We have demonstrated that an optical fibre-based pH sensor can be utilised to accurately assess pH in a biological environment. Initial measurements were performed on 5 μL drops of culture medium containing individual female mouse reproductive cells (cumulus-oocyte-complexes, COCs), with the goal of obtaining a biomarker of individual cell health during assisted reproductive processes. Improvements to the measurement procedure were found to reduce fluorescence signal variability, enabling improved measurement precision compared to previous studies. Results show the application of treatments which serve to increase lactic acid production by the COC, and thus induce an acidification of the local microenvironment, are detectable by the pH sensor. 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.
Reactive Oxygen Species (ROS) cause DNA damage and defective function in sperm and also affects the developmental competence of embryos. It is therefore critical to monitor ROS in sperm, oocytes and developing embryos. In particular, hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) is a ROS important to normal cell function and signalling as well as its role in oxidative stress. Here we report the development of a fluorescent sensor for H<sub>2</sub>O<sub>2</sub> using carboxyperoxyfluor-1 (CPF1) in solution and attached to a glass slide or multi-mode optical fibre. CPF1 increases in fluorescence upon reaction with H<sub>2</sub>O<sub>2</sub> to non-invasively detect H<sub>2</sub>O<sub>2</sub> near developing embryos. These probes are constructed by immobilising CPF1 to the optical fibre tip a polyacrylamide layer. Also reported is a new dual optical fibre sensor for detecting both H<sub>2</sub>O<sub>2</sub> and pH that is functional at biologically concentrations of H<sub>2</sub>O<sub>2</sub> and can sense pH to 0.1 units. This research shows promise for the use of optical fibre sensors for monitoring the health of developing embryos. Furthermore, these sensors are applicable for use beyond embryos such as detecting stress in endothelial cells involved in cardiovascular dysfunction.