Analytical Methods (v.8, #44)

Front cover (7839-7840).

Contents list (7841-7846).

Portable point-of-care diagnostic devices by Wei Zhang; Siyuan Guo; Wildemar Stefânio Pereira Carvalho; Yaxin Jiang; Michael J. Serpe (7847-7867).
The detection of specific species of interest (i.e., analytes) in samples (blood, urine, saliva, water, and food) at low concentrations is of utmost importance for improving human health and maintaining a high quality of life. While this is mostly achievable in lab-based settings found in the developed world, this is a major hurdle to overcome in resource-limited regions found in developing countries. Therefore, new technologies capable of detecting analytes in these challenging regions need to be developed. This review details the development of point-of-care diagnostics for detecting DNA, proteins, bacteria/pathogens, and other species that show promise for solving this major health issue, and improving the quality of life for those in the developing world.

Simultaneous electrochemical quantification of naproxen, acetaminophen and diclofenac using a bare carbon paste electrode by D. S. Guzmán-Hernández; M. A. Martínez-Cruz; M. T. Ramírez-Silva; M. Romero-Romo; S. Corona-Avendaño; L. H. Mendoza-Huizar; M. Palomar-Pardavé (7868-7872).
It is shown, for the first time, that a bare carbon paste electrode can be used for the simultaneous quantification of anti-inflammatory drugs: naproxen (NPX), diclofenac (DCF) and acetaminophen (ACT) in aqueous media. The analytical features are: 19 ± 7, 4.1 ± 1.9 and 3.7 ± 1.5 μM as detection limits of DCF, NPX and ACT, respectively, while the sensitivity of this quantification was 93.0 ± 0.7, 40.0 ± 0.3, and 54.0 ± 1.8 μA mM−1 for ACT, NPX and DCF, respectively. The analytical performance of this electrode is compared with that reported for the quantification of these drugs using HPLC, diffuse reflectance photometry, and other electrodes.

A method for the measurement of lactate, glycerol and fatty acid production from 14C-glucose in primary cultures of rat epididymal adipocytes by Ana Cecilia Ho-Palma; Floriana Rotondo; María del Mar Romero; Serena Memmolo; Xavier Remesar; José Antonio Fernández-López; Marià Alemany (7873-7885).
We have developed a method for the analysis of the main metabolic products of utilization of glucose by isolated adipocytes. They were incubated for 24 h with 14C-glucose. The final label distribution and cold levels of medium glucose, lactate and glycerol were estimated. Medium lactate was extracted using ion-exchange resin minicolumns prepared with centrifugation-filtering tubes in which the filter was substituted by the resin. This allowed complete washing using only 0.2 mL. Repeated washings allowed for complete recovery of fractions with low volumes passing through or retained (and eluted), which permitted precise counting and a sufficient amount of sample for further analyses. Lactate was separated from glucose and glycerol; glucose was then separated by oxidizing it to gluconate with glucose oxidase, and glycerol was separated in parallel by phosphorylation with ATP and glycerol kinase. Cells' lipid was extracted with ether and saponified. Glycerides-glycerol and fatty acids (from the soaps) were counted separately. The complete analysis of cells incubated with labelled glucose resulted in about half of the glucose metabolized in 24 h, 2/3rds of the incorporated glucose label was found as lactate, and 14% as free glycerol. Their specific activities per carbon were the same as that of glucose. Production of fatty acids took about 5% of the label incorporated, an amount similar to that of glycerides-glycerol and estimated carbon dioxide. The procedure described is versatile enough to be used under experimental conditions, with a high degree or repeatability and with only about 3% of the label not accounted for.

Use of near infrared reflectance imaging spectroscopy to map wool and silk fibres in historic tapestries by John K. Delaney; Paola Ricciardi; Lisha Glinsman; Michael Palmer; Julia Burke (7886-7890).
The analytical identification of natural fibres such as wool and silk in historic tapestries is often done by visual inspection of fibre samples using polarized light microscopy. Identification of these fibres, however, can be achieved in situ by comparing vibrational features in the near infrared (2000 to 2400 nm), which relate to the secondary structure of these proteins. Specifically, the vibrational combination features associated with the amide A, II and III groups in the 2100 to 2400 nm spectral region can be used to separate the α-helix structure (wool) from β-sheet (silk). Overtones of these vibrational features in the 1500 to 1600 nm range have also been found to be a useful marker for β-sheet and α-helix content. Here we demonstrate how these overtone features can be used to separate and map wool and silk fibres in two tapestries, The Mazarin Tapestry (c.1500) and The Procession to Calvary (1530/1550) both in the collection of the National Gallery of Art, Washington, DC. It is known that artisans use the matte and shine of wool and silk respectively, along with natural coloured dyes, to create the ‘palette’ used in pictorial tapestries. Knowledge of where and how these fibres are used is of interest to conservators. This chemical method also offers the potential to map regions of degradation of silk in situ, by monitoring loss of β-sheet content due to environmental or mechanical stress.

