Showing papers in "Mikrochimica Acta in 2018"

A review on chemiresistive room temperature gas sensors based on metal oxide nanostructures, graphene and 2D transition metal dichalcogenides

Abstract: Room-temperature (RT) gas sensing is desirable for battery-powered or self-powered instrumentation that can monitor emissions associated with pollution and industrial processes. This review (with 171 references) discusses recent advances in three types of porous nanostructures that have shown remarkable potential for RT gas sensing. The first group comprises hierarchical oxide nanostructures (mainly oxides of Sn, Ni, Zn, W, In, La, Fe, Co). The second group comprises graphene and its derivatives (graphene, graphene oxides, reduced graphene oxides, and their composites with metal oxides and noble metals). The third group comprises 2D transition metal dichalcogenides (mainly sulfides of Mo, W, Sn, Ni, also in combination with metal oxides). They all have been found to enable RT sensing of gases such as NOx, NH3, H2, SO2, CO, and of vapors such as of acetone, formaldehyde or methanol. Attractive features also include high selectivity and sensitivity, long-term stability and affordable costs. Strengths and limitations of these materials are highlighted, and prospects with respect to the development of new materials to overcome existing limitations are discussed.

Metastable α-AgVO3 microrods as peroxidase mimetics for colorimetric determination of H2O2

Abstract: Single phase metastable α-AgVO3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion were synthesized by direct coprecipitation at room temperature. They are shown to be viable peroxidase mimics that catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of H2O2. Kinetic analysis indicated typical Michaelis–Menten catalytic behavior. The findings were used to design a colorimetric assay for H2O2, best measured at 652 nm. The method has a linear response in the 60 to 200 μM H2O2 concentration range, with a 2 μM detection limit. Benefitting from the chemical stability of the microrods, the method is well reproducible. It also is easily performed and highly specific.

Metal oxide nanoparticles in electrochemical sensing and biosensing: a review

Abstract: This review (with (318) refs) describes progress made in the design and synthesis of morphologically different metal oxide nanoparticles made from iron, manganese, titanium, copper, zinc, zirconium, cobalt, nickel, tungsten, silver, and vanadium. It also covers respective composites and their function and application in the field of electrochemical and photoelectrochemical sensing of chemical and biochemical species. The proper incorporation of chemical functionalities into these nanomaterials warrants effective detection of target molecules including DNA hybridization and sensing of DNA or the formation of antigen/antibody complexes. Significant data are summarized in tables. The review concludes with a discussion or current challenge and future perspectives.

Surface modification and chemical functionalization of carbon dots: a review

Abstract: Surface functional groups strongly affect the properties of carbon dots (CDs). Amino, carboxy, and hydroxy groups are most commonly encountered in CDs, and they can be introduced via covalent and noncovalent modification. This article (with 116 refs.) reviews the progress made in the past few years. Following an introduction into the field, a large section covers methods for covalent modification (via amide coupling reactions, silylation, and other reactions including esterification, sulfonylation and copolymerization). Next section reviews methods for noncovalent modifications (π interactions, complexation/chelation, and electrostatic interactions). The resulting modified CDs are powerful nanomaterials for targeting and extracting analytes, and in drug release. The modification of the surface also affects fluorescence quantum yields, complexation capacity, the color of fluorescence, and their quenching capability. Current challenges are critically assessed in the concluding section.

Electrochemical nonenzymatic sensing of glucose using advanced nanomaterials

Abstract: An overview (with 376 refs.) is given here on the current state of methods for electrochemical sensing of glucose based on the use of advanced nanomaterials. An introduction into the field covers aspects of enzyme based sensing versus nonenzymatic sensing using nanomaterials. The next chapter cover the most commonly used nanomaterials for use in such sensors, with sections on uses of noble metals, transition metals, metal oxides, metal hydroxides, and metal sulfides, on bimetallic nanoparticles and alloys, and on other composites. A further section treats electrodes based on the use of carbon nanomaterials (with subsections on carbon nanotubes, on graphene, graphene oxide and carbon dots, and on other carbonaceous nanomaterials. The mechanisms for electro-catalysis are also discussed, and several Tables are given where the performance of sensors is being compared. Finally, the review addresses merits and limitations (such as the frequent need for working in strongly etching alkaline solutions and the need for diluting samples because sensors often have analytical ranges that are far below the glucose levels found in blood). We also address market/technology gaps in comparison to commercially available enzymatic sensors.

