The integration of discrete optical excitation and detection components in a microfluidic platform is an
important pre-requisite for realisation of Lab-on-a-chip devices. This research presents a microfluidic
system made of polymer material with integrated miniaturized vertical cavity surface emitting laser
(VCSEL) source. The light emitted by the VCSEL is detected by a conventional 5 mm diameter
photodiode. The ability to read and detect microbeads encoded with through holes in the silicon
substrate verified successful integration of a functional VCSEL in the polymer microchip.
The microfluidic system was composed of two processed polymer chips that are bonded together. The
substrate contains cavities to accommodate VCSEL components. The second polymer chip
(superstrate) contains the microfluidic channel network. The conventional photodiode detector was
easily mounted on top of the superstrate. Polymer chip substrates and master templates for hot
embossing were fabricated by rapid prototyping technology. Fabricated masters were then moulded
into thermoplastic polycarbonate (PC) substrate by hot embossing. Generated polymer sheets with
embossed structures were diced into polymer chips and subsequently bonded together using a
customised procedure to provide a complementary moulded cavity which accommodates the VCSEL.
The optically encoded microbeads are illuminated with a VCSEL which is operated with a power of 0.7
mW. As the bead flows along the channel (illuminated with the VCSEL), the emitted light from the
VCSEL device is modulated by the bar code and subsequently detected by the photodiode. Signal
measurements confirm that different levels of the VCSEL light can be reproducibly detected by
customized Labview software.
A novel integrated microsystem for multiplex processing of encoded microbeads on a single microchip
is presented. Conventional bio-analysis of proteins and DNA requires a combination of different
techniques including: accurate delivery of reagents, mixing, then reaction at controlled temperature to
yield a detectable product. Standard laboratory bio-assays require intervention at several stages to
manipulate samples. Furthermore, ultra sensitive quantification with a colorimetric or fluorescent label
is required to obtain the necessary results. This process is time consuming and labour intensive.
However the new multiplex microsystem reported here enhances logical bio-assay development due to
the integration of a compact optical detection system with customized analysis software in an enclosed
microfluidic environment. The bioassay was realised by careful integration of a Peltier cell and
associated control electronics which enabled specific identification of a hybridized DNA sequence
from a 4 x 4 cDNA library at a fixed temperature of 42<sup>o</sup>C. The multiple fluorescence measurements of
complementary hybridised DNA at the surface of encoded microbeads was confirmed. Thus, the
complete integration of the different bio-assay components on a single multiplex assay platform
provides distinct advantages of reduced sample volume, rapid analysis and low cost.
The first on-chip injection and manipulation of optically encoded, silicon microbeads in a microfluidic platform is reported. Encoded microbeads of different shapes and sizes were fabricated in silicon via standard microfabrication techniques. The optical signature consisted of a series of lithographically defined bar-codes, which can be identified by a laser detection system. <i>In-situ</i> identification of encoded microbeads was possible at microbead velocities ≤ 50 cm per second. The microbeads can also be transported within a channel network in accordance with the encoded optical signature of each bead. The microbead transport is controlled by the laminar flow of a liquid in pressure driven microchannels.
Hydrodynamic pulsing facilitated single and multiple injection of microbeads from a reservoir into the laminar fluid stream of a branched microfluidic network. Careful control of the fluid velocity and alteration of the microchannel geometry also enabled manipulation of microbead velocity. The incorporation of five pillars to retain microbeads at a specific location within the microchannel network
formed the basis of a reaction chamber for on chip functionalization of microbeads. The principle of hydrodynamic switching was utlized to re-direct the transport of microbeads at a branched microfluidic
network. In the final part of this research we verify that this microbead technology is suitable for detection of specific target DNA.
With the continuing advances in the miniaturization of analytical techniques, and in particular of microchip capillary electrophoresis, the challenge of rapid metal complex speciation can now be taken up. The discrimination between different chemical species of metal ions is important as the environmental toxicity, biological activity and availability of many metals is often species dependent. Extensive electrophoresis studies have focused on speciation of low molecular
weight metal complex speciation. However, limited research has focused on the separation of different stoichiometries of species within the same metal-ligand system. This new research demonstrates the first rapid separation of individual species in equilibrium within selected metalligand systems by microchip electrophoresis. The transfer of speciation ability within a single metal-ligand system from capillary electrophoresis to microchip electrophoresis has been demonstrated with considerable success. This emphasises the immense future potential for microchip electrophoresis in the field of rapid chemical speciation.
Phenol red was retained in cellulose acetate loaded with plasticiser. The resultant polymer enabled optical determination of physiological pH . Continuous pH measurements were achieved in whole blood with a flow cell and customised fibre optic probe.