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

Abstract

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.

A Silk‐Based Functionalization Architecture for Single Fiber Imaging and Sensing

“…[ 26 ] These peak ratio and photobleaching observations are also in agreement with recent data on the structurally related pH‐sensitive fluorophore carboxynaphthofluorescein deployed on an optical fiber. [ 25 ] The effect of photobleaching was minimized in subsequent experiments by irradiating all OCTpH probes 100 times prior to collecting fluorescence measurements, similar to the protocol reported by McLennan et al. [ 25 ]…”

“…[ 25 ] The effect of photobleaching was minimized in subsequent experiments by irradiating all OCTpH probes 100 times prior to collecting fluorescence measurements, similar to the protocol reported by McLennan et al. [ 25 ]…”

“…[ 16 ] Instead, a number of methods have been developed for attaching an increased quantity of organic fluorophores to an optical fiber tip, for example by plasma deposition, [ 17 ] silanization, [ 18–20 ] polyelectrolyte layering, [ 21 ] or by growth of an organic polymer. [ 22–25 ] These approaches generally require long reaction times, [ 20 ] repetitive layering, [ 18,21 ] and/or extreme temperatures. [ 17 ] Importantly, they are not compatible with the design of an OCT fiber probe, which requires a coating that does not detrimentally alter the shape of the imaging light beam.…”

Ex-Vivo Measurement of the pH in Aqueous Humor Samples by a Tapered Fiber-Optic Sensor

“…The first fiber-optic pH sensor, described more than 40 years ago by Peterson et al, was developed for pH measurement in blood [ 5 ]. Recently, applications of fiber-optic sensors were described for pH measurement in brain tissue [ 6 ], lungs [ 7 , 8 , 9 ], bladder and kidneys [ 10 , 11 ], oocytes [ 12 ], blood and subcutaneous tissue [ 13 , 14 ], breast tissue [ 15 ] and in lung cancer cells [ 16 ].…”

Protein detection enabled using functionalised silk-binding peptides on a silk-coated optical fibre

“…16,17 Optical bre probes have been developed for a number of applications, including the detection of biological analytes such as metal ions, [18][19][20][21] small biomolecules, 22,23 and pH measurement. [24][25][26][27] However, there are few reports on the detection of proteins and other large biomolecules using such systems. 28,29 This is a signicant limitation since biological processes and associated disease states are invariably controlled by these large biomolecules.…”