making them
impractical for use in many situations.
Development of the microfluidic device
The research team set out to overcome these obstacles by
developing a device that enables fast, easy-to-use point-of-care
(POC) diagnosis from only a very small sample. In earlier research,
the team developed a device in the form of a microchip which 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 drastically
improves the method's sensitivity through a signal amplification
method called laminar flow-assisted dendritic amplification (LFDA).
First, DNA fragments which bond to specific miRNA sequences are
fixed to a glass surface along with the miRNA sample to be analyzed,
and then sandwiched under a layer of PDMS with channels in it
Figure 1. New power-free RNA detection
Left: Fabricated microchip. Right: Microchannel
Emptied of air in a vacuum, the PDMS layer induces a pump effect
which pulls amplification reagents, inserted at the channel inlets,
into the channels and into contact with the miRNA, creating
fluorescence-labeled dendritic structures that grow over time and
can be quickly detected.
The sensitivity of this technique drastically reduces the sample
quantity required for diagnosis to only 0.25 attomoles (10-18 mole),
a thousand-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 for millions in
developing countries and around the world.
Hideyuki Arata, Hiroshi Komatsu, Kazuo Hosokawa, and Mizuo Maeda
"Rapid and Sensitive MicroRNA Detection with Laminar Flow-Assisted
Dendritic Amplification on Power-Free Microfluidic Chip". PLoS ONE,