A novel pencil graphite electrode modified with an iron-based conductive metal-organic framework exhibited good ability in simultaneous sensing bisphenol A and bisphenol S.

Bisphenol A (BPA) and its substitute bisphenol S (BPS) are desirable materials widely used in manufacturing plastic products but can pose carcinogenic risks to humans. A new conductive iron-based metal-organic framework (Fe-HHTP)-modified pencil graphite electrode (PGE) for electrochemically sensing BPA and BPS was prepared and fully characterized by SEM, TEM, FT-IR, XRD, and XPS. Results showed that the optimal conditions for preparing Fe-HHTP/PGE were a pH of 6.5, a Fe-HHTP concentration of 2 mg·mL-1, a deposition potential of 0 V, and a deposition time of 100 s. The Fe-HHTP/PGE prepared under such conditions harbored a significant electrocatalytic activity with a detection limit of 0.8 nM for BPA and 1.7 nM for BPS (S/N = 3). Correspondingly, the electrochemical response current was linearly correlated to BPA and BPS, ranging from 0.01 to 100 µM. Fe-HHTP/PGE also obtained satisfactory recoveries by 93.8-102.1% and 96.0-101.3% for detecting BPA and BPS in plastic food packaging samples. Our work has provided a novel electrochemical tool to simultaneously detect BPA and BPS in food packaging samples and environmental matrixes.

Electrochemical Sensor Based on Glassy-Carbon Electrode Modified with Dual-Ligand EC-MOFs Supported on rGO for BPA.

The electronic conductive metal-organic frameworks (EC-MOFs) based on a single ligand are not suitable for the accurate detection of bisphenol A (BPA) due to the limitations of their electron-transfer-based sensing mechanism. To overcome this drawback, we developed EC-MOFs with novel dual-ligands, 2,3,6,7,10,11-hexahydroxy-sanya-phenyl (HHTP) and tetrahydroxy 1,4-quinone (THQ), and metal ions. A new class of 2D π-conjugation-based EC-MOFs (M-(HHTP)(THQ)) was synthesized by a self-assemble technique. Its best member (Cu-(HHTP)(THQ)) was selected and combined with reduced graphene (rGO) to form a Cu-(HHTP)(THQ)@rGO composite, which was thoroughly characterized by X-ray diffraction, field scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Cu-(HHTP)(THQ)@rGO was drop-cast onto a glassy carbon electrode (GCE) to obtain a sensor for BPA detection. Cyclic voltammetry and electrochemical impedance tests were used to evaluate the electrode performance. The oxidation current of BPA on the Cu-(HHTP)(THQ)@rGO/GCE was substantially higher than on unmodified GCE, which could be explained by a synergy between Cu-(HHTP)(THQ) (which provided sensing and adsorption) and rGO (which provided fast electron conductivity and high surface area). Cu-(HHTP)(THQ)@rGO/GCE exhibited a linear detection range for 0.05-100 µmol·L-1 of BPA with 3.6 nmol·L-1 (S/N = 3) detection limit. We believe that our novel electrode and BPA sensing method extends the application perspectives of EC-MOFs in the electrocatalysis and sensing fields.

An electrochemical sensor based on a glassy carbon electrode modified with sandwich structured ZIF-67@rGO for bisphenol A measurement.

The low conductivity of metal-organic frameworks seriously impedes their electrocatalytic performance. In this study, we prepared a fabricated sandwich structure composed of a Co-based zeolitic imidazolate framework (ZIF-67) and reduced graphene oxide (rGO) through a facile and simple one-pot hydrothermal reaction. This framework of nanocomposites, which are modified with a glassy carbon electrode, constructed a bisphenol A (BPA) electrochemical sensor for the first time. Operational parameters such as pH, electrolytes, the amount of modifiers, deposition potentials and deposition time were optimised for the sensitive detection of BPA. The performance of electrodes was evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction and transmission electron microscopy. With differential pulse voltammetry, the detection concentration of BPA ranged from 0.05 µmol L-1 to 100 µmol L-1. The results revealed that the hierarchical nanocomposites demonstrated better electrocatalytic performance with large electrochemically active surface areas, high sensitivity and a low limit of detection (5.2 nmol L-1), compared with a physical mixture of ZIF-67 and rGO at the same ratio. These impressive features originate from the synergistic effects of ZIF-67 and rGO. This study presents a new strategy using metal-organic framework composite materials for the sensitive detection of BPA.

