Photoelectrochemical (PEC) urea splitting is of great significance for urea wastewater remediation and hydrogen production with low energy consumption simultaneously. Nickel hydroxides as electrocatalysts have been widely investigated for urea electrolysis. However, it is an open question how to synthesize highly catalytic Ni(OH)2 for the PEC urea splitting. Herein, we take advantage of the instability of metal–organic frameworks (MOFs) to perform an in situ synthesis of Ni(OH)2 catalysts on the surface of TiO2 nanorod arrays. This transformed Ni(OH)2 (T-Ni(OH)2) possesses a superior PEC catalytic activity for water/urea splitting in comparison to the Ni(OH)2 prepared by the impregnation method. The in situ transition of a Ni-MOF is accomplished through an electrochemical treatment under AM1.5G illumination in a KOH-and-urea mixed electrolyte. The specific transition mechanism of Ni-MOFs is the substitution of ligands with OH− in a 1 M KOH electrolyte and the successive phase transition. The T-Ni(OH)2@TiO2 photoanode delivers a high photocurrent density of 1.22 mA cm−2 at 1.23 VRHE, which is 4.7 times that of Ni(OH)2@TiO2 prepared with the impregnation method. The onset potential of T-Ni(OH)2@TiO2 is negatively shifted by 118 mV in comparison to TiO2. Moreover, the decline of photocurrent during the continuous test can be recovered after the electrochemical and light treatments.

DNA-based supramolecular hydrogels are important and promising biomaterials for various applications due to their inherent biocompatibility and tunable physicochemical properties. The three-dimensional supramolecular matrix of DNA formed by non-covalently dynamic cross-linking provides exceptional adaptability, self-healing, injectable and responsive properties for hydrogels. In addition, DNA hydrogels are also ideal bio-scaffold materials owing to their tissue-like mechanics and intrinsic biological functions. Technically, DNA can assemble into supramolecular networks by pure complementary base pairing; it can also be combined with other building blocks to construct hybrid hydrogels. This review focuses on the development and construction strategies of DNA hydrogels. Assembly and synthesis methods, diverse responsiveness and biomedical applications are summarized. Finally, the challenges and prospects of DNA-based supramolecular hydrogels are discussed.

Spherical bimetallic cobalt-lanthanum oxides were loaded on the surface of electrospun carbon fiber by simple hydrothermal method and an electrochemical sensor was successfully constructed for simultaneous detection of amlodipine and acetaminophen. Carbon fiber, as an electron transport channel, is cooperated with bimetallic oxides to provide uniformly dispersed active sites and enhance the conductivity of the composite. The linear relationships between amlodipine and acetaminophen are 10-1000 µM and 5-1600 µM, and the detection limits are 0.86 µM and 0.25 µM, respectively. Furthermore, experiments reveal that the sensor exhibits good stability, and satisfactory recovery rate has been obtained in the detection of two practical drugs.

The detection method with potential ability to diagnose drugs in human serum rapidly, highly sensitivity and selectivity is of vital importance for clinical diagnosis. In this paper, an electrochemical sensor on the basis of composite material modified by zeolitic imidazolate framework (ZIF) on carbon nanofiber (CNF) surface is constructed, which is used for ultra-sensitive determination of adrenaline (AD). CoMnZIF-CNF combines the good conductivity of carbon nanofibers and the high electrocatalysis of CoMnZIF, which can improve the reaction activity and the sensing effect of adrenaline. The proposed sensor shows a good linear relationship between AD concentration from 5 to 1000 μM, and the detection limit is 0.22 μM. Meanwhile, CoMnZIF-CNF demonstrated the remarkable selectivity, significant repeatability and stability, as well as excellent reproducibility. Besides, through the analysis of AD in serum electrolyte, the practicability of the sensor was evaluated and the recovery rate was between 97.51 and 102.53%. On the basis of the results, the prepared sensor has a vital application prospect in detecting AD in actual sample analysis.

This paper proposes a novel electrochemical aptasensor that integrates molecular imprinting techniques for trace analysis of cortisol. This sensor is based on functionalized graphene and nitrogen-doped carbon quantum dots. The morphology and structure of the modified electrode were characterized by scanning electron microscopy and Raman spectroscopy. The functional monomer aptamer and the template molecule cortisol were adsorbed on the electrode by electrostatic adsorption to construct an imprinted sensing platform. Under the optimal conditions, such as the concentration of template molecule, the ratio of template to functional monomer, the elution and adsorption time, the sensor exhibits linearity and a low detection limit of 10-12-10-8 M and 3.3 × 10-13 M, which is more sensitive than other reported cortisol analysis methods. In addition, this sensor can realize the determination of cortisol in salivary samples with high recovery values, showing great development potential in the field of life sciences.

