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Analytica Chimica Acta (v.758, #)
Sandwich-type immunosensors and immunoassays exploiting nanostructure labels: A review by Xiaomei Pei; Bing Zhang; Juan Tang; Bingqian Liu; Wenqiang Lai; Dianping Tang (pp. 1-18).
Display Omitted► Sandwich-type immunosensors and immunoassays exploiting nanostructure labels. ► Nanolabel-based electrochemical immunosensing and immunoassay. ► Nanolabel-based optical immunosensors and immunoassays. ► Nanolabel-based mass-sensitive immunosensing. ► Nanolabel-based multianalyte immunoassays.Methods based on sandwich-type immunosensors and immunoassays have been developed for detection of multivalent antigens/analytes with more than one eptiope due to the use of two matched antibodies. High-affinity antibodies and appropriate labels are usually employed for the amplification of detectable signal. Recent research has looked to develop innovative and powerful novel nanoparticle labels, controlling and tailoring their properties in a very predictable manner to meet the requirements of specific applications. This articles reviews recent advances, exploiting nanoparticle labels, in the sandwich-type immunosensors and immunoassays. Routine approaches involve noble metal nanoparticles, carbon nanomaterials, semiconductor nanoparticles, metal oxide nanostructures, and hybrid nanostructures. The enormous signal enhancement associated with the use of nanoparticle labels and with the formation of nanoparticle-antibody-antigen assemblies provides the basis for sensitive detection of disease-related proteins or biomolecules. Techniques commonly rely on the use of biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tag-doped nanoparticles. Rather than being exhaustive, this review focuses on selected examples to illustrate novel concepts and promising applications. Approaches described include the biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tage-doped nanoparticles. Further, promising application in electrochemical, mass-sensitive, optical and multianalyte detection are discussed in detail.
Keywords: Immunosensor; Immunoassay; Sandwich assay mode; Nanoparticle label
Development of new reference materials for the determination of cadmium, chromium, mercury and lead in polycarbonate by Kil Jae Lee; Yeo Jin Lee; Young Rak Choi; Jeong Sook Kim; Youn Sung Kim; Soo Bong Heo (pp. 19-27).
Display Omitted► RMs for the determination of Cd, Cr, Hg and Pb in polycarbonate were developed. ► Double ID-ICP-MS technique was used for characterization of candidate RMs. ► The certified values for the elements ranged from 51.7 to 1133mgkg−1. ► The relative expanded uncertainties were shown to be less than 5.4%. ► New RMs were found to be suitable for the RoHS compliant tests.Reference materials for quantitative determination of Cd, Cr, Hg and Pb in polycarbonate were developed. Reference materials with two concentration level of elements were prepared by adding appropriate amounts of chemicals to a blank polycarbonate base material. It was shown that ten bottles with triplicate analysis are enough to demonstrate the homogeneity of these candidate reference materials. The statistical results also showed no significant trends in both short-term stability test for four weeks and long-term stability test for twelve months. The certification of the four elements was carried out by isotope-dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS) with microwave-assisted digestion. Certification of candidate reference materials in a single laboratory was confirmed with interlaboratory comparison participated by a certain number of well-recognized testing laboratories in Korea. The certified values and expanded uncertainties ( k=2) for the candidate reference material with low level and the one with high level were (51.7±2.1)mgkg−1 Cd, (103.8±2.9)mgkg−1 Cd, (98.8±4.5)mgkg−1 Cr, (1004±49.8)mgkg−1 Cr, (107.4±4.6)mgkg−1 Hg, (1133±50.7)mgkg−1 Hg, (94.8±3.7)mgkg−1 Pb and (988.4±53.6)mgkg−1 Pb, respectively. The reference materials developed in this study demonstrated their suitability for the quality assurance in Cd, Cr, Hg and Pb analysis for the implementation of RoHS Directive.
Keywords: Polycarbonate; Reference materials; Homogeneity; Stability; Isotope-dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS)
The effect of cooking and washing rice on the bio-accessibility of As, Cu, Fe, V and Zn using an on-line continuous leaching method by Nolan S. Horner; Diane Beauchemin (pp. 28-35).
