Fluorescence immunosensor based on p-acid-encapsulated silica nanoparticles for tumor marker detection

A novel, simple and highly sensitive amplified fluorescence label-free immunosensor by using p-acid-encapsulated silica nanomaterials has been developed for the first time. 4,4'-(2,5-Dimethoxy-1,4-phenylene)bis(ethyne-2,1-diyl)dibenzoic acid (p-acid) and p-acid-encapsulated silica were prepared, and characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, ultraviolet visible spectroscopy (UV-vis) and fluorescence spectroscopy. In layer-by-layer self-assembling processes using (3-aminopropyl)triethoxysilane, p-acid@SiO(2) was assembled on the glass substrate. Antibody was immobilized on the surface of p-acid@SiO(2) with N,N'-carbonyldiimidazole. The functional nanomaterials present good analytical properties with a calibration range of 0.1-100 ng mL(-1), and allow the detection of carcinoembryonic antigen (CEA) at a concentration as low as 0.04 ng mL(-1). What is important is that the as-synthesized p-acid@SiO(2) nanomaterials could be further extended for the detection of other biomarkers or biocompounds.     

A novel electrochemical immunosensor based on colabeled silica nanoparticles for determination of total prostate specific antigen in human serum

A novel electrochemical immunosensor using functionalized silica nanoparticles (Si NPs) as protein tracer has been developed for the detection of prostate specific antigen (PSA) in human serum. The immunosensor was carried out based on a heterogeneous sandwich procedure. The PSA capture antibody was immobilized on the gold electrode via glutaraldehyde crosslink. After reaction with the antigen in human serum, Si NPs colabeled with detection antibody and alkaline phosphatase (ALP) was sandwiched to form the immunocomplex on the gold electrode. ALP carried by Si NPs convert nonelectroactive substrate into the reducing agent and the latter, in turn, reduce metal ions to form electroactive metallic product on the electrode. Linear sweep voltammetry (LSV) was used to quantify the amount of the deposited silver and give the analytical signal for PSA. The parameters including the concentration of the ALP used to functionalize the Si NPs and the enzyme catalytic reaction time have been studied in detail and optimized. Under the optimum conditions of immunoreaction and electrochemical detection, the electrochemical immunosensor was able to realize a reliable determination of PSA in the range of 1–35 ng/mL with a detection limit of 0.76 ng/mL. For six human serum samples, the results performed with the electrochemical immunosensor were in good agreement with those obtained by chemiluminescent microparticle immunoassay (CMIA), indicating that the electrochemical immunosensor could satisfy the need of practical sample detection.     

Piezoelectric immunosensor based on magnetic nanoparticles with simple immobilization procedures

A novel method for immobilizing antibodies (antigens) based on magnetic nanoparticles has been proposed for piezoelectric immunoassay. The goat-anti-IgG antibody (IgGAb) as the model analyte was first covalently immobilized to magnetic nanoparticles, which were surface modified with amino-groups. The magnetic bio-nanoparticles (MBN-s) formed were attached to the surfaces of quartz crystal with the help of a permanent magnet. The detection of immunoglobulin G (IgG) was performed with the sensor prepared. The process of immobilization and immunoreaction was monitored by frequency recording. From the SEM images of the sensor surface before and after immobilization of MBN, one can see that the MBN was homogeneously adsorbed on sensor surface. The piezoelectric immunosensor can determine IgG in the range of 0.6-34.9 μg ml⁻¹ with a detection limit of 0.36 μg ml⁻¹. The MBN and immunocomplex layer can easily be removed simply by taking away the magnetic field, making the piezoelectric sensor easy to be regenerated.     

A label-free electrochemical immunosensor based on gold nanoparticles for detection of paraoxon

An electrochemical immunosensor for the direct determination of paraoxon has been developed based on the biocomposites of gold nanoparticles loaded with paraoxon antibodies. The biocomposites are immobilized on the glassy carbon electrode (GCE) using Nafion membrane. On the immunosensor prepared paraoxon shows well-shaped CV with reduction and oxidation peaks located −0.08 and −0.03 mV versus SCE, respectively. The detection of paraoxon performed at −0.03 mV is beneficial for guaranteeing sufficient selectivity. The amount of the biocomposite consisting gold nanoparticles loaded with antibodies and the volume of Nafion solution used for fabricating the immunosensor have been studied to ensure sensitivity and conductivity of the immunosensor. The immunosensor has been employed for monitoring the concentrations of paraoxon in aqueous samples up to 1920 μg l⁻¹ with a detection limit of 12 μg l⁻¹.     

