A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Solution structure of the sheep prion PrP〚142-166〛: a possible site for the conformational conversion of prion protein

In order to get deeper insight into the molecular forces responsible for prion pathogenic conversion, conformational properties of a synthetic linear peptide derived from the globular core of sheep prion protein were studied by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopies. The studied peptide encompassing the 〚142–166〛 (in human numbering) region of sheep prion protein, folds in physiological conditions into a β-hairpin like tertiary structure, whereas, in the non-pathogenic form of protein and in trifuoroethanol (TFE), the region is engaged in largely α-helical conformation. Such structural duality of the fragment indicates a possible transconformational site within prion protein and may explain one of the early structural causes of prion diseases.     

Ag@C core–shell structure composites-decorated Ag nanoparticles: zero current potentiometry for detection of hydrogen peroxide

Ag@C core–shell structure composites were successfully synthesized by hydrothermal method, and then Ag nanoparticles were decorated on the surface of Ag@C by reduction of AgNO₃. The morphology, composition and structure of the Ag@C@Ag composites were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Cyclic voltammetry and amperometry were used to evaluate the electrocatalytic performance of the Ag@C@Ag/GCE for detection of H₂O₂. Meanwhile, a new electrochemical method of zero current potentiometry was used for electrochemical detection of H₂O₂. The linear range and the detection limit were from 0.2 to 10, and 0.07 μM, respectively.     

Fabrication of polymeric micelles with core–shell–corona structure for applications in controlled drug release

Thermo-responsive polymeric micelles of poly (ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-g-lactide)-b-poly(N-isopropylacrylamide) (PEG-P(HEMA-PLA)-PNIPAM) with core–shell–corona structure were fabricated for applications in controlled drug release. The graft copolymer of PEG-P(HEMA-PLA)-PNIPAM was self-assembled into core–shell micelles with a densely PLA core and mixed PEG/PNIPAM shells at 25 °C in aqueous media. By increasing the temperature above the lower critical solution temperature of PNIPAM, these core–shell micelles could be converted into core–shell–corona micelles because of the collapse of PNIPAM block on the PLA core as the inner shell and the soluble PEG block stretching outside as the outer corona. Anticancer drug doxorubicin (DOX) was loaded in the polymeric micelles as a model drug. Compared with polymeric micelles formed by liner PEG-b-PLA-b-PNIPAM triblock copolymer, these polymeric micelles exhibited higher loading capacity, and release of DOX from the polymeric micelles with core–shell–corona structure was well-controlled.     

CuS–MWCNT based electrochemical sensor for sensitive detection of bisphenol A

The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.     

A photopatterned SERS substrate with a sandwich structure for multiplex detection

Substrate photopatterning has provided versatile applications in biomedical fields. Herein, an universal and efficient photoligation reaction has been used to prepare a patterned capture substrate for a sandwich SERS immunoassay. Photoirradiation induces mild and efficient immobilization of antibodies at the desired region of a gold surface, and the antibody-antigen interaction helps the substrate to capture the antigens in solution specifically. After exposing to SERS probes, i.e., the gold nan...     

A photopatterned SERS substrate with a sandwich structure for multiplex detection

Substrate photopatterning has provided versatile applications in biomedical fields. Herein, an universal and efficient photoligation reaction has been used to prepare a patterned capture substrate for a sandwich SERS immunoassay. Photoirradiation induces mild and efficient immobilization of antibodies at the desired region of a gold surface, and the antibody-antigen interaction helps the substrate to capture the antigens in solution specifically. After exposing to SERS probes, i.e., the gold nan...     

A fluorescence “on–off” sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet–visible (UV–vis) spectra, fluorescence spectra, ¹H NMR and ¹³C NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris–HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0–50 μM, with a detection limit of 1.92 × 10⁻⁷ M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 × 10¹² M⁻¹. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).     

