Stimuli responsive hydrogels containing fluorophore groups can alter their properties in response to external triggers such as pH and ionic strength, resulting in a difference in fluorescence intensity. Herein, we report the synthesis of stimuli responsive fluorescent hydrogels, which can be combined with the conventional media used for plant transformation cultures and can generate optical signals from environmental changes. A systematic study was conducted to synthesize hydrogels with porous microstructures which will enhance nutrition delivery and facilitate the media exchange, while chemically linked fluorophore groups enable monitoring of changes in local pH or ion concentration through swelling/collapsing of the hydrogels. Our approach involves use of an ionizable fluorophore: fluorescein, which can exist in three tautomeric forms, depending on the pH. This molecule transforms into the most fluorescently active form above pH 5 and it is almost entirely fluorescence inactive in its neutral form. Therefore, combining tailor-designed fluorescein bearing monomers with hydrophilic, biocompatible monomers such as hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) is a promising approach to obtain stimuli responsive hydrogels with a fast and reversible pH response in the targeted pH range (pH 5.3 to 5.7). Fluorescence spectroscopy measurements, thermogravimetric analyses and dynamic mechanical analyses were conducted to evaluate pH response, thermal stability, and mechanical properties of the hydrogels, respectively. Hydrophilicity of the hydrogels was examined via water contact angle measurements and swelling studies, and the morphology was evaluated via scanning electron microscopy.

pH-responsive fluorescent hydrogels to probe plant medium

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