One of the main problems associated with the application of sensors for continuous monitoring in the (aqueous) environment is related to biofouling of the sensitive membranes.1 Silicone rubber is the material of choice in optical and electrochemical sensors for oxygen monitoring. This material provides excellent oxygen permeability (300-400 x 10^−13 cm^2s−1Pa^−1), but one of its main drawbacks arises from its high degree of biocompatibility as it behaves as an excellent support for all kinds of microorganisms originating a rapid fouling of the sensor head. We present herein the application of novel oxygen-sensitive luminescent membranes for optical fiber sensors aimed to overcome this undesirable limitation by integrating in their design new biofouling- resistant polymer coatings.
Four different oxygen indicators have been synthesised and spectroscopically characterised for their application towards preparation of the sensitive membranes. The indicators belong to a family of luminescent ruthenium(II) and osmium(II) tris-chelate complexes with substituted and unsubstituted 1,10-phenanthroline.
The indicator molecules have been immobilised into poly(dimethylsiloxane) or phosphorylcholine(PC)-containing polymer layers.2 Their emission lifetimes embedded into the different materials are comparable, pointing out a similar microenvironment of the luminescent probe in the tested polymers. Nevertheless the different oxygen sensitivity observed might be a consequence of a lower solubility of the analyte gas in the PC-containing materials compared to siloxanes.
In a different study the effect of several siloxanes on the oxygen sensitivity of the indicator membranes has been evaluated, following the luminescence quenching process by steady-state and time-resolved measurements. The good agreement between both results (Stern-Volmer plots) indicates dynamic quenching of the photoexcited dye by the analyte.
The selected silicone membranes have been coated with four different antibiofouling layers and their effect on the sensor response has been tested. Results will be presented showing the spectroscopic and analytical features of these optodes both in gas and aqueous phase. We have observed that the presence of PC coating decrease the oxygen response by 2-20% of that shown by the original (uncoated) membranes, regardless the type of coating applied. Several studies are in progress in order to evaluate the antifouling capabilities of the novel sensing layers.