Display Omitted► Cooking long grain brown or white rice does not affect the bio-accessibility of arsenic. ► Four toxic As species in saliva and gastric juice leachates were separated by one method. ► Washing rice a few min prior to cooking removes about 90% of bio-accessible arsenic. ► Cooking long grain brown or white rice appears to convert some species to As(III). ► On-line leaching provides in a few min similar results to 2h/reagent batch methods.A previously developed method based on continuous on-line leaching with artificial gastro-intestinal fluids was used to determine the bio-accessible fraction of As, Cu, Fe, V and Zn in brown and white rice from California by inductively coupled mass spectrometry (ICP-MS). Saliva generally accounted for the largest percentage of total element leached in comparison to gastric and intestinal juices. Arsenic speciation analysis was performed on the saliva and gastric juice leachates using ion exchange chromatography coupled to ICP-MS. The four most toxic species of As (As(III), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and As(V)), as well as Cl− in the gastric juice leachate, were successfully separated within 5.5min using a simple nitric acid gradient. While cooking rice had relatively little effect on total bio-accessibility, a change in species from As(V) and DMA to As(III) was observed for both types of rice. On the other hand, washing the rice with doubly deionized water prior to cooking removed a large percentage of the total bio-accessible fraction of As, Cu, Fe, V and Zn.
Keywords: Arsenic; Rice; Bio-accessibility; Speciation analysis; Inductively coupled plasma mass spectrometry; On-line leaching
New approaches based on modified Gaussian models for the prediction of chromatographic peaks by J.J. Baeza-Baeza; C. Ortiz-Bolsico; M.C. García-Álvarez-Coque (pp. 36-44).
Display Omitted► Modified Gaussian models expressed as a function of experimental halfwidths. ► Enhancement of peak models through the application of restrictions. ► Peak models checked on chromatographic peaks of diverse origin and asymmetry. ► Increased reliability of the peak models in tasks requiring peak fitting and prediction. ► Parabolic-Lorentzian Gaussian improved applicability for optimisation of peak resolution.The description of skewed chromatographic peaks has been discussed extensively and many functions have been proposed. Among these, the Polynomially Modified Gaussian (PMG) models interpret the deviations from ideality as a change in the standard deviation with time. This approach has shown a high accuracy in the fitting to tailing and fronting peaks. However, it has the drawback of the uncontrolled growth of the predicted signal outside the elution region, which departs from the experimental baseline. To solve this problem, the Parabolic-Lorentzian Modified Gaussian (PLMG) model was developed. This combines a parabola that describes the variance change in the peak region, and a Lorentzian function that decreases the variance growth out of the peak region. The PLMG model has, however, the drawback of its high flexibility that makes the optimisation process difficult when the initial values of the model parameters are far from the optimal ones. Based on the fitting of experimental peaks of diverse origin and asymmetry degree, several semiempirical approaches that make use of the halfwidths at 60.65% and 10% peak height are here reported, which allow the use of the PLMG model for prediction purposes with small errors (below 2–3%). The incorporation of several restrictions in the algorithm avoids the indeterminations that arise frequently with this model, when applied to highly skewed peaks.
Keywords: Liquid chromatography; Peak profile; Modified Gaussian models; Peak prediction; Peak halfwidths
An alternative quadrilinear decomposition algorithm for four-way calibration with application to analysis of four-way fluorescence excitation–emission–pH data array by Chao Kang; Hai-Long Wu; Yong-Jie Yu; Ya-Juan Liu; Shu-Rong Zhang; Xiao-Hua Zhang; Ru-Qin Yu (pp. 45-57).
