Development and evaluation of a rapid lateral flow immunochromatographic strip assay for screening 19-nortestosterone

The lateral flow strip test for 19-nortestosterone is one kind of immunochromatographic assay. Nitrocellulose membrane was separately immobilized with goat anti-rabbit IgG (control line) and 19-NT-OVA conjugate (test line). Anti-19-NT polyclonal antibody labeled with colloidal gold particles acted as the detector reagent. The assay is qualitatively, not quantitatively, judged with positive or negative result. We tested the sensitivity of the strip using spiked swine urine, and each specimen was independently measured by LC/MS/MS. The sensitivity, measure by eye, was determined to be 200 ng/mL. The assay time was less than 15 min, and so suitable for on-site rapid test.     

Aptamer-based zearalenone assay based on the use of a fluorescein label and a functional graphene oxide as a quencher

Microchimica Acta - A versatile and cost-effective aptamer-based fluorescence quenching assay is described for the detection of the mycotoxin zearalenone (ZEN). Exfoliated functional graphene oxide...     

Three kinds of lateral flow immunochromatographic assays based on the use of nanoparticle labels for fluorometric determination of zearalenone

Colloidal gold, quantum dots and polystyrene microspheres were used as labels in three kinds of lateral flow immunochromatographic assays (ICAs) for the detection of zearalenone (ZEN) in cereal samples. The assays allow ZEN to be quantified within 20 min. The LODs are 10 μg·L^?1 of ZEN for the colloidal gold-based ICA, and 1 μg·L^?1 for both the quantum dot and polystyrene microsphere based ICAs. The respective data are 60 μg·kg^?1, 6 μg·kg^?1 and 6 μg·kg^?1, respectively, for spiked samples and cereals. Only minor cross-sensitivity occurred between ZEN and fusarium toxins, and no cross-sensitivity if found for aflatoxin B₁, T-2 mycotoxin, ochratoxin A, deoxynivalenol, and fumonisin B₁. LODs of the three assays are lower than the maximum limits of ZEN set by most standardization agencies.

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Graphical abstract Schematic presentation of three lateral flow immunochromatographic assays (ICAs) based on the use of (a) colloidal gold (CG), (b) fluorescent quantum dots (QD), and (c) polystyrene microspheres (PMs) as signalling labels for the rapid and sensitive determination of zearalenone (ZEN) in cereal samples.

     

Fluorometric determination of microRNA via FRET between silver nanoclusters and CdTe quantum dots

This paper describes a CdTe quantum dot-based fluorescence resonance energy transfer (FRET) based assay for the detection of the breast cancer biomarker microRNA. The method relies on energy transfer between DNA-templated silver nanoclusters (AgNCs) and CdTe QDs. Interaction between double strand oligonucleotide and QDs can be detected qualitatively through gel analysis and quantitatively by the signal amplification from AgNCs to QDs via FRET, best measured at an excitation wavelength of 350 nm and at emission wavelengths of 550 and 590 nm. Three microRNAs (microRNA-21, microRNA-155 and Let-7a) were quantified to verify the feasibility of the method, and a high sensitivity for microRNAs was achieved. Fluorescence intensity increases linearly with the log of the concentration of microRNA 155 in the 5.0 pM to 50 nM range, with a 1.2 pM detection limit.

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Graphical abstract Schematic presentation of a quantum dot-based (QD-based) fluorescence resonance energy transfer technique for the detection of microRNA (miRNA). The method relies on energy transfer between DNA-templated silver nanoclusters (AgNCs) and QDs.

     

Improvement of sensitivity in flow analysis by exploiting a multi-reversed software-assisted system

A multi-reversed flow system software-assisted was developed for improvement of sensitivity in flow analysis. The performance of the flow system proposed was evaluated by using as a model the conventional Griess’ colorimetric reaction for determination of nitrite in waters. The manifold incorporated three 3-way solenoid valves, a relay box solenoid actuated, a peristaltic pump, and a photometric detector. A tailored software was designed and written in Visual Basic 6.0 which allows full control of all flow system components and simultaneous acquisition and processing of the data. The sensitivity measured as the slope of the calibration curve was improved 2.5- and 1.4-fold regarding those obtained by continuous- and stopped-flow systems, respectively. Other valuable features such as analytical throughput of 55 determinations per hour, limit of detection of 5 μg L⁻¹ (3σ_blank/slope), relative standard deviation < 2% (n = 8), and a linear dynamic range up to 1800 μg L⁻¹ were also achieved.     

Fluorometric determination of quercetin by using graphitic carbon nitride nanoparticles modified with a molecularly imprinted polymer

The authors describe a fluorescent probe for sensitive and selective determination of quercetin, an indicator for the freshness of drinks. The probe consists of silica ball encapsulated graphitic carbon nitride (g-C₃N₄) modified with a molecularly imprinted polymer (MIP). It was synthesized via reverse microemulsion. The resulting MIP@g-C₃N₄ nanocomposite was characterized by fluorescence spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray powder diffraction. Quercetin quenches the fluorescence of the MIP@g-C₃N₄ probe. The effect was used to quantify quercetin in grape juice, tea juice, black tea, and red wine by fluorometry (λ_exc?=?350 nm, λ_em?=?460 nm). Response is linear in the 10–1000 ng mL^?1 quercetin concentration range. The detection limit is 2.5 ng mL^?1, recoveries range between 90.7 and 94.1%, and relative standard deviations are between 2.1 and 5.5%.

