A biophotonic approach to measure pH in small volumes in vitro: Quantifiable differences in metabolic flux around the cumulus‐oocyte‐complex (COC)

• Published in: Journal of biophotonics 2020-03, Vol.13 (3), p.e201960038-n/a
• Main Authors: McLennan, Hanna J., Saini, Avishkar, Sylvia, Georgina M., Schartner, Erik P., Dunning, Kylie R., Purdey, Malcolm S., Monro, Tanya M., Abell, Andrew D., Thompson, Jeremy G.
• Format: Article
• Language: English
• Subjects: Additives; biomarker; Biomarkers; biophotonic; Cell culture; Cobalt; Cobalt chloride; cumulus oocyte complex; DNA damage; Eggs; Fluorescence; fluorescence sensing; Gametocytes; Lactic acid; Metabolic flux; micro‐environment; Oocytes; optical fibre; pH effects; pH sensing; Photobleaching; Phototoxicity; Reproduction; Statistical analysis; Toxicity
• ISSN: 1864-063X; 1864-0648
• DOI: 10.1002/jbio.201960038

Unfertilised eggs (oocytes) release chemical biomarkers into the medium surrounding them. This provides an opportunity to monitor cell health and development during assisted reproductive processes if detected in a non‐invasive manner. Here we report the measurement of pH using an optical fibre probe, OFP1, in 5 μL drops of culture medium containing single mouse cumulus oocyte complexes (COCs). This allowed for the detection of statistically significant differences in pH between COCs in culture medium with no additives and those incubated with either a chemical (cobalt chloride) or hormonal treatment (follicle stimulating hormone); both of which serve to induce the release of lactic acid into the medium immediately surrounding the COC. Importantly, OFP1 was shown to be cell‐safe with no inherent cell toxicity or light‐induced phototoxicity indicated by negative DNA damage staining. Pre‐measurement photobleaching of the probe reduced fluorescence signal variability, providing improved measurement precision (0.01‐0.05 pH units) compared to previous studies. This optical technology presents a promising platform for the measurement of pH and the detection of other extracellular biomarkers to assess cell health during assisted reproduction. Unfertilised eggs (oocytes) release chemical biomarkers into their surrounding medium, providing an opportunity to directly monitor cell health. This study measured pH using an optical fibre probe, OFP1, in the immediate micro‐environment around single mouse cumulus oocyte complexes (COCs). Statistically significant decreases in pH were observed around COCs treated to increase lactic acid production and decrease local pH. This technology presents a promising platform to assess cellular health signals during assisted reproduction.