FeS2−AuNPs Nanocomposite as Mimicking Enzyme for Constructing Signal‐off Sandwich‐type Electrochemical Immunosensor Based on Electroactive Nickel Hexacyanoferrate as Matrix

In this work, a novel sandwich‐type electrochemical immunosensor with electroactive nickel hexacyanoferrate nanoparticles (NiHCFNPs) as matrix was constructed for α‐fetoprotein (AFP) detection in a signal‐off manner by using FeS₂?AuNPs nanocomposite catalyzed insoluble precipitation to significantly inhibit the electrochemical signal. Initially, the NiHCFNPs with excellent electrochemical property was modified on the electrodeposited nano‐Au electrode to obtain a strong initial electrochemical signal. Subsequently, another nano‐Au layer was formed for immobilization of capture antibody (Ab₁). In the presence of target AFP, the prepared FeS₂?AuNPs‐Ab₂ bioconjugate could be specifically recognized and immobilized on electrode through the sandwich‐type immunoreaction. The FeS₂ with large specific surface areas were used as scaffolds to load abundant mimicking enzyme AuNPs. With the help of hydrogen peroxide (H₂O₂), FeS₂?AuNPs with peroxidase‐like activity accelerated the 4‐chloro‐1‐naphthol (4‐CN) oxidation with generation of insoluble precipitation on electrode, which would greatly hinder the electron transfer and thus caused the decrease of electrochemical signal for quantitative determination of AFP. This approach achieved a wide dynamic linear range from 0.0001 to 100 ng mL^?1 with an ultralow limit detection of 0.028 pg mL^?1. Especially, the proposed AFP immunosensor can be applied to detect human serum samples with satisfactory results, indicating a potential application in clinical monitoring of tumor biomarkers.     

Highly Sensitive Electrochemical Hydrogen Peroxide Sensor Based on Iron Oxide‐Reduced Graphene Oxide‐Chitosan Modified with DNA‐Celestine Blue

The present study describes a novel and very sensitive electrochemical assay for determination of hydrogen peroxide (H₂O₂) based on synergistic effects of reduced graphene oxide‐ magnetic iron oxide nanocomposite (rGO‐Fe₃O₄) and celestine blue (CB) for electrochemical reduction of H₂O₂. rGO‐Fe₃O₄ nanocomposite was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X‐ray diffraction (XRD), electrochemical impedance spectroscopy and cyclic voltammetry. Chitosan (Chit) was used for immobilization of amino‐terminated single‐stranded DNA (ss‐DNA) molecules via a glutaraldehyde (GA) to the surface of rGO‐Fe₃O₄. The MTT (3‐(4,5‐Dim ethylt hiazol‐2‐yl)‐2,5‐diphenylt etrazolium bromide) results confirmed the biocompatibility of nanocomposite. Experimental parameters affecting the ss‐DNA molecules immobilization were optimized. Finally, by accumulation of the CB on the surface of the rGO‐Fe₃O₄‐Chit/ssDNA, very sensitive amperometric H₂O₂ sensor was fabricated. The electrocatalytic activity of the rGO‐Fe₃O₄‐Chit/DNA‐CB electrode toward H₂O₂ reduction was found to be very efficient, yielding very low detection limit (DL) of 42 nM and a sensitivity of 8.51 μA/μM. Result shows that complex matrices of the human serum samples did not interfere with the fabricated sensor. The developed sensor provided significant advantages in terms of low detection limit, high stability and good reproducibility for detection of H₂O₂ in comparison with recently reported electrochemical H₂O₂ sensors.     

Design of Sensitive Biocompatible Quantum‐Dots Embedded in Mesoporous Silica Microspheres for the Quantitative Immunoassay of Human Immunodeficiency Virus‐1 Antibodies

