Sensor and biosensor preparation, optimisation and applications of Prussian Blue modified electrodes

A Label and Probe-Free Zika Virus Immunosensor Prussian Blue@carbon Nanotube-Based for Amperometric Detection of the NS2B Protein

Zika virus (ZIKV) is a mosquito-borne infection, predominant in tropical and subtropical regions causing international concern due to the ZIKV disease having been associated with congenital disabilities, especially microcephaly and other congenital abnormalities in the fetus and newborns. Development of strategies that minimize the devastating impact by monitoring and preventing ZIKV transmission through sexual intercourse, especially in pregnant women, since no vaccine is yet available for the prevention or treatment, is critically important. ZIKV infection is generally asymptomatic and cross-reactivity with dengue virus (DENV) is a global concern. An innovative screen-printed electrode (SPE) was developed for amperometric detection of the non-structural protein (NS2B) of ZIKV by exploring the intrinsic redox catalytic activity of Prussian blue (PB), incorporated into a carbon nanotube–polypyrrole composite. Thus, this immunosensor has the advantage of electrochemical detection without adding any redox-probe solution (probe-less detection), allowing a point-of-care diagnosis. It was responsive to serum samples of only ZIKV positive patients and non-responsive to negative ZIKV patients, even if the sample was DENV positive, indicating a possible differential diagnosis between them by NS2B. All samples used here were confirmed by CDC protocols, and immunosensor responses were also checked in the supernatant of C6/36 and in Vero cell cultures infected with ZIKV.

Paper-based electrochemical sensor for on-site detection of the sulphur mustard

Herein, we report a novel paper-based electrochemical sensor for on-site detection of sulphur mustards. This sensor was conceived combining office paper-based electrochemical sensor with choline oxidase enzyme to deliver a sustainable sensing tool. The mustard agent detection relies on the evaluation of inhibition degree of choline oxidase, which is reversibly inhibited by sulphur mustards, by measuring the enzymatic by-product H₂O₂ in chronoamperometric mode. A nanocomposite constituted of Prussian Blue nanoparticles and Carbon Black was used as working electrode modifier to improve the electroanalytical performances. This bioassay was successfully applied for the measurement of a sulphur mustard, Yprite, obtaining a detection limit in the millimolar range (LOD = 0.9 mM). The developed sensor, combined with a portable and easy-to-use instrumentation, can be applied for a fast and cost-effective detection of sulphur mustards.

Synthesizing Electrodes Into Electrochemical Sensor Systems

Electrochemical sensors that can determine single/multiple analytes remain a key challenge in miniaturized analytical systems and devices. In this study, we present in situ synthesis and modification of gold nanodendrite electrodes to create an electrochemical system for the analysis of hydrogen peroxide. The sensor system consisted of the reference and counter electrodes as well as the working electrode. Electrochemical reduction of graphene oxide, ErGO, on the thin-film gold and gold nanodendrite working electrodes was used to achieve an efficient sensor interface for the adsorption of a biomimetic electrocatalytic sensor material, Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin complex, with as high as 10^-10 mol cm^-2 surface coverage. The sensor system demonstrated a detection limit of 0.3 µM H₂O₂ in the presence of oxygen. Electrochemical determination of hydrogen peroxide in plant material in the concentration range from 0.09 to 0.4 µmol (gFW)^-1 using the electrochemical sensor system was shown as well as in vivo real-time monitoring of the hydrogen peroxide dynamics as a sign of abiotic stress (intense sunlight). Results of the electrochemical determination were in good agreement with the results of biochemical analysis with the spectrophotometric detection. We anticipate that this method can be extended for the synthesis and integration of multisensor arrays in analytical microsystems and devices for the quantification and real-time in vivo monitoring of other analytes and biomarkers.

A paper-based electrochemical sensor for H2O2 detection in aerosol phase: Measure of H2O2 nebulized by a reconverted ultrasonic aroma diffuser as a case of study

The outbreak of COVID-19 is caused by high contagiousness and rapid spread of SARS-CoV-2 virus between people when an infected person is in close contact with another one. In this overall scenario, the disinfection processes have been largely improved. For instance, some countries have approved no-touch technologies by vaporizing disinfectants such as hydrogen peroxide, with the overriding goal to boost the safety of the places. In the era of sustainability, we designed an electrochemical paper-based device for the assessment of hydrogen peroxide nebulized by a cost-effective ultrasonic aroma diffuser. The paper-based sensor was fabricated by modifying via drop-casting a filter paper-based screen-printed electrode with a dispersion of carbon black-Prussian Blue nanocomposite, to assess the detection of hydrogen peroxide at −0.05 V vs Ag/AgCl. The use of paper-based modified screen-printed electrode loaded with phosphate buffer allowed for monitoring the concentration of hydrogen peroxide in aerosol, without any additional sampling instrument to capture the nebulized solution of hydrogen peroxide at a concentration up to 7% w/w. Hydrogen peroxide, a reconverted ultrasonic aroma diffuser, and the paper-based electrochemical sensor assisted by smartphone have demonstrated how different low-cost technologies are able to supply an useful and cost-effective solution for disinfection procedures.

