Sulfur-Doped Graphene-Based Electrochemical Sensors for Fast and Sensitive Determination of (R)-(+)-Limonene from Beverages.

Two sensors based on sulfur-doped graphene, a gold nanoparticle paste modified with 5,10,15,20-tetraphenyl-21H,23H-porphine and 5,10,15,20-tetrakis (pentafluorophenyl chloride)-21H,23H-iron (III) porphyrin, were proposed for the determination of R-limonene in beverages (triple sec liqueur and limoncello). Differential pulse voltammetry was the method used to characterize and validate the proposed sensors. The response characteristics showed that the detection limits for both sensors were 3 × 10 mol L, while the quantification limits were 1 × 10 mol L.

Nanographene-based electrochemical sensors for ultrasensitive determination of sorbic acid from food.

Ultrasensitive determination of sorbic acid in food is essential for the assessment of the food quality. Therefore, two sensors based on nanographene decorated with gold nanoparticle paste modified with metal porphyrins (Zn protoporphyrin IX, and 2,3,7,8,12,13,17,18 octaethyl, 21H, 23H-porphirine Mn(III) chloride) were proposed for the determination of sorbic acid in food (bakery products and mayonnaise). Square-wave voltammetry was used for the characterization and validation of the proposed sensors.

Disposable stochastic sensors for fast analysis of ibuprofen, ketoprofen, and flurbiprofen in their topical pharmaceutical formulations.

Three disposable stochastic sensors based on maltodextrin (dextrose equivalent = 4-7) and nanostructures (copper monolayer, carbon monolayer and carbon-copper composite layer) deposited using cold plasma on copy paper were proposed for the fast analysis of ibuprofen, ketoprofen and flurbiprofen in pharmaceutical formulation samples. The widest linear concentration ranges recorded were: for ibuprofen 1 fmol/L - 1 mmol/L when the disposable stochastic sensor based on carbon monolayer was used, for ketoprofen 1 fmol/L - 1 mmol/L when the disposable stochastic sensors based on copper monolayer and carbon-copper composite layer were used, and for flurbiprofen 1 fmol/L - 10 mmol/L when the disposable stochastic sensor based on carbon-copper composite layer was used. The lowest limit of detection recorded for each non-steroidal anti-inflammatory drug was 1 fmol/L.

Fast screening test for molecular recognition of levodopa and dopamine in biological samples using 3D printed stochastic microsensors.

The simultaneous assay of levodopa and dopamine is essential for diagnosis and treatment of neurodegenerative diseases and brain cancer. 3D stochastic microsensors based on multi-walled carbon nanotubes (MWCNTs), gold nanoparticles (AuNPs) and 1-adamantyloleamide (AOA) was used for the simultaneous molecular recognition of levodopa and dopamine in biological samples (whole blood, urine, and brain tissue). The proposed 3D stochastic microsensors presented low limits of quantification, and high sensitivities.

Rhodamine B - as New Chromophore for the Determination of Melatonin in Biological, Food, and Pharmaceutical Samples.

Aim And Objective: Melatonin is an essential biomarker for sleep-related disorders. Reliable methods of analysis are needed for melatonin. Therefore, a new chromophore (Rhodamine B) was proposed for the assay of melatonin; this method succeeded to enlarge the working concentration range and to decrease the limit of determination comparing with the method that just used the native fluorescence of melatonin.

Myoglobin-silver reduced graphene oxide nanocomposite stochastic biosensor for the determination of luteinizing hormone and follicle-stimulating hormone from saliva samples.

A silver reduced graphene oxide (Ag-rGO) nanocomposite paste was prepared for the assay of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in children's saliva. The paste was modified with a solution of myoglobin (Myb) to form the stochastic biosensor, to improve the sensitivity of the method. The Ag-rGO powder and Myb-Ag-rGO paste were morphologically and structurally characterized by SEM, TEM and XRD measurements.

Advances in immunosensors for clinical applications.

Immunoassay technique performs a fast, simple, reliable, and sensitive analysis of different compounds, being applied in several areas of interest such as clinical analysis for medical diagnosis, as well as in environmental analysis, and food quality control. The latest research activities in this field are represented by the attempts to achieve a low limit of detection by developing of new signal amplification strategies, eliminate the interferences, and decrease the cost of analysis.

Molecular Recognition of Nitrites and Nitrates in Water Samples Using Graphene-Based Stochastic Microsensors.

