Analytica Chimica Acta (v.917, #C)

High-performance integrated field-effect transistor-based sensors by R. Adzhri; M.K. Md Arshad; Subash C.B. Gopinath; A.R. Ruslinda; M.F.M. Fathil; R.M. Ayub; M. Nuzaihan Mohd Nor; C.H. Voon (1-18).
Field-effect transistors (FETs) have succeeded in modern electronics in an era of computers and hand-held applications. Currently, considerable attention has been paid to direct electrical measurements, which work by monitoring changes in intrinsic electrical properties. Further, FET-based sensing systems drastically reduce cost, are compatible with CMOS technology, and ease down-stream applications. Current technologies for sensing applications rely on time-consuming strategies and processes and can only be performed under recommended conditions. To overcome these obstacles, an overview is presented here in which we specifically focus on high-performance FET-based sensor integration with nano-sized materials, which requires understanding the interaction of surface materials with the surrounding environment. Therefore, we present strategies, material depositions, device structures and other characteristics involved in FET-based devices. Special attention was given to silicon and polyaniline nanowires and graphene, which have attracted much interest due to their remarkable properties in sensing applications.Display Omitted
Keywords: Field-effect transistor; Nanowire; Nano-sized materials; Silicon; Polyaniline; Graphene;

Evaluation of the availability of bound analyte for passive sampling in the presence of mobile binding matrix by Jianqiao Xu; Shuyao Huang; Ruifen Jiang; Shufen Cui; Tiangang Luan; Guosheng Chen; Junlang Qiu; Chenyang Cao; Fang Zhu; Gangfeng Ouyang (19-26).
Elucidating the availability of the bound analytes for the mass transfer through the diffusion boundary layers (DBLs) adjacent to passive samplers is important for understanding the passive sampling kinetics in complex samples, in which the lability factor of the bound analyte in the DBL is an important parameter. In this study, the mathematical expression of lability factor was deduced by assuming a pseudo-steady state during passive sampling, and the equation indicated that the lability factor was equal to the ratio of normalized concentration gradients between the bound and free analytes. Through the introduction of the mathematical expression of lability factor, the modified effective average diffusion coefficient was proven to be more suitable for describing the passive sampling kinetics in the presence of mobile binding matrixes. Thereafter, the lability factors of the bound polycyclic aromatic hydrocarbons (PAHs) with sodium dodecylsulphate (SDS) micelles as the binding matrixes were figured out according to the improved theory. The lability factors were observed to decrease with larger binding ratios and smaller micelle sizes, and were successfully used to predict the mass transfer efficiencies of PAHs through DBLs. This study would promote the understanding of the availability of bound analytes for passive sampling based on the theoretical improvements and experimental assessments.Display Omitted
Keywords: Passive sampling kinetics; Diffusion boundary layer; Mobile binding matrix; Lability factor; Polycyclic aromatic hydrocarbons; Sodium dodecylsulphate;

A novel miniaturized zinc oxide/hydroxylated multiwalled carbon nanotubes as a stir-brush microextractor device for carbamate pesticides analysis by Fonthip Makkliang; Proespichaya Kanatharana; Panote Thavarungkul; Chongdee Thammakhet (27-36).
A novel miniaturized “stir-brush microextractor” was prepared using a zinc oxide/hydroxylated multiwalled carbon nanotubes (ZnO/MWCNTs–OH) coated stainless steel brush connected to a small dc motor. The synthesized zinc oxide on each strand of stainless steel had a flower-like nanostructure when observed by a scanning electron microscope (SEM). This structure produced a large surface area before it was coated with the hydroxylated multiwalled carbon nanotubes sorbent. Under optimal conditions, the developed device provided a good linearity for the extraction of carbofuran and carbaryl, in the range of 25–500 ng mL−1 and 50–500 ng mL−1, respectively, with low limits of detection of 17.5 ± 2.0 ng mL−1 and 13.0 ± 1.8 ng mL−1. It also provided a good stir-brush-to-stir-brush reproducibility (% relative standard deviation < 5.6%, n = 6). The device was applied for the extraction and preconcentration of carbamate pesticides in fruit and vegetable samples prior to analysis with a gas chromatograph coupled with a flame ionization detector (GC–FID). Carbofuran was found at 9.24 ± 0.93 ng g−1 and carbaryl was detected at 7.05 ± 0.61 ng g−1 with good recoveries in the range of 73.7 ± 10.0% to 108.4 ± 2.6% for carbofuran and 75.7 ± 10.0% to 111.7 ± 5.7% for carbaryl.Display Omitted
Keywords: Trace analysis; Carbamate pesticides; Zinc oxide; Multiwalled carbon nanotubes; Miniaturized solid phase extraction;

