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

Highly Fluorescent ZnO Composite of N-doped Carbon Dots From Dregea Volubilis for Fluorometric Determination of Glucose in Biological Samples

A nano-sensor based on N-doped carbon dots (NCDs)@ZnO (NCZ) composite was fabricated and efficacy for detecting glucose from human blood and urine samples in a straightforward manner was examined. The composite was prepared following a green hydrothermal method under ambient condition using a novel plant material, Dregea volubilis fruit and structural and optical properties were evaluated using standard techniques. The composite exhibited excellent characteristics including good photostability, biocompatibility, low toxicity, and strong fluorescence, with a decent quantum yield of up to 59%. The NCZ composite has been very sensitive and could selectively detect glucose in urine and blood samples. Selective glucose quenching was efficacious at different concentrations of glucose (1-6 mM) and in the pH range of 7-8, limit of detection was 0.25 mM. The potential uses of carbon-based materials have grown, thanks to the excellent sensing/detection capabilities of the NCZ composite as well as the capacity to prevent nanoparticle aggregation, opening up new possibilities for the development of environmentally benign nano-sensors.

Chiral probes for biosensing

Chiral inorganic nanomaterials have emerged as a highly promising area of research in nanoscience due to their exceptional light-matter interaction and vast potential applications in chiral sensing, asymmetric catalysis, enantiomer separation, and negative-index materials. We present an overview of the latest advances in chiral inorganic nanomaterials including chiral individual nanoparticles, chiral assemblies, and chiral film-based sensors over the past ten years. Additionally, we discuss the challenges and future perspectives for developing chiral nanomaterials in biosensing applications.

Diethylenetriamine-β-CD-modified carbon quantum dots for selective fluorescence sensing of Hg2+ and Fe3+ and cellular imaging

Diethylenetriamine-β-cyclodextrin-modified carbon quantum dots (3 N-CQDs) were synthesized via a one-step hydrothermal method using citric acid as the carbon source and diethylenetriamine-β-cyclodextrin (3 N-β-CD) as the nitrogen source. The successful preparation of 3 N-CQDs were revealed by infrared absorption spectroscopy, ultraviolet (UV)-visible absorption spectroscopy, fluorescence spectroscopy, XRD, XPS, TEM, and TG. Further spectroscopic studies showed that the synthesized carbon quantum dots offered good anti-interference capability. The relative fluorescence quantum yield was 67.2 %. The limits of detection for Hg²⁺ and Fe³⁺ were 0.25 µM and 0.57 μM, respectively. Cytotoxicity and imaging studies showed that the prepared carbon quantum dots had low cytotoxicity, good biocompatibility, and good cellular imaging capability for HeLa cells. They offered fluorescent sensing of Hg²⁺ and Fe³⁺ in live cells. Therefore, 3 N-CQDs were ideal fluorescent probes for the detection of Hg²⁺ and Fe³⁺ in water.

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

CeO2 quantum dots for highly selective and ultrasensitive fluorescence detection of 4-nitrophenol via the fluorescence resonance energy transfer mechanism

A rapid and simple fluorescence probe based on CeO₂ quantum dots (QDs) was developed for highly selective and ultrasensitive direct determination of 4-nitrophenol (4-NP). CeO₂ QDs were prepared using the sol-gelmethod with the precursor of Ce(NO₃)₃·6H₂O as a cerium source. The products were characterized through high-resolution electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The fluorescent probe based on CeO₂ QDs exhibited a broad linear response to the concentration of 4-NP in the range of 0.005-75.00 μM and provided a low detection limit of 1.50 nM. The fluorescence of CeO₂ QDs was quenched by 4-NP through the fluorescence resonance energy transfer mechanism owing to the well overlaps between the fluorescence emission spectrum of CeO₂ QDs with the ultraviolet absorption spectrum of 4-NP. This result was confirmed by the time-resolved fluorescence spectra and the evaluation of the interaction distance between CeO₂ QDs and 4-NP. The prepared CeO₂ QDs are successfully applied to the determination of 4-NP in real water samples, where the spiked recoveries range from 98.2% to 102.4%.

