A novel electrochemical sensor for formaldehyde based on palladium nanowire arrays electrode in alkaline media

Double-Cabin Galvanic Cell-Synthesizing Nanoporous, Flower-like, Pb-Containing Pd-Au Nanoparticles for Nonenzymatic Formaldehyde Sensor

In this work, a novel formaldehyde sensor was constructed based on nanoporous, flower-like, Pb-containing Pd-Au nanoparticles deposited on the cathode in a double-cabin galvanic cell (DCGC) with a Cu plate as the anode, a multiwalled carbon nanotube-modified glassy carbon electrode as the cathode, a 0.1 M HClO4 aqueous solution as the anolyte, and a 3.0 mM PdCl2 + 1.0 mM HAuCl4 + 5.0 mM Pb(ClO4)2 + 0.1 M HClO4 aqueous solution as the catholyte, respectively. Electrochemical studies reveal that the stripping of bulk Cu can induce underpotential deposition (UPD) of Pb during the galvanic replacement reaction (GRR) process, which affects the composition and morphology of Pb-containing Pd-Au nanoparticles. The electrocatalytic activity of Pb-containing nanoparticles toward formaldehyde oxidation was examined in an alkaline solution, and the experimental results showed that formaldehyde mainly caused direct oxidation on the surface of Pb-containing Pd-Au nanoparticles while inhibiting the formation of CO poison to a large degree. The proposed formaldehyde sensor exhibits a linear amperometric response to formaldehyde concentrations from 0.01 mM to 5.0 mM, with a sensitivity of 666 μA mM-1 cm-2, a limit of detection (LOD) of 0.89 μM at triple signal-to-noise, rapid response, high anti-interference ability, and good repeatability.

Recent Advances in Electrochemical Sensors for Formaldehyde

Formaldehyde, a ubiquitous indoor air pollutant, plays a significant role in various biological processes, posing both environmental and health challenges. This comprehensive review delves into the latest advancements in electrochemical methods for detecting formaldehyde, a compound of growing concern due to its widespread use and potential health hazards. This review underscores the inherent advantages of electrochemical techniques, such as high sensitivity, selectivity, and capability for real-time analysis, making them highly effective for formaldehyde monitoring. We explore the fundamental principles, mechanisms, and diverse methodologies employed in electrochemical formaldehyde detection, highlighting the role of innovative sensing materials and electrodes. Special attention is given to recent developments in nanotechnology and sensor design, which significantly enhance the sensitivity and selectivity of these detection systems. Moreover, this review identifies current challenges and discusses future research directions. Our aim is to encourage ongoing research and innovation in this field, ultimately leading to the development of advanced, practical solutions for formaldehyde detection in various environmental and biological contexts.

IoT Electrochemical Sensor with Integrated Ni(OH)2-Ni Nanowires for Detecting Formaldehyde in Tap Water

Simple, low-cost methods for sensing volatile organic compounds that leave no trace and do not have a detrimental effect on the environment are able to protect communities from the impacts of contaminants in water supplies. This paper reports the development of a portable, autonomous, Internet of Things (IoT) electrochemical sensor for detecting formaldehyde in tap water. The sensor is assembled from electronics, i.e., a custom-designed sensor platform and developed HCHO detection system based on Ni(OH)₂-Ni nanowires (NWs) and synthetic-paper-based, screen-printed electrodes (pSPEs). The sensor platform, consisting of the IoT technology, a Wi-Fi communication system, and a miniaturized potentiostat can be easily connected to the Ni(OH)₂-Ni NWs and pSPEs via a three-terminal electrode. The custom-made sensor, which has a detection capability of 0.8 µM/24 ppb, was tested for an amperometric determination of the HCHO in deionized (DI) and tap-water-based alkaline electrolytes. This promising concept of an electrochemical IoT sensor that is easy to operate, rapid, and affordable (it is considerably cheaper than any lab-grade potentiostat) could lead to the straightforward detection of HCHO in tap water.

