CURRENT RESEARCH TOPICS
Electronic Sensors
of Dielectrophoretic actuation for microfluidics based single cell diagnostics:
The dielectric response of cells offer insight into many aspects of their
physiological condition. It can detect the loss of ions that occurs during
programmed cell death or the uptake of ions by multidrug resistant cancer cells.
For portable and low cost applications it is highly desirable to interrogate
cells using an all-electronic approach. In collaboration with G. Bridges, we
have demonstrated an all-electrical approach to dielectric cell diagnostics
that uses a combination of (10 kHz to 10 MHz) electric fields for stimulus and capacitance
(at ~1-2 GHz) for sensing. We demonstrated use of a sub-attofarad (~2 GHz
microwave interferometer) differential capacitance sensor to detect single
cells passing over co-planar electrodes while simultaneously dielectrophoretically
actuating cells. We have theoretically and experimentally determined the
fundamental limits of this approach due to the shear-induced rotation of cells
(Phys.Rev.E). Using this approach we have
demonstrated mechanical differentiation of cancer cells and dielectric
detection of the onset of programmed cell death (apoptosis) in a bioprocess
(Biomicrofluidics). As a result of this work a two-population model of bulk dielectric
response that better explained the link to physiological changes (BioTech and BioEngg). This
work was highlighted in the Genetic Engineering and Biotechnology News (Sept
2013, Vol. 33).
Figure 1. Signal form cells as they pass sensing electrodes. Note some cells are attracted ( pDEP) and some are repulsed (nDEP)
Figure 2. Signal from a signal 6 micron PSS bead passing over electrodes at a centre of mass altitude of ~6 microns

Figure 3. H-channel flow design, used bring cells into the analysis region at the bottom of the die. Die is ~15mmx15mm.
Sensors for Structural Health Monitoring
of Civil Infrastructure:
We adapted instrumentation from SPM for use in the monitoring of civil
structures such as bridges. We adapted a capacitance sensor for use in a novel
passive wireless strain sensor and fiber optics techniques were adapted for
fiber Bragg grating (FBG) strain sensors. The FBG work demonstrated the use of
a gas cell reference with a swept frequency laser for a long-term frequency
standard to improve the precision of FBG measurements for civil infrastructure
monitoring. In collaboration with G. Bridges (Manitoba) I have pioneered
several passive wireless sensors that are based on resonant RF cavities, where
the resonant frequency is modulated by a measurand. The sensor can then be
interrogated remotely using microwave pulse-echo techniques. We have
demonstrated that the sensor that can be interrogated at a distance of 8 m with
a resonant frequency resolution of less than 10 ppm. This resolution is
suitable for civil monitoring applications where strain resolution of less than
10 ppm is required.
Figure 4. Schematic of pulse echo technique used to interrogate RF cavity sensors. With pulse echo a range of over 8 m is achievable.
Figure 5. Interrogator electronics with resonant peak on oscilloscope.
Conducting and conjugated
polymer sensors and devices:
Collaborations between Thomson and Freund (Chemistry), has led to the discovery
of several new approaches to fabricating electronic sensors and devices. A new
electronic device based on conductivity modulation through field-induced motion
of ions in conjugated polymers has been demonstrated in several proof-of-concept
devices including a memory storage device.
This work has been published as a communication in Advanced Materials. Thomson/Freud used this approach on
a 400 nm cross-bar device in a cross bar configuration to demonstrates that the
approach of electrochemically depositing the active layer after the
lithographic fabrication of the cross bar is feasible. An important advantage of this system is
that it is compatible with conventional CMOS electronics and requires no electrolyte. Fruend and Thomson have also
collaborated on developing sensors and artificial photosynthetic systems.
Conducting polymer and capacitive sensors for detection of volatile vapors and
carbon dioxide from grain spoilage have been demonstrated in a laboratory
setting.
Nanoprobe Measurements for Electronic Materials Analysis: In
collaboration with G.E. Bridges, I have pioneered several scanning probe
techniques for integrated circuit (IC) testing. SPM: Scanning probe microscopy
(SPM) has developed into a powerful set of tools for the analysis of most
material properties with nanometer resolution. Our group has contributed to
advances in this field for the last 20 years. Our recent contributions are the
demonstration of a new method to map currents in integrated circuits and also
to image high frequency phenomena such as surface acoustic waves. We have also
demonstrated tip induced electric field actuation of micro-resonators with
simultaneous detection via cantilever detection.