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Ion-Selective Electrodes (ISEs)
Ion-Selective electrodes (ISEs) are routinely used worldwide in clinical chemistry for well over a billion measurements per year. However, the lifetime of these sensors is often limited by lipids and hydrophobic proteins that adsorb onto or are extracted into their polymeric matrixes. Thus, preventing long-term implantation of receptor-based chemical sensors in the human body, and has limited the use of these sensors in the food industry and environmental monitoring.
In our research, we take advantage of the properties of perfluorinated matrixes ((i)chemically very inert, (ii)inhibit cell growth, (iii)have extremely low polarity and polarizability) to develop electrodes with enhanced selectivities, long life-time and wider applications.With our designed fluorophilic ionic additives, we have developed the first electrodes with fluorous phase for cation and anion sensing.
We have also developed the first perflouropolymeric matrix discovering previously unknown fluoropolymer blends. Receptor-doped pH sensors have also been developed. With further optimization, we will design different fluorophilic receptors for other analytes and test these electrodes in real-life samples.
Ion-Selective Electrodes With Ionophore-Doped Sensing Membranes covers topics essential for graduate students or others starting work in the field of ion selective electrodes.Philippe Buhlmann's and Li D. Chen's recent review and tutorial:
A PDF can be downloaded here.
This review will be a chapter in the eight volume book serieswhich will be avalible soon.
Ion-Selective Electrodes With Ionophore-Doped Sensing Membranes. In; Steed, A. W., Ed, Gale P., Ed;
Electrochemical Sensors for Nonionic Species
There is also great demand for selective sensors capable of determining nonionic species Development of such sensors poses a significant challenge. Suitable electrochemical methods that have been developed include voltammetry and amperometry. As with potentiometry, a fluorous solvent may be used as the sensing matrix with these techniques. Unfortunately, the solubilities of conventional electrolytes are insufficiently soluble to lower the resistance of the solution. Using the novel electrolyte tetrabutylammonium tetrakis(2,4-bis(perfluorohexyl)phenyl)borate, we demonstrated cyclic voltammetry in a completely fluorous solvent for the first time. This will help lead the way for further development of electrochemical sensors for uncharged analytes.
Ion-Selective Electrodes (ISEs):Low Detection Limit
Sensors with low detection limit are requied in the fields of environmental and industrial process monitoring as well as for analyses in clinical chemistry. Therefore, in our research, we are interested in the design of a new type of electrochemical sensor for the highly selective ionophore-based analysis at nanomolar and lower concentrations. These new devices distinguish themselves from previous electrochemical sensors by the application of two types of complexing agents (also called ionophores). Besides low detection limits and the ease of production, the combination of two types of ionophores in a unit construction system is expected to allow the easy fine-tuning of the selectivities and sensitivities of these new electrochemical devices.
Electrochemical Sensors based on Three Dimentionally Ordered Macroporous (3DOM) Carbon
3DOM carbon is prepared in Prof. Stein's group (University of Miinnesota) and used as anode material in battery. Due to its well-connected wall and pore structures, 3DOM carbon has high electronic conductivity. Moreover, the filling of pores with solution containing ionic additives will provide a continous pathway for ions as well.
We have succefully developed solid contact ISEs based on 3DOM carbon, which provide excellent potential stability (the drift is only about 0.01 mV/h) and good resistances to interferences, such as light and oxygen. The electrochemical properties are under investigation. Moreover, 3DOM carbon will also be used for the detection of nonionic species in voltammetry.
Scanning Tunneling Microscopy (STM)
STM is the second area of my research interests. Since its invention in the early 1980s, STM has become one of the most powerful tools for surface observations at the molecular and atomic scale. Unfortunately, the differentiation of chemical species with conventional STM is often very difficult. We have recently shown that chemically modified STM tips can be used for the recognition of specific chemical groups. The modified STM tips chemically interact with the imaged samples. The resulting STM images reflect the chemical selectivity of the tip-sample interactions. This exciting new application of molecular recognition promises to become a very general approach to selective surface imaging with high resolution. Present research focuses on the evaluation of various chemical interaction types that may be used for this approach. Efforts to use hydrogen bond and coordination bond interactions are under way. Also, the possibility of distinguishing between different spatial orientations of particular functional groups is being tested. We will use the new STM method to observe in-situ chemical surface reactions and to demonstrate various applications in nanotechnology and biosciences.