Relative true profiles (dash-dot lines) and resolved profiles (solid lines) with N=6 for the simulated EX–EM–pH type four-way data array ( a homo=5%).Display Omitted► A new quadrilinear decomposition algorithm for four-way calibration is presented. ► Simulations and experiments show RSWAQLD has the feature of fast convergence. ► The proposed algorithm can resist the influence of the excess factors. ► The analysis of real four-way fluorescence data corroborated above-mentioned features.A novel quadrilinear decomposition algorithm for four-way calibration (third-order tensor calibration), which was called as regularized self-weighted alternating quadrilinear decomposition (RSWAQLD), has been developed in this work. It originates from the alternating trilinear decomposition (ATLD) algorithm, inherits the philosophy behind self-weighting operation from the self-weighted alternating trilinear decomposition (SWATLD) algorithm. The RSWAQLD algorithm is based on a nearby least-squares scheme, in which two extra terms are added to each loss function, making it more stable and flexible. Experiment shows that RSWAQLD has the features of fast convergence and being insensitive to the excess estimated factors in the model. Owing to its unique optimizing approach, RSWAQLD is much more efficient than four-way PARAFAC. Moreover, the performance of RSWAQLD is quit stable as the number of factors used in calculation varies (as long as it is no less than the true number of factors). Such a feature will simplify the analysis of four-way data arrays, since it is unnecessary to spend a lot of time and effort on accurately determining the appropriate number of factors in the matrix. In addition, the result of four-way fluorescence excitation–emission–pH data, as well as that of simulated data, illustrated that RSWAQLD can not only remain the “higher-order advantage” but also provide a satisfying result even in high collinear systems.
Keywords: Four-way calibration (third-order tensor calibration); RSWAQLD; Four-way PARAFAC; Chemometrics; Third-order data array; Fluorescence
New discrimination method combining hit quality index based spectral matching and voting by Sanguk Lee; Hyeseon Lee; Hoeil Chung (pp. 58-65).
Display Omitted► A discrimination method, called hit quality index (HQI)-voting, has been developed. ► It effectively utilizes HQI as a judgment factor for group determination. ► It is based on sample-to-sample spectral matching without modeling, so the model over-fitting is not an issue. ► It improved the discrimination for geographical origins of agricultural samples and similar petroleum products.A new discrimination method, called hit quality index (HQI)-voting, that uses the HQI for discriminant analysis has been developed. HQI indicates the degree of spectral matching between two spectra as known. In this method, a library sample yielding the highest HQI value for an unknown sample was initially searched and a group containing this sample was chosen as the group for the unknown sample. When overall spectral features of two groups are quite close to each other, many library samples with similar HQI values could be available for an unknown sample. In this situation, the simultaneous consideration of multiple votes (several library samples with close HQI values) for final decision would be more robust. In order to evaluate the discrimination performance of HQI-voting, three different near-infrared (NIR) spectroscopic datasets composed of two sample groups were used: (1) domestic and imported sesame samples, (2) domestic and imported Angelica gigas samples, and (3) diesel and light gas oil (LGO) samples. For the purpose of comparison, principal component analysis–linear discriminant analysis (PCA–LDA), partial least squares–discriminant analysis (PLS–DA) as well as k-nearest neighbor ( k-NN) were also performed using the same datasets and the resulting accuracies were compared. The discrimination performances improved with the use of HQI-voting in comparison with those resulted from PCA–LDA and PLS–DA. The overall results support that HQI-voting is a comparable discrimination method to that of existing factor-based multivariate methods.
Keywords: Hit quality index (HQI); Voting; Discriminant analysis; Sesame; Angelica gigas; Diesel; Light gas oil
A novel amperometric biosensor for superoxide anion based on superoxide dismutase immobilized on gold nanoparticle-chitosan-ionic liquid biocomposite film by Lu Wang; Wei Wen; Huayu Xiong; Xiuhua Zhang; Haoshuang Gu; Shengfu Wang (pp. 66-71).
