Carbon Quantum Dots from Amino Acids Revisited: Survey of Renewable Precursors toward High Quantum-Yield Blue and Green Fluorescence

Anna Kolanowska; Grzegorz Dzido; Maciej Krzywiecki; Mateusz M Tomczyk; Dariusz Łukowiec; Szymon Ruczka; Sławomir Boncel

doi:10.1021/acsomega.2c04751

Carbon Quantum Dots from Amino Acids Revisited: Survey of Renewable Precursors toward High Quantum-Yield Blue and Green Fluorescence

ACS Omega. 2022 Nov 1;7(45):41165-41176. doi: 10.1021/acsomega.2c04751. eCollection 2022 Nov 15.

Authors

Anna Kolanowska^{1

2

3}, Grzegorz Dzido⁴, Maciej Krzywiecki⁵, Mateusz M Tomczyk², Dariusz Łukowiec⁶, Szymon Ruczka^{1

7}, Sławomir Boncel^{1

7}

Affiliations

¹ Faculty of Chemistry, Department of Organic Chemistry, Bioorganic Chemistry and Biotechnology, Silesian University of Technology, Krzywosutego 4, 44-100Gliwice, Poland.
² Faculty of Chemistry, Department of Physical Chemistry and Technology of Polymers, Silesian University of Technology, Strzody 9, 44-100Gliwice, Poland.
³ Biotechnology Centre, Silesian University of Technology, Krzywoustego 8, 44-100Gliwice, Poland.
⁴ Faculty of Chemistry, Department of Chemical Engineering and Process Design, Silesian University of Technology, Strzody 7, 44-100Gliwice, Poland.
⁵ Institute of Physics-CSE, Silesian University of Technology, Konarskiego 22B, 44-100Gliwice, Poland.
⁶ Materials Research Laboratory, Faculty of Mechanical Engineering, Silesian University of Technology, Konarskiego 18A, 44-100Gliwice, Poland.
⁷ Centre for Organic and Nanohybrid Electronics, Silesian University of Technology, Konarskiego 22B, 44-100Gliwice, Poland.

Abstract

Carbon quantum dots (CQDs) were synthesized via a green, one-step hydrothermal method. As CQD precursors, nine amino acids of different structural descriptors (negatively/positively charged in water, polar, hydrophobic, sulfur-containing, and other/complex ones) were surveyed: Asp, Cys, Gly, His, Leu, Lys, Phe, Pro, and Ser. The reactions were performed in an autoclave in the presence of citric acid at 180 °C for 24 h and yielded core-shell CQDs. CQDs were comprehensively characterized by transmission electron microscopy, dynamic light scattering, Raman, UV/Vis, infrared, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. At the excitation wavelength of λ_ex = 350 nm, Cys-, Phe-, Leu-, and Lys-based CQDs displayed the highest quantum yield blue fluorescence-90 ± 5, 90 ± 4, 87 ± 5, and 67 ± 3%, respectively-superior to the conventional fluorescent dyes. Strikingly, for Lys- and Phe-CQDs, dissimilar trends in the excitation-emission wavelength relationships were identified, that is, constantly strong red shifts versus excitation wavelength-independent emission. Cys- and Lys-CQDs were water-dispersible toward the narrow unimodal distribution of hydrodynamic diameters-0.6 and 2.5 nm, respectively. Additionally, Lys- and Cys-CQDs, with high absolute zeta potential values, formed stable aqueous colloids in a broad range of pH (2, 7, and 12). The results constitute important premises for water-based applications of CQDs, such as bioimaging or photocatalysis.