The authors describe a dye-sensitized photoelectrochemical immunoassay for the tumor marker carcinoembryonic antigen (CEA). The method employs the rhodamine dye Rh123 with red color and absorption maximum at 500 nm for spectral sensitization, and a 3D nanocomposite prepared from graphene oxide and MoS2 acting as the photoelectric conversion layer. The nanocomposite with flower-like 3D architectures was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. A photoelectrochemical sandwich immunoassay was developed that is based on the use of the nanocomposite and based on the specific binding of antibody and antigen, and by using a secondary antibody labeled with Rh123 and CdS (Ab2-Rh123@CdS). Under optimal conditions and at a typical working voltage of 0 V (vs. Hg/HgCl2), the photocurrent increases linearly 10 pg mL?1 to 80 ng mL?1 CEA concentration range, with a 3.2 pg mL?1 detection limit.
Graphical abstract Flower-like GO-MoS2 complex with high efficiency of electron transport was synthesized to construct photoelectrochemical platform. The sandwich-type immunoassay was built on this platform based on specific binding of antigen and antibody. Carcinoembryonic antigen in sample was detected sensitively by using sensitization of rhodamine dye Rh123 as signal amplification strategy.
We describe a label-free electrochemical immunosensor for the carcinoembryonic antigen (CEA). It is based on a nanocomposite consisting of electrochemically reduced graphene oxide, gold nanoparticles (AuNPs), and poly(indole-6-carboxylic acid). Coupled to nanoparticle-amplification techniques and modified with ionic liquid (IL), this immunoassay shows high sensitivity and good selectivity for CEA. At the best working voltage of 0.95 V (vs. Ag/AgCl), the lower detection limit is 0.02 ng·mL?1, and the response to CEA is linear in the range from 0.02 to 90 ng·mL?1. The method was applied to the determination of CEA in spiked serum samples and gave recoveries in the range from 98.5 % to 102 %.
Graphical abstract A label-free electrochemical immunosensor was fabricated for the carcinoembryonic antigen (CEA) with a detection limit of 0.02 ng·mL?1. It is based on a nanocomposite consisting of electrochemically reduced graphene oxide (erGO), gold nanoparticles (Au NP), and poly(indole-6-carboxylic acid) (PICA).
The authors describe an immunoassay for the determination of carcinoembryonic antigen (CEA) tumor markers by depositing a polydopamine-Pb(II) nanocomposite on the surface of a glassy carbon electrode. The nanocomposite acts as a redox system that displays a large specific surface and provides a strong current signal at ?0.464 V (vs. Ag/AgCl). After the deposition of PDA-Pb2+ on glassy carbon electrode, the electrode was additionally coated with a chitosan-gold nanocomposite. The immunoassay platform was obtained by immobilization of antibodies against carcinoembryonic antigens by using glutaraldehyde and blocking with bovine albumin. Owing to its large surface, good electrical conductivity and powerful current response, the immunoassay has a wide linear range that extends from 1 fg·mL?1 to 100 ng·mL?1, with a detection limit as low as 0.26 fg·mL?1. The results obtained with this immunoassay when determining CEAs in human serum were found to be consistent with those obtained by ELISAs.
Graphical abstract Schematic of an ultrasensitive electrochemical immunosensor for the carcinoembryonic antigen. It is based on a glassy carbon electrode modified with a polydopamine-Pb(II) nanocomposite acting as a signal-inherent substrate.
The authors describe a voltammetric immunoassay for the carcinoembryonic antigen (CEA). It is based on the use of a self-assembled magnetic nanocomposite as multifunctional signal amplification platform. The core of the nanocomposite consists of Fe3O4 microspheres, and the shell of zirconium hexacyanoferrate loaded with gold nanoparticles (AuNPs@ZrHCF@Fe3O4). The material was synthesized by an electrostatic self-assembly process which is caused by the strong interaction between cyano groups and AuNPs. The surface of the Fe3O4 microspheres was functionalized with amino groups to facilitate the immobilization of ZrHCF which acts as an electron mediator. The nanocomposite was placed on a glassy carbon electrode which then displays noteworthy electrocatalytic activity toward the reduction of hydrogen peroxide (H2O2). The AuNPs serve as a support for the immobilization of antibodies by the interaction between AuNPs and amino groups on antibodies to construct a covalent Au-N bond. This facilitates electron transfer on the electrode surface using H2O2 as the electrochemical probe. Square wave voltammetry (measured typically at +0.2 V vs. SCE) was carried out to record the electrochemical behavior. Under the optimal conditions, a response is linear in the 0.5 pg·mL?1 to 50 ng·mL?1 CEA concentration range, and the detection limit is as low as 0.15 pg·mL?1 (S/N =?3). The method is selective, highly stable and acceptably reproducible.