Magnetic nanoparticle based solid-phase extraction of heavy metal ions: A review on recent advances

Abstract: This review (with 151 refs) focuses on recent progress that has been made in magnetic nanoparticle-based solid phase extraction (SPE), pre-concentration and speciation of heavy metal ions. In addition, it discusses applications to complex real samples such as environmental, food, and biological matrices. The introduction addresses current obstacles and limitations associated with established SPE approaches and discusses the present state of the art in different formats of off-line and on-line SPE. The next section covers magnetized inorganic nanomaterials for use in SPE, with subsections on magnetic silica, magnetic alumina and titania, and on magnetic layered double oxides. A further section treats magnetized carbonaceous nanomaterials for use in SPE, with subsections on magnetic graphene and/or graphene oxides, magnetic carbon nanotubes and magnetic carbon nitrides. We then discuss the progress made in SPE based on the use of magnetized organic polymers (mainly non-imprinted and ion-imprinted polymer). This is followed by shorter sections on the use of magnetized metal organic frameworks, magnetized ionic liquids and magnetized biosorbents. All sections include discussions of the nanomaterials in terms of selectivity, sorption capacity, mechanisms of sorption and common routes for material synthesis. A concluding section addresses actual challenges and discusses perspective routes towards further improvements.

Intrinsic peroxidase-like activity of rhodium nanoparticles, and their application to the colorimetric determination of hydrogen peroxide and glucose

Abstract: The intrinsic peroxidase-like activity of rhodium nanoparticles (RhNPs) and their use as catalytic labels for sensitive colorimetric assays is presented. RhNPs catalyze the oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue reaction product with a maximum absorbance at 652 nm. Kinetic studies show catalysis to follow Michaelis-Menten kinetics and a “ping-pong” mechanism. The calculated kinetic parameters indicate high affinity of RhNPs for both the substrate TMB and H2O2. In fact, they are better than other peroxidase mimicking nanomaterials and even the natural enzyme horseradish peroxidase. On the other hand, RhNPs exhibit no reactivity towards saccharides, thiols, amino acids and ascorbic acid. Based on these findings, a sensitive and selective colorimetric method was worked out for the determination of H2O2 in real samples with a linear response in the 1–100 μM concentration range. By employing glucose oxidase, the glucose assay has a linear range that covers the 5 to 125 μM glucose concentration range. The detection limits are <0.75 μM for both species. The methods were applied to the determination of H2O2 in spiked pharmaceutical formulations, and of glucose in soft drinks and blood plasma. Figures of merit include (a) good accuracy (with errors of <6%), (b) high recoveries (96.5–103.7%), and (c) satisfactory reproducibility (<6.3%).

Layered vanadium(IV) disulfide nanosheets as a peroxidase-like nanozyme for colorimetric detection of glucose.

Abstract: The authors have discovered that vanadium disulfide (VS2) nanosheets, synthesized by a hydrothermal method, exert stable peroxidase-like activity. The catalytic activity, with H2O2 as a cosubstrate, follows Michaelis-Menten kinetics and varies with temperature, pH value and H2O2 concentration. Two-dimensional VS2 sheets acting as peroxidase (POx) mimics can replace horseradish peroxidase due to their availability, robustness, and reusability. The POx-like activity of VS2 sheets was exploited to design a colorimetric glucose assay by using 3,3′,5,5′-tetramethylbenzidine as a substrate and by working at an analytical wavelength of 652 nm. The assay covers the 5 to 250 μM glucose concentration range with a 1.5 μM detection limit. It was applied to the analysis of glucose in fruit juice. In our perception, the peroxidase-like nanozyme out of the family of transition metal dichalcogenides presented here has a wide scope in that it may stimulate promising biocatalytic applications in biotechnology and analytical chemistry.