A novel sandwich‐type electrochemiluminescence (ECL) immunosensor was developed to enable the sensitive detection of HIV‐1 antibodies. This system incorporated mesoporous silica (mSiO₂) complexed with quantum dots (QDs) and nano‐gold particles, which were assembled to enhance signal detection. Magnetic beads were used by immobilizing the secondary anti‐IgG antibody. This was first employed to capture HIV‐1 antibody (Ab) to form a Fe₃O₄/anti‐IgG/Ab complex. A high loading and signal‐enhanced nanocomposite (hereafter referred to as Au‐mSiO₂‐CdTe) was used as a HIV‐1 antigen label. The Au‐mSiO₂‐CdTe nanocomposite was conjugated with the Fe₃O₄/anti‐IgG/Ab complex to form an immunocomplex (hereafter referred to as Fe₃O₄/anti‐IgG/Ab/HIV‐1/CdTe‐mSiO₂‐Au). This complex could be further separated by an external magnetic field to produce ECL signals. Due to the large specific surface area and pore volume of mSiO₂, the loading of the CdTe QDs was markedly increased. Thus, the loaded QDs released a powerful chemiluminescent signal with a concordantly increased sensitivity of the immunosensor. The immunosensor was highly sensitive, and displayed a linear range of responses for HIV‐1 antibody across a dilution range of 1 : 1500 through 1 : 50 with the detection limit of 1 : 4500. The immunoassay can be a promising candidate in early diagnosis of HIV infection.     

Electrochemiluminescence Immunosensor Based on Functionalized Graphene/Fe3O4‐Au Magnetic Capture Probes for Ultrasensitive Detection of Tetrodotoxin

An ultrasensitive electrochemiluminescence (ECL) immunosensor for the detection of tetrodotoxin (TTX) is proposed, which are composed of the branched poly‐(ethylenimine) (BPEI) functionalized graphene (BGNs)/Fe₃O₄‐Au magnetic capture probes and luminol‐capped gold nanocomposites (luminol‐AuNPs) as the signal tag. Herein, a typical sandwich immunecomplex was constructed on the glassy carbon electrode. The BGNs/Fe₃O₄‐Au hybrids could efficiently conjugate primary antibody via the Au−S chemical bonds or Au−N chemical bonds and rapidly separate under external magnetic field. The introduction of BPEI to GO could enhance the luminol‐ECL intensity. Meanwhile, the multifunctional nanocomposites have been proved with good water‐solubility, excellent electron transfer, outstanding stability, etc. The luminescent luminol‐AuNPs, a high efficient electrochemiluminescence marker, can be assembled on the second antibody, which can produce the ECL signal to achieve the determination of TTX. This proposed ECL immunosensor with a linear range from 0.01–100 ng/mL can be applied in the detection of TTX in real samples with satisfactory results.     

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.     

A Renewable Potentiometric Immunosensor Based on Fe3O4 Nanoparticles Immobilized Anti‐IgG

A renewable potentiometric immunosensor for detection of immunoglobulin G (IgG) has been developed by magnetic force attraction of Fe₃O₄ nanoparticles immobilized goat‐anti‐human IgG antibody. For preparing sensitive film of the sensor, cysteine was bonded on the nano‐Fe₃O₄ particles surface. The cysteine functionalized magnetic nanoparticles was attracted on a solid paraffin carbon paste electrode surface to covalently immobilize of anti‐immunoglobulin G (anti‐IgG) by employing a conventional glutaraldehyde‐crosslinking method. The immunosensor showed a specific response to human immunoglobulin G in the range of 0.1–1.2 ng/mL with a detection limit of 0.023 ng/mL. The immunosensor based on the magnetic nanoparticles was made easily by this method. It can be used expediently, renewed easily and low‐cost relatively. The renewable potentiometric immunosensor with better stability and higher sensitivity can be employed extensively in clinical diagnosis, monitoring of disease and environmental studies and etc.     

A Prostate Specific Antigen Immunosensor Based on Biotinylated‐Antibody/Cyclodextrin Inclusion Complex: Fabrication and Electrochemical Studies

Immobilization of biomolecules with a proper orientation is considered as a basis for diverse biotechnological applications. Herein, we report a host‐guest inclusion complexation between β‐cyclodextrin (β‐CD) and biotin as a versatile approach for the immobilization of biomolecules. As a practical application, a sandwich‐type electrochemical immunosensor was designed for the determination of prostate specific antigen (PSA). The immunosensor was fabricated by in situ electropolymerization of poly(N‐acetylaniline) onto a rGO‐modified Pt electrode. Then, β‐CD was covalently grafted onto the over‐oxidized polymer backbone. For improving the efficiency of the assay, AuNPs were casted on the polymeric film, on the surface of which thionine (TH) as an electron mediator was covalently immobilized. Using a host‐guest inclusion complexation between β‐CD and biotin, a β‐CD/biotin‐Ab₁/PSA/Ab₂‐horseradish peroxidase (HRP) sandwich was formed on the electrode surface. The analytical signal was produced via electrochemical reduction of TH_ox, generated by biocatalytic oxidation of the TH_red in the presence of HRP/H₂O₂. Under optimal conditions, the proposed sensor responded linearly to PSA in the range from 10.0 pg mL⁻¹ to 25.0 ng mL⁻¹, with a low detection limit of 6.7 pg mL⁻¹ (S/N=3). Kinetic parameters of the interaction of β‐CD with Ab₁ were also investigated. Finally, the applicability of the immunosensor was successfully investigated for the detection of PSA in human serum samples.     