Graphical abstract A self-assembly magnetic nanocomposite for voltammetric immunoassay of CEA. GCE glassy carbon electrode; Au NPs gold nanoparticles; ZrHCF zirconium hexacyanoferrate; CEA carcinoembryonic antigen; Anti-CEA CEA antibody; BSA bovine serum albumin; SWV square wave voltammetry. A high sensitive voltammetric immunoassay method has been used for detecting CEA, It is based on a self-assembled magnetic nanocomposite (Au NPs@ZrHCF@Fe3O4) as multifunctional signal amplification platform.
A dual enhancing strategy has been employed to develop a sandwich type of electrochemical immunoassay for the prostate specific antigen (PSA). The signal is enhanced by using Pt-Cu hierarchical trigonal bipyramid nanoframes (HTBNFs) and a composite consisting of Fe3O4 nanoparticles and reduced graphene oxide in polydopamine that serve to capture the primary antibody (Ab1). This nanocomposite shows better electrical conductivity than Fe3O4 and reduced graphene oxide (RGO), respectively, alone. The Pt-Cu HTBNFs were used to label the secondary antibody (Ab2) and act as tags for signal amplification by virtue of their outstanding electrochemical reduction activity towards H2O2. At a working potential of +0.1 V (vs. SCE), the interference by dissolved oxygen can be avoided. This immunoassay is highly sensitive, with a linear range that extends from 0.1 pg?mL?1 to 5 ng?mL?1 and an ultralow detection limit of 0.03 pg?mL?1.
Graphical abstract Schematic of the dual amplification strategy in the immunosensor for the prostate specific antigen (PSA) that is based on the use of a first antibody (Ab1) conjugated to a Fe3O4-reduced graphene oxide nanocomposite (Fe3O4-RGO), and of Pt-Cu trigonal bipyramid nanoframes as a label for the second antibody (Ab2).
Tungsten disulfide (WS2) nanosheets were obtained by exfoliating WS2 bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl4 while fabricating the WS2 nanosheets. In this way, the GNPs were self-assembled on WS2 nanosheets to form a GNPs/WS2 nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS2 nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS2 nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL?1. The detection limit is 0.5 pg mL?1 (at S/N =?3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples.
Graphical abstract Schematic presentation of the fabrication of Au/WS2 nanocomposites by in-situ ultrasonication and the procedure for the CEA photoelectrochemical immunosensor preparation, and the photocurrent response towards the carcinoembryonic antigen.
The authors describe a voltammetric immunoassay for the carcinoembryonic antigen (CEA). A GCE was modified by electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with tannic acid (TA). Subsequently, four-armed poly(ethylene glycol) (PEG) was assembled onto the modified surface through hydrogen bonding. The fabrication steps were characterized by scanning electron microscopy, energy dispersive spectroscopy, fourier transform infrared spectroscopy, contact angle measurements, electrochemical impedance spectroscopy and differential pulse voltammetry. The PEG/TA-PEDOT surface is shown be super-hydrophilic and to possess anti-fouling capability. Antibody against CEA was then covalently immobilized on the electrode. By using hexacyanoferrate as an electrochemical probe and at a working potential of 0.18 V vs SCE, the amperometric response is linear in the 10 ag·mL?1 to 1.0 ng·mL?1 CEA concentration range, and the detection limit is as low as 4.8 ag·mL?1 (at an S/N ratio of 3). The assay was applied to the quantification of CEA in 1:10 diluted human serum samples. Recoveries ranged from 103.7 to 108.7%, and relative standard deviations from 2.9 to 4.8%.
