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.