Professor Eric Bakker

Research

Chemical Sensors and Nanoscale Analysis

Our group is interested in the understanding and development of electrochemical and optical sensor principles and the use of nanoscale materials for clinical, bioanalytical and environmental applications. Currently, the principal directions include the study of trace level potentiometric sensors and their coupling to nanoparticle labeled bioassays, instrumentally controlled ion extraction based sensors, and nanosphere and microsphere-based fluorescent detection principles including chemically selective scanning probe microscopy.

Trace Level Potentiometric Sensors

This project develops the theoretical and experimental foundation for establishing potentiometric with detection limits in the micromolar to picomolar range. The understanding and chemical suppression of zero current ion fluxes at ion-selective membranes and their influence on the lower detection limit and selectivity of potentiometric sensors is a key aspect of this research. The fundamental limits of such sensors in confined sample volumes is explored, as potentiometry is known not to be dependent on scaling laws. All solid state multilayer films are explored for this purpose, using conducting polymer underlayers. If successful, this methodology may become one of the most sensitive detection methods in terms of the total amount of measurable ions. Further, in analogy to established voltammetric sensors, we couple the highly sensitive potentiometric detection to analyte enrichment processes for a further drastically improved detection limit that may surpass that of any other routine electrochemical method. The third large aim of this research is to use potentiometric sensors as transducers for biorecognition events at or near ion-selective membranes, including the detection of nanoparticle labeled bioreagents. Lastly, novel detection concepts will be explored that make use of ion fluxes at ion-selective membranes to design novel sensor concepts. Collaborators in this research are Erno Pretsch, ETH Zurich, Switzerland, Roland De Marco, Curtin University, and Joseph Wang, University of California at San Diego. We also enjoy a good cooperation with Prince of Songkla University in Thailand on this topic.

Instrumentally Controlled Extraction Based Sensors

Here, electrochemical multipulse techniques are explored to place ion-selective polymeric membranes under instrumental control. The main thrust of this work is the development of drastically improved sensors for the polyionic anticoagulant heparin and its antidote protamine that are stable and fully reversible. The studies include coulometrically controlled polyion releasing membranes for continuous on-line heparin-protamine titration experiments and the use of thin layer coulometry for sensors with high robustness. Additionally, numerous examples of promising ISE response principles that make use of ion fluxes are adapated to the new interrogation technique. Sensors with extremely high sensitivities, highly reproducible behavior in situations where traditional ion sensors fail, and the exploration of the time dependent potential response within a single pulse for multidimensional interrogation of the system are explored. Finally, a novel approach to the detection of surface confined biorecognition events at liquid-liquid interfaces is studied using the ion for which the membrane is selective as a marker. A collaborator in this research are Roland De Marco, Curtin University.

Microsphere and Nanosphere Based Sensors

This research focus blurs the lines between chemical sensors and bead-based assays, with the goal of developing a simple particle based total clinical analysis system. Specifically, micron-sized fluorescent probes selective for clinically relevant ions and metabolites are developed on the basis of extraction and membrane transport principles to expand the uses of microsphere-based chemistries. Our group is involved in the receptor synthesis, polymeric synthesis, particle fabrication and characterization, and sensor development of this research. The final beads are interrogated spectroscopically, using spatially resolved microspectroscopy, analytical flow cytometry and related methods, and on imaging fibers.

Ion-sensitive polymeric microspheres are attached to scanning probes for the establishment of chemically selective scanning probe microscopy. Collaborators with this research are Roland De Marco and Thomas Becker at Curtin University.

Another direction involves the use of optical reporters based on fluorescent nanomaterials in order to fabricate nanoscale assemblies that function as sophisticated optical indicators for a variety of biomolecules. Nanosphere fabrication is performed with a novel spinning disk reactor technology in collaboration with the group of Colin Raston at the University of Western Australia.

Group Members

• Dr. Ewa Grygolowicz-Pawlak (postdoc)
• Dr. Craig Bullen (postdoc with Colin Raston, UWA)
• Sven Ernst (Honours Student)
• Agnieszka Zdanowicz (Honours Student)
• Dr. Debbie Sylvester-Dean (Curtin Research Fellow)

Education

• Diploma of Chemistry, 1989, Swiss Federal Institute of Technology
• Doctor of Natural Science, 1993, Swiss Federal Institute of Technology

Recognitions

• ARC Australian Professorial Fellow, 2009-2013
• Roche Prize for Sensor Technology, 2004
• Alumni Professor, Auburn University, 2001-2005
• Young Investigator Award, Society for Electroanalytical Chemistry, 2001
• H-index of citations: 44

Selected Publications

Out of more than 170 publications:

• Potentiometric Detection of DNA Hybridization A. Numnuam, K. Y. Chumbimuni-Torres, Y. Xiang, R. Bash, P. Thavarungkul, P. Kanatharana, E. Pretsch, J. Wang, E. Bakker, J. Am. Chem. Soc., 130 (2008) 410-411.
• Direct Sensing of Total Acidity with Polymer Membrane Ion-Selective Electrodes K. L. Gemene, E. Bakker, Anal. Chem., 80 (2008) 3743-3750.
• Aptamer-Based Potentiometric Measurements of Proteins Using Ion-Selective Microelectrodes A. Numnuam, K. Y. Chumbimuni-Torres, Y. Xiang, R. Bash, P. Thavarungkul, P. Kanatharana, E. Pretsch, J. Wang, E. Bakker, Anal. Chem., 80 (2008) 707-712.
• Multiplexed Flow Cytometric Sensing of Blood Electrolytes in Physiological Samples Using Fluorescent Bulk Optode Microspheres C. Xu, K. Wygladacz, R. Retter, M. Bell, E. Bakker, Anal. Chem., 79 (2007) 9505-9512.
• Multicolor Quantum-dot Encoding for Polymeric Particle-Based Optical Ion Sensors C. Xu, E. Bakker, Anal. Chem., 79 (2007) 3716-3723.