Our research efforts are focused on the exploration and development of novel non-equilibrium detection methods for optical and electrochemical ion selective sensors relevant to applications in clinical, biological and environmental analysis. Current research projects include exploring of photoresponsive optical ion-selective sensors, normal pulse chronopotentiometric sensors, electrochemical and optical sensors for anticoagulants.

Photoresponsive optical ion-selective sensors. (Collaborators: Prof. John Westall, Department of Chemistry, OSU, Dr. Shane Peper, Pacific Northwest National Laboratory) Ion-selective optical sensors (ion optodes) are optical counterparts of ion selective electrodes (ISEs). To date, ion optodes have been used in a passive mode, under conditions of thermodynamic equilibrium. Very recently we have introduced for the first time the concept of a photoresponsive ion-selective optical sensor.

Within our concept of a photoresponsive ion probe we assign different sensor functionalities such as recognition, reporting, and photosensitivity to different molecules. Through combination of numerous well-known passive ion-selective systems with a limited number of photochemical reactions, we can design a variety of active ion probes for applications where passive sensing principles are inadequate.

We will explore active probes for optically controlled titration that can be used for the determination of the intracellular buffer capacity with respect to hydrogen and metal ions. A new approach for active detection of surface binding events for highly selective recognition of biomolecules will be studied. The optical active probes will be developed for the detection of polyions such as anticoagulants. Light regulated selectivity of an ionophore allows us to overcome fundamental enthalpy-entropy compensation relationship and utilize the ionophores with extremely high affinity to the analyte that can not be used within the framework of passive detection.

We will fabricate the photoresponsive ion-selective probes as the polymeric bead-based analytical assays at micrometer and nanometer scale. The detection schemes will employ fluorescence microscopy and flow cytometry.

Development of these techniques for well-established sensing systems will allow extension of these methods to a number of optical sensors based on different principles and will have a profound impact on the field of chemical sensors. In the future we envision the development a variety of active optical biosensors. Light controlled active optical sensors may act like chemical actuators that can be used for spatially and temporally photo-controlled reagent delivery.

We will study fundamental aspects of optically triggered transport processes and develop the theoretical description using classical diffusion approach to the mass transport phenomena and finite element simulation. The results of these fundamental studies of light-regulated highly selective ion-exchange processes in polymeric matrices may expand far beyond the chemical sensor field, create a basic knowledge about a new class of photochemical processes, and impact numerous areas in polymer and material chemistry related to separation science, “smart” materials, energy storage and conversion, and nanotechnology.

Normal pulse chronopotentiometric sensors. The world of electrochemical sensors has traditionally been divided between potentiometry and non-equilibrium electrochemistry.  In the past decade several novel analytical methods based on a nonequilibrium response mechanism have been developed for the ISEs. Ion fluxes in the ISEs can be controlled by means of nonequilibrium electrochemical methods such as normal pulse chronopotentometry. These techniques give a remarkable improvement in sensitivity, allow one to drastically reduce detection limits, perform multianalyte detection with a single sensor, distinguish activity and total concentration of an analyte, determine polyionic compounds such as anticoagulants, and detect surface binding events.

We are primarily interested in the development of solid contact galvanostatic sensors using conducting polymers as transduction layers between the electrode and polymeric ion-selective membranes.

Sensors for anticoagulants. (Collaborators: Prof. Rich Carter, Department of Chemistry, OSU; Prof. Philippe Buhlmann, Department of Chemistry, University of Minnesota) One of the most important applications of non-equilibrium optical and electrochemical ion-selective sensors is the detection of anticoagulants such as polyion heparin. Inaccurate monitoring of heparin concentration during open-heart and bypass surgery is responsible for 30% of postoperative complications.

We work towards next generation of anticoagulant sensors. In this project we plan to synthesize novel ionophores containing guanidinium moieties for highly selective heparin recognition and utilize fluorous polymers as membrane materials with better biocompatibility.