Electrochromism and electrochemical magnetism in Ni–Fe Prussian blue

We studied the electrochemical and magnetic properties of NiFe Prussian blue. The NiFe Prussian blue was synthesized on Ni electrodes in the form of thin films by an electrochemical technique. Measurements of its magnetic properties show that NiFe Prussian blue with the Fe^{III-low spin (LS)}–CN–Ni^II structure exhibits ferromagnetic properties, with T _c (critical temperature)=25 K. On the other hand, the reduced form, which has the Fe^II-LS–CN–Ni^II structure, is paramagnetic. This means that the magnetic properties can be controlled between ferromagnetic and paramagnetic by an electrochemical method. Furthermore, it is well known that NiFe Prussian blue exhibits electrochromic properties. Hence, this compound is a multifunctional, molecule-based compound in which optical and magnetic properties can be controlled by an electrochemical redox reaction. Contribution to the special issue on “Magnetic field effects in Electrochemistry.”     

Nanosilver-doped DNA polyion complex membrane for electrochemical immunoassay of carcinoembryonic antigen using nanogold-labeled secondary antibodies

A simple and sensitive electrochemical immunoassay protocol was developed for the detection of carcinoembryonic antigen (CEA) using nanosilver-doped DNA polyion complex membrane (PIC) as sensing interface. To construct such an immunosensor, double-stranded DNA was initially assembled onto the surface of thionine/Nafion-modified screen-printed carbon electrode to adsorb silver ions with positive charges, then silver ions were reduced to nanosilver particles with the aid of NaBH₄, and then anti-CEA antibodies were immobilized on the nanosilver surface. Gold nanoparticles conjugated with horseradish peroxidase-labeled anti-CEA were employed as signal antibodies for the detection of CEA with a sandwich-type assay format. Under optimal conditions, the immunosensor exhibited a dynamic range of 0.03-32 ng mL⁻¹ with a low detection limit of 10 pg mL⁻¹ CEA. Intra- and inter-assay imprecision (CVs) were <9.5% and 6.5%, respectively. The response could remain 90.1% of the original current at 30th day. 50 real samples were evaluated using the immunosensor and the enzyme-linked immunosorbent assay, respectively, and received in accordance with those two methods.     

Lateral flow immunodipstick for visual detection of aflatoxin B1 in food using immuno-nanoparticles composed of a silver core and a gold shell

An immunodipstick assay with a lateral flow strip was developed for fast screening of food for aflatoxin B₁ (AFB₁) using the respective monoclonal antibody immobilized on nanoparticles with a silver core and a gold shell (AgAu) as detection reagent. The membrane-based immunodipstick consisted of a test line containing AFB₁ conjugated to bovine serum albumin, and a control line with goat anti-mouse IgG. One to two colored lines are formed on the membrane by using the red AgAu nanoparticles coated with anti-AFB₁ as signaling reagents. Under optimal conditions, the dipstick exhibits a lower visual detection limit of 0.1 ng?mL^?1 of AFB₁. Compared to the use of pure gold nanoparticles, the AgAu nanoparticles strongly enhance the sensitivity of the assay, and the reproducibility and stability are comparable. The assay was evaluated with naturally contaminated samples including rice, wheat, sunflower, cotton, chillies, and almonds, and a good correlation was found with data obtained with a commercially available enzyme-linked immunosorbent assay. The simple and non-instrumental dipstick method may further be extended to the screening of other mycotoxins in food.     

Carbon nanotube-based symbiotic coaxial nanocables with nanosilica and nanogold particles as labels for electrochemical immunoassay of carcinoembryonic antigen in biological fluids

A feasible and practicable amperometric immunoassay strategy for sensitive screening of carcinoembryonic antigen (CEA) in human serum was developed using carbon nanotube (CNT)-based symbiotic coaxial nanocables as labels. To construct such a nanocable, a thin layer of silica nanoparticles was coated on the CNT surface by sonication and sol-gel methods, and then colloidal gold nanoparticles were assembled on the amino-functionalized SiO₂/CNTs, which were used for the label of horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA-Au/SiO₂/CNT). In the presence of analyte CEA, the sandwich-type immunocomplex was formed on an anti-CEA/Au/thionine/Nafion-modified glassy carbon electrode by using HRP-anti-CEA-Au/SiO₂/CNTs as detection antibodies. To embody the advantages of the protocol, the analytical properties of variously modified electrodes were compared in detail on the basis of different nanolabels. Under optimal conditions, the cathodic peak currents of the electrochemical immunosensor were proportional to the logarithm of CEA concentration over the range from 0.01 to 12 ng mL⁻¹ in pH 5.5 HAc-NaAc containing 5 mM H₂O₂. At a signal-to-noise ratio of 3, the detection limit (LOD) is 5 pg mL⁻¹ CEA. Intra- and inter-assay coefficients of variation were below 9.5%. Meanwhile, the selectivity and stability of the immunosensor were acceptable. In addition, the technique was evaluated by spiking CEA standards in pH 7.4 PBS and with 35 clinical serum specimens, receiving excellent accordance with results from commercially available electrochemiluminescent enzyme-linked immunoassay.     