Targeted Delivery and Site-Specific Activation of β-Cyclodextrin-Conjugated Photosensitizers for Photodynamic Therapy through a Supramolecular Bio-orthogonal Approach

Targeted delivery of photosensitizers using hydrophilic and tumor-directing carriers and site-specific activation of their photocytotoxicity are two common strategies to enhance the specificity of anticancer photodynamic therapy. We report herein a novel supramolecular bio-orthogonal approach to integrate these two functions. A β-cyclodextrin-substituted aza-boron-dipyrromethene-based photosensitizer was first complexed with a ferrocene-substituted black-hole quencher to inhibit its photosensitizing ability. Upon encountering the adamantane moieties that had been delivered to target cancer cells through specific binding of the conjugated peptide to the overexpressed epidermal growth factor receptor, the ferrocene-based guest species were displaced due to the stronger binding interactions between β-cyclodextrin and adamantane, thereby restoring the photodynamic activity of the photosensitizer. Hence, this two-step process enabled targeted delivery and site-specific activation of the photosensitizer, as demonstrated through a series of experiments in aqueous media, in a range of cancer cell lines and in tumor-bearing nude mice.

Shining light on chiral inorganic nanomaterials for biological issues

The rapid development of chiral inorganic nanostructures has greatly expanded from intrinsically chiral nanoparticles to more sophisticated assemblies made by organics, metals, semiconductors, and their hybrids. Among them, lots of studies concerning on hybrid complex of chiral molecules with achiral nanoparticles (NPs) and superstructures with chiral configurations were accordingly conducted due to the great advances such as highly enhanced biocompatibility with low cytotoxicity and enhanced penetration and retention capability, programmable surface functionality with engineerable building blocks, and more importantly tunable chirality in a controlled manner, leading to revolutionary designs of new biomaterials for synergistic cancer therapy, control of enantiomeric enzymatic reactions, integration of metabolism and pathology via bio-to nano or structural chirality. Herein, in this review our objective is to emphasize current research state and clinical applications of chiral nanomaterials in biological systems with special attentions to chiral metal- or semiconductor-based nanostructures in terms of the basic synthesis, related circular dichroism effects at optical frequencies, mechanisms of induced optical chirality and their performances in biomedical applications such as phototherapy, bio-imaging, neurodegenerative diseases, gene editing, cellular activity and sensing of biomarkers so as to provide insights into this fascinating field for peer researchers.

Injectable Thixotropic β-Cyclodextrin-Functionalized Hydrogels Based on Guanosine Quartet Assembly

Facile method for the preparation of β–cyclodextrin–functionalized hydrogels based on guanosine quartet assembly was described. A series of seven hydrogels were prepared by linking β–cyclodextrin molecules with guanosine moieties in different ratios through benzene–1,4–diboronic acid linker in the presence of potassium hydroxide. The potassium ions acted as a reticulation agent by forming guanosine quartets, leading to the formation of self–sustained transparent hydrogels. The ratios of the β–cyclodextrin and guanosine components have a significant effect on the internal structuration of the components and, correspondingly, on the mechanical properties of the final gels, offering a tunablity of the system by varying the components ratio. The insights into the hydrogels’ structuration were achieved by circular dichroism, scanning electron microscopy, atomic force microscopy, and X–ray diffraction. Rheological measurements revealed self–healing and thixotropic properties of all the investigated samples, which, in combination with available cyclodextrin cavities for active components loading, make them remarkable candidates for specific applications in biomedical and pharmaceutical fields. Moreover, all the prepared samples displayed selective antimicrobial properties against S. aureus in planktonic and biofilm phase, the activity also depending on the guanosine and cyclodextrin ratio within the hydrogel structure.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light-matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light-matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.

From MonoBINOL to BisBINOL: Expanded Enantioselective Fluorescent Recognition of Amino Acids

Condensation of the methoxymethyl-protected (R)-3,3'-diformyl-1,1'-bi-2-naphthol (BINOL) with (pyridine-2,6-diylbis(methylene))bis(triphenyl phosphonium)dibromide in the presence of a base followed by deprotection gave a new bisBINOL-based fluorescent probe (R,R)-4. This compound showed expanded substrate scope in the recognition of amino acids with good enantioselective fluorescence responses toward 17 common amino acids. Two diastereomeric imines were synthesized from the condensation of (R,R)-4 with l- and d-valine, and the reactions of these imines with Zn(OAc)₂ were investigated by various spectroscopic methods for a better understanding of the enantioselective fluorescent recognition process.

