06/25/2008
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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