Produced by a cascade of electrochemical and chemical reactions, electrochemiluminescence (ECL) can be used for analytical measurements, as it is both highly sensitive and specific. Our goal is to develop an ECL method capable of detecting bacteria down to the single-entity level through the use of microfluidics. This would eliminate the need for time-consuming culture and amplification techniques, which often take 1-2 days to complete. Rapid detection is important because even a single bacterium can produce a lethal infection. Our group has demonstrated that, in the presence of bacteria (E. coli K12), a decrease in ECL (proportional to the concentration of bacteria) occurs in the bulk solution when compared to solution without bacteria. We are currently designing , fabricating, testing, and optimizing a system to image and measure ECL of droplets of electro-active luminophore Ruthenium (II) trisbypyridine (Ru(bpy)₃²⁺) with coreactant tripropylamine (TPA). The Ru(bpy)₃²⁺/TPA couple was chosen because of their well-known abilities verified in ECL literature. Our system consists of electrodes stencil-painted with graphite and Ag/AgCl onto a glass slide, which are then bonded to an engraved PDMS slab to form microfluidic channels. We are using an Electron multiplier Charge Coupled Device (EmCCD) camera mounted on an epifluorescent microscope to observe the intensity of the ECL. Measuring ECL intensity is important for future bacterial applications because the amount of bacteria in the sample will correlate to the intensity of ECL produced. We are using microfluidic-sized droplets because decreasing the volume of sample increases the local concentration, with the goal of moving towards single-entity detection in mind. This work is a steppingstone towards a faster, highly sensitive method of detecting an ultra-low number of bacteria.

Frederique Deiss

IUPUI

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