Magnetic Nanoparticles and Carbon Quantum Dots: Interdisciplinary Nanoparticles for Sensing and/or Education

Abstract

In this work, a sensing strategy for detection and identification of proteins with magnetic nanoparticles (MNPs) and carbon quantum dots (CQDs) was developed. In this sense, mixed ferrites of general formula M0.5Zn0.5Fe2O4 (M=Mn or Ni) were first investigated. Therefore, the hydro/solvothermal synthesis of these magnetic nanoparticles was performed under different conditions (solvent, reaction time and base concentration). Based on the magnetic properties of the two MNPs investigated, the mixed ferrite of formula Mn0.5Zn0.5Fe2O4 (MnZn) synthesized using water showed the greatest potential for sensing. Since among all synthesized MNPs, this sample displayed the highest saturation magnetization value ( M S  50 emu/g), lower crystallite size around 12 nm and superparamagnetic behavior. Once the first part of the doctoral thesis was concluded, the next step was to find a fluorescence probe. In this regard, it was performed the synthesis, as well as the application of branched poliethylenimine-functionalized carbon quantum dots (CQDs.BPEI). These new carbon-based nanoparticles were found to be protein-responsive. Since CQDs.BPEI were able to detect eight different proteins (four metallic and four non-metallic) even using concentrations in the range of 5 – 40 nM. Fluorescence titrations performed at 298 and 310 K displayed the fluorescence quenching through collisional mechanism. Therefore, 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 CQDs.BPEI, it was developed a “nose” based methodology to identify proteins. Using materials as cheap as Cu2+ and ethylenediaminetetraacetic acid, the chemical “nose” approach was able to discriminate six different proteins at 40 nM concentration in phosphate buffered saline (PBS, pH 7.4). The identification accuracy of the random unknown set was 90% with all misclassification occurring for albumin proteins (e.g., Bovine Serum Albumin and Human Serum Albumin). The displayed results evidence the great potential of CQDs.BPEI as a protein-responsive probe to detect and identify proteins. Taken together, MnZn and CQDs.BPEI were capable to build up a powerful protein sensing approach. In addition, realizing the great potential of CQDs in the educational field, it was also developed and successfully applied (for more than 70 students from biotechnology, pharmacy, engineers and geology courses) a lab experiment to demonstrate lightrelated quantum phenomena.