We demonstrate frequency differential CARS (D-CARS) using femtosecond laser pulses linearly chirped by glass
elements of high group-velocity dispersion. By replicating the Pump-Stokes pair into a pulse train at twice the
laser repetition rate, and controlling the instantaneous frequency difference by glass dispersion, we adjust the
Raman frequency probed by each pair in an intrinsically stable way. The resulting CARS intensities are detected
simultaneously by a single photomultiplier as sum and difference using lock-in detection. We demonstrate
imaging of living cells with strongly suppressed non-resonant background. We also show D-CARS using a single
femtosecond laser source.
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 present details of the development of a optical biochip, with integrated on-chip laser excitation, for fluorescence
intensity cell based assays. The biochip incorporates an "active surface" for the control and manipulation of fluorescent
species placed directly on the device. The active elements of the biochip are one-dimensional periodic sub-wavelength
corrugations fabricated on a thin gold film. We have made fluorescence intensity measurements of both an organic dye
(Cy5), and immobilized and fluorescently labeled (with 705 nm emitting quantum dots), mammalian tumor cells in
contact with the active surface. Here we show that the presence of the periodic grating can be used to control both the
excitation and fluorescence generation process itself. We demonstrate that the gratings convert evanescent surface optical
modes into well-defined beams of radiation in the far-field and at the surface of the device this produces highly
contrasting regions of fluorescence excitation providing regions of high spatial selectivity.
We have measured the pulsed light-current characteristics of a series of InGaN/GaN quantum well light-emitting diodes which were annealed post-growth at different temperatures as a function of their operating temperature. The light output at a fixed current density increases with the temperature of measurement, reaches a maximum and then decreases for all the diodes. The measurement temperature at which the maximum light output occurs and the magnitude of the light output depend on the post-growth thermal anneal temperature. The thermal anneal temperature is thought to affect the acceptor concentration in the p-doped cap layer, which also changes the carrier mobility. A simulation, incorporating carrier leakage, is used to reproduce the experimental behavior where the acceptor concentration is changed to represent the effects of the different anneal temperatures.