The study of chiral recognition on ibuprofen enantiomers by a fluorescent probe based on β-cyclodextrin modified ZnS:Mn quantum dots

In this paper, a fluorescence method for chiral detection of ibuprofen and its enantiomer was developed. The L-cystenine-capped ZnS:Mn quantum dots were synthesized and functionalized with β-cyclodextrin (β-CD-QDs). The β-CD-QDs exhibited different quenching effect to the S-(+)-ibuprofen and the R-(-)-ibuprofen based on the advantage of the inclusion complex of cyclodextrin. It was found that the quenching of β-CD-QDs by S-(+)-ibuprofen was due to the formation of inclusion complex through both static quenching and photoinduced electron transfer, but only slight quenching with the R-(-)-ibuprofen. The stability constants derived from Hildebrand-Benesi method and absorption titration experiments were applied to determine the stability constants of the formed complexes, the double reciprocal plots suggest that a conclusion complex with a ratio of 1:1 was formed between β-CD-QDs and S-(+)-ibuprofen, but did not with the R-(-)-ibuprofen. The fluorescence intensity of the β-CD-QDs was linearly dependent on the concentration of the S-(+)-IBP in the range of 0-0.5 nmol/L with an limit of detection of 0.29 nmol/L.

Cyclodextrins and inorganic nanoparticles: Another tale of synergy

In this review, we summarize the recent research focused on the combination of inorganic nanoparticles and α-, β- and γ- cyclodextrins. Our intention is to highlight the most relevant publications on the synthesis of nanoparticle-cyclodextrin (NP-CD) nanohybrids, with CDs acting as reducing agents or through the post-synthetic modification of inorganic nanoparticles with CDs. We also discuss the new or enhanced properties that arise from the host-guest capabilities of the CDs and inorganic nanoparticles. Finally, we illustrate the potential applications of these materials in numerous research fields.

Fluorescence resonance energy transfer between carbon quantum dots and silver nanoparticles: Application to mercuric ion sensing

Fluorescence resonance energy transfer (FRET) process as a practical and competitive sensing strategy was utilized between carbon quantum dots (C-dots) and silver nanoparticles (Ag NPs) for the determination of mercuric ions. The novel synthesized C-dots with the quantum yield of 84% acted as the donor and Ag NPs operated as the acceptor in the FRET process leading to the fluorescence quenching of the C-dots. In the presence of Hg(II) ions, the FRET-quenched fluorescence emission of the C-dots-Ag NPs system was recovered owing to oxidation of Ag NPs by Hg(II) ions, so that the turn-on fluorescence intensity was directly proportional to the Hg(II) ion concentration. Accordingly, combination of the FRET system with the redox reaction was firstly utilized to construct an innovative turn-off/on fluorescent sensor for the quantification of Hg(II) ion. The calibration plot was linear in the concentration range 0.5-500.0 nmol L^-1 with a determination coefficient (R²) of 0.9965. The limit of detection and limit of quantification were 0.10 and 0.35 nmol L^-1, respectively, according to the IUPAC definition. The method was applied for the determination of Hg(II) ion in lake water, wastewater and tea samples, and the proper relative recoveries (98.0-104.0%) were obtained for the spiked samples. The method has high potential to diagnose trace values of mercuric ions in real samples with high sensitivity and repeatability.

Facile and label-free fluorescence sensing of β-galactosidase activity by graphene quantum dots

β-Galactosidase (β-Gal), as a glycoside hydrolase, is closely associated with cell senescence and primary ovarian cancer. However, there is still lack of facile and rapid sensing approach to monitor the β-Gal activity. In this work, a label-free and convenient sensing strategy to detect β-Gal activity has been proposed based on fluorescent graphene quantum dots (GQDs). In the presence of β-Gal, 4-nitrophenyl-β-D-galactopyranoside (NPGal) can be hydrolyzed into 4-nitrophenol (4-NP), which serves as a good quencher to quench the fluorescence of GQDs. The quenching mechanism is proven to be inner filter effect (IFE). Due to the specificity of the enzymatic reaction, this sensing method displays excellent selectivity and high sensitivity. A broad dynamic range from 20 to 200 U L^-1 and a detection limit of 4.4 U L^-1 for the β-Gal assay are achieved. Compared with the previously reported methods, this sensing strategy only needs one fluorescent nanomaterial without any modification and avoids time-consuming handling steps. Therefore, the sensing strategy based on fluorescent GQDs offers great potential for the recognition of disease-correlated enzyme activity.

