Showing papers in "Analyst in 2012"

Recent advances in electrochemical sensing for hydrogen peroxide: a review

Abstract: Due to the significance of hydrogen peroxide (H(2)O(2)) in biological systems and its practical applications, the development of efficient electrochemical H(2)O(2) sensors holds a special attraction for researchers Various materials such as Prussian blue (PB), heme proteins, carbon nanotubes (CNTs) and transition metals have been applied to the construction of H(2)O(2) sensors In this article, the electrocatalytic H(2)O(2) determinations are mainly focused on because they can provide a superior sensing performance over non-electrocatalytic ones The synergetic effect between nanotechnology and electrochemical H(2)O(2) determination is also highlighted in various aspects In addition, some recent progress for in vivo H(2)O(2) measurements is also presented Finally, the future prospects for more efficient H(2)O(2) sensing are discussed

Modern analytical techniques in metabolomics analysis

Abstract: Metabolomics is the comprehensive assessment of endogenous metabolites and attempts to systematically identify and quantify metabolites from a biological sample. Small-molecule metabolites have an important role in biological systems and represent attractive candidates to understand disease phenotypes. Metabolites represent a diverse group of low-molecular-weight structures including lipids, amino acids, peptides, nucleic acids, organic acids, vitamins, thiols and carbohydrates, which makes global analysis a difficult challenge. The recent rapid development of a range of analytical platforms, including GC, HPLC, UPLC, CE coupled to MS and NMR spectroscopy, could enable separation, detection, characterization and quantification of such metabolites and related metabolic pathways. Owing to the complexity of the metabolome and the diverse properties of metabolites, no single analytical platform can be applied to detect all metabolites in a biological sample. The combined use of modern instrumental analytical approaches has unravelled the ideal outcomes in metabolomics, and is beneficial to increase the coverage of detected metabolites that can not be achieved by single-analysis techniques. Integrated platforms have been frequently used to provide sensitive and reliable detection of thousands of metabolites in a biofluid sample. Continued development of these analytical platforms will accelerate widespread use and integration of metabolomics into systems biology. Here, the application of each hyphenated technique is discussed and its strengths and limitations are discussed with selected illustrative examples; furthermore, this review comprehensively highlights the role of integrated tools in metabolomic research.

Facile magnetization of metal–organic framework MIL-101 for magnetic solid-phase extraction of polycyclic aromatic hydrocarbons in environmental water samples

Abstract: The unusual properties such as high surface area, good thermal stability, uniform structured nanoscale cavities and the availability of in-pore functionality and outer-surface modification make metal–organic frameworks (MOFs) attractive for diverse analytical applications. However, integration of MOFs with magnets for magnetic solid-phase extraction for analytical application has not been attempted so far. Here we show a facile magnetization of MOF MIL-101(Cr) for rapid magnetic solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. MIL-101 is attractive as a sorbent for solid-phase extraction of pollutants in aqueous solution due to its high surface area, large pores, accessible coordinative unsaturated sites, and excellent chemical and solvent stability. In situ magnetization of MIL-101 microcrystals as well as magnetic solid-phase extraction of PAHs was achieved simultaneously by simply mixing MIL-101 and silica-coated Fe3O4 microparticles in a sample solution under sonication. Such MOF-based magnetic solid-phase extraction in combination with high-performance liquid chromatography gave the detection limits of 2.8–27.2 ng L−1 and quantitation limits of 6.3–87.7 ng L−1 for the PAHs. The relative standard deviations for intra- and inter-day analyses were in the range of 3.1–8.7% and 6.1–8.5%, respectively. The results showed that hydrophobic and π–π interactions between the PAHs and the framework terephthalic acid molecules, and the π-complexation between PAHs and the Lewis acid sites in the pores of MIL-101 play a significant role in the adsorption of PAHs.