Mixed valence Mn(II)/Mn(III) [3 x 3] grid complexes: structural, electrochemical, spectroscopic, and magnetic properties

Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.     

Highly sensitive electrochemical immunoassay for human IgG using double-encoded magnetic redox-active nanoparticles

A new sandwich-type electrochemical immunoassay was developed for the detection of human IgG using doubly-encoded and magnetic redox-active nanoparticles as recognition elements on the surface of a glassy carbon electrode modified with anti-IgG on nanogold particles. The recognition elements were synthesized by coating magnetic Fe₃O₄ nanoparticles with Prussian blue nanoparticles and then covered with peroxidase-labeled anti-IgG antibodies (POx-anti-IgG) on Prussian blue nanoparticles. The immunoelectrode displays very good electrochemical properties towards detection of IgG via using double-encoded magnetic redox-active nanoparticles as trace and hydrogen peroxide as enzyme substrate. Its limit of detection (10 pmol·L^?1) is 10-fold better than that of using plain POx-anti-IgG secondary antibodies. The method was applied to the detection of IgG in serum samples, and an excellent correspondence with the reference values was found.     

Ultrasensitive electrochemiluminescent immunosensor based on dual signal amplification strategy of gold nanoparticles-dotted graphene composites and CdTe quantum dots coated silica nanoparticles

A facile and ultrasensitive electrochemiluminescent (ECL) immunosensor for detection of prostate-specific antigen (PSA) was designed by using CdTe quantum dots coated silica nanoparticles (SiO₂@QDs) as bionanolabels. To construct such an electrochemiluminescence immunosensor, gold nanoparticles-dotted graphene composites were immobilized on the working electrode, which can increase the surface area to capture a large amount of primary antibodies as well as improve the electronic transmission rate. The as-prepared SiO₂@QDs used as bionanolabels, showed good ECL performance and good ability of immobilization for secondary antibodies. The approach provided a good linear response ranging from 0.005 to 10 ng?mL^?1 with a low detection limit of 0.0032 ng?mL^?1. Such immunosensor showed good precision, acceptable stability, and reproducibility. Satisfactory results were obtained for determination of PSA in human serum samples. Therefore, the proposed method provides a new promising platform of clinical immunoassay for other biomolecules.     

Sandwich-type electrochemical immunosensor for sensitive determination of IgG based on the enhanced effects of poly-L-lysine functionalized reduced graphene oxide nanosheets and gold nanoparticles

Journal of Solid State Electrochemistry - Poly-L-lysine functionalized reduced graphene oxide nanosheets (PLL-rGO) were prepared and thoroughly characterized with transmission electron microscopy,...     

Synthesis and electrochemical characterization of carbon nanotubes decorated with nickel nanoparticles for use as an electrochemical capacitor

Attachment of nickel nanoparticles on multiwalled carbon nanotubes (MWCNTs) was conducted to explore the influence of Ni loading on the electrochemical capacitance of MWCNT electrodes. A chemical impregnation leaded to homogeneously disperse Ni particles onto the surface of MWCNTs, and the Ni particles were found to be an average size of 30–50 nm. The capacitive behavior of the MWCNT electrodes was investigated in 6 M KOH, by using cyclic voltammetry (CV), charge–discharge cycling, and ac electrochemical impedance spectroscopy. CV measurements showed that the Faradaic current was found to increase with the Ni coverage, indicating that the presence of Ni would enhance the pseudocapacitance through the redox process. Equivalent circuit analysis indicated that both of electrical connection and charge transfer resistances accounted for the major proportion of the overall resistance and were found to decrease with the amount of nickel. A linearity relationship between the total capacitance and the Ni population reflected that each Ni particle exhibits an identical electrochemical activity in enhancing the electrochemical capacitance. The overall electrochemical capacitance (including double layer capacitance and pseudocapacitance) of Ni-MWCNT electrode can reach a maximum of 210 F/g over 500 cycles.     

A sandwich electrochemical immunosensor for Salmonella pullorum and Salmonella gallinarum based on a screen-printed carbon electrode modified with an ionic liquid and electrodeposited gold nanoparticles

