Current Analytical Chemistry - Volume 12, Issue 5, 2016

Background: Nucleic acid amplification test (NAAT) provides the highest levels of sensitivity and specificity for sequence-specific detection of DNA and RNA associated with pathogens and diseases. Currently, these tests are largely limited to laboratory use, as they require considerable sample preparation and expensive instrumentation. However, emerging microfluidic lab-on-a-chip technology enables lowcost, easy-to-use, palm-sized NAAT devices, widening NAAT applications to point-of-care (POC) diagnostics. Here, we review the evolution of microfluidic-based molecular diagnostics with a focus on work that has been carried out in our laboratory as an instructive case study. Methods: We discuss technology pathways for integration of pathogen lysis, nucleic acid isolation, amplification, and quantitative detection of DNA and RNA in a microfluidic format suitable for POC diagnostics. In addition, novel microfluidic approaches for plasma extraction, and enzymatic amplification reaction-diffusion-based method (nuclemeter technology) for end-point quantification are described. Results: Simplifications in design and operation of the microfluidic-based molecular (nucleic acid) diagnostics can be realized with modifications to solid-phase extraction methods to isolate, purify, and concentrate nucleic acid; the use of isothermal amplification; pre-loaded, paraffin-encapsulated reagents; chemical heating; and Smartphone-based detection. Conclusion: The future development of microfluidic-based POC devices is to fully integrate multiple processes required for genetic analysis on a single microfluidic format platform. There is an urgent need for such inexpensive, POC, molecular diagnostic systems at the bedside, at home, in doctors’ and dentists’ offices, clinics, and pharmacies, and especially in resource-limited regions of the world.

Mild and efficient synthetic procedures were developed for the preparation of a series of adenine, thymine and uracil-derivatives in high yields. In this respect, four derivatives were derived by introducing various substituents flanked by two methylene groups at the 1- and 9- positions of pyrimidine and purine bases, respectively. The other two were prepared from 6-amino-1,3-dimethyluracil or 5,6-diamino- 1,3-dimethyluracil by diazotization or aldehyde condensation. The photophysical characterization in a number of organic solvents with diverse polarities and in aqueous solutions at various pH, have been subjected to multiple regression analysis with more than ten different solvent parameters. The effects of solvent polarity and hydrogen bonding on the absorption and emission spectra were interpreted in the light of theoretical predictions. The validity of the regression models has been established from the linearity of the calculated and observed transition energy relating to absorption spectra and Stokes shift. This deep investigation provides realistic depiction of solvent effects on absorption and emission spectral properties of nucleobase derivatives.

In the present study, an on-line preconcentration system for the determination of Cd and Zn was developed. This system involves solid-phase extraction of metals using a minicolumn filled with Amberlite XAD-2 modified with 2-(5-bromo-2- pyridylazo)-5-diethylaminophenol (Br-PADAP) and detected by flame atomic absorption spectrometry (FAAS). After the preconcentration step, hydrochloric acid was used in the elution process, in order to transport the analytes directly to the spectrometer flame. A Doehlert design was used to optimize the variables involved in the preconcentration performance. The developed system provides enrichment factors of 30 and 88 fold, limit of detection of 0.63 and 0.38 μgL-1 and precision (RSD, 20.0 μgL-1, N = 10) of 4.3 and 5.4% for Cd and Zn, respectively. The optimized procedures were applied in the determination of Cd in fertilizer samples and Zn in drinking water. Accuracy was accessed by Cd determination in a certified reference material (NIST SRM 1573a, tomato leaves) and using a spike test for zinc in water samples. A test was applied to compare the results obtained in this study with the values of the certified reference materials and the results are not significantly different (95% confidence level), which confirms the accuracy of the developed procedures.

The purpose of this paper is to develop a new method for determining total antioxidants capacity (TAC) in urine. In our study, Na2S2O3 and mixed urine were used to evaluate the linearity and precision of the iodine starch agar method. The areas of urine diffusion in samples from 44 coronary heart disease patients and 44 healthy subjects were determined by the iodine starch agar method. The results have shown that the linearity and precision for iodine starch agar method were acceptable, because the R2s in linear experiment of Na2S2O3 and urine were 0.999 and 0.995, respectively; variation coefficients of urine diffusion area in high and low levels within-run, between-run, between-day were all less than 10%. The difference of TAC in urine between the coronary heart disease group (Median= 0.95) and healthy group (Median= 1.13) was statistically significant (p=0.001). The iodine starch agar method is a simple and convenient assay to determine total antioxidant capacity in urine.

