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

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. 

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.