Schematic representation of the assembly process of SOD/GNPs-CS-IL/GCE.Display Omitted► SOD was immobilized in gold nanoparticles-chitosan-ionic liquid (GNPs-CS-IL) film. ► The biosensor was constructed by one-step ultrasonic electrodeposition of GNPs-CS-IL onto GCE. ► The biosensor showed excellent analytical performance for O2− real-time analysis.A novel superoxide anion (O2−) biosensor is proposed based on the immobilization of copper-zinc superoxide dismutase (SOD) in a gold nanoparticle-chitosan-ionic liquid (GNPs-CS-IL) biocomposite film. The SOD-based biosensor was constructed by one-step ultrasonic electrodeposition of GNP-CS-IL composite onto glassy carbon electrode (GCE), followed by immobilization of SOD on the modified electrode. Surface morphologies of a set of representative films were characterized by scanning electron microscopy. The electrochemical performance of the biosensor was evaluated by cyclic voltammetry and chronoamperometry. A pair of quasi-reversible redox peaks of SOD with a formal potential of 0.257V was observed at SOD/GNPs-CS-IL/GCE in phosphate buffer solution (PBS, 0.1M, pH 7.0). The effects of varying test conditions on the electrochemical behavior of the biosensor were investigated. Furthermore, several electrochemical parameters were calculated in detail. Based on the biomolecule recognition of the specific reactivity of SOD toward O2−, the developed biosensor exhibited a fast amperometric response (<5s), wide linear range (5.6–2.7×103nM), low detection limit (1.7nM), and excellent selectivity for the real-time measurement of O2−. The proposed method is promising for estimating quantitatively the dynamic changes of O2− in biological systems.
Keywords: Abbreviations; O; 2; −; superoxide anion; SOD; superoxide dismutase; GNPs-CS-IL; gold nanoparticle-chitosan-ionic liquid; GCE; glassy carbon electrode; ROS; reactive oxygen species; GNPs; gold nanoparticles; CS; chitosan; IL; ionic liquid; XOD; xanthine oxidase; XAN; xanthine; [bmim][BF; 4; ]; 1-butyl-3-methylimidazolium tetrafluoroborate; CV; cyclic voltammetry; E; 0; ′; formal potential; E; pa; peak potential; E; pc; cathodic peak potential; E; p; peak-to-peak separation; AA; ascorbic acid; UA; uric acidSuperoxide anion; Superoxide dismutase; Gold nanoparticles; Ionic liquid; Ultrasonic electrodeposition
Ultrasensitive electrochemical immunosensor for zeranol detection based on signal amplification strategy of nanoporous gold films and nano-montmorillonite as labels by Rui Feng; Yong Zhang; He Li; Dan Wu; Xiaodong Xin; Sen Zhang; Haiqin Yu; Qin Wei; Bin Du (pp. 72-79).
Display Omitted► The immunosensor based on nanoporous gold films and nano-montmorillonite. ► Nano-montmorillonite with innocuity, and adsorptivity can be used as labels. ► Determine zeranol utilizing peculiar immunology reaction of antibody and antigen.Nano-montmorillonites belong to aluminosilicate clay minerals with innocuity, high specific surface area, ion exchange, and favorable adsorption property. Due to the excellent properties, montmorillonites can be used as labels for the electrochemical immunosensors. In this study, nano-montmorillonites were converted to sodium montmorillonites (Na-Mont) and further utilized for the immobilization of thionine (TH), horseradish peroxidase (HRP) and the secondary anti-zeranol antibody (Ab2). The modified particles, Na-Mont-TH-HRP-Ab2 were used as labels for immunosensors to detect zeranol. This protocol was used to prepare the immunosensor with the primary antibody (Ab1) immobilized onto the nanoporous gold films (NPG) modified glassy carbon electrode (GCE) surface. Within zeranol concentration range (0.01–12ngmL−1), a linear calibration plot ( Y=0.4326+8.713 X, r=0.9996) was obtained with a detection limit of 3pgmL−1 under optimal conditions. The proposed immunosensor showed good reproducibility, selectivity, and stability. This new type of immunosensors with montmorillonites and NPG as labels may provide potential applications for the detection of zeranol.
Keywords: Nano-montmorillonites; Nanoporous gold films; Zeranol; Electrochemical immunosensor
Multi-class, multi-residue analysis of pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers and novel flame retardants in fish using fast, low-pressure gas chromatography–tandem mass spectrometry by Yelena Sapozhnikova; Steven J. Lehotay (pp. 80-92).
