Beta-cyclodextrin-modified CdSe/ZnS quantum dots for sensing and chiroselective analysis

The Trace Detection of Nitrite Ions Using Neutral Red Functionalized SH-β-Cyclodextrin @Au Nanoparticles

A novel fluorescence sensor of NR-β-CD@AuNPs was prepared for the trace detection of nitrite in quantities as low as 4.25 × 10-3 μg∙mL-1 in an aqueous medium. The fluorescence was due to the host-guest inclusion complexes between neutral red (NR) molecules and gold nanoparticles (AuNPs), which were modified by per-6-mercapto-beta-cyclodextrins (SH-β-CDs) as both a reducing agent and a stabilizer under microwave radiation. The color of the NR-β-CD@AuNPs changed in the presence of nitrite ions. A sensor was applied to the determination of trace nitrites in environmental water samples with satisfactory results.

Highly sensitive sensing of hydroquinone and catechol based on β-cyclodextrin-modified carbon dots

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples. The properties of C-dot@β-CD nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The sensing behaviors of C-dot@β-CD toward CC and HQ were investigated by fluorescence spectroscopy. Based on the host–guest chemistry between C-dot@β-CD and phenolic compounds, which can quench C-dot@β-CD fluorescence, the prepared C-dot@β-CD nanocomposites could be used for the sensitive and selective detection of CC or HQ across a wide linear range (0.1 to 10 μM) with detection limits of 47.9 and 20.2 nM, respectively. These results showed that the synthesized C-dot@β-CD nanocomposite exhibited strong fluorescence and high degree of water solubility and thus, it is suitable for use as a nanoprobe for detecting CC or HQ in real water samples.

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples.

Fabrication of Stable and Luminescent Copper Nanocluster-Based AIE Particles and Their Application in β-Galactosidase Activity Assay

Thiolated copper nanoclusters (CuNCs) with aggregation-induced emission characteristic are becoming a novel luminescent material, but it is still a challenging task to retain its bright luminescence in a neutral solution. In this work, we report a new copper nanocluster with aggregation-induced emission (AIE) enhancement property using a hydrophobic molecule as the protecting ligand, and brightly luminescent AIE particles of copper nanocluster were prepared via hydrophobic interaction. These CuNCs AIE particles possess uniform rod-like shapes, with sizes in hundreds of nanometer, and an intense luminescence; more importantly, its luminescence remains stable in neutral and alkaline solutions. It is found that 4-nitrophenol is able to effectively quench the luminescence of CuNC AIE particles through strong hydrophobic interaction and electron transfer between them. This strong quenching effect was adopted to develop a luminescent assay for β-galactosidase at physiological condition. This work presents a demonstration of preparing CuNC AIE particles with bright luminescence at neutral condition and gives an example of the use of AIE particles in monitoring the enzyme activity.

Chiral Optical Properties of Tapered Semiconductor Nanoscrolls

Large surface-to-volume ratio, one-dimensional quantum confinement, and strong optical activity make chiral nanoscrolls ideal for the detection and sensing of small chiral molecules. Here, we present a simple physical model of chiroptical phenomena in multilayered tapered semiconductor nanoscrolls. Our model is based on a linear transformation of coordinates, which converts nanoscrolls into flat but topologically distorted nanoplatelets whose optical properties can then be treated analytically. As an illustrative application example, we analyze absorption and circular dichroism spectra of CdSe nanoscrolls using an eight-band model of CdSe. We show that the optical activity of the nanoscrolls originates from the chiral distortion of their crystal lattice and determine selection rules for the optically active interband transitions. The results of our study may prove useful for the modeling and design of semiconductor nanoscrolls and nanoscroll-based materials.

Ratiometric sensing of metabolites using dual-emitting ZnS:Mn2+ quantum dots as sole luminophore via surface chemistry design