Precise and rapid solvent-assisted geometric protein self-patterning with submicron spatial resolution for scalable fabrication of microelectronic biosensors

Precise and high-resolution coupling of functional proteins with micro-transducers is critical for the manufacture of miniaturized bioelectronic devices. Moreover, electrochemistry on microelectrodes has had a major impact on electrochemical analysis and sensor technologies, since the small size of microelectrode affects the radial diffusion flux of the analyte to deliver enhanced mass transport and electrode kinetics. However, a large technology gap has existed between the process technology associated with such microelectronics and the conventional bio-conjugation techniques that are generally used. Here, we report on a high-resolution and rapid geometric protein self-patterning (GPS) method using solvent-assisted protein-micelle adsorption printing to couple biomolecules onto microelectrodes with a minimum feature size of 5 μm and a printing time of about a minute. The GPS method is versatile for micropatterning various biomolecules including enzymes, antibodies and avidin-biotinylated proteins, delivering good geometric alignment and preserving biological functionality. We further demonstrated that enzyme-coupled microelectrodes for glucose detection exhibited good electrochemical performance which benefited from the GPS method to maximize effective signal transduction at the bio-interface. These microelectrode arrays maintained fast convergent analyte diffusion displaying typical steady-state I-V characteristics, fast response times, good linear sensitivity (0.103 nA mm^-2 mM^-1, R² = 0.995) and an ultra-wide linear dynamic range (2-100 mM). Our findings provide a new technical solution for the precise and accurate coupling of biomolecules to a microelectronic array with important implications for the scaleup and manufacture of diagnostics, biofuel cells and bioelectronic devices that could not be realized economically by other existing techniques.

Development of a multiparametric (bio)sensing platform for continuous monitoring of stress metabolites

There is a growing need for real-time monitoring of metabolic products that could reflect cell damages over extended periods. In this paper, we report the design and development of an original multiparametric (bio)sensing platform that is tailored for the real-time monitoring of cell metabolites derived from cell cultures. Most attractive features of our developed electrochemical (bio)sensing platform are its easy manufacturing process, that enables seamless scale-up, modular and versatile approach, and low cost. In addition, the developed platform allows a multiparametric analysis instead of single-analyte analysis. Here we provide an overview of the sensors-based analysis of four main factors that can indicate a possible cell deterioration problem during cell-culture: pH, hydrogen peroxide, nitric oxide/nitrite and lactate. Herein, we are proposing a sensors platform based on thick-film coupled to microfluidic technology that can be integrated into any microfluidic system using Luer-lock connectors. This platform allows obtaining an accurate analysis of the secreting stress metabolites during cell/tissues culture.

Designing of Nanomaterials-Based Enzymatic Biosensors: Synthesis, Properties, and Applications

Among the many biological entities employed in the development of biosensors, enzymes have attracted the most attention. Nanotechnology has been fostering excellent prospects in the development of enzymatic biosensors, since enzyme immobilization onto conductive nanostructures can improve characteristics that are crucial in biosensor transduction, such as surface-to-volume ratio, signal response, selectivity, sensitivity, conductivity, and biocatalytic activity, among others. These and other advantages of nanomaterial-based enzymatic biosensors are discussed in this work via the compilation of several reports on their applications in different industrial segments. To provide detailed insights into the state of the art of this technology, all the relevant concepts around the topic are discussed, including the properties of enzymes, the mechanisms involved in their immobilization, and the application of different enzyme-derived biosensors and nanomaterials. Finally, there is a discussion around the pressing challenges in this technology, which will be useful for guiding the development of future research in the area.

Determination of the Antioxidant Activity of Samples of Tea and Commercial Sources of Vitamin C, Using an Enzymatic Biosensor

Antioxidants are synthetic or natural compounds capable of preventing or delaying oxidative damage caused by chemical species that can oxidize cell biomolecules, such as proteins, membranes, and DNA, leading to the development of various pathologies, such as cancer, atherosclerosis, Parkinson, Alzheimer, and other diseases serious. In this study, an amperometric biosensor was used to determine the antioxidant activity of teas and effervescent products based on vitamin C, available on the market. A sensor composed of three electrodes was used. The performance of the following electrochemical mediators was evaluated: meldola blue combined with Reineck salt (MBRS), Prussian blue (PB), and cobalt phthalocyanine (CoPC), as well as the time of polymerization in the enzymatic immobilization process and the agitation process during chronoamperometric measurements. Prussian blue proved to be more efficient as a mediator for the desired purposes. After optimizing the construction stages of the biosensor, as well as the operational parameters, it presented stability for a period of 7 months. The results clearly indicate that the biosensor can be successfully used to detect fraud in products called "antioxidants" or even in drugs containing less ascorbic acid than indicated on the labels. The detection limit was set at 4.93 µmol·L^-1.