Artificial Chiral Probes and Bioapplications

The development of artificial chiral architectures, especially chiral inorganic nanostructures, has greatly promoted research into chirality in nanoscience. The nanoscale chirality of artificial chiral nanostructures offers many new application opportunities, including chiral catalysis, asymmetric synthesis, chiral biosensing, and others that may not be allowed by natural chiral molecules. Herein, the progress achieved during the past decade in chirality-associated biological applications (biosensing, biolabeling, and bioimaging) combined with individual chiral nanostructures (such as chiral semiconductor nanoparticles and chiral metal nanoparticles) or chiral assemblies is discussed.

Enantioselective Fluorescent Recognition of Free Amino Acids: Challenges and Opportunities

Fluorescent probes that can discriminate enantiomers of amino acids in organic media or aqueous solution are discussed. This Minireview focuses on recent progress in the studies of three classes of probes including those made of cyclodextrins, 1,1'-binaphthyl compounds, and nanomaterials, and uses them to illustrate the design strategies, applications, and limitations in this area. These probes are potentially useful for rapid analysis of asymmetric reactions for amino acid synthesis as well as the real-time imaging of amino acids in biological systems. The challenges in these applications are analyzed. Working in this field of enantioselective fluorescent recognition of amino acids offers great opportunities to make new scientific discoveries and to develop important practical applications.

PtNPs-GNPs-MWCNTs-β-CD nanocomposite modified glassy carbon electrode for sensitive electrochemical detection of folic acid

A novel electrochemical sensor, platinum nanoparticles/graphene nanoplatelets/multi-walled carbon nanotubes/β-cyclodextrin composite (PtNPs-GNPs-MWCNTs-β-CD) modified carbon glass electrode (GCE), was fabricated and used for the sensitive detection of folic acid (FA). The PtNPs-GNPs-MWCNTs-β-CD nanocomposite was easily prepared with an ultrasound-assisted assembly method, and it was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical behavior of FA at PtNPs-GNPs-MWCNTs-β-CD/GCE was investigated in detail. Some key experimental parameters such as pH, amount of PtNPs-GNPs-MWCNTs-β-CD composite, and scan rate were optimized. A good linear relationship (R² = 0.9942) between peak current of cyclic voltammetry (CV) and FA concentration in the range 0.02-0.50 mmol L^-1 was observed at PtNPs-GNPs-MWCNTs-β-CD/GCE. The detection limit was 0.48 μmol L^-1 (signal-to-noise ratio = 3). A recovery of 97.55-102.96% was obtained for the determination of FA in FA pills (containing 0.4 mg FA per pill) at PtNPs-GNPs-MWCNTs-β-CD/GCE, indicating that the modified electrode possessed relatively high sensitivity and stability for the determination of FA in real samples.

β-Cyclodextrin-Immobilized Ni/Graphene Electrode for Electrochemical Enantiorecognition of Phenylalanine

In this work, a Ni/graphene (Ni/G) electrode was designed and fabricated by plasma-enhanced chemical vapor deposition (PECVD) for the ultrasensitive recognition of d- and l-phenylalanine. Through a single-step PECVD process, the Ni/G electrode can achieve better hydrophilicity and larger catalytic surface area, which is beneficial for the electrochemical recognition of bio-objects. After surface modification with β-cyclodextrin, the Ni/G electrode can distinguish d-phenylalanine from l-phenylalanine according to a 0.09 V peak shift in differential pulse voltammetry tests. Moreover, this Ni/G electrode achieved a detection limit as low as 1 nM and a wide linear range from 1 nM to 10 mM toward l-phenylalanine, with great storage stability and working stability.

Optical nanoprobes for chiral discrimination

Chiral recognition can be achieved by exploiting chiral properties of nanoparticles within various colorimetric and luminescent sensing systems.