Development of a stable biosensor based on a SiO2 nanosheet–Nafion–modified glassy carbon electrode for sensitive detection of pesticides

SiO₂ nanosheets (SNS) have been prepared by a chemical method using montmorillonite as raw material and were characterized by scanning electron microscopy and X-ray diffraction. SiO₂ nanosheet–Nafion nanocomposites with excellent conductivity, catalytic activity, and biocompatibility provided an extremely hydrophilic surface for biomolecule adhesion. Chitosan was used as a cross-linker to immobilize acetylcholinesterase (AChE), and Nafion was used as a protective membrane to efficiently improve the stability of the AChE biosensor. The AChE biosensor showed favorable affinity for acetylthiocholine chloride and catalyzed the hydrolysis of acetylthiocholine chloride with an apparent Michaelis–Menten constant of 134 μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition by pesticides of the enzymatic activity of AChE, detection of the amperometric response from thiocholine on the biosensor is a simple and effective way to biomonitor exposure to pesticides. Under optimum conditions, the biosensor detected methyl parathion, chlorpyrifos, and carbofuran at concentrations ranging from 1.0?×?10^?12 to 1?×?10^?10?M and from 1.0?×?10^?10 to 1?×?10^?8?M. The detection limits for methyl parathion, chlorpyrifos, and carbofuran were 5?×?10^?13?M. The biosensor developed exhibited good sensitivity, stability, reproducibility, and low cost, thus providing a new promising tool for analysis of enzyme inhibitors.

Liquid chromatography–fluorescence detection for simultaneous analysis of sulfonamide residues in honey

A rapid, accurate LC analytical method has been developed for determination of eight sulfonamides (sulfacetamide, sulfapyridine, sulfamerazine, sulfamethoxypyridazine, sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine) in honey. The sample was dissolved in phosphoric acid solution (pH 2). After filtration, the sample solution was cleaned by use of two solid-phase extraction (SPE) cartridges-an aromatic sulfonic cation-exchange cartridge and an Oasis HLB cartridge. The eight sulfonamides were then derivatized with fluorescamine and the derivatives were determined by LC with fluorescence detection at excitation and emission wavelengths of 405 and 495 nm, respectively. Average recoveries at three fortification levels in the range 0.02-0.50 mg kg(-1) in twelve different kinds of honey were 73.5-94.1% with coefficients of variation of 4.35-16.60%. The limit of detection (LOD) was 0.002 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine was 0.005 mg kg(-1). The limit of quantitation (LOQ) was 0.005 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole, and sulfadimethoxine was 0.010 mg kg(-1). The method is suitable for determination of multiresidue sulfonamides in the various kinds of honey.     

Immobilization of Ni–Pd/core–shell nanoparticles through thermal polymerization of acrylamide on glassy carbon electrode for highly stable and sensitive glutamate detection

The preparation of a persistently stable and sensitive biosensor is highly important for practical applications. To improve the stability and sensitivity of glutamate sensors, an electrode modified with glutamate dehydrogenase (GDH)/Ni–Pd/core–shell nanoparticles was developed using the thermal polymerization of acrylamide (AM) to immobilize the synthesized Ni–Pd/core–shell nanoparticles onto a glassy carbon electrode (GCE). The modified electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Electrochemical data showed that the prepared biosensor had remarkably enhanced electrocatalytic activity toward glutamate. Moreover, superior reproducibility and excellent stability were observed (relative average deviation was 2.96% after continuous use of the same sensor for 60 times, and current responses remained at 94.85% of the initial value after 60 d). The sensor also demonstrated highly sensitive amperometric detection of glutamate with a low limit of detection (0.052 μM, S/N = 3), high sensitivity (4.768 μA μM⁻¹ cm⁻²), and a wide, useful linear range (0.1–500 μM). No interference from potential interfering species such as l-cysteine, ascorbic acid, and l-aspartate were noted. The determination of glutamate levels in actual samples achieved good recovery percentages.     

FRET detection of amyloid β-peptide oligomerization using a fluorescent protein probe presenting a pseudo-amyloid structure

A FRET-based sensor protein presenting amyloid-like structures was successfully constructed for detecting the oligomeric assemblies of amyloid β-peptide (Aβ) wild-type and FAD-related mutants.     

Novel peptide–protein assay for identification of antimicrobial peptides by fluorescence quenching

The specific interaction of peptides with proteins is often a key factor which determines biological activities. The determination of K(d) values of such interactions is commonly performed with fluorescence polarization. However, fluorescence polarization assays are prone to false-positive results due to the potential for non-specific interactions and only afford very low signal-to-background ratios. Here, we present as an alternative a fluorescence resonance energy transfer based quenching assay to measure peptide-protein interactions in solution. In a test setup where antimicrobial peptides were tested for their affinity towards the protein DnaK, the assay provided high specificity and good reproducibility and correlated with the results obtained by fluorescence polarization methods. Furthermore, we established a fast prescreening method which will allow a highly efficient screening of peptide libraries by reducing the amount of sample by 98% compared to conventional fluorescence polarization assays.     