Fabrication of novel electrochemical sensor based on bimetallic Ce-Ni-MOF for sensitive detection of bisphenol A.

In this paper, a novel bimetallic Ce-Ni metal-organic frameworks (Ce-Ni-MOF) are synthesized by hydrothermal reaction, using 1,3,5-benzenetricarboxylic acid as a ligand. In particular, the bimetallic Ce-Ni-MOF with the largest specific surface area and catalytic sites was synthesized when the molar ratio of Ce3+ to Ni2+ was 3:7. Bimetallic Ce-Ni-MOF is added to the traditional conductive material of multiwall carbon nanotubes (MWCNTs) to play their synergistic effect, improve the conductivity, specific surface area, and catalytic site of the MWCNTs. A novel bisphenol A (BPA) sensor was successfully prepared by a self-assembled multilayer strategy of Ce-Ni-MOF/MWCNTs modified glassy carbon electrodes (GCE). Field emission scanning electron microscopy, powder X-ray diffraction, and transmission electron microscope were carried out to characterize the Ce-Ni-MOF/MWCNTs. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used as a sensitive analytical method for the determination of BPA, and a wider linear dynamic range of BPA determination in 0.1 µmol·L-1 to 100 µmol·L-1 with a detection limit of 7.8 nmol·L-1 (S/N = 3). The proposed method was applied to measure the content of BPA in different brands of drinking water with satisfying recovery from 97.4 to 102.4%. Graphical abstract.

Highly sensitive aptamer based on electrochemiluminescence biosensor for label-free detection of bisphenol A.

Bisphenol A (BPA), a typical endocrine disruptor, is widely used as a key monomer in the packaging industry. Residual monomer can transfer from the package material to the food and thereby pose a risk to the health of the consumer, so determination of BPA migration is highly important for food safety control. In this study, a simple but sensitive electrochemiluminescence (ECL) biosensor, which combines the characteristics of high selectivity of an aptamer and high sensitivity of ECL, has been developed to detect BPA from package materials. The aptamer was immobilized on a gold electrode surface through Au-S interaction. The aptamer was then hybridized with complementary DNA (CDNA) to form double-stranded DNA (dsDNA). Ru(phen)32+ can intercalate into the grooves of dsDNA and acts as an ECL indicator; high ECL intensity can therefore be detected from the electrode surface. In the presence of BPA, which can competitively bind with the aptamer owing to their high affinity, Ru(phen)32+ is released from the electrode surface and the ECL of the system is decreased. The decreasing ECL signal has a linear relationship with BPA in the range of 0.1-100 pM with a detection limit of 0.076 pM. The developed biosensor has been applied to detect migration of BPA from different categories of canned drink with satisfactory results.

Self-assembly of cellulose nanoparticles as electrolyte additive for capillary electrophoresis separation.

In this work, a new cellulose derivative, octadecyl modified quaternized cellulose (ODMQC), was synthesized and used as additive in the background electrolyte for capillary electrophoresis. The derivative bearing hydrophobic groups and hydrophilic groups can self-assemble into a stable nano-scaled micelle structure in aqueous solution. When ODMQC was added in running buffer, the capillaries were shown to generate applicable anodal EOF over the investigated range of pH 3.0-12.0. Due to the lack of UV active groups, the ODMQC did not disturb the UV detection. It is shown that ODMQC-added capillaries allow the separation of basic proteins by reducing their adsorption onto the capillary wall. Also, the addition of ODMQC provides adequate separation of aromatic acids with low pKa values and improved separation of sulfa drugs. Moreover, it is demonstrated that the addition of ODMQC can incorporate an additional reversed-phase mechanism that improves the separation of neutral analytes.