Gold Nanowires – Assisted Prussian Blue Enhancing Peroxidase – Like Activity for the Non-enzymatic Electrochemically Sensing H2O2 Released From Living Cells

Prussian blue nanoparticles (PBNPs) have peroxidase-like activity for H₂O₂. However, PB alone have poor electrochemical performances. Herein, a strategy was proposed by direct in-situ growth PBNPs onto gold nanowires (AuNWs) surface to obtain the peroxidase-like activity with about 4.05 times higher than that of PBNPs alone. PBNPs@AuNWs was employed to construct a non - enzymatic electrochemical H₂O₂ sensor with the detection limit of 5.3×10⁻⁹ mol/L (S/N=3). The sensor was successfully used to detect H₂O₂ in human serum samples or secreted from living HeLa cells. It may be a competitive candidate for H₂O₂ assaying in biological samples or cellular investigation.     

A Novel Magnetism‐assisted Electrochemical Immunosensor with Sub‐Picomolar Sensitivity

A novel electrochemical immunosensor based on a magnetic glassy carbon electrode (MGCE) was developed for the quantitative determination of human immunoglobulin G (IgG). The immunosensing interface was fabricated by initially depositing silver nanoparticles on the MGCE surface and then immobilizing anti‐human IgG antibodies via the magnetic force between MGCE and Fe₃O₄ nanoparticles. The antibodies were covalently bonded to the amine‐functionalized Fe₃O₄ nanoparticles. Under optimal conditions, the magnetism‐assisted immunosensor exhibited a wide linear range from 0.1 pg/mL to 1.0 µg/mL with the detection limit of 0.05 pg/mL. Furthermore, the immunosensor displayed the advantages of good reproducibility and satisfactory stability.     

Nanomagnet Bioconjugates with anti-CRP Polyclonal Antibodies as Nanobioprobes for Enhanced Impedimetric Detection of CRP

Selective purification of biological materials for their detection in complex sample matrix is a general challenge for many researchers working in the field of diagnostics. Magnetic nanoparticles functionalized with biological molecules that impart biomolecular selectivity are therefore of major interest as capture probes thus allowing for magnetic separations. Nanoparticles can also be used for the enhanced detection of biomarkers. In this work, an ultrasensitive sandwich-based impedimetric immunosensor was fabricated for the detection of C-reactive protein antigen (CRPAg). Stable and oriented immobilization of anti-CRP monoclonal antibody was achieved onto electrografted phenylethylamine derivatized with succinic anhydride and phenylboronic acid via carbodiimide chemistry. The detection of CRPAg was achieved using Electrochemical Impedance Spectroscopy (EIS). The enhancement of the impedance charge-transfer resistance (R_CT) signal was achieved using the sandwich approach. The anti-CRP polyclonal antibody was immobilized in an oriented manner onto magnetic nanoparticles functionalized with phenylboronic acid. The increase in the change in charge-transfer resistance (ΔR_CT) values was linearly proportional to the concentration of CRPAg in the range 10 to 200 ng mL⁻¹ covering the clinical range for CRPAg detection and with a detection limit of 0.34 ng mL⁻¹.     

In situ synthesis of a Prussian blue nanoparticles/graphdiyne oxide nanocomposite with high stability and electrocatalytic activity

Herein we report an in situ synthesis of Prussian blue nanoparticles (PB) on graphdiyne oxide (GDYO) which acts as an excellent substrate. The hybrid was then used as an electrode with high electrochemical catalytic activity towards hydrogen peroxide. The PB/GDYO hybrid was prepared by simply adding FeCl₃ to GDYO solution, and then mixing with Fe(CN)₆^3 − at room temperature. The GDYO was able to anchor PB in nanoparticle form and stabilize it in neutral and weakly basic solutions. The hybrid was investigated by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical measurements. The PB/GDYO hybrid showed high electrochemical catalytic activity and stability for the detection of hydrogen peroxide.     