BSA-templated MnO2 nanoparticles as both peroxidase and oxidase mimics

Abstract: Inorganic nanomaterials that mimic enzymes are fascinating as they potentially have improved properties relative to native enzymes, such as greater resistance to extremes of pH and temperature and lower sensitivity to proteases. Although many artificial enzymes have been investigated, searching for highly-efficient and stable catalysts is still of great interest. In this paper, we first demonstrated that bovine serum albumin (BSA)-stabilized MnO(2) nanoparticles (NPs) exhibited highly peroxidase-, oxidase-, and catalase-like activities. The activities of the BSA-MnO(2) NPs were evaluated using the typical horseradish peroxidase (HRP) substrates o-phenylenediamine (OPD) and 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of either hydrogen peroxide or dissolved oxygen. These small-sized BSA-MnO(2) NPs with good dispersion, solubility and biocompatibility exhibited typical Michaelis-Menten kinetics and high affinity for H(2)O(2), OPD and TMB, indicating that BSA-MnO(2) NPs can be used as satisfactory enzyme mimics. Based on these findings, BSA-MnO(2) NPs were used as colorimetric immunoassay tags for the detection of goat anti-human IgG in place of HRP. The colorimetric immunoassay using BSA-MnO(2) NPs has the advantages of being fast, robust, inexpensive, easily prepared and with no HRP and H(2)O(2) being needed. These water-soluble BSA-MnO(2) NPs may have promising potential applications in biotechnology, bioassays, and biomedicine.

Quantum dot enabled detection of Escherichia coli using a cell-phone.

Abstract: We report a cell-phone based Escherichia coli (E. coli) detection platform for screening of liquid samples. In this compact and cost-effective design attached to a cell-phone, we utilize anti-E. coli O157:H7 antibody functionalized glass capillaries as solid substrates to perform a quantum dot based sandwich assay for specific detection of E. coli O157:H7 in liquid samples. Using battery-powered inexpensive light-emitting-diodes (LEDs) we excite/pump these labelled E. coli particles captured on the capillary surface, where the emission from the quantum dots is then imaged using the cell-phone camera unit through an additional lens that is inserted between the capillary and the cell-phone. By quantifying the fluorescent light emission from each capillary tube, the concentration of E. coli in the sample is determined. We experimentally confirmed the detection limit of this cell-phone based fluorescent imaging and sensing platform as ∼5 to 10 cfu mL−1 in buffer solution. We also tested the specificity of this E. coli detection platform by spiking samples with different species (e.g., Salmonella) to confirm that non-specific binding/detection is negligible. We further demonstrated the proof-of-concept of our approach in a complex food matrix, e.g., fat-free milk, where a similar detection limit of ∼5 to 10 cfu mL−1 was achieved despite challenges associated with the density of proteins that exist in milk. Our results reveal the promising potential of this cell-phone enabled field-portable and cost-effective E. coli detection platform for e.g., screening of water and food samples even in resource limited environments. The presented platform can also be applicable to other pathogens of interest through the use of different antibodies.

Peroxidase-like activity of water-soluble cupric oxide nanoparticles and its analytical application for detection of hydrogen peroxide and glucose

Abstract: Water-soluble cupric oxide nanoparticles are fabricated via a quick-precipitation method and used as peroxidase mimetics for ultrasensitive detection of hydrogen peroxide and glucose. The water-soluble CuO nanoparticles show much higher catalytic activity than that of commercial CuO nanoparticles due to their higher affinity to hydrogen peroxide. In addition, the as-prepared CuO nanoparticles are stable over a wide range of pH and temperature. This excellent stability in the form of aqueous colloidal suspensions makes the application of the water-soluble CuO nanoparticles easier in aqueous systems. A colorimetric assay for hydrogen peroxide and glucose has been established based on the catalytic oxidation of phenol coupled with 4-amino-atipyrine by the action of hydrogen peroxide. This analytical platform not only confirms the intrinsic peroxidase-like activity of the water-soluble cupric oxide nanoparticles, but also shows its great potential applications in environmental chemistry, biotechnology and medicine.