Highly sensitive real-time detection of intracellular oxidative stress and application in mycotoxin toxicity evaluation based on living single-cell electrochemical sensors

Single-cell electrochemical sensor is widely used in the local selective detection of single living cells because of its high spatial-temporal resolution and sensitivity, as well as its ability to obtain comprehensive cellular physiological states and processes with increased accuracy. Functionalized nanoprobes can detect the oxidative stress response of cells in single-cell electrochemical sensors. Moreover, the T-2 toxin is one of the most toxic mycotoxins and widely occurs in field crops. T-2 toxin can cause mitochondrial damage in cells and increase intracellular reactive oxygen species (ROS) in various cells. As the most representative free radical of intracellular ROS, H₂O₂ can effectively reflect the toxic effects of intracellular T-2 toxin. In this study, a functionalized gold nanoprobe was used to dynamically monitor the production of H₂O₂ in a single live human hepatoma cell HepG2 stimulated by mycotoxin T-2. The concentration of H₂O₂ produced by HepG2 cells stimulated by T-2 toxin at 1 ppb-1 ppm was linearly correlated, R² = 0.99055, and LOD = 0.13807 ng mL^-1. Sample spiking experiments were conducted, and the recovery rate of spiking was 81.19%-130.17%. A comparative analysis of differences in the current produced by multiple toxins, HT-29 cells, as well as single cells in cell populations, was performed. This method can be applied in real-time monitoring of mycotoxin toxicity during food processing in living cells and provides a novel idea for enhancing food quality and safety in a nanoenvironment.

Prussian blue-carboxylated MWCNTs/ZIF-67 composite: a new electrochemical sensing platform for paracetamol detection with high sensitivity

In this study, the composite of Prussian blue-carboxylated MWCNTs/ZIF-67 (PB-MWCNTs-COOH/ZIF-67) was synthesized and used as modified electrode material to fabricate an electrochemical sensor for the determination of paracetamol (PAR). In this sensor system, negatively charged MWCNTs-COOH as support for the immobilization of positively charged PB can effectively avoid the agglomeration of PB and enhance the stability, conductivity and catalytic activity of the composite. ZIF-67 particles coating outside PB-MWCNTs-COOH promotes the concentration of PAR. Benefiting from the synergistic effect, the PB-MWCNTs-COOH/ZIF-67 based sensor exhibits significantly improved electrochemical sensing behavior toward the oxidation of PAR. Under the optimum conditions, the PAR sensor presents wide linear ranges of 0.01-70 μM with a low limit of detection of 3.3 nM (S/N = 3). The method also possesses long-term stability, good reproducibility and selectivity, and was employed to the determination of PAR contents in PAR tablets sample.

Sonochemical coating of Prussian Blue for the production of smart bacterial-sensing hospital textiles

In healthcare facilities, environmental microbes are responsible for numerous infections leading to patient's health complications and even death. The detection of the pathogens present on contaminated surfaces is crucial, although not always possible with current microbial detection technologies requiring sample collection and transfer to the laboratory. Based on a simple sonochemical coating process, smart hospital fabrics with the capacity to detect live bacteria by a simple change of colour are presented here. Prussian Blue nanoparticles (PB-NPs) are sonochemically coated on polyester-cotton textiles in a single-step requiring 15 min. The presence of PB-NPs confers the textile with an intensive blue colour and with bacterial-sensing capacity. Live bacteria in the textile metabolize PB-NPs and reduce them to colourless Prussian White (PW), enabling in situ detection of bacterial presence in less than 6 h with the bare eye (complete colour change requires 40 h). The smart textile is sensitive to both Gram-positive and Gram-negative bacteria, responsible for most nosocomial infections. The redox reaction is completely reversible and the textile recovers its initial blue colour by re-oxidation with environmental oxygen, enabling its re-use. Due to its simplicity and versatility, the current technology can be employed in different types of materials for control and prevention of microbial infections in hospitals, industries, schools and at home.

