Hongfei Ji

Fe(III)-based metal–organic framework-derived core–shell nanostructure: Sensitive electrochemical platform for high trace determination of heavy metal ions

A new core-shell nanostructured composite composed of Fe(III)-based metal-organic framework (Fe-MOF) and mesoporous Fe3O4@C nanocapsules (denoted as Fe-MOF@mFe3O4@mC) was synthesized and developed as a platform for determining trace heavy metal ions in aqueous solution. Herein, the mFe3O4@mC nanocapsules were prepared by calcining the hollow Fe3O4@C that was obtained using the SiO2 nanoparticles as the template, followed by composing the Fe-MOF. The Fe-MOF@mFe3O4@mC nanocomposite demonstrated excellent electrochemical activity, water stability and high specific surface area, consequently resulting in the strong biobinding with heavy-metal-ion-targeted aptamer strands. Furthermore, by combining the conformational transition interaction, which is caused by the formation of the G-quadruplex between a single-stranded aptamer and high adsorbed amounts of heavy metal ions, the developed aptasensor exhibited a good linear relationship with the logarithm of heavy metal ion (Pb2+ and As3+) concentration over the broad range from 0.01 to 10.0nM. The detection limits were estimated to be 2.27 and 6.73 pM toward detecting Pb2+ and As3+, respectively. The proposed aptasensor showed good regenerability, excellent selectivity, and acceptable reproducibility, suggesting promising applications in environment monitoring and biomedical fields.

Protein-templated cobaltous phosphate nanocomposites for the highly sensitive and selective detection of platelet-derived growth factor-BB.

We synthesized novel Co3(PO4)2-based nanocomposites with 3D porous architectures via self-assembly; here, bovine serum albumin (BSA) and aptamer were used as organic phases to produce Co3(PO4)2@BSA and Co3(PO4)2@Apt nanocomposites, respectively. The formation mechanism of Co3(PO4)2-based nanocomposites was described based on characterizations of their physio-chemical performance, and the developed nanocomposites were applied as scaffold materials to construct a novel electrochemical aptasensor and detect platelet-derived growth factor-BB (PDGF-BB). The PDGF-BB targeting aptamer must be immobilized onto the Co3(PO4)2@BSA-modified electrode to detect PDGF-BB, whereas Co3(PO4)2@Apt-based aptasensor may be directly used to determine the target protein. Electrochemical impedance spectroscopy results showed that the developed Co3(PO4)2@BSA- and Co3(PO4)2@Apt-based aptasensors present highly sensitive detection ability toward PDGF-BB. Due to the special nanoflower structure, the Co3(PO4)2@BSA-based aptasensor features a detection limit of 3.7 pg mL(-1); while the limit of detection of the Co3(PO4)2@Apt-based aptasensor is 61.5 pg mL(-1), which is the possible bioactivity loss of the aptamer in Co3(PO4)2@Apt nanocomposite. The two detection limits obtained are still much lower than or comparable with those of previously reported aptasensors. The Co3(PO4)2@BSA- and Co3(PO4)2@Apt-based aptasensors showed high selectivity, stability, and applicability for detecting the desired protein. This finding indicates that the Co3(PO4)2-based nanocomposites could be used as an electrochemical biosensor for various detection procedures in the biomedical field.

Two-Dimensional Zirconium-Based Metal–Organic Framework Nanosheet Composites Embedded with Au Nanoclusters: A Highly Sensitive Electrochemical Aptasensor toward Detecting Cocaine

Two-dimensional (2D) zirconium-based metal-organic framework nanosheets embedded with Au nanoclusters (denoted as 2D AuNCs@521-MOF) were prepared via a one-pot method under mild conditions. The optimized 2D AuNCs@521-MOF nanosheets not only possessed high specific surface area, physicochemical stability, and good electrochemical activity but also exhibited strong bioaffinity toward biomolecule-bearing phosphate groups. Consequently, a large amount of cocaine aptamer strands can be immobilized onto the substrate modified by 2D AuNCs@521-MOF nanosheet, further leading to the formation of a constructed biosensitive platform, which can be used to successfully detect cocaine through the specific binding interactions between cocaine and aptamer strands. The results demonstrated that the 2D AuNCs@521-MOF-based aptasensor had high sensitivity for detecting cocaine within the broad concentration range of 0.001-1.0 ng·mL-1 and the low limit of detection of 1.29 pM (0.44 pg·mL-1) and 2.22 pM (0.75 pg·mL-1) as determined by electrochemical impedance spectroscopy and differential pulse voltammetry, respectively. As expected, with the advantages of high selectivity, repeatability, stability, and simple operation, this new strategy is believed to exhibit great potential for simple and convenient detection of cocaine.

Plasma polyacrylic acid and hollow TiO2 spheres modified with rhodamine B for sensitive electrochemical sensing Cu(II)

We report a novel nanocomposite of hollow TiO2 microspheres and plasma polyacrylic acid (TiO2@PPAA) modified with rhodamine B (TiO2@PPAA-RhB). This nanocomposite was further used as an electrochemical sensor for the ultra-sensitive and selective detection of Cu2+ in water. A gold electrode was modified with hollow TiO2 nanospheres, followed by the closely bonded layer of PPAA via plasma polymerization. Subsequently, the carboxyl groups of TiO2@PPAA nanocomposites were activated to ester groups by N-hydroxysuccinimide/1-ethyl-3-(3-dimethylaminoprolyl) carbodiimide hydrochloride. The resultant activated ester groups reacted with the amino groups on rhodamine to form the amide groups, leading to the modification of TiO2@PPAA nanocomposites with rhodamine. Considering the synergistic effect of strong electrostatic interaction between the carboxyl groups of PPAA and Cu2+, the direct adsorption of Cu2+ on the TiO2 surface, and the coordination chemistry formed between Cu2+ and rhodamine, the developed electrochemical biosensor exhibited high sensitivity of Cu2+ detection, with a detection limit of 0.404 pM within the range of 0.001–10 nM of Cu2+. Therefore, the fabricated electrochemical sensor based on TiO2@PPAA-RhB can be obtained via plasma polymerization and represents a highly promising tool for use in environmental monitoring.

Aptasensor Based on Hierarchical Core–Shell Nanocomposites of Zirconium Hexacyanoferrate Nanoparticles and Mesoporous mFe3O4@mC: Electrochemical Quantitation of Epithelial Tumor Marker Mucin-1

A novel nanostructured hierarchical core–shell nanocomposite of zirconium hexacyanoferrate (ZrHCF) and a mesoporous nanomaterial composed of Fe3O4 and carbon nanospheres (denoted as ZrHCF@mFe3O4@mC) was prepared and used as a novel platform for an aptasensor to detect the epithelial tumor marker mucin-1 (MUC1) sensitively and selectively. The prepared ZrHCF@mFe3O4@mC nanocomposite exhibited good chemical functionality, water stability, and high specific surface area. Therefore, large amounts of aptamer molecules resulted in high sensitivity of the developed electrochemical aptasensor toward traces of MUC1. The constructed sensor also showed a good linear relationship with the logarithm of MUC1 concentration in the broad range of 0.01 ng·mL–1 to 1.0 μg·mL–1, with a low detection limit of 0.90 pg·mL–1. The fabricated ZrHCF@mFe3O4@mC-based aptasensor exhibited not only high selectivity because of the formation of aptamer–MUC1 complex but also good stability, acceptable reproducibility, and applicability. The proposed novel strategy based on a newly prepared hierarchical core–shell nanocomposite demonstrated outstanding biosensing performance and presents potential applications in biomedical fields.