The authors describe an upconversion nanoparticle-based (UCNP–based) fluorometric method for ultrasensitive and selective detection of Cu2+. The UCNPs show a strong emission band at 550 nm under near-infrared excitation at 980 nm. The principle of the strategy is that gold nanoparticles (AuNP) can quench the fluorescence of UCNP. In contrast, the addition of L-cysteine (Cys) can induce the aggregation of AuNP, resulting in a fluorescence recovery of the UCNPs. On addition of Cu2+, it oxidizes Cys to cystine and is reduced to Cu+. The Cu+ thusformed can be oxidized cyclically to Cu2+ by dissolved O2, which catalyzes and recycles the whole reaction. Thus, the aggregation of AuNP is inhibited and the fluorescence recovered by Cys is quenched. Under the optimal condition, the quenching efficiency shows a good linear response to the concentrations of Cu2+ in the 0.4–40 nM range. The limit of detection is 0.16 nM, which is 5 orders of magnitude lower than the U.S. Environmental Protection Agency limit for Cu2+ in drinking water (20 μM). The method has been further applied to monitor Cu2+ levels in real samples. The results of detection are well consistent with those obtained by atomic absorption spectroscopy.
Graphical abstract Gold nanoparticles (AuNP) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNP) were used in a fluorometric method for detection of Cu2+ based on a cyclic catalytic oxidation amplification strategy.
The authors describe a colorimetric assay for the determination of organophosphorous pesticides (OPPs) based on enzyme-triggered deposition of silver nanoparticles on the surface of gold nanoparticles (AuNP). In this method, alkaline phosphatase (ALP) catalyzes the dephosphorylation of the substrate p-aminophenyl phosphate (p-APP) to form p-aminophenol (p-AP) which is capable of reducing Ag(I) ion to Ag metal which is spontaneously deposited on the surface of AuNP to form Au@Ag NPs. As a result, the color of the colloidal solution first changes from red to yellow, and then to gray with further increases in the thickness of the Ag shell. This can be detected visually or by spectrophotometry. OPPs act as inhibitors of ALP so that the dephosphorylation of p-APP is blocked and silver deposition on the AuNP is retarded or completely suppressed. As a result, the color change from red to yellow is less distinct. This finding forms the basis for the determination of OPPs. Under optimum conditions, the absorbance at 370 nm depends linearly on the logarithm of inhibitor concentration over the ranges from 0.05 to 500 μg?L?1 and from 0.1 to 500 μg?L?1, with detection limits of 0.025 μg?L?1 for methamidophos and 0.036 μg?L?1 for malathion (at an S/N ratio of 3). Both values are much lower than the maximum residue limits specified in the U.S. Department of Agriculture and European Union pesticide regulations. The validation and practicability of this method for the measurement of OPPs was demonstrated by analyzing (spiked) tap water and lake water.
Graphical abstract The alkaline phosphatase (ALP) activity is inhibited by organophosphorus pesticides (OPPs). As a result, the ALP-trigged formation of core-shell gold-silver nanoparticles depends on the amount of OPPs, which showed different absorbances and colors.
The authors report on a surface molecular imprinting strategy for synthesizing magnetic and molecularly imprinted core-shell polymer nanoparticles (MMIPs) with a typical size of 320 nm. The triazophos-imprinted polymer shell on 180-nm magnetite particles (modified with 3-methacryloxypropyl trimethoxysilane) was obtained by radical polymerization of ethylene glycol dimethacrylate in the presence of triazophos, this followed by extractive removal of triazophos. The resulting MMIPs possess large binding capacity, high recognition selectivity, and fast binding kinetics for triazophos. They can be easily separated from a solution by using a magnet. These features result in a convenient and selective solid-phase extraction procedure for triazophos prior to its determination by UV spectrometry or by GC analysis. The method was successfully applied to the extraction and clean-up of triazophos residues in spiked homogenates of vegetables with recoveries in the range of 89.2 ~ 99.0%. The detection limits for triazophos by the UV assay and GC assay are 0.93 nM and 0.32 nM, respectively.
