530 Physik
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We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore.
This study introduces a thermally responsive, polymer-based electrode system. The key component is a surface-attached, temperature-responsive poly(oligoethylene glycol) methacrylate (poly(OEGMA)) type polymer bearing photoreactive benzophenone and carboxy groups containing side chains. The responsive behavior of the polymer in aqueous media has been investigated by turbidimetry measurements. Polymer films are formed on gold substrates by means of the photoreactive 2(dicyclohexylphosphino)benzophenone (DPBP) through photocrosslinking. The electrochemical behavior of the resulting polymer-substrate interface has been investigated in buffered [Fe(CN)6](3-)/[Fe (CN)6](4-)solutions at room temperature and under temperature variation by cyclic voltammetry (CV). The CV experiments show that with increasing temperature structural changes of the polymer layer occur, which alter the output of the electrochemical measurement. Repeated heating/cooling cycles analyzed by CV measurements and pH changes analyzed by quartz crystal microbalance with dissipation monitoring (QCM-D) reveal the reversible nature of the restructuring process. The immobilized films are further modified by covalent coupling of two small biomolecules - a hydrophobic peptide and a more hydrophilic one. These attached components influence the hydrophobicity of the layer in a different way the resulting change of the temperature-caused behavior has been studied by CV indicating a different state of the polymer after coupling of the hydrophobic peptide.