The Application of Prussian Blue Nanoparticles in Tumor Diagnosis and Treatment

Prussian blue nanoparticles (PBNPs) have attracted increasing research interest in immunosensors, bioimaging, drug delivery, and application as therapeutic agents due to their large internal pore volume, tunable size, easy synthesis and surface modification, good thermal stability, and favorable biocompatibility. This review first outlines the effect of tumor markers using PBNPs-based immunosensors which have a sandwich-type architecture and competitive-type structure. Metal ion doped PBNPs which were used as T1-weight magnetic resonance and photoacoustic imaging agents to improve image quality and surface modified PBNPs which were used as drug carriers to decrease side effects via passive or active targeting to tumor sites are also summarized. Moreover, the PBNPs with high photothermal efficiency and excellent catalase-like activity were promising for photothermal therapy and O2 self-supplied photodynamic therapy of tumors. Hence, PBNPs-based multimodal imaging-guided combinational tumor therapies (such as chemo, photothermal, and photodynamic therapies) were finally reviewed. This review aims to inspire broad interest in the rational design and application of PBNPs for detecting and treating tumors in clinical research.

LDI-MS scanner: Laser desorption ionization mass spectrometry-based biosensor standardization

Amperometric biosensors have been widely utilized for the cost-effective and rapid analysis of various bioanalytes, for example glucose. However, a lack of standardization and validation procedures remains a major limitation in biosensor development. Therefore, despite rapid advances in material science driving the development of amperometric biosensors, to date only a few biosensors, detecting a limited range of analytes, are available on the market. It is believed, once this issue is addressed, it can significantly facilitate the next step in the overall concept "go to the market" production and implementation of amprerometric biosensors for a large industrial scale. Herein, we report on the use of laser desorption ionization mass spectrometry (LDI-MS) for the standardization of amperometric biosensors, based upon a complete and non-destructive characterization and validation of layer-by-layer (LbL) biosensors at each fabrication step. We reveal that specific ionization pathways of mediators, polymers and enzymes from the biosensor surface allows for robust quality control during LbL biosensor manufacture. Furthermore, this LDI-MS approach can also be used to monitor, and therefore ensure, the encapsulation of enzymes in one-step nanobiosensors. Specifically, we show that LDI-MS can be used for the rapid chemical profiling of LbL biosensors and one-step synthesized nanobiosensors, as well as to assess their synthesis quality and to monitor for batch-to-batch and intra- and inter-day changes in their function and behavior. Our novel approach will thus contribute to the future development, improved design and fine tuning of both conventional LbL-fabricated amperometric biosensors and one-step designed nanobiosensors.

Plasmonic active film integrating gold/silver nanostructures for H2O2 readout

A nanostructured Ag/Au adhesive film for H₂O₂ reagentless determination is here proposed. The film has been realised onto ELISA polystyrene microplates. Microwells surface has been initially modified with a gold nanoparticles (AuNPs)/polydopamine thin-film. The pristine AuNPs-decorated film was later functionalized with catechin (Au-CT) allowing a uniform formation of a plasmonic active nanostructured silver network in presence of Ag⁺. Changes in localized surface plasmon resonance (LSPR) of the silver network upon addition of H₂O₂ has been used as analytical signal, taking advantage of the etching phenomenon. The Ag/Au nanocomposite-film is characterized by a well-defined (LSPR_max = 405 ± 5 nm), reproducible (intraplate RSD ≤ 9.8%, n = 96; inter-plate RSD ≤ 11.4%, n = 480) and stable LSPR signal. The film's analytical features have been tested for H₂O₂ and glucose (bio)sensing. Satisfactory analytical performances were obtained both for H₂O₂ (linear range 1-200 μM, R² = 0.9992, RSD ≤ 6.3%, LOD = 0.2 μM) and glucose (linear range 2-250 μM, R² = 0.9998, RSD ≤ 8.9%, LOD = 0.4 μM). As proof of applicability, the determination of the two analytes in soft drinks has been carried out achieving good and reproducible recoveries (84-111%; RSD ≤ 9%). The developed nanostructured film overcomes analytical drawbacks associated with the use of colloidal dispersions in plasmonic assays carried out in solution; the low cost, robustness, ease of use and possibility of coupling enzymatic reactions appears very promising for (bio)sensors based on the detection of H₂O₂.

One-step modification of nano-polyaniline/glucose oxidase on double-side printed flexible electrode for continuous glucose monitoring: Characterization, cytotoxicity evaluation and in vivo experiment