Graphical abstract The core-shell magnetic molecularly imprinted polymer nanoparticles (MMIPs) with a nanoscale triazophos-imprinted polymer shell were prepared by surface imprinting onto the surfaces of 3-methacryloxypropyl trimethoxysilane (MATS) modified Fe3O4 magnetic nanoparticles. They were successfully applied for the extraction and clean-up of ultra trace triazophos residues in spiked homogenates of vegetable samples. MMIPs exhibit the larger binding capacity, faster binding kinetics, higher recognition selectivity, good reusability and stability, and excellent magnetic responses.
This study presents a method for the selective determination of Hg(II) using electromembrane extraction (EME), followed by square wave anodic stripping voltammetry (SWASV), using a gold nanoparticle-modified glassy carbon electrode, (AuNP/GCE). By applying an electrical potential of typically 60 V for 12 min through a thin supported liquid membrane (1-octanol), Hg(II) ions are extracted from a donor phase (i.e., the sample solution) to an acidic acceptor solution (15 μL) placed in the lumen of a hollow fiber. The influences of experimental parameters during EME were optimized using face-centered central composite design. The calibration plot, established at a working voltage of 0.55 V (vs. Ag/AgCl), extends from 0.2 to 10 μg.L?1 of Hg(II). The limit of detection, at a signal to noise ratio of 3, is 0.01 μg.L?1 and the relative standard deviations (for 5 replicate determinations at 3 concentration levels) are between 7.5 and 8.7 %. The method was successfully applied to the determination of Hg(II) in spiked real water samples to give recoveries ranging from 89 to 97 %. The results were validated by cold vapor atomic absorption spectroscopy.
Graphical abstract Hg(II) ions were extracted from a donor phase into an acidic acceptor phase (15 μL) placed in the lumen of a hollow fiber using electromembrane extraction. The acceptor phase was then analyzed using anodic stripping voltammetry.
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 method for the fabrication of a nanohybrid composed of carbon dots (C-dots) and gold nanoparticles (AuNPs) by in-situ reduction of C-dots and hydroauric acid under alkaline conditions. The process does not require the presence of surfactant, stabilizing agent, or reducing agent. The hybrid material was deposited in a glassy carbon electrode (GCE), and the modified GCE exhibited good electrocatalytic activity toward the oxidation of nitrite due to the synergistic effects between carbon dots and AuNPs. The findings were used to develop an amperometric sensor for nitrite. The sensor shows a linear response in the concentration range from 0.1 μmol?L-1 to 2 mmol?L-1 and a low detection limit of 0.06 μmol?L-1 at the signal-to-noise ratio of 3.
Graphical abstract Fabrication, characterization and electrochemical behavior of a glassy carbon electrode modifid with carbon dots and gold nanoparticles for sensing nitrite in lake water.
The authors describe a method for the differentiation of penicillamine (PA) enantiomers by using CdSe/ZnS quantum dots (QDs) modified with β-cylodextrin (β-CD-CdSe/ZnS QDs). Selective enantiorecognition of L-PA and D-PA was accomplished by virtue of selective host-guest interaction between the PAs and the β-CD pockets on the QDs. The fluorescence intensity of the modified QDs decreases in the presence of L-PA. On the contrary, it increases in the presence of D-PA. These findings form the basis for a new method for recognition of PA enantiomers. Under optimized conditions, a linear relationship exists between fluorescence intensity and D-PA concentration in the 0.1 to 5.0 mg L?1 range, and between 0.8 and 5.0 mg L?1 for L-PA. Detection limits are 0.06 mg L?1 for D-PA, and 0.2 mg L?1 for L-PA. The potential of this method has been demonstrated by the determination of D-PA in pharmaceutical formulations and L-PA in (spiked) environmental samples.
Graphical abstract Selective and specific enantiorecognition of penicillamine (PA) enantiomers using β-cylodextrin modified CdSe/ZnS quantum dots is described. Fluorescence intensity increases in the presence of D-PA, but it decreases in the presence of L-PA. Results were the basis for analytical applications.