Display Omitted► A method for analysis of POPs and novel flame retardants in catfish was developed. ► The method is based on a QuEChERS extraction, d-SPE clean-up and low pressure GC/MS–MS. ► The method validation demonstrated good recoveries and low detection limits. ► The method was successfully applied for analysis of catfish samples from the market.A multi-class, multi-residue method for the analysis of 13 novel flame retardants, 18 representative pesticides, 14 polychlorinated biphenyl (PCB) congeners, 16 polycyclic aromatic hydrocarbons (PAHs), and 7 polybrominated diphenyl ether (PBDE) congeners in catfish muscle was developed and evaluated using fast low pressure gas chromatography triple quadrupole tandem mass spectrometry (LP-GC/MS–MS). The method was based on a QuEChERS (quick, easy, cheap, effective, rugged, safe) extraction with acetonitrile and dispersive solid-phase extraction (d-SPE) clean-up with zirconium-based sorbent prior to LP-GC/MS–MS analysis. The developed method was evaluated at 4 spiking levels and further validated by analysis of NIST Standard Reference Materials (SRMs) 1974B and 1947. Sample preparation for a batch of 10 homogenized samples took about 1h/analyst, and LP-GC/MS–MS analysis provided fast separation of multiple analytes within 9min achieving high throughput. With the use of isotopically labeled internal standards, recoveries of all but one analyte were between 70 and 120% with relative standard deviations less than 20% ( n=5). The measured values for both SRMs agreed with certified/reference values (72–119% accuracy) for the majority of analytes. The detection limits were 0.1–0.5ngg−1 for PCBs, 0.5–10ngg−1 for PBDEs, 0.5–5ngg−1 for select pesticides and PAHs and 1–10ngg−1 for flame retardants. The developed method was successfully applied for analysis of catfish samples from the market.
Keywords: Persistent organic pollutants; Novel flame retardants; QuEChERS sample preparation; Fast gas chromatography tandem mass spectrometry; Catfish analysis
Selective trace enrichment of acidic pharmaceuticals in real water and sediment samples based on solid-phase extraction using multi-templates molecularly imprinted polymers by Yan-Ping Duan; Chao-Meng Dai; Ya-Lei Zhang; Ling-Chen (pp. 93-100).
Display Omitted► A novel multi-templates MIP was prepared using acidic pharmaceuticals mix as the template. ► Optimization of a protocol of extraction based on molecularly imprinted solid phase extraction (MISPE). ► Application of the optimized protocol for the extraction of acidic pharmaceuticals from real environmental samples.A novel multi-templates molecularly imprinted polymer (MIP), using acidic pharmaceuticals mixture (ibuprofen (IBP), naproxen (NPX), ketoprofen (KEP), diclofenac (DFC), and clofibric acid (CA)) as the template, was prepared as solid-phase extraction (SPE) material for the quantitative enrichment of acidic pharmaceuticals in environmental samples and off-line coupled with liquid chromatography–mass spectrometry (LC/MS/MS). Washing solvent was optimized in terms of kind and volume for removing the matrix constituents nonspecifically adsorbed on the MIP. When 1L of water sample spiked at 1μg/L was loaded onto the cartridge, the binding capacity of the MIP cartridge were 48.7μg/g for KEP, 60.7μg/g for NPX, 52μg/g for CA, 61.3μg/g for DFC and 60.7μg/g for IBP, respectively, which are higher than those of the commercial single template MIP in organic medium (e.g. toluene) reported in the literature. Recoveries of the five acidic pharmaceuticals extracted from 1L of real water samples such as lake water and wastewater spiked at 1μg/L were more than 95%. The recoveries of acidic pharmaceuticals extracted from 10-g sediment sample spiked at the 10ng/g level were in the range of 77.4–90.6%. To demonstrate the potential of the MIP obtained, a comparison with commercial C18 SPE cartridge was performed. Molecularly imprinted solid-phase extraction (MISPE) cartridge showed higher recoveries than commercial C18 SPE cartridge for acidic pharmaceuticals. These results showed the suitability of the MISPE method for the selective extraction of a group of structurally related compounds such as acidic pharmaceuticals.