Determination of l-DOPA at an optimized poly(caffeic acid) modified glassy carbon electrode by Ahmad Rohanifar; Amila M. Devasurendra; Joshua A. Young; Jon R. Kirchhoff (7891-7897).
A thin layer of poly(caffeic acid) was electrodeposited onto the surface of a glassy carbon (GC) electrode under potentiostatic conditions in aqueous solution. This system was utilized for the detection of 3,4-dihydroxy-l-phenylalanine (l-DOPA) by square wave voltammetry (SWV) after the experimental parameters of pH, step, amplitude, and frequency were studied by a full factorial design (FFD) to identify the significant parameters and their interactions. The results showed that pH, step, and amplitude were significant, whereas frequency did not significantly impact response. Subsequently, a central composite design (CCD) was performed for the three significant factors in order to further optimize the method. The optimum conditions were pH: 4.8; step potential: 5 mV; amplitude: 88 mV. Under these optimized conditions, the modified electrode demonstrated high selectivity for l-DOPA in the presence of common biological interferences such as ascorbic acid and uric acid by the observation of three distinctive and well resolved oxidation peaks. The sensor was simple to prepare, provided short analysis times, and exhibited a linear range from 1.0–50.0 μM with a detection limit of 0.14 μM for analysis of l-DOPA.

A tetraphenylethene functionalized rhodamine sensor RbTPE has been synthesized by the condensation of tetraphenylethene-aldehyde and rhodamine B hydrazide. RbTPE exhibited an aggregation-induced emission effect in the THF/water system, and displayed high selectivity and sensitivity for HCl vapor in the solid state. The solid-state emission of RbTPE can be reversibly switched between blue and red due to the stronger protonation of the rhodamine amino group by HCl. A satisfactory nonlinear relationship was observed upon exposure to HCl vapor in the range of 0–500 ppm, and the detection limit was as low as 20 ppm. After exposing the post-test product RbTPE–HCl to NH3 vapor for a few minutes, the spirolactam ring closed and the signals restored, which showed that RbTPE could be used as a “naked-eye” and reversible sensor for detecting HCl and NH3.

A gas–liquid interface will be formed when volatilized methyl aldehyde gas begins to dissolve in solution, and metal ions in solution will be reduced slowly under appropriate experimental conditions, offering an effective way for the controlled synthesis of metal nanomaterials (NPs) without aggregation. Herein, we developed a novel controllable synthesis of platinum nanoparticles (Pt NPs) based on the gas–liquid interfacial reaction. The obtained Pt NPs were characterized by transmission electron microscopy and X-ray diffraction. Then, the Pt NPs were applied for electrochemical sensing, indicating that they had excellent properties to catalyze H2O2, and could detect H2O2 with a low detection limit of 0.05 μM in a wide linear range of 0.5–375 μM. This study may provide a general platform for the controlled synthesis of nanomaterials and can be extended to other optical, electronic, and magnetic nanocompounds.

The detection of l-tryptophan (Trp) in the extracellular matrix (ECM) of solid tumors is important, particularly in metastatic tumors, which catabolize Trp to kynurenine to escape from host immune system-mediated recognition. The presence of a co-existing amino acid such as l-tyrosine (Tyr) in the ECM routinely interferes with the detection of Trp. The current study demonstrates the development of aptamer-assisted ultra-sensitive and label free biosensor (aptasensor) based on the constant current-potentiometric striping analysis (CC-PSA) technique used for quantitative Trp analysis. To prepare the aptasensor, a gold electrode was first decorated with carboxylated multiwall carbon nanotubes (MWCNTs) and then armed with Trp aptamer molecules (Apt). The engineered aptasensor was characterized electrochemically by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and CC-PSA. For this biosensor, the limit of detection (LOD) was found to be 6.4 × 10−11 M (S/N = 3) and two linear detection ranges (i.e. 1.0 × 10−10 to 1.0 × 10−5 and 1.0 × 10−5 to 3.0 × 10−4 M) were observed in the calibration graph. For proof-of-technology, the aptasensor was used for the detection of Trp in biological samples such as cow's milk and human blood serum, saliva, and urine samples. Taking a good facet of the proposed aptasensor into account, it was implemented for the detection of the Trp consumption rate in various human cancer cell lines such as HepG2 (hepatocarcinoma), 1321NI (astrocytoma), Calu-6 (lung carcinoma), NCI-H1299 (lung carcinoma), and HT29 (colorectal carcinoma).

