Analytical Methods (v.9, #32)

Front cover (4633-4634).

Contents list (4635-4640).

Coupling solid-phase microextractions and surface-enhanced Raman scattering: towards a point-of-need tool for hepatic cancer screening by Jennifer H. Granger; Aleksander Skuratovsky; Marc D. Porter; Courtney L. Scaife; Jill E. Shea; Qun Li; Sean Wang (4641-4646).
A method for performing rapid, highly portable immunoassays at low limits of detection (LoD) has been developed by combining solid-phase microextraction membranes, gold nanoparticle labels, and surface-enhanced Raman scattering. The capability of this methodology is demonstrated through measurements of alphafetoprotein, a marker used to screen individuals for hepatocellular carcinoma, directly from human serum at an estimated LoD of 3 pg mL−1 in ∼2 min.

Subcritical water extraction (SWE), a ‘green’ and efficient extraction technology, was applied to extract phenolic antioxidants from pomegranate peel in this study. In single-factor experiments, the effects of extraction temperature (100–220 °C), time (5–80 min) and the water/solid ratio (20–60 mL g−1) on the extraction yields of total phenolics (TP), total flavonoids (TF), and major phenolic compounds (punicalagin, punicalin, and ellagic acid) from pomegranate peel were investigated, as well as their antioxidant capacities. The results showed that the yields of phenolic compounds and antioxidant activities were significantly affected by these parameters. The highest levels of TP (314.65 mg GAE per g), TF (153.66 mg RE per g), and antioxidant activities (DPPH and ABTS radical-scavenging abilities) were observed at 130 °C for 20 min with a solid/water ratio of 50 mL g−1. The highest yield of punicalagin (81.04 mg g−1) from pomegranate peel was also observed under these conditions. However, punicalin and ellagic acid yields both continued to increase with increasing temperature and extension of time. Subsequently, on the basis of the single-factor experiments, three independent variables, temperature (X1, 110–150 °C), time (X2, 10–30 min), and the water/solid ratio (X3, 40–60 mL g−1), were optimized to maximize the total phenolic yields (Y1) and DPPH antioxidant activities (Y2) by a response surface methodology with a three-factor, three-level Box–Behnken design. The optimized conditions for phenolic antioxidant extraction were 126.1 °C, 18.5 min, and a water/solid ratio of 54.8 mL g−1, and the corresponding predicted values of Y1 and Y2 were 323.10 mg GAE per g and 476.81 mg Trolox equivalent antioxidant capacity (TEAC) per g, respectively.

Alternative method for lactulose quantification in the presence of lactose in milk using HILIC with refractive index detection by Leandra Natália de Oliveira Neves; Rafael Guzella de Carvalho; Jair Adriano Kopke de Aguiar; Paulo Henrique Fonseca da Silva (4657-4662).
An alternative chromatographic method, HILIC-RID, has been developed for lactulose quantification in the presence of lactose in milk samples. Eighteen commercial UHT milk samples were analyzed. The best separation results were achieved with a mobile phase composed of acetonitrile–water (75 : 25) using an isocratic flow of 1 mL min−1. The limits of detection and quantification were 22.68 ± 8.10 and 75.61 ± 27.01 mg L−1, respectively. Recovery ranged from 98.5 to 103.6% for three lactulose fortification levels. All samples presented low coefficients of variation (0.31–2.16%) for lactulose quantification, indicating good method reproducibility. ANOVA test showed all samples differ from the others at the 99% confidence level and allowed an inference about the lack of uniformity in Brazilian UHT milk. A lactulose amount above 600 mg L−1 found in a specific sample indicated a possible recirculation occurrence during its processing. The results attested the applicability of the HILIC-RID method as an alternative tool for quality control, heat damage investigation and food inspection.

Silver nanoprisms (AgNPrs) have been coated with end-group functionalized thermo-responsive poly-(N-isopropylacrylamide) (PNIPAM) synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The effect of the density of the polymer coating on the plasmonic properties in the visible range of light are investigated for various local environmental conditions such as temperature, pH and chloride ion concentration employing UV/VIS spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). It has been found that contrary to uncoated AgNPrs, the polymer modified AgNPrs resist against degradation processes induced by chloride ions. Depending on the surface coverage of the AgNPrs with the polymer, the degradation process can be used to adjust the optical properties of the AgNPrs. The functionalized PNIPAM modified AgNPrs display a thermal responsive behaviour, which can be observed as a reversible shift of the plasmon peak upon heating and cooling above or below the lower critical solution or phase transition temperature of the polymer (LCST). The modified AgNPrs could be employed to sense Cl in a concentration range promising for the diagnosis of cystic fibrosis. Based on the present results we also present a more general concept for the use of polymer decorated silver nanoprisms as improved sensors for the microenvironment of the particles making use of the local field enhancement, polymer coating, as well as switching of the plasmon response, which enables fine-tuning of plasmon resonances and ultimately dynamic sensing with coated triangular silver nanoprisms.