Keywords: Acidic pharmaceuticals; Multi-templates molecularly imprinted polymer; Solid-phase extraction; Real water; Sediment
Measurement of microchannel fluidic resistance with a standard voltage meter by Leah A. Godwin; Kennon S. Deal; Lauren D. Hoepfner; Louis A. Jackson; Christopher J. Easley (pp. 101-107).
Display Omitted► Standard voltage meter used to measure fluidic resistance. ► Manual measurement takes a few seconds, akin to electrical resistance measurements. ► Measurement error is reduced compared to other approaches. ► Amenable to dynamic measurement of fluidic resistance.A simplified method for measuring the fluidic resistance ( R fluidic) of microfluidic channels is presented, in which the electrical resistance ( R elec) of a channel filled with a conductivity standard solution can be measured and directly correlated to R fluidic using a simple equation. Although a slight correction factor could be applied in this system to improve accuracy, results showed that a standard voltage meter could be used without calibration to determine R fluidic to within 12% error. Results accurate to within 2% were obtained when a geometric correction factor was applied using these particular channels. When compared to standard flow rate measurements, such as meniscus tracking in outlet tubing, this approach provided a more straightforward alternative and resulted in lower measurement error. The method was validated using 9 different fluidic resistance values (from ∼40 to 600kPasmm−3) and over 30 separately fabricated microfluidic devices. Furthermore, since the method is analogous to resistance measurements with a voltage meter in electrical circuits, dynamic R fluidic measurements were possible in more complex microfluidic designs. Microchannel R elec was shown to dynamically mimic pressure waveforms applied to a membrane in a variable microfluidic resistor. The variable resistor was then used to dynamically control aqueous-in-oil droplet sizes and spacing, providing a unique and convenient control system for droplet-generating devices. This conductivity-based method for fluidic resistance measurement is thus a useful tool for static or real-time characterization of microfluidic systems.
Keywords: Fluidic resistance; Conductivity; Voltage meter; Microfluidic variable resistor; Droplet fluidics
A multi-pumping flow-based procedure with improved sensitivity for the spectrophotometric determination of acid-dissociable cyanide in natural waters by Rejane M. Frizzarin; Fábio R.P. Rocha (pp. 108-113).
Display Omitted► Inexpensive, fast and environmentally friendly spectrophotometric determination of acid dissociable cyanide. ► Novel analytical method based on the reaction with the Cu(I) complex with 2,2′-biquinoline 4,4′-dicarboxylic acid. ► Long pathlength spectrophotometry exploited for the first time to increase sensitivity in discolorimetry. ► Pulsed flow to improve gas-diffusion efficiency. ► One of the lowest detection limits without impairing the sample throughput or using toxic chemicals.An analytical procedure with improved sensitivity was developed for cyanide determination in natural waters, exploiting the reaction with the complex of Cu(I) with 2,2′-biquinoline 4,4′-dicarboxylic acid (BCA). The flow system was based on the multi-pumping approach and long pathlength spectrophotometry with a flow cell based on a Teflon AF 2400® liquid core waveguide was exploited to increase sensitivity. A linear response was achieved from 5 to 200μgL−1, with coefficient of variation of 1.5% ( n=10). The detection limit and the sampling rate were 2μgL−1 (99.7% confidence level), and 22h−1, respectively. Per determination, 48ng of Cu(II), 5μg of ascorbic acid and 0.9μg of BCA were consumed. As high as 100mgL−1 thiocyanate, nitrite or sulfite did not affect cyanide determination. Sulfide did not interfere at concentrations lower than 40 and 200μgL−1 before or after sample pretreatment with hydrogen peroxide. The results for natural waters samples agreed with those obtained by a fluorimetric flow-based procedure at the 95% confidence level. The proposed procedure is then a reliable, fast and environmentally friendly alternative for cyanide determination in natural waters.