Ionic liquid–graphene hybrid nanosheets-based electrochemical sensor for sensitive detection of methyl parathion

In this work, ionic liquid–graphene nanosheets (IL–GNs) were synthesised and used as an enhanced material for sensitive detection of methyl parathion (MP) by electrochemical method. IL–GNs were characterised by UV–Vis spectroscopy, transmission electron microscopy (TEM), X-ray photo-electron spectroscopy (XPS), Fourier transform Infrared (FT-IR) spectroscopy and Raman spectroscopy, which confirmed that IL was successfully covered on the surface of GNs. Significantly, due to the coupling of excellent properties of GNs and IL, the IL–GNs-modified glassy carbon electrode (IL–GNs/GCE) showed higher signals for MP response than the GNs/GCE and bare GCE. At the IL–GNs/GCE, the peak currents increase linearly with the concentration of MP in the range of 5.3 ng/mL to 2.6 μg/mL with the detection limit of 1.1 ng/mL, which was better than other enzyme-based and enzymeless sensors. The IL–GNs-based electrochemical sensor was also successfully demonstrated for the detection of water sample with satisfactory results. Furthermore, the proposed electrochemical sensor exhibited satisfied stability and reproducibility. The simple sensing platform can be extended to detect other organophosphate pesticide.     

Synthesis of bifunctional core–shell particles with a porous zeolite core and a responsive polymeric shell

The aim of our work is the synthesis and characterization of colloidal core–shell particles with a zeolite core and an environmentally responsive shell. We have synthesized colloidal ZSM-5 zeolite and modified the surface with 3-(trimethoxysilyl)propyl methacrylate in order to introduce double bonds at the surface. The cross-linked polymeric shell was prepared by precipitation polymerization using the functionalized zeolite particles as seeds. We employed thermoresponsive poly(N-isopropylacrylamide) and pH-responsive poly(vinylpyridine) as the polymeric shell, respectively. The temperature- and pH-depending swelling and deswelling of the core–shell particles were characterized with dynamic light scattering techniques. Transmission electron microscopy pictures show the morphology of the synthesized particles. It is proposed that these types of bifunctional core–shell particles could be of use for controlled uptake and release applications and separation of molecules.     

Highly sensitive determination of recombinant human erythropoietin-α in aptamer-based affinity probe capillary electrophoresis with laser-induced fluorescence detection

Recombinant human erythropoietin-α (rHuEPO-α) has been widely used in clinic for anemia treatment. The detection and quantification of rHuEPO-α is essential for monitoring this widespread recombinant glycoprotein pharmaceutical. In this paper, we developed a new affinity probe capillary electrophoresis/laser-induced fluorescence (APCE/LIF) method for the detection of rHuEPO-α by using a specific single-stranded DNA aptamer probe for the first time. In this method, the complex of aptamer-rHuEPO-α and the free aptamer can be well separated and identified by their migration and fluorescence intensity after systematic optimization. The existence of sodium cation in the sample buffer and running buffer played a critical role for stabilizing complex and enhancing the separation efficiency, additionally, suitable high voltage and sample buffer additives were also important for improving the peak height of the complex. Under the optimized conditions, the method was successfully applied for the quantification of rHuEPO-α in physiological buffer, artificial urine and human serum. The linear range for rHuEPO-α was from 0.2 to 100 nM and the limit of detection was 0.2 nM (i.e. 7.4 ng/mL). Further binding experiments using fluorescein isothiocyanate-labeled rHuEPO-α (F-rHuEPO-α) and N-deglycosylated F-rHuEPO-α demonstrated that the oligosaccharides moiety was of importance in the specific interaction between rHuEPO-α and its aptamer.     

