Cite this: Lab Chip, 2013, 13, 3698
A lab-in-a-droplet bioassay strategy for centrifugal
microfluidics with density difference pumping, power
to disc and bidirectional flow control3
Received 2nd May 2013,
Accepted 20th June 2013
DOI: 10.1039/c3lc50545f
www.rsc.org/loc
Guanghui Wang,
ab
Ho-Pui Ho,*
a
Qiulan Chen,
a
Alice Kar-Lai Yang,
c
Ho-Chin Kwok,
a
Shu-Yuen Wu,
a
Siu-Kai Kong,
c
Yiu-Wa Kwan
d
and Xuping Zhang
b
In this paper, we present a lab-in-a-droplet bioassay strategy for a centrifugal microfluidics or lab-on-a-disc
(LOAD) platform with three important advancements including density difference pumping, power to disc
and bidirectional flow control. First, with the water based bioassay droplets trapped in a micro-channel
filled with mineral oil, centrifugal force due to the density difference between the water and oil phases
actuates droplet movement while the oil based medium remains stationary. Second, electricity is coupled
to the rotating disc through a split-core transformer, thus enabling on-chip real-time heating in selected
areas as desired and wireless programmable functionality. Third, an inertial mechanical structure is
proposed to achieve bidirectional flow control within the spinning disc. The droplets can move back and
forth between two heaters upon changing the rotational speed. Our platform is an essential and versatile
solution for bioassays such as those involving DNA amplification, where localized temperature cycling is
required. Finally, without the loss of generality, we demonstrate the functionality of our platform by
performing real-time polymerase chain reaction (RT-PCR) in a linear microchannel made with PTFE (Teflon)
micro-tubing.
Introduction
The importance of developing high-throughput and low-cost
bioassay devices could not be more emphasized nowadays as
the demand for better healthcare and disease treatment is
constantly increasing. In light of the miniaturization revolu-
tion brought by the microelectronics technologies, a ‘‘lab-on-a-
chip’’ (LOC) approach for conducting biological tests has
emerged in recent years.
1–5
Meanwhile, in the past decade,
there has been much ongoing research effort reported on the
lab-on-a-disc (LOAD) microfluidics platform or centrifugal
microfluidics platform for biomedical and clinical diagnostic
applications.
6–10
The LOAD platform offers a very simple
solution, which alleviates the pumping problem by introdu-
cing centrifugal force through spinning the LOC device
platform. Since centrifugal force is present everywhere on
the disc, sample propulsion capability is at the user’s disposal
practically anywhere within the disc’s boundary. No external
pump is required at all. Sample movement can be manipu-
lated by varying the spinning speed or the spinning direction.
Because of the obvious advantages in terms of sample
actuation and direct compatibility with existing CD-ROM
readers,
11
centrifugal microfluidics has been studied by many
researchers. Recent reviews written by Madou et al.,
8
Gorkin
et al.
9
and Nolte
7
have provided a comprehensive summary of
the device physics and reported applications of centrifugal
microfluidics. Basic microfluidic operations such as flow
control using passive capillary valves, single-use active valves
based on a melting-wax technique, siphoning, volume meter-
ing, mixing and flow switching have been demonstrated.
7,9
Over the years, a range of applications including nucleic acid
amplification through polymerase chain reaction (PCR)
12
and
loop-mediated isothermal amplification (LAMP),
13
enzyme-
linked immunosorbent assays (ELISA),
14,15
cell counting,
16
cell
lysing,
17
cell staining,
18
single cell entrapment,
19,20
and DNA
hybridization
21
have been reported. It is clear that the LOAD
platform is a viable approach for practical bioassays.
The situation however is far from satisfactory. There are
three major problems or shortages for existing LOAD systems.
First, our literature search has revealed a common phenom-
enon: until now all reported cases of LOAD application are
passive devices. Nearly all applications are limited to simple
a
Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin ,
Hong Kong, P. R. China. E-mail: ghwang001@gmail.com; hpho@ee.cuhk.edu.hk;
Tel: +852 3943 8279
b
Institute of Optical Communication Engineering, Nanjing University, Nanjing
210093, P. R. China
c
School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, P.
R. China
d
School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, Hong
Kong, P. R. China
3
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3lc50545f
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