Abstract
Development of a biocompatible pH sensor is of importance in biomedical applications, particularly for in vivo measurement, providing necessary information for clinical diagnosis and treatment such as chronic wounds and foetal acidosis. Traditional pH-indicator based optical sensors have problems of dye-leaching and photobleaching that restrict their uses in long-term monitoring. In this work, a dye-free fibre optic pH sensor is proposed consisting of a U-shape multimode optical fibre coated with a hybrid organic-inorganic composite film. The film is formed by cross-linking ethyl cellulose with a silica matrix at an optimised ethyl cellulose/silica molar ratio of 0.0065 via weakly interacted hydrogen bonding. This bonding is affected by hydrogen concentration (i.e., pH) in a solution resulting in a morphological change of the polymer aggregation presented in the silica matrix leading to refractive index change of the film. The developed sensor shows a reversible response to pH from 4.5 to 12.5 and exhibits linear correlation between transmitted light power and pH with a limit of agreement (LoA) between the sensor and a commercial probe of ±0.2 pH. For a clinically important range of pH values between 6 and 8 the LoA is ±0.1 pH. The sensor has low cross-sensitivity to temperature as the maximum interpreted pH change attributed to the power change is 0.12 pH when the temperature changes from 21 °C to 39 °C. To demonstrate biomedical relevance, the sensor is used to monitor pH of human serum. An in-house cytotoxicity assay is conducted with mouse fibroblast cell revealing that the film is not cytotoxic.
Highlights
Bare silica optical fibres (Ø: 125 μm) and circular glass coverslips (Ø: 22 mm) were separately coated with the prepared film by dip coating for conducting direct contact and elution methods in cytotoxicity assays, respectively
Elution Method: 4 glass coated glass coverslips were placed inside a borosilicate glass vial along with 5 mL of growth medium for 24h at room temperature
After 24h growth of cells, the growth medium was removed from the cells, and eluate media incubated with the different samples applied to each well
Summary
Bare silica optical fibres (Ø: 125 μm) and circular glass coverslips (Ø: 22 mm) were separately coated with the prepared film by dip coating for conducting direct contact and elution methods in cytotoxicity assays, respectively. The same drying conditions as described in sensor fabrication section were used and fibres and glass coverslips are sterilised with UV before incubation with culture media. A well plate (CorningTM CostarTM 96-Well, Cell Culture-Treated, FlatBottom Microplate; Fisher; Cat no: 10695951), was used for both the direct contact and the elution trials.
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