Peroxidase-like activity of chitosan stabilized silver nanoparticles for visual and colorimetric detection of glucose

Abstract: Chitosan stabilized silver nanoparticles (Ch-Ag NPs) were successfully synthesized by a one-step method and were found to possess intrinsic peroxidase-like activity, could catalytically oxidize substrates, such as TMB, and OPD, by H2O2 to produce a typical colour reaction such as from colorless to blue for TMB and from colorless to red for OPD. Our results demonstrate that the Ch-Ag NPs exhibit higher thermal and pH durance than HRP, thus could be suitable in a wider range of harsh conditions. Results of electron paramagnetic resonance (ESR) suggest that the catalyse-mimic activity of the Ch-Ag nanostructures effectively catalyzed the decomposition of H2O2 into ˙OH radicals. Based on this finding, a simple, sensitive and selective visual and colorimetric method with TMB as substrate has been designed for glucose detection when combined with glucose oxidase (GOx). This colorimetric method can be used for detection of glucose in biological samples with a detection limit as low as 100 nM and a dynamic range from 5.0 × 10−6 to 2.0 × 10−4 M.

Microwave-assisted synthesis of carbon nanodots through an eggshell membrane and their fluorescent application.

Abstract: Carbon nanodots (C-Dots) as a new form of carbonaceous nanomaterials have aroused much interest and intensive research due to their inspiring properties. Compared to traditional semiconductor quantum dots, these newly emergent nanodots possess a number of advantageous characteristics, among which low-toxicity is particularly fascinating. More and more research into C-Dots have focused on synthesis methods and biology-related applications. Microwave-assisted approaches have attracted attention because microwave treatment can provide intensive and efficient energy, and as a consequence shorten the reaction time. In this article, we designed a “green”, rapid, eco-friendly and waste-reused approach to synthesize fluorescent and water-soluble C-Dots from eggshell membrane (ESM) ashes according to a microwave-assisted process. ESM selected as the carbon source was a common protein-rich waste in daily life and can be obtained easily and cheaply. The C-Dots from our method showed the maximal fluorescence emission peak at 450 nm and the fluorescence quantum yield was about 14%. We further designed a sensitive probe for glutathione based on the fluorescence turn off and on of the C-Dots–Cu2+ system, which showed a linear range of 0.5–80 μmol L−1 and detection limit of 0.48 μmol L−1. In general, the C-Dots prepared briefly and inexpensively from ESM revealed excellent fluorescent property with promising potential for applications such as sample detection and biotechnology.

Extracting biological information with computational analysis of Fourier-transform infrared (FTIR) biospectroscopy datasets: current practices to future perspectives

Abstract: Applying Fourier-transform infrared (FTIR) spectroscopy (or related technologies such as Raman spectroscopy) to biological questions (defined as biospectroscopy) is relatively novel. Potential fields of application include cytological, histological and microbial studies. This potentially provides a rapid and non-destructive approach to clinical diagnosis. Its increase in application is primarily a consequence of developing instrumentation along with computational techniques. In the coming decades, biospectroscopy is likely to become a common tool in the screening or diagnostic laboratory, or even in the general practitioner's clinic. Despite many advances in the biological application of FTIR spectroscopy, there remain challenges in sample preparation, instrumentation and data handling. We focus on the latter, where we identify in the reviewed literature, the existence of four main study goals: Pattern Finding; Biomarker Identification; Imaging; and, Diagnosis. These can be grouped into two frameworks: Exploratory; and, Diagnostic. Existing techniques in Quality Control, Pre-processing, Feature Extraction, Clustering, and Classification are critically reviewed. An aspect that is often visited is that of method choice. Based on the state-of-art, we claim that in the near future research should be focused on the challenges of dataset standardization; building information systems; development and validation of data analysis tools; and, technology transfer. A diagnostic case study using a real-world dataset is presented as an illustration. Many of the methods presented in this review are Machine Learning and Statistical techniques that are extendable to other forms of computer-based biomedical analysis, including mass spectrometry and magnetic resonance.

