A review on recent advances in hydrogen peroxide electrochemical sensors for applications in cell detection

Hydrogen peroxide (H₂O₂) is a very simple bioactive small molecule. In living organisms, H₂O₂ plays an important role in intracellular signaling. It is involved in many physiological processes including cellular physiology, intracellular signaling, oxidative damage and disease progression. The tumor microenvironment enriched with H₂O₂. Several electrochemical sensors have been developed and some have been put on the market. Such electrochemical sensors provide efficient, cost-effective, rapid and highly selective method of H₂O₂ detection. So far, much progress has been made in the designing of materials and construction of H₂O₂ sensors. This review describes the advances in the application of H₂O₂ electrochemical sensors in cell detection. Enzyme-based sensors have been applied in diverse applications. In addition, recent advancements in nanotechnology have improved the development of nanozymes-based sensors. The application of noble metals, metal oxides, polymers, carbon materials and other two-dimensional materials in the design of H₂O₂ sensors are discussed in detail. Moreover, the bio-stimulant types of H₂O₂ sensor are summarized. Finally, the challenges and future perspectives in the application of H₂O₂ electrochemical sensors in biological detection are discussed.     

Data‐Driven Identification of Hydrogen Sulfide Scavengers

Hydrogen sulfide (H₂S) is an important signaling molecule whose up‐ and down‐regulation have specific biological consequences. Although significant advances in H₂S up‐regulation, by the development of H₂S donors, have been achieved in recent years, precise H₂S down‐regulation is still challenging. The lack of potent/specific inhibitors for H₂S‐producing enzymes contributes to this problem. We expect the development of H₂S scavengers is an alternative approach to address this problem. Since chemical sensors and scavengers of H₂S share the same criteria, we constructed a H₂S sensor database, which summarizes key parameters of reported sensors. Data‐driven analysis led to the selection of 30 potential compounds. Further evaluation of these compounds identified a group of promising scavengers, based on the sulfonyl azide template. The efficiency of these scavengers in in vitro and in vivo experiments was demonstrated.     

Recent progress in applications of graphene oxide for gas sensing: A review

This paper is a review of the recent progress on gas sensors using graphene oxide (GO). GO is not a new material but its unique features have recently been of interest for gas sensing applications, and not just as an intermediate for reduced graphene oxide (RGO). Graphene and RGO have been well known gas-sensing materials, but GO is also an attractive sensing material that has been well studied these last few years. The functional groups on GO nanosheets play important roles in adsorbing gas molecules, and the electric or optical properties of GO materials change with exposure to certain gases. Addition of metal nanoparticles and metal oxide nanocomposites is an effective way to make GO materials selective and sensitive to analyte gases. In this paper, several applications of GO based sensors are summarized for detection of water vapor, NO₂, H₂, NH₃, H₂S, and organic vapors. Also binding energies of gas molecules onto graphene and the oxygenous functional groups are summarized, and problems and possible solutions are discussed for the GO-based gas sensors.     

Metal–Organic Frameworks for Electrocatalytic Sensing of Hydrogen Peroxide

The electrochemical detection of hydrogen peroxide (H₂O₂) has become more and more important in industrial production, daily life, biological process, green energy chemistry, and other fields (especially for the detection of low concentration of H₂O_2). Metal organic frameworks (MOFs) are promising candidates to replace the established H₂O₂ sensors based on precious metals or enzymes. This review summarizes recent advances in MOF-based H₂O₂ electrochemical sensors, including conductive MOFs, MOFs with chemical modifications, MOFs-composites, and MOF derivatives. Finally, the challenges and prospects for the optimization and design of H₂O₂ electrochemical sensors with ultra-low detection limit and long-life are presented.     

Electrochemical Sensors Using Two‐Dimensional Layered Nanomaterials

Two‐dimensional (2D) layered nanomaterials, e.g. graphene and molybdenum disulfide (MoS₂), have rapidly emerged in material sciences due to their unique physical, chemical and mechanical properties. In the meanwhile, there is a growing interest in constructing electrochemical sensors for a wide range of chemical and biological molecules by using these 2D nanomaterials. In this review, we summarize recent advances on using graphene and MoS₂ for the development of electrochemical sensors for small molecules, proteins, nucleic acids and cells detection. We also provide our perspectives in this rapidly developing field.     