An electrochemical aptamer sensor based on gold nanoparticles (AuNPs) was developed for highly specific sensing of melamine (MEL), which combines molecularly imprinted polymers (MIPs) and aptamers. AuNPs were synthesized by simple reduction of sodium citrate and characterized by transmission electron microscopy. The MIP membranes with particular recognition sites were formed by electropolymerization of dopamine (DA) with polythymine (poly T) aptamers as functional monomers and melamine as template molecules. Under optimal experimental conditions, this molecularly imprinted electrochemical aptamer sensor (MIEAS) exhibits a linear relationship between 10-12 M and 10-4 M for detecting MEL with the detection limit of 6.7 × 10-13 M. Moreover, this sensor displays excellent selectivity, reproducibility and stability. The milk samples analysis has confirmed the potential application of this MIEAS to quantitative detection of melamine.

Curcumin is used as a natural pigment and flavoring agent and food additive in food processing industries. Also, curcumin has a wide range of applications in the medical industry and clinical treatment because of its anti-cancer, anti-oxidation, anti-coagulant, anti-HIV choleretic and hypolipidemic effects. Therefore, it is crucial to properly control the concentration of curcumin in food and medicine. In our work, a new and simple method for quantitative detection of curcumin was established by developing a “turn-off” fluorescence probe based on upconvert luminescent carbon quantum dots (p-CDs). The carbon quantum dots were synthesized with p-aminobenzoic acid (PABA) and ethanol by solvothermal method and have specific up-conversion luminescence properties which could be applied in other sensing field. In this sensor, the sensing mechanism of this fluorescent probe was based on the internal filter effect (IFE) between curcumin and p-CDs, the increasing in the concentration of curcumin causes the selective fluorescence quenching of p-CDs. Under optimum conditions, the fluorescence quenching intensity of p-CDs has a good liner relationship with curcumin in the range of 0.4-45 μΜ and with a detection limit of 0.133 μM. What's more, the fluorescent “turn-off” probe constructed with p-CDs exhibited high accuracy and recovery in the analysis of actual sample curry powder, demonstrating the fluorescence “turn-off” probe has potential application for the detection of curcumin in the complex matrixes.

The sensitive determination of VB2 has broad analytical applications. In this work, a novel VB2 electrochemical sensor based on hydrothermal method was constructed to uniformly grow molybdenum disulfide and silver nanoparticles on the surface of electrospun carbon fiber. MoS2-Ag-CNF was characterized by scanning electron microscope, EDS spectrum, cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. The sensor exhibited a high sensitivity of 0.05 μΜ to 40 μΜ with a fast response time and a low detection limit of 0.02 μM. The electrode also showed outstanding selectivity toward various interferences. These results indicate that the MoS2-Ag-CNF nanocomposites may be promising electrode materials for electrochemical biosensing.

In this work, we integrated the superiority of good conductivity, large surface area of carbon fibers and the catalytic property, good biocompatibility of polymer sulfosalicylic acid to construct a novel electrochemical sensor to detect theophylline in drug analysis. The morphology of nanocomposite was characterized by scanning electron microscopy (SEM). The polymerization between monomers was observed by Fourier transform infrared spectroscopy (FTIR). The composite between carbon material and polymer was verified by Raman spectrum. Under the optimal experimental conditions, the concentration of theophylline (0.6∼137 μM) and the peak current value revealed a good linear relationship and the limit of detection as low as 0.2 μM. In addition, the proposed sensor exhibits repeatability, stability and ease of selectivity.

Controllable integration of nanoparticles (NPs) and metal-organic frameworks (MOFs) is crucial for expanding the applications of MOF-based materials. In this study, we demonstrate the facile encapsulation of pre-synthesized NPs into carboxylic acid based MOFs using NPs@metal oxide core-shell nanostructures as the self-template. The shell dissolved gradually in the mildly acidic growth solution created by dissociation of the ligands and thus directing the growth of the MOF crystals by providing metal ions. With protection of the metal oxide shell, various NPs (Au NPs, Au nanorods, Pd nanocubes, and Pt-on-Au dendritic NPs) could be encapsulated easily without being aggregated or dissolved in the reaction mixture. Importantly, instead of forming the exact replicate of the self-template, the obtained NP@MOF heterostructures exhibited a yolk-shell morphology with a central cavity and a certain degree of mesoporosity. The formation of the well-defined yolk-shell structure was demonstrated to be dependent on both the choice of the solvent and the dissolution behavior of the metal oxide shell. Finally, the obtained heterostructures were employed for heterogeneous catalysis, in which the size selectivity of the MOF shell was perfectly retained.