A water soluble Al3+ selective colorimetric and fluorescent turn-on chemosensor and its application in living cell imaging

Abstract: An efficient water soluble fluorescent Al3+ receptor, 1-[[(2-furanylmethyl)imino]methyl]-2-naphthol (1-H) was synthesized and characterized by physico-chemical and spectroscopic tools along with single crystal X-ray crystallography. High selectivity and affinity of 1-H towards Al3+ in HEPES buffer (DMSO/water: 1/100) of pH 7.4 at 25 °C showed it to be suitable for detection of intracellular Al3+ by fluorescence microscopy. Metal ions, viz. alkali (Na+, K+), alkaline earth (Mg2+, Ca2+), and transition-metal ions (Ni2+, Zn2+, Cd2+, Co2+, Cu2+, Fe3+, Cr3+/6+, Hg2+) and Pb2+, Ag+ did not interfere. The lowest detection limit for Al3+ was calculated to be 6.03 × 10−7 M in 100 mM HEPES buffer (DMSO/water: 1/100). Theoretical calculations have also been included in support of the configuration of the probe–aluminium complex.

Ratiometric optical oxygen sensing: a review in respect of material design

Abstract: The quantitative determination of oxygen concentration is essential for a variety of applications ranging from life sciences to environmental sciences. Optical oxygen sensing allows non-invasive measurements with biological objects, parallel monitoring of multiple samples, and imaging. In general, ratiometric optical oxygen sensing is more desirable, due to its advantages of selectivity, insensitivity to ambient or scattered light, and elimination of instrumental fluctuation. Moreover, it can provide the perceived colour change, which would be useful not only for the ratiometric method of detection but also for rapid visual sensing. Mainly focusing on material design for ratiometric measurement, this review describes the overall progress made in the past ten years on ratiometric optical ground-state triplet oxygen sensing and offers a critical comparison of various methods reported in the literature. It also provides a development blueprint for ratiometric optical oxygen sensing.

Highly selective and sensitive detection of Cu2+ with lysine enhancing bovine serum albumin modified-carbon dots fluorescent probe

Abstract: Based on the ability of lysine (Lys) to enhance the fluorescence intensity of bovine serum albumin modified-carbon dots (CDs-BSA) to decrease surface defects and quench fluorescence of the CDs-BSA-Lys system in the presence of Cu2+ under conditions of phosphate buffer (PBS, pH = 5.0) at 45 °C for 10 min, a sensitive Lys enhancing CDs-BSA fluorescent probe was designed. The environment-friendly, simple, rapid, selective and sensitive fluorescent probe has been utilized to detect Cu2+ in hair and tap water samples and it achieved consistent results with those obtained by inductively coupled plasma mass spectroscopy (ICP-MS). The mechanism of the proposed assay for the detection of Cu2+ is discussed.

Advances in microfluidics for environmental analysis

Abstract: During the past few years, a growing number of groups have recognized the utility of microfluidic devices for environmental analysis. Microfluidic devices offer a number of advantages and in many respects are ideally suited to environmental analyses. Challenges faced in environmental monitoring, including the ability to handle complex and highly variable sample matrices, lead to continued growth and research. Additionally, the need to operate for days to months in the field requires further development of robust, integrated microfluidic systems. This review examines recently published literature on the applications of microfluidic systems for environmental analysis and provides insight in the future direction of the field.