Graphical abstract Schematic of an electrochemical immunosensor for the carcinoembryonic antigen (CEA). It is based on the use of tannic acid (TA) and poly(ethylene glycol) (PEG), both deposited on a glassy carbon electrode (GCE), and using hexacyanoferrate as the electrochemical probe. The sensor has a wide linear range and a 4.8 ag·mL?1 detection limit.
Diphenyl diselenide was immobilized on chitosan loaded with magnetite (Fe3O4) nanoparticles to give an efficient and cost-effective nanosorbent for the preconcentration of Pb(II), Cd(II), Ni(II) and Cu(II) ions by using effervescent salt-assisted dispersive magnetic micro solid-phase extraction (EA-DM-μSPE). The metal ions were desorbed from the sorbent with 3M nitric acid and then quantified via microflame AAS. The main parameters affecting the extraction were optimized using a one-at-a-time method. Under optimum condition, the limits of detection, linear dynamic ranges, and relative standard deviations (for n?=?3) are as following: Pb(II): 2.0 ng·mL?1; 6.3–900 ng·mL?1; 1.5%. Cd(II): 0.15 ng·mL?1; 0.7–85 ng·mL?1, 3.2%; Ni(II): 1.6 ng·mL?1,.6.0–600. ng·mL?1, 4.1%; Cu(II): 1.2 ng·mL?1, 3.0–300 ng·mL?1, 2.2%. The nanosorbent can be reused at least 4 times.
Graphical abstract Fe3O4-chitosan composite was modified with diphenyl diselenide as a sorbent for separation of metal ions by effervescent salt-assisted dispersive magnetic micro solid-phase extraction.
A dual-responsive sandwich-type immunosensor is described for the detection of interleukin 6 (IL-6) by combining electrochemiluminescent (ECL) and electrochemical (EC) detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures. A composite was prepared from TiO2 (anatase) mesocages (AMCs) and a carboxy-terminated ionic liquid (CTIL) and then placed on a glassy carbon electrode (GCE). In the next step, the ECL probe Ru(bpy)3(II) and antibody against IL-6 (Ab1) were immobilized on the GCE. Octahedral anatase TiO2 mesocrystals (OAMs) served as the matrix for immobilizing acid phosphatase (ACP) and secondary antibody (Ab2) labeled with horseradish peroxidase (HRP) to form a bioconjugate of type Ab2-HRP/ACP/OAMs. It was self-assembled on the GCE by immunobinding. 1-Naphthol, which is produced in-situ on the surface of the GCE due to the hydrolysis of added 1-naphthyl phosphate by ACP, is oxidized by HRP in the presence of added H2O2. This results in an electrochemical signal (typically measured at 0.4 V vs. Ag/AgCl) that increases linearly in the 10 fg·mL?1 to 90 ng·mL?1 IL-6 concentration range with a detection limit of 0.32 fg·mL?1. Secondly, the oxidation product of 1-naphthol quenches the ECL emission of Ru(bpy)32+. This leads to a decrease in ECL intensity which is linear in the 10 ag·mL?1 to 90 ng·mL?1 concentration range, with a detection limit of 3.5 ag·mL?1. The method exhibits satisfying selectivity and good reproducibility which demonstrates its potential in clinical testing and diagnosis.
Graphical abstract A dual-responsive sandwich-type immunosensor was fabricated for the detection of interleukin 6 by combining electrochemiluminescence and electrochemical detection based on the use of two kinds of TiO2 mesocrystal nanoarchitectures.
