Xin Ran

Bridged β-cyclodextrin-functionalized MWCNT with higher supramolecular recognition capability: The simultaneous electrochemical determination of three phenols

A rapid and sensitive electrochemical sensor based on disulfides bridged β-cyclodextrin dimer-functionalized multi-walled carbon nanotube (DBβ-CD-MWCNT) nanohybrids with higher supramolecular recognition capability was successfully constructed for the first time. Simultaneous trace analysis of three phenols (4-aminophenol, 4-AP; 4-chlorophenol, 4-CP; 4-nitrophenol, 4-NP) in tap-water and wastewater samples was performed based on the constructed sensor. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy were utilized to characterize the properties of the modified electrode. The proposed DBβ-CD-MWCNT-modified electrode displayed electrochemical signal superior to those of β-CD-MWCNT and MWCNT towards 4-AP, 4-CP, and 4-NP. Under optimal conditions, differential pulse voltammetry was used to simultaneously quantify 4-AP, 4-CP, and 4-NP within the concentration range of 0.01-20, 0.1-200, and 0.1-200 µM, respectively. The detection limits (S/N=3) of the DBβ-CD-MWCNT nanohybrid electrode for 4-AP, 4-CP, and 4-NP were 0.0042, 0.028, and 0.048 µM, respectively. Satisfactory results revealed that this proposed electrochemical sensor can provide a promising candidate for the simultaneous trace analysis of 4-AP, 4-CP, and 4-NP in environmental monitoring of water and wastewater samples. The present work might broaden the channel toward the application of bridged CD in the electrochemical sensing or biosensing.

A comparison study of macrocyclic hosts functionalized reduced graphene oxide for electrochemical recognition of tadalafil

The present work described the comparison of β-cyclodextrin (β-CD) and p-sulfonated calix[6]arene (SCX6) functionalized reduced graphene oxide (RGO) for recognition of tadalafil. In this study, tadalafil and two macrocycles (β-CD and SCX6) were selected as the guest and host molecules, respectively. The inclusion complexes of β-CD/tadalafil and SCX6/tadalafil were studied by UV spectroscopy and molecular simulation calculations, proving the higher supermolecular recognition capability of SCX6 than β-CD towards tadalafil. The β-CD@RGO and SCX6@RGO composites were prepared by a wet-chemical route. The obtained composites were characterized by Fourier transform infrared spectrometry, thermogravimetric analysis, atomic force microscopy, and zeta potential. The SCX6@RGO showed a higher electrochemical response than β-CD@RGO, which was caused by the higher recognition capability of SCX6 than β-CD. By combining the merits of SCX6 and the RGO, a sensitive electrochemical sensing platform was developed based on the SCX6@RGO nanohybrids. A linear response range of 0.1-50 μM and 50-1000 μM for tadalafil with a low detection limit of 0.045 μM (S/N=3) was obtained by using this method. The constructed sensing platform was successfully used to determine tadalafil in herbal sexual health products and spiked human serum samples, suggesting its promising analytical applications for the trace level determination of tadalafil.

Simultaneous determination of two flavonoids based on disulfide linked β-cyclodextrin dimer and Pd cluster functionalized graphene-modified electrode

In the present work, ultrafine Pd clusters with a uniform size of ∼2.0 nm were monodispersed on the surface of reduced graphene oxide (RGO) using a clean and green approach in the absence of additional reductants and surfactants. Disulfide linked β-cyclodextrin dimer (SS-β-CD) was non-covalently bonded to the surface of Pd@RGO. By combining the merits of Pd@RGO and the SS-β-CD, a highly sensitive electrochemical sensing platform was developed based on the SS-β-CD–Pd@RGO nanohybrids. Simultaneous electrochemical detection of baicalin and luteolin using a SS-β-CD–Pd@RGO nanohybrid-modified electrode is described for the first time. The SS-β-CD showed a higher supramolecular recognition capability than the native β-CD, which may be caused by the cooperative binding abilities of two adjacent CD units. Due to the synergistic effects from the Pd@RGO (e.g. good electrochemical properties and large surface area) and SS-β-CD (e.g. hydrophilic external surface, high supramolecular recognition, and good enrichment capability), the SS-β-CD–Pd@RGO modified electrode was found to have linear response ranges of 0.02–20.00 μM for baicalin and 0.01–10.00 μM for luteolin with relatively low detection limits of 0.0052 μM for baicalin and 0.0070 μM for luteolin. The results indicated that SS-β-CD–Pd@RGO nanohybrids are excellent sensing materials for the electrochemical determination of flavonoids. The proposed method could be successfully utilized to detect baicalin and luteolin in serum samples, and has a promising application in practice.