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Graphical abstract Schematic of the synthesis of the MIP@g-C₃N₄ by a reverse microemulsion method. The probe was applied for the selective recognition and fluorometric determination of quercetin.

     

Aptamer based fluorometric determination of ATP by exploiting the FRET between carbon dots and graphene oxide

The authors describe a fluorometric aptamer based assay for adenosine triphosphate (ATP). It is based on the use of carbon dots (CDs) and graphene oxide (GO). The resultant CD-aptamer is adsorbed on the surface of GO via π-stacking and hydrophobic interaction, and the fluorescence of CD-aptamer is quenched via fluorescence resonance energy transfer (FRET) between CDs and GO. If ATP is present, it will bind to the aptamer and the CD-aptamer will be desorbed from GO. This will suppress FRET and the fluorescence of the CDs is restored. Under the optimal conditions and at typical excitation/emission wavelengths of 358/455 nm, the assay has a 80 pM detection limit and a linear range that extends from 0.10 to 5.0 nM concentrations of ATP. The method was successfully applied to the determination of ATP in yogurt samples. This method can also be conceivably applied to the detection of other analytes for which appropriate aptamers are available.

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Graphical abstract Schematic of a novel fluorometric ATP assay based on the fluorescence resonance energy transfer (FRET) between aptamer modified carbon dots (CD-aptamer) and graphene oxide (GO). CD-aptamer was used as the energy donor and molecular recognition probe, and GO acted as energy acceptor. This assay exhibits high sensitivity and selectivity with a detection limit as low as 80 pM.

     

A glassy carbon electrode modified with graphene quantum dots and silver nanoparticles for simultaneous determination of guanine and adenine

Microchimica Acta - A glassy carbon electrode (GCE) was modified with graphene quantum dots (GQDs) carrying silver nanoparticles. The modified GCE displays excellent performance in the...     

Colorimetric aggregation assay based on array of gold and silver nanoparticles for simultaneous analysis of aflatoxins,ochratoxin and zearalenone by using chemometric analysis and paper based analytical devices

A fluorometric assay was introduced to determine Acinetobacter baumannii (A. baumannii) in blood samples by utilizing Zr-MOFs both as functional coating for magnetic Fe3O4 nanoparticles to provide modification surface (Zr-mMOF) and as fluorescein carrier to produce fluorescence signals (F@UIO-66-NH2). Through strong Zr-O-P bonding, two distinct terminal phosphate-labeled A. baumannii and lipopolysaccharide (LPS) specific aptamers were attached onto Zr-MOFs to fabricate the magnetic core-shell capture probe (denoted as Zr-mMOF-p-Ab-Apt) and signal probe (denoted as F@UIO-66-NH2-p-LPS-Apt), respectively. After successive incubation with A. baumannii in blood samples and magnetic separation, the sandwich-type composite of capture probe/A. baumannii cells/signal probe was treated with high concentration of anionic phosphate ions to destroy the nano-structure of UIO-66-NH2 in the signal probe and fast release of fluorescein to produce amplified fluorescence signals. Due to the high aptamer modification efficiency of Zr-mMOF-p-Ab-Apt (up to 93%) and its strong affinity to A. baumannii, the enrichment efficiency of this capture probe has reached to 96.7%. Further, due to the high fluorescein loading efficiency of UIO-66-NH2 and our novel amplification strategy to destroy F@UIO-66-NH2-p-LPS-Apt to release and amplify fluorescein signals at 512 nm in the presence of high concentration of anionic phosphate ions, the sensitivity of this method has reached 10 cfu mL−1. This method allows enrichment and determination of A. baumannii within ~2.5 h. The limit of detection of A. baumannii in blood samples is 10 cfu mL−1 with a linear range of 101–105 cfu mL−1. This indicates the potential of this assay for diagnosis of bloodstream infection in early stage.     

Detection of DNA damage by exploiting the distance dependence of the electrochemiluminescence energy transfer between quantum dots and gold nanoparticles

Microchimica Acta - We have developed a platform to detect DNA damage induced by perfluorooctanoic acid (PFOA) by measuring the electrochemiluminescence (ECL) of a layer-by-layer electrostatic...     

Reusable sensor based on functionalized carbon dots for the detection of silver nanoparticles in cosmetics via inner filter effect

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots (a-CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440 nm. The presence of cit-AgNPs produces a remarkably quenching of a-CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in “turn-on” of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23 × 10⁻⁵ to 6.19 × 10⁻⁵ mol L⁻¹, with limits of detection (LOD) and quantification (LOQ) of 5.17 × 10⁻⁶ and 1.72 × 10⁻⁵ mol L^−1, respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods.     