Solid-phase extraction based on ground methacrylate monolith modified with gold nanoparticles for isolation of proteins by María Vergara-Barberán; María Jesús Lerma-García; Ernesto Francisco Simó-Alfonso; José Manuel Herrero-Martínez (37-43).
In this study, a novel polymeric material functionalized with gold nanoparticles (AuNPs) was prepared as solid-phase extraction (SPE) sorbent for isolation of proteins. The sorbent was synthesized from a powdered poly(glycidyl-co-ethylene dimethacrylate) monolith, and modified with ammonia, followed by immobilization of AuNPs on the pore surface of the material. To evaluate the performance of this SPE support, proteins were selected as test solutes, being the extraction conditions and other parameters (loading capacity and regenerative ability of sorbent) established. The results indicated that this sorbent could be employed to selectively capture proteins according to their pI, on the basis of the strong affinity of these biomacromolecules towards to AuNPs surface. The applicability of this sorbent was demonstrated by isolating protein species of interest (bovine serum albumin, cytochrome c and lectins in European mistletoe leaves), followed by SDS-PAGE analysis.Display Omitted
Keywords: Gold nanoparticles; Glycidyl methacrylate monolith; Proteins; Solid-phase extraction;

Tandem air-agitated liquid–liquid microextraction as an efficient method for determination of acidic drugs in complicated matrices by Mohammad Bazregar; Maryam Rajabi; Yadollah Yamini; Alireza Asghari; Maryam Hemmati (44-52).
A rapid and simple microextraction method with a high sample clean-up, termed as tandem air-agitated liquid–liquid microextraction (TAALLME), is described. This method is based upon the tandem implementation of the air-agitated liquid–liquid microextraction (AALLME), and this approach improves the applicability of the dispersive liquid–liquid microextraction (DLLME) methods in complicated matrices. With very simple tools, the three non-steroidal anti-inflammatory drugs diclofenac, ibuprofen, and mefenamic acid were efficiently extracted, with an overall extraction time of 7 min. By performing the first AALLME, these acidic analytes, contained in an aqueous sample solution (donor phase, 8.0 mL), were extracted into the organic solvent (1,2-dichloroethane, 37 μL), and their simple back-extraction into the aqueous acceptor solution (pH, 10.01, 51 μL) was obtained in 2 min by a second implementation of AALLME. Response surface methodology (RSM) was used for optimization of the experimental parameters. The pH values 2.94 and 10.01 were obtained for the donor and acceptor phases, respectively, and the volumes 99.5 and 51 μL were obtained for the organic solvent and the acceptor phase, respectively, as the optimal extraction conditions. Under the optimized conditions, tandem AALLME-HPLC-UV provided a good linearity in the range of 0.5–4000 ng mL−1, limits of detection (0.1–0.3 ng mL−1), extraction repeatabilities (relative standard deviations (RSDs) below 7.7%, n = 5), and the enrichment factors (EFs) of 80–104. Finally, the applicability of the proposed method was evaluated by the extraction and determination of the drugs under study in the wastewater and human plasma samples.Display Omitted
Keywords: Tandem air-agitated liquid–liquid microextraction (TAALLME); Air-agitated liquid–liquid microextraction; Complicated matrices; Non-steroidal anti-inflammatory drugs (NSAIDs);