Electrochemical detection of cholesterol based on competitive host–guest recognition using a β-cyclodextrin/poly(N-acetylaniline)/graphene-modified electrode

A sensitive and selective electrochemical approach for cholesterol sensing based on a competitive host–guest recognition between β-cyclodextrin (β-CD) and a signal probe (methylene blue)/target molecule (cholesterol) using a β-CD/poly(N-acetylaniline)/graphene (β-CD/PNAANI/Gra)-modified electrode was developed. Due to the host–guest interaction, MB molecules can enter into the hydrophobic inner cavity of β-CD, and the β-CD/PNAANI/Gra modified glassy carbon electrode displays a remarkable anodic peak. In the presence of cholesterol, a competitive interaction to β-CD occurs and the MB molecules are displaced by cholesterol. This results in a decreased oxidation peak current of MB as MB is a well known redox probe and hence can be easily detected using the differential pulse voltammetery technique. A linear response range of 1.00 to 50.00 μM for cholesterol with a low detection limit of 0.50 μM (S/N = 3) was obtained by using the indirect method. The proposed method could be successfully utilized to detect cholesterol in serum samples, and may be expanded to analysis of other non-electroactive species. Besides, the host–guest interaction between cholesterol and β-CD was studied by molecular modeling calculations, which revealed that the complexation could reduce the energy of the system and the complex of 2 : 1 host–guest stoichiometry had the lowest ΔE value of −10.45 kcal mol−1. The molecular docking studies suggested that hydrogen bonding, electrostatic interactions, and hydrophobic interactions should be the major driving forces for the formation of the inclusion complex.

Synthesis of well-dispersive 2.0 nm Pd–Pt bimetallic nanoclusters supported on β-cyclodextrin functionalized graphene with excellent electrocatalytic activity

In this work, ultrasmall Pd–Pt bimetallic nanoclusters with a uniform size of 2.0 nm monodispersed on β-cyclodextrin functionalized reduced graphene oxide (β-CD-RGO) were successfully prepared in aqueous solution at room temperature within 30 min without the need for any organic solvent or high temperature. The integration of β-CD and RGO was responsible for the formation of the monodispersed 2.0 nm Pd–Pt bimetallic nanoclusters. Inspired by the monodisperse, ultrasmall, and pristine properties of the Pd–Pt clusters, the Pd–Pt@β-CD-RGO nanohybrid displayed enhanced activity for methanol and ethanol oxidation in alkaline media in comparison with the commercial Pd/C catalysts. This facile and simple method is of significance for the preparation of bimetallic nanocatalysts with high catalytic activity on suitable supporting materials.

A FRET-based fluorescent approach for labetalol sensing using calix[6]arene functionalized MnO2@graphene as a receptor

A turn-on fluorescent sensing platform for labetalol determination has been developed based on competitive host–guest interaction between p-sulfonated calix[6]arene (SCX6) and signal probe/target molecules by using SCX6 functionalized MnO2@reduced graphene oxide (SCX6-MnO2@RGO) as a receptor. Rhodamine 6G (R6G) and labetalol were selected as the probe and target molecules, respectively. When R6G enters into the SCX6 host, its fluorescence is quenched by MnO2@RGO. However, on addition of labetalol to the preformed R6G·SCX6-MnO2@RGO complex, the R6G molecule is displaced by labetalol from the host of SCX6, leading to a “switch-on” fluorescence response. This is due to the fact that the binding constant of the labetalol/SCX6 complex is much higher than that of R6G/SCX6. The fluorescence intensity of the SCX6-MnO2@RGO·R6G complex increased linearly with increasing concentration of labetalol ranging from 1.0 to 18.0 μM. The proposed method showed a detection limit of 0.25 μM for labetalol. In addition, 2D NMR and molecular modeling studies indicated that the salicylamide part of the labetalol molecule inserted into the cavity of SCX6, while the phenylpropyl group located outside of the SCX6 host.