Self‐Assembled Discrete Molecules for Sensing Nitroaromatics

Efficient sensing of trace amount nitroaromatic (NAC) explosives has become a major research focus in recent time due to concerns over national security as well as their role as environment pollutants. NO₂‐containing electron‐deficient aromatic compounds, such as picric acid (PA), trinitrotoluene (TNT), and dinitrotoluene (DNT), are the common constituents of many commercially available chemical explosives. In this article, we have summarized our recent developments on the rational design of electron‐rich self‐assembled discrete molecular sensors and their efficacy in sensing nitroaromatics both in solution as well as in vapor phase. Several π‐electron‐rich fluorescent metallacycles (squares, rectangles, and tweezers/pincers) and metallacages (trigonal and tetragonal prisms) have been synthesized by means of metal–ligand coordination‐bonding interactions, with enough internal space to accommodate electron‐deficient nitroaromatics at the molecular level by multiple supramolecular interactions. Such interactions subsequently result in the detectable fluorescence quenching of sensors even in the presence of trace quantities of nitroaromatics. The fascinating sensing characteristics of molecular architectures discussed in this article may enable future development of improved sensors for nitroaromatic explosives.     

Highly Selective Nanostructured Electrochemical Sensor Utilizing Densely Packed Ultrathin Gold Nanowires Film

The number of studies conducted about nonenzymatic electrochemical sensors has increased in recent years due to the development of more stable and robust electrodes using noble metals. One of the key aspects for achieving high sensing performance including detection limit and sensitivity is the design of electrode architecture. Herein, we report a new electrochemical sensing platform featuring ultrathin standing gold nanowires (AuNWs) for nonenzymatic detection of hydrogen peroxide (H₂O₂). The use of AuNWs resulted in an increased electron transfer efficiency due to the higher active surface area compared to traditional gold film electrodes. This sensor demonstrates good selectivity, reproducibility, a linear range up to 49.5 mM of H₂O₂ with a sensitivity of 0.185±0.003 mAmM^?1cm^?2 and a limit of detection of 111 μM. The biological relevance of this sensor was tested in cell culture media to illustrate the performance of the proposed sensing electrode in complex biological media.     

The sensing mechanism of fluoride anion for a novel molecule D2: Desilylation and intramolecular charge transfer

In this work, the sensing mechanism of a new fluoride chemosensor 12‐([tert‐butyldiphenylsilyl]oxy)‐8a,13a‐dihydro‐7H‐benzo[de]benzo[4,5]imidazo[2,1‐a]‐isoquinolin‐7‐one (abbreviated as D2) is investigated using density functional theory (DFT) and time‐dependent DFT (TDDFT) methods. The theoretical electronic spectra (vertical excitation energies and fluorescence peak) reproduced previous experimental results (D. Li et al., Spectrochim. Acta A Mol. Biomol. Spectrosc. 2017 , 185, 173), which confirms the rationality of the theoretical level used in this work. The constructed potential energy curve of the desilylation process suggests that the low barrier could be responsible for the rapid response to fluoride anions. Analyses of the binding energies show that only fluoride anion can be detected by D2 chemosensor in dimethylsulfoxide (DMSO). In view of the excitation process, the strong intramolecular charge transfer (ICT) process of the S₀ → S₁ transition explains the red shift of the absorption peak of the D2 sensor with the addition of fluoride anions. This work not only presents a straightforward sensing mechanism of sensing of the fluoride anion by the D2 chemosensor but should also play an important role in the synthesis and design of fluorescent sensors in future.     

Advances of Metal‐Organic Frameworks in Energy and Environmental Applications

Nowadays, energy shortage and environmental pollution issues are increasingly severe and urgent to be solved. The effective storage and use of environmentally friendly fuels and removal of harmful gases from the environment are great challenges and of great importance both for the environment protection and for human health. Porous metal‐organic frameworks (MOFs) are highly ordered crystalline materials formed by the self‐assembly process of metal ions and organic ligands. Their good features such as ultrahigh porosity, large surface area, structural diversity and functionalities make them promising candidates for applications in energy and environmental fields. MOF thin films and MOF composites have also been investigated to further enhance the properties and introduce new functionalities. This review provides an overview of the synthesis methods of pristine MOFs, MOF thin films and MOF composites, and significant advances of MOFs in energy and environment applications such as energy storage (H₂, CH₄), CO₂ capture and separation, adsorption removal and sensing of harmful gases in the environment.     