Keywords: Flow analysis; Multi-pumping; Spectrophotometry; Liquid-core waveguide; Acid-dissociable cyanide; Gas-diffusion
A highly sensitive isotope-coded derivatization method and its application for the mass spectrometric analysis of analytes containing the carboxyl group by Jiapeng Leng; Haoyang Wang; Li Zhang; Jing Zhang; Hang Wang; Yinlong Guo (pp. 114-121).
Display Omitted► A novel MS-based isotope reagent DMPP was developed for the derivatization toward carboxyl group. ► The simple and rapid labeling reaction was carried out under mild conditions with high specificity. ► The LODs of analytes containing the carboxyl and excess labeling reagent were greatly reduced. ► Enhanced accuracy in peptide sequencing was achieved by the introduction of isotope-coded DMPP.A novel isotope labeling reagent d0-/ d6-2, 4-dimethoxy-6-piperazin-1-yl pyrimidine (DMPP) has been developed for derivatization toward the carboxyl group based on carbodiimide chemistry for mass spectrometry (MS) analysis. The strengths of this derivatization strategy involve fast labeling (15s), low chemical background and general access to most carboxylic analytes. This has been demonstrated using a series of compounds containing carboxylic acids, including peptides and proteins. To enhance the MS response of the derivatized analytes, the design of DMPP has been based on integration of the theoretical consideration of high gas-phase hydrogenation capacity and hydrophobicity. In addition, the high abundance product ions at m/ z 225 and m/ z 231 from d0-/ d6-DMPP labeled carboxylic acids indicate high efficiency of the gas-phase cleavage induced by the labeling reagent. Quantitative determination of these ions can also be used in single reaction monitoring to achieve extremely high sensitivity toward the target analytes. This has subsequently been used to determine trace free fatty acids in human urine. Furthermore, the DMPP labeled peptides also provide additional sequence information in MALDI–MS/MS because of the formation of sequence-related isotope fragment ions. This DMPP-oriented labeling technique is expected to be a promising tool for the MS detection of many varieties of compounds containing carboxyl groups.
Keywords: Chemical derivatization; Carboxyl group; Isotope labeling; Mass spectrometry
Comparison of the performance of three ion mobility spectrometers for measurement of biogenic amines by Zeev Karpas; Ana V. Guamán; Antonio Pardo; Santiago Marco (pp. 122-129).
The response to different amounts of TMA (in μg) that were placed in a headspace vial as a function of time for the VG-Test (top) and the GDA (bottom). Note that the ratio [TMA/(TMA+TEP)] (top) and [TMA/(TMA+RIP)] (bottom) and the clearance time increase with the amount of TMA deposited in the vial.Display Omitted► First comparison of performance of IMS devices. ► Gas-phase ion chemistry affected by operational parameters. ► Limits of detection quite similar despite differences in devices. ► LODs determined in controlled continuous flow and in headspace vapor. ► Exponential dilution of headspace studies.The performance of three different types of ion mobility spectrometer (IMS) devices: GDA2 with a radioactive ion source (Airsense, Germany), UV-IMS with a photo-ionization source (G.A.S. Germany) and VG-Test with a corona discharge source (3QBD, Israel) was studied. The gas-phase ion chemistry in the IMS devices affected the species formed and their measured reduced mobility values. The sensitivity and limit of detection for trimethylamine (TMA), putrescine and cadaverine were compared by continuous monitoring of a stream of air with a given concentration of the analyte and by measurement of headspace vapors of TMA in a sealed vial. Preprocessing of the mobility spectra and the effectiveness of multivariate curve resolution techniques (MCR-LASSO) improved the accuracy of the measurements by correcting baseline effects and adjusting for variations in drift time as well as enhancing the signal to noise ratio and deconvolution of the complex data matrix to their pure components. The limit of detection for measurement of the biogenic amines by the three IMS devices was between 0.1 and 1.2ppm (for TMA with the VG-Test and GDA, respectively) and between 0.2 and 0.7ppm for putrescine and cadaverine with all three devices. Considering the uncertainty in the LOD determination there is almost no statistically significant difference between the three devices although they differ in their operating temperature, ionization method, drift tube design and dopant chemistry. This finding may have general implications on the achievable performance of classic IMS devices.