The single-step modification of the nanostructured polyaniline (PANI)/glucose oxidase (GOD) enzyme on double-sided, screen-printed, flexible electrodes doped with Prussian blue (PB), has been achieved and successfully applied in continuous glucose monitoring in vivo, and its biocompatibility has been evaluated systematically. The proposed fabrication procedure is simple, low cost, and suitable for large-scale production. PB doped with carbon ink catalyzes the reduction of hydrogen peroxide (H₂O₂) in low-voltage conditions, which could help eliminate interferences. And the PANI/GOD nanostructure makes the GOD enzyme more stable for long-term, in vivo monitoring. More importantly, a polyurethane (PU) layer is deposited on the electrode's surface as a diffusion limiting membrane that enhanced the linear range and biocompatibility. In tests in vitro, the proposed biosensor achieved a linear range of 0-12 mM and a good sensitivity of 16.66 μA·mM^-1·cm^-2(correlation coefficient R² = 0.9962) with an excellent specificity to glucose. The biosensor exhibits long-term stability, with a maximum lifespan of 14 days when stored in phosphate buffer solution at 4 °C, and achieves a sensitivity of 120%. The biocompatibilities of the electrode materials have also been systematically evaluated in cytotoxicity and cell adhesion tests to ensure the safety of implantation. In experiments in vivo, the biosensor can successfully monitor the glucose level fluctuation of rats after 24 h following implantation. Overall, the biosensor fabricated with the double-side, screen-printing process, satisfies the glucose monitoring range in vivo and eliminates various types of interference, thus establishing a new, large-scale production procedure for flexible in vivo biosensors.

Electroactive magnetic microparticles for the selective elimination of cesium ions in the wastewater

To improve operability as well as the removal efficiency for cesium ions in the wastewater treatment, a novel electrochemically switched ion exchange (ESIX) technique by using electroactive Prussian-blue(PB)-based magnetic microparticles (PB@Fe₃O₄ microparticle) with different uniform particle sizes in the range of 300-900 nm as the adsorption materials was developed. The obtained PB@Fe₃O₄ microparticle were characterized by Scanning electron microscopy (SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and Thermogravimetric analysis (TGA). It is found that the PB can be well coated on the surface of Fe₃O₄ microsphere, which can be easily adsorbed on the magnetic electrode substrate for the electrochemical adsorption of Cs⁺ ions. Electrochemical adsorption of 97% Cs⁺ on PB/Fe₃O₄ was achieved in less than 10 min, and the maximum adsorption capacity was 16.13 mg/g, and the distribution coefficient (K_D) of Cs⁺ ions reached as high as 3938. In addition, the electrochemical adsorption behavior of PB@Fe₃O₄ microparticle fitted well with the Freundlich adsorption isotherm and the Pseudo-second-order kinetic models. It is expected that such an ESIX technique using PB@Fe₃O₄ microparticle can be applied for the separation and recovery of dilute Cs⁺ ions from cesium-contaminated solution in a practical process.

A Highly Sensitive Amperometric Glutamate Oxidase Microbiosensor Based on a Reduced Graphene Oxide/Prussian Blue Nanocube/Gold Nanoparticle Composite Film-Modified Pt Electrode

A simple method that relies only on an electrochemical workstation has been investigated to fabricate a highly sensitive glutamate microbiosensor for potential neuroscience applications. In this study, in order to develop the highly sensitive glutamate electrode, a 100 µm platinum wire was modified by the electrochemical deposition of gold nanoparticles, Prussian blue nanocubes, and reduced graphene oxide sheets, which increased the electroactive surface area; and the chitosan layer, which provided a suitable environment to bond the glutamate oxidase. The optimization of the fabrication procedure and analytical conditions is described. The modified electrode was characterized using field emission scanning electron microscopy, impedance spectroscopy, and cyclic voltammetry. The results exhibited its excellent sensitivity for glutamate detection (LOD = 41.33 nM), adequate linearity (50 nM-40 µM), ascendant reproducibility (RSD = 4.44%), and prolonged stability (more than 30 repetitive potential sweeps, two-week lifespan). Because of the important role of glutamate in neurotransmission and brain function, this small-dimension, high-sensitivity glutamate electrode is a promising tool in neuroscience research.

Hybrid Pectin-Based Sorbents for Cesium Ion Removal

In this paper, beads-shaped hybrid sorbents composed of pectin and Prussian blue were prepared. Various ratios of pectin and Prussian blue in hybrid sorbents were tested. Obtained sorbents had high and roughly constant sorption capacity in a broad pH range (4–10), in which also the swelling index and stability of sorbents were satisfactory. The preliminary sorption studies proved that almost 100% of cesium removal efficiency may be achieved by using the proper sorbent dose. The sorption capacity of the hybrid sorbent with a 1:1 ratio of pectin to Prussian blue equaled q = 36.5 ± 0.8 mg/g (dose 3 g/L, pH = 6, temp. = 22 ± 1 °C, t = 24 h). The obtained results showed that the prepared hybrid pectin-based sorbents are promising for cesium ions removal.