Ligandless dispersive liquid–liquid microextraction (DLLME) combined with syringe to syringe back extraction was applied for the extraction and preconcentration of Pb prior to analysis by flame atomic absorption spectrometry. In DLLME, Pb was extracted into a small volume of 1,2-dichlorobenzene. After separation of the organic phase by centrifugation, Pb enriched in the 1,2-dichlorobenzene phase was back extracted into 80 μL of 0.1 mol L−1 HNO3 using two syringes. The experimental parameters affecting the extraction efficiency of Pb such as the extraction and disperser solvent type and volume, pH, ultrasound extraction time, HNO3 solution volume of back extraction and number of injections were investigated and optimized. Under the optimal conditions, satisfactory linearity, sensitivity and reproducibility were obtained. Finally, the applicability of this newly developed method was investigated for the analysis of Pb in real water samples.

A novel and alternative electroanalytical method for the determination of ramipril (RAM) using a glassy carbon electrode (GCE) modified with nanostructured carbon black (CB) is reported. The electrochemical sensor was obtained by a simple drop coating strategy, and the designed architecture consisted of a GCE modified with CB within a dihexadecylphosphate film. The remarkable electrocatalytic activity of CB towards RAM electrooxidation was verified, and from different electrochemical assays, the number of electrons involved in the RAM oxidation was determined and, therefore, an electrooxidation reaction for RAM molecules was proposed. Under optimised experimental conditions, RAM was determined by square-wave adsorptive anodic stripping voltammetry. The analytical curve of RAM was linear from 1.98 × 10−6 to 2.42 × 10−5 mol L−1, with a limit of detection of 4.27 × 10−7 mol L−1. The proposed voltammetric procedure was successfully applied for the determination of RAM in pharmaceutical products and biological samples.

A new fluorescence chemosensor for Zn2+ with a remarkable red shift in emission spectra by Reza Azadbakht; Mostafa Koolivand; Javad Khanabadi (4688-4694).
A new fluorescent chemosensor with a remarkable red shift in emission spectra based on naphthalene groups for quantification of zinc ions was synthesized and investigated. It was found that sensor H2L exhibited a remarkably large red shift in emission upon complexation with Zn2+ ions. The limit of detection (LOD) was calculated to be 4.98 × 10−9 M. The fluorescence behavior of the prepared compound resembles with IMP and INH logic gates.

Research on a beef tenderness detection method using a bionic mastication system based on a pressure sensor by Xiaodan Wang; Hongmei Wang; Yingming Cai; Jiahui Jin; Lingtao Zhu; Liping Xu (4695-4701).
Beef tenderness is a significant factor which influences consumer purchase opinion. Conventional assessment of tenderness requires lengthy procedures with tedious sample preparations. An objective and rapid bionic mastication system combined with a pressure sensor and strain gauge for assessing beef tenderness was developed in this study. Samples of the mid-region of each longissimus dorsi (LD) were placed in the mastication system, and the reaction force was converted into voltage by a pressure sensor in tandem with a strain gauge and used to predict beef tenderness. Sensory evaluation and Warner–Bratzler Shear Force (WBSF) evaluation of samples from the same LD muscle were used for comparison and this system's accuracy rate was verified to be 92.86% and 97.14%, respectively. In addition, pork longissimus muscles and chicken breast were detected by this system. The results were compared with sensory evaluation and WBSF evaluation as well, the accuracy of which reached 90.00% or even higher. The novel bionic mastication system in tandem with a pressure sensor for beef tenderness detection has a high accuracy. What's more, the testing time of each sample is less than 2 minutes. As a result, this system is capable of beef tenderness detection with inexpensive price, operational convenience, stability, celerity and high accuracy. Besides, this system can detect the tenderness of pork and chicken as well, which means that the system has universality.