Sodium‐Ion Storage Properties of FeS–Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium‐ion storage properties of FeS–reduced graphene oxide (rGO) and Fe₃O₄‐rGO composite powders with crumpled structures have been studied. The Fe₃O₄‐rGO composite powder, prepared by one‐pot spray pyrolysis, could be transformed to an FeS‐rGO composite powder through a simple sulfidation treatment. The mean size of the Fe₃O₄ nanocrystals in the Fe₃O₄‐rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders were 740 and 442 mA h g^?1, and their initial charge capacities were 530 and 165 mA h g^?1, respectively. The discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders at the 50th cycle were 547 and 150 mA h g^?1, respectively. The FeS‐rGO composite powder showed superior sodium‐ion storage performance compared to the Fe₃O₄‐rGO composite powder.     

Capacitance Polypyrrole‐based Impedimetric Immunosensor for Interleukin‐10 Cytokine Detection

In the present study, we developed a novel label‐free capacitance impedimetric immunosensor based on the immobilization of the human monoclonal antibody anti‐interleukin‐10 (anti‐IL‐10 mAb) onto polypyrrole (PPy)‐modified silicon nitride (Si₃N₄) substrates. The immunosensor was used for the detection of the recombinant interleukin‐10 antigen (rh IL‐10) that may be secreted in patients at the early stage of inflammation. The immunosensor was created by chemical deposition of PPy conducting layer on pyrrole?silane (SPy)‐treated Si/SiO₂/Si₃N₄ substrates (Si/SiO₂/Si₃N₄?SPy), followed by anti‐IL‐10 mAb immobilization through carboxyl‐functionalized diazonium (CMA) protocol and carbodiimide chemistry. The surface characterization and the biofunctionalization steps were characterized by SEM, FTIR and cyclic voltammetry (CV) while the detection process was carried out by using electrochemical impedance spectroscopy (EIS) analyses. The created immunosensor showed two linear fittings (R²=0.999) for the detection of rh IL‐10 within the concentration range from 1–50 pg/mL. It exhibited high sensitivity (0.1128 (pg/mL)^?1) with a very low limit of detection (LOD)=0.347 pg/mL, more particularly, at the low concentration range (1–10 pg/mL). Thus, this developed polypyrrole‐based immunosensor represents a promising strategy for creation of miniaturized label‐free, fast and highly sensitive biosensors for diagnosis of inflammation biomarkers at very low concentrations with reduced cost.     

Magnetic Nanohybrids Loaded with Bimetal Core–Shell–Shell Nanorods for Bacteria Capture,Separation, and Near‐Infrared Photothermal Treatment

A novel antimicrobial nanohybrid based on near‐infrared (NIR) photothermal conversion is designed for bacteria capture, separation, and sterilization (killing). Positively charged magnetic reduced graphene oxide with modification by polyethylenimine (rGO–Fe₃O₄–PEI) is prepared and then loaded with core–shell–shell Au–Ag–Au nanorods to construct the nanohybrid rGO–Fe₃O₄–Au–Ag–Au. NIR laser irradiation melts the outer Au shell and exposes the inner Ag shell, which facilitates controlled release of the silver shell. The nanohybrids combine physical photothermal sterilization as a result of the outer Au shell with the antibacterial effect of the inner Ag shell. In addition, the nanohybrid exhibits high heat conductivity because of the rGO and rapid magnetic‐separation capability that is attributable to Fe₃O₄. The nanohybrid provides a significant improvement of bactericidal efficiency with respect to bare Au–Ag–Au nanorods and facilitates the isolation of bacteria from sample matrixes. A concentration of 25 μg mL^?1 of nanohybrid causes 100 % capture and separation of Escherichia coli O157:H7 (1×10⁸ cfu mL^?1) from an aqueous medium in 10 min. In addition, it causes a 22 °C temperature rise for the surrounding solution under NIR irradiation (785 nm, 50 mW cm^?2) for 10 min. With magnetic separation, 30 μg mL^?1 of nanohybrid results in a 100 % killing rate for E. coli O157:H7 cells. The facile bacteria separation and photothermal sterilization is potentially feasible for environmental and/or clinical treatment.     