Fluorometric determination and imaging of glutathione based on a thiol-triggered inner filter effect on the fluorescence of carbon dots

The authors describe a sensitive method for determination of glutathione (GSH) that is based on a thiol-triggered inner filter effect on the fluorescence of N-doped carbon dots (N-doped CDs). N-doped CDs with a quantum yield as high as 31% were prepared by a one-pot procedure, and 5,5′-dithiobis-(2-nitrobenzoic acid) was employed as a reagent for GSH recognition. The reaction product (5-thio-2-nitrobenzoic acid; TNB) acts as an absorber of the 410-nm light used to photo-excite the N-doped CDs. Hence, the fluorescence of N-doped CDs (peaking at 510 nm) is reduced with increasing concentrations of GSH. As little as 30 nM of GSH can be detected by this method. The approach was successfully applied to (a) food analysis, (b) an investigation of an oxidative stress model, and (c) to live cells imaging. The method does not require the surface of N-doped CDs to be chemically modified, and a linkage between receptor and fluorophore is not needed. In our perception, the method may become a viable tool for the detection and imaging of thiols.

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Graphical abstract Fluorescence sensing strategy for glutathione detection based on a thiol-triggered inner filter effect via new N-doped carbon dots and application to food analysis, oxidative stress study and cell imaging.

     

Antimicrobial properties of biosynthesized silver nanoparticles studied by flow cytometry and related techniques

This work reports the effect of silver bionanoparticles (Bio(AgNPs) synthesized by Actinobacteria CGG 11n on selected Gram (+) and Gram (–) bacteria. Flow cytometry, classical antibiogram method and fluorescent microscopy approach was used for evaluation of antimicrobial activity of Bio(AgNPs) and their combination with antibiotics. Furthermore, the performed research specified the capacity of flow cytometry method as an alternative to the standard ones and as a complementary method to electromigration techniques. The study showed antibacterial activity of both BioAgNPs and the combination of antibiotics/BioAgNPs against all the tested bacteria strains in comparison with a diffusion, dilution and bioautographic methods. The synergistic effect of antibiotics/BioAgNPs combination (e.g. kanamycin, ampicillin, neomycin and streptomycin) was found to be more notable against Pseudomonas aeruginosa representing a prototype of multi‐drug resistant “superbugs” for which effective therapeutic options are very limited.     

Formation of efficient catalytic silver nanoparticles on carbon nanotubes by adenine functionalization

Stuck together: Adenine/carbon nanotube hybrids trigger the formation of controlled-size catalytic silver nanoparticles on the nanotube surface. The catalytic efficiency of the resulting species was assessed in the oxidation of 2-methylhydroquinone to its corresponding benzoquinone, with complete recovery and without loss of activity of the catalyst.     

Electrocatalytic dechlorination of chloroacetic acids by silver nanoparticles modified glassy carbon electrode

A simple potentiostatic method was employed to prepare silver nanoparticles deposited on glassy carbon electrode. The silver nanoparticles exhibit extraordinary electrocatalytic activities toward the reduction process of chloroacetic acids. The electrochemical behavior of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid has been investigated by cyclic voltammetry at the silver nanoparticles-modified glassy carbon electrode in 0.1 M LiClO₄ solution; each compound exhibits a series of reduction peaks which represent sequential dechlorination steps up to acetic acid. The electrocatalytic dechlorination mechanism for chloroacetic acids was also discussed in this work.     

Colorimetric and visual read-out determination of cyanuric acid exploiting the interaction between melamine and silver nanoparticles

We present two colorimetric procedures for the determination of cyanuric acid, using silver nanoparticle-based (AgNPs) probes. The first is making use of melamine-modified AgNPs which bind to cyanuric acid through hydrogen bonding to form a large conjugate network that enhances the aggregation of AgNPs to produce an absorbance peak at 640 nm and a green coloration. In the second assay, melamine is directly added to the sample in order to form a stable complex with cyanuric acid. AgNPs are then added, resulting in the formation of an absorbance peaking at 525 nm and a color change from green (blank sample) to purple or orange-red as a function of cyanuric acid concentration. Matrix effects, that originate from the interaction of alkaline earth metals with the charged surface of the AgNPs, are mitigated through a matrix-matched calibration. In this manner, spectral transitions can be selectively attributed to the concentration of cyanuric acid, which can be even visually quantified at low mg L^?1 levels with minimum sample pre-treatment and without sophisticated instrumentation.

Chemiluminescence reactions of luminol system catalyzed by nanoparticles of a gold/silver alloy

The chemiluminescence (CL) of luminol–H₂O₂ system is strongly enhanced on addition of nanoparticles composed of a gold/silver alloy (ratio 5:4). The effect is attributed to a catalytically enhanced decomposition of H₂O₂ to produce reactive oxygen species. A reaction mechanism is proposed. Organic compounds containing hydroxy, amino, or thiol groups (such as amino acids, dopamine, pyrocatechol) can inhibit the CL signal of the system. It is concluded that the system has a large potential in terms of the determination of such compounds.