Background: Considering that BPA has emerged as a major public health issue, there is an urgent need to establish a simple, effective, and highly sensitive method for monitoring the levels of BPA. The aim of this work was to construct an electrochemical sensor for the detection of BPA by the combination of molecularly imprinted technique and MWCNTs. The optimization of test conditions and the performance of the imprinted sensor were discussed. The application of the sensor in real water samples was evaluated. Methods: The sensor was prepared by electropolymerizing o-phenylenediamine with bisphenol A after depositing carboxylfunctionalized multi-walled carbon nanotubes onto the surface of a glassy carbon electrode. The template can be quickly removed in methanol–acetic acid (1:1, v/v) solution. The formation of PoPD film was monitored by FT-IR spectra. The morphological structures of the modified electrodes were tested by SEM. K3[Fe(CN)6] served as an electrochemical probe in this work. Cyclic voltammetry and linear sweep voltammetry were employed for the electrochemical characterization of the sensor. Results: The molecularly imprinted polymer based sensor displayed an excellent recognition capacity toward BPA compared with other structurally similar molecules, and the existence of some inorganic ions and organic compounds has no obvious effect on the determination of the analyte. Additionally, the decrease of the peak current of K3Fe(CN)6 was proportional to the BPA concentration in the range of 4.0 x 10-7 to 8 .0 x 10-5 mol L-1 with a limit of detection of 6.0 x 10-8 mol L-1. The prepared sensor also showed stable repeatability. The results in real samples obtained by the proposed method agreed with those obtained from high performance capillary electrophoresis method. Conclusion: An electrochemical sensor for BPA based on electropolymerization of the oPD in the presence of BPA on the MGCE has been successfully fabricated. When the resulting sensor was applied to the determination of BPA, it presented high sensitivity, stability and selectivity. In addition, the fabrication procedure was quite simple. The use of MWCNTs enhanced the sensitivity of detection and resulted in a better LOD; in combination with the specific selectivity of the molecularly imprinting technique, the proposed sensor provided a bright potential for the determination of BPA in practical samples.

Diketopiperazines (DKPs) are cyclic dipeptides which have been detected in a variety of natural products, especially in thermally treated or fermented foods and beverages, providing a metallic bitter taste. DKPs, mainly due to their characteristic heterocyclic system, have been reported to exhibit a broad spectrum of biological activities including antimicrobial, antiviral, antitumor, antihyperglycaemic and antimutagenic. DKPs are formed from unprotected linear dipeptides under basic conditions especially if the necessary head-to-tail folding is not prevented by steric constraints. A methodology to identify DKPs in complex matrices is of high importance. Up to now, only a few studies have reported the MS fragmentation patterns on a certain number of DKPs. The purpose of this study was to develop a liquid chromatography method for separation and identification of DKPs in complex matrices (i.e. food and beverages) as well as a high resolution mass spectrometry method providing accurate full scan MS and MSn data in order to investigate the fragmentation pattern and confirm the chemical formula and structure of DKPs containing aromatic amino acids. Our results which were supported by in silico DFT energy calculations, revealed different and common fragmentation pathways as well as a series of characteristic fragment ions which are representative of the amino acid residues. The role of MSn was signified by the results since it provided a clear picture of the fragmentation cascades. The obtained fragments are diagnostic and could be used to distinguish cyclic dipeptides in different matrices.

Background: Nicotine is the main tobacco alkaloid that leads to smoking addiction. Human serum albumin (HSA) is the most abundant protein present in the circulatory system. Nuclear magnetic resonance (NMR) has been widely used for studying the interactions of small molecules with macromolecules. The proton spin relaxation rate of the small molecule has proved to be a suitable parameter in ligand– macromolecule complex studies. Objective: In-depth study nicotine interact with HSA. Method: Spin-lattice relaxation, molecular modeling, fluorescence, FT-IR and CD spectrometers were chosen for this study. Results: HSA caused a change in the H-4 and H-9 of a nicotine proton environment. The values of normalized affinity index for the H-4/H-9 proton were (7996.9 ± 374.4) and (6840.8 ± 351.6) L·mol-1, respectively. Nicotine showed a good fit with Sudlow site II, and hydrogen bonds performed a significant function in the nicotine–HSA interaction. Citric acid exerted a slight effect, whereas malic acid exhibited an evident effect on the interaction. FT-IR and CD results revealed that nicotine–HSA interaction slightly affected the secondary structure of HSA. Conclusion: Nicotine can effectively combine with HSA and influence the native structure of HSA.