A Novel Biomimetic Hydrogen Peroxide Biosensor Based on Pt Flowers‐decorated Fe3O4/Graphene Nanocomposite

A sensitive and selective amperometric H₂O₂ biosensor was obtained by utilizing the electrodeposition of Pt flowers on iron oxide‐reduced graphene oxide (Fe₃O₄/rGO) nanocomposite modified glassy carbon electrode (GCE). The morphology of Fe₃O₄/rGO and Pt/Fe₃O₄/rGO was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The step‐wise modification and the electrochemical characteristics of the resulting biosensor were characterized by cyclic voltammetry (CV) and chronoamperometry methods. Thanks to the fast electron transfer at the Pt/Fe₃O₄/rGO electrode interface, the developed biosensor exhibits a fast and linear amperometric response upon H₂O₂. The linear range of Pt/Fe₃O₄/rGO is 0.1∼2.4 mM (R²=0.998), with a sensitivity of 6.875 μA/mM and a detection limit of 1.58 μM (S/N=3). In addition, the prepared biosensor also provides good anti‐interferent ability and long‐term stability due to the favorable biocompatibility of the electrode interface. The proposed sensor will become a reliable and effective tool for monitoring and sensing the H₂O₂ in complicate environment.     

Gold‐Iron Bimetallic Nanoparticles Impregnated Reduced Graphene Oxide Based Nanosensor for Label‐free Detection of Biomarker Related to Non‐alcoholic Fatty Liver Disease

We report for the first time a microwave assisted, one pot, direct, and facile synthesis of monodispersed iron‐gold bimetallic nanoparticles (BNP_Au‐Fe) using glucose as a reducing agent in merely 90 s. The as such synthesized BNP_Au‐Fe were thoroughly characterized using UV‐Vis, XRD, TEM, EDX, elemental mapping, and raman spectroscopy. These BNP_Au‐Fe were further impregnated with reduced graphene oxide (rGO) and coated onto glassy carbon electrode (GCE) to develop a sensor probe for label free electrochemical detection of acetaminophen, which is considered to be a most potent biomarker related to non‐alcoholic fatty liver disease. The sensor probe was systematically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The BNP_Au‐Fe‐rGO nanocomposite matrix showed the sensing of acetaminophen with a wide dynamic range between 50 and 800 nM with detection limit (DL) of 0.14 nM (±0.05) nM (RSD<4.12 %) that was lower compared to previously reported acetaminophen sensors. To show the practical application of the sensor probe, acetaminophen was detected in human urine samples, which showed the percentage recovery between 86.65 % and 91.32 %. To the best of our knowledge, this is the first report where BNP_Au‐Fe impregnated rGO was used to detect acetaminophen. Interferences due to various molecules such as glucose, serum albumin, glycine, glutamic acid, alanine, citric acid, and ascorbic acid were tested individually and in mixed sample. Long‐term stability of sensor probe was examined which was found to be stable up to 12 weeks. The sensor fabricated using BNP_Au‐Fe‐rGO nanocomposite has many attractive features such as; simplicity, rapidity, and label free detection, hence it could be a method of choice for acetaminophen detection in clinical settings.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

The Signal‐Enhanced Label‐Free Immunosensor Based on Assembly of Prussian Blue‐SiO2 Nanocomposite for Amperometric Measurement of Neuron‐Specific Enolase