A simple pre-column derivatization method for the determination of mancozeb technical (fungicide) by reverse phase HPLC-UV by Narendra H. Petha; Rama S. Lokhande; Devender T. Seshadri; Raju M. Patil; Tanaji S. Bhagat; Jitendra G. Patil (4702-4708).
A simple and fast pre-column derivatization high performance liquid chromatographic method for the technical analysis of mancozeb was developed and validated in the present study. The mobile phase consists of a mixture of acetonitrile and 0.1% (v/v) formic acid in the proportion 60 : 40. This was found to give a sharp peak of the S-ethyl derivative of mancozeb (S-ethyl ethylene bis-dithiocarbamate) at a retention time of 9.12 minutes. HPLC analysis of mancozeb was carried out at a wavelength of 272 nm with a flow rate of 1.0 mL per minute. The linear regression analysis data for the calibration curve showed a good linear relationship with a regression coefficient of 0.999 in the concentration range of 8.2 mg L−1 to 32.3 mg L−1 for the derivative of mancozeb technical. The method was validated for specificity, linearity, precision and accuracy.

Improved protocols for pre-processing Raman spectra of formalin fixed paraffin preserved tissue sections by O. Ibrahim; A. Maguire; A. D. Meade; S. Flint; M. Toner; H. J. Byrne; F. M. Lyng (4709-4717).
Although formalin fixed paraffin preserved (FFPP) tissues are a major resource for retrospective studies of disease progression, their use in vibrational spectroscopy studies has been undermined by issues of contributions of substrate and paraffin wax which persist in the spectra and can compromise spectral analysis. Recognising the microcrystalline nature of the wax in the tissue, which are inhomogeneously oriented with respect to the polarisation of the Raman source laser, in this study, we have developed a novel method for removing the paraffin wax contributions to the spectra using matrices of multiple wax spectra. FFPP tissue sections from the oral mucosa were obtained and, with no further chemical processing, the Raman spectral analysis of two regions, epithelium and connective tissue were compared. Matrices of multiple wax spectra were collected from different regions and subtracted from the epithelial and connective tissue spectra using a least squares analysis with non-negative constraints. Spectra of multiple cell components such as DNA and RNA were used in fitting the least squares model to reduce the residual error. The use of a data matrix of multiple wax spectra, as opposed to a single spectrum, results in a more accurate removal of the wax, hence reducing its contribution to spectral analysis. In unprocessed FFPP tissue sections, the contribution of the glass substrate is seen to be minimised in comparison to chemically dewaxed FFPP tissue sections. Contributions of the glass substrate were also successfully removed digitally using the same methodology. The combined results indicate that direct analysis of FFPP tissue sections is feasible using Raman spectroscopy, avoiding the need for chemical dewaxing. Additionally, the ability to use glass slides is very important in translation to the clinic.

In this work, we developed a low-cost and sensitive electrochemical sensor for nonenzymatic detection of glucose based on ball-in-ball hollow ternary nickel cobalt sulfide spheres (NiCo2S4). A facile anion exchange method to synthesize the hollow structure of NiCo2S4 is demonstrated. The synthesized hollow NiCo2S4 was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical sensing properties of NiCo2S4 towards glucose were evaluated. Due to the synergetic effects from both Ni and Co species with multiple valence transitions and the high surface area of the hollow NiCo2S4, the nanostructure exhibited good performance towards glucose oxidation. A simple and selective sensing platform for the assay of glucose has been developed in 0.1 M KOH solution at 0.55 V. The sensor displays a wide linear range from 0.005 to 2 mM with a detection limit of 2 μM for glucose detection. For the determination of glucose in serum samples, the results are satisfactory when compared to those obtained from a local hospital.

A sensitive colorimetric aptasensor with a triple-helix molecular switch based on peroxidase-like activity of a DNAzyme for ATP detection by Kosar Shahsavar; Morteza Hosseini; Ehsan Shokri; Mohammad Reza Ganjali; Huangxian Ju (4726-4731).
A DNAzyme-based colorimetric aptasensor has been fabricated for fast readout and facile detection of adenosine triphosphate (ATP). The sensor consists of an ATP-specific aptamer flanked with cytosine-rich arms at both ends (5′ & 3′) and a peroxidase mimicking DNAzyme which were complexed together to form a functional triple-helix molecular switch (THMS). The DNAzyme strand serves as a signal transduction probe (STP) in the molecular switch. In the presence of ATP, the aptamer binds to it and the THMS complex disassembles. Subsequently the released DNAzyme sequence can form a catalytic G-quadruplex DNAzyme leading to obvious color change. This sensor provides an efficient and stable diagnostic system whilst conserving the inherent catalytic activity of the DNAzyme and the selectivity of the aptamer. The aptasensor response was linear for ATP concentration between 5 and 230 nM (R2 = 0.9854) with a detection limit of 2.4 nM (S/N = 3). Besides, ATP can be detected in human serum samples with satisfactory results, which demonstrates the potential applications for real analysis.