A Sensitive Signal-off Electrochemical Aptasensor for Thrombin Detection using PB−Au@MoS2 Nanomaterial as Both Platform and Signal Reporter

Human serum is one of the effective samples for point-of-care testing (POCT). Sensitive and quick determination of thrombin content in human serum samples is important. An electrochemical aptasensor based on Prussian blue and Au nanoparticles loaded MoS₂ nanoflowers (PB−Au@MoS₂) hybrid was constructed. By using PB−Au@MoS₂ as both a substrate and a signal reporter, this aptasensor could demonstrate excellent performance for thrombin detection with a detection linear range from 0.01 pM to 30 nM and detection limit down to 1 fM. This work may provide a strategy to establish effective and sensitive sensing devices for thrombin in clinical diagnosis.     

磁性普鲁士蓝纳米颗粒的合成及其化学修饰电极的制作

利用FeSO₄与FeCl₃合成了超细磁性Fe₃O₄纳米颗粒, 并进一步利用该纳米颗粒与铁氰酸钾在酸性溶液(pH～2)中的化学反应成功制备了一种新型的磁性普鲁士蓝纳米颗粒; 研究了该磁性颗粒的磁学性能, 通过磁力将其修饰于固体石蜡碳糊电极表面制成了化学修饰电极, 考察了该电极对过氧化氢的电催化还原及对水合肼的电催化氧化特性. 该化学修饰电极可对过氧化氢和水合肼进行测定, 线性范围分别为过氧化氢2×10^－6～5×10^－3 mol/L, 水合肼7.2×10^－7～3.6×10^－4 mol/L. 利用磁性普鲁士蓝纳米颗粒制得的修饰电极具有催化性能高、稳定性好、表面易更新等优点.     

Electrochemical Conversion of Magnetic Nanoparticles Using Disposable Working Electrode in a 3D‐Printed Electrochemical Cell

Exploration of new property/function of nanomaterials is always a strong impetus in the nanoscience field. Here, a new method of electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) is proposed to endow MNPs with signal generation ability for sensing. Briefly, high potential was applied to split H₂O to generate acid, while Fe₃O₄ MNPs reacted with H⁺ and produce ferric/ferrous ions, which further reacted with K₄Fe(CN)₆ to yield Prussian blue (PB) through potential cycling. The ECC method worked well on both home‐made and commercial MNPs with different sizes. The generated PB possessed strong electrochemical activity for further applications. Interestingly, an uneven deposition of PB on working electrode and undesired contamination of the reference and counter electrodes were found when using commercial integrated three‐electrode chip. A 3D‐printed electrochemical cell was designed to facilitate the ECC and avoid drawbacks of commercial integrated electrode. The 3D‐printed electrochemical cell was proven to solve the problem above through spatial separation of electrodes and thus facilitated the ECC process. An electrochemical sensor for H₂O₂ detection based on the catalysis ability of ECC‐based PB exhibited a linear response from 5 μM to 1 mM, a high sensitivity of 269 μA mM^?1 cm^?2 and a low detection limit of 0.16 μM (S/N=3), which suggests its promising application prospect in electrochemistry‐related analysis.     

Prussian Blue/Reduced Graphene Oxide Composite for the Amperometric Determination of Dopamine and Hydrogen Peroxide

Prussian blue has significant application for the construction of electrochemical biosensors. In this work, Prussian blue-reduced graphene oxide modified glass carbon electrodes were successfully fabricated using electrochemical deposition. The high surface area of graphene oxide enhanced the deposition of Prussian blue and the resulting electrocatalytic activity. Infrared spectroscopy and scanning electron microscopy showed that the relatively porous Prussian blue was on the surface of reduced graphene oxide. Cyclic voltammetry showed that Prussian blue-coated reduced graphene oxide composite films improved electron transfer compared to Prussian blue films. The Prussian blue-reduced graphene oxide composite film provided higher response for the reduction of hydrogen peroxide and the oxidation of dopamine compared with the Prussian blue film due to synergistic effects between the reduced graphene oxide and Prussian blue particles. The sensitivity of the electrode was 0.1617 µA µM^?1 cm^?2. The linear dynamic range extended from 0.5 µM to 0.7 mM dopamine with a limit of detection equal to 125 nM. This work provided a versatile strategy for the design and construction of sensitive amperometric sensors with robust electrocatalytic behavior.     

