| Summary: | Thermoresponsive hydrogels containing gold nanoparticles (AuNPs) were explored for their potential use as colorimetric sensors. The shrinking and swelling behaviour of thermoresponsive polymers cross-linked by AuNPs induces a colour change around the LeST. Formulation of the AuNPs cross-linked thermoresponsive polymer in an agarose gel allows naked eye visualisation of the colour change, overcoming the opaque appearance of the AuNPs cross-linked thermoresponsive polymer alone above the LeST. A thermoresponsive polymer, PPEGMA was prepared using a bifunctional RAFT agent, cross-linked with AuNP and subsequently dispersed in an agarose hydrogel. Upon raising the temperature above the LeST, the thermoresponsive hydrogel construct underwent a colour change from red to blue, due to the AuNPs moving closer together as a result of the shrunken state of the polymer. This colour change was reversible as the temperature was cycled above and below the LeST. Similar data was achieved using another thermoresponsive polymer, PNIPAM. The thermoresponsive hydrogel constructs were characterised by NMR; UV-Vis absorption to measure LeST transition and TEM to establish AuNPs distribution. The proof-of-principle colorimetric sensing approach was extended by modifying the thermoresponsive polymer to include pendant boronic acid group. In the presence of a target (fructose), the hydrogel construct underwent a colour change from blue to red, due to swelling of the polymer below the LeST induced by fructose binding to the boronic acid groups present in the polymer. The colorimetric sensor was also modified for detection of an enzyme, elastase. A synthetic peptide (Pro-Ala-Ala-Ala-Ala) was conjugated to a PNIPAM polymer and the response to the enzyme was observed by the colour change from red to blue, due to the shrinking of the polymer when the peptide was cleaved by elastase. This colorimetric sensor has the potential to be applied in a rapid, cost-effective, and simplified test kit for biomedical applications
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