Visible‐Light‐Driven Janus Microvehicles in Biological Media

A light‐driven multifunctional Janus micromotor for the removal of bacterial endotoxins and heavy metals is described. The micromotor was assembled by using the biocompatible polymer polycaprolactone for the encapsulation of CdTe or CdSe@ZnS quantum dots (QDs) as photoactive materials and an asymmetric Fe₃O₄ patch for propulsion. The micromotors can be activated with visible light (470–490 nm) to propel in peroxide or glucose media by a diffusiophoretic mechanism. Efficient propulsion was observed for the first time in complex samples such as human blood serum. These properties were exploited for efficient endotoxin removal using lipopolysaccharides from Escherichia coli O111:B4 as a model toxin. The micromotors were also used for mercury removal by cationic exchange with the CdSe@ZnS core–shell QDs. Cytotoxicity assays in HeLa cell lines demonstrated the high biocompatibility of the micromotors for future detoxification applications.     

Press-transferred carbon black nanoparticles on board of microfluidic chips for rapid and sensitive amperometric determination of phenyl carbamate pesticides in environmental samples

The authors describe a strategy for rapid and sensitive determination of phenyl carbamate pesticides in environmental samples. It consists of the following steps: (a) Enrichment and clean-up of the analytes using a C18 microtip based procedure; (b) alkaline hydrolysis of the carbamates (carbofuran, isoprocarb and carbaryl) to form phenol derivatives; and (c) fast separation and amperometric detection in a microfluidic chip (MCs). The microchips were fabricated by using press-transferred carbon black nanoparticles (CB-NPs) as electrochemical sensing nanomaterial. The excellent electrochemical behavior of the CB-NPs coupled to the microchip warrants good separation and allows for the voltammetric determination (best at a working voltage of +0.70 V vs Ag/AgCl) of the carbamates within < 6 min. The authors also describe a rapid procedure for the clean-up and enrichment of the carbamates from real samples by using a C18 microtip. The procedure allowed a 10-fold enrichment of the analytes, and this led to a detection limits in ?the 0.7 to 1.2 μM concentration range. The assay was applied to samples of river, lake and irrigation water that were spiked with carbamates at 50 and 100 μM levels. Recoveries are in the 87 to 108 % range, and RSDs (n = 3) in the 5 to 11 % range. The exploitation of the such nanomaterials coupled to microfluidics and microextraction procedures for real sample analysis in our preception represents a most viable tool for the analysis of complex real samples, for on-site environmental monitoring, and for rapid diagnosis.

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Graphical abstract Press-printed carbon black nanoparticles films on board of microfluidic chips.

     

Supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer for the determination of vanillin in food samples

An on-line supported liquid membrane-piezoelectric detection system, based on a molecularly imprinted polymer (SLM-QCM-MIP) manifold, has been developed and applied to the quantitative determination of vanillin in food samples. The analyte is extracted from a donor phase into the hydrophobic membrane, and then back extracted into a second aqueous phase used as the acceptor solution. The quantification of vanillin was performed using a quartz crystal microbalance modified with a molecularly imprinted polymer (MIP). The method shows a linear range between 5 and 65 μM, with a relative standard deviation of ±4.8% (at 5 μM). The method was validated by analysing food samples and comparing the results with an SLM based on spectrophotometric quantification.     

2, 4‐Dimethylpenta‐1, 3‐dien‐ und 2, 4‐Dimethylpentadienyl‐Komplexe des Rhodiums und Iridiums

