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Receptor-Based Chemical Sensors With Three-Dimensionally Ordered Macroporous Carbon Contacts

Recent Research from Professor Philippe Buhlmann and their research group.

In a collaboration between the research groups of Professors Philippe Buhlmann and Andreas Stein, ion-selective electrodes (ISEs) with three-dimensionally ordered macroporous (3DOM) carbon as novel solid contact were developed and found to exhibit much higher signal stability than previously reported solid-contacted ISEs.

Chemical sensors based on receptor-doped polymeric membranes have been developed for over 60 analytes. They are routinely used in clinical chemistry for well over a billion measurements per year. However, to be suitable as implantable sensors for human health monitoring, receptor-based ISEs need to be small and robust, and the sensor outputs needs to be stable over long periods. In conventional ISEs, the sensing membrane is interposed between the sample and an inner filling solution, but unfortunately use of such inner filling solutions impedes miniaturization. Self-assembled monolayers and conducting polymers have been used to replace the inner filling solution, but the low redox capacitance, and pH and light sensitivity limit the stability of the resulting sensors.

Figure 1. Left: SEM image of 3DOM carbon. Right: Schematic structure of 3DOM carbon-contacted ISE.

For this project, 3DOM carbon substrates are synthesized by graduate student Melissa Fierke from the Stein group (Figure 1, left). Due to the well-interconnected pore and wall structures with wall thicknesses of a few tens of nanometers, 3DOM carbon provides high ionic conductivity and electrical conductivity. Graduate student Chun-Ze Lai from the Buhlmann group uses the 3DOM carbon substrates to prepare and characterize chemical sensors (Figure 1, right)

The theoretical ionic and redox responses of receptor-based potassium-selective electrodes confirm the suitability of 3DOM carbon as solid contact. Moreover, the 3DOM carbon-contacted electrodes exhibit unprecedented potential stability. The potential drift for freshly prepared electrodes is only 11.7 1.0 uV/h and does not increase over one month while in contact with aqueous sample. Moreover, the electrodes shows good resistance to the interference from O2 and light.

Figure 2. Schematic bicontinuous electron- and ion-conducting structure of the interlayer of doped 3DOM carbon.

The high stability of the 3DOM carbon-contacted SC-ISEs is related to the bicontinuous electron- and ion-conducting structure of the interlayer. On one hand, the well-interconnected wall structure of the 3DOM carbon provides a continuous pathway for electron conduction. On the other hand, ionic conductivity is provided by a continuous network of interconnected pores that are filled with the ionophore-doped solvent polymeric phase.

The excellent potential stability makes 3DOM carbon-contacted ISEs very promising for miniaturization and implantation. This work has been published on-line on May 18 in Analytical Chemistry

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