This article describes an electrochemical immunosensor for rapid determination of Salmonella pullorum and Salmonella gallinarum. The first step in the preparation of the immunosensor involves the electrodeposition of gold nanoparticles used for capturing antibody and enhancing signals. In order to generate a benign microenvironment for the antibody, the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate was used to modify the surface of a screen-printed carbon electrode (SPCE). The single steps of modification were monitored via cyclic voltammetry and electrochemical impedance spectroscopy. Based on these findings, a sandwich immunoassay was worked out for the two Salmonella species by immobilizing the respective unlabeled antibodies on the SPCE. Following exposure to the analytes, secondary antibody (labeled with HRP) is added to form the sandwich. After adding hydrogen peroxide and thionine, the latter is oxidized and its signal measured via CV. A linear response to the Salmonella species is obtained in the 10⁴ to 10⁹ cfu · mL⁻¹ concentration range, and the detection limits are 3.0 × 10³ cfu · mL⁻¹ for both species (at an SNR of 3). This assay is sensitive, highly specific, acceptably accurate and reproducible. Given its low detection limit, it represents a promising tool for the detection of S. pullorum, S. gallinarum, and - conceivably - of other food-borne pathogens by exchanging the antibody.

We describe an electrochemical sandwich assay based on a screen-printed carbon electrode, gold nanoparticles and ILs and capable of detecting Salmonella pullorum and Salmonella gallinarum. The preparation is outlined in the Schematic.

     

Dispersive magnetic solid phase extraction using octadecyl coated silica magnetite nanoparticles for the extraction of tetracyclines in water samples

Magnetite nanoparticles coated with silica and hydrophobic octadecyl layers were successfully synthesized and used in magnetic solid phase extraction of tetracyclines from water samples. The magnetite nanoparticles facilitated a convenient magnetic separation of sorbent from an aqueous sample, the octadecyl layer helped to enhance the adsorption ability and the silica layer helped to prevent the aggregation of the magnetite nanoparticles. The effect of various parameters on the extraction efficiency were optimized including the amount of sorbent, sample pH, stirring rate, extraction time and desorption conditions. Under the optimum conditions, the recoveries were in the range of 82 to 88%, the calibration curves were linear over the concentration range of 0.002 to 1.0 μg/mL for oxytetracycline and 0.01 to 1.0 μg/mL for tetracycline and chlortetracycline, respectively. The developed method had several advantages such as simplicity, convenience, cost-effectiveness and high extraction efficiency.     

Rapid quantitative detection of capsaicinoids in serum based on an electrochemical immunosensor with a dual-signal amplification strategy

Journal of Solid State Electrochemistry - In this paper, a dual-signal amplified electrochemical immunosensor for quantitative detection of capsaicinoids in serum was reported, which could be used...     

A highly sensitive electrochemiluminescence immunosensor based on magnetic nanoparticles and its application in CA125 determination

A novel electrogenerated chemiluminescence (ECL) immunoassay based on enzyme amplification and magnetic nanoparticle enrichment was developed, and carbohydrate antigen 125 (CA125) was chosen as the analyte. Fe₃O₄ magnetic nanoparticles loaded with anti-CA125 were synthesized. The sandwich-type immunoassay was performed on the magnetic force-controlled carbon paste electrode via the immunoreactions among glucose oxidase-labeled anti-CA125, CA125, and anti-CA125 on the surface of magnetic nanoparticles. ECL was generated by the reaction between luminol and hydrogen peroxide. Hydrogen peroxide was produced during the enzymatic reaction with glucose and markedly increased in the presence of CA125 antigen. The CA125 concentrations were determined within the range of 0–10?mU?mL^?1, and the detection limit was 8.0 μU mL^?1. The CA125 immunosensor was more sensitive than those previously reported. The proposed ECL method also provided a simple selectivity immunoassay protocol, which was applied in the determination of CA125 in clinical serum samples.     

基于纳米材料的电化学免疫传感器在传染性病原体POCT中的应用

传染性病原体POCT对于及时有效控制传染病尤为关键。相比于传统检测方法,基于电化学免疫传感器的传染性病原体检测具有快速、灵敏、准确、易于小型化和集成化等优势,尤其适用于传染病POCT。新兴的纳米材料因其独特的理化性质可用于修饰传感器界面或作为生物分子的固载基质以及信号标记物等,有助于构建出高选择性和高灵敏度的电化学免疫传感器。在本文中,我们着重阐述了不同结构的纳米材料修饰的电化学免疫传感器在传染性病原体POCT检测中的应用,进一步介绍了基于纳米材料的电化学免疫传感器与不同检测技术联用在传染性病原体POCT中的应用,并对其发展前景做出了展望。     

Nanocomposites of gold nanoparticles and graphene oxide towards an stable label-free electrochemical immunosensor for detection of cardiac marker troponin-I