Computational optimization of the configuration of a spatially resolved spectroscopy sensor for milk analysis by Rodrigo Watté; Ben Aernouts; Robbe Van Beers; Annelies Postelmans; Wouter Saeys (53-63).
A global optimizer has been developed, capable of computing the optimal configuration in a probe for spatially resolved reflectance spectroscopy (SRS). The main objective is to minimize the number of detection fibers, while maintaining an accurate estimation of both absorption and scattering profiles. Multiple fibers are necessary to robustify the estimation of optical properties against noise, which is typically present in the measured signals and influences the accuracy of the inverse estimation. The optimizer is based on a robust metamodel-based inverse estimation of the absorption coefficient and a reduced scattering coefficient from the acquired SRS signals. A genetic algorithm is used to evaluate the effect of the fiber placement on the performance of the inverse estimator to find the bulk optical properties of raw milk. The algorithm to find the optimal fiber placement was repeatedly executed for cases with a different number of detection fibers, ranging from 3 to 30. Afterwards, the optimal designs for each considered number of fibers were compared based on their performance in separating the absorption and scattering properties, and the significance of the differences was tested. A sensor configuration with 13 detection fibers was found to be the combination with the lowest number of fibers which provided an estimation performance which was not significantly worse than the one obtained with the best design (30 detection fibers). This design resulted in the root mean squared error of prediction (RMSEP) of 1.411 cm−1 (R 2 = 0.965) for the estimation of the bulk absorption coefficient values, and 0.382 cm−1 (R 2 = 0.996) for the reduced scattering coefficient values.Display Omitted
Keywords: Optical sensor design; Milk; Visible and near-infrared spectroscopy; Scattering; Absorption; Metamodeling;

FRET-based modified graphene quantum dots for direct trypsin quantification in urine by Chung-Yan Poon; Qinghua Li; Jiali Zhang; Zhongping Li; Chuan Dong; Albert Wai-Ming Lee; Wing-Hong Chan; Hung-Wing Li (64-70).
A versatile nanoprobe was developed for trypsin quantification with fluorescence resonance energy transfer (FRET). Here, fluorescence graphene quantum dot is utilized as a donor while a well-designed coumarin derivative, CMR2, as an acceptor. Moreover, bovine serum albumin (BSA), as a protein model, is not only served as a linker for the FRET pair, but also a fluorescence enhancer of the quantum dots and CMR2. In the presence of trypsin, the FRET system would be destroyed when the BSA is digested by trypsin. Thus, the emission peak of the donor is regenerated and the ratio of emission peak of donor/emission peak of acceptor increased. By the ratiometric measurement of these two emission peaks, trypsin content could be determined. The detection limit of trypsin was found to be 0.7 μg/mL, which is 0.008-fold of the average trypsin level in acute pancreatitis patient's urine suggesting a high potential for fast and low cost clinical screening.Display Omitted
Keywords: Trypsin; GQD; FRET; BSA; Coumarin;

A novel fluorescent aptasensor based on silica nanoparticles, PicoGreen and exonuclease III as a signal amplification method for ultrasensitive detection of myoglobin by Khalil Abnous; Noor Mohammad Danesh; Ahmad Sarreshtehdar Emrani; Mohammad Ramezani; Seyed Mohammad Taghdisi (71-78).
Measurement of myoglobin (Mb) in human blood serum is of great interest for quick diagnosis of acute myocardial infarction (AMI). In this study, a novel fluorescent aptasensor was designed for ultrasensitive and selective detection of Mb, based on target-induced high fluorescence intensity, complementary strand of aptamer (CS), PicoGreen (PG) dye, exonuclease III (Exo III) and silica nanoparticles coated with streptavidin (SNPs-Streptavidin). The developed aptasensor obtains characteristics of SNPs as enhancers of fluorescence intensity, Exo III as an enzyme which selectively digests the 3'-end of double-stranded DNA (dsDNA), PG as a fluorescent dye which could selectively bind to dsDNA and high selectivity and sensitivity of aptamer (Apt) toward its target. In the absence of Mb, no free CS remains in the environment of SNPs-Streptavidin, resulting in a weak fluorescence emission. In the present of Mb, dsDNA-modified SNPs-Streptavidin complex forms, leading to a very strong fluorescence emission. The developed fluorescent aptasensor exhibited high specificity toward Mb with a limit of detection (LOD) as low as 52 pM. In addition, the designed fluorescent aptasensor was efficiently used to detect Mb in human serum.Display Omitted
Keywords: Fluorescent aptasensor; Myoglobin; Silica nanoparticles; Exonuclease III; PicoGreen;