Differential quantification of SCCA1 and SCCA2 cancer antigens using a hydrogel biochip by Aleksei A. Tikhonov; Maria V. Tsybulskaya; Veronika I. Butvilovskaya; Elena N. Savvateeva; Pavel V. Belousov; Dmitry V. Kuprash; Olga N. Solopova; Maria A. Chernichenko; Michail M. Filushin; Alla Yu. Rubina (7920-7928).
Methods employing hydrogel-based microarrays (biochips) allow the simultaneous monitoring of protein interactions with different antibodies immobilized in gel elements. The method was applied for the simultaneous differential quantification of two highly homologous antigens of squamous cell carcinomas (SCCs) SCCA1 and SCCA2 in a single analysis. Two panels of monoclonal antibodies against recombinant SCCA1 and SCCA2 were generated, and two antibodies, C5 (anti-SCCA1) and A11 (anti-SCCA2), were selected for further evaluation based on their ability to specifically interact with their cognate antigens. Using a sandwich analysis, these antibodies were further tested in combination with anti-SCCA antibodies (H31 and SCC107) recognizing both of the SCCA antigens, thus allowing a quantitative independent measurement of both antigens. The intra- and inter-assay coefficients of variation for all resultant tests did not exceed 10% for the range of SCCA concentrations tested and were independent of whether SCCA1 and SCCA2 concentrations were determined simultaneously. The lower limit of detection (LOD) was estimated as 0.006 ng ml−1 for SCCA1 and 0.011 ng ml−1 for SCCA2 using the SCC107-Cy5 developing antibody and 0.014 ng ml−1 and 0.01 ng ml−1 concentrations, respectively, of the H31-Cy5 developing antibody. This assay provides a simple and accurate procedure for the differential quantitation of SCCA1 and SCCA2 using a single analysis of human serum on a biochip.

A chemiluminescent aptasensor for simultaneous detection of three antibiotics in milk by Liling Hao; Huajie Gu; Nuo Duan; Shijia Wu; Zhouping Wang (7929-7936).
In this study, a highly sensitive and specific multiplex chemiluminescent method for the simultaneous detection of three antibiotics was fabricated. Thiolated hybridized complementary strand (cDNA) modified N-(4-aminobutyl)-N-ethylisoluminol (ABEI) functionalized flowerlike gold nanostructures (AuNFs) were used as signal probes. Oxytetracycline (OTC), tetracycline (TET) and kanamycin (Kana) aptamers that were fixed onto the bottom of microtiter plates were used as recognition molecules. Targets and signal probes can competitively combine with the fixed aptamers. Thus, OTC, TET and Kana can be simultaneously detected based on an ABEI–H2O2–P-iodophenol (PIP) steady-state chemiluminescence (CL) system and the CL intensity is related to the negative logarithm of the concentrations of OTC/TET/Kana, respectively. The ranges are 0.05 to 5 ng mL−1, 0.05 to 5 ng mL−1, and 0.005 to 0.5 ng mL−1, and the detection limits are 0.02, 0.02 and 0.002 ng mL−1 (S/N = 3), respectively. The capability of the bioassay in milk was also studied using the standard addition recovery method, and the results showed a good consistency with the ones that were obtained from a commercial ELISA method. Owing to the advantages of a simple operation procedure, and excellent selectivity and specificity, the proposed biosensor demonstrated great potential in the application of food safety and multiplex nanosensors.

Simultaneous electrochemical deposition of an e-rGO/β-CD/MnO2 ternary composite for a self-powered supercapacitor based caffeine sensor by S. Selvam; B. Balamuralitharan; S. N. Karthick; K. V. Hemalatha; K. Prabakar; Hee-Je Kim (7937-7943).
A self-powered supercapacitor based on a caffeine sensor electrode has been developed using an electrochemically deposited rGO/β-CD/MnO2 ternary composite with ionic liquid assistance. This typical composite electrode was prepared from electrochemically reduced e-rGO followed by the addition of β-cyclodextrin and MnO2 from Mn(CH3COOH)2·4H2O on FTO surfaces. The composite material is indexed to the corresponding crystalline phase of MnO2 in the XRD investigation and Mn 3p, Mn 2p, C 1s, and O 1s signals were identified from XPS analysis. The cyclic voltammetry study reveals that the potential of the caffeine samples and the square wave voltammetry peak currents indicate an increasing trend for caffeine oxidation. The sensor expressed a sensitivity of 0.187 μA cm2μM−1 with a linear range of 10–550 μM (n = 3.12). The corresponding supercapacitor also exhibited a specific capacitance of 352 F g−1 and it showed a very good life time from a long term cyclic test. The proposed ternary composite electrodes may be suitable electrodes for self-powered sensor devices.

