Background
Burn wounds are extremely vulnerable to infection with common pathogens. Many of the pathogens that commonly infect burn wounds aren't dangerous to healthy people but can become deadly to patients with compromised immune systems, such as those with large burn wounds. It is important to detect and treat infections in burns as early as possible. The earlier an infection is detected, the sooner treatment can begin and the higher the likelihood of a positive outcome is.
One of the worst types of bacteria commonly found in burn wounds is Pseudomonas aeruginosa. While infecting a host and setting up a biofilm P. aeruginosa produces a large amount of virulence factors (molecules that help the bacteria survive and kill). Some of these virulence factors are electrochemically active. This is a characteristic that can be taken advantage of for early detection.
My thesis was based on creating a system with innovative electrodes that were affordable and integratable with current wound dressing technologies (bandages etc.). The system had be capable of delivering point of care detection and treatment for P. aeruginosa infections. {The sensitive parts of the system overview graphic below have been blurred while the work based on the thesis awaits publication.}
Potentiostats and Square Wave Voltammetry
The virulence factor targeted by my system is redox active, meaning it can be detected via electrochemical analysis. The technique I used was called Square Wave Voltammetry (SWV). SWV combines staircase and square waveforms. Cycling the voltage with the complex SWV waveform forces the redox active analyte to oxidize and reduce over and over again. To have these precise waveforms, three electrodes were needed. The electrodes are called the working, counter and reference electrodes. The surface of the working electrode is where the redox reaction takes place. The counter electrode supplies electrons to the system. The reference electrode is used to maintain the voltage of the working electrode. Three electrodes are needed as it would otherwise be extremely difficult to maintain the right voltage between two electrodes while the current is changing.
The current is sampled twice during each cycle and the readings are subtracted from each other. This differential sampling eliminates the capacitive current and leaves behind only the faradaic current (the current due to the reduction and oxidation of the analyte at the working electrodes surface). The more analyte, the higher the current.
A potentiostat was needed to run complex electrochemical analyses like SWV; However potentiostats are typically too expensive and bulky for use in point of care diagnostic and treatment systems. An alternative open source design, created by a team from Harvard was assembled. The open-source potentiostat was designed around an RFduino MCU and a software interface for IOS called TechBasic. The MCU was capable of Bluetooth connections with a smart phone.
Some modifications needed to be made to the hardware as well as the embedded and app softwares to fit my needs. An example of these modifications was the extra circuit designed to heat an element for the treatment system that was added onto the potentiostat. The embedded and app software had to be amended to allow the user to use this circuit and provide treatment when an infection was detected.
Electrodes
This section is being withheld until the papers publication.