Sensing at Your Fingertips: Glove‐based Wearable Chemical Sensors

In this review, we detail the evolution and recent progress of glove‐based wearable electrochemical sensors with focus on forensic, security, and defense applications. Glove‐based wearable sensors offer the ability to have rapid, on‐site chemical and biological threat assessment, ranging from explosive and gunshot residues to drugs of abuse and pesticides, critical for timely and informed incident management and investigation. Additionally, these field deployable systems offer the ability for law enforcement to complete on‐the‐spot qualitative chemical testing for immediate forensic evidence collection in connection to mechanical ‘swipe’ sampling. Recent advances have been made for translation of this class of wearable electrochemical sensors to increase the sensory perspective of robotics, demonstrating the progression to robotic skin with chemical analysis capability suitable for translation to remote chemical analysis in hazardous scenarios. Critical to such progress have been advances in flexible electrochemically‐compatible materials and design, with increasing functionality, leveraging from advances in wearable biosensors and electronic miniaturization. Indeed, the customization potential of these wearable systems is great, yet challenges remain for advancing these systems from prototypes to more ubiquitous devices readily deployed in the field. With significant attention these challenges can be overcome, creating new opportunities for further decentralization of electrochemical analyses using these flexible and intuitive glove‐based wearable sensing systems for significant impact on fields such as forensics, defense, biomedical, robotics and beyond.     

CuO–ZnO Micro/Nanoporous Array‐Film‐Based Chemosensors: New Sensing Properties to H2S

CuO–ZnO micro/nanoporous array‐films are synthesized by transferring a solution‐dipped self‐organized colloidal template onto a device substrate and sequent heat treatment. Their morphologies and structures are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectrum analysis. Based on the sensing measurement, it is found that the CuO–ZnO films prepared with the composition of [Cu²⁺]/[Zn²⁺]=0.005, 0.01, and 0.05 all show a nice sensitivity to 10 ppm H₂S. Interestingly, three different zones exist in the patterns of gas responses versus H₂S concentrations: a platform zone, a rapidly increasing zone, and a slowly increasing zone. Further experiments show that the hybrid CuO–ZnO porous film sensor exhibits shorter recovery time and better selectivity to H₂S gas against other interfering gases at a concentration of 10 ppm. These new sensing properties may be due to a depletion layer induced by p–n junction between p‐type CuO and n‐type ZnO and high chemical activity of CuO to H₂S. This work will provide a new construction route of ZnO‐based sensing materials, which can be used as H₂S sensors with high performances.     

A Series of Multifunctional Metal–Organic Frameworks Showing Excellent Luminescent Sensing,Sensitization, and Adsorbent Abilities

A series of highly luminescent‐active metal–organic frameworks (MOFs) 1 – 3 with hierarchical pores have been rationally constructed and fully characterized. The predesigned semi‐rigid hexacarboxylate ligand hexa[4‐(carboxyphenyl)oxamethyl]‐3‐oxapentane acid (H₆L) has been adapted with various space‐directed N donors (i.e., 2,2’‐bipyridine, 4,4′‐di(1H‐imidazol‐1‐yl)‐1,1′‐biphenyl, and 1,3,5‐tri(1H‐imidazol‐1‐yl)benzene) from a bidentate V‐shape to a tridentate Y‐shape. This family of multifunctional MOF materials represents a variety of potential applications in the following aspects: first, as luminescent sensors that show a fast and sensitive detection for pollutant CrO₄^2? and Cr₂O₇^2? ions in aqueous media; second, as adsorbents that can rapidly remove harmful organic dyes; third, as an antenna that can effectively sensitize visible‐light‐emitting Tb³⁺ ions. These multifunctional MOF materials combine optical‐sensing, adsorption, and sensitization properties, thus are very useful in many potential applications. Furthermore, these materials have proved to be reusable.     

A Novel Hydrogen Peroxide Amperometric Sensor Based on Hierarchical 3D Porous MnO2−TiO2 Composites

A novel nanocomposite electrode based on hierarchical 3D porous MnO₂?TiO₂ for the application in hydrogen peroxide (H₂O₂) sensors has been explored. This electrode was fabricated by growing TiO₂ cross‐linked nanowires on a commercial fluorine tin oxide (FTO) glass via a hydrothermal process and subsequent deposition of 3D honeycomb‐like MnO₂ nanowalls using an electrodeposition method (denoted as 3D MNS‐TNW@FTO). The obtained 3D MNS‐TNW@FTO electrode was characterized by scanning electron microscopy (SEM), Raman spectroscopy, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). Based on such a unique 3D porous framework and the existence of MnO₂, the electrode demonstrates a good performance in the detection of H₂O₂, with two linear ranges from 9.8 to 125 μM and 125 μM–1.0 mM, a good selectivity of 8.02 μA mM^?1 cm^?2, and a low detection limit of 4.5 μM. In addition, the simplicity of the developed low‐cost fabrication process provides an efficient method for the mass production of electrocatalytical MnO₂?TiO₂ nanocomposites on commercial FTO glass for H₂O₂ sensing applications and can be adapted for other electrochemical sensors for various biochemical targets. It thus is beneficial for the practical usage in bioanalysis.     