Bismuth-coated screen-printed electrodes for the simple voltammetric determination of formaldehyde

For the first time, bismuth modified electrodes have been used for the voltammetric detection of formaldehyde (FM). The well-known method of forming formaldehyde hydrazone (FAH) in the presence of hydrazine sulphate was used to convert the hydrated form of FM into its electrochemically active derivative. Various experimental conditions for differential pulse voltammetry were studied to achieve the best analytical performance. The FAH reduction current (FM response) reaches its maximum value at a pH of a phosphate buffer solution of 5.2 ± 0.1 in the presence of 0.09-0.12 M hydrazine sulfate on a bismuth film preliminarily precipitated for 8-12 min from acidic Bi(III) acetate solutions at an electrolysis potential of -1.0 V on the surface of a screen-printed carbon electrode (SPCE). A dendritic-like film structure was created on the SPCE surface. Under the optimized conditions a linear calibration curve over the range of 0.01-5 mg L^-1 (0.33-167 μM) FM was achieved, with a detection limit of 0.002 mg L^-1 (0.06 μM). The determination of FM in waste water, melt water from snow within the city industrial zone, and a widely used pharmaceutical preparation "Endofalk®" with good results revealed the potential applicability of a bismuth modified SPCE (BiSPCE) for trace analysis.

Flow Injection Amperometric Measurement of Formalin in Seafood

Formalin is illegally used as an antibacterial and a preservative in seafood products. It is extremely important for public health reasons to be able to simply, rapidly, and accurately detect formalin in fresh seafood. In this work, we developed a flow injection amperometric (FI-Amp) formalin sensor based on a glassy carbon electrode modified with a composite of palladium particles and carbon microspheres (PdPs-CMs/GCE). The CMs were decorated with PdPs via an electroless deposition method. The surface morphology of the CMs and the PdPs-CMs composite was characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). The electrochemical behavior and measurement of formalin at the PdPs-CMs/GCE was evaluated by cyclic voltammetry and amperometry. The modified electrode demonstrated good electrocatalytic performance for the oxidation of formalin. The synthesis method and FI-Amp operating conditions were optimized. Under the optimal conditions, the developed sensor showed a linear range of 0.025 to 15.00 mmol L^-1 and a detection limit of 8 μmol L^-1. Repeatability (RSD < 4.1%, n = 30), reproducibility (RSD = 0.25%, n = 5), stability (RSD = 3.2%, n = 80), and selectivity were good. The fabricated sensor achieved recoveries of formalin in seafood between 96 ± 1 to 105 ± 3 (n = 3).

Controlled preparation and gas sensitive properties of two-dimensional and cubic structure ZnSnO3

Two-dimensional (2D) ZnSnO₃ is a promising candidate for future gas sensors due to its high chemical response and excellent electronic properties. However, the preparation of 2D ZnSnO₃ nanosheets by utilizing soluble inorganic salts and nonorganic solvents remains a challenge. In this work, 2D ZnSnO₃ was synthesized via a facile graphene oxide (GO)-assisted co-precipitation method, in which inorganic salts in the aqueous phase replaced metal organic salts in a non-aqueous system. Meanwhile, a "dissolution and recrystallization" mechanism was proposed to explain the transformation from 3D nanocubes to 2D nanosheets. In comparison, the 2D ZnSnO₃ nanosheets showed a higher response to formaldehyde (HCHO) at low operating temperature (100 °C). The response (R_a/R_g) of the 2D ZnSnO₃ sensor to 10 ppm HCHO was as high as 57, which was approximately 5 times the response of the ZnSnO₃ nanocubes sensor. However, the ZnSnO₃ nanocubes sensor showed better gas sensing performance to ethanol at high temperature (200 °C). Different gas-sensitive properties were attributed to the different gas diffusion and adsorption processes caused by the morphology and nanostructure. Moreover, both sensors could detect either 0.1 ppm HCHO or ethanol at their optimum operating temperature. This work presents a relatively economical method to prepare 2D compound metal oxides, provides a novel "dissolution and recrystallization" mechanism for 2D multi-metal oxide preparation, and sheds light on the great potential of high-efficiency HCHO and/or ethanol gas sensors.

