Abstract
A novel cationic water-soluble conjugated polyelectrolyte (CPE) of polyfluorene that contains 15% fraction of 2,1,3-benzothiadiazole (BT) units (PFC3NBT) has been obtained. PFC3NBT demonstrates intramolecular energy transfer from the fluorene segments to BT sites when negatively charged species (SDS or DNAs) are added, following by a shift in emission color from blue to green, has been developed. The high density of positive charges and pendent short alkyl chains of N-propyltrimethylammoniums endow PFC3NBT with high solubility and high fluorescence quantum efficiency of 33.6% in water. The fluorescence emission properties were investigated in the presence of adverse buffer solutions, different surfactants and DNA strands. Interesting fluorescence emission quenching at short wavelength and fluorescence resonance energy transfer (FRET) induced light-on at BT sites were observed and discussed in detail. Very different from previous reports, the fluorescence emission spectra transition happens with an enhancement of integrated fluorescent intensity. The analytes induced a light-up sensing system was studied with a PFC3NBT/SDS complex mode and confirmed with DNA/DNA-FAM sensing systems. More exciting preliminary results on label-free sensing of tumor markers were also reported by investigating the unique fluorescence response to 11 kinds of proteins. These results provide a new insight view for designing CPEs with light-up and label-free features for biomolecular sensing.
Highlights
Water soluble, fluorescent π-conjugated polyelectrolytes (CPEs), featured with π-conjugated polymers with water-soluble side chains have attracted much attention in the fields of highly sensitive fluorescence-based sensors [1,2,3,4,5,6,7] and organic electronics [8,9,10,11,12]
As described in previous reports [16,26], if the acceptor fraction BT units was less than 10%, which would result in a low fluorescence resonance energy transfer (FRET) efficiency from polyfluorene segments to BT sites, while, when the fraction of BT units was larger than 20%, the PL spectra of CPEs would display a broad tail from 500 to 650 nm [16]
FRET from fluorene segments to BT sites can explain the changes of PL spectrum, but it cannot give phenomenon is very different from the results reported by Heeney [32]
Summary
Dense Short-Alkyl-Chain-Bridged Cationic Ions: Analyte-Induced Light-Up and Label-Free Fluorescent. Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts &
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