A novel multiplexed immunochromatographic assay (ICA) based on a time-resolved chemiluminescence (CL) strategy was developed for quantitative detection of β-agonists, by utilizing ractopamine (RAC) and clenbuterol (CLE) as the models. Different from conventional multiplexed ICA methods which usually require two or more test lines, this strategy was developed for detection of two β-agonists by using only one test line on the nitrocellulose membrane. In this study, horseradish peroxidase and alkaline phosphatase were used as the signal probes to label RAC antibody and CLE antibody, respectively. The two CL reactions with flash type and glow type kinetics characteristics were triggered simultaneously by injecting the coreactants, then the signals for RAC and CLE detections were recorded at 3 s and 300 s after coreactants injection, respectively. Owing to the utilization of CL detection, this protocol showed ideal sensitivity for quantitation. Under the optimal conditions, the detection limits for RAC and CLE were 0.17 ng mL−1 and 0.067 ng mL−1 (S/N = 3), respectively. The whole assay process can be accomplished within 20 min without complicated sample pretreatment. The proposed method was successfully applied for the detection of RAC and CLE in spiked swine urine. It opens up a new pathway for designing a low cost, time-efficiency and multiplexed strategy for rapid screening and field assay.Display Omitted
Keywords: Ractopamine; Clenbuterol; Chemiluminescence; Multiplexed immunoassay; Immunochromatographic assay strip;

Identification of catecholamine neurotransmitters using fluorescence sensor array by Forough Ghasemi; M. Reza Hormozi-Nezhad; Morteza Mahmoudi (85-92).
A nano-based sensor array has been developed for identification and discrimination of catecholamine neurotransmitters based on optical properties of their oxidation products under alkaline conditions. To produce distinct fluorescence response patterns for individual catecholamine, quenching of thioglycolic acid functionalized cadmium telluride (CdTe) quantum dots, by oxidation products, were employed along with the variation of fluorescence spectra of oxidation products. The spectral changes were analyzed with hierarchical cluster analysis (HCA) and principal component analysis (PCA) to identify catecholamine patterns. The proposed sensor could efficiently discriminate the individual catecholamine (i.e., dopamine, norepinephrine, and l-DOPA) and their mixtures in the concentration range of 0.25–30 μmol L−1. Finally, we found that the sensor had capability to identify the various catecholamines in urine sample.Display Omitted
Keywords: Catecholamine neurotransmitters; Sensor array; Quantum dots; Fluorescence; Oxidized catecholamines;

It still confronts an outstanding challenge to screen efficient antibacterial drugs from millions of potential antibiotic candidates. In this regard, a sandwiched microarray platform has been developed to culture live bacteria and carry out high-throughput screening antibacterial drugs. The optimized lectin-hydrogel microarray can be used as an efficient bacterial capturing and culturing platform, which is beneficial to identify spots and collect data. At the same time, a matching drug-laden polyacrylamide microarray with Luria–Bertani (LB) culture medium can be generated automatically and accurately by using a standard non-contacting procedure. A large number of microscale culture chambers (more than 100 individual samples) between two microarrays can be formed by linking two aligned hydrogel spots using LB culture medium, where live bacteria can be co-cultured with drug candidates. Using Staphylococcus aureus (S. aureus) and four well-known antibiotics (amoxicillin, vancomycin, streptomycin and chloramphenicol) as model system, the MIC (minimum inhibitory concentration) values of the antibiotics can be determined by the drug induced change of bacterial growth, and the results demonstrate that the MIC values of amoxicillin, vancomycin and streptomycin are 1.7 μg mL−1, 3.3 μg mL−1 and 10.3 μg mL−1, respectively.Display Omitted
Keywords: Lectin-hydrogel microarrays; Sandwiched microarray platform; Bacterium; Antibiotics;

