Two-dimensional inorganic nanosheets: production and utility in the development of novel electrochemical (bio)sensors and gas-sensing applications

Silver-manganese nanocomposite modified screen-printed carbon electrode in the fabrication of an electrochemical, disposable biosensor strip for cystic fibrosis

A silver-manganese nanocomposite was successfully prepared by the urea hydrolysis method and used to detect chloride ions in sweat electrochemically. The synthesis involves the reaction of manganese sulphate, silver nitrate, and urea at 100 °C for 24 h. The crystalline nature of the particle was studied by diffraction analysis and found to be mixed-phase oxides of manganese alongside the oxides of silver. Morphological studies revealed the presence of quasi-prism-like structures, which is characteristic of β-MnO₂. A disposable sensor was fabricated by screen-printing the catalyst and used for the electrochemical detection of chloride ions in sweat. The sensor exhibited good selectivity, a sensitivity of 22.93 ± 0.64 µA mM^-1 cm^-2 in solution and 3010 ± 60 µA (log mM) ^-1 cm^-2 for the fabricated sensor strip with a detection range from 5 mM up to 200 mM. The detection limit is 207 ± 7 µM (S/N = 3) in solution and 17 ± 6 µM for the fabricated sensor strip. The relative standard deviation (RSD) of sensor response is 2.38%. A prototype of the biosensor strip was fabricated and validated using real samples. This brings the possibility of developing a real-time biosensor strip for cystic fibrosis in point-of-care testing applications.

In situ synthesis of Co-doped MoS2 nanosheet for enhanced mimicking peroxidase activity

To enhance the catalytic activity of two-dimensional layered materials as versatile materials, the modification of transition metal dichalcogenide nanosheets such as MoS₂ by doping with heteroatoms has drawn great interests. However, few reports are available on the study of the enzyme-like activity of doped MoS₂. In this study, a facile in situ hydrothermal method for the preparation of various ultrathin transition metals (Fe, Cu, Co, Mn, and Ni) doped MoS₂ nanosheets has been reported. Through the density functional theory (DFT) and steady-state kinetic analysis, the Co-doped MoS₂ nanosheets exhibited the highest peroxidase-like catalytic activity among them. Furthermore, a typical colorimetric assay for H₂O₂ was presented based on the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB) by Co-MoS₂. The proposed colorimetric method showed excellent tolerance under extreme conditions and a broad linear range from 0.0005 to 25 mM for H₂O₂ determination. Concerning the practical application, in situ detection of H₂O₂ generated from SiHa cells was also fulfilled, fully confirming the great practicability of the proposed method in biosensing fields.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-022-07201-z.

PtS2 nanosheets as a peroxidase-mimicking nanozyme for colorimetric determination of hydrogen peroxide and glucose

Using an ultrasonication-assisted liquid exfoliation method, we have synthesized PtS₂ nanosheets with good reproducibility. Herein, intrinsic peroxidase-like activity was for the first time demonstrated for PtS₂ nanosheets, which can catalyze H₂O₂ oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate a colored solution. The catalytic mechanism of PtS₂ nanosheets was investigated, which indicated that acceleration of the electron transfer between TMB and H₂O₂ was the main reason for the peroxidase-like activity of PtS₂ nanosheets. Based on these observations, we exploited PtS₂ nanosheets integrated into dopamine-functionalized hyaluronic acid (HA-DA) hydrogel microspheres by droplet microfluidics to construct PtS₂ nanosheet- and PtS₂@HA-DA microsphere-based sensors for highly sensitive determination of H₂O₂. When coupled with glucose oxidase, we further developed two glucose sensors based on the above two methods. Among them, the linearity of the PtS₂ nanosheet-based spectrophotometry was in the range of 0.5 to 150 μM and the limit of detection as low as 0.20 μM. The linearity of the microsphere-based colorimetry was in the range 200 to 12,000 μM with a detection limit of 29.95 μM. Both of the glucose sensors can be applied to the determination of glucose in human serum with reliable results and reproducibility.