A new method based on dispersive liquid–liquid microextraction (DLLME) combined with high-performance liquid chromatography with fluorescence detection has been established to detect citrinin, alternariol and alternariol monomethyl ether in fruit juices. The effective parameters in the DLLME process, including sodium chloride percentage, pH, and volumes of extraction and dispersive solvents, were optimized using the response surface methodology based on a central composite design. Under the optimum conditions, mean recoveries of the three mycotoxins from fruit juices were in the range of 80.1–93.4% with relative standard deviations lower than 5.7%. The detection limits were in the range of 0.022–0.203 ng mL−1. A comparison of this method with previous methods demonstrated that the proposed method is an accurate, rapid and reliable sample-pretreatment method that gives very good enrichment factors and detection limits for extracting and determining citrinin, alternariol and alternariol monomethyl ether in fruit juices.

Preparation and evaluation of surface molecularly imprinted polymers as stationary phase columns for high performance liquid chromatography by Huan Xiao; Jingdong Peng; Huanjun Peng; Lingli Bu; Ziyu Pan; Yan He; Yu Chen; Fang Chen; Chengbin Gong; Qian Tang (7951-7958).
Herein, highly selective surface molecularly imprinted polymers (SMIPs) were prepared on the surface of silica microspheres and employed as a new stationary phase for high performance liquid chromatography (HPLC). In this paper, myricetin was selected as the template and successfully grafted onto the derivatized silica particles (size: 5 μm), and acetonitrile/methanol were used as the porogen and co-solvent. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermo-gravimetric analysis (TGA) were used as characterization measures, and the results illustrated that the polymers were successfully synthesized. The obtained uniform polymer particles were packed in stainless steel columns (250 mm × 4.6 mm) and evaluated as the imprinted stationary phase. Then the packed columns were connected to an Agilent 1100 series HPLC system to separate a mixture of four flavonoids. The SMIP stationary phase showed a good effect on the separation of the flavonoid mixture.

A high-throughput BIA-MPA method for the simultaneous determination of amiloride and furosemide by P. F. Pereira; W. P. da Silva; M. C. Marra; R. A. A. Muñoz; E. M. Richter (7959-7965).
In this work, a simple and fast batch injection analysis system with multiple pulse amperometric detection (BIA-MPA) was developed for the simultaneous determination of amiloride (AMD) and furosemide (FMD). A sample plug (150 μL) was directly injected into the unmodified boron-doped diamond (BDD) electrode immersed in 0.1 mol L−1 borate buffer (pH = 10). Simple and fast sample pre-treatment steps were required (dissolution and dilution). The analytical characteristics of the proposed method include good stability (RSD < 1.1%; n = 20), low detection limits (0.13 and 0.94 mg L−1 for AMD and FMD, respectively), high throughput (72 injections per h) and minimal waste production (∼150 μL by analysis). The results obtained with the BIA-MPA method were compared to those obtained by HPLC; similar results were obtained (at a 95% confidence level).

A very simple one-pot synthesis of nicotinamide adenine dinucleotide (NAD)-functionalized silver nanoparticles in an aqueous solution at room temperature without hazardous reducing agents wherein NADH is employed as the functional molecule for highly selective optical sensing of mercuric ions (Hg2+) in an aqueous solution based on an absorption and emission method, with a detection limit of 0.02 nM. NADH was used as the reducing and stabilizing agent for the formation and stabilization of silver nanoparticles, and cetyltrimethylammonium bromide (CTAB) was used as the growth agent for the silver nanoparticles. The NADH-stabilized silver nanoparticles were used as an optical sensor for the detection of mercuric ions. The potential sensing ability of these synthesized silver nanoparticles is utilized to design an absorption and emission-based sensor platform for mercuric ions with high sensitivity and selectivity in the presence of other interfering metal cations, including Pb2+, Cd2+, Ce2+, Cu2+, Ni2+, Li+, Na+, K+ and Ca2+. The facile biomolecule-assisted synthesis of anisotropically structured silver nanoparticles and the direct detection of mercuric ions at the nano-molar concentration level in the presence of other interfering metal ions in water are the main advantages of the present system. The ultrasensitive nature of the sensing platform is ascribed to the NAD-functionalized anisotropic silver nanostructures. The present optical sensor is very simple to prepare, cost effective, and time saving; no external assemblies are attached on the surface of the silver nanoparticles. This method does not require the use of organic co-solvents, enzymatic reactions, light-sensitive dye molecules, lengthy protocols, surface modification of nanoparticles, or sophisticated instrumentation, thereby overcoming most of the limitations of conventional methods.

Back cover (7973-7974).