Enhanced gas sensing by assembling Pd nanoparticles onto the surface of SnO2 nanowires

SnO₂ nanowires with an average 0.6 μm in length and about 25 nm in diameter were prepared by a hydrothermal method. The sensors were fabricated using SnO₂ nanowires assembled with Pd nanocrystals. The sensing properties of the sensors such as selectivity, response-recovery time and stability were tested at 290 °C. After assembling Pd nanocrystals onto the surface of SnO₂ nanowires, the gas sensing properties of the sensors toward H₂S were improved. The sensors based on Pd nanoparticle@SnO₂ nanowires exhibit high stability owing to stable single crystal structure. The mechanism of promoting sensing properties with Pd nanoparticles is discussed.     

Preparation of Trace Fe2P Modified N,P Co-doped Carbon Materials and their Application to Hydrogen Peroxide Detection

The determination of hydrogen peroxide (H₂O₂) based on electrochemical sensors is highly attractive in the fields of environmental monitoring and biosensing, however development of non-precious metal-based electrocatalysts with high performances remains challenging. Here, a new non-enzymatic H₂O₂ sensor has been reported by using Fe₂P modified N,P co-doped carbon (Fe₂P/NP-C) materials as sensing materials. Fe₂P/NP-C materials were synthesized by pyrolysis of polydopamine coating Fe-based coordination polymer nanoparticles, which were obtained by direct mixing FeCl₃ and sodium hexametaphosphate at room temperature. The electrochemical tests display that Fe₂P/NP-C-based non-enzymatic H₂O₂ sensor exhibited detection limit of 60 μM and linear range from 0.1 mM to 1 mM, respectively. This work presents a new avenue to design of non-precious metal-based electrocatalysts for chemical sensing and biosensing applications.     

Prussian Blue Nanocubes‐SnO2 Quantum Dots‐Reduced Graphene Oxide Ternary Nanocomposite: An Efficient Non‐noble‐metal Electrocatalyst for Non‐enzymatic Detection of H2O2

Developing non‐noble‐metal electrocatalyst for non‐enzymatic H₂O₂ sensing is highly attractive. A facile, two‐step approach has been utilized for the synthesis of PBNCs/SnO₂ QDs/RGO ternary nanocomposite. TEM, SEM, XPS, and XRD techniques were used to the characterize the structural and morphological properties of synthesized ternary nanocomposite. The synthesized ternary nanocomposite has been examined as an electrode material for the electrochemical detection of H₂O₂ using the Amperometry technique. Under optimum conditions, PBNCs/SnO₂ QDs/RGO ternary nanocomposite performed very well in the electrocatalytic reduction of H₂O₂ with a linear dynamic range from 25–225 μM (R²=0.996) with a low detection limit of 71 nM (S/N=3). Compared to the recent literature, PBNCs/SnO₂QDs/RGO ternary nanocomposite based modified electrode exhibit a wider linear dynamic range with a low detection limit. Furthermore, PBNCs/SnO₂ QDs/RGO ternary nanocomposite based modified electrode showed an excellent anti‐interference ability against various common interfering agents. The practical applicability of this ternary nanocomposite based modified electrode was further extended to determine the H₂O₂ in tap water with acceptable recovery. The present performance of PBNCs/SnO₂ QDs/RGO ternary nanocomposite material towards H₂O₂ sensing might widen its application for developing a new type of non‐noble metal‐based non‐enzymatic electrochemical biosensors.     