A signal‐enhanced label‐free electrochemical immunosensor was constructed by the employment of Prussian blue doped silica dioxide (PB‐SiO₂) nanocomposite. At first, PB‐SiO₂ nanocomposite which was produced by using a microemulsion method was used to obtain a nanostructural monolayer on a glassy carbon electrode (GCE) surface. Next amino‐functionalized interface were prepared by self‐assembling 3‐aminopropyltriethoxy silane (APTES) on the PB‐SiO₂ nanoparticle surface. Then chitosan stabled gold nanoparticle (CS‐nanoAu) was subsequently attached, while the entire surface was finally loaded with neuron‐specific enolase antibody (anti‐NSE) via the adsorption of gold nanoparticle. The sensitivity of the proposed immunosensor has greatly improved as the PB‐SiO₂ nanostructural sensing film provides plenty of active sites which might catalyze the reduction of H₂O₂. The immunosensor exhibited good linear behavior in the concentration range from 0.25–5.0 and 5.0–75 ng/mL for the quantitative analysis of neuron‐specific enolase (NSE), a putative serum marker of small‐cell lung carcinoma (SCLC), with a limit of detection of 0.08 ng/mL. The resulting NSE immunosensor showed high sensitivity and long‐term lifetime which can be attributed to the extremely high catalytic activity and biocompatibility of CS‐nanoAu/APTES/PB‐SiO₂ nanostructural multilayers.     

Label‐free Electrochemical Aptasensor for Carcino‐embryonic Antigen Based on Ternary Nanocomposite of Gold Nanoparticles,Hemin and Graphene

In this report, a label‐free electrochemical aptasensor for carcino‐embryonic antigen (CEA) was successfully developed based on a ternary nanocomposite of gold nanoparticles, hemin and graphene nanosheets (AuNPs‐HGNs). This nanocomposite was prepared by decorating gold nanoparticles on the surface of hemin functionalized graphene nanosheets via a simple wet‐chemical strategy. The aptamer can be assembled on the surface of AuNPs‐HGNs/GCE (glassy carbon electrode) through Au‐S covalent bond to form the sensing interface. Hemin absorbed on the graphene nanosheets not only acts as a protective agent of graphene sheets, but also as an in situ probe base on its excellent redox properties. Gold nanoparticles provide with both numerous binding sites for loading CEA binding aptamer (CBA) and good conductivity to promote the electron transfer. The current changes, which are caused by CEA specifically binding on the modified electrode, are exploited for the label‐free detection of CEA in a very rapid and convenient protocol. Therefore, the method has advantages of high sensitivity, wide linear range (0.0001–10 ng mL^?1), low detection limit (40 fg mL^?1) and attractive specificity. The results illustrate that the proposed label‐free electrochemical aptasensor has a potential application in the biological or clinical target analysis for its simple operation and low cost.     

Green synthesis of reduced graphene oxide/Fe3O4/Ag ternary nanohybrid and its application as magnetically recoverable catalyst in the reduction of 4‐nitrophenol

Materials having both magnetic and catalytic properties have shown great potential for practical applications. Here, a reduced graphene oxide/iron oxide/silver nanohybrid (rGO/Fe₃O₄/Ag NH) ternary material was prepared by green synthesis of Ag on pre‐synthesized rGO/Fe₃O₄. The as‐prepared rGO/Fe₃O₄/Ag NH was characterized using Fourier transform infrared spectroscopy, X‐ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. rGO sheets were covered with Fe₃O₄ (8–16 nm) and Ag (18–40 nm) nanoparticles at high densities. The mass percentages were 13.47% (rGO), 62.52% (Fe₃O₄) and 24.01% (Ag). rGO/Fe₃O₄/Ag NH exhibited superparamagnetic behavior with high saturated magnetization (29 emu g⁻¹ at 12 kOe), and efficiently catalyzed the reduction of 4‐nitrophenol (4‐NP) with a rate constant of 0.37 min⁻¹, comparable to those of Ag‐based nanocatalysts. The half‐life of 4‐NP in the presence of rGO/Fe₃O₄/Ag NH was ca 1.86 min. rGO/Fe₃O₄/Ag NH could be magnetically collected and reused, and retained a high conversion efficiency of 94.4% after the fourth cycle. rGO/Fe₃O₄/Ag NH could potentially be used as a magnetically recoverable catalyst in the reduction of 4‐NP and environmental remediation.     