Synergic effect of silver nanoparticles and carbon nanotubes on the simultaneous voltammetric determination of hydroquinone, catechol, bisphenol A and phenol

Abstract: A glassy carbon electrode (GCE) was modified with multi-walled carbon nanotubes (MWCNT) and silver nanoparticles (AgNPs) and applied to the simultaneous determination of hydroquinone (HQ), catechol (CC), bisphenol A (BPA) and phenol by using square-wave voltammetry. The MWCNTs were deposited on the GCE and the AgNPs were then electrodeposited onto the MWCNT/GCE by the application of 10 potential sweep cycles using an AgNP colloidal suspension. The modified GCE was characterized by using SEM, which confirmed the presence of the AgNPs. The electrochemical behavior of the material was evaluated by using cyclic voltammetry, and by electrochemical impedance spectroscopy that employed hexacyanoferrate as an electrochemical probe. The results were compared to the performance of the unmodified GCE. The modified electrode has a lower charge-transfer resistance and yields an increased signal. The peaks for HQ (0.30 V), CC (0.40 V), BPA (0.74 V) and phenol (0.83 V; all versus Ag/AgCl) are well separated under optimized conditions, which facilitates their simultaneous determination. The oxidation current increases linearly with the concentrations of HQ, CC, BPA and phenol. Detection limits are in the order of 1 μM for all 4 species, and the sensor is highly stable and reproducible. The electrode was successfully employed with the simultaneous determination of HQ, CC, BPA and phenol in spiked tap water samples.

Nanoparticle assisted laser desorption/ionization mass spectrometry for small molecule analytes

Abstract: Nanoparticle assisted laser desorption/ionization mass spectrometry (NPs-ALDI-MS) shows remarkable characteristics and has a promising future in terms of real sample analysis. The incorporation of NPs can advance several methods including surface assisted LDI-MS, and surface enhanced LDI-MS. These methods have advanced the detection of many thermally labile and nonvolatile biomolecules. Nanoparticles circumvent the drawbacks of conventional organic matrices for the analysis of small molecules. In most cases, NPs offer a clear background without interfering peaks, absence of fragmentation of thermally labile molecules, and allow the ionization of species with weak noncovalent interactions. Furthermore, an enhancement in sensitivity and selectivity can be achieved. NPs enable straightforward analysis of target species in a complex sample. This review (with 239 refs.) covers the progress made in laser-based mass spectrometry in combination with the use of metallic NPs (such as AuNPs, AgNPs, PtNPs, and PdNPs), NPs consisting of oxides and chalcogenides, silicon-based NPs, carbon-based nanomaterials, quantum dots, and metal-organic frameworks.

A pregnancy test strip for detection of pathogenic bacteria by using concanavalin A-human chorionic gonadotropin-Cu 3 (PO 4 ) 2 hybrid nanoflowers, magnetic separation, and smartphone readout

Abstract: Pregnancy test strips are widely used in daily life. A commercial pregnancy test strip was modified to obtain a point-of-care device for the detection of pathogenic bacteria. Hybrid nanoflowers were prepared from concanavalin A, human chorionic gonadotropin, and Cu3(PO4)2 via a one-pot method. They were used as signaling probes in an off-the-shelf pregnancy test strip. This modified lateral flow immunoassay can detect Escherichia coli O157:H7 with a detection limit of 4 CFU·mL−1, and Salmonella typhimurium with a detection limit of 3 CFU·mL−1. Conceivably, the method has high potential as a portable and cost-effective tool for rapid determination of a wide range of analytes, especially in resource-constrained settings.

Voltammetric aptasensor for bisphenol A based on the use of a MWCNT/Fe 3 O 4 @gold nanocomposite

Abstract: The present study describes an electrochemical aptamer-based method for the determination of bisphenol A (BPA). It is making use of gold nanoparticles (AuNPs) immobilized on a conjugate between multiwalled carbon nanotubes and thiol-functionalized magnetic nanoparticles (MWCNT/Fe3O4-SH) that are modified with an aptamer. The nanocomposite was characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, elemental mapping analysis and energy dispersive X-ray diffraction. The aptasensor, typically operated at 0.20 V (vs. Ag/AgCl), has a linear response in the 0.1 to 8 nM BPA concentration range, a low detection limit (0.03 nM), and high sensitivity (86.43 μA nM−1 cm−2). Voltammetric experiments were performed by using the hexacyanoferrate redox system as an electrochemical probe. The results indicate that the presence of AuNPs, magnetic nanoparticles and MWCNTs results a synergistic electrochemical augmentation. The method is highly selective, sensitive, efficient and environmentally friendly. The method was successfully applied to the determination of BPA in spiked real samples.

