A method is described for the determination of the pesticide chlorothalonil (CLT). It is based on the finding that citrate-capped gold nanoparticles (AuNPs) undergo aggregation on exposure to chlorothalonil. This is accompanied by a visually detectable color change from wine red to blue. The effect is due to the interaction of the cyano group of chlorothalonil with gold nanoparticles. The assay may also be performed by using a spectrometer. The ratio of absorbances at 700 nm and 520 nm (A700/A520) linearly drops in the 5 to 100 ng·mL?1 CLT concentration range, with a 3.6 ng·mL?1 detection limit. This is below the Chinese guideline value for cucumber. The method is rather simple and does not require any modification of the AuNPs or the utilization of antibody. It was successfully applied to the determination of CLT in (spiked) cucumber samples. Recoveries ranged from 80.4 to 97.4%, and the analytical results compared well with those obtained by HPLC.
Graphical abstract Schematic of the assay. The strong interaction of the cyano group of acetamiprid with gold nanoparticles (AuNPs) via Au-N bond induces the aggregation of gold nanoparticles, and this is accompanied by a color change from red to purple.
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 a voltammetric immunosensor with antibody immobilized on a glassy carbon electrode (GCE) modified with N-doped graphene (N-GS), electrodeposited gold nanoparticles (AuNPs) and chitosan (Chit). The preparation is simple and the thickness of the electrodeposited films can be well controlled. Due to the specific advantages of N-GS, AuNPs and Chit, the electrode has a large specific surface, improved conductivity, high stability. A new label-free immunosensor for the model antigen (alpha fetoprotein, AFP) detection was then designed by employing N-GS-AuNP-Chit as the antibody immobilization and signal amplification platform. Differential pulse voltammetry and electrochemical impedance spectroscopy were used for the characterization of the stepwise assembly process. Under the optimized conditions, at a typical working potential of +0.20 V (vs. SCE), and by using hexacyanoferrate as an electrochemical probe, the immunosensor has a detection limit as low as 1.6 pg mL?1 and a linear analytical range that extends from 5 pg mL?1 to 50 ng mL?1. AFP was quantified in spiked human serum samples with acceptable precision.
Graphical Abstract Schematic of sensitive and effective label-free electrochemical immunosensor for the detection of AFP based on N-GS-AuNP-Chit as signal amplification matrix.
The fucosylated Golgi protein 73 (fuc-GP73) has been used as a criterion to distinguish hepatocellular carcinoma (HCC) from other chronic liver diseases. We describe an amperometric aptasensor for ultrasensitive detection of fuc-GP73 that uses a thiolated aptamer against GP73 as the capture probe, and gold nanoparticles (AuNPs) modified with Avidinlens culinaris agglutinin (A-LCA) as the detection probe. The AuNPs on the surface of a gold electrode provide a large surface for immobilization of A-LCA, so that they can be heavily loaded with biotinylated horse radish peroxidase (B-HRP) via avidin-biotin interactions. This results in enhanced analytical sensitivity. Under optimized conditions and a typical working potential as low as 48 mV (vs. SCE), the dynamic response of the electrode covers the 10 pg·mL?1 to 25 ng·mL?1 fuc-GP73 concentation range, with a 7 pg·mL?1 detection limit (for an S/N ratio of 3). The assay is precise, selective and reproducible. It was applied to the determination of fuc-GP73 in serum.
Graphical abstract Schematic of an electrochemical aptasensor for the determination of fucosylated golgi protein 73 (fuc-gp73) based on the avidin-Lens culinaris agglutinin (A-LCA) and biotinylated horse radish peroxidase (B-HRP). It was applied to serum analysis with good sensitivity, selectivity and reproducibility.
CdTe quantum dots (QDs) were integrated with polyethyleneimine-coated carbon dots (PEI-CDs) to form a dually emitting probe for heparin. The red fluorescence of the CdTe QDs is quenched by the PEI-CDs due to electrostatic interactions. In the presence of heparin, the blue fluorescence of PEI-CDs remains unaffected, while its quenching effect on the fluorescence of CdTe QDs is strongly reduced. A ratiometric fluorometric assay was worked out. The ratio of the fluorescences at 595 and 436 nm serves as the analytical signal. Response is linear in the concentration range of 50–600 ng·mL?1 (0.1–1.2 U·mL?1) of heparin. The limit of detection is 20 ng·mL?1 (0.04 U·mL?1). This makes the method a valuable tool for heparin monitoring during postoperative and long-term care. This assay is relatively free from the interference by other analogues which commonly co-exist with heparin in samples, and it is more robust than single-wavelength based assays.