Cesium ion-exchange resin using sodium dodecylbenzenesulfonate for binding to Prussian blue

Radioactive Cs ions are extremely harmful to the human body, causing cancers and other diseases. Treatments were performed on radioactive Cs present in wastewater after use in industrial or medical fields. Prussian blue (PB) has been widely used for the removal of Cs ions from water but its colloidal structure hinders reuse, making it problematic for practical use. To solve this problem, we used a commercial macroporous polymer resin as a PB matrix. To provide an efficient anchor for PB, the surface of the polymer resin was decorated with sodium dodecylbenzenesulfonate to produce a negatively charged surface. The successful chemical binding between the polymer resin and PB prevented leakage of the latter during adsorption and crosslinked structure of the matrix provided regeneration of the adsorbent. The adsorbent maintained its removal efficiency after five repeats of the regeneration process. The PB-based, Cs ion-exchange resin showed excellent selectivity toward Cs ions and good reusability, maintaining its high adsorption capacity.

Continuous Energy Harvesting and Motion Sensing from Flexible Electrochemical Nanogenerators: Toward Smart and Multifunctional Textiles

Here, we demonstrate the utilization of biocompatible Prussian blue (PB) active coatings onto polyester-carbon nanotube (CNT) threads to enable a fiber-based platform for both power harvesting and continuous motion sensing. First, we show experimental evidence supporting that the mechanistic power generating mechanical-electrochemical coupling in an electrochemical generator (ECG) is best achieved with K-ion insertion, in contrast to the expected preference for Li-ion insertion for batteries. We then construct KPB fibers and demonstrate power generation in an ECG device up to 3.8 μW/cm² at low frequencies relevant to human motion in either an aqueous or polymer gel electrolyte media. Further, by stitching these yarns into gloves or arm sleeves, our results show the continuous monitoring of finger or arm motion, respectively, during slow and repetitive human motion. Overall, our work demonstrates an ECG platform that overcomes the performance and integration barriers toward combined textile integration and human motion sensing while leveraging common materials and understanding extending from alkali metal-ion batteries.

Density-functional-theory-predicted symmetry lowering from cubic to tetragonal in nickel hexacyanoferrate

Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanoferrate, Ni2+ 3[Fe3+(CN)6]2·nH2O, predict the existence of a tetragonal (P 4 m2) crystal structure that is energetically degenerate with the previously reported cubic (F 43m) structure for this PBA. The proposed tetragonal structure satisfies observations, such as X-ray diffraction and magnetic measurements, that have been reported previously. A van der Waals corrected exchange-correlation functional is used in the DFT+U computations for an improved description of hydrogen bonding. The results provide strong support for a revised and simplified crystallographic description of Ni2+ 3[Fe3+(CN)6]2·nH2O, and show how H2O molecules stabilize the crystal structure and affect its magnetic and electronic properties. The symmetry lowering in nickel hexacyanoferrate is attributed to the hydration shell of the interstitial nickel cation. Calculations strongly suggest a maximum of n = 7 interstitial H2O molecules per formula unit for nickel hexacyanoferrate at room temperature, and a higher water content at temperatures below T ≃ 200 K. Since the symmetry lowering relies on the presence of interstitial H2O molecules, this revised crystallographic description may be applicable more generally to the large class of F 43m-structured PBAs.

Optimized deposition time boosts the performance of Prussian blue modified nanoporous gold electrodes for hydrogen peroxide monitoring

Prussian blue (PB) modified nanoporous gold (NPG) electrodes exhibit great potential for improving the detection sensitivity and stability for hydrogen peroxide monitoring. The NPG provides large surface-to-volume ratio as well as diffusion 'highways' to assist the transfer of the ions. In the present work, we optimized the deposition time for NPG fabrication and examine the electrochemical performance of the electrodes. A critical deposition time on the electrochemical performances including linear range, operational stability and sensitivity was experimentally determined. Below and above such a deposition time, two different growth patterns of the microstructures were observed. This transition of deposited structures corresponding to the critical time results in different pathways for electron transfer and ion diffusivity through PB lattice.

The sweet detection of rolling circle amplification: Glucose-based electrochemical genosensor for the detection of viral nucleic acid

Herein, an isothermal padlock probe-based assay for the simple and portable detection of pathogens coupled with a glucose oxidase (GOx)-based electrochemical readout is reported. Infectious diseases remain a constant threat on a global scale, as in recurring pandemics. Rapid and portable diagnostics hold the promise to tackle the spreading of diseases and decentralising healthcare to point-of-care needs. Ebola, a hypervariable RNA virus causing fatalities of up to 90% for recent outbreaks in Africa, demands immediate attention for bedside diagnostics. The design of the demonstrated assay consists of a rolling circle amplification (RCA) technique, responsible for the generation of nucleic acid amplicons as RCA products (RCPs). The RCPs are generated on magnetic beads (MB) and subsequently, connected via streptavidin-biotin bonds to GOx. The enzymatic catalysis of glucose by the bound GOx allows for an indirect electrochemical measurement of the DNA target. The RCPs generated on the surface of the MB were confirmed by scanning electron microscopy, and among other experimental conditions such as the type of buffer, temperature, concentration of GOx, sampling and measurement time were evaluated for the optimum electrochemical detection. Accordingly, 125 μg mL^-1 of GOx with 5 mM glucose using phosphate buffer saline (PBS), monitored for 1 min were selected as the ideal conditions. Finally, we assessed the analytical performance of the biosensing strategy by using clinical samples of Ebola virus from patients. Overall, this work provides a proof-of-concept bioassay for simple and portable molecular diagnostics of emerging pathogens using electrochemical detection, especially in resource-limited settings.

