Philip Matthews

Assistant Professor

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Graduate Student Supervision

Master's Student Supervision (2010-2017)
Fluorescent implantable elastomer tags for the measurement of oxygen in insects (2017)

Implantable fibre-optic probes are commonly used to measure the oxygen partial pressure (PO₂) within the haemolymph and tissues of insects, but they are highly invasive and traumatic. Furthermore, they can only measure the PO₂ of one spot of the insect’s body at a time. The objective of this thesis was to develop Fluorescent Implantable Elastomer Tags (FIETs) as an alternative to fibre-optic probes. These FIETs were characterized in terms of their uniformity in size, response to PO₂ and photodegradation. I assessed their viability for in vivo measurements by testing them in an autofluorescent system in situ. I constructed a microfluidic chip to produce the FIETs, and characterized their uniformity. To establish the FIETs response to PO2, they were exposed to oxygen (O₂) gas in nitrogen, ranging from 0 to 0.2 atm O₂. Holding the FIETs within steady-state environments of 0, 0.1 and 0.2 atm O2 and constantly illuminating them for 60 seconds with the excitation light source determined the degree of photodegradation. The FIETs were tested within an autofluorescent system by creating an O₂ gradient within a block of 0.5% (w/v) agar. My results indicate that 72% of the emulsions produced by the microfluidic chip are highly uniform when 1% sodium dodecyl sulfate (SDS) in water is used as the continuous phase. In comparison, only 55% of emulsions are highly uniform when 5% Kolliphor in water is used. FIET diameters ranged from 110 – 401 μm for 1% SDS and 67-120 μm for 5% Kolliphor. The FIETs exhibit a linear response to PO₂ (R²=0.963), which is improved when fluorescence is normalized to fluorescence in anoxia (R²=0.983). Photodegradation occurred over 60 seconds, causing a 31.6%, 6.1% and 359.7% drift in measured PO₂ within 0.2, 0.1 and 0.02 atm O₂ respectively. The FIETs were able to detect an O₂ gradient within 0.5% agar. These results suggest that the FIETs are a viable option for measuring O₂ in insects in vivo, although improvements can be made to the uniformity and photostability of the FIETS. Future work should focus on the FIETs response to confounding factors such as temperature.

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