Synergetic catalytic effect of rGO,Pd, Fe3O4 and PPy as a magnetically separable and recyclable nanocomposite for coupling reactions in green media

In this paper, rGO/Pd–Fe₃O₄@PPy as an efficient stable nanocomposite was synthesized. To understand the synergetic effects of rGO, Pd, Fe₃O₄ and PolyPyrrole, the performance of rGO/Pd–Fe₃O₄@PPy as a heterogeneous recyclable nanocatalyst in the green synthesis of C‐C and C‐O coupling products, as well as different conditions are studied. Synthesized rGO/Pd–Fe₃O₄@PPy was characterized by FT‐IR, XRD, FE‐SEM, EDS, TGA and AFM analysis. Best results are obtained under sonication in H₂O for C‐C coupling and by ball‐milling for C‐O coupling. The benefits of this method include: green solvents and conditions, absence of external base, low reaction times with high yield and easy work‐up method.     

Encapsulating Au‐Fe3O4 Nanodots into AIE‐active Supramolecular Assemblies: Ambient Visible‐light Harvesting “Dip‐Strip” Photocatalyst for C−C/C−N Bond Formation Reactions

The present study demonstrates the development of a supramolecular porous ensemble consisting of hetero‐oligophenylene derivative 6 and Au‐Fe₃O₄ nanodots. Supramolecular assemblies of AIE‐active hetero‐oligophenylene derivative 6 served as reactors for the generation of Au‐Fe₃O₄ nanodots. The as prepared supramolecular ensemble functioned as an efficient recyclable photocatalytic system for C(sp²)?H bond activation of anilines for the construction of quinoline carboxylates. Interestingly, the “dip catalyst” prepared by depositing PTh‐co‐PANI‐6: Au‐Fe₃O₄ nanodots on a filter paper served as a recyclable strip (up to 10 cycles) for C?C/C?N bond formation reaction.     

Ultrasensitive Electrochemical Immunosensor for Detection of Tumor Necrosis Factor‐α Based on Functionalized MWCNT‐Gold Nanoparticle/Ionic Liquid Nanocomposite

A novel and highly sensitive electrochemical immunosensor was developed for the detection of protein biomarker tumor necrosis factor‐alpha (TNF‐α) based on immobilization of TNF‐α‐antibody (anti‐TNF‐α) onto robust nanocomposite containing gold nanoparticles (AuNP), multiwalled carbon nanotubes (MWCNTs) and ionic liquid (1‐buthyl‐3‐methylimidazolium bis (trifluoromethyl sulfonyl)imide). Functionalized MWCNT‐gold nanoparticle was produced by one‐step synthesis based on the direct redox reaction. The electrochemical properties of nanocomposite were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The anti‐TNF‐α was immobilized or entrapped in the nanocomposite and used in a sandwich type complex immunoassay with anti‐TNF‐α labeled with horseradish peroxidase as secondary antibody. Under optimum conditions, the immunosensor could detect TNF‐α in a linear range from 6.0 to 100 pg mL^?1 with a low detection limit of 2.0 pg mL^?1. The simple fabrication method, high sensitivity, good reproducibility, stability, as well as acceptable accuracy for TNF‐α detection in human serum samples are the main advantages of this immunosensor, which might have broad applications in protein diagnostics and bioassay.     

A Facile Approach to Fabricate Water‐soluble Au‐Fe3O4 Nanoparticle for Liver Cancer Cells Imaging

Au‐Fe₃O₄ nanoparticles were widely used as nanoplatforms for biologic applications through readily further functionalization. Dopamine (DA)‐coated superparamagnetic iron oxide (SPIO) nanoparticles (DA@Fe₃O₄) have been successfully synthesized using a one‐step process by modified coprecipitation method. Then 2–3 nm gold nanoparticles were easily conjugated to DA@Fe₃O₄ nanoparticles by the electrostatic force between gold nanoparticles and amino groups of dopamine to afford water‐soluble Au‐Fe₃O₄ hybrid nanoparticles. A detailed investigation by dynamic light scatting (DLS), transmission electron microscopy (TEM), fourier transform infrared (FT‐IR) and X‐ray diffraction (XRD) were performed in order to characterize the physicochemical properties of the hybrid nanoparticles. The hybrid nanoparticles were easily functionalized with a targeted small peptide A54 (AGKGTPSLETTP) and fluorescence probe fluorescein isothiocyanate (FITC) for liver cancer cell BEL‐7402 imaging. This simple approach to prepare hybrid nanoparticles provides a facile nanoplatform for muti‐functional derivations and may be extended to the immobilization of other metals or bimolecular on SPIO surface.