Practical and Efficient: A Pocket-Sized Device Enabling Detection of Formaldehyde Adulteration in Vegetables

Formaldehyde, as a carcinogenic substance, is often intentionally used to adulterate vegetables to increase their shelf life, and the adhesive tape used to attach labels can also leave formaldehyde on the surface of vegetables. However, as the "gold" standard, gas chromatography (GC) and high-performance liquid chromatography (HPLC) are expensive for individual tests and confined to the laboratory owing to their size and a suitable detector (low-cost, portable, fast detection speed) to check formaldehyde contamination in vegetables not being available. Here, we tested formaldehyde contamination in vegetables using a low-cost and hand-held detector combined with a screen-printed electrode (SPE) amperometric sensor and an open-sourced potentiostat. The analyzer can detect a concentration of 100 μmol/L formaldehyde and achieve a good linear range between 100 and 1000 μmol/L. Furthermore, the detector successfully identified formaldehyde contamination in 53 samples of six different kinds of vegetables even after residual formaldehyde on the surface was evaporated. Most importantly, under the practicability-oriented idea, a cost-effective strategy was implemented for this detector design rather than using other pricey methods (e.g., photolithography, electron-beam evaporation, chemical deposition), which enormously reduces the cost (under ∼USD 0.5 per test) and meets all of the requirements of ASSURED device. We believe this cheap, portable detector could help law-enforcing authorities, healthcare workers, and customers to screen formaldehyde contamination easily. Also, the cost-saving strategy is appropriate for low-income areas, where there is a lack of laboratories, funds, and trained experts.

Luminescence turn-on response of naphthalene diimide based chemosensor with Formaldehyde: A novel stratagem for estimation of formaldehyde in storage fish samples

A new strategy has been developed for selective estimation of toxic Formaldehyde (FA) in storage fish samples by a simple chemosensor (BNDI) based on naphthalene diimide core in aqueous medium at neutral pH. The rapid "lightning-up" fluorescence feature of BNDI has been implied to detect and estimate aqueous FA selectively at very low concentration. The chemosensing properties of BNDI with aqueous FA have been established through a unique interaction pattern which is proven by different spectroscopic and theoretical analysis.

A novel tool for the adsorption of dsDNA: Electrochemical reduction of Pd nanoparticles onto reduced-keratin particles extracted from wool wastes

This work outlines the fabrication of a novel electrochemical platform for the dsDNA adsorption, using one of the most sustainable materials, wool fabric waste, and Pd²⁺ ions. To develop a functional material with a significant adsorption capability, the waste wool was subjected to the chemical reduction process, and the keratin-SH (KerSH) particles were extracted in powder form. These particles were used in the adsorption of Pd²⁺ ions by monitoring with the UV-vis spectra. The dispersion of the KerSH-Pd²⁺ particles was subsequently drop-casted onto a glassy carbon electrode (GCE) and electrochemically reduced to the GCE/KerSH-PdNPs composite by chronoamperometry at -0.4 V for 500 s. It was found that the KerSH particles were self-assembled by revealing chemically attractive NH₂ groups after the electrochemical PdNPs deposition. A GCE/KerSH-PdNPs composite was then employed in the electrochemical dsDNA detection by Differential Pulse Voltammetry (DPV), using the oxidation signals of guanine and adenine bases at 0.8 V and 1.2 V, respectively. Accordingly, relatively stable, repeatable, and reproducible dsDNA adsorption was ensured through the positively charged-NH₂ groups of KerSH-PdNPs. This finding reveals the potential of textile waste for various electrochemical applications, such as DNA biosensors for environmental, pharmaceutical, and medicinal fields.