Immunosensor for prostate-specific antigen using Au/Pd@flower-like SnO2 as platform and Au@mesoporous carbon as signal amplification

In the present work, a sandwich-type electrochemical immunosensor for ultrasensitive determination of prostate-specific antigen (PSA) was designed by using Au/Pd@SnO2 as sensing platform and gold@mesoporous carbon nanocomposites (Au@CMK-3) as signal amplification. In this work, Au@CMK-3 was prepared for immobilizing large amounts of redox probe-methylene blue (MB), horseradish peroxidase (HRP), and secondary antibodies (Ab2), leading to the formation of Au@CMK-3–MB–Ab2–HRP bioconjugate. Furthermore, Au/Pd@SnO2 was utilized as the biosensor platform to immobilize the primary antibodies (Ab1) leading a further enhancement in the sensitivity of immunosensor. With the synergistic effects among the Au/Pd@SnO2 platform, the Au@CMK-3 nanocarrier, the ultrafine Pd NPs electrocatalyst, and HRP enzymatic reactions, an almost doubled amplified detection signal was achieved in the presence of H2O2, so as to improve the detection limit of the proposed immunosensor effectively. The constructed immunosensor exhibited desirable performance for determination of PSA with a wide linearity in the range from 0.01 to 100 ng mL−1 and a relatively low detection limit of 3 pg mL−1. The proposed immunosensor was also used to determine PSA in human serum with satisfactory results, implying potential applications in immunoassays.

Ultrasensitive Electrochemical Detection of Clostridium perfringens DNA Based Morphology-Dependent DNA Adsorption Properties of CeO2 Nanorods in Dairy Products

Foodborne pathogens such as Clostridium perfringens can cause diverse illnesses and seriously threaten to human health, yet far less attention has been given to detecting these pathogenic bacteria. Herein, two morphologies of nanoceria were synthesized via adjusting the concentration of NaOH, and CeO2 nanorod has been utilized as sensing material to achieve sensitive and selective detection of C. perfringens DNA sequence due to its strong adsorption ability towards DNA compared to nanoparticle. The DNA probe was tightly immobilized on CeO2/chitosan modified electrode surface via metal coordination, and the DNA surface density was 2.51 × 10−10 mol/cm2. Under optimal experimental conditions, the electrochemical impedance biosensor displays favorable selectivity toward target DNA in comparison with base-mismatched and non-complementary DNA. The dynamic linear range of the proposed biosensor for detecting oligonucleotide sequence of Clostridium perfringens was from 1.0 × 10−14 to 1.0 × 10−7 mol/L. The detection limit was 7.06 × 10−15 mol/L. In comparison, differential pulse voltammetry (DPV) method quantified the target DNA with a detection limit of 1.95 × 10−15 mol/L. Moreover, the DNA biosensor could detect C. perfringens extracted DNA in dairy products and provided a potential application in food quality control.

Highly-effective palladium nanoclusters supported on para-sulfonated calix[8]arene-functionalized carbon nanohorns for ethylene glycol and glycerol oxidation reactions

Non-Pt noble metal clusters like Pd clusters are considered as promising electrocatalysts for fuel cells, but they suffer from problems such as easy aggregation during the catalysis reactions. To solve these problems, we demonstrate a water-based method for the synthesis of ultrasmall Pd clusters with an average size of 2.5 nm uniformly dispersed on single-walled carbon nanohorns functionalized by para-sulfonated calix[8]arene (SCX8–SWCNHs) at room temperature without organic solvents. The high dispersibility of the 2.5 nm Pd clusters is caused by the large amount of SCX8 (with many negative charges of –SO3−) on SWCNHs. The large amount of negative charges from –SO3− enhances the interactions between the supports and metal precursors, resulting in the in situ growth of the highly dispersed Pd clusters. The Pd@SCX8–SWCNHs nanocatalyst exhibits increased catalytic activity for the electrooxidation of ethylene glycol and glycerol when compared with that of the Pd/C catalyst in alkaline media, which is ascribed to the high dispersity and ultrafine properties of the Pd clusters. This simple and facile approach has major importance for the preparation of electrocatalysts with high electrocatalytic activity on suitable supports.