3D Printed Graphene Electrodes Modified with Prussian Blue: Emerging Electrochemical Sensing Platform for Peroxide Detection

3D printing technologies have been considered an important technology due to the ease manufacturing of objects, freedom of design, waste minimization, and fast prototyping. In chemistry, this technology potentializes the fabrication of conductive electrodes in large scale for sensing applications. Herein, we reported the modification of a 3D printed graphene electrode with Prussian blue. The modified electrode (3DGrE/PB) was characterized by microscopy (SEM and AFM) and spectroscopic techniques, and its electrochemical properties were compared to the traditional electrodes: glassy carbon, gold, and platinum. The 3DGrE/PB was used in the sensing of hydrogen peroxide in real-world samples of milk and mouthwash, and the results obtained according to the technique of batch-injection analysis were satisfactory for the concentration range typically found in such samples. Thus, 3DGrE/PB can be used as a new platform for sensing of molecular targets.

Wearable biomolecule smartsensors based on one-step fabricated berlin green printed arrays

The wearable smart detection of body biomolecules and biomarkers is being of significance in the practical fields. Hydrogen peroxide (H₂O₂) is a product of some enzyme-catalyzed biomolecular reactions. The detection of H₂O₂ could reflect the concentration information of the enzyme reaction biomolecule substrate such as glucose. A high-performance berlin green (BG) carbon ink for monitoring H₂O₂ was prepared in this work. And we have successfully developed the wearable smartsensors for detecting H₂O₂ and glucose based on one-step fabricated BG arrays by screen-printing technology. Comparing with other detection methods, these sensors are wearable, movable, flexible and biocompatible for monitoring biomolecules. As a result, the sensors exhibited good sensitivity, specificity, stability and reproductivity towards H₂O₂ and glucose. Additionally, there also received stable response after near one hundred times stretching and thousands of bending. Moreover, the wearable sensors could be easily remotely controlled by a smart phone, when integrated with wireless into the device. In prospective studies, the one-step fabricated wearable smartsensors is of great significance in developing a straightforward, highly-efficient and low-cost method for actual detection of biomolecules reflecting body health status, and would potentially be applied in the artificial intelligence (AI) fields.

Screen-Printed Soft-Nitrided Carbon Electrodes for Detection of Hydrogen Peroxide

Nitrogen-doped carbon materials have garnered much interest due to their electrocatalytic activity towards important reactions such as the reduction of hydrogen peroxide. N-doped carbon materials are typically prepared and deposited on solid conductive supports, which can sometimes involve time-consuming, complex, and/or costly procedures. Here, nitrogen-doped screen-printed carbon electrodes (N-SPCEs) were fabricated directly from a lab-formulated ink composed of graphite that was modified with surface nitrogen groups by a simple soft nitriding technique. N-SPCEs prepared from inexpensive starting materials (graphite powder and urea) demonstrated good electrocatalytic activity towards hydrogen peroxide reduction. Amperometric detection of H₂O₂ using N-SPCEs with an applied potential of −0.4 V (vs. Ag/AgCl) exhibited good reproducibility and stability as well as a reasonable limit of detection (2.5 µM) and wide linear range (0.020 to 5.3 mM).

A Prussian Blue ZnO Carbon Nanotube Composite for Chronoamperometrically Assaying H2O2 in BT20 and 4T1 Breast Cancer Cells

A Prussian Blue (PB) zinc oxide carbon nanotube sensing composite was developed for the rapid assaying of H₂O₂ generated from BT20 and 4T1 breast cancer cells, important for elucidating mechanisms governing apoptosis of these cell lines. The combination of H₂O₂'s transient nature along with matrix effects makes monitoring this molecule in biological samples a challenge. The standard addition method (SAM) was coupled with chronoamperometric sensing (CA) to overcome these obstacles. An electrocatalyst composite consisting of refluxed zinc oxide nanoparticles (NPs) tethered to carboxylic acid-functionalized multiwalled carbon nanotubes (ZnO/COOH-MWNTs) was electrostatically attached to PB for signal enhancement. Optimization of the sensor was achieved via adjusting solution pH and stirring time to optimize PB electrostatic attachment to ZnO/COOH-MWNTs prior to its deposition onto the working glassy carbon electrode (GCE) surface. CA SAM showed the ability to accurately measure H₂O₂ within the 1-21 μM range, suitable for monitoring cancer cell line apoptosis resistance scenarios and offering analytical advantages over standard enzyme-linked immunosorbent assays (ELISA) for rapid, matrix-effect-free analysis.