2, 4‐Dimethylpenta‐1, 3‐diene and 2, 4‐Dimethylpentadienyl Complexes of Rhodium and Iridium The complexes [(η⁴‐C₇H₁₂)RhCl]₂ ( 1 ) (C₇H₁₂ = 2, 4‐dimethylpenta‐1, 3‐diene) and [(η⁴‐C₇H₁₂)₂IrCl] ( 2 ) were obtained by interaction of C₇H₁₂ with [(η²‐C₂H₄)₂RhCl]₂ and [(η²‐cyclooctene)₂IrCl]₂, respectively. The reaction of 1 or 2 with CpTl (Cp = η⁵‐C₅H₅) yields the compounds [CpM(η⁴‐C₇H₁₂)] ( 3a : M = Rh; 3b : M = Ir). The hydride abstraction at the pentadiene ligand of 3a , b with Ph₃CBF₄ proceeds differently depending on the solvent. In acetone or THF the “half‐open” metallocenium complexes [CpM(η⁵‐C₇H₁₁)]BF₄ ( 4a : M = Rh; 4b : M = Ir) are obtained exclusively. In dichloromethane mixtures are produced which additionally contain the species [(η⁵‐C₇H₁₁)M(η⁵‐C₅H₄CPh₃)]BF₄ ( 5a : M = Rh; 5b : M = Ir) formed by electrophilic substitution at the Cp ring, as well as the η³‐2, 4‐dimethylpentenyl compound [(η³‐C₇H₁₃)Rh{η⁵‐C₅H₃(CPh₃)₂}]BF₄ ( 6 ). By interaction of 2, 4‐dimethylpentadienyl potassium with 1 or 2 the complexes [(η⁴‐C₇H₁₂)M(η⁵‐C₇H₁₁)] ( 7a : M = Rh; 7b : M = Ir) are generated which show dynamic behaviour in solution; however, attempts to synthesize the “open” metallocenium cations [(η⁵‐C₇H₁₁)₂M]⁺ by hydride abstraction from 7a , b failed. The new compounds were characterized by elemental analysis and spectroscopically, 4b and 5a also by X‐ray structure analysis.     

Magnetic Fields Enhanced the Performance of Tubular Dichalcogenide Micromotors at Low Hydrogen Peroxide Levels

Propulsion at the microscale has attracted significant research interest. In this work, a numerical simulation to explain the speed boost of up to 34 % experienced by transition metal dichalcogenides (TMD) based micromotors under the effect of applied magnetic fields is described. The simulations show that, when an external magnetic field is applied, the flow regime changes from turbulent to laminar. This causes an increase in the residence time of the fuel over the catalyst surface, which enhances the oxygen production. The more efficient generation and growth of the bubbles lead to an increase of the capillary force exerted by them. Interestingly, the effect is more pronounced as the level of fuel decrease. The validity of the model is also proven by comparing both theoretical and experimental results. Interestingly, the speed enhancement in magnetic mode depends on geometrical factors only, as a similar phenomenon was observed in a variety of microjets with a variable surface roughness. The understanding of such phenomena will open new avenues for understanding and controlling the motion behavior of high-towing-force catalytic micromotors.     

Screen-printed electrodes modified with carbon nanotubes or graphene for simultaneous determination of melatonin and serotonin

Single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and graphene have been tested as carbon allotropes for the modification of carbon screen-printed electrodes (CSPEs) to simultaneously determine melatonin (MT) and serotonin (5-HT). Two groups of CSPEs, both 4 mm in diameter, were explored: The first includes commercial SWCNT, MWCNT and graphene, the second includes SWCNT, MWCNT, graphene oxide nanoribbons and reduced nanoribbons that were drop casted on the electrodes. The carbon nanomaterials enhanced the electroactive area in the following order: CSPE

Carbon nanomaterials on screen-printed electrodes: smart electrochemistry for fast, simultaneous and reliable detection of serotonin the molecule of happiness and melatonin the molecule of darkness.

     

Evaluation of high-performance liquid chromatography for determination of phenolic compounds in pear horticultural cultivars

Summary An analytical evaluation of an HPLC method with diode array detection to separate and quantify polyphenolic compounds from pears has been made. The method was applied to the quantitative analysis of phenolics from five pear horticultural cultivars (“Agua”, “Blanquilla”, “Conference”, “Pasagrana” and “Decana”) in both peel and pulp matrices and evaluated for precision and accuracy. Precision was taken as the reproducibility in peak area of the polyphenols of interest as well as in the slope of calibration graphs. Values ranged 2–5%. Accuracy was evaluated by recovery of all polyphenolic compounds from both peel and pulp in all pears investigated. Accuracy values ranged 92–102%, and were independent of the polyphenolic structure, horticultural cultivar and matrix. Identification was by comparing retention times and UV spectra with those of standards when commercially available. When not available commercially, provisional identification was according to spectral characteristics as well as from isolation and hydrolysis data. Application of the method revealed differences between peel and pulp in all cases studied; the higher levels of phenolics were found in the peels. “Decana” and “Pasagrana” cultivars showed the highest phenolic content compounds whereas “Conference” showed the lowest.     