A nanocomposite modified with dibenzo-18-crown-6 was synthesized and applied as a new sorbent for the preconcentration of thallium(I) via ultrasound assisted-solid phase extraction. This extraction step was combined with electrothermal atomic absorption spectrometry to determine ultra-trace amounts of thallium(I). The nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectrometry, field emission scanning electron microscopy and transmission electron microscopy. Under the optimized conditions, a dynamic linear range from 7.0 to 435 ng L?1, a detection limit of 1.8 ng L?1 and a quantification limit of 6.0 ng L?1 were obtained. Also, the intra- and inter-day relative standard deviations for 20.0 ng mL?1 Tl(I) were calculated as ±4.8% and ±5.1%, respectively. The adsorbent was applied to the determination of thallium(I) in the environmental, biological and standard samples with satisfactory results.
Graphical abstract A magnetic nanocomposite was synthesized as adsorbent from halloysite nanotubes and a crown ether. Tl(I) ions were extracted selectively and determined by electrothermal atomic absorption spectrometry.
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 report on a simple strategy for sensitive determination of the activity of terminal deoxynucleotidyl transferase (TdT) using copper nanoclusters (CuNCs) as fluorescent probes. TdT-polymerized long chain AT-rich DNA serves as a template for the synthesis of the CuNCs, and TdT activity is detected fluorometrically at excitation/emission wavelengths of 340/570 nm. The protocol relies on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs. The calibration plot is linear in the 0.7 to 14 U L?1 activity range, with a 60 mU L?1 detection limit (at a signal-to-noise ratio of 3). The protocol was applied to determine TdT activity in acute lymphatic leukemia cells. This approach is selective, simple, convenient and cost-efficient because a complex DNA sequence is not required. In our perception, the method provides a viable new platform for monitoring the activity and inhibition of TdT.
Graphical abstract Based on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs with strong fluorescence, a turn-on fluorescence assay for TdT activity is presented.
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.
An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell of molecularly imprinted polymer (Ag@MIP). The MIP is prepared by using bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10?9 mol·L?1.
Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).
The authors have developed an electrochemical sensor for cadmium(II) that is based on the use of a conventional fluorine doped tin oxide (FTO) electrode modified with polymeric electrospun nanofibers consisting of polyamide 6 (PA6) and chitosan which were further modified with gold nanoparticles (AuNPs). The materials were characterized by infrared spectroscopy, thermal analysis (DSC and TGA), and scanning electron microscopy. The modified electrode was applied to the detection of Cd(II) by square wave voltammetry. Response is linear in the 25 to 75 μg ? L?1 Cd(II) concentration range, with a detection limit of 0.88 μg ? L?1. The relative standard deviations are 4.6% and 8.2% for intra- and inter-electrode measurements, respectively. Mercury(II), lead(II), and copper(II) did not significantly interfere.
Graphical abstract The sensing platform developed can detect cadmium(II) with a detection limit of 0.88 μg L?1, with no significant interference by mercury(II) and lead(II).
The authors describe an array for chemiluminescence (CL) based determination of cardiac troponin T (cTnT), an important cardiovascular disease marker. The tracing tag consists of silver nanoparticles (AgNPs) loaded with guanine-rich DNA sequences and detection antibody in a high numerical ratio. The loaded AgNPs were then reacted with hemin to form a hemin/G-quadruplex DNAzyme. A disposable immunosensor array was fabricated by immobilizing capture antibody on corresponding sensing sites on a glass chip. Once a sandwich immunocomplex is formed on the array, the tracing tag catalyzes the CL reaction of the luminol-p-iodophenol and H2O2 system to produce a CL signal, which is collected by a CCD camera. An intuitive CL image is obtained containing all of the spots on the array. Under optimal conditions, the method shows a wide linear range over 4 orders of magnitude (from 0.003 to 270 ng·L?1), a detection limit down to 84 fg·L?1, and a throughput as high as 44 tests·h?1. The results obtained with serum samples are in acceptable agreement with reference values. The AgNP-based tracing tag as well as the immunoassay method shows a promising potential for point-of-care testing for the early clinical diagnosis of cardiovascular disease.
