Abstract
Polyethylene glycol (PEG) is a polymer of vital biological importance. It has characteristic properties such as high hydrophilicity, biocompatibility and lack of toxicity. We prepared PEG hydrogel based on photosensitive PEG macromers, which were synthesized by modifying an eight-branched PEG with different chromophores, i.e. nitrocinnamate (NC) and anthracene (AN). Upon photo-irradiation, these PEG macromers rapidly formed a hydrogel in the absence of initiators. Particularly, physical properties of PEG-AN hydrogel such as swellability, absorption and topography were controlled by alternating the irradiation wavelength between 365 and 254 nm. The photocrosslinked PEG gel provides a nice medium for immobilizing or transferring functional ingredients to make gel films for various purposes of application, such as wound healing. Originally, we tried to use PEG gel to trap a tripeptide growth factor, i.e. glycine-histidine-lysine (GHK), to make a medicinal formulation for promoting wound recovery. This tripeptide has a high affinity for copper ions, and copper binding directly influences its biological activity. This property leads us to attach fluorophore to the peptide to design highly selective sensors for the detection of copper ion in aqueous solution. To optimize the fluorescence response and selectivity of the peptide ligands, we synthesized several molecules based on glycine-histidine-lysine, and investigated the fluorescent quenching characteristics caused by copper ions. Herein, we successfully identified fluorescent molecules with excellent detection properties toward Cu 2+ like selectivity, molecular sensitivity, and applicability in a wide range of pH. Our study demonstrates the significance of ionophore-fluorophore relationship in the design of fluorescent probes for analytes such as Cu 2+. Additionally, the concept of incorporating sulfonamide moiety in the binding motif as an effective factor to obtain a highly selective probe could be applied to other systems of organic fluorescent sensors for Cu 2+. Based on these selective peptide motifs studied in aqueous solution, we have developed surface-oriented sensors for the fluorescent detection of copper ions. In the first strategy, several peptide lipids were used to construct fluorescent sensors at air-water and air-solid interfaces (Langmuir monolayers and Langmuir-Blodgett films). Both intramolecular and intermolecular mechanisms were successfully utilized to achieve the fluorescent quenching caused by copper ions. In the other strategy, photocrosslinked PEG hydrogel was used as a solid matrix and peptide molecules were immobilized within the gel matrix simultaneously during photocrosslinking process. These surface sensors worked efficiently for the fluorescent detection of copper ions and exhibited excellent selectivity and reversibility. Our results provide important clues to developing PEG-GHK-fluorophore systems for wound healing in which fluorescence is used as transduction signal for probing in situ the role of copper ions in the biological process.