Hydrothermal Synthesis of Nitrogen-Doped and Excitation-Dependent Carbon Quantum Dots for Selective Detection of Fe3+ in Blood Plasma

Abstract

In the last two decades, fluorescent carbon quantum dots (CQDs) have attracted intense interest as a new fluorescent nanomaterial with unique properties. This material offers significant advantages compared with conventional dyes and inorganic QD systems, and is used extensively in many different fields, especially in bioimaging and sensor applications. Despite all the positive values they offer, the production of CQD systems with excitation wavelength-dependent nature and high quantum yield (QY) is still a scientific challenge. In this study, we proposed the fabrication of CQD through a facile and easy-to-tune hydrothermal method using cheap and biocompatible precursors such as urea and lactic acid. The effect of experimental parameters including synthesis time, temperature, and mass ratio of the precursors, were determined to obtain the highest QY (48%). The as-prepared nitrogen-doped (N-doped) CQDs exhibited robust stability in the dark and in a wide range of pH values with excitation wavelength-dependent properties. Additionally, CQDs showed remarkable sensitivity and selectivity in the sensing of Fe3+ in blood plasma with a linear correlation in the range of 0–1000 μM, indicating the high potential of CQDs in practical applications. Lastly, cytotoxicity and antibacterial activity tests demonstrated the low toxicity and high biocompatibility of proposed CQDs. Considering the facile and efficient synthetic method, easy-to-tune optical properties, excitation-dependent nature, high fluorescence activity, and low cytotoxicity, we strongly anticipate that N-doped CQDs could provide unique advantages in various biomedical applications including diagnosis, bioimaging, and biosensors.

Green Synthesis of Various Heteroatom‐doped Carbon Quantum Dots from Urine, Whey, and Their Mixture: The Optimization of Synthesis and Potential Applications

“…From this spectrum, prominent bands were detected at 3032, 1602, 1406, and 1130 cm −1 were assigned to υ (−NH)/ υ (C−H), δ (C=C)/ υ (C=O), υ (C−H), and υ (C−N), respectively [46,47] . The hydrophilic groups such as υ (−NH) and υ (C=O) enable the high stability of CQDs in the water phase [6,48,49] . However, υ (C−H), δ (C=C), and, υ (C−N) functional groups indicate the polyaromatic nature of the material [7,8] .…”

“…[6][7][8]42,43] Another weak peak at 338 nm showed the presence of n-π* transition of C=O bonds. [6][7][8]44,45] Also, a broad weak peak at 494 nm was attributed to functional surface states. The presence of various transitions may be due to the complex content of human-originated urine as the precursor.…”

“…[2,23] Contrary to top-down strategies, through bottom-up approaches, CQDs are synthesized via the treatment of carbon-based small molecules as precursor material by various methods including microwave synthesis, pyrolysis, combustion, thermal decomposition, solvothermal, and hydrothermal synthesis. [6][7][8]24,25] Of these approaches, the hydrothermal method is the most preferred synthesis procedure due to its simplicity, low cost, high flexibility in the selection of the precursor material, and non-toxic and environmentally friendly nature which are essential for green synthesis routes. [6][7][8] Recently, there has been a lot of interest in the use of biomass waste from many sources, including food, agriculture, and domestic waste, as precursors in the manufacture of CQDs.…”

“…[6][7][8]24,25] Of these approaches, the hydrothermal method is the most preferred synthesis procedure due to its simplicity, low cost, high flexibility in the selection of the precursor material, and non-toxic and environmentally friendly nature which are essential for green synthesis routes. [6][7][8] Recently, there has been a lot of interest in the use of biomass waste from many sources, including food, agriculture, and domestic waste, as precursors in the manufacture of CQDs. [15,26] Biomass waste has a rich content of carbon (C), oxygen (O), and nitrogen (N) as main components.…”

“…Also, in most cases, biomass waste contains various trace elements such as phosphorus (P), sulfur (S), and, potassium (K). These trace elements take part in the structure of CQDs as doped heteroatoms and may provide unique optical characteristics including enhanced PL activity and creation of new energy levels to form trap states leading to excitation‐dependent PL characteristics [6,27,28] . Various biomass wastes including walnut shell, [29] orange peel, [30] crop straws, [1] watermelon peel, [31] orange juice, [32] and lemon peel [33] have been employed for the fabrication of CQDs.…”