Background: In this work, the chemical polymerization of P-NPhPy on the polyester fibers in the mixed solution of sodium dodecyl benzene sulphonate (SDBS) with FeCl3 by chemical method is reported. A new SPME syringe suitable for fabricated fiber is designed and used to extract some VOCs from water samples and analysis by GC-FID. In fact the purpose of this paper was the presentation of a new chemically synthesized fiber and a new syringe. Results show that designed syringe and chemically synthesized new fibers have the capability of coupling by GC-FID and trace analysis of water pollutants. Methods: The P-NPhPy fiber was employed for analyzing four VOCs (Acetaldehyde, Benzene, Benzaldehyde, p-Xylene) in water by headspace SPME using gas chromatography- flame ionization detection (GC-FID). Results: Poly N-phenyl pyrrole (P-NPhPy) was chemically-deposited on the polyester fiber's surface in the mixed electrolytes of sodium dodecyl benzene sulphonate (SDBS) with FeCl3 by chemical method. The Transform Infrared spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) techniques are used for analysis of morphology and the compositions of synthesized P-NPhPy. The SEM results show that the morphology of P-NPhPy is nanosized and cabbage shape. Poly N-phenyl pyrrole Coated Polyester applied as a fiber for solid phase microextraction (SPME). Conclusion: Results showed that P-NPhPy synthesized fiber can suitably use for the extraction and analysis of analytes. The effects of the extraction parameters including fiber length, exposure time and sampling temperature on the extraction efficiency were optimized by experimental design method. Relative standard deviations (RSDs) were determined ≤ 5%. Detection limits were between 60 and 80 μg. L-1.

Dyes represent an extreme environmental hazard and are extensively found in the waste water of industrial discharges. Therefore, the fabrication of an effective photocatalyst for the degradation of pollutants is necessary. In this work, the photocatalytic degradation of methyl orange (MO) in aqueous solution under UV light irradiation was investigated using zinc oxide (ZnO) nanoparticles that were chemically prepared by the sol-gel technique. Several analytical tools, such as X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDAX), transmission electron microscopy (TEM), nitrogen adsorption and infrared spectroscopy (FT-IR) were utilised to investigate the morphology and composition of the synthesised nanoparticles. The sharp intense peaks of ZnO confirmed the good crystalline nature of ZnO, and EDAX analysis revealed that the fabricated ZnO nanoparticles were comprised mainly of zinc and oxygen atoms. From the TEM and SEM analyses, it was observed that the ZnO nanoparticles exhibited a spherical shape, and the surface area of the catalyst was measured to be 42.12 m2 g_1. The photodegradation experiments demonstrated that the ZnO bleaches MO upon exposure ultraviolet light (UV) and the colour irreversibly changes from orange to colourless. The results obtained revealed that the fabricated ZnO powder (80.11% MO removal) had a better photocatalytic activity than the commercial ZnO powder (64.30% MO removal). The photocatalytic decolourisation of the dye followed a first-order kinetics, and the observed rate constant values changed with the MO concentration. The development of this photocatalyst can be considered a breakthrough for the large-scale use of photocatalysis to solve issues around the contamination of water and to address serious environmental pollution problems.