Graphical abstract In the presence of heparin, the fluorescence of polyethyleneimine-coated carbon dots (PEI-CDs) at 436 nm remains unaffected, while its quenching effect on the fluorescence of CdTe at 595 nm is strongly reduced.
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.
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%.
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.
We describe an immunochromatographic electrochemical biosensor (IEB) for highly specific and sensitive determination of Hg(II) ions. The IEB is based on the use of a new monoclonal antibody (McAb) against Hg(II) ions that affects the recognition of an antigen. The McAb is placed on the surface of gold nanoparticles (AuNPs) and can recognize the antigen only in the absence of Hg(II) ions. This detection scheme was used to design an immunochromatographic test strip using dually labeled AuNPs along with electrochemical detection. Signal amplification was accomplished by a competitive reaction and the use of horseradish peroxidase. Following immunochromatography, the test zone was cut out and transferred into a reaction cell loaded with a substrate solution containing ortho-phenylenediamine and H2O2. After 10-min incubation with horseradish peroxidase, square wave voltammetry was performed with a screen-printed electrode. Under optimal conditions and a working voltage of ?0.57 V, the IEB displays a linear response in the 0.1 to 200 ng.mL?1 Hg(II) concentration range and a 30 pg.mL?1 limit of detection. It was applied to the determination of Hg(II) in (spiked) waters and milk where its sensitivity by far surpassed the maximum allowed contamination levels. This sensitive IEB therefore possesses substantial advantages over other assays. In addition, the detection scheme may be extended to other metal ions for which appropriate antibodies are available.
Graphical abstract We developed an immunochromatographic electrochemical biosensor (IEB) for highly specific and sensitive determination of Hg(II) ions in water and milk by using a new anti-Hg2+ monoclonal antibody (McAb). The linear range and limit of detection is 0.1–200 ng·mL?1 and 30 pg.mL?1, respectively.
This work describes the preparation of carbon dots doped with terbium(III) (Tb-CDs) via a hydrothermal method, starting from terbium ion and ethylenediamine. The size, composition and spectral properties of the Tb-CDs were characterized by transmission electron microscopy, infrared spectra, and fluorescence spectra. The results show that doping of the CDs with Tb(III) reduces the particle size and results in more uniform particles, while fluorescence (at excitation/emission peaks of 380/475 nm) is strongly enhanced. The interaction between Tb-CDs and ct-DNA results in fluorescence quenching of Tb-CDs. The findings were exploited to design a quenchometric method for the determination of ct-DNA. The signal drops linearly in the 80 ng·mL?1 to 50 μg·mL?1 ct-DNA concentration range, and the detection limit is 53 ng·mL?1. The method was applied to the determination of ct-DNA in spiked samples and gave satisfactory results. The possible fluorescence quenching mechanism (which is mainly static) was investigated using the Stern–Volmer equation and thermodynamic equations.
Graphical abstract A kind of carbon dots doped with terbium(III) (Tb-CDs) were prepared via a hydrothermal method, using terbium ion and ethylenediamine as precursor. Doping with Tb(III) reduced the particle size of CDs and results in uniform particle size and stronger fluorescence. The interaction between the Tb-CDs and dsDNA results in quenching of the fluorescence of Tb-CDs and can be applied to determination of dsDNA.
We describe a colorimetric assay for the determination of the activity of cellulase and xylanase. Following enzymatic hydrolysis, reductive saccharides are produced which are capable of directly reducing auric acid to form gold nanoparticles (AuNPs). The AuNPs are of fuchsia color and possess a strong plasmonic absorption band at 550 nm. Reaction conditions such as temperature, reaction time, and pH of the solution were optimized. A linear relationship between the concentrations of saccharide and the plasmon absorption of gold nanoparticles at 550 nm allowed for quantitative detection of the saccharides formed in solution, from which the hydrolase activity can be calculated. The detection limits for cellulase and xylanase are 0.14 and 0.080 IU mL?1. The results were compared with those of the 3,5-dinitrosalicylic acid method and showed the established method to be reliable and accurate.
Graphical abstract Following enzymatic hydrolysis, reductive saccharides are produced which are capable of directly reducing auric acid to form colloidal gold. The plasmon absorption of the colloidal gold is directly proportional to the amount of reductive saccharides, which can be used to calculate the activity of hydrolase indirectly.