3D-Printed Low-Cost Spectroelectrochemical Cell for In Situ Raman Measurements

Raman spectroelectrochemistry is a powerful technique for characterizing structural changes of materials during electrochemical reactions and investigating the mechanism of film deposition and adsorption processes on the surfaces of electrodes. Moreover, in situ measurements enable identification of catalytic sites and reaction intermediates, which facilitates the comprehension of reaction mechanisms. The limitations of this technique include the high-cost and the complexity of the experimental arrangement required by commercial spectroelectrochemical cells (SEC). Thus, 3D-printing technology emerges as an excellent alternative for the production of SEC, with desirable shape, low-cost, and robustness in a short period of time. In this work, an SEC and a 3D-printed working electrode were fabricated from acrylonitrile-butadiene-styrene (ABS) and conductive graphene polylactic acid (PLA) filaments, respectively. The proposed SEC and the 3D-printed electrode were printed within 3.5 h with an estimated cost of materials of less than US $2. Then, the 3D-printed SEC and the electrode were used in a study of structural changes of Prussian blue according to different voltage bias.

Frontiers in Electrochemical Sensors for Neurotransmitter Detection: Towards Measuring Neurotransmitters as Chemical Diagnostics for Brain Disorders

It is extremely challenging to chemically diagnose disorders of the brain. There is hence great interest in designing and optimizing tools for direct detection of chemical biomarkers implicated in neurological disorders to improve diagnosis and treatment. Tools that are capable of monitoring brain chemicals, neurotransmitters in particular, need to be biocompatible, perform with high spatiotemporal resolution, and ensure high selectivity and sensitivity. Recent advances in electrochemical methods are addressing these criteria; the resulting devices demonstrate great promise for in vivo neurotransmitter detection. None of these devices are currently used for diagnostic purposes, however these cutting-edge technologies are promising more sensitive, selective, faster, and less invasive measurements. Via this review we highlight significant technical advances and in vivo studies, performed in the last 5 years, that we believe will facilitate the development of diagnostic tools for brain disorders.

Modified Electrodeposited Cobalt Foam Coatings as Sensors for Detection of Free Chlorine in Water

Metal foams offer a substantial specific surface area and sturdy frame, which makes them great candidates for various applications such as catalysts, sensors, heat sinks, etc. Cobalt and its various compounds are being considered as a cheaper alternative for precious and rare metal catalysts. The cobalt foams have been electrodeposited under galvanostatic and current pulse modes; the porous surface was created using a dynamic hydrogen bubble template. In order to obtain the highest porosity, four different solutions were tested, as well as a wide current density window (0.6–2.5 A/cm²), in addition many different combinations of pulse durations were applied. The effects of surfactant (isopropanol) on porosity were also investigated. The morphology of obtained foams was examined by SEM coupled with EDS, and XRD spectroscopy. True surface area was estimated based on the values of a double electric layer capacitance that was extracted from EIS data. Cobalt foams were modified using K3[Fe(CN)6] solution and cyclic voltammetry to form a cobalt hexacyanoferrate complex on the foam surface. In order to find optimal modification conditions, various potential scan rates and numbers of cycles were tested as well. Free chlorine sensing capabilities were evaluated using chronoamperometry.

Direct Observation of Charge Transfer and Magnetism in Fe4Co4 Cyanide-Bridged Molecular Cubes

We have studied the zero-dimensional cubane molecular correspondent of a Prussian blue analogue Cs-Fe₄Co₄ at low temperature and high magnetic field by means of L-edge X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We probe the magnetic and electronic structures of Fe and Co separately upon light irradiation, which allows us to observe directly the electron transfer coupled to a spin transition phenomenon within the molecular cubes and to investigate the nature of the metastable photoexcited state. The magnetic moments in the photoexcited state are found to be M = 1.3μ_B ( M_spin = 0.59μ_B with large orbital moment, M_orbit = 0.74μ_B) for low-spin Fe^III and M = 1.5μ_B ( M_spin = 1.08μ_B with orbital moment, M_orbit = 0.41μ_B) for high-spin Co^II at 2 K and 6.8 T. From our results, we evidence that a strong antiferromagnetic coupling between the metal ions can be ruled out.