Highly sensitive ECL-PCR method for detection of K-ras point mutation

A highly sensitive electrochemiluminescence-polymerase chain reaction (ECL-PCR) method for K-ras point mutation detection is developed. Briefly, K-ras oncogene was amplified by a Ru(bpy)32 (TBR)-labeled forward and a biotin-labeled reverse primer, and followed by digestion with MvaI restriction enzyme, which only cut the wild-type amplicon containing its cutting site. The digested product was then adsorbed to the streptavidin-coated microbead through the biotin label and detected by ECL assay. The experiment results showed that the different genotypes can be clearly discriminated by ECL-PCR method. It is useful in point mutation detection, due to its sensitivity, safety, and simplicity.     

Development of a sensitive enzyme immunoassay for the detection of phenyl-β-d-thioglucuronide in human urine

Immunoassays for the measurement of glucuronides in human urine can be a helpful tool for the assessment of human exposure to toxic chemicals. Therefore an enzyme immunoassay (EIA) for the specific detection of phenyl-β-d-thioglucuronide was developed. The immunoconjugate was formed by coupling p-aminophenyl-β-d-thioglucuronide to the carrier protein thyroglobulin leaving an exposed glucuronic acid. The hapten-protein conjugate was adsorbed to gold colloids in order to enhance the immunogenic effect. Rabbits were injected with the immunogold conjugates to raise polyclonal antibodies. The resulting competitive assay showed an inhibition by phenyl-β-d-thioglucuronide at sample concentrations of 23.0 ± 1.3 ng/mL (50% B/B₀) and a high cross-reactivity to p-aminophenyl-β-D-thioglucuronide (120%). Little cross-reactivities (< 2%) were observed for potential urinary cross reactants. In addition human urine samples were incubated with β-glucuronidase in order to investigate the EIA for specific matrix effects. An integration of high-performance liquid chromatography (HPLC) and EIA was developed in an attempt to decrease the matrix effects and increase the sensitivity of the overall method. The hyphenated technique HPLC-EIA may be used to monitor human exposure to toxic thiophenol which is excreted by mammals as urinary phenyl thioglucuronide.     

Core–shell magnetic Fe3O4/CNC@MOF composites with peroxidase-like activity for colorimetric detection of phenol

Rapid and accurate detection of phenolic wastewater from industries has created global concern. Herein, core–shell magnetic cellulose nanocrystal supported MOF (Fe₃O₄/CNC@ZIF-8) with robust peroxidase-like activity was synthesized with tannic acid as modifier and bridge. The peroxidase-mimic catalytic activity of as-prepared Fe₃O₄/CNC@ZIF-8 was further investigated using o-phenylenediamine (OPD) as peroxidase substrates in the presence of H₂O₂. Moreover, the experimental conditions were optimized and the kinetic analysis results showed that Fe₃O₄/CNC@ZIF-8 had higher affinity towards both the substrate OPD and H₂O₂ than horseradish peroxidase (HRP). Finally, a phenol colorimetric assay with a linear range of 2–200 µM and a detection limit of 0.316 µM was constructed. The catalytic mechanism of Fe₃O₄/CNC@ZIF-8 with phenol was further investigated by fluorescence test and the generated ·OH was proved to act a crucial role to produce quinoid radicals. Additionally, the synthesized magnetic material had excellent stability and recyclability and ease to separation. These results suggest that the Fe₃O₄/CNC@ZIF-8 may be one of the promising candidates as peroxidase mimic for colorimetric detection of phenol.

     

Gold–platinum alloy nanowires as highly sensitive materials for electrochemical detection of hydrogen peroxide

The exploitation of the unique electrical properties of nanowires requires an effective assembly of nanowires as functional materials on a signal transduction platform. This paper describes a new strategy to assemble gold–platinum alloy nanowires on microelectrode devices and demonstrates the sensing characteristics to hydrogen peroxide. The alloy nanowires have been controllably electrodeposited on microelectrodes by applying an alternating current. The composition, morphology and alloying structures of the nanowires were characterized, revealing a single-phase alloy characteristic, highly monodispersed morphology, and controllable bimetallic compositions. The alloy nanowires were shown to exhibit electrocatalytic response characteristics for the detection of hydrogen peroxide, exhibiting a high sensitivity, low detection limit, and fast response time. The nanowire's response mechanism to hydrogen peroxide is also discussed in terms of the synergistic activity of the bimetallic binding sites, which has important implications for a better design of functional nanowires as sensing materials for a wide range of applications.