Electrodes modified with 3D graphene composites: a review on methods for preparation, properties and sensing applications

Abstract: Three-dimensional (3D) porous networks of planar 2D graphene have attractive features with respect to sensing. These include a large electroactive surface area, good inner and outer surface contact with the analyte, ease of loading with (bio)catalysts, and good electrochemical sensitivity. 3D free-standing graphene can even be used directly as an electrode. This review (with 140 refs.) covers the progress made in the past years. Following an introduction into the field (including definitions), a large section is presented that covers methods for the synthesis of 3D graphene (3DG) (including chemical vapor deposition, hydrothermal methods, lithography, support assisted synthesis and chemical deposition, and direct electrochemical methods). The next section covers the key features of 3DG and its composites for use in electrochemical sensors. This section is subdivided into sections on the uses of 3D porous graphene, 3DG composites with metals and metal oxides, composites consisting of 3DG and organic polymers, and electrodes modified with 3DG, 3DGs decorated with carbon nanotubes, and others. The review concludes with a discussion of future perspectives and current challenges. Graphical Abstract A schematic of the key characteristics of three-dimensional (3D) graphene.

S,N-doped carbon dots as a fluorescent probe for bilirubin

Abstract: Carbon dots doped with sulfur and nitrogen (S,N-CDs) were utilised to design a paper-stripe based fluorescent probe for the detection of bilirubin. The S,N-CDs were synthesized through a microwave assisted route by using citric acid as carbon source and L-cysteine as a source of nitrogen and sulfur. The S,N-CDs exhibit bright blue fluorescence emission with a peak at 452 nm. Fluorescence is quenched by Fe(III) but selectively restored by bilirubin. The quenched fluorescent probe exhibit significant selectivity and sensitivity for bilirubin in the 0.2 nM to 2 nM concentration range, with a 0.12 nM detection limit. The method was applied to the determination of bilirubin in spiked human serum and urine samples. The method was used to design a paper based test stripe as a point of care device for visual bilirubin detection.

Halloysite nanotubes in analytical sciences and in drug delivery: A review

Abstract: Halloysite (HNT) is a natural inorganic mineral that has many applications in manufacturing. This review (with 192 references) covers (a) the chemical properties of halloysites, (b) the effects of alkali and acid etching on the loading capacity and the release behavior of halloysites, (c) the use of halloysite nanotubes in analytical sciences and drug delivery, and (d) recent trends in the preparation of magnetic HNTs. Synthetic methods such as co-precipitation, thermal decomposition, and solvothermal method are discussed, with emphasis on optimal magnetization. In the analytical field, recent advancements are summarized in terms of applications of HNT-nanocomposites for extraction and detection of heavy metal ions, dyes, organic pollutants, and biomolecules. The review also covers methods for synthesizing molecularly imprinted polymer-modified HNTs and magnetic HNTs. With respect to drug delivery, the toxicity, techniques for drug loading and the various classes of drug-halloysite nanocomposites are discussed. This review gives a general insight on the utilization of HNT in analytical determination and drug delivery systems which may be useful for researchers to generate new ideas.

Red emitting and highly stable carbon dots with dual response to pH values and ferric ions

Abstract: The authors describe strongly red-emitting carbon dots (CDs) which were obtained via microwave synthesis using phenylenediamine as the carbon source. The structural and optical properties of the resultant CDs are studied in some detail. The CDs possess (a) longwave emission (peaking at 620 nm under 470 nm excitation), (b) a quantum yield of ~15%, (c) a size of typically 3.8 nm; and (d) good photostability. The CDs have a pH-dependet response that covers the pH 5 to 10 range, and their fluorescence is quenched by ferric ions. The CDs can detect ferric ions in aqueous samples in the 0 to 30 μM concentration range with a lower detection limit of 15 nM. The CDs were also used to image pH values and ferric ions in E. coli bacteria.