Two stochastic microsensors based on graphene powders and protoporphyrin IX were proposed for the simultaneous assay of nitrite and nitrate in water samples. The proposed microsensors can provide a fast screening of water samples with a qualitative and quantitative analysis for NO and NO at very low concentration levels. The linear concentration ranges were wide, covering clean as well as polluted waters.

Pattern recognition of 8-hydroxy-2'-deoxyguanosine in biological fluids.

8-Hydroxy-2'-deoxyguanosine (8-OHdG), a product of oxidative DNA damage, which has been used as a sensitive and reliable marker of oxidative stress and carcinogenesis, is found in high levels in biological fluids of leukemia patients. A reliable screening method based on pattern recognition of 8-OHdG using stochastic sensors designed with graphene materials decorated with nanoparticles of TiOAg or TiOAu was developed. 5,10,15,20-Tetraphenyl-21H,23H porphyrin (P), 2,6-bis((E)-2-(furan-2-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py1), and 2,6-bis((E)-2-(thiophen-3-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py2) were used as modifiers of the graphene paste in the design of sensors.

Fast Screening of Whole Blood Samples and Pharmaceutical Compounds for Enantiorecognition of Free L-T3 , L-T4 , and D-T4.

A fast screening method of whole blood was proposed for enantiorecognition of free L-T3 , L-T4 , and D-T4 . Stochastic microsensors based on four inulins (IN, IQ, TEX, and HD) immobilized on diamond paste (DP) were used for recognition of free L-T3 , L-T4 , and D-T4 . For the enantiorecognition of free L-T4 and D-T4 in whole blood and pharmaceutical samples, the best microsensor was the one based on TEX/DP (wide linear concentration ranges, and low limits of quantification).

Pattern recognition of neurotransmitters using multimode sensing.

Background: Pattern recognition is essential in chemical analysis of biological fluids. Reliable and sensitive methods for neurotransmitters analysis are needed.

New Method: Therefore, we developed for pattern recognition of neurotransmitters: dopamine, epinephrine, norepinephrine a method based on multimode sensing.

Flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter. A review.

Dopamine (DA) is one of the most important catecholamine neurotransmitters in the human central nervous system in the brain and plays a key role in the functioning of the renal, hormonal, and cardiovascular systems. Abnormal levels of dopamine are related to neurological disorders, such as schizophrenia and Parkinson's disease and the control and fluctuations of the amount of dopamine are extremely important in monitoring with analytical systems in the human brain. This review covers the attributes of flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter and points out the advantages and disadvantages in the implementation thereof.

Enantioanalysis of pipecolic acid with stochastic and potentiometric microsensors.

Stochastic and potentiometric microsensors based on porphyrins and polymeric surfactants such as polysodium N-undecanoyl-L-leucylvanilate and polysodium N-undecanoyl-L-vanilate were developed for enantioselective assay of pipecolic acid. The matrices used for the design of the stochastic sensors were diamond paste and graphite paste, while the matrix used for the design of potentiometric sensors was carbon paste. The response characteristics of the microsensors were determined for the enantiomers of pipecolic acid.

Amperometric biosensor based on diamond paste for the enantioanalysis of L-lysine.

An amperometric biosensor was proposed for the enantioanalysis of L-lysine. The biosensor is based on the impregnation of L-lysine oxidase in diamond paste. The potential used for the determination of l-lysine was 650 mV.

Determination of L- and D-fucose using amperometric electrodes based on diamond paste.

Monocrystalline diamond (natural diamond, synthetic-1 and synthetic-2) based electrochemical electrodes were designed for the analysis of L- and D-fucose. Response characteristics of the electrochemical electrodes were determined using cyclic voltammetry and differential pulse voltammetry (DPV). L-fucose was determined using DPV with electrodes based on natural diamond, synthetic-1 and synthetic-2, respectively, at 240 mV using NaCl as the electrolyte (pH 3.

Carbon and diamond paste microelectrodes based on Mn(III) porphyrins for the determination of dopamine.

Three Mn(III) porphyrins were used for the design of carbon paste and diamond paste based microelectrodes, which were employed for the determination of dopamine in pharmaceutical and biological samples using differential pulse voltammetry (DPV). The limits of detection lie between 1.6 x 10(-13) and 2.

Simultaneous determination of L- and D-T4 using a sequential injection analysis/sensors system.

