Colorimetric determination and recycling of gold(III) ions using label-free plasmonic H0.3MoO3 nanoparticles.

A low-cost and environment-friendly sensor was developed for visual determination of gold ions (Au3+) by using label-free hydrogen doped molybdenum oxide (H0.3MoO3) nanoparticles as ratio probes. According to the characterization results of transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectra, Au3+ is easily reduced to red Au nanoparticles (AuNPs) by blue H0.3MoO3 nanoparticles. The color change of the solution depends on the concentration of Au3+, which makes it possible to detect Au3+ visually. Under optimal experimental conditions of pH 4.6, H0.3MoO3 nanoparticles concentration of 0.075 mg·mL-1, and reaction time of 7 min, the sensor offers a satisfactory determination range from 0.5 to 70 µM and a good determination limit of 0.45 µM for Au3+. The concentration of Au3+ as low as 10 µM can be directly distinguished through the naked eye. Additionally, the colorimetric probe has also been proved applicable in environmental water samples. More importantly, the resulting AuNPs have good stability and oxidase-like activity, which may be directly used in sensing, catalysis, energy, and other fields.

A ratiometric fluorescence sensor for ascorbic acid determination based on an AND-NAND logic pair.

An AND-NAND logic pair is reported based on non-purified carbon quantum dots (CDs) for ascorbic acid (AA) detection. In the logic operation, molybdenum oxide nanosheets (MoO3 NSs) and AA are used as two signal inputs. In the presence of AA, MoO3 NSs are reduced to plasmonic molybdenum oxide, which decreases the CD fluorescence intensity because of a static quenching, dynamic quenching, and internal filtration effect. Meanwhile, the AA is oxidized to dehydroascorbic acid and forms fluorescent 3-(dihydroxyethyl) furo [3,4-b] quinoxaline-1-one with o-phenylenediamine from non-purified CDs. On this basis, an AND-NAND logic pair was constructed and used as a ratiometric fluorescence sensor for highly sensitive detection of AA. The method has a wide linear range of 0.05-50 µM, and a detection limit of 34 nM. In addition, it was used to detect AA in fresh fruit. Potential applications include chemical computing, optoelectronic devices, biomedical science, and environmental monitoring. HIGHLIGHTS: 1. A ratiometric fluorescence sensor based on AND-NAND logic pair constructed by CDs and MoO3 NSs was successfully fabricated. 2. The ratiometric fluorescence sensor exhibited satisfactory linear range, high sensitivity, and good selectivity for AA. 3. The ratiometric fluorescence method was able to detect AA in fresh fruit with good results comparable to official fluorescence methods.

One-step synthesis of N-doped carbon dots, and their applications in curcumin sensing, fluorescent inks, and super-resolution nanoscopy.

Nitrogen-doped carbon dots (N-CDs) with fluorescence excitation/emission maxima at 365/450 nm were prepared by a one-step hydrothermal approach. The dots possess remarkable photostability, fluorescence blinking and good biocompatibility, and this favors utilization in stochastic optical reconstruction microscopy (STORM). A spatial resolution down to ~60 nm was achieved when imaging HeLa cells using 647-nm laser excitation. This opens new possibilities for various super-resolution techniques based on stochastic optical switching. The remarkable optical properties of the N-CDs also enable them to be applied as invisible security ink for use in patterning, information storage and anti-counterfeiting. Further, it is found that the fluorescence of the N-CDs can be quenched by curcumin with high efficiency due to a combination of inner filter effect and static quenching. Based on this, a fluorometric assay with a detection limit of 21 ng mL-1 was developed for the determination of curcumin. Graphical abstract Schematic representation of the applications of N-doped carbon dots (N-CDs). Curcumin quenches the fluorescence of N-CDs with high efficiency. The remarkable optical properties of the N-CDs enable them to be applied in fluorescent ink, cell imaging and stochastic optical reconstruction microscopy (STORM).

Preparation of two ionic liquid bonded stationary phases and comparative evaluation under mixed-mode of reversed phase/ hydrophilic interaction/ ion exchange chromatography.

The present work describes the preparation of two ionic liquid and carboxyl acid silane reagents via photo-initiated thiol-ene click chemistry that have been bonded to silica to afford two mixed-mode stationary phases (Sil-C4Im-C9Co and Sil-C9Im-C4Co). The two stationary phases provided satisfactory retention repeatability and efficiencies. The influence of acetonitrile content, salt concentration and pH of the mobile phase was investigated to clarify the retention properties of the prepared stationary phases. The results showed that the prepared Sil-C4Im-C9Co and Sil-C9Im-C4Co undergo multiple interactions with solutes under different chromatographic conditions. The retention mechanisms were further studied by the linear energy solvation relationship and Van't Hoff plots. Finally, the stationary phases were employed to separate hydrophobic solutes (alkylbenzenes and polycyclic aromatic hydrocarbons) under reversed phase liquid chromatography (RPLC) mode, hydrophilic solutes (carboxylic acids, nucleosides and bases) under hydrophilic interaction liquid chromatography (HILIC) mode and inorganic anions under ion-exchange chromatography (IEC) mode, providing excellent performance and varying selectivity when compared with a commercial column. The bonding method in this work is feasible and the prepared stationary phases are promising when employed in RPLC/HILIC/IEC mixed-mode chromatography applications.