A three-dimensional porous network graphene aerogel (GAs) with large specific area and excellent conductivity was loaded with β-cyclodextrin polymer (Pβ-CD) to serve as a support for immobilization of antibodies. A highly sensitive immunosensor for the cancer marker carbohydrate antigen 15–3 (CA15–3) was designed based on the use of Pβ-CD/GAs. The large specific area of GAs warrants high loading with antibodies, and their excellent electrical conductivity warrants strong electrical signals. Based on the synergistic effect of GAs and Pβ-CD, an immunoassay was designed that is making use of hexacyanoferrate as an electrochemical probe and having a pleasantly low working potential of 0.2 V (vs. SCE). Response is linear in the 0.1 mU mL?1 to 100 U mL?1 activity range, and the lower detection limit is 0.03 mU mL?1 (at S/N =?3). The immunoassay is stable, selective and reproducible. It was applied to the analysis of spiked samples, and results were satisfactory.
Graphical abstract Schematic of an electrochemical immunoassay for the carbohydrate antigen 15–3. It is based on the use of β-cyclodextrin polymer and a graphene aerogel.
The authors describe a signal amplification strategy for highly sensitive detection of the prostate-specific antigen (PSA). This is accomplished by a combination of two methods, viz. (a) improved surface-initiated enzymatic polymerization (SIEP), and (b) the use of nanoflowers prepared from C60 fullerene and Methylene Blue (C60/MB) modified with a long single-strand DNA. C60/MB acts as a novel electrochemical indicator. The C60/MB nanoflowers improve the load of MB and promote the electron transfer. The integration of the SIEP technique and the C60/MB nanomaterial also results in improved loading of MB on the nucleic acid. Ultimately, dual cascade signal amplification is accomplished. The biosensor was constructed as follows: (a) Gold nanospheres were modified with antibody 2 (Ab2) and a thiolated oligonucleotide (referred to as S0). (2) S0 is then extended by the SIEP reaction. (3) The redox indicator C60/MB is then connected to the extended guanine-rich ssDNA which then yields the amperometric signal. (4) A sandwich immunoassay is performed by capturing the nanoprobe oy type Ab2-Au-S0 on the gold electrode modified with multi-walled carbon nanotubes (MWCNTs) and protein A. Current is measured by using differential pulse voltammetry (DPV). The synergic effect of the biofunctional nanomaterial and the signal amplification strategy greatly improves the performance of this immunoassay. Under optimized conditions and at a working voltage of typically ?0.18 V (vs Ag/AgCl), the assay has a linear range that extends from 15 pg·mL?1 to 8 ng·mL?1 of PSA. The detection limit is as low as 1.7 pg·mL?1 (at an S/N ratio of 3). In our perception, this dual amplification scheme has a wide scope in that it may become applicable to numerous other immunoassays.
Graphical abstract C60/Methylene blue nanoflowers, a novel electrochemical indicator, connect with the long single-stranded DNA (ssDNA) extended by the improved surface-initiated enzymatic polymerization method. This amplification strategy is utilized to construct a sandwich prostate-specific antigen (PSA) immunosensor.
The authors describe a method for signal amplification in electrochemical aptasensors. It is based on the induction of an increased electrochemical current by the aptamer captured on a glassy carbon electrode (GCE). The phosphate groups on the aptamer backbone are brought to reaction with added molybdate to form a redox-active molybdophosphate precipitate on the surface of the GCE that generates a strong electrochemical current. To further enhance sensitivity, gold nanorods (GNRs) were selected as a support for the immobilization of aptamers. The aptasensor was applied to the determination of the cancer biomarker carcinoembryonic antigen (CEA) in a sandwich format. Antibody against CEA, CEA (antigen) and GNRs modified with CEA aptamer were sequentially captured on the GCE. The resulting aptasensor, best operated at a voltage as low as 0.18 V vs. Ag/AgCl, is highly sensitive and has a wide linear range that extends from 0.1 pg·mL?1 to 10 ng·mL?1 of CEA. This amplification strategy uses an aptamer as both the recognition probe and signal probe and therefore simplifies signal transduction. Conceivably, this detection scheme may be adapted to numerous other electrochemical bioassays if respective antibodies and aptamers are available.
Graphical abstract Schematic presentation of an electrochemical aptasensor based on aptamer induced electrochemical current for the detection of cancer biomarker carcinoembryonic antigen (CEA). Gold nanorods (GNR) are chosen for the immobilization of aptamers to increase the loading of aptamers.
