Our group is interested in the understanding and development of electrochemical and optical sensor principles for clinical, bioanalytical and environmental applications. Currently, the principal directions include the study of trace level potentiometric sensors, pulsed chronopotentiometric sensors, and microsphere-based fluorescent detection principles.

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 will be explored, as potentiometry is known not to be dependent on scaling laws. If successful, this methodology may become one of the most sensitive detection methods in terms of the total amount of measurable ions. Further, we will, in analogy to established voltammetric sensors, couple the highly sensitive potentiometric detection to analyte enrichment processes for a further drastically improved detection limit that will likely 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 DNA. 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, and Joseph Wang, Arizona State University.

Pulsed Chronopotentiometric 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 will include coulometrically controlled polyion releasing membranes for continuous on-line heparin–protamine titration experiments. 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.

Total Bead-Based Clinical Analysis Systems

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.

Education

Recognitions

• Roche Prize for Sensor Technology, 2004
• Alumni Professor, Auburn University, 2001-2005
• Young Investigator Award, Society for Electroanalytical Chemistry, 2001

Selected Publications

• Gemene K. L.;Bakker, E., Flash chronopotentiometric sensing of the polyions protamine and heparin at ion-selective membranes . Analytical Biochemistry 2009 , 386 , 276-281.
• Xu Y. D.;Bakker, E., Ion Channel Mimetic Chronopotentiometric Polymeric Membrane Ion Sensor for Surface-Confined Protein Detection . Langmuir 2009 , 25 , 568-573.
• Bakker E.;Chumbimuni-Torres, K., Modern directions for potentiometric sensors . Journal of the Brazilian Chemical Societ 2008 , 19 , 621-629.