Rapidly detecting antibiotics with magnetic nanoparticle coated CdTe quantum dots

A reusable magnetic-quantum dot material (MNP–SiO₂–QD) with good magnetic properties and high fluorescence retention was successfully fabricated from linked magnetic nanoparticles and quantum dots. The resulting material can qualitatively and quantitatively detect four kinds of antibiotics and maintain high recovery rates.

A reusable magnetic-quantum dot material with good magnetic property and high fluorescence retention can qualitatively and quantitatively detect four kinds of antibiotics.

Photosensitized H2 Evolution and NADPH Formation by Photosensitizer/Carbon Nitride Hybrid Nanoparticles

The broadband C₃N₄ semiconductor absorbs in the UV region, λ = 330-380 nm, a feature limiting its application for light-to-energy conversion. The unique surface adsorption properties of C₃N₄ allow, however, the binding of a photosensitizer, operating in the visible-solar spectrum to the surface of C₃N₄. Coupling of the energy levels of the photosensitizer with the energy levels of C₃N₄ allows effective photoinduced electron-transfer quenching and subsequent charge separation in the hybrid structures. Two methods to adsorb a photosensitizer on the C₃N₄ nanoparticles are described. One is exemplified by the adsorption of Zn(II)-protoporphyrin IX on C₃N₄ using π-π interactions. The second method utilizes the specific binding interactions of single-stranded nucleic acids on C₃N₄ and involves the binding of a Ru(II)-tris-bipyridine-modified nucleic acid on the C₃N₄ nanoparticles. Effective electron-transfer quenching of the photoexcited photosensitizers by C₃N₄ proceeds in the two hybrid systems. The two hybrid photosystems induce the effective photosensitized reduction of N,N'-dimethyl-4,4'-bipyridinium, MV²⁺, to MV^+•, in the presence of Na₂EDTA as a sacrificial electron donor. The generation of MV^+• is ca. 5-fold higher as compared to the formation of MV^+• in the presence of the photosensitizer alone (in the absence of C₃N₄). The effective generation of MV^+• in the photosystems is attributed to the efficient quenching of the photosensitizers, followed by effective charge separation of the electrons in the conduction band of C₃N₄ and the holes in the oxidized photosensitizer. The subsequent transfer of the conduction-band electrons to MV²⁺ and the oxidation of Na₂EDTA by the oxidized photosensitizers lead to the effective formation of MV^+•. The photogenerated MV^+• by the two hybrid photosystems is used to catalyze H₂ evolution in the presence of Pt nanoparticle catalysts and to mediate the reduction of NADP⁺ to NADPH, in the presence of ferredoxin-NADP⁺ reductase, FNR. The ability to couple the photogenerated NADPH to drive NADP⁺-dependent biocatalytic transformations is demonstrated.

β-cyclodextrin modified quantum dots as pseudo-stationary phase for direct enantioseparation based on capillary electrophoresis with laser-induced fluorescence detection

In recent years, quantum dots (QDs) have attracted a tremendous amount of attention due to their compelling features. In this work, a kind of composite QDs based on β-cyclodextrin (β-CD) and its derivatives modification was prepared, and for the first time utilized to separate and determine enantiomers in the combined system of capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). By taking advantages of the inclusion complexation of β-CD and the fluorescence property of QD core, the composite QDs were added into the running buffer as pseudo-stationary phase. The resultant CE-LIF method accomplished enantioseparation for six groups of model analytes without need of capillary preparation and analyte derivatization. The effects of composite QDs concentration, the pH value and concentration of the running buffer on resolution have been investigated individually. The RSDs of interday and intraday repeatability were in the range of 2.7-8.1%, 0.7-3.9%, and 1.5-3.8% for the peak area, migration time and resolution, respectively. The theoretical calculation results of the binding energies and binding constant further validated the interaction mechanism of composite QDs and target analytes. Furthermore, this developed method was successfully applied to the analysis of the active components (catechin and epicatechin) in Chinese herb Catechu, and the recoveries were in the range of 92.2-108%. The experimental results suggested that the preparation strategy of the composite QDs is appropriate for enantioseparation of more enantiomers by adjusting the modifiers on the surface of QDs, which is particularly promising for electrophoretic enantioseparation based on fluorescence detection, especially for those analytes lacking proper derivative functional groups.