Graphene-based field effect transistor in two-dimensional paper networks by Aldrine Abenoja Cagang; Irfan Haider Abidi; Abhishek Tyagi; Jie Hu; Feng Xu; Tian Jian Lu; Zhengtang Luo (101-106).
We demonstrate the fabrication of a graphene-based field effect transistor (GFET) incorporated in a two-dimensional paper network format (2DPNs). Paper serves as both a gate dielectric and an easy-to-fabricate vessel for holding the solution with the target molecules in question. The choice of paper enables a simpler alternative approach to the construction of a GFET device. The fabricated device is shown to behave similarly to a solution-gated GFET device with electron and hole mobilities of ∼1256 cm2 V−1 s−1 and ∼2298 cm2 V−1 s−1 respectively and a Dirac point around ∼1 V. When using solutions of ssDNA and glucose it was found that the added molecules induce negative electrolytic gating effects shifting the conductance minimum to the right, concurrent with increasing carrier concentrations which results to an observed increase in current response correlated to the concentration of the solution used.Display Omitted
Keywords: Graphene field effect transistors; Paper analytical devices; Two-dimensional paper networks; Paper microfluidics;

Designing an electrochemical sensor for versatile clinical applications is a sophisticated task and how dedicatedly functionalized composite materials can perform on this stage is a challenge for today and tomorrow's Nanoscience and Nanotechnology. In the present work, we demonstrate a new strategy for the development of novel electrochemical sensor based on catalytic nanocomposite film. Fullerene-C60 and multi-walled carbon nanotubes (MWCNTs) were dropped on the pre-treated carbon paste electrode (CPE) and copper nanoparticles (CuNPs) electrochemically deposited on the modified CPE to form nanocomposite film of CuNPs/C60/MWCNTs/CPE. In this work, an electrochemical method based on square wave voltammetry (SWV) employing CuNPs/C60/MWCNTs/CPE has been presented for the recognition and determination of paracetamol (PT). Developed electrochemical sensor was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. The composite film made the fabricated sensor to display high sensitivity and good selectivity for PT detection. The influence of the optimization parameters such as pH, accumulation time, deposition potential, scan rate and effect of loading of composite mixture of C60-MWCNTs and CuNPs on the electrochemical performance of the sensor were evaluated. A linear range from 4.0 × 10−9 to 4.0 × 10−7 M for PT detection was obtained with a detection limit of 7.3 × 10−11 M. The fabricated sensor was successfully applied to the detection of PT in biological samples with good recovery ranging from 99.21 to 103%.Display Omitted
Keywords: Composite film; Copper nanoparticles; MWCNTs; Sensor; Paracetamol; Fullerene-C60 etc;

A new type of stimuli-responsive polymeric (SRP) coating has been prepared for use in open tubular capillary electrochromatography (OT-CEC), by grafting poly(2-dimethylaminoethylmethacrylate)-block-poly(acrylic acid) (PDMAEMA-b-PAA) as a Y-shaped block copolymer with two dissimilar chain compositions onto the inner walls of aminopropyl-modified silica capillaries. The grafting process introduced weakly charged functional groups from the PAA and PDMAEMA, enabling the generation of electroendosmotic flow with magnitude and direction adjustable by changing the pH of the running buffer electrolyte. This stimuli-responsive PDMAEMA-b-PAA block copolymer was found to provide excellent resolution of various acidic and basic compounds, leading to efficient analyte separation. When operated in the OT-CEC mode, separation selectivities could be readily manipulated via differential contributions from chromatographic and electrophoretic mechanisms, simply by changing the pH or the ionic strength of the running buffer electrolyte.Display Omitted
Keywords: pH-responsive polymers; Zwitterion properties; pH effects; Ionic strength effects; Open-tubular capillary electrochromatography;