4-Hydroxy-2-nonenal, a lipid peroxidation product, as a biomarker in diabetes and its complications: challenges and opportunities

Over 30 million Americans are diagnosed with diabetes and this number is only expected to increase. There are various causes that induce complications with diabetes, including oxidative stress. In oxidative stress, lipid peroxidation-derived reactive carbonyl species such as 4-hydroxy-2-nonenal (4-HNE) is shown to cause damage in organs that leads to diabetic complications. We provided evidence to show that 4-HNE or/and 4-HNE-protein adducts are elevated in various organ systems of diabetic patients and animal models. We then discussed the advantages and disadvantages of different methodologies used for the detection of 4-HNE in diabetic tissues. We also discussed how novel approaches such as electrochemistry and nanotechnology can be used for monitoring 4-HNE levels in biological systems in real-time. Thus, this review enlightens the involvement of 4-HNE in the pathogenesis of diabetes and its complications and efficient methods to identify it. Furthermore, the article presents that 4-HNE can be developed as a biomarker for end-organ damage in diabetes such as diabetic cardiac complications.

Structural and Optical Response of Polymer-Stabilized Blue Phase Liquid Crystal Films to Volatile Organic Compounds

Engineering useful mechanical properties into stimuli-responsive soft materials without compromising their responsiveness is, in many cases, an unresolved challenge. For example, polymer networks formed within blue-phase liquid crystals (BPs) have been shown to form mechanically robust films, but the impact of polymer networks on the response of these soft materials to chemical stimuli has not been explored. Here, we report on the response of polymer-stabilized BPs (PSBPs) to volatile organic compounds (VOCs, using toluene as a model compound) and compare the response to BPs without polymer stabilization and to polymerized nematic and cholesteric phases. We find that PSBPs generate an optical response to toluene vapor (change in reflection intensity under crossed polars) that is sixfold greater in sensitivity than the polymerized nematic or cholesteric phases and with a limit of detection (140 ± 10 ppm at 25 °C) that is relevant to the measurement of permissible exposure limits for humans. Additionally, when compared to BPs that have not been polymerized, PSBPs respond to a broader range of toluene vapor concentrations (5000 vs <1000 ppm) over a wider temperature interval (25-45 vs 45-53 °C). We place these experimental observations into the context of a simple thermodynamic model to explore how the PSBP response reflects the effect of toluene on competing contributions of double-twisted LC cylinders, disclinations, and polymer network to the free energy that controls the PSBP lattice spacing. Overall, we conclude that the mechanical and thermal stability of PSBPs, when combined with their optical responsiveness to toluene, make this class of self-supporting LCs a promising one as the basis of passive and compact (e.g., wearable) sensors for VOCs.

Facile and scalable fabrication of nanostructured nickel thin film electrodes for electrochemical detection of formaldehyde

Fluorine doped tin oxide (FTO) substrates were deposited with thin metallic nickel films, having distinguishable surface morphologies, via a rapid, facile, and scalable approach i.e., aerosol assisted chemical vapor deposition (AACVD). The growth patterns of the nickel deposits were studied, showing a coalescing behavior as a function of the deposition time in a hierarchical fashion. These studies were followed by electrochemical measurements to design an efficient sensor for formaldehyde detection. The electrochemical responses were correlated with the surface characteristics of the films, whereas the optimized parameters were subjected to the evaluation of sensing performances. The developed sensor demonstrated a detection limit of 8.3 × 10^-6 M and a sensitivity of 0.18 A M^-1 within a linear range of 0-6.5 mM. Further, the sensor showed a response time of less than 5 s, selectivity against similar concentrations of methanol and formaldehyde, and recovery of ∼102% in a spiked fruit juice sample. Finally, the commercial viability of the fabrication procedure is tested using batch production analysis, and the high reproducibility of the data shows a promising future in mass production. It is envisaged that such low-cost fabrication procedures can be converted into many useful applications in the future.

Synthesis of Polyaniline/Graphene Nanocomposites and Electrochemical Sensing Performance for Formaldehyde

Background:

Formaldehyde has been recognized as the important liquid environmental pollutant which can cause health risk. Great effort has been devoted to detecting formaldehyde in liquid environment. It is of important significance to develop a sensitive method for measuring formaldehyde from the environmental and health viewpoints.

Methods:

Polyaniline/graphene nanocomposites have been prepared by a simple in-situ polymerization process using graphene and aniline as the raw materials. The nanocomposites were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) and high-resolution TEM (HRTEM). The polyaniline/graphene nanocomposites were applied to modify the glassy carbon electrode for the detection of formaldehyde by cyclic voltammetry (CV) method.

