Low-Cost Sensing Using a Mobile Phone with Electrochemiluminescence Detection

Submission note: A thesis submitted in total fulfillment Of the requirements for the degree of Doctor of Philosophy to the School of Molecular Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.

This thesis was a recipient of the Nancy Millis Award for theses of exceptional merit.

The recent development of using paper as a microfluidic material for sensor fabrication has made the concept of widespread low-cost diagnostic sensors plausible. By using paper as the microfluidic material, the overall cost of the measurement is kept minimal. To keep the costs of these diagnostic devices truly low-cost, they should also be able to be used without the aid of extra instrumentation or scientific personnel. This can be achieved by coupling the diagnostic sensors with a ubiquitous mobile device such as a mobile phone. In the developing world alone, greater than 90% of people have access to a mobile phone. The sensors described in this thesis are readily coupled with the camera on a mobile phone, as the detection method the sensor uses is electrochemiluminescence (ECL). ECL is a light emitting reaction that produces light when a voltage is applied. The light produced is proportional to the concentration of the analyte being detected. This is an important advantage over electrochemical modes, as the camera on a mobile phone is very good at detecting light, which helps with achieving low limits of detection. This thesis describes the evolution of how paper was first combined with ECL for mobile phone detection using the mobile phone camera for detection. A model analyte was detected to 250 micrometres in this way. The next step removed the need for external potentiostatic initiation by using the phone’s audio output to electrochemically initiate the ECL reaction. This was shown using a model analyte and a biologically relevant analyte; L-proline. The model analyte and L-proline were both detected to levels of 100 micrometres. These limits of quantitations (LOQ) were acceptable, however further improvements were achieved. This was accomplished by using two methods; first with the use of a transparent electrode material, indium tin oxide coated polyethylene terepthalate (PET ITO). The second method used the concept of ECL quenching. By using the PET ITO the sensitivity was enhanced, obtaining a LOQ of 50 micrometres. The ECL quenching provided proof-of-concept for a new detection method using only a mobile phone. It also provided a LOQ of 50 micrometres. Thus, this thesis describes how the concept of coupling paper, ECL and a mobile phone was first brought to fruition and then how the sensor was further improved and optimized for increased sensitivity and suitability for biologically relevant analytes.