Innovative sandwich assay with dual optical and SERS sensing mechanisms for bacterial detection by Brooke Pearson; Panxue Wang; Alexander Mills; Shintaro Pang; Lynne McLandsborough; Lili He (4732-4739).
The increased incidence of food pathogen outbreaks placed a new emphasis on the requirement of a rapid, sensitive, and reliable detection method for pathogens in food samples. Surface-enhanced Raman spectroscopy (SERS) is a technique that tremendously enhances the weak Raman scattering of an analyte by using a metallic nano-substrate. Herein, we developed an innovative SERS sandwich assay which is based on 3-mercaptophenylboronic acid (3-MPBA) as a capturer and reporter for the detection of bacteria. Using Salmonella enterica and Listeria monocytogenes as model bacteria, we have identified a unique bacterial SERS signal upon the interaction between the captured bacteria, 3-MBPA and silver nanoparticles (AgNPs), which was used as the base for reliable detection of bacteria using SERS mapping. Both optical and chemical (SERS mapping) imaging were used as mechanisms for bacterial detection and quantification. Our assay achieved sensitive and reliable detection of as low as 102 CFU mL−1 for Salmonella with great capability for quantification. The total analytical time for optical detection is 1.25 hours and for SERS imaging is 3 hours. Our assay represents an innovative platform for rapid, sensitive and reliable detection of total bacteria for an array of industrial applications.

Schisandrin is the major active ingredient of S. chinensis, which provides anti-AD activity. The objective of this study was to develop a method to study the comparative pharmacokinetics and brain distribution of schisandrin in normal and AD rats. Therefore, an efficient UPLC-MS/MS method for the determination of schisandrin in rat plasma and brain microdialysate has been developed and validated. The method showed good linearity over a wide concentration range (r > 0.99), and the obtained lower limit of quantification was 0.5 ng mL−1 for the analyte in brain microdialysate samples. The intra-day and inter-day precision and accuracy of the analyte were well within acceptance criteria (±15%). The validated method has been successfully applied to comparing the pharmacokinetic and brain distribution profiles of schisandrin in normal and AD rat plasma and brain microdialysate. The results demonstrated that significant differences in the pharmacokinetic parameters of schisandrin were observed between the two groups, while the absorption of schisandrin in the AD group was significantly better than that in the normal group. The increase of schisandrin content in the brain provides a pharmacodynamic material basis for its anti-AD activity. The study will provide new ideas for the progression and development of AD therapy, and finding novel target drugs for AD therapy.

In this study, a simple, inexpensive and sensitive method named emulsification liquid–liquid microextraction based on deep eutectic solvents (ELLME-DES) was used for the extraction of sulfonamides (SAs) from water samples, including sulfadiazine (SDZ), sulfamerazine (SMR), sulfametoxydiazine (SDD) and sulfamethoxazole (SMX). In a typical experiment, eight kinds of DESs (as water-miscible extraction solvents) were added to 1.5 mL of sample solution containing target analytes, respectively. A homogeneous solution was formed immediately. Injection of THF (as an emulsifying agent) into the homogeneous solution provided a turbid state. After extraction, phase separation (aqueous phase/DES rich phase) was performed by centrifugation. The DES rich phase was withdrawn using a micro-syringe and submitted to isocratic reverse-phase HPLC with UV detection. Under optimum conditions obtained by response surface methodology (RSM) and the desirability function, the best conditions were when the parameters were 193 μL of DES4, 100 μL of THF and an ultrasonication time of 17 min. The recoveries of SDZ, SMR, SDD and SMX were 86.54%, 88.48%, 80.78% and 74.65%, respectively. This procedure was successfully applied to the determination of target analytes in spiked water samples. It showed highly satisfactory results and potential for rapid extraction of SAs from water samples combining with the method of ELLME-DES.

Facile fabrication of an “off–on” photoelectrochemical aptasensor for kanamycin detection based on polypyrrole/CeO2 by Jiaxin Lv; Qin Lei; Qiyou Xiao; Xiaomin Li; Yujie Huang; He Li (4754-4759).
In this work, an “off–on” photoelectrochemical sensing strategy for the determination of trace kanamycin is proposed by using a kanamycin aptamer as the sensing unit, gold nanoparticles (AuNPs) and polypyrrole as the signal amplification unit and cerium dioxide as the photoelectric active material. The proposed method has a good linear range from 0.5–200 μg L−1 with a detection limit of 0.2 μg L−1 (S/N = 3). The present aptasensor showed excellent specificity and high sensitivity when it was used to determine the amount of kanamycin in milk and kanamycin sulfate injection.

Back cover (4761-4762).