(627j) Simultaneous Measurement of pH and Bacterial Markers in a Single Sensor

Pseudomonas aeruginosa is one of the leading causes of
gram-negative bacterial infection in hospitals. Significantly impacting people
with compromised immune systems, Pseudomonas aeruginosa is an important
bacterium to study both in the medical and scientific communities. Unique to
this species is its production of pyocyanin, a redox-active quorum sensing
molecule (QSM) linked to biofilm formation. Because it is redox-active,
pyocyanin can be directly detected electrochemically in solution. We have shown
that it possible to detect this QSM with very high sensitivity using
microfabricated nanofluidic electrode assemblies (NEAs). The development of
these devices has ultimately led to a growing interest in their medical
applications. One potential application is the integration of these sensors in
smart bandages, a type of wound dressing that will incorporate an array of
sensors for early diagnosis of infections. The reference electrode integrated
in our NEAs is uniquely sensitive to both proton concentration and electro-active
species, making it possible to simultaneously monitor pH and pyocyanin
concentration using a single sensor.

To test the device's dual ability
to monitor pH and pyocyanin, samples of 100 µM pyocyanin in 100 mM phosphate
buffer were created at different pH values (4.3, 7.0, and 10.4) through the
addition of HCl acid or NaOH base. Samples were loaded into a NEA connected to
a potentiostat (CHI842C) to control the applied potentials, which ranged from
-0.75 to 0.00 V, vs. the integrated palladium hydride reference electrode. Using
square-wave voltammetry to detect the presence of pyocyanin, all sample scans
were performed at an amplitude voltage of 0.05 volts and a frequency of 15 Hz.
As the pH of the sample was varied, a shift in the maximum peak potential was observed.
Further analysis showed a linear correlation between pH and the peak potential
with a change of 37 mV per pH unit. The ability to simultaneously measure the
concentration of pyocyanin and the pH of a fluid sample highlights the device's
future medical application as part of a smart bandage where pH is linked to
general bacterial infection and the presence of pyocyanin indicates the existence
of Pseudomonas aeruginosa. Other electro-active molecules can also be
detected by changing the applied potentials and functionalizing the sensor to potentially
detect other bacterial species as well.