Keywords: Ion mobility spectrometry; Comparison of performance; Biogenic amines; Signal processing; Sensitivity; Vapor concentration
An electronic channel switching-based aptasensor for ultrasensitive protein detection by Hongbo Li; Cui Wang; Zaisheng Wu; Limin Lu; Liping Qiu; Hui Zhou; Guoli Shen; Ruqin Yu (pp. 130-137).
.Display Omitted► Target IgE is successfully designed to serve as a barrier to separate enzyme from its substrate. ► This sensing platform of electronic channel switching-based aptasensor can be simply manipulated. ► The stable hairpin structure of anti-IgE aptamer is utilized to detect target IgE. ► The sensor is ultrasensitive sensitivity, excellent selectivity and small volume of sample. ► It is a powerful platform to be further expanded to detect more kinds of proteins and even cells.Due to the ubiquity and essential of the proteins in all living organisms, the identification and quantification of disease-specific proteins are particularly important. Because the conformational change of aptamer upon its target or probe/target/probe sandwich often is the primary prerequisite for the design of an electrochemical aptameric assay system, it is extremely difficult to construct the electrochemical aptasensor for protein assay because the corresponding aptamers cannot often meet the requirement. To circumvent the obstacles mentioned, an electronic channel switching-based (ECS) aptasensor for ultrasensitive protein detection is developed. The essential achievement made is that an innovative sensing concept is proposed: the hairpin structure of aptamer is designed to pull electroactive species toward electrode surface and makes the surface-immobilized IgE serve as a barrier that separates enzyme from its substrate. It seemingly ensures that the ECS aptasensor exhibits most excellent assay features, such as, a detection limit of 4.44×10−6μgmL−1 (22.7fM, 220zmol in 10-μL sample) (demonstrating a 5 orders of magnitude improvement in detection sensitivity compared with classical electronic aptasensors) and dynamic response range from 4.44×10−6 to 4.44×10−1μgmL−1. We believe that the described sensing concept here might open a new avenue for the detection of proteins and other biomacromolecules.
Keywords: Electrochemical analysis; Aptasensor; Immunoglobulin E; Aptamer–protein interaction; Electronic channel switching
Highly water-soluble, near-infrared emissive BODIPY polymeric dye bearing RGD peptide residues for cancer imaging by Shilei Zhu; Jingtuo Zhang; Jagadeesh Janjanam; Jianheng Bi; Giri Vegesna; Ashutosh Tiwari; Fen-Tair Luo; Jianjun Wei; Haiying Liu (pp. 138-144).
BODIPY polymeric dye bearing cancer-homing cyclic arginine–glycine–aspartic acid peptide residues is used for selective near-infrared imaging of breast cancer cells (MDA-MB-231) through specific cooperative bindings of cancer-homing RGD peptides to αvβ3 integrins of cancer cells.Display Omitted► Highly water-soluble near-infrared emissive BODIPY polymeric dye bearing bromide groups (polymerA) was prepared. ► BODIPY polymeric dye bearing RGD peptides (polymerB) was prepared by post-polymerization functionalization. ► PolymerB was used for specific near-infrared fluorescence imaging of breast cancer cells.Near-infrared emissive BODIPY polymeric dye bearing cancer-homing cyclic arginine–glycine–aspartic acid (RGD) peptide residues (polymerB) was prepared by post-polymerization functionalization of BODIPY polymeric dye bearing bromo groups through tetra(ethylene glycol) tethered spacers (polymerA) with thiol-functionalized RGD cancer-homing peptide through thioether bonds under a mild basic condition. PolymerB possesses excellent water solubility, good photostability, biocompatibility and resistance to nonspecific interactions to normal endothelial cells, and can efficiently detect breast tumor cells through specific cooperative binding of cancer-homing RGD peptides to αvβ3 integrins of cancer cells while its parent polymerA without RGD residues fails to target cancer cells.
Keywords: BODIPY dye; Conjugated polymer; Cancer imaging; Fluorescence; RGD peptide