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Highly Selective Receptor-Based Chemical Sensors With Picomolar Detection Limits

Recent research from the group of Professors Philippe Buhlmann and Andreas Stein and their research groups.

The use of 3DOM carbon substrates prepared by graduate student Melissa Fierke and REU (Research Experience for Undergraduates) student Nic Petkovich (Stein group) permitted graduate student Chunze Lai and REU student Marti Joyer (Buhlmann group) to demonstrate ion-selective electrodes (ISEs) with a 4.3 parts per trillion detection limit for silver ions.

Ion-selective electrodes based on receptor-doped polymeric membranes are routinely used for well over a billion measurements per year. A major advantage of this type of sensor is their high selectivity, which results from the use of highly optimized receptors. While the detection limit of most of these sensors has been until recently in the micromolar range, the efficient use of buffered inner filling solutions has permitted to lower detection limits by several orders of magnitude. Unfortunately, the optimization of these inner filling solutions depends on the membrane selectivity, diffusion coefficients and—most importantly—the anticipated sample, which can make the procedure cumbersome to perform under real-life conditions. Much easier to use are solid-contact ion-selective electrodes (SC-ISEs), which offer an alternative approach to potentiometric sensing with extremely low detection limits.

Left: SEM image of 3DOM carbon. Right: Schematic structure of 3DOM carbon-contacted ISE.

The work by the Buhlmann and Stein groups shows that picomolar detection limits can be achieved with SC-ISEs with three-dimensionally ordered macroporous (3DOM) carbon contacts, which have been shown in 2007 by the same groups to exhibit unprecedented long-term stabilities and good resistance to the interferences from oxygen and light. The detection limit of 3DOM carbon-contacted electrodes with plasticized poly(vinyl chloride) as membrane matrix can be improved with a high polymer content of the sensing membrane, a large ratio of ionophore and ionic sites, and an optimized conditioning of the sensing membranes. This permits detection limits as low as 4.0×10-11 M for Ag+, which is more than two orders of magnitude lower than for any previously reported SC-ISE.

The excellent detection limit of this silver ion selective sensor suggests that 3DOM carbon-contacted ISEs are a promising approach to highly selective routine analysis of environmental pollutants with parts per trillion detection limits.

This work has been published on-line on June 13 in Journal of Solid State Electrochemistry

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