A lateral flow immunoassay for straightforward determination of fumonisin mycotoxins based on the quenching of the fluorescence of CdSe/ZnS quantum dots by gold and silver nanoparticles

Abstract: A lateral flow immunoassay (LFIA) was developed for the determination of fumonisin mycotoxins. The fluorescence of CdSe/ZnS quantum dots (QDs), observed at excitation/emission wavelengths of 365/525 nm, is suppressed by the addition of silver nanoparticles (SNPs) or gold nanoparticles (GNPs) because SNPs overlap the excitation bands of the QDs, and GNPs overlap the emission bands. The fluorescence of the QDs is recovered upon addition of fumonisins, allowing for the sensitive detection in “positive mode” of the target mycotoxin by monitoring the changes of the QDs fluorescence intensity. The SNPs are found to be the most effective quenchers, while the use of GNPs allows for an efficient recovery of fluorescence and can be employed in the LFIA. The method was successfully applied to the fluorometric determination of fumonisins in spiked maize flour samples. The visual detection limit is at the ng·mL−1 level. This is four times lower compared to the colorimetric LFIA based on the use of the conventional gold NPs.

Colorimetric aptasensor for Campylobacter jejuni cells by exploiting the peroxidase like activity of Au@Pd nanoparticles.

Abstract: The authors describe a method for colorimetric determination of Campylobacter jejuni (C. jejuni) in milk samples. It is based on the interaction of a specific DNA aptamer with surface protein in the cell membranes of C. jejuni. Specific binding of the aptamer with the cell membrane leads to an uptake of aptamer from solution. As a result, the concentration of aptamer floating in the solution is reduced. In the presence of large quantities of aptamer, the surface of added Au@Pd nanoparticles (NPs) is covered with aptamer via electrostatic interactions. Hence, they cannot act as a peroxidase mimic and oxidize the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to give a blue product. However, when the aptamer is bound by the target cells, the surface of the NPs is not blocked by aptamer and the NPs exert a strong peroxidase -like activity. Under defined experimental conditions, the intensity of the blue color increases with the concentration of C. jejuni, and as little as 100 CFU·mL−1 can bedetected in milk.

Selective adsorption and determination of hexavalent chromium ions using graphene oxide modified with amino silanes

Abstract: Novel adsorbents are described for the preconcentration of chromium(VI). Graphene oxide (GO) was modified with various amino silanes containing one, two, or three nitrogen atoms in the molecule. These include 3-aminopropyltriethoxysilane (APTES), N-(3-trimethoxysilylpropyl)ethylenediamine (TMSPEDA), and N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMSPDETA). The resulting GO derivatives were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray fluorescence spectrometry (EDXRF). Adsorption studies show that these GO based sorbents are highly selective for Cr(VI) in the presence of Cr(III) at pH 3.5. Although the amino silanes applied in modification of GO contain different numbers of nitrogen atoms, the maximum adsorption capacities of GO derivatives are very similar (13.3–15.1 mg·g−1). Such results are in accordance with spectroscopy studies which show that the amount of amino silanes attached to GO decreases in the order of APTES > TMSPEDA > TMSPDETA. The APTES-modified GO was applied to selective and sensitive extraction of Cr(VI) ions prior to quantitation by low-power EDXRF using the Cr Kα line. The Cr(VI) ions need not be eluted from the solid adsorbent. The method has a 0.17 ng·mL−1 detection limit, and the recovery is 99.7 ± 2.2% at a spiking level of 10 ng·mL−1. The method was successfully applied to the determination of Cr(VI) in water samples.

Determination of the activity of alkaline phosphatase by using nanoclusters composed of flower-like cobalt oxyhydroxide and copper nanoclusters as fluorescent probes.