We herein present an effective and versatile platform for ratiometric sensing of metabolites using intrinsically dual-emitting ZnS:Mn²⁺ quantum dots (QDs) as sole reporter. To avoid notoriously non-specific interactions, a special triple-layer "filter screen" around the inorganic QD core is rationally constructed, which is made of oleic acid, cetyltrimethyl ammonium bromide and bio-enzymes. In the presence of the analytes, the in-situ enzymatic H₂O₂ molecules diffuse and pass through the "filter screen" along the molecule interspace, which then reacts with the inorganic core and leads to more dramatically quenching of the Mn²⁺ emission. The ratiometric signal readout is so distinct that can be observed by naked eyes (from orange to violet). In contrast, various coexisting bio-molecules, due to larger size, are well prevented from penetrating the filter screen by steric hindrance effect. So, various potential interfering substances do not disturb the assay. Under optimal conditions, five kinds of the corresponding substrates, namely glucose, cholesterol, lactate, xanthine and uric acid are well quantified by the emission intensity ratio of I₄₇₀/I₆₁₅, and the linear ranges are 0.1-200µM, 0.1-200µM, 1-200µM, 1-200µM and 1-200µM, respectively. The detection limits can even reach quasi-picomole levels. Because of favorable analytical performances (excellent selectivity, appropriate sensitivity and broad linear range), the proposed system can direct assay the analytes in blood without any sample pre-treatment.

Smart Gating Multi-Scale Pore/Channel-Based Membranes

Smart gating membranes are important and promising in membrane science and technology. Rapid progress in developing smart membranes is transforming technology in many different fields, from energy and environmental to the life sciences. How a specific smart behavior for controllable gating of porous membranes can be obtained, especially for nano- and micrometer-sized multi-scale pore/channel-based membrane systems is addressed.

Cyclodextrin-clicked silica/CdTe fluorescent nanoparticles for enantioselective recognition of amino acids

Fluorescent sensors based on semiconductor quantum dots (QDs) have been immensely investigated for achiral molecular recognition. For chiral discrimination of amino acids (AAs), we herein report a versatile fluorescent sensor, i.e., CdTe QDs encapsulated with cyclodextrin (CD) clicked silica via layer-by-layer modification. The as-obtained hybrid molecular recognition platform exhibited excellent chirality sensing of AAs at micromolar concentrations in water. By taking advantage of the inclusion complexation of CD and the optical properties of the QD core, chiral discrimination was realized on the basis of the different binding energies of the CD-AA enantiomer complexes, as revealed using density-functional theory calculation. The fluorescent probe exhibited linearly enhanced photoluminescence with increased concentration of d-histidine at 0-60 μM and L-histidine at 0-20 μM. These water-soluble fluorescent sensors using a chiral host with a covalently linked chromophore may find applications in the robust sensing of a wide range of achiral and chiral molecules in water.

Multichannel Detection and Differentiation of Explosives with a Quantum Dot Array

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform, faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each color quantum dot is functionalized with a different surface receptor via a facile ligation process. These receptors undergo nonspecific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range.

Cyclodextrin capped CdTe quantum dots as versatile fluorescence sensors for nitrophenol isomers

Cyclodextrin (CD) capped CdTe quantum dots (QDs) were prepared with uniform dimension (average diameter ∼5 nm) and high quantum yield (ca. 65%). By taking advantage of the inclusion complexation of CD, β-CD-CdTe QDs exhibited strong fluorescence quenching in a linear relationship with the concentration of o-, m- and p-nitrophenol in the range of 20-100 μM. The detection limit reached 0.05 μM for o-/p-nitrophenol and 0.3 μM for m-nitrophenol. The fluorescence decay study revealed the stabilization effect of CD covering on CdTe QDs and fine-tuning of the fluorescence for selective ultrasensitive detection of nitrophenol isomers.

Sensitive fluorimetric assays for α-glucosidase activity and inhibitor screening based on β-cyclodextrin-coated quantum dots

A fluorescence method was established for a α-glucosidase activity assay and inhibitor screening based on β-cyclodextrin-coated quantum dots. p-Nitrophenol, the hydrolysis product of the α-glucosidase reaction, could quench the fluorescence of β-cyclodextrin-coated quantum dots via an electron transfer process, leading to fluorescence turn-off, whereas the fluorescence of the system turned on in the presence of α-glucosidase inhibitors. Taking advantage of the excellent properties of quantum dots, this method provided a very simple, rapid and sensitive screening method for α-glucosidase inhibitors. Two α-glucosidase inhibitors, 2,4,6-tribromophenol and acarbose, were used to evaluate the feasibility of this screening model, and IC50 values of 24 μM and 0.55 mM were obtained respectively, which were lower than those previously reported. The method may have potential application in screening α-glucosidase inhibitors.