Determination of cholic acid in body fluids by β‑cyclodextrin-modified N-doped carbon dot fluorescent probes

An easy, dependable, and sensitive cholic acid activity experiment was designed based on β‑cyclodextrin-modified carbon dot (β‑CD-CD) nanoprobes with specific host-guest recognizing ability and photoelectron transfer capability. The β‑CD-CD nanoprobes were characterized by infrared, ultraviolet-visible, and fluorescence spectroscopy and transmission electron microscopy. The fluorescence of the probes under optimized conditions linearly responded to cholic acid concentration from 0 to 650 μmol·L^-1 with a detection limit of 25 nmol·L^-1. The probes also performed well in detecting cholic acid in serum and urine samples with an average recovery rate of 97.1%-103.4%. Thus, this study provides a reliable, rapid, and easy method of cholic acid detection in body fluids that can be potentially applied in medical studies.

Electrochemical aptasensor for aflatoxin B1 based on smart host-guest recognition of β-cyclodextrin polymer

Developing a simple and reliable method for the detection of the highly concerning mycotoxin, aflatoxin B1 (AFB1), is of great importance to food safety monitoring. In this study, a simple electrochemical aptasensor was presented for the detection of AFB1 based on the host-guest recognition between ferrocene and β-cyclodextrin (β-CD). Fc-labeled aptamer of AFB1 first hybridized with its complementary Fc-cDNA. Two ferrocene molecules were brought closely together and couldn't enter into the cavity of β-CD modified on the electrode. Negligible signal could be observed. Once AFB1 captured the aptamer from the AFB1-sensitive dsDNA, Fc-cDNA was released and subsequently entered into the cavity of β-CD to form inclusion complexes, giving rise to an distinct increase of R_et and peak current because of the molecular recognition of β-CD. AC impedance method is more sensitive than DPV method. The electrochemical aptasensor displayed a sensitive response to AFB1 in a wide linear range of 0.1 pg/mL to 10 ng/mL, with a low detection limit of 0.049 pg/mL (0.147 pmol/mL) by AC impedance detection, which is 10-100 lower than previously reported methods. The aptasensor has good selectivity and reliability, which has been successfully applied to the determination of AFB1 in real peanut oil samples with recoveries ranging from 94.5% to 106.7% and inter-assay RSD lower than 11.51%.

Ultrasensitive electrochemical detection of methyl parathion pesticide based on cationic water-soluble pillar[5]arene and reduced graphene nanocomposite

We report a rapid, sensitive and selective electrochemical sensor based on pillar[5]arene (CP5) reduced graphene (rGO) nanohybrid-modified glassy carbon electrode CP5-rGO/GCE for the trace detection of methyl parathion (MP) by differential pulse voltammetry (DPV) for the first time. Compared to beta-cyclodextrin (β-CD)-functionalized reduced graphene (rGO)-modified GCE β-CD-rGO/GCE, the proposed CP5-rGO/GCE sensor exhibits excellent electrochemical catalytic activity, rapid response, high sensitivity, good reproducibility and anti-interference ability towards MP. The recognition mechanism of β-CD/MP and CP5/MP was studied by ¹H NMR. The results indicate a higher supramolecular recognition capability between CP5 and MP compared to that between β-CD and MP. The β-CD-rGO and CP5-rGO nano-composites were prepared via a wet chemistry approach. The resulting nano-composites have been characterized by thermogravimetric analysis (TGA), fourier transform infrared spectrometry (FTIR), charge transfer resistance (R_ct) and zeta potential. The CP5-rGO/GCE combines the merits of CP5 and rGO, and is used for quantitative detection of MP. It has a low detection limit of 0.0003 μM (S/N = 3) and a linear response range of 0.001–150 μM for MP. This method has been used to detect MP in soil and waste water samples with satisfactory results. This study provides a promising electrochemical sensing platform and is a promising tool for the rapid, facile and sensitive analysis of MP.

A promising electrochemical sensing platform for the detection of methyl parathion based on cationic water-soluble pillar[5]arene reduced graphene nanocomposite.

Glucose oxidation performance is improved by the use of a supramolecular self-assembly of glucose oxidase and catalase

A multi-enzymes complex was assembled successfully via host/guest interactions, and it was used for rapid transformation of glucose.

