Water-soluble Carbon Quantum Dots Research Articles

Ellagic acid-functionalized fluorescent carbon dots for ultrasensitive and selective detection of mercuric ions via quenching

The authors report on a strategy for the fabrication of water soluble carbon quantum dots (CDs) functionalized with ellagic acid. They also demonstrate highly selective detection of Hg2+ ions in aqueous media via fluorescence quenching. The CDs were prepared via a one-step technique using tannic acid as the carbon source and directly surface functionalized during nanoparticle synthesis. Following photoexcitation at 210nm they exhibit excitation-independent emission that peaks at 340nm. The CDs display strong affinity for Hg2+ and binding result in quenching of fluorescence. This effect can be used to quantify Hg2+ in concentration down to 10pM and with detection limit as low as 0.24pM. The ultrasensitive detection of Hg2+ ions is demonstrated by analyzing Hg2+-spiked water and tap-water samples.

Preparation and Characterization of Water-soluble Carbon Quantum Dots/Mesoporous Silica with High Fluorescence Intensity

A simple hydrothermal approach is used to prepare water-soluble carbon quantum dots (W-CQDs) by using glucose as the precursor and PEO106PPO70PEO106 (F127) as the controlling agent. The homogeneous W-CQDs have an average size of 2.6 nm and show well dispersibility. W-CQDs/mesoporous SiO2 composites are synthesized by using mesoporous SiO2 as the carrier. The as-synthesized composites are characterized by SEM, TEM, XRD, and fluorescence spectrometry. The fluorescence intensity and quantum yield of the composite are higher than those of W-CQDs.

A “Turn-On” thiol functionalized fluorescent carbon quantum dot based chemosensory system for arsenite detection

Carbon quantum dots (CQDs) have emerged out as promising fluorescent probes for hazardous heavy metals detection in recent past. In this study, water soluble CQDs were synthesized by facile microwave pyrolysis of citric acid & cysteamine, and functionalized with ditheritheritol to impart thiol functionalities at surface for selective detection of toxic arsenite in water. Microscopic analysis reveals that the synthesized CQDs are of uniform size (diameter ∼5nm) and confirmed to have surface SH groups by FT-IR. The functionalized probe is then demonstrated for arsenite detection in water by “Turn-On” read out mechanism, which reduces the possibility of false positive signals associated with “turn off’ probes reported earlier. The blue luminescent functionalized CQDs exhibit increase in fluorescence intensity on arsenite addition in 5–100ppb wide detection range. The probe can be used for sensitive detection of arsenite in environmental water to a theoretical detection limit (3s) of 0.086ppb (R2=0.9547) with good reproducibility at 2.6% relative standard deviation. The presented reliable, sensitive, rapid fCQDs probe demonstrated to exhibit high selectivity towards arsenite and exemplified for real water samples as well. The analytical performance of the presented probe is comparable to existing organic & semiconductor based optical probes.

Microwave-assisted synthesis of luminescent and biocompatible lysine-based carbon quantum dots

Abstract Water-soluble carbon quantum dots presenting strong blue photoluminescence with the quantum yield up to 23.3% are simply prepared by microwave treatment of lysine as a building block within 5 min in household microwave oven. The formation of lysine-based carbon quantum dots is estimated to proceed through the microwave induced thermal polyamidation and the subsequent carbonization reaction. More importantly, the control experiments using the other amino acids having linear structures reveals that the branched molecular structure of lysine (AB 2 type polyamidation monomer) is one of prerequisite points to obtain strongly luminescent carbon quantum dots with high mass yield. Lysine-based carbon quantum dots are highly nontoxic and biocompatible, enabling bioimaging of cellular media with high degree of pysiological safety.

Size dependent photoluminescence property of hydrothermally synthesized crystalline carbon quantum dots

In this work, simple hydrothermal synthesis of water soluble Carbon quantum dots (CQDs) of different sizes has been reported. The effect of synthesis temperature and synthesis time on the particle size has also been shown. The structures of all the as-prepared samples were studied by field emission scanning electron microscope and high resolution transmission electron microscope. Fourier transformed infrared spectrophotometer analyzes the different bonding present in the sample whereas Raman spectrophotometer quantifies the hybridization state of the prepared samples. UV–vis spectrophotometer gives the variation of absorbance of all the samples with wavelength. Dynamic light scattering study shows the variation of particle size with deposition condition and corresponding zeta potential gives the idea about the stability of the CQD solutions. The photoluminescence (PL) properties of the as prepared CQDs were also studied in detail. It is noticed that with the increase of excitation wavelength, the PL emissions for the different samples were red shifted. The results have been explained in terms of the excitation dependent emission, variations in size of the CQD and presence of different functional groups on the surface of CQDs.

Green synthesis of carbon quantum dots from lemon peel waste: applications in sensing and photocatalysis

Water soluble carbon quantum dots were synthesized from lemon peel waste and were used for Cr6+ detection and photocatalytic degradation of methylene blue dye.

Carbon quantum dots: synthesis, characterization, and assessment of cytocompatibility

A simple method for the synthesis of water-soluble carbon quantum dots (CQDs) has been developed by chemical oxidation treatment of the flour. The as-synthesized CQDs were monodispersed sphere particles with the approximate diameter of 5-8nm, and exhibited strong fluorescence, excitation-dependent photoluminescence behavior and high photostability in a wide range of pH values. We investigated the cytotoxicity of as-prepared CQDs using rat mesangial cells (RMC). Compared with CdTe quantum dots, CQDs show no apparent cytotoxicity and much better biosafety property. The as-synthesized CQDs were also tested to label and image RMC in vitro and demonstrated to be highly promising biological fluorescent probes.

A simple one-step hydrothermal route towards water solubilization of carbon quantum dots from soya-nuggets for imaging applications

A high yield simple synthetic approach for water soluble photoluminescent carbon quantum dots via a single step, hydrothermal process, was described. Photoluminescent multi-colored emissions were used to label E. coli cells.

Preparation of carbon quantum dots based on starch and their spectral properties.

A simple method for the synthesis of water-soluble carbon quantum dots (CQDs) has been developed based on chemical oxidation of starch. The structures and optical properties of the CQDs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence spectroscopy (PL) and transmission electron microscopy. The CQDs were found to emit bright blue fluorescence and disperse uniformly. The effects of ambient temperature, light and pH on the properties of CQDs were studied. The CQDs exhibited good chemical stability, good photostability and pH sensitivity. Furthermore, the interaction between CQDs and bovine serum albumin (BSA) was investigated.

Solution reduction synthesis of amine terminated carbon quantum dots

Highly luminescent water soluble carbon quantum dots (CQDs) with narrow size distributions have been prepared via a simple room temperature, solution-phase synthesis. The CQDs, stabilised by covalently bound allylamine ligands to minimise surface oxidation, exhibit an excitation wavelength dependent blue luminescence with a quantum yield of 25%.

Rapid Detection of Bacteria by Carbon Quantum Dots

This work demonstrated a fluorescence measurement method for rapid detection of bacteria and their counting by using water-soluble carbon quantum dots (CQDs) as a fluorescence marker while sewage water bacteria were detection target bacteria. Highly luminescent water-soluble CQDs were prepared by carbonizing waste part of rice straw materials in a furnace under in-sufficient air flow. Bacteria in a LB media with < 100 nm of water soluble CQDs were cultured for 30-40 minutes. The multi colored bacterial cell images were obtained by using fluorescence microscopy. Our results showed that CQDs prepared in water phase were highly luminescent, stable, and successfully conjugated with bacterial cell membrane only. Also we could count the total number of bacteria within a shortest time from any sample of environment.