Access Type

Open Access Thesis

Date of Award

January 2015

Degree Type


Degree Name



Biomedical Engineering

First Advisor

Gregory W. Auner


Some types of bacteria and fungus can use iron or non-ferrous metals for their metabolic process. Sulfate-reducing bacteria can corrode pipes in the oil industry and high-end machinery. Both aerobic and anaerobic bacteria often degrade fuel quality and cause fuel system corrosion or alter the chemical properties of the fluid. This causes significant economic damage and safety concerns. Therefore, there is a need for a system to continuously monitor fuel or lubricant oil for the presence of bacteria and fungus.

The main goal of this project was to develop a sensor that can detect bacteria and other ferrous and non-ferrous debris that are present in the lubricant of high-end machinery in real-time. Utilizing optical techniques to detect and size these particulates. This sensor features a robust optical system paired with microfluidics. When fluid passes within a sampling channel, the particles in the fluid blocks the laser that is passing through the channel. This laser blockage was detected by a photodetector, creating a microfluidic micro counter.

A novel chip fabrication approach was used with fused silica (a high-quality SiO2 glass). Its material characteristics were locally modified using femtosecond laser pulses to (a) change the fused silica index of refraction, and (b) change its susceptibility to HF etching. The index of refraction change is used to create optical waveguides within the fused silica substrate (this process is called as femtoWriteTM), and the second process (femtoEtchTM) was used to shape the fused silica. This phenomenon occurs due to the ultrashort light pulse whose wavefront has little absorption until deep within the fused silica substrate. The damage or defects created beneath the surface render that portion of the fused silica susceptible to rapid etching by HF.

The efficacy of the chip was shown by spiking 1) ceramic microparticles, 2) Pseudomonas aeruginosa bacteria which causes alkylaromatic degradation, in 5W30 motor oil. These two proofs-of-concept represent two key types of particles which must be monitored in hydrocarbons and fuel systems.

Each of the above particles and biologicals were successfully detected from a 3ml of the oil sample. Ceramic beads, of 100μm size, were used with a concentration 100mg /3ml of oil. The spike voltage and intensity was strong when a bead was passing through the light source with a flowrate of 3ml/min. The spike was dropped from 4.55V to 2.79V with a greater significance of detection in 0.01 seconds. In this case, Pseudomonas aeruginosa bacteria showed less intensity comparing with beads with a voltage drop from 3.469V to 3.441V in 0.02 seconds.