To date, two-dimensional (2D) and three-dimensional (3D) metal organic frameworks (MOFs) have been promising materials for applications in electrocatalysis, separation, and sensing. However, the exploration of a simple method for simultaneous fabrication of 2D/3D MOFs on a surface remains challenging. Herein, a one-step and in situ electrosynthesis strategy for fabrication of 2D Hemin-bridged MOF sheets (Hemin-MOFs) or 2D/3D Zn­(II)-MOF hybrid nanocomposites on an electrode is reported. It exhibits varied morphologies at different electrodeposition times and attains a 2D/3D complex morphology by adding 1,3,5-benzenetricarboxylic acid (H3BTC) as an organic ligand. The morphology and size of 2D Hemin-MOFs are important factors that influence their performance. Since Pt nanoparticles (PtNPs) are grown on 2D Hemin-MOF sheets, this composite can serve as the peroxidase mimics and PtNPs can act as an anchor to capture the antibody. Therefore, this hybrid nanosheet-modified electrode is used as an electrochemical sensing platform for ultrasensitive pig immunoglobulin G (IgG) and the surface-protective antigen (Spa) protein of Erysipelothrix rhusiopathiae immunodetection. Moreover, this work provides a new avenue for the electrochemical synthesis of 2D/3D MOF hybrid nanocomposites with a high surface area and biomimetic catalysts.

Sensitive simultaneous electrochemical sensing of phytohormones indole-3-acetic acid and salicylic acid based on a novel poly(L-Proline) nanoparticles–carbon dots composite consisting of multiwalled carbon nanotubes was reported in this study. The poly(L-Proline) nanoparticles–carbon dots composite was facilely prepared by the hydrothermal method, and L-Proline was used as a monomer and carbon source for the preparation of poly(L-Proline) nanoparticles and carbon dots, respectively. Then, the poly(L-Proline) nanoparticles–carbon dots–multiwalled carbon nanotubes composite was prepared by ultrasonic mixing of poly(L-Proline) nanoparticles–carbon dots composite dispersion and multiwalled carbon nanotubes. Scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy, energy dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry were used to characterize the properties of the composite. poly(L-Proline) nanoparticles were found to significantly enhance the conductivity and sensing performance of the composite. Under optimal conditions, the composite-modified electrode exhibited a wide linear range from 0.05 to 25 μM for indole-3-acetic acid and from 0.2 to 60 μM for salicylic acid with detection limits of 0.007 μM and 0.1 μM (S/N = 3), respectively. In addition, the proposed sensor was also applied to simultaneously test indole-3-acetic acid and salicylic acid in real leaf samples with satisfactory recovery.

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