Determination of Staphylococcus aureus B-1266 by an Enzyme-Free Electrochemical Immunosensor Incorporating Magnetite Nanoparticles

A simple and inexpensive immunosensor is reported for the rapid determination of Staphylococcus aureus B-1266 that uses Fe₃O₄–SiO₂–NH₂ nanoparticles as the direct signal label. The electrochemical immunoassay procedure includes the incubation of bacteria with excess magnetite nanoparticles, the magnetic separation of the free nanoparticles, a labeled immunocomplex formation on the surface of a planar electrode, and the electrochemical response from the magnetite nanoparticles in the immunocomplex. The electrochemical immunosensor allows for the selective and accurate detection of S. aureus from 10 to 105?CFU?mL^?1 with a relative standard deviation lower than 10%. The limit of detection was 8.7?CFU?mL^?1.     

Nanogold-functionalized magnetic beads with redox activity for sensitive electrochemical immunoassay of thyroid-stimulating hormone

A new electrochemical immunosensor for sensitive determination of thyroid-stimulating hormone (TSH) was designed by using redox-active nanogold-functionalized magnetic beads (GoldMag) as signal tags on the nanogold–graphene interface. To construct such GoldMag nanostructures, polyethyleneimine-functionalized magnetic beads (PEI-MBs) were initially prepared by using a wet chemical method, and the electroactive thionine molecules and gold nanoparticles were then alternately immobilized on the surface of PEI-MBs by using an opposite-charged adsorption technique and an in situ synthesis method, respectively. The synthesized GoldMag nanostructures were utilized as signal tags for the label of horseradish peroxidase-anti-TSH conjugates (HRP-anti-TSH). With a sandwich-type immunoassay format, the conjugated signal tags on the transducer were increased with the increasing TSH concentration in the sample, thus enhancing the signal of the electrochemical immunosensor due to the labeled HRP toward the catalytic reduction of H₂O₂. Under optimal conditions, the current was proportional to the logarithm of TSH concentration ranging from 0.01 to 20 μIU mL⁻¹ in pH 6.0 HAc–NaAc containing 6 mM H₂O₂. The detection limit (LOD) was 0.005 μIU mL⁻¹ TSH at 3s_B. The immunosensor displayed an acceptable reproducibility, stability and selectivity. In addition, the methodology was evaluated with human serum specimens, receiving good correlation with results from commercially available electrochemiluminescent analyzer.     

Anodic‐Stripping Voltammetric Immunoassay for Ultrasensitive Detection of Low‐Abundance Proteins Using Quantum Dot Aggregated Hollow Microspheres

A new anodic‐stripping voltammetric immunoassay protocol for detection of IgG1, as a model protein, was designed by using CdS quantum dot (QD) layer‐by‐layer assembled hollow microspheres (QDHMS) as molecular tags. Initially, monoclonal anti‐human IgG1 specific antibodies were anchored on amorphous magnetic beads preferably selective to capture F_ab of IgG1 analyte from the sample. For detection, monoclonal anti‐human IgG1 (F_c‐specific) antibodies were covalently coupled to the synthesized QDHMS. In a sandwich‐type immunoassay format, subsequent anodic‐stripping voltammetric detection of cadmium released under acidic conditions from the coupled QDs was conducted at an in situ prepared mercury film electrode. The immunoassay combines highly efficient magnetic separation with signal amplification by the multilayered QD labels. The dynamic concentration range spanned from 1.0 fg mL^?1 to 1.0 μg mL^?1 of IgG1 with a detection limit of 0.1 fg mL^?1. The electrochemical immunoassay showed good reproducibility, selectivity, and stability. The analysis of clinical serum specimens revealed good accordance with the results obtained by an enzyme‐linked immunosorbent assay method. The new immunoassay is promising for enzyme‐free, and cost‐effective analysis of low‐abundance biomarkers.     

Separation/Concentration‐signal‐amplification in‐One Method Based on Electrochemical Conversion of Magnetic Nanoparticles for Electrochemical Biosensing

We propose a separation/concentration‐signal‐amplification in‐one method based on electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) to develop a facile and sensitive electrochemical biosensor for chloramphenicol (CAP) detection. Briefly, aptamer‐modified magnetic nanoparticles (MNPs‐Apt) was designed to capture CAP in sample, then the MNPs‐Apt composite was conjugated to Au electrode through the DNA hybridization between the unoccupied aptamer and a strand of complementary DNA. The ECC method was applied to transfer MNPs labels to electrochemically active Prussian blue (PB). The anodic and cathodic currents of PB were taken for signal readout. Comparing with conventional methods that require electrochemically active labels and related sophisticated labelling procedures, this method explored and integrated the magnetic and electrochemical properties of MNPs into one system, in turn realized magnetic capturing of CAP and signal generation without any additional conventional labels. Taking advantages of the high abundance of iron content in MNPs and the refreshing effect deriving from ECC process, the method significantly promoted the signal amplification. Therefore, the proposed biosensors exhibited linear detection range from 1 to 1000 ng mL⁻¹ and a limit of detection down to 1 ng mL⁻¹, which was better than or comparable with those of most analogues, as well as satisfactory specificity, storage stability and feasibility for real samples. The developed method may lead to new concept for rapid and facile biosensing in food safety, clinic diagnose/therapy and environmental monitoring fields.     