Understanding the molecular information contained in principal component analysis of vibrational spectra of biological systems

Abstract: K-means clustering followed by Principal Component Analysis (PCA) is employed to analyse Raman spectroscopic maps of single biological cells. K-means clustering successfully identifies regions of cellular cytoplasm, nucleus and nucleoli, but the mean spectra do not differentiate their biochemical composition. The loadings of the principal components identified by PCA shed further light on the spectral basis for differentiation but they are complex and, as the number of spectra per cluster is imbalanced, particularly in the case of the nucleoli, the loadings under-represent the basis for differentiation of some cellular regions. Analysis of pure bio-molecules, both structurally and spectrally distinct, in the case of histone, ceramide and RNA, and similarly in the case of the proteins albumin, collagen and histone, show the relative strong representation of spectrally sharp features in the spectral loadings, and the systematic variation of the loadings as one cluster becomes reduced in number. The more complex cellular environment is simulated by weighted sums of spectra, illustrating that although the loading becomes increasingly complex; their origin in a weighted sum of the constituent molecular components is still evident. Returning to the cellular analysis, the number of spectra per cluster is artificially balanced by increasing the weighting of the spectra of smaller number clusters. While it renders the PCA loading more complex for the three-way analysis, a pair wise analysis illustrates clear differences between the identified subcellular regions, and notably the molecular differences between nuclear and nucleoli regions are elucidated. Overall, the study demonstrates how appropriate consideration of the data available can improve the understanding of the information delivered by PCA.

Electrochemical determination of glutathione: a review

Abstract: The physiological importance of glutathione and glutathione disulfide is evident from their implications in an array of medical conditions including diabetes, Parkinson's disease and cancer. As such the need for simple, rapid and cheap assays to aid clinical diagnostics and treatment is clear. These requirements are, in principle at least, ideally suited to electrochemical detection. Accordingly a large array of voltammetric methods ultimately aimed at making cheap and most likely disposable electrodes have been reported. This critical review analyses the context in which physiological glutathione measurement can be undertaken electrochemically and compares it to current assay approaches, while also covering the current literature for glutathione disulfide detection. The various characteristics and limitations of the methodologies are compared and contrasted, with the analytical parameters (matrix, pH, limit of detection, etc.) tabulated to aid comparison.

Turn-on fluorescent chemosensor for Zn(II) via ring opening of rhodamine spirolactam and their live cell imaging.

Abstract: A new rhodamine based selective and sensitive turn-on fluorescent Zn2+chemosensor has been developed. A prominent fluorescence enhancement was found in the presence of Zn2+, which was accompanied by changes in the absorption spectrum. The new sensor showed ‘naked-eye’ detection of Zn2+ ions: a color change of the solution from colorless to pink. Furthermore, by means of confocal laser scanning microscopy experiments, it has been demonstrated that it can be used as a fluorescent probe for monitoring Zn2+ in living cells.

A turn-on and reversible fluorescence sensor for zinc ion.

Abstract: A simple 2-hydroxy-1-naphthaldehyde (receptor 1) serves as a selective chemosensor for Al3+ based on chelation-enhanced fluorescence (CHEF). The receptor 1 exhibited a high association constant with micromolar detection for Al3+ in EtOH–H2O solution.

A ratiometric fluorescent chemosensor for iron: discrimination of Fe2+ and Fe3+ and living cell application

Abstract: A newly designed probe, 6-thiophen-2-yl-5,6-dihydrobenzo[4,5]imidazo-[1,2-c] quinazoline (HL1) behaves as a highly selective ratiometric fluorescent sensor for Fe2+ at pH 4.0–5.0 and Fe3+ at pH 6.5–8.0 in acetonitrile–HEPES buffer (1/4) (v/v) medium. A decrease in fluorescence at 412 nm and increase in fluorescence at 472 nm with an isoemissive point at 436 nm with the addition of Fe2+ salt solution is due to the formation of mononuclear Fe2+ complex [FeII(HL)(ClO4)2(CH3CN)2] (1) in acetonitrile–HEPES buffer (100 mM, 1/4, v/v) at pH 4.5 and a decrease in fluorescence at 412 nm and increase in fluorescence at 482 nm with an isoemissive point at 445 nm during titration by Fe3+ salt due to the formation of binary Fe3+ complex, [FeIII(L)2(ClO4)(H2O)] (2) with co-solvent at biological pH 7.4 have been established. Binding constants (Ka) in the solution state were calculated to be 3.88 × 105 M−1 for Fe2+ and 0.21 × 103 M−1/2 for Fe3+ and ratiometric detection limits for Fe2+ and Fe3+ were found to be 2.0 μM and 3.5 μM, respectively. The probe is a “naked eye” chemosensor for two states of iron. Theoretical calculations were studied to establish the configurations of probe–iron complexes. The sensor is efficient for detecting Fe3+in vitro by developing a good image of the biological organelles.