Abstract: The authors describe a sensitive fluorometric method for the determination of the activity of alkaline phosphatase (ALP). It is based on the use of a composite prepared consisting of flower-like cobalt oxyhydroxide (CoOOH) and copper nanoclusters (CuNCs). On formation of the CuNC-CoOOH aggregates, the fluorescence of the CuNCs is quenched by the CoOOH sheets. If, however, the CoOOH sheets are reduced to Co(II) ions in the presence of ascorbic acid (AA), fluorescence recovers. AA is formed in-situ by hydrolysis of the substrate ascorbic acid 2-phosphate (AA2P) as catalyzed by ALP. Thus, the ALP activity can be detected indirectly by kinetic monitoring of the increase in fluorescence, best at excitation/emission wavelengths of 335/410 nm. The assay allows ALP to be determined in 0.5 to 150 mU·mL−1 activity range and with a 0.1 mU·mL−1 detection limit. The method was successfully applied to the determination of ALP activity in (spiked) human serum samples. The assay has attractive features in being of the off-on type and immune against false positive results.

Electrochemical immunosensor for the breast cancer marker CA 15-3 based on the catalytic activity of a CuS/reduced graphene oxide nanocomposite towards the electrooxidation of catechol

Abstract: The authors report on an electrochemical immunosensor for the tumor marker carbohydrate antigen 15–3 (CA15–3). It is based on the use of a composite consisting of reduced graphene oxide (RGO) and copper sulfide (CuS) that was placed on a screen-printed graphite electrode. The electrode shows excellent activity towards the oxidation of catechol acting as an electrochemical probe, best at a working potential of 0.16 V. The electrode was modified with antibody against CA15–3. Once the analyte (CA15–3) binds to the surface of the electrode, the response to catechol is reduced. The assay has a linear response in the 1.0–150 U mL−1 CA15–3 concentration range, with a 0.3 U mL−1 lower detection limit and a sensitivity of 1.88 μA μM−1 cm−2. The immunosensor also shows good reproducibility (2.7%), stability (95% of the initial values after storing for four weeks). The method was successfully applied to the determination of CA15–3 in serum samples, and results were found to compare well to those obtained by an ELISA. Conceivably, this nanocomposite based detection scheme has a wider scope and may be applied to numerous other immunoassays.

Advances in the design of nanomaterial-based electrochemical affinity and enzymatic biosensors for metabolic biomarkers: A review.

Abstract: This review (with 340 refs) focuses on methods for specific and sensitive detection of metabolites for diagnostic purposes, with particular emphasis on electrochemical nanomaterial-based sensors. It also covers novel candidate metabolites as potential biomarkers for diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis. Following an introduction into the field of metabolic biomarkers, a first major section classifies electrochemical biosensors according to the bioreceptor type (enzymatic, immuno, apta and peptide based sensors). A next section covers applications of nanomaterials in electrochemical biosensing (with subsections on the classification of nanomaterials, electrochemical approaches for signal generation and amplification using nanomaterials, and on nanomaterials as tags). A next large sections treats candidate metabolic biomarkers for diagnosis of diseases (in the context with metabolomics), with subsections on biomarkers for neurodegenerative diseases, autism spectrum disorder and hepatitis. The Conclusion addresses current challenges and future perspectives.

Aptamer based SERS detection of Salmonella typhimurium using DNA-assembled gold nanodimers

Abstract: The authors describe a surface-enhanced Raman scattering (SERS) based aptasensor for Salmonella typhimurium (S. typhimurium). Gold nanoparticles (AuNPs; 35 nm i.d.) were functionalized with the aptamer (ssDNA 1) and used as the capture probe, while smaller (15 nm) AuNPs were modified with a Cy3-labeled complementary sequence (ssDNA 2) and used as the signalling probe. The asymmetric gold nanodimers (AuNDs) were assemblied with the Raman signal probe and the capture probe via hybridization of the complementary ssDNAs. The gap between two nanoparticles is a “hot spot” in which the Raman reporter Cy3 is localized. It experiences a strong enhancement of the electromagnetic field around the particle. After addition of S. typhimurium, it will be bound by the aptamer which therefore is partially dehybridized from its complementary sequence. Hence, Raman intensity drops. Under the optimal experimental conditions, the SERS signal at 1203 cm−1 increases linearly with the logarithm of the number of colonies in the 102 to 107 cfu·mL−1 concentration range, and the limit of detection is 35 cfu·mL−1. The method can be performed within 1 h and was successfully applied to the analysis of spiked milk samples and performed very well and with high specificity.