Design of a composite amperometric enzyme electrode for the control of the benzoic acid content in food

A graphite–Teflon–tyrosinase composite biosensor for the determination of benzoic acid in foodstuffs is reported. The biosensor functioning is based on the inhibition effect of benzoic acid on the biocatalytic activity of the enzyme in a reversed micelle working medium formed with ethyl acetate as the continuous phase, a 0.05 mol l⁻¹ phosphate buffer solution of pH 7.4 (5%) as the aqueous dispersed phase, and 0.10 mol l⁻¹ dioctyl sulfosuccinate (AOT) as the emulsifying agent. A potential value of −0.10 V, and a constant enzyme-substrate (phenol) concentration of 2.0×10⁻⁴ mol l⁻¹ were selected to carry out the amperometric inhibition measurements. The tyrosinase inhibition process by benzoic acid is reversible and of the competitive type, with an apparent inhibition constant of 0.016 mmol l⁻¹. The composite bioelectrodes allow the regeneration of the electrode surface by polishing and exhibit long-term operation and stability. A limit of detection of 9.0×10⁻⁷ mol l⁻¹ benzoic acid was obtained. An interference study from other substances which can be found in foodstuffs together with benzoic acid was performed. Taking advantage of the capabilities of reversed micelles as universal solubilization media, the composite tyrosinase electrode was used for the determination of benzoic acid in two different kind of samples: mayonnaise sauce, which is a highly hydrophobic matrix, and Cola soft drinks, a hydrophilic matrix for which practically no sample treatment is necessary.     

Fast and simultaneous detection of prominent natural antioxidants using analytical microsystems for capillary electrophoresis with a glassy carbon electrode: a new gateway to food environments

This paper examines for the first time the analytical possibilities of fast and simultaneous detection of prominent natural antioxidants including examples of flavonoids and vitamins using a CE microchip with electrochemical detection (ED). Unpinched injection conditions, zone electrophoretic separation and amperometric detection were carefully assayed and optimised. Analysis involved the zone electrophoretic separation of arbutin, (+)-catechin and ascorbic acid in less than 4 min using a borate buffer (pH 9.0, 50 mM), employing 2 kV as the separation voltage and +1.0 V as the detection potential. In addition, the separation of different 'couples' of natural antioxidants of food significance including (+)-catechin and ascorbic acid, (+)-catechin and rutin, as well as arbutin and phlorizdin is proposed. To demonstrate the potential and future role of CE microsystems, analytical possibilities and a new route in the raw sample analysis are presented. The preliminary results obtained allow the proposal of CE-ED microchips as a real gateway to microanalysis in foods.     

Ligand Bridged Heterodinuclear Transition Metal Complexes – Syntheses,Structures and Electrochemical Investigations

The syntheses of the homo‐ and hererobimetallic compounds [L_n¹M(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n] ( 2a‐5d ), [(C₉H₇)CMe₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n] ( 6a‐c ), and [(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n]₂Fe ( 7a‐b ) are reported with ¹ML_n = Rh(cod) 2 , Ir(cod) 3 , Mn(CO)₃ 4 and FeCp 5 , ²ML_n = Rh(cod) a , Ir(cod) b , Mn(CO)₃ c and FeCp d , respectively. Crystal structures of 3a, 3b and 5c are described showing two different ligand conformations in form of two rotamers. The energetic difference between these both rotamers is insignificant small in the gas phase according to DFT calculations. The rotation barrier for the species has been determined to 23 kJ/mol. According to the absence of intermolecular interactions in the solid state, the preference for one of the conformers is deduced from packing effects. All complexes are investigated by cyclic voltammetry. The shift of the redox potentials with respect to the mononuclear reference systems is a suitable tool to determine intermetallic electronic interaction. For some compounds, the normal behaviour with an increasing separation of the redox potentials is observed. A second group of complexes shows the opposite behaviour with a decreasing in the potential differences. A mechanism of intramolecular catalytic oxidation is supposed for that species.