Ultrasensitive aptamer biosensor for arsenic(III) detection in aqueous solution based on surfactant-induced aggregation of gold nanoparticles

Abstract: This paper reports the colorimetric and resonance scattering (RS)-based biosensor for the ultrasensitive detection of As(III) in aqueous solution via aggregating gold nanoparticles (AuNPs) by the special interactions between arsenic-binding aptamer, target and cationic surfactant. Aptamers and the cationic surfactant could assemble to form a supramolecule, which prevented AuNPs from aggregating due to the exhaustion of cationic surfactant. The introduction of As(III) specifically interacted with the arsenic-binding aptamer to form the aptamer-As(III) complex, so that the following cationic surfactant could aggregate AuNPs and cause the remarkable change in color and RS intensity. The results of circular dichroism (CD) and scanning probe microscope (SPM) testified to the formation of the supramolecule and aptamer-As(III) complex, and the observation of transmission electron microscope (TEM) further confirmed that the aggregation of AuNPs could be controlled by the interactions among the aptamer, As(III) and cationic surfactant. The variations of absorbance and RS intensity were exponentially related to the concentration of As(III) in the range from 1 to 1500 ppb, with the detection limit of 40 ppb for the naked eye, 0.6 ppb for colorimetric assay and 0.77 ppb for RS assay. Additionally, the speed of the present biosensor was rapid, and it also exhibited high selectivity over other metal ions with an excellent recovery for detection in real water samples, suggesting that the proposed biosensor will play an important role in environmental detection.

Metal-organic framework templated synthesis of Co3O4 nanoparticles for direct glucose and H2O2 detection.

Abstract: Co(3)O(4) nanoparticles (NPs) with an average diameter of about 20 nm were synthesized by using MOFs as a template. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the as-prepared Co(3)O(4) NPs. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to confirm the structure of the Co(3)O(4) NPs. Then the Co(3)O(4) NPs were modified on a glassy carbon electrode (GCE) to obtain a non-enzymatic glucose and H(2)O(2) sensor. The NPs show electrocatalytic activity toward oxidation of glucose and H(2)O(2) in alkaline medium. For glucose detection, the developed sensor shows a short response time (less than 6 s), a high sensitivity of 520.7 μA mM(-1) cm(-2), a detection limit of 0.13 μM (S/N = 3), and good selectivity. The high concentration of NaCl does not poison the electrode. Its application for the detection of glucose in a human blood serum sample shows good agreement with the results obtained from the hospital. Furthermore, the proposed sensor was used for the detection of H(2)O(2). The results indicate that the detection limit and sensitivity for H(2)O(2) are 0.81 μM and 107.4 μA mM(-1) cm(-2), respectively. Determination of H(2)O(2) concentration in a disinfectant sample by the proposed biosensor also showed satisfactory result. The high sensitivity and low detection limit can be attributed to the excellent electrocatalytic performance of the as-prepared Co(3)O(4) NPs. These results demonstrate that the as-prepared Co(3)O(4) NPs have great potential applications in the development of sensors for enzyme-free detection of glucose and H(2)O(2).