Dual-aptamer based electrochemical sandwich biosensor for MCF-7 human breast cancer cells using silver nanoparticle labels and a poly(glutamic acid)/MWNT nanocomposite

Abstract: This paper reports on a sensitive and selective method for the detection of Michigan Cancer Foundation-7 (MCF-7) human breast cancer cells and MUC1 biomarker by using an aptamer-based sandwich assay. A biocompatible nanocomposite consisting of multiwall carbon nanotubes (MWCNT) and poly(glutamic acid) is placed on a glassy carbon electrode (GCE). The sandwich assay relies on the use of a mucin 1 (MUC1)-binding aptamer that is first immobilized on the surface of modified GCE. Another aptamer (labeled with silver nanoparticles) is applied for secondary recognition of MCF-7 cells in order to increase selectivity and produce an amplified signal. Differential pulse anodic stripping voltammetry was used to follow the electrochemical signal of the AgNPs. Under the optimal condition, the sensor responds to MCF-7 cells in the concentration range from 1.0 × 102 to 1.0 × 107 cells·mL−1 with a detection limit of 25 cells. We also demonstrate that the MUC1 tumor marker can be detected by the present biosensor. The assay is highly selective and sensitive, acceptably stable and reproducible. This warrants the applicability of the method to early diagnosis of breast cancer.

Advances in the use of functional composites of β-cyclodextrin in electrochemical sensors.

Abstract: β-Cyclodextrin (β-CD) possess a hydrophobic inner cavity and a hydrophilic exterior surface. They exhibit excellent inclusion properties with the guest molecules that match cavity size, and β-CD-based materials drew widespread attention in electrochemical sensors. The hydroxy groups at the edge of the cavity can form hydrogen bonds and undergo electrostatic and dipole-dipole interactions with other molecules. This review (with 109 refs.) reveals β-CD-based detection mechanisms from the viewpoint of the size/shape-fit concept, and summarizes the current state of multiple electrochemical sensors based on the use of β-CD and functionalized β-CD such as carboxymethyl-β-CD, mono-(6-ethanediamine-6-deoxy)-β-CD, hydroxypropyl-β-CD, thio-β-cyclodextrin, and others.

Plasmonic DNA hotspots made from tungsten disulfide nanosheets and gold nanoparticles for ultrasensitive aptamer-based SERS detection of myoglobin

Abstract: A nanohybrid mediated SERS substrate was prepared by in-situ synthesis and assembly of gold nanoparticles (AuNPs) on exfoliated nanosheets of tungsten disulfide (WS2) to form plasmonic hotspots The nanohybrid surface was functionalized with specific aptamers which imparted high selectivity for the cardiac marker myoglobin (Mb) The fabricated aptasensor was read by SERS using a 532 nm laser and demonstrated significant signal enhancement, and this allowed Mb to be determined in the 10 f mL-1 to 01 μg mL-1 concentration range The study presents an approach to synergistically exploit the unique chemical and electromagnetic properties of both WS2 and AuNPs for many-fold enhancement of SERS signals Graphical abstract Schematic presentation of a nanohybrid-mediated SERS substrate prepared by in-situ assembly of gold nanoparticles (AuNPs) reduced on exfoliated nanosheets of tungsten disulfide (WS2) to form plasmonic hot spots Specific aptamers immobilized on the SERS surface impart high sensitivity and selectivity for the cardiac marker myoglobin (Mb)

Determination of norfloxacin or ciprofloxacin by carbon dots fluorescence enhancement using magnetic nanoparticles as adsorbent.