Simultaneous determination of cytokinins by high performance liquid chromatography with resonance Rayleigh scattering and mechanism discussion.

A reliable, highly sensitive and highly selective method of high performance liquid chromatography associated with resonance Rayleigh scattering (HPLC-RRS) was developed to detect three cytokinins, namely, 6-benzylaminopurine (BA), kinetin (KT) and zeatin (ZT). In this work, Pd(ii) is added into the system to form ternary ion association complexes for the first time, which results in a lower limit of detection and extends the application of HPLC-RRS. The experimental conditions were optimized. In order to investigate the reaction mechanism, the ternary ion association complexes were characterized by ultraviolet-visible spectrophotometry, dynamic light scattering, scanning electron microscopy and density functional theory calculations. In a HAc-NaAc buffer solution (pH = 4.1), a ternary complex of cytokinin : Pd(ii) : EryB (1 : 1 : 2) was formed. The detection limits (S/N = 3) of BA, KT, and ZT were 0.9, 1.5 and 2.3 ng mL-1, respectively. In addition, this method was applied for the simultaneous detection of cytokinins in real samples with satisfactory results.

A quadruple-channel fluorescent sensor array based on label-free carbon dots for sensitive detection of tetracyclines.

A quadruple-channel fluorescent sensor array based on label-free carbon dots (CDs) was fabricated to detect and discriminate a series of tetracyclines (TCs), including chlortetracycline (CTC), oxytetracycline (OTC), tetracycline (TC) and doxycycline (DOX). Blue-emitting carbon dots (B-CDs) and green-emitting carbon dots (G-CDs) were prepared to serve as four sensing elements. When the TCs were directly mixed with CDs, the fluorescence quenching phenomenon appeared. Since different TCs exhibited different affinities for sensing elements, the sensor array displays a distinct fluorescence pattern of the fluorescence intensity variation (F0 - F)/F0 for each of these TCs, which is further analyzed by principal component analysis (PCA). The present fluorescent sensor array has the capacity to differentiate TCs at a low concentration of 1 µM. Meanwhile, quantitative detection with a lower limit (0.30 µM) for TCs could be achieved by applying a single element. Moreover, a high accuracy (100%) examination of unknown samples is acquired. Finally, the fluorescent sensor array performs well in distinguishing binary mixtures and could also recognize TCs in milk.

A synergistic coordination strategy for colorimetric sensing of chromium(III) ions using gold nanoparticles.

We report a simple, facile, and reliable colorimetric system for detection of chromium(III) ions (Cr3+) using citrate- and thiourea-modified gold nanoparticles (AuNPs). The colorimetric sensing strategy is based on the synergistic coordination interaction of citrate and thiourea toward Cr3+ on the surface of AuNPs, leading to the aggregation of AuNPs which produces a color change from red to purple. Under the optimal conditions, this colorimetric sensing system shows an excellent selectivity and sensitivity for Cr3+, and the limit of detection (LOD) is estimated to be 0.05 µM at a signal-to-noise ratio of 3, which is far below the current standard stipulated by U.S. Environmental Protection Agency (1.9 µM). Moreover, this LOD is one and a half orders of magnitude lower than those of previously reported modified AuNPs-based colorimetric methods. Visual color change can be observed when 50 µM of Cr3+ was introduced to the sensing system. Furthermore, this colorimetric sensing system can be employed for detection of Cr3+ in diluted natural water samples.

Direct visual detection of MnO2 nanosheets within seconds.

The increasing application of nanomaterials will inevitably lead to their release into the environment, which may pose a threat to the environment and human health. As such, there is an urgent need to detect various nanomaterials. In the present work, we present a novel, rapid, and simple visual detection of MnO2 nanosheets in buffer solution and environmental water sample. In this assay, a redox reaction between MnO2 nanosheets and 3,3',5,5'-tetramethylbenzidine (TMB) occurred, leading to the oxidation of TMB to TMB diimine. This redox reaction generated different colors dependent on the concentration of MnO2 nanosheets, including colorless, blue, green, and yellow, which allowed semiquantitative detection of MnO2 nanosheets with the naked eye. The detection range of the visual assay was 2-15 µg/mL, and the minimum concentration of MnO2 nanosheets can be visually detected at concentrations down to 2.0 µg/mL. Moreover, the developed visual assay showed a high selectivity to MnO2 nanosheets over Mn(2+) ions, tetramethylammonium hydroxide, hydrogen peroxide, graphene oxide, and graphitic carbon nitride nanosheets.