Determination of global DNA methylation level by capillary electrophoresis using octyl-modified quaternized cellulose as an electrolyte additive.

A new cellulose derivative, octyl-modified quaternized cellulose (OMQC), was synthesized and used as electrolyte additive for the analysis of 5-methylcytosine by capillary electrophoresis with UV detection. While added in the background electrolyte, OMQC carrying octyl groups and quaternary ammonium groups exhibited dynamic coating ability. Capillary coated with OMQC was able to generate a stable anodal electro-osmotic flow even at pH 12.0. After several running conditions were optimized, a new method for quantification of genomic methylation level was developed on the basis of hydrolysis of DNA by formic acid and separation of nucleic acid bases by capillary electrophoresis. Cytosine and 5-methylcytosine were separated with a resolution near 4.0 in less than 10 min. The detection limits (S/N = 3) were 1.1 and 1.5 µg/mL for cytosine and 5-methylcytosine, respectively.

Synthesis of a SiO2/TiO2 hybrid boronate affinity monolithic column for specific capture of glycoproteins under neutral conditions.

A unique boronate-functionalized SiO2/TiO2 hybrid monolithic column was synthesized by a facile approach. Although a conventional boronic acid, 4-vinylphenylboronic acid, was used as the affinity ligand, the prepared monolithic column exhibited specific capacity to capture glycoproteins including antibodies in aqueous solution at neutral pH. With the incorporation of titania, the monolith was highly hydrophilic, and the procedure of affinity chromatography could be performed under aqueous organic-solvent-free conditions.

One-step synthesis of an organic-inorganic hybrid boronate affinity monolithic column with synergistic co-monomers.

An organic-inorganic hybrid and synergistic boronate affinity (BA) monolithic column was synthesized by a novel "one-step" approach. We report on the synthesis of a unique organic-inorganic hybrid affinity monolith by using TEOS, the organic silane, N-(ß-aminoethyl)-γ-aminopropyltriethoxysilane (AEAPTES) and γ-MAPS as the co-precursors, 4-vinylphenylboronic acid as the functionalized monomer, and azobisisobutyronitrile (AIBN) as the initiator. Due to the presence of amino groups in the AEAPTES molecule, the prepared monolith exhibits several attractive properties. The monolith will be more hydrophilic and can bind with cis-diol compounds at neutral pH by a mechanism of intermolecular B-N coordination. The resulting hybrid boronate affinity monoliths have potential applications in specific recognition and enrichment of cis-diol biomolecules under neutral conditions.

Quaternized celluloses as new dynamic coatings in capillary electrophoresis for basic protein separation.

In this work, a series of quaternized celluloses (QCs), homogeneously synthesized in the NaOH/urea aqueous solutions, were studied as dynamic coatings for capillary electrophoresis. Capillaries coated with these cationic cellulose derivatives at the concentration as low as 3 µg/mL were able to generate a stable, reversed electroosmotic flow. The effects of QC molecular parameters, such as the degree of cationic substitution and molecular weight, and the effect of buffer pH on the EOF mobility as well as the separation of basic proteins were investigated in detail. It was shown that the use of QC coatings in CE could drastically reduce the analysis time and improve the separation performance within a broad pH range. Five basic proteins, that is, lysozyme, ribonuclease A, cytochrome C, bovine pancreatic trypsin inhibitor, and chymotrypsinogen were baselinely separated even at pH 8.0. The separation efficiency and analysis reproducibility demonstrated that the QC coatings were efficient in minimizing the adsorption of basic proteins on the fused silica capillary. The successful performance was further demonstrated for biosample analysis.