Electrochemical Enantiomer Recognition Based on sp³-to-sp² Converted Regenerative Graphene/Diamond Electrode

It is of great significance to distinguish enantiomers due to their different, even completely opposite biological, physiological and pharmacological activities compared to those with different stereochemistry. A sp³-to-sp² converted highly stable and regenerative graphene/diamond electrode (G/D) was proposed as an enantiomer recognition platform after a simple β-cyclodextrin (β-CD) drop casting process. The proposed enantiomer recognition sensor has been successfully used for d and l-phenylalanine recognition. In addition, the G/D electrode can be simply regenerated by half-minute sonication due to the strong interfacial bonding between graphene and diamond. Therefore, the proposed G/D electrode showed significant potential as a reusable sensing platform for enantiomer recognition.

Precise supramolecular control of surface coverage densities on polymer micro- and nanoparticles

We report herein the controlled surface functionalization of micro- and nanoparticles by supramolecular host-guest interactions. Our idea is to exploit the competition of two high-affinity guests for binding to the surface-bound supramolecular host cucurbit[7]uril (CB7). To establish our strategy, surface azide groups were introduced to hard-sphere (poly)methylmethacrylate particles with a grafted layer of poly(acrylic acid), and a propargyl derivative of CB7 was coupled to the surface by click chemistry. The amount of surface-bound CB7 was quantified with the high-affinity guest aminomethyladamantane (AMADA), which revealed CB7 surface coverage densities around 0.3 nmol cm-2 indicative of a 3D layer of CB7 binding sites on the surface. The potential for surface functionalization was demonstrated with an aminoadamantane-labeled rhodamine (Ada-Rho) as a second high-affinity guest. Simultaneous incubation of CB7-functionalized particles with both high-affinity guests, AMADA and Ada-Rho, revealed a simple linear relationship between the resulting surface coverage densities of the model fluorescent dye and the mole fraction of Ada-Rho in the incubation mixture. This suggests a highly modular supramolecular strategy for the stable immobilization of application-relevant molecules on particle surfaces and a precise control of their surface coverage densities.

Innovative Strategy Based on a Novel Carbon-Black-β-Cyclodextrin Nanocomposite for the Simultaneous Determination of the Anticancer Drug Flutamide and the Environmental Pollutant 4-Nitrophenol

In the present work, a noncovalent and eco-friendly approach was proposed to prepare a carbon-black/β-cyclodextrin (CB/β-CD) nanocomposite. CB/β-CD-nanocomposite-modified screen-printed carbon electrodes were applied for the simultaneous determination of the anticancer drug flutamide (Flut) and the environmental pollutant 4-nitrophenol (4-NP). The electrochemical performance of the proposed sensor relied on the conductivity of CB, the different binding strengths of the guests (Flut and 4-NP) to the host (β-CD), and the different reduction potentials of the nitroaromatic compounds. Fascinatingly, the proposed sensor exhibited an excellent electrochemical performance with high sensitivity, selectivity, and reproducibility. The obtained wide linear ranges were 0.05-158.3 and 0.125-225.8 μM for Flut and 4-NP. The low detection limits of 0.016 and 0.040 μM with the higher sensitivities of 5.476 and 9.168 μA μM^-1 cm^-2 were achieved for the determination of Flut and 4-NP, respectively. The practical feasibility of the proposed sensor was studied in tap-water and human-serum samples.

Sweet Switch: Sugar-Responsive Bioactive Surfaces Based on Dynamic Covalent Bonding

Smart bioactive surfaces that can modulate interactions with biological systems are of great interest. In this work, a surface with switchable bioactivity in response to sugars has been developed. It is based on dynamic covalent bonding between phenylboronic acid (PBA) and secondary hydroxyls on the "wide" rim of β-cyclodextrin (β-CD). The system reported consists of gold surface modified with PBA-containing polymer brushes and a series of functional β-CD derivatives conjugated to diverse bioactive ligands (CD-X). CD-X molecules are attached to the surface to give specified bioactivity such as capture of a specific protein or killing of attached bacteria. Subsequent treatment with cis-diol containing biomolecules having high affinity for PBA (e.g. fructose) leads to the release of CD-X together with the captured proteins, killed bacteria, and so forth from the surface. The surface bioactivity is thereby "turned off". Effectively, this constitutes an on-off bioactivity switch in a mild and noninvasive way, which has the potential in the design of dynamic bioactive surfaces for biomedical applications.

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.