Surface functionalized fluorescent CdS QDs: selective fluorescence switching and quenching by Cu(2+) and Hg(2+) at wide pH range

Fluorescent CdS QDs surface functionalized with organic functional unit, N-(2-hydroxybenzyl)-cysteine (L), has been synthesized using simple wet chemical approach in a single step. The as-prepared L-CdS QDs showed good fluorescence at 542 nm. Fluorescence sensor studies of L-CdS QDs showed selective fluorescence switching (542-600 nm) for Cu(2+) ions and quenching for Hg(2+) ions in aqueous solution. High selectivity of L-CdS QDs for Cu(2+) ions have been confirmed by interference studies. Interestingly, L-CdS QDs showed enhancement in the fluorescence intensity (4-fold) upon reducing pH from 2.0 to 10.0 without changing λmax. Importantly, selective fluorescent switching and quenching for Cu(2+) and Hg(2+) was observed from 2.0 to 10.0 pH range. The practical application of L-CdS QDs fluorescence sensing for Cu(2+) and Hg(2+) have also been demonstrated in real samples such as river, pond, tap and ground water.

Metal ion induced fluorescence resonance energy transfer between crown ether functionalized quantum dots and rhodamine B: selectivity of K+ ion

A ratiometric fluorescent metal ion sensor based on the mechanism of fluorescence resonance energy transfer between 15-crown-5-ether capped CdSe/ZnS quantum dots and 15-crown-5-ether attached rhodamine B.

A novel water-soluble quantum dot–neutral red fluorescence resonance energy transfer probe for the selective detection of megestrol acetate

Megestrol acetate can specifically quench the fluorescence intensity of the β-CD-QD–NR FRET probe at low concentration levels.

Functional holey graphene oxide: a new electrochemically transformed substrate material for dopamine sensing

Increasing active sites through generating holes within the basal plane of graphene sheets is an effective strategy to enhance catalytic performance in various applications such as sensors, electrocatalysis, and electronics.

Predicting self-assembly and structure in diluted aqueous solutions of modified mono- and bis-β-cyclodextrins that contain naphthoxy chromophore groups

Mono-cyclodextrins, whose appended groups contain a naphthoxy moiety, form tail-to-tail non-covalent dimers in water solution. Bis-CDs do not exhibit self-association.

β-Cyclodextrin functionalised gold nanoclusters as luminescence probes for the ultrasensitive detection of dopamine

A novel luminescence probe based on mono-6-amino-β-cyclodextrin (NH₂-β-CD) functionalised gold nanoclusters (β-CD-AuNC) was designed for dopamine (DA) detection.

ZrO2-β-cyclodextrin catalyzed synthesis of 2,4,5-trisubstituted imidazoles and 1,2-disubstituted benzimidazoles under solvent free conditions and evaluation of their antibacterial study

A series of 2,4,5-trisubstituted imidazoles and 1,2-disubstituted benzimidazoles catalyzed by ZrO₂-supported-β-cyclodextrin (ZrO₂-β-CD) under solvent free conditions have been synthesized and characterized by spectral methods.

Evaluation of photoluminescence quenching for assessing the binding of nitroaromatic compounds to a tyrosyl bolaamphiphile self-assembly

Quenching effects of the aromatic stacking and hydrophilic interactions between nitroaromatic compounds and a fluorophore with phenolic groups were investigated.

Luminescent sensors based on quantum dot–molecule conjugates

We illustrate the principles underlying the rational construction of luminescent sensors by combining semiconductor nanocrystal and molecular components, and describe the representative examples of sensors for ionic and molecular analytes.

β-Cyclodextrin functionalized Mn-doped ZnS quantum dots for the chiral sensing of tryptophan enantiomers

A versatile, multi-functional photoluminescence platform for chiral recognition and sensing of tryptophan enantiomers is fabricated based on cyclodextrin modified Mn-ZnS quantum dots.

Carbon Dot Based Sensing of Dopamine and Ascorbic Acid

We demonstrate carbon dot based sensor of catecholamine, namely, dopamine and ascorbic acid. Carbon dots (CDs) were prepared from a green source: commercially available Assam tea. The carbon dots prepared from tea had particle sizes of ∼0.8 nm and are fluorescent. Fluorescence of the carbon dots was found to be quenched in the presence of dopamine and ascorbic acid with greater sensitivity for dopamine. The minimum detectable limits were determined to be 33 μM and 98 μM for dopamine and ascorbic acid, respectively. The quenching constants determined from Stern-Volmer plot were determined to be 5 × 10−4 and 1 × 10−4 for dopamine and ascorbic acid, respectively. A probable mechanism of quenching has been discussed in the paper.