Graphical abstract Schematic presentation of silver nanoparticles (AgNPs) functionalized with hemin/G-quadruplex DNAzyme for highly sensitive chemiluminescence (CL) immunoassay of cardiac troponin T (cTnT) on a glass chip array.
A stir foam composed of graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) was prepared for use in micro-solid phase extraction sorbent of preservative agents and antioxidants from cosmetic products. The extracted analytes were quantified by GC-MS. Under the optimized conditions, the calibration plots are linear in the concentration ranges between 5.0 μg·L?1 to 1.0 mg·L?1 for benzoic acid, of 10.0 μg·L?1 to 1.0 mg·L?1 for 2-methyl-3-isothiazolinone (MI), and between 1.0 μg·L?1 and 1.0 mg·L?1 for both 3-tert-butyl-4-hydroxyanisole (BHA) and 2,6-di-tert-butyl-p-hydroxytoluene (BHT). The LODs are 1.0 μg·L?1 for benzoic acid, 5.0 μg·L?1 for MI and 0.5 μg·L?1 for both BHA and BHT. The stir-foam can be easily prepared, is inexpensive and well reproducible (RSDs <3%, for n?=?6). It can be re-used for up to 12 times after which extraction efficiency has dropped to 90%. The method was successfully applied to the determination of preservatives and antioxidants in cosmetic samples. Recoveries from spiked samples ranged between 94.5?±?2.1% and 99.8?±?1.8%.
Graphical abstract A stir foam was prepared from graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) and is shown to be a most viable sorbent for the microextraction of trace amounts of preservative agents and antioxidants from cosmetic products.
Reduced graphene oxide hollow microspheres (rGO HMS) were encapsulated with gold nanoparticles (AuNPs) by spray drying. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the AuNP/rGO HMS. When placed on a glassy carbon electrode (GCE), it exhibits excellent electrochemical catalytic properties towards the oxidation of nitrite. The electrocatalytic properties were studied using various electrochemical techniques. Compared to AuNP-decorated graphene sheet based electrodes documented in the literature, the one presented here provides a larger surface area. This enhances the catalytic activity towards nitrite. The electrode, typically operated at a working potential of 0.82 V (vs. SCE), has a linear response in the 5.0 μM to 2.6 mM nitrate concentration range, and a detection limit as low as 0.5 μM (at an S/N ratio of 3).
Graphical abstract Schematic presentation of the synthesis of graphene hollow microspheres encapsulated with of gold nanoparticles (AuNP/rGO HMS) through a spray drying technique. The material was applied to the electrochemical determination of nitrite.
A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4 NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L?1 for AC, 5–100 (0.7) μmol L?1 for EP, and 6.5–145 (3) μmol L?1 for MT.
Graphical abstract A novel electrochemical sensor based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4) for the simultaneous detection of the acetaminophen, epinephrine and melatonin was fabricated
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).
Europium(III)-doped carbon dots (Eu-CDs) were prepared from citric acid and europium nitrate via a one-pot pyrolytic method. The Eu-CDs emit intense blue fluorescence (with excitation/emission peaks at 365/465 nm), are water soluble and biocompatible. On addition of 2,6-dipicolinic acid (DPA; an anthrax biomarker), ligand-to-ion energy transfer occurs from DPA to Eu(III) which has a red emission peaking at 615 nm. This results in an increase of the intensity of the red fluorescence. DPA can be detected by the ratio of fluorescence intensities at 616 and 475 nm. The method has an analytical range that extends from 5 to 700 nmol·L?1, with a 5 nmol·L?1 detection limit. The Eu-CDs also were incorporated into a test paper for visual detection of DPA with a portable UV lamp and a smartphone. In this case, the detection limit is 1 μmol·L?1. The Eu-CDs internalize well into HeLa cells, and this paves the way to bioimaging.
Graphical abstract Schematic of a method for visual detection of 2,6-dipicolinic acid (DPA, an anthrax biomarker) by using a test stripe impregnated with europium(III)-doped carbon dots (Eu-CDs).