The electroactive multilayer films of polyelectrolytes and Prussian blue nanoparticles and their application for H2O2 sensors

Prussian blue (PB) nanoparticles were immobilized in polyelectrolyte (PE) multilayers of various compositions and thickness. Films containing nanoparticles and poly(allylamine hydrochloride) (PAH) were formed using the layer-by-layer adsorption method. A layer of branched poly(ethyleneimine) (PEI) was used to anchor the multilayer structure at the surface of a gold electrode. The films exhibited electroactive properties, increasing with the number of deposited PB layers. The properties of PEI/(PB/PAH) _n multilayers were then compared with the ones containing additionally the conductive polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS). We found that the addition of the conductive, water-soluble polymer enhances the electroactive properties of the multilayer films. It also increased sensitivity of the multilayer-covered electrodes for electrochemical detection of hydrogen peroxide.     

Self‐Assembled Prussian Blue Nanoparticles Based Electrochemical Sensor for High Sensitive Determination of H2O2 in Acidic Media

In this paper, self‐assembled Prussian blue nanoparticles (PBNPs) on carbon ceramic electrode (CCE) were developed as a high sensitive hydrogen peroxide (H₂O₂) electrochemical sensor. The PBNPs film was prepared by a simple dipping method. The morphology of the PBNPs‐modified CCE was characterized by scanning electron microscopy (SEM). The self‐assembled PB film exhibited sufficient mechanical, electrochemical stability and high sensitivity in compare with other PB based H₂O₂ sensors. The sensor showed a good linear response for H₂O₂ over the concentration range 1 μM–0.26 mM with a detection limit of ca. 0.7 μM (S/N=3), and sensitivity of 754.6 mA M^?1 cm^?2. This work demonstrates the feasibility of self‐assembled PBNPs‐modified CCE for practical sensing applications.     

Prussian blue-doped nanogold microspheres for enzyme-free electrocatalytic immunoassay of p53 protein

We report on a new enzyme-free electrochemical immunoassay for the sensitive detection of the p53 protein (p53; a model analyte) by using a screen-printed carbon electrode modified with monoclonal mouse anti-human p53 antibody tagged with gold nanoparticles. First, nanogold microspheres doped with Prussian Blue were synthesized by a reverse micelle method. The resulting microspheres were used to label polyclonal anti-p53 antibody which then was applied in a sandwich immunoassay in pH 6.5 buffer solution using the Prussian Blue in the particles as the redox-active reporter. The electrochemical signal of the immunosensor is shown to increase with the concentration of the analyte (p53 protein) in the range from 0.5 to 80 U mL^?1, with a detection limit of 0.1 U mL^?1. No non-specific adsorption was observed. Coefficients of variation for intra-assay and inter-assay were below 8.5 % and 11.5 %, respectively. In addition, the method was applied to the analysis of 15 human serum samples, and a good relationship was found between the new immunoassay and the referenced electro-chemiluminescence method.

A Green Approach to the Synthesis of Well‐structured Prussian Blue Cubes for the Effective Electrocatalytic Reduction of Antiprotozoal Agent Coccidiostat Nicarbazin

For the first time, a robust electrochemical sensor to detect the coccidiostat nicarbazin (NCZ) is developed through the green synthesis of Prussian blue cubes from Volvariella volvacea (paddy straw mushroom) extract. Recently, numerous articles were reported about the issue that the prophylactic drugs were injected excessively as a feed additive for fattening the chickens in short period. It is a significant concern that the level of coccidiostat NCZ exceeds the residue limits in the tissues of the meat; mainly, in chicken and eggs. Therefore, it is crucial to develop a sensitive, reproducible and long‐lasting sensor for the real‐time detection of NCZ. Thus, we have generated an electrochemical sensor through the economic screen‐printed carbon electrode (SPCE) modification method. Eco‐friendly Prussian blue cubes are fabricated on the carbon film of SPCE. As a result, the modified electrode showed exceptional electrocatalytic ability towards NCZ and the reduction peak currents are correlated to the concentrations of NCZ. It retains the more extensive working range between 1.25×10⁻⁷ to 1.53×10⁻³ mol L⁻¹, and it possesses a very low limit of detection as well as the appreciable sensitivity. This method is successfully applied to the recognition of NCZ in the samples of chicken meat and eggs.