Metal–organic framework MIL-53(Al) as a solid-phase microextraction adsorbent for the determination of 16 polycyclic aromatic hydrocarbons in water samples by gas chromatography–tandem mass spectrometry

Abstract: In this paper, the potential applications of metal–organic framework (MOF) materials as fiber coatings for the solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs) in water samples were explored. Fibers coated with MIL-53(Al, Cr, Fe) materials were fabricated by an adhesive method for SPME. The quantitation was performed by gas chromatography–tandem mass spectrometry (GC–MS/MS) using the multiple reaction monitoring mode. Among the three MIL-53(M) coatings, MIL-53(Al) showed the highest extraction efficiency towards PAHs under the current fabrication procedure. Under optimized conditions, the MIL-53(Al)-coated fiber showed good precision (relative standard deviation 0.98) for aqueous solutions containing 16 PAH . The fiber also offered high thermal and chemical stability. The method developed based on MIL-53(Al) SPME–GC–MS/MS was successfully applied in the analysis of real water samples. Based on the simulation results, the PAHs were adsorbed on MIL-53(Al) primarily through the hydrophobic and π–π interactions between PAHs and the organic linker of the material. The results presented in this paper indicate that water-stable MOF materials have great potential for the SPME of aromatic compounds in water samples.

Colorimetric assay for parallel detection of Cd2+, Ni2+ and Co2+ using peptide-modified gold nanoparticles

Abstract: A colorimetric assay has been developed for parallel detection of Cd(2+), Ni(2+) and Co(2+) utilizing peptide-modified gold nanoparticles (P-AuNPs) as a sensing element based on its unique surface plasmon resonance properties. The functional peptide ligand, CALNNDHHHHHH, was self-assembled on gold nanoparticles (AuNPs) to produce P-AuNPs probe. The P-AuNPs probe could be used to simultaneously detect and showed different responses to the three ions Cd(2+), Ni(2+) and Co(2+) in an aqueous solution based on the aggregation-induced color change of AuNPs. The method showed good selectivity for Cd(2+), Ni(2+) and Co(2+) over other metal ions, and detection limit as low as 0.05 μM Cd(2+), 0.3 μM Ni(2+) or 2 μM Co(2+). To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA and imidazole were applied to mask Co(2+) and Ni(2+) for detecting Cd(2+), glutathione and EDTA were applied to mask Cd(2+) and Co(2+) for detecting Ni(2+), and glutathione and imidazole were applied to mask Cd(2+) and Ni(2+) for detecting Co(2+). Finally, the simple and cost-effective probe could be successfully applied for simultaneously detecting Cd(2+), Ni(2+), and Co(2+) in river water. Because this novel P-AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies, the sensing system shows potential application in the developing region for monitoring water quality.

Quantification strategies for elemental imaging of biological samples using laser ablation-inductively coupled plasma-mass spectrometry

Abstract: This review provides analysts with critical insights of current approaches for quantification by laser ablation-inductively coupled plasma-mass spectrometry in the field of elemental imaging. This encompasses both calibration strategies that have been used with success in imaging biological samples, as well as those with potential to improve analytical accuracy and precision if applied to imaging. Methods reviewed include the use of CRMs, laboratory prepared matrix matched standards, internal standardisation, online standard addition and a variety of novel approaches that makes elemental imaging accessible to a wider base of analysts. The importance of quantification and factors affecting its use in imaging will also be considered.

All-solid-state potassium-selective electrode using graphene as the solid contact

Abstract: Graphene sheets are used for the first time to fabricate a new type of solid-contact ion-selective electrode (SC-ISE) as the intermediate layer between an ionophore-doped solvent polymeric membrane and a glassy carbon electrode. The new transducing layer was characterized by transmission electron microscopy, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The performance of the new K+−selective electrodes was examined by a potentiometric water layer test, potentiometric measurements, and current reversal chronopotentiometry. The obtained potentiometric sensors were characterized with a calibration line of slope close to Nernstian (59.2 mV/decade) within the activity from 10−4.5 to 0.1 M. The high capacitance of the graphene solid contacts results in a signal that is stable over one week. The short response time is less than 10 s for activities higher than 10−5 M. The potential drift of the electrodes was calculated from the slope of the curves at longer times (ΔE/Δt = 1.2 × 10−5 V s−1 (I = 1 nA) and ΔE/Δt = 5.5 × 10−5 V s−1 (I = 5 nA)). All the results indicate that graphene is a promising material for use as a transducer layer for SC-ISEs.