Abstract: The authors describe a method for the determination of norfloxacin (NOR) or ciprofloxacin (CIP). It is making use of a combination of fluorescence enhancement and magnetic solid-phase extraction (MSPE). Sulfur-doped carbon dots (S-CDs) are used as a fluorescent probe. They were prepared by a one-pot method using poly(4-styrenesulfonic acid-co-maleic acid) (PSMA) as a source for carbon and sulfur. NOR or CIP act as sensitizers of fluorescence (with excitation/emission maxima at 324/412 nm), probably due to strong hydrogen bond interaction and charge transfer with the S-CDs. The S-CDs were characterized by using TEM, XRD, XPS, FT-IR, UV-Vis and fluorescence spectroscopies. Response is linear in the 0.02-1.25 μM NOR concentration range, and the detection limit is 4.6 nM. The respective data for CIP are 0.02-1.0 μM and 6.7 nM. The average recoveries of NOR and CIP residues from spiked bovine raw milk are 96.2%~105.2% and 92.3%~102.5%. Graphical abstract Sulfur doped carbon dots (S-CDs) were synthesized by a hydrothermal method using poly(4-styrenesulfonic acid-co-maleic acid) (PSMA). Norfloxacin (NOR) or ciprofloxacin (CIP) was extracted by magnetic nanoparticles (MNPs), they were detected by carbon dots fluorescence enhancement.

Solvothermal synthesis of phosphorus and nitrogen doped carbon quantum dots as a fluorescent probe for iron(III)

Abstract: Carbon quantum dots (CQDs) doped with phosphorus and nitrogen were prepared via a hydrothermal method starting from citric acid, urea and phosphoric acid in dimethylformamide solution. The size, morphology, surface composition, energy levels, and optical properties of the CQDs were characterized. They show both green down-conversion and up-conversion fluorescence. Ferric ions (Fe3+) are found to quench the fluorescence. Cyclic voltammetry was used to identify the HOMO and LUMO levels of the doped CQDs. The quenching mechanism, as confirmed by energy level calculations and absorption spectra, can be attributed to the selective coordination of Fe3+ by the surface functional groups on the CQDs. This facilitates the photo-induced electron transfer from the CQDs to the d orbitals of Fe3+. The CQDs are shown to be viable fluorescent probes for determination of Fe3+ with high selectivity and sensitivity. The assay has a linear response in the 0.1 μM to 0.9 μM Fe3+ concentration range and a 50 nM as limit of detection (at a S/N ratio of 3).

Microfluidic paper-based device for colorimetric determination of glucose based on a metal-organic framework acting as peroxidase mimetic

Abstract: This work presents a microfluidic paper-based analytical device (μPAD) for glucose determination using a supported metal-organic framework (MOF) acting as a peroxidase mimic. The catalytic action of glucose oxidase (GOx) on glucose causes the formation of H2O2, and the MOF causes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to form a blue-green product with an absorption peak at 650 nm in the detection zone. A digital camera and the iOS feature of a smartphone are used for the quantitation of glucose with the S coordinate of the HSV color space as the analytical parameter. Different factors such as the concentration of TMB, GOx and MOF, pH and buffer, sample volume, reaction time and reagent position in the μPAD were optimized. Under optimal conditions, the value for the S coordinate increases linearly up to 150 μmol·L−1 glucose concentrations, with a 2.5 μmol·L−1 detection limit. The μPAD remains stable for 21 days under conventional storage conditions. Such an enzyme mimetic-based assay to glucose determination using Fe-MIL-101 MOF implemented in a microfluidic paper-based device possesses advantages over enzyme-based assays in terms of costs, durability and stability compared to other existing glucose determination methods. The procedure was applied to the determination of glucose in (spiked) serum and urine.

Electrochemical determination of dopamine and uric acid using a glassy carbon electrode modified with a composite consisting of a Co(II)-based metalorganic framework (ZIF-67) and graphene oxide

Abstract: A composite was prepared from a Co(II)-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) by an in situ growth method. The material was electrodeposited on a glassy carbon electrode (GCE). The modified GCE was used for the simultaneous voltammetric determination of dopamine (DA) and uric acid (UA), typically at working potentials of 0.11 and 0.25 V (vs. SCE). The morphology and structure of the nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The modified electrode exhibits excellent electroanalytical performance for DA and UA owing to the synergistic effect of the high electrical conductivity of GO and the porosity of ZIF-67. By applying differential pulse voltammetry, a linear response is found for DA in the 0.2 to 80 μM concentration range, and for UA between 0.8 and 200 μM, with detection limits of 50 and 100 nM (at S/N = 3), respectively. Further studies were performed on the effect of potential interferents, and on electrode stability and reproducibility. The modified GCE was applied to the simultaneous detection of DA and UA in spiked human urine and gave satisfying recoveries.