Proton‐Conductive 3D LnIII Metal–Organic Frameworks for Formic Acid Impedance Sensing

Metal‐organic frameworks (MOFs) as new classes of proton‐conducting materials have been highlighted in recent years. Nevertheless, the exploration of proton‐conducting MOFs as formic acid sensors is extremely lacking. Herein, we prepared two highly stable 3D isostructural lanthanide(III) MOFs, {(M(μ₃‐HPhIDC)(μ₂‐C₂O₄)_0.5(H₂O))?2 H₂O}_n (M=Tb ( ZZU‐1 ); Eu ( ZZU‐2 )) (H₃PhIDC=2‐phenyl‐1H‐imidazole‐4,5‐dicarboxylic acid), in which the coordinated and uncoordinated water molecules and uncoordinated imidazole N atoms play decisive roles for the high‐performance proton conduction and recognition ability for formic acid. Both ZZU‐1 and ZZU‐2 show temperature‐ and humidity‐dependent proton‐conducting characteristics with high conductivities of 8.95×10^?4 and 4.63×10^?4 S cm^‐1 at 98 % RH and 100 °C, respectively. Importantly, the impedance values of the two MOF‐based sensors decrease upon exposure to formic acid vapor generated from formic aqueous solutions at 25 °C with good reproducibility. By comparing the changes of impedance values, we can indirectly determine the concentration of HCOOH in aqueous solution. The results showed that the lowest detectable concentrations of formic acid aqueous solutions are 1.2×10^?2 mol L^?1 by ZZU‐1 and 2.0×10^?2 mol L^?1 by ZZU‐2 . Furthermore, the two sensors can distinguish formic acid vapor from interfering vapors including MeOH, N‐hexane, benzene, toluene, EtOH, acetone, acetic acid and butane. Our research provides a new platform of proton‐conductive MOFs‐based sensors for detecting formic acid.     

Recent Advances in the Preparation and Applications of Organo‐functionalized Porous Materials

Organo‐functionalized materials with porous structure offer unique adsorption, catalytic and sensing properties. These unique properties make them available for various applications, including catalysis, CO₂ capture and utilization, and drug delivery. The properties and the performance of these unique materials can be altered with suitable modifications on their surface. In this review, we summarize the recent advances in the preparation and applications of organo‐functionalized porous materials with different structures. Initially, a brief historical overview of functionalized porous materials is presented, and the subsequent sections discuss the recent developments and applications of various functional porous materials. In particular, the focus is given on the various methods used for the preparation of organo‐functionalized materials and their important roles in the heterogenization of homogeneous catalysts. A special emphasis is also given on the applications of these functionalized porous materials for catalysis, CO₂ capture and drug delivery.     

Graphene Quantum Dots Assembled with Metalloporphyrins for “Turn on” Sensing of Hydrogen Peroxide and Glucose

Noncovalent and multifunctional hybrids have been generated via π–π stacking and electrostatic interactions by combining the nanometer‐scale graphene structure of graphene quantum dots (GQDs) with Fe^III 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)porphine (FeTMPyP). The inner filter effect (IFE) of FeTMPyP on the GQDs results in substantial PL quenching of the GQDs. The quenched PL of GQDs by the FeTMPyP can be switched back “on” in response to the reaction between FeTMPyP and H₂O₂, which causes rupture of the cyclic tetrapyrrolic nucleus with consequential loss of iron from FeTMPyP, and then proceeds further to produce colorless dipyrroles and monopyrroles. This “turn on” system can be applied for simple and convenient H₂O₂ sensing and can be further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) through the oxidation of glucose and formation of H₂O₂. Because of the inherent synthetic control available for the design of metalloporphyrins, the GQDs‐based optical sensing approach described here has the potential to be highly versatile for other target analytes.     

Rational Syntheses of CdII and PbII Metal‐Organic Frameworks for Luminescence Sensing of Nitroaromatics,Ferric and Chromate Ions

The metal‐organic frameworks (MOFs), {[Cd(L)(H₂O)] · CH₃OH · DMF} ( 1 ) and [Pb(L)(DMF)] ( 2 ) (L = 2,4‐dihydroxybenzaldehyde nicotinoylhydrazone), were synthesized and characterized using microanalyses, IR spectroscopy, and single‐crystal X‐ray diffraction. Single crystal X‐ray analyses revealed that both 1 and 2 exhibit 2D grid networks. The photoluminescence investigation indicates that 1 and 2 could be a prospective candidate for developing luminescencent sensors for the selective sensing of nitrobenzene, which is used as a precursor for explosives. The luminescent properties of 1 and 2 in different solvents were investigated and corroborated by theoretical calculations. Additionally compounds 1 and 2 also show selective sensing ability for Fe³⁺ as well as for CrO₄^2– ions.