Polypyrrole/silica/magnetite nanoparticles as a sorbent for the extraction of sulfonamides from water samples

A magnetic solid‐phase extraction sorbent of polypyrrole/silica/magnetite nanoparticles was successfully synthesized and applied for the extraction and preconcentration of sulfonamides in water samples. The magnetite nanoparticles provided a simple and fast separation method for the analytes in water samples. The silica coating increased the surface area that helped to increase the polypyrrole layer. The polypyrrole‐coated silica provided a high extraction efficiency due to the π–π and hydrophobic interactions between the polypyrrole and sulfonamides. Several parameters that affected the extraction efficiencies, i.e. the amount of sorbent, pH of the sample, extraction time, extraction temperature, ionic strength, and desorption conditions were investigated. Under the optimal conditions, the method was linear over the range of 0.30–200 μg/L for sulfadiazine and sulfamerazine, and 1.0–200 μg/L for sulfamethazine and sulfamonomethoxine. The limit of detection was 0.30 μg/L for sulfadiazine and sulfamerazine and 1.0 μg/L for sulfamethazine and sulfamonomethoxine. This simple and rapid method was successfully applied to efficiently extract sulfonamides from water samples. It showed a high extraction efficiency for all tested sulfonamides, and the recoveries were in the range of 86.7–99.7% with relative standard deviations of < 6%.     

Bismuth Film Electrode for Analysis of Tetracycline in Flow Injection System

A bismuth film was prepared on glassy carbon electrode (GCE) and used in a flow injection amperometric system to analyze tetracycline. Bismuth film electrode (BiFE) preparation and flow injection amperometric parameters were optimized. System performances of BiFE were compared to GCE. BiFE was validated with three different lots of real sample, 250 mg tetracycline capsules, the results showed good agreement, i.e., between 240 and 260 mg per capsule. Good relative recoveries were also obtained in the range of 86–106%.     

A stir foam composed of graphene oxide,poly(ethylene glycol) and natural latex for the extraction of preservatives and antioxidant

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%.

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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.

     

Disposable Electrodes for Capacitive Immunosensor

Disposable electrodes were fabricated by coating chromium (5 nm) and gold (200 nm) on glass strips (5.0 mm×25.4 mm) and used in a label‐free immunosensor. Human serum albumin (HSA) and its antigen (anti‐HSA) were used as a model system. Electropolymerization of o‐phenylenediamine was used for the immobilization of anti‐HSA by covalent binding. A linear relationship was obtained in the range from 1.0×10^?14 to 1.0×10^?9 M with a limit of detection of 8.0×10^?15 M. Each modified electrode can be reused up to 30 times. The developed system was applied for human serum samples and compared to Albumin BCG method.     

A Novel Reconfigurable Optical Biosensor Based on DNA Aptamers and a DNA Molecular Beacon

In order to alter a typical molecular aptamer beacon (MAB) to detect a different analyte there is currently a need to change the whole sensor unit including the expensive labeling fluorophores. In this work a DNA-based reconfigurable molecular aptamer beacon was developed. It is composed of two parts: a variable part and a constant part. The variable part comprises an aptamer strand and its complementary strand while the constant part is an oligonucleotide doubly labeled with a Förster Resonance Energy Transfer (FRET) pair and the two parts become joined via DNA hybridization. The sensor exists in two conformations: a folded (high FRET) and an unfolded (low FRET) in the absence and presence of the aptamer-target binding respectively. This sensor can be reconfigured by washing away the aptamer and the complementary strand using proper complementary strands, called washers. As a proof of the principle, a sensor that bound the enzyme thrombin, an analyte with a strong binding, was first constructed and then reconfigured to bind adenosine, selected as an analyte with a weak binding. We believe that the design is of universal use applicable to many types of aptamers.     

