NH2-rich Carbon Quantum Dots: A protein-responsive probe for detection and identification

In this study, we report the synthesis and application of polyethylenimine, ethylenediamine branched-functionalized carbon quantum dots (CQDs.BPEI) for protein sensing. These carbon-based nanoparticles were found to act as a protein-responsive platform. On this basis, the CQDs.BPEI system was able to detect eight different proteins (four metallic and four non-metallic), even using concentrations in the range of 5–40 nM, depending on the analyte protein. The fluorescence titrations performed at 298 and 310 K displayed fluorescence quenching, which can be explained through a collisional mechanism. It was also possible to conclude that the fluorescence quench comes from the amino acid residues on the surface of the proteins. To further check the potential of the system, we developed a "nose"-based methodology to identify proteins. Using materials, such as copper acetate and ethylenediaminetetraacetic acid, our chemical "nose" approach was able to discriminate 40 nM proteins in phosphate buffered saline (pH 7.4). In this case, the identification accuracy of the random unknown set was 83%. Overall, the results evidence the potential of CQDs.BPEI as a protein-responsive probe to detect and identify proteins.