A sequential injection analysis system was selected for the simultaneous determination of L- and D-T4 in raw material and pharmaceutical products, because of the highest precision and accuracy, the lower consumption of sample and buffer, and the flexibility of selecting different buffers accordingly with the type of sensors utilized as detectors. An amperometric biosensor based on D-amino acid oxidase was used as detector for D-T4 and an immunosensor based on anti-L-T4 was used as detector for L-T4. The SIA/biosensors system can be used reliably on-line in synthesis process control, for the simultaneous assay of L- and D- T4 with a frequency of more than 30 samples per hour.

Enantioanalysis of (-)butaclamol using vancomycin and teicoplanin as chiral selectors.

Butaclamol is an antipsychotic drug used in the treatment of schizophrenia. The macrocyclic antibiotics, vancomycin and teicoplanin, are proposed as chiral selectors for the design of the enantioselective, potentiometric membrane electrodes (EPMEs) for the assay of (-)butaclamol. The slopes of the electrodes are near-Nernstian for the assay of (-) butaclamol with linear concentration ranges between 10(-10) and 10(-7) mol/L and between 10(-9) and 10(-7) mol/L for vancomycin and teicoplanin based EPMEs.

Application of porphyrins in flow-injection analysis: a review.

Porphyrins and metalloporphyrins fulfil a very important role in the metabolism of living organisms through biological pigments or biochromes and are therefore also employed in numerous applications in analytical chemistry. In flow-injection analysis the role of porphyrins and metalloporphyrins are centered as either that of analyte or that of a reagent or modifier in the determination of other species. This paper covers the attributes of porphyrin and metallophorphyrin complexes as enhancements in chemical analysis in flow-injection systems and points out the advantages and disadvantages in the implementation thereof.

Macrocyclic antibiotics as chiral selectors in the design of enantioselective, potentiometric membrane electrodes for the determination of S-flurbiprofen.

Construction of three novel enantioselective, potentiometric membrane electrodes based on carbon paste impregnated with different macrocyclic antibiotics vancomycin and teicoplanin as chiral selectors are described. The solutions for the construction of electrodes were prepared in phosphate buffer pH 4 for the vancomycin-based electrode (VCM), pH 6 and pH 6/40% acetonitrile solutions for teicoplanin-based electrodes, TCP I and II, respectively. The proposed electrodes were applied in the assay of S-flurbiprofen raw material and its pharmaceutical formulation by use of direct potentiometry, VCM electrode exhibiting the best enantioselectivity.

Sequential injection spectrophotometric determination of ritodrine hydrochloride using 4-aminoantipyrine.

A sequential injection spectrophotometric determination of ritodrine hydrochloride is described. The method is based on the condensation of aminoantipyrine with phenols in the presence of an alkaline oxidizing agent to yield a pink coloured product the absorbance of which is monitored at 503nm. Different sequential injection analysis (SIA) parameters including reagent concentrations have been optimised and used to obtain the analytical figures of merit.

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction.

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255mul sample/standard followed by 170mul tetra base and then 128mul chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector.

Sequential injection spectrophotometric determination of iron as Fe(II) in multi-vitamin preparations using 1,10-phenanthroline as complexing agent.

A sequential injection analysis (SIA) system is proposed for the determination of iron (II). Fe(II) was determined by SIA based on the reaction between 1,10-phenanthroline and iron (II), yielding an orange-red colour complex with absorption maximum at 512nm. The method involved aspiration of 187mul sample/standard zone followed by a zone of a reagent solution containing 140mul of 7.

Spectrophotometric determination of magnesium in pharmaceutical preparations by cost-effective sequential injection analysis.

A simple and rapid, inexpensive spectrophotometric method was proposed for magnesium assay in pharmaceutical preparations by sequential injection analysis (SIA). The method is based on the reaction between o-cresolphthalein complexone (CPC) and Mg(II) in alkaline media, yielding a pink colored complex with absorption maximum at 570nm. Since the formation constant between Ca-CPC and Mg-CPC is similar, initially a sample/standard solution was aspirated into the holding coil followed by a mixture of masking-buffer solutions.

Simultaneous determination of l-thyroxine (l-T(4)), d-thyroxine (d-T(4)), and l-triiodothyronine (l-T(3)) using a sensors/sequential injection analysis system.

Requirements of high purity and enantiopurity for the raw materials of active substances used for the pharmaceutical formulations involved utilization of high reliable analytical techniques for the analysis of the active compound. Sequential injection analysis system with electrochemical sensors as detectors proved to be a very good alternative for the chromatographic methods, as it is more reliable, not expensive, and faster. Drugs containing only l-thyroxine (l-T(4)) or both l-T(4) and l-triiodothyronine (l-T(3)) are formulated for the dysfunctions of thyroid.