Capacitive biosensor for detection of endotoxin

A capacitive biosensor for the detection of bacterial endotoxin has been developed. Endotoxin-neutralizing protein derived from American horseshoe crab was immobilized to a self-assembled thiol layer on a biosensor transducer (Au). Upon injection of a sample containing endotoxin, a decrease in the observed capacitive signal was registered. Endotoxin could be determined under optimum conditions with a detection limit of 1.0 × 10⁻¹³ M and linearity ranging from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹⁰ M. Good agreement was achieved when applying endotoxin preparations purified from an Escherichia coli cultivation to the capacitive biosensor system, utilizing the conventional method for quantitative endotoxin determination, the Limulus amebocyte lysate test as a reference. The capacitive biosensor method was statistically tested with the Wilcoxon signed rank test, which proved the system is acceptable for the quantitative analysis of bacterial endotoxin (P < 0.05). Figure The flow-injection capacitive biosensor system and the capacitive properties of the transducer surface, where C_SAM is the capacitance change of the self-assembled thiol monolayer, C_P is the capacitance change of the protein layer, C_a is the capacitance change of the analyte layer and C_Total is the total capacitance change measured at the working electrode/solution interface (modified from Limbut et al., 2006. Biosens Bioelectron 22: 233-240)     

One-step preparation of porous copper nanowires electrode for highly sensitive and stable amperometric detection of glyphosate

A simple and sensitive amperometric method for the detection of glyphosate based on a porous copper nanowire electrode is presented. The porous nanowires were fabricated simply by a one-step electrodeposition using hydrogen bubbles generated during the deposition to produce pores. These porous nanowires provided a 1.4 times larger surface area than a porous copper film. After the fabrication process the porous copper nanowires can be applied directly as a working electrode with the same custom-built flow cell. The detection was carried out by measuring the oxidation signal of copper; this increased with the concentration of glyphosate due to dissolution of the copper from the electrode. Under optimal conditions, the responses of the sensor were linear between 0.010–5.0 µmiol L^?1, with a limit of detection of 10.0 nmol L^?1 (S/N = 3). The large surface area of the electrode minimised the corrosion effect, as observed by the remarkably stable response (95 injections of 0.20 µmol L^?1 of glyphosate were possible). When applied in order to detect glyphosate in fresh fruit and vegetable samples, the concentrations were found in the range of non-detectable to (0.104 ± 0.005) µmiol L^?1. These results indicated that the fabrication process can be used to produce a new form of working electrode for glyphosate detection.     

New sulfonate composite functionalized with multiwalled carbon nanotubes with cryogel solid‐phase extraction sorbent for the determination of β‐agonists in animal feeds

A new mixed‐mode cation‐exchange sulfonate composite functionalized with multiwalled carbon nanotubes with polyvinyl alcohol cryogel was fabricated and used for the first time as a solid‐phase extraction sorbent for the determination of β‐agonists in animal feeds. Feed samples were extracted with 0.20 M phosphoric acid and methanol (1:4, v/v) using ultrasonication, cleaned‐up using the developed sorbent to which the β‐agonists bound then finally eluted with 5.0% ammonia in methanol and analyzed by high‐performance liquid chromatography. Various parameters that affected the extraction efficiency were optimized. Under the optimal conditions, the developed sorbent strongly interacted with β‐agonists by cationic exchange and hydrophobic and hydrophilic interactions, that provided a high extraction efficiency in the range of 92.8 ± 3.7–104.4 ± 2.3% over a range of 0.04–2.0 mg/kg for salbutamol and ractopamine, and 0.40–8.0 mg/kg for clenbuterol. The relative standard deviations were less than 6.0%. The developed method was successfully applied for the determination of β‐agonists in various types of animal feed and effectively reduced any matrix interference.     

Fritless Xterra Particles Encapsulated Within a Poly(butylmethacrylate) Based Monolith for Use in CEC

Fritless columns were fabricated by encapsulating packing material within monolith for capillary electrochromatography. They were applied for separation of 3,4-methylenedioxymethamphetamine and metabolites. The packing material was suspended in polymerisation mixture and then forced into a pre-treated capillary following by polymerisation. This made the preparation much easier, saved time, cost and showed less tendency towards bubble formation with better resolution than with packed column. Using this fritless column, migration time of all analytes increased with buffer concentration and amount of organic component in mobile phase, but decreased on increasing the pH from 3.0 to 4.5 and then increased above pH 4.5.