Results:

The polyaniline/graphene nanocomposites consist of hexagonal graphite phase. The polyaniline particles are dispersed and attached to the surface of the graphene nanosheet-shaped morphology. The thickness of the graphene nanosheets is less than 50 nm. The electrocatalytic performance of the polyaniline/graphene nanocomposites modified glassy carbon electrode towards formaldehyde was obtained. The potential of the irreversible oxidation peak is located at +0.19 V. The polyaniline/graphene nanocomposites modified glassy carbon electrode shows a wide linear range of 0.0001-2 mM and low detection limit of 0.085 μM.

Conclusion:

The nanocomposites modified glassy carbon electrode possesses good reproducibility and stability. The polyaniline/graphene nanocomposites show great application potential for the electrochemical sensors to detect formaldehyde in liquid environments.

Formation and Corrosion Behavior of Nickel/Alumina Nanocomposites

Ni nanopillars (Ni NPs) composite materials formation technology was presented. The morphological and structural properties of the composite material were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction. The corrosion resistance of the nanocomposite materials has been studied by potentiodynamic polarization curves analysis. The composite represents the array of vertically ordered Ni NPs with the identical size in alumina matrix. XRD investigation indicates that Ni NPs are polynanocrystalline material. It has been shown that Ni NPs and the composite material have sufficient corrosion resistance in a 0.9% aqueous NaCl solution. Porous alumina matrix is the neutral and protective component of the composite. These nanocomposite materials can be excellent candidates for practical use in different applications.

Synthesis, growth mechanisms, and applications of palladium-based nanowires and other one-dimensional nanostructures

Palladium-based nanostructures have attracted the attention of researchers due to their useful catalytic properties and unique ability to form hydrides, which finds application in hydrogen storage and hydrogen detection. Palladium-based nanowires have some inherent advantages over other Pd nanomaterials, combining high surface-to-volume ratio with good thermal and electron transport properties, and exposing high-index crystal facets that can have enhanced catalytic activity. Over the past two decades, both synthesis methods and applications of 1D palladium nanostructures have advanced greatly. In this review, we start by discussing different types of 1D palladium nanostructures before moving on to the different synthesis approaches that can produce them. Next, we discuss factors including kinetic vs. thermodynamic control of growth, oxidative etching, and surface passivation that affect palladium nanowire synthesis. We also review efforts to gain insight into growth mechanisms using different characterization tools. We discuss the effects of concentration of capping agents, reducing agents, metal halides, pH, and sacrificial oxidation on the growth of Pd-based nanowires in solution, from shape control, to yield, to aspect ratio. Various applications of palladium and palladium alloy nanowires are then discussed, including electrocatalysis, hydrogen storage, and sensing of hydrogen and other chemicals. We conclude with a summary and some perspectives on future research directions for this category of nanomaterials.

Voltammetric sensing of formaldehyde by using a nanocomposite prepared by reductive deposition of palladium and platinum on polypyrrole-coated nitrogen-doped reduced graphene oxide

The study presents the synthesis of polypyrrole-coated palladium platinum/nitrogen-doped reduced graphene oxide nanocomposites (PdPt-PPy/N-rGO NC) via direct the reduction of Pd(II) and Pt(II) in the presence of pyrrole monomer, N-rGO and L-cysteine as the reducing agent. X-ray diffraction confirmed the presence of metallic Pd and Pt from the reduction of Pd and Pt cations. Transmission electron microscopy images revealed the presence of Pd, Pt and PPy deposition on N-rGO. Impedance spectroscopy results gave a decreased charge transfer resistance due to the presence of N-rGO. The nanocomposites were synthesized with different Pd/Pt ratios (2:1, 1:1 and 1:2). A glassy carbon electrode (GCE) modified with the nanocomposite showed enhanced electrochemical sensing capability for formaldehyde in 0.1 M sulfuric acid solution. Cyclic voltammetry showed an increase in the formaldehyde oxidation peak current at the GCE modified with Pd₂Pt₁ PPy N-rGO. At a typical potential of 0.45 V (vs. SCE), the sensitivity in the linear segment was 345.8 μA.mM ^-1. cm^-2. The voltammetric response was linear between 0.01 and 0.9 mM formaldehyde concentration range, with a 27 µM detection limit (at S/N = 3). Graphical abstract Schematic presentation of formaldehyde detection by Pd₂Pt₁-PPy/nitrogen-doped reduced Graphene Oxide Nanocomposite (Pd₂Pt₁-PPy /N-Gr NC). The decrease of charge transfer resistance and the agglomeration of deposited metals in the presence of N-rGO enhance the current response of the electrochemical sensor.

