Discrimination of proteins through interaction with pyrene-labelled polymer aggregates

A pyrene-labelled PDMAEMA (2-(dimethylamino)ethyl methacrylate) polymer was synthesized through a controlled radical RAFT polymerisation approach. An average pyrene content of 3.65% was determined by UV/Vis and ¹H NMR measurements. DLS measurements reveal the formation of polymer aggregates with an average size of 172 nm in aqueous phosphate buffer indicating the presence of hydrophobic interactions between pyrene and/or DMAEMA moieties of adjacent polymer chains. Furthermore, this aggregation results in the appearance of two characteristic emission bands at 394 and 488 nm analyzed by fluorescence measurements. Based on spectral changes of the so-called monomer and excimer emission intensity, the specific discrimination of various non-metallo- and metallo proteins was realized using an optical fingerprint approach. DLS and fluorescence measurements show a significant dependence of the structural characteristics of the analytes on the presence of different binding modes between the hydrophilic DMAEMA side groups of the polymer and the proteins, resulting in a molecular disassembly of the aggregates and/or fluorescence quenching. Furthermore, pH, temperature and ionic strength dependence of the sensor polymer with BSA was investigated to optimise the external parameters. Based on these results, the most specific discrimination of the analyzed proteins was obtained using a sodium chloride concentration of 50 mM and a pH of 7.0. This study gives fundamental insights into the sensing performance of a novel one-component pyrene-based polymer system and its application as a protein sensor.