The authors describe a rapid, low-cost and sensitive approach for the determination of carbohydrate antigen 19–9 (CA 19–9) in whole blood by using magnetized carbon nanotubes (MCNTs) and a lateral flow strip biosensor (LFSB). MCNTs were synthesized by depositing magnetite (Fe3O4) nanoparticles on multiwalled carbon nanotubes (CNTs) via co-precipitation of ferric and ferrous ions within a dispersion of shortened multiwalled CNTs. Antibody against CA 19–9 (Ab1) was covalently immobilized on the MCNTs and were used to capture CA 19–9 in blood. After magnetic separation, the MCNT-Ab1-CA 19–9 complexes are applied to the LFSB, in which a capture antibody (Ab2) and a secondary antibody (Ab3) are immobilized on the test zone and control zone of the LFSB, respectively. The captured MCNTs on the test zone and control zone are producing characteristic brown bands, and this enables CA 19–9 to be visually detected. Quantitation is accomplished by reading the intensities of the bands with a portable strip reader. Under optimized conditions, the assay has a detection limit as low as 30 U·mL?1 of CA19–9 in blood. This is below the cutoff value (37 U mL?1) of CA 19–9. The assay duration for blood samples is 35 min. In our perception, the assay represents a rapid and low-cost tool for rapid determination of CA19–9 in blood that holds promise for clinical applications, particularly in limited resource settings.
Graphical abstract Schematic of a rapid, low-cost and sensitive approach to detect carbohydrate antigen 19–9 (CA 19–9) in whole blood by using magnetized carbon nanotubes (MCNT) and a lateral flow strip biosensor. The approach offers new opportunities for detecting protein markers in whole blood avoiding sample purification and pre-treatment. This may lead to a new tool for disease diagnosis and monitoring disease recurrence.
We describe a micro fluxgate based device with rectangular magnetic core for the determination of prostate specific antigen (PSA) labeled with Dynabeads. A sandwich immunoassay was employed where PSA is captured on a gold film modified with a self-assembled monolayer of antibody. The secondary antibody is labeled with Dynabeads. By applying a DC magnetic fields in the range of 460 to 700 μT, PSA can be detected with detection limit as low as 0.1 ng mL?1. This micro fluxgate-based assay offers the advantages of miniaturization, simple and conveniently manipulation, re-usability and stability. In our perception, it offers a viable approach towards clinical determination of PSA or other biomarkers.
Graphical abstract A separable detection method based on micro fluxgate and immunomagnetic beads was developed for detection of prostate specific antigen (PSA). Sandwich immunoassay was employed where PSA is captured on a gold film modified with a self-assembled monolayer of antibody. By applying a DC magnetic fields in the range of 460 to 700 μT, PSA can be detected with detection limit as low as 0.1 ng mL?1, and this bio-sensing system can also give an approximate quantitation to the concentrations of them.
CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL?1 to 100 ng·mL?1 CEA concentration range with a 0.4 fg·mL?1 detection limit. The assay was applied to the determination of CEA in human serum samples.
Graphical abstract Schematic of the assay: GCE-glassy-carbon electrode, Ab- Antibody, BSA- Bovine serum albumin, Ag- Antigen. CdSe:Eu nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen.
A magnetic sorbent was fabricated by coating the magnetized graphene oxide with polystyrene (PS) to obtain a sorbent of the type GO-Fe3O4@PS. The chemical composition and morphology of the sorbent were characterized. The sorbent was employed for the enrichment of polycyclic aromatic hydrocarbons (PAHs) from water samples. Various parameters affecting the enrichment were investigated. The PAHs were then quantified by gas chromatography with flame ionization detection. Linear responses were found in the range of 0.03–100 ng mL?1 for naphthalene and 2-methylnaphthalene, and of 0.01–100 ng mL?1 for fluorene and anthracene. The detection limits (at an S/N ratio of 3) range between 3 and 10 pg mL?1. The relative standard deviations (RSDs) for five replicates at three concentration levels (0.05, 5 and 50 ng mL?1) of analytes ranged from 4.9 to 7.4%. The method was applied to the analysis of spiked real water samples. Relative recoveries are between 95.8 and 99.5%, and RSD% are <8.4%.
