In situ deposition of MOF-74(Cu) nanosheet arrays onto carbon cloth to fabricate a sensitive and selective electrocatalytic biosensor and its application for the determination of glucose in human serum.

A new electrocatalytic biosensor (MOF-74(Cu) NS-CC) based on the in situ deposition of MOF-74(Cu) nanosheet on carbon cloth via a bottom-up synthetic approach in a glass tube was developed. The electrocatalytic activity of the deposited MOF-74(Cu) NS was demonstrated in the oxidation of glucose to gluconate under alkaline conditions. The results revealed that the proposed method of in situ formation of MOF-74(Cu) NS onto a carbon cloth surface in a multi-layer solution is capable to generate a stable MOF-74(Cu) NS-CC electrode with excellent sensing performance. When the as-synthesized MOF-74(Cu) NS-CC was applied directly as the working electrode for glucose sensing, it showed much higher conductivity and redox activity than MOF-74(Cu) NS-GCE. With the potential applied at 0.55 V (vs. Ag/AgCl), this new electrocatalytic biosensor exhibits an excellent linear relationship between current density and concentration of glucose. Moreover, a wide linear range of detection (1.0 to 1000 µM) was observed. The limit of detection was found to be 0.41 µM (S/N = 3). The response sensitivity is 3.35 mA mM-1 cm-2 when the concentration of glucose is in the range 1-100 µM and 3.81 mA mM-1 cm-2 for the 100-1000 µM concentration range. This study provides a low-cost, easy to prepare, and reproducible methodology for the synthesis of highly redox-active nanomaterials based on the in situ formation of two-dimensional MOF-74(Cu) NS for the development of new electrocatalytic biosensors. Graphical abstract.

Fluorometric determination of the activity of inorganic pyrophosphatase and its inhibitors by exploiting the peroxidase mimicking properties of a two-dimensional metal organic framework.

A copper(II)-based two-dimensional metal-organic framework with nanosheet structure (CuBDC NS) that possesses peroxidase (POx) mimicking activity was prepared. In the presence of hydrogen peroxide, the system catalyses the oxidation of terephthalic acid to a blue-fluorescent product (excitation = 315 nm; emission = 425 nm). Pyrophosphate has a very strong affinity for Cu2+ ion and blocks the POx-mimicking activity of the CuBDC NS. If, however, inorganic pyrophosphatase is present, the POx mimicking activity is gradually restored because pyrophosphate is hydrolyzed. The findings were used to design a method for the determination of the activity of inorganic pyrophosphatase by fluorometry. Fluorescence increases linearly in the 1-50 mU·mL-1 inorganic pyrophosphatase activity range. The limit of detection is 0.6 mU·mL-1 (S/N = 3). Graphical abstract A copper(II)-based two-dimensional metal-organic framework (CuBDC NS) is described that possesses POx-mimicking activity. Inorganic pyrophosphate (PPi) was hydrolyzed to phosphate in the presence of inorganic pyrophosphatase (PPase). Hence, it cannot coordinate with Cu2+ in CuBDC NS, its structure was well-conserved to catalyses the oxidation of terephthalic acid (H2BDC) to produce a blue fluorescent product (oxBDC) in the presence of hydrogen peroxide (H2O2).

Facile synthesis of Fe3O4/g-C3N4/HKUST-1 composites as a novel biosensor platform for ochratoxin A.

A fluorescent biosensor for ochratoxin A was fabricated on the basis of a new nanocomposite (Fe3O4/g-C3N4/HKUST-1 composites). Fe3O4/g-C3N4/HKUST-1 was synthesized in this work for the first time, which combined HKUST-1 with g-C3N4 to improve its chemical stability. Fe3O4/g-C3N4/HKUST-1 composites have strong adsorption capacity for dye-labeled aptamer and are able to completely quench the fluorescence of the dye through the photoinduced electron transfer (PET) mechanism. In the presence of ochratoxin A (OTA), it can bind with the aptamer with high affinity, causing the releasing of the dye-labeled aptamer from the Fe3O4/g-C3N4/HKUST-1 and therefore results in the recovery of fluorescence. The fluorescence intensity of the biosensor has a linear relationship with the OTA concentration in the range of 5.0-160.0ng/mL. The LOD of sensor is 2.57ng/mL (S/N=3). This fluorescence sensor based on the Fe3O4/g-C3N4/HKUST-1 composites has been applied to detect OTA in corn with satisfying results.

Highly sensitive visual detection of Avian Influenza A (H7N9) virus based on the enzyme-induced metallization.

Development of convenient but sensitive method for influenza detection is highly important in immediate and effective clinical treatment. In this study, an ultrasensitive colorimetric approach combining the advantages of the convenience of the enzyme-induced metallization and the high specificity of enzyme-linked immunosorbent assay for the detection of influenza virus A (H7N9 as model) has been developed. Two rounds of amplification are utilized to enhance the detection sensitivity. The amplification of enzymatic reaction combines with the specific optical properties of gold nanoparticles causing the enhancing of the optical signal immensely. In addition, the increased surface area and the magnetic enrichment effect also enable the magnetic bead (MB) to catch a large number of alkaline phosphatase (ALP) and detection antibody (Ab2), thus very small amounts of the virus can be easily detected. Compared with conventional method, this approach exhibits outstanding sensitivity for ALP detection, 0.2U/L of ALP can be distinguished with a spectrometer and 2U/L with the naked eye. And as low as 25 pg/mL of H7N9 can be detected by the naked eye. This approach shows an extensive horizon for bioassays and is available in clinical diagnosis with the advances of simplification, effectiveness, low cost and sensitive readout.