A stable label-free amperometric immunosensor is presented based on gold nanoparticles and graphene oxide nanocomposites for detection of cardiac troponin-I in the early diagnosis of myocardial infarction. For designing of the sensing platform, firstly the nanocomposites based on GO and AuNPs were prepared and anchored on electrode surfaces. The formed nanocomposites provided a platform with big surface area for loading anti-cTnI capture antibody, and worked as a bridge for fast electron transfer subsequently increased the sensitivity. Moreover, the linkages between AuNP, GO, and electrodes were based on covalent bonding by aryldiazonium salt coupling chemistry, which favors the stability of the sensing interface. Finally, the anti-cTnI detection antibody was immobilized on GO tailored with ferrocene molecules, functioning as the signal reporter for the detection of cTnI. The modification process was monitored using electrochemistry, SEM, XPS. The herein immunosensor demonstrates a good selectivity and high sensitivity against human-cTnI, and is capable of detecting cTnI at concentrations as low as 0.05 ng mL⁻¹, which is 100 times lower than that possible by conventional methods. It is potential to design the portable sensing platform based on AuNPs and GO nanocomposites for future point-of-care diagnostics.     

Disposable electrochemical immunosensor for myeloperoxidase based on the indium tin oxide electrode modified with an ionic liquid composite film containing gold nanoparticles, poly(o-phenylenediamine) and carbon nanotubes

A disposable electrochemical myeloperoxidase (MPO) immunosensor was fabricated based on the indium tin oxide electrode modified with a film composed of gold nanoparticles (AuNPs), poly(o-phenylenediamine), multi-walled carbon nanotubes and an ionic liquid. The composite film on the surface of the electrode was prepared by in situ electropolymerization using the ionic liquid as a supporting electrolyte. Negatively charged AuNPs were then adsorbed on the modified electrode via amine-gold affinity and to immobilize MPO antibody. Finally, bovine serum albumin was employed to block possible remaining active sites on the AuNPs. The modification of the electrode was studied by cyclic voltammetry and scanning electron microscopy. The factors affecting the performance of the immunosensor were investigated in detail using the hexacyanoferrate redox system. The sensor exhibited good response to MPO over two linear ranges (from 0.2 to 23.4 and from 23.4 to 300 ng.mL^?1), with a detection limit of 0.05 ng.mL^?1 (at an S/N of 3).

Turn-on fluorometric immunosensor for diethylstilbestrol based on the use of air-stable polydopamine-functionalized black phosphorus and upconversion nanoparticles

The preparation of air-stable black phosphorus (BP) is challenging because atomic layers of BP degrade rapidly on exposure to oxygen. A strategy is presented for the synthesis of BP functionalized with polydopamine (PDA/BP). Dopamine was self-polymerized to yield polydopamine (PDA) which then was used to coat the surface of BP. PDA can be easily reduced and this prevents BP degradation. PDA/BP also is a viable matrix for the adsorption of proteins due to the presence of functional groups. Without any chemical activation, diethylstilbestrol (DES)-specific monoclonal antibody was adsorbed on the PDA/BP surface. PDA/BP quenches the fluorescence antigen-modified NaYF₄:Yb,Ho,Nd upconversion nanoparticles (UCNPs; photoexcited at 808 nm) via specific immuno recognition. Exposure to DES causes the dissociation of UCNP from the PDA/BP surface and fluorescence at 475, 525, 545 and 660 nm to recover. This is due to the DES competition with antigen for binding to the antibody. Based on this competitive immuno mechanism, a turn-on fluorometric immunoassay was constructed. It has a response that covers the 0.1 to 1000 ng mL^?1 DES concentration range with a detection limit of 83 pg mL^?1. This method was successfully applied to the determination of DES in spiked food and human urine samples.

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Graphical abstract Air-stable polydopamine-functionalized black phosphorus was obtained by modification of black phosphorus with polydopamine and then was coupled with specific monoclonal antibody. Combined with antigen-modified upconversion nanoparticles, a turn-on fluorometric immunoassay was constructed to detect diethylstilbestrol.

     

Lipid,protein and poly(NIPAM) coated mesoporous silica nanoparticles for biomedical applications

In the past decade, mesoporous silica nanoparticles (MSNs) as nanocarriers have showed much potential in advanced nanomaterials due to their large surface area and pore volume. Especially, more and more MSNs based nanodevices have been designed as efficient drug delivery systems (DDSs) or biosensors. In this paper, lipid, protein and poly(NIPAM) coated MSNs are reviewed from the preparation, properties and their potential application. We also introduce the preparative methods including physical adsorption, covalent binding and self-assembly on the MSNs' surfaces. Furthermore, the interaction between the aimed cells and these molecular modified MSNs is discussed. We also demonstrate their typical applications, such as photodynamic therapy, bioimaging, controlled release and selective recognition in biomedical field.