Nanoscale Phase Ion Transfer Reactions For Sensing Applications

Abstract

Chemical recognition by complexation may occur in homogenous solution phase or in a separate phase that is immiscible with water. The former lays the foundation for molecular probes, complexing agents and indicators, the latter is at the heart of electrochemical detection and sensing. This talk shows that nanoscale materials allow us to blur the lines between the two previously separate concepts. With suspensions of appropriately doped micelles or emulsions of hydrophobic nanospheres we achieve short diffusion distances that are approaching those in homogeneous phase. Water insoluble recognition elements can now be used to effect sample concentration changes in analogy to homogenous reagents, and the combination of an ensemble of reagents may be used to develop functional toolboxes that are truly innovative. Examples will include the development of nanoscale probes for exhaustive ion sensing, the use of light to induce oscillating sample concentration changes in a selective and reproducible manner, the introduction of a nanoscale mimic of complexometric titration reagents with much improved selectivities, and pH independent nanoscale sensing based on the incorporation of potential sensitive dyes.
The talk will also describe the electrochemical response of ion-selective films that are just 200 nm thick, in which case the film is underlaid with a conducting polymer (electropolymerized polyoctylthiophene). Here, even in voluminous samples, a cyclic voltammetric interrogation results in a complete equilibration of the sensing film at each applied potential value. This makes it possible to utilize the sensing film under ionophore deficient conditions. Several ionophores embedded in the film each give voltammetric peak signatures, allowing one to detect multiple sample ions at the same time with excellent selectivity. Real world applications of this principle will be presented, along with an explanation of the phenomena.

Bio

Eric Bakker's research is in the area of analytical chemistry, more specifically in Electroanalysis and Optochemical Sensors. The group aims to develop new environmental and bioanalytical sensing strategies with examples that are of practical importance. We have made progress in establishing a calibration free sensing strategy based on combining principles of thin layer coulometry and ion-selective membranes. Part of this work has gone in direction of desalination strategies using permselective membranes and forming the scientific basis for an interdisciplinary environmental EU project. Paper based exhaustive sensors for halides have also been developed based on this chemical principle