Background: Corrosion in industrial structures has generated much concern with regard to material loss, especially in the oil production. Organicmolecules can act as inhibitors because they can be adsorbed at the metal-solution interface, replacing the water molecules and thereby inhibiting the metal dissolution. In general the imidazoline derivatives have unique structure that make them efficient corrosion inhibitors in CO2 environments. Castor oil is the only unsaturated fatty acid occurring in natural vegetable oils with a functional hydroxyl group in the 12C. The presence of OH groups in the fatty acid chains makes the oil unusually polar. Therefore, based on its molecular structure, castor oil or its derivatives can be used as an effective corrosion inhibitor. Methods: Inhibitor used was a hydroxyethyl-imidazoline derivate based on castor oil. Concentrations of inhibitor used were 5, 10, 25, 50 and 100 ppm. Corrosivesolutionusedwasa CO2 saturated mixture (90:10, of 3% NaCl solution and diesel) at 50°C. Corrosion tests were carried out by real-time monitoring and EIS measurements. Results: Real-time monitoring showed that the castor oil-based imidazoline has an inhibition efficiency greater than 99%. From EIS measurementstwodifferentbehaviors were obtained. Evolution of the EIS spectra was similar for additions of 5, 10 and 25 ppm, and for 50 and 100 ppm it was different. For 5, 10 and 25 ppm the evolution of the spectrum in the high frequency region was the characteristic fingerprint of the self-assembled of the oil-based imidazolines. However, for 50 and 100 ppm after 9 hours, the time constant decreased as time passed. This behavior could be due to the presence of the functional groups in the oily-tail which tend to interact with the metallic surface forming a denser inhibitor film. The molecular reactivity (HOMO and LUMO) of the optimized molecule of inhibitor showed that LUMO is moved to unusual location the middle of the molecule due to the presence of double bond in 39C-41C and the hydroxyl group in 45C. Conclusion: Real-time corrosion measurements showed that the inhibition efficiency was greater than 99%. From EIS measurements two different behaviors are observed. Presence of the functional groups in the alkyl chain tend to interact with the metal surface. Quantum chemical calculations showed that LUMO is located in the alkyl chain, favoring a flat-adsorption process.

New hollow fiber based liquid phase microextraction (HF-LPME) technique followed by high performance liquid chromatography (HPLC) coupled with ultraviolet (UV) detector was introduced for detection and determination of terazosin in urine and plasma samples. The effect of different parameters which influence extraction efficiency such as organic membrane solvent, donor/acceptor phase composition, extraction time, stirring rate, salt concentration and extraction temperature were studied. Following optimization, extraction recoveries more than 86% were obtained in different biological matrices which resulted in preconcentration factors higher than 161 and an acceptable repeatability (1.25 < RSD% <2.30, n=3). The method presents good linearity with coefficiency higher than 0.9994. Finally, the proposed method was applied for detection and determination of terazosin in urine and plasma samples.

The constituents of the essential oil of Orobanche alba Stephan growing wild in Iran using GC-FID and GC-MS were identified. Forty components were identified, constituting approximately 96.09% of the oil. The oil was rich in Geranyl acetate (26.0%), Palmitic acid (12.5%), Geranial (11.8%) and Neral (10.2%). The results obtained showed that the essential oil of O. alba Stephan consists of twelve oxygenated monoterpene compounds (62.1%).

Background: Polymer based adsorbents and their modified forms by various ligands have been effectively used for separation, preconcentration, determination and removal of heavy metal ions from different matrices. This paper proposes a solid phase extraction method based on 5-amino-1,10-phenanthroline (5-Aphen) functionalized glycidyl methacrylate-methyl methacrylate-divinylbenzene (GMA-MMA-DVB) crosslinked-polymeric microspheres for the determination of Fe (II), Ni (II), Pb (II) and Zn (II) in herbal tea samples employing flame atomic absorption spectrometry (FAAS). Methods: The prepared adsorbent was characterized by FT-IR spectroscopy and BET. Several experimental variables affecting the sensitivity and efficiency of SPE method for the metal ions studied were investigated in detail by FAAS. Results: The optimal values of the adsorbent amount, pH, eluent properties, and flow rates were determined. The preconcentration factor and detection limits of the proposed SPE method and the maximum capacity of the adsorbent were found. The validity of the method was verified by the analysis of certified reference material. The developed method was successfully applied to herbal tea samples for the simultaneous preconcentration of Fe (II), Ni (II), Pb (II) and Zn (II) ions. Conclusion: The SPE method based on 5- Aphen functionalized GMA-MMA-DVB for some trace metal ions in herbal tea samples is simple, accurate, fast, low cost, high preconcentration factor and environmentally friendly. This method can also be employed to evaluate the possible risk associated with heavy metal-contaminated foods.