Imidazoline derivative templated synthesis of broccoli-like Bi2S3 and its electrocatalysis towards the direct electrochemistry of hemoglobin

Electrocatalysis by Heme Enzymes—Applications in Biosensing

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a plethora of biotechnological applications. This work focuses on biosensing devices based on heme proteins, in which they are electronically coupled to an electrode and their activity is determined through the measurement of catalytic currents in the presence of substrate, i.e., the target analyte of the biosensor. After an overview of the main concepts of amperometric biosensors, we address transduction schemes, protein immobilization strategies, and the performance of devices that explore reactions of heme biocatalysts, including peroxidase, cytochrome P450, catalase, nitrite reductase, cytochrome c oxidase, cytochrome c and derived microperoxidases, hemoglobin, and myoglobin. We further discuss how structural information about immobilized heme proteins can lead to rational design of biosensing devices, ensuring insights into their efficiency and long-term stability.

Bioelectrocatalysis of Hemoglobin on Electrodeposited Ag Nanoflowers toward H2O2 Detection

Hydrogen peroxide (H2O2) is a partially reduced metabolite of oxygen that exerts a diverse array of physiological and pathological activities in living organisms. Therefore, the accurate quantitative determination of H2O2 is crucial in clinical diagnostics, the food industry, and environmental monitoring. Herein we report the electrosynthesis of silver nanoflowers (AgNFs) on indium tin oxide (ITO) electrodes for direct electron transfer of hemoglobin (Hb) toward the selective quantification of H2O2. After well-ordered and fully-grown AgNFs were created on an ITO substrate by electrodeposition, their morphological and optical properties were analyzed with scanning electron microscopy and UV-Vis spectroscopy. Hb was immobilized on 3-mercaptopropionic acid-coated AgNFs through carbodiimide cross-linking to form an Hb/AgNF/ITO biosensor. Electrochemical measurement and analysis demonstrated that Hb retained its direct electron transfer and electrocatalytic properties and acted as a H2O2 sensor with a detection limit of 0.12 µM and a linear detection range of 0.2 to 3.4 mM in phosphate-buffered saline (PBS). The sensitivity, detection limit, and detection range of the Hb/AgNF/ITO biosensor toward detection H2O2 in human serum was also found to be 0.730 mA mM-1 cm-2, 90 µM, and 0.2 to 2.6 mM, indicating the clinical application for the H2O2 detection of the Hb/AgNF/ITO biosensor. Moreover, interference experiments revealed that the Hb/AgNF/ITO sensor displayed excellent selectivity for H2O2.

Bismuth-Based Photocatalysts for Solar Photocatalytic Carbon Dioxide Conversion

Photocatalytic CO₂ conversion into solar fuels is an effective means for simultaneously solving both the greenhouse effect and energy crisis. In the past ten years, bismuth-based photocatalysts for environmental remediation have experienced a golden period of development. However, solar photocatalytic CO₂ conversion has only been developed over the past five years and, until now, no reviews have been published on bismuth-based photocatalysts for the photocatalytic conversion of CO₂ . For the first time, solar photocatalytic CO₂ conversion systems are reviewed herein. Synthetic methods and photocatalytic CO₂ performances of bismuth-based photocatalysts, including Sillén-structured BiOX (X=Cl, Br, I); Aurivillius-structured Bi₂ MO₆ (M=Mo, W); and Scheelite-structured BiVO₄ , Bi₂ S₃ , BiYO₃ , and BiOIO₃ , are summarized. In addition, activity-enhancing strategies for this photocatalyst family, including oxygen vacancies, bismuth-rich strategy, facet control, conventional type II heterojunction, Z-scheme heterojunction, and cocatalyst deposition, are reviewed. Finally, the main mechanistic research methods, such as in situ FTIR spectroscopy and theoretical calculations, are presented. Challenges and research trends reported in studies of bismuth-based photocatalysts for photocatalytic CO₂ conversion are discussed and summarized.

Graphene Oxide Directed One-Step Synthesis of Flowerlike Graphene@HKUST-1 for Enzyme-Free Detection of Hydrogen Peroxide in Biological Samples

A novel metal-organic framework (MOF)-based electroactive nanocomposite containing graphene fragments and HKUST-1 was synthesized via a facile one-step solvothermal method using graphene oxide (GO), benzene-1,3,5-tricarboxylic acid (BTC), and copper nitrate (Cu(NO₃)₂) as the raw materials. The morphology and structure characterization revealed that the GO could induce the transformation of HKUST-1 from octahedral structure to the hierarchical flower shape as an effective structure-directing agent. Also, it is interesting to find out that the GO was torn into small fragments to participate in the formation of HKUST-1 and then transformed into the reduction form during the solvothermal reaction process, which dramatically increased the surface area, electronic conductivity, and redox-activity of the material. Electrochemical assays showed that the synergy of graphene and HKUST-1 in the nanocomposite leaded to high electrocatalysis, fast response, and excellent selectivity toward the reduction of hydrogen peroxide (H₂O₂). Based on these remarkable advantages, satisfactory results were obtained when the nanocomposite was used as a sensing material for electrochemical determination of H₂O₂ in the complex biological samples such as human serum and living Raw 264.7 cell fluids.

TiO2 nanoparticle modified organ-like Ti3C2 MXene nanocomposite encapsulating hemoglobin for a mediator-free biosensor with excellent performances

TiO2 nanoparticle modified organ-like Ti3C2 MXene (TiO2-Ti3C2) nanocomposite has been synthesized and then used to immobilize hemoglobin (Hb) to fabricate a mediator-free biosensor. The morphology and structure of TiO2-Ti3C2 nanocomposite were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Spectroscopic and electrochemical results revealed that TiO2-Ti3C2 nanocomposite is an excellent immobilization matrix with biocompatibility for redox protein, affording good protein bioactivity and stability. Due to the special organ-like hybrid structure of TiO2-Ti3C2, the direct electron transfer of Hb is facilitated and the prepared biosensors displayed good performance for the detection of H2O2 with a wide linear range of 0.1-380 μM for H2O2 (sensitivity of 447.3 μA mM(-1) cm(-2)), an extremely low detection limit of 14 nM for H2O2. Especially, numerous TiO2 nanoparticles with excellent biocompatibility on the surface of the nanocomposite may provide a protective microenvironment for Hb to make the prepared biosensor improve long-term stability. The TiO2-Ti3C2 based biosensor retains 94.6% of the initial response to H2O2 after 60-day storage. TiO2-Ti3C2 nanocomposite could be a promising matrix for the fabrication of mediator-free biosensors, and might find wide potential applications in environmental analysis and biomedical detection.