Responsive Photonic Hydrogel-Based Colorimetric Sensors for Detection of Aldehydes in Aqueous Solution

In this work, we present a fast and efficient strategy for the preparation of responsive photonic hydrogels for aldehyde sensing by combining the self-assembly of monodisperse carbon-encapsulated Fe₃O₄ nanoparticles (NPs) and in situ photopolymerization of polyacrylamide (PAM) hydrogels. The responsive photonic hydrogels exhibit structural color variation after being treated with formaldehyde aqueous solution, which can be attributed to the chemical reaction between the amide groups in the hydrogels and the formaldehyde. We have also shown that the photonic hydrogels can be used to determine the concentration of formaldehyde and to differentiate aldehydes through a facile reflection spectra shift and color change. This study provides a facile strategy for the visualized determination of aldehyde in aqueous solution.

A Formaldehyde Sensor Based on Molecularly-Imprinted Polymer on a TiO₂ Nanotube Array

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO₂-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO₂-NTA.

Defect-free functionalized graphene sensor for formaldehyde detection

Graphene has attracted much attention for sensing applications in recent years. Its largest surface-to-volume ratio makes graphene sensors able to potentially detect a single molecule and its extremely high carrier mobility ensures low electrical noise and energy consumption. However, pristine graphene is chemically inert and weakly adsorbs gas molecules, while defective and/or doped graphene has stronger adsorption ability (high sensitivity). The high sensitivity is related to the increased number of defects or traps in graphene where the gas molecules can be readily grafted, changing the sensor resistance. Nonetheless, similar resistance changes could be induced under exposure to different gases, resulting in a lack of selectivity. Functional groups differ drastically from defects or traps since the former selectively anchor specific molecules. Here, we comparatively investigate three functionalization routes and optimize a defect-free one (2,3,5,6,-Tetrafluorohydroquinone, TFQ molecules) for the fabrication of graphene gas sensors. We use TFQ organic molecules as chemical recognition links between graphene and formaldehyde, the most common indoor pollutant gas. The sensor demonstrates a high response and a good selectivity for formaldehyde compared with interfering organic vapours. Particularly, the sensor has a strong immunity to humidity. Our results highlight that defect-free functionalization based on organic molecules not only increases the sensor's response but also its selectivity, paving the way to the design of efficient graphene-based sensors.

Electrocatalysis on copper–palladium alloys for amperometric formaldehyde sensing

A co-evaporated Cu–Pd thin film combinatorial library was screened for electrocatalytic oxidation of formaldehyde by scanning droplet cell microscopy. The best activity was found for 7.5 at% Pd and an amperometric sensor was fabricated and tested.

Cuprous oxide template synthesis of hollow-cubic Cu2O@PdxRuynanoparticles for ethanol electrooxidation in alkaline media

Surfactant-free and low Pd loading Cu₂O@Pd_xRu_yhollow-cubes were facilely prepared and their electrocatalytic performance for ethanol electrooxidation were investigated.

PdPt bimetallic alloy nanowires-based electrochemical sensor for sensitive detection of ascorbic acid

A novel PdPt bimetallic alloy nanowires-based electrochemical sensor for sensitive detection of ascorbic acid with remarkable electrocatalytic activity in a wide linear range (0.01–0.97 mM) and a detection limit as low as 0.2 μM.

An electrochemical impedimetric sensor based on biomimetic electrospun nanofibers for formaldehyde

Herein, simple molecular recognition sites for formaldehyde were designed on electrospun polymer nanofibers.