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 authors report an aptaelectrode based on graphene modified iron-oxide chitosan hybrid (CHIT-IO-GR) nanocomposite film deposited on fluorine tin oxide (FTO) for the detection of the Mycobacterium tuberculosis specific antigen MPT64. The biotinylated DNA aptamer sequence specific to the MPT64 was immobilized onto the CHIT-IO-GR/FTO electrode by using streptavidin-biotin interactions. XRD, FT-IR, FE-SEM and electrochemical studies were applied to monitor the steps of the fabrication. The aptaelectrode, operated best at typical voltage of 0.44 V, exhibited a limit of detection (LOD) of 0.9 fg?mL?1 within 20 min. The biosensor retained about 80% of its initial activity after 10 uses. The potential application of the aptasensor was established by spike-in studies to obtain recoveries between 83 and 95%.
Graphical abstract An electrochemical aptaelectrode based on nanocomposite consisting of chitosan (CHIT), iron-oxide nanoparticles (IO) and functionalized graphene (GR) has been fabricated to detect M. tb antigen MPT64 with an LOD of 0.9 fg?mL?1 within 20 min.
The authors describe a method for signal amplification of label-free voltammetric immunosensors. A glassy carbon electrode (GCE) was modified with Prussian Blue-platinum nanoparticles (PB-PtNPs) as a redox-active species that gives a strong amperometric signal at 0.18 V (vs. Ag/AgCl). Benefitting from the excellent electrical conductivity and the strong catalytic activity to H2O2, the modified GCE gives a strongly enhanced signal. The PB-PtNPs were incorporated into a polyaniline (PANI) hydrogel to further enhance the signal. The signal response of the PB-PtNP-PANI/GCE is larger by a factor of 7.6 than that of PB-PtNP/GCE. In order to further improve electrical conductivity and immobilize antibody, gold nanoparticles (AuNPs) were deposited on the surface of the PB-PtNP-PANI hydrogel. The AuNP-PB-PtNP-PANI hydrogel nanocomposite on the GCE was used in an immunosensor for the model analyte carcinoma antigen 125 (CA125), a biomarker for epithelial ovarian cancer, by immobilizing the respective antibody on the modified GCE. A linear response found for the 0.01 to 5000 U mL?1 CA125 concentration range, with a detection limit of 4.4 mU mL?1 (at an S/N ratio of 3). The electrochemical sensitivity is as high as 119.76 μA·(U/mL)?1·cm?2. The detection of CA125 in human serum showed satisfactory accuracy compared to a commercial chemiluminescent microparticle immunoassay (CMIA).
Graphical abstract Schematic of a nanocomposites consisting of gold nanoparticles, Prussian Blue, platinum nanoparticles and polyaniline hydrogel as a signal multi-amplification sensing substrate for the ultrasensitive immuno detection of carcinoma antigen 125 (CA125).
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.
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 conductive hydrogel acting as a redox-active species was synthesized by crosslinking phytic acid as a ligand and lead(II) as the metal ion. The resulting gelatine-like material displays excellent redox activity and facilitates the transport of electrons and ions. Gold nanoparticles were electrochemically deposited on the hydrogel film, and antibody against cytokeratin antigen was immobilized thereon. An amperometric immunosensor for cytokeratin antigen 21–1 (CYFRA21-1), a kind of biomarker of lung cancer, was obtained by deposition of the composite on a glassy carbon electrode. If operated at ? 0.58 V (vs. Ag/AgCl), the sensor exhibits a linear detection range that extends from 50 fg mL?1 to 100 ng mL?1 CYFRA21-1, and a 38 fg mL?1 detection limit (at a signal to noise ratio of 3). The quantitation of CYFRA21-1 in (spiked) human serum samples showed satisfactory accuracy compared to an ELISA.
Graphical abstract A conductive hydrogel acting as a redox-active species was synthesized by crosslinking phytic acid as a ligand and lead(II) as the metal ion, which was used to fabricate an ultrasensitive label-free amperometric immunosensor for tumor marker.
The authors describe a quartz crystal microbalance based aptasensor for the determination of Pb2+. In order to enhance its response, oligonucleotide-embellished gold nanoparticles (AuNPs) were used to amplify the frequency changes. The method is based on the use of specific aptamers immobilized on the surface of the quartz crystal microbalance (QCM) and the binding of Pb2+, which prevents the self-assembly of the AuNPs on the QCM. Trace concentrations of Pb2+ can be determined by monitoring the change in the response frequency of the QCM. The method has a 4 nmol?L?1 detection limit and works in the 5 to 200 nmol?L?1 Pb2+ concentration range. This aptasensor also shows adequate selectivity for Pb2+ over potentially interfering metal ions.
Graphical abstract Schematic of the assay. The specific aptamer SAP does not readily combine with its partial complementary strand CSAP in the presence of Pb(II) ion. Thus, the mass change on the crystal is inversely proportional to the concentration of Pb(II).
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.
