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    Ionophore based optical sensors using hydrophilic polymer matrix – Ratiometric, pH independent ion-selective optodes

    Year: 2023

    Journal: Talanta, Volume 253, 2023-02-01, page 124038

    Authors: Konefał, Anna; Piątek, Piotr; Paterczyk, Bohdan; Maksymiuk, Krzysztof; Michalska, Agata

    Keywords: Ion-selective optodes; Nile blue; Nile red; Optical transducer; Ratiometric sensing

    Classical approach for cation selective optode sensing requires high lipophilicity of receptor matrix and optical transducer dye, its application is restricted to relatively narrow pH range. We propose an alternative approach to ion-selective optodes, benefiting from rather hydrophilic polymer - plasticized polycaprolacton. This results in presence of lipophlic (plasticizer) and hydrophilic (sample/polycaprolactone) domains within the nanoprobes proposed. In consequence, this approach allows benefiting from alternative optical transducer: Nile blue dye and its unique properties and in consequence to benefit from new optical transduction mechanism allowing ratiometric sensing with no restriction for the sample pH. The response mechanism involves ionophore and ion pair composed of cation-exchanger and Nile blue cation dissolved in the plasticizer phase. Analyte incorporation to the phase occurs on expense of dye cation release to the hydrophilic phase. Ultimately a red staining of plasticizer phase is observed due to incorporation of neutral dye molecules formed in course of spontaneous hydrolysis occurring in water phase. Thus herein proposed optodes offer observable emission change at two wavelengths (increase of intensity emission as well as decrease) allowing ratiometric sensing in a broad concentration range. Moreover, herein proposed approach is applicable both in acidic and alkaline media, also in the absence of buffer, thus it mitigates significant constrain of classical optodes. As model system potassium or calcium selective nanospheres were prepared.
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