Graphical abstract A magnetic sorbent was fabricated by polystyrene coated on the magnetic graphene oxide for the extraction and preconcentration of PAHs in water samples prior to their determination by gas chromatography with flame ionization detection.
The authors describe a fluorometric assay for ochratoxin A (OTA) that is based on the use of graphene oxide and RNase H-aided amplification. On addition of OTA, cAPT is replaced from the APT/cAPT hybridization complex and then hybridizes with RNA labeled with a fluorophore at the 5′-end. Eventually, the fluorophore is released by RNase H cleavage. As the concentration of OTA increases, more cAPTs are displaced, this leading to fluorescence enhancement (best measured at excitation/emission wavelengths of 495/515 nm). This RNase H-assisted cycle response results in strong signal amplification. The limit of detection, calculated on the basis of a signal to noise ratio of 3, is 0.08 ng·mL?1. Response is linear in the 0.08–200 ng·mL?1 OTA concentration range. The method is highly selective for OTA over ochratoxin B and aflatoxin B1. It was applied to the determination of OTA in red wine samples spiked at levels of 1, 7, and 50 ng·mL?1, and the recoveries ranged from 90.9 to 112%.
The authors describe a sensitive and rapid upconversion fluorescence based immunoassay for the neonicotinoid insecticide imidaclothiz (IMI). Upconversion nanoparticles (UCNPs) consisting of hexagonal phase NaYF4:Yb,Er were functionalized with amino groups and coupled to antibody against IMI. Gold nanoparticles (AuNPs) were used to label the antigen (analyte). Competitive binding of IMI and AuNPs-labeled IMI to the UCNPs-labeled antibody results in a change in the fluorescence of the UCNPs at excitation/emission wavelengths of 980/544 nm. Under optimal conditions, the concentration of IMI producing a 50% saturation of the signal (SC50) is 18.9 ng mL?1, and the limit of detection is 2.1 ng mL?1. The method was applied to the determination of IMI in (spiked) paddy water, soil, pear, rice, apple, tomato, pakchoi and cabbage. Average recoveries range from 67.4% to 104.6%, and relative standard deviations from 1.9% to 10.3%. The results correlate well with those obtained by HPLC, the relative correlation coefficient (R2) being 0.9811.
Graphical abstract Based on inner filter effect (IFE), a novel immunoassay for imidaclothiz (IMI) was developed by using upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) as labels. Competitive binding of IMI and AuNPs-labeled IMI to the UCNPs-labeled antibody results in a change in the fluorescence of the UCNPs at excitation/emission wavelengths of 980/544 nm.
A polydopamine-based molecularly imprinted polymer was deposited on the surface of magnetite (ferroferric oxide) nanoparticles (Fe3O4@PDA MIPs) and is shown to be an efficient and fairly specific sorbent for the extraction of various ochratoxins. The MIPs were characterized by IR spectroscopy and transmission electron microscopy. The adsorption capacities, evaluated through the langmuir adsorption isotherm model, are 1.8, 0.23 and 0.17 mg·g?1 for ochratoxin A, ochratoxin B and ochratoxin C, respectively. Parameters such as the amount of magnetic MIPs, pH value, time for ultrasonication, elution solvent and volume were optimized. Following desorption from the MIP with acetonitrile, the ochratoxins were quantified by HPLC with fluorometric detection. Under optimal experimental conditions, the calibration plots are linear in the range of 0.01–1.0 ng·mL?1 of OTA, 0.02–2.0 ng·mL?1 of OTB, and 0.002–0.2 ng·mL?1 of OTC. The LODs are between 1.8 and 18 pg·mL?1, and the recoveries from spiked samples are 71.0% - 88.5%, with RSDs of 2.3–3.8% in case of rice and wine samples. The MIPs can be re-used for at least 7 times.
Graphical abstract Schematic of the preparation of a magnetic molecularly imprinted polymer based on self-polymerization of dopamine in weakly alkaline solution. Ochratoxins are recognized owing to homologous cavities in the MIPs, and quantified by HPLC after desorption with acetonitrile.
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.
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.
