Optical biochips may incorporate both optical and microfluidic components as well as integrated light emitting
semiconductor devices. They make use of a wide range of materials including polymers, glasses and thin metal films
which are particularly suitable if low cost devices are envisaged. Precision laser micromachining is an ideal flexible
manufacturing technique for such materials with the ability to fabricate structures to sub-micron resolutions and a
proven track record in manufacturing scale up.
Described here is the manufacture of a range of optical biochip devices and components using laser micromachining
techniques. The devices employ both microfluidics and electrokinetic processes for biological cell manipulation and
characterization. Excimer laser micromachining has been used to create complex microelectrode arrays and microfluidic
channels. Excimer lasers have also been employed to create on-chip optical components such as microlenses and
waveguides to allow integrated vertical and edge emitting LEDs and lasers to deliver light to analysis sites within the
Ultra short pulse lasers have been used to structure wafer level semiconductor light emitting devices. Both surface
patterning and bulk machining of these active wafers while maintaining functionality has been demonstrated. Described
here is the use of combinations of ultra short pulse and excimer lasers for the fabrication of structures to provide ring
illumination of in-wafer reaction chambers.
The laser micromachining processes employed in this work require minimal post-processing and so make them ideally
suited to all stages of optical biochip production from development through to small and large volume production.
An optical biochip is being developed for monitoring the sensitivity of biological cells to a range of environmental
changes. Such changes may include external factors such as temperature but can include changes within the suspending
media of the cell. The ability to measure such sensitivity has a broad application base including environmental
monitoring, toxicity evaluation and drug discovery. The device under development, capable of operating with both
suspension and adherent cell populations, employs electrokinetic processes to monitor subtle changes in the physicochemical
properties of cells as environmental parameters are varied. As such, the device is required to maintain cells in
a viable condition for extended periods of time.
The final device will employ integrated optical illumination of cells using red emitting LED or laser devices with light
delivery to measurement regions achieved using integrated micro-optical components. Measurements of electrokinetic
phenomena such as dielectrophoresis and electrorotation will be achieved through integrated optical detectors.
Environmental parameters can be varied while cells are actively retained within a measurement structure. This enables
the properties and sensitivity of a cell population to be temporally tracked.
The optical biochip described here uses a combination of microfabrication techniques including photolithographic and
laser micromachining processes. Here we describe the design and manufacturing processes to create the components of
the environmental monitoring strutures of the optical biochip.
We have developed a range of optical biochip devices for conducting live and fixed cell-based assays. The devices
encompass the ability to process an entire assay including fluorescently labelling cells, a microfluidic system to transport
and maintain cells to deliver them to an optical area of the device for measurement, with the possibility of a
incorporating a sorting step in between. On-chip excitation provided by red emitting LED and lasers define the excitation
wavelength of the fluorophore to be incorporated into the assay readout. The challenge for such an integrated
microfluidic optical biochip has been to identify and characterise a longterm fluorescent label suitable for tracking cell
proliferation status in living cells.
Traditional organic fluorophores have inherent disadvantages when considering their use for an on-chip device requiring
longterm cellular tracking. This has led us to utilise inorganic quantum dots (QDots) as fluorophores for on- chip assays.
QDs have unique properties such as photostability, broad absorption and narrow emission spectra and are available in a
range of emission wavelengths including far red. They also have much higher quantum efficiencies than traditional
organic fluorophores thus increasing the possible dynamic range for on-chip detection. Some of the QDots used have the
added advantage of labelling intact cells and being retained and distributed among daughter cells at division, allowing
their detection for up to 6 generations. The use of these QDs off-chip has suggested that they are ideal for live cell, nonperturbing
labelling of division events, whereby over time the QD signal becomes diluted with each generation.
Here we describe the use of quantum dots as live cell tracers for proliferating populations and the potential applications
in drug screening and optical biochip environments.
We demonstrate complete integration of a fluorescence-based assay in that the analyte well is also an optical emitter.
Laser machining is used to create 'active micro-wells' within semiconductor light emitting diode and laser structures.
These are then used to optically excite fluorescently-labelled beads in solution within the well. The results show
efficient illumination on a par with traditional lamp-based excitation. This technology therefore provides active microwell
plates with completely localized excitation, confined to the analysis well, that can be engineered via the micro-well
geometry. The micro-wells have also been machined within the cavity of lasing semiconductor structures and coherent
emission maintained. Thus lasing multi-well plates are also realizable.
Excimer laser micromachining provides a flexible means for the manufacture and rapid prototyping of miniaturized systems such as Biofactory-on-a-Chip devices. Biofactories are miniaturized diagnostic devices capable of characterizing, manipulating, separating and sorting suspension of particles such as biological cells. Such systems operate by exploiting the electrical properties of microparticles and controlling particle movement in AC non- uniform stationary and moving electric fields. Applications of Biofactory devices are diverse and include, among others, the healthcare, pharmaceutical, chemical processing, environmental monitoring and food diagnostic markets. To achieve such characterization and separation, Biofactory devices employ laboratory-on-a-chip type components such as complex multilayer microelectrode arrays, microfluidic channels, manifold systems and on-chip detection systems. Here we discuss the manufacturing requirements of Biofactory devices and describe the use of different excimer laser micromachined methods both in stand-alone processes and also in conjunction with conventional fabrication processes such as photolithography and thermal molding. Particular attention is given to the production of large area multilayer microelectrode arrays and the manufacture of complex cross-section microfluidic channel systems for use in simple distribution and device interfacing.
The miniaturised Biofactory-on-a-Chip devices described here are integrated systems capable of the rapid analysis of small volume particulate samples and have applications in areas such as medical and biological cell diagnostics, chemical detection and water quality control. The devices use the A.C. electrokinetic phenomena of dielectrophoresis, travelling wave dielectrophoresis and electrorotation to manipulate, separate and characterise particle systems by exploiting their dielectric properties. Biofactory fabrication makes use of conventional photolithographic processes along with precision excimer laser ablation based micromachining. Using this combination of technologies, a wide range of manufacturing issues have been addressed and are discussed here. For instance, reliable interconnection of multilayer electrodes has been achieved using laser machining of via- holes between lithographically produced electrodues. Also, accurate fluidic microchannel systems with varying curved cross-sections that allow the smooth transport of a sample through the device whilst eliminating problems of particle trapping have been developed using excimer laser machining. Although the biofactory devices presented here have been applied to the fractionation of micro-organisms such as E. coli from red blood cells, the flexibility of design allows these devices to perform a wide range of complex bioprocessing function in a single, low-cost and miniaturised package.