A fluorescent turn-on probe for bisulfite based on hydrogen bond-inhibited CN isomerization mechanism

Abstract: A fluorescence turn-on probe for bisulfite has been developed by taking advantage of the specific reaction of bisulfite and aldehyde in combination with the hydrogen bond inhibited C=N isomerization mechanism. The practical value of this selective and sensitive fluorescent probe was confirmed by its application to detection of bisulfite in granulated sugar.

Rapid analysis of whole blood by paper spray mass spectrometry for point-of-care therapeutic drug monitoring

Abstract: Paper spray mass spectrometry is applied to oncology drugs in fresh whole blood samples supported on filter paper substrates instead of dry blood as done previously. Addition of the coagulant alum clotted the blood and allowed for immediate sample analysis. The coagulant did not interfere with the function of the paper spray nor did it add features to the mass spectra. Quantitative analysis of therapeutic drugs in the blood was achieved utilizing internal standards which were pre-spotted onto the filter paper. Eight oncology drugs were examined, with lower limits of detection ranging between 0.5 and 17 ng mL−1 and linear dynamic ranges greater than two orders of magnitude. Inter-day accuracies of quality controls for pazopanib ranged from 102 to 118%, with imprecisions of 9 to 13%. This one-step method requires 10 μL of blood, a drop of solvent, and takes 45 seconds per trial. These results indicate applicability to point-of-care therapeutic drug monitoring in a clinical setting.

Gold nanorods as surface enhanced Raman spectroscopy substrates for sensitive and selective detection of ultra-low levels of dithiocarbamate pesticides.

Abstract: We report the use of gold nanorods as solution-based SERS substrates for the detection of ultralow-levels of three different dithiocarbamate fungicides: thiram, ferbam and ziram. Gold nanorods are attractive to use as SERS substrates due to the ability to tune the surface plasmon resonance of the nanoparticles to the laser excitation wavelength of the Raman spectrometer equipped with a 785 nm diode laser. The gold nanorods are synthesized using a seed-mediated growth method and characterized using UV-Visible spectroscopy, zeta potential, and TEM. The gold nanorods have an aspect ratio of 2.19 ± 0.21 and have an average length of 37.81 ± 4.83 nm. SERS spectra are acquired at different concentrations of each fungicide and calibration curves are obtained by monitoring the intensity of the band arising from the ν(C–N) stretching mode coupled to the symmetric δ(CH3) motion. The limits of detection and limits of quantitation are obtained for each fungicide. The limits of detection are 11.00 ± 0.95 nM, 8.00 ± 1.01 nM, and 4.20 ± 1.22 nM for thiram, ferbam, and ziram respectively. The limits of quantitation are 34.43 ± 0.95 nM, 25.61 ± 1.01 nM, and 12.94 ± 1.22 nM for thiram, ferbam, and ziram respectively. It can be seen that the three different dithiocarbamates can be detected in the low nM range based on the limits of detection that are achieved.

Bacteriophage based probes for pathogen detection

Abstract: Rapid and specific detection of pathogenic bacteria is important for the proper treatment, containment and prevention of human, animal and plant diseases Identifying unique biological probes to achieve a high degree of specificity and minimize false positives has therefore garnered much interest in recent years Bacteriophages are obligate intracellular parasites that subvert bacterial cell resources for their own multiplication and production of disseminative new virions, which repeat the cycle by binding specifically to the host surface receptors and injecting genetic material into the bacterial cells The precision of host recognition in phages is imparted by the receptor binding proteins (RBPs) that are often located in the tail-spike or tail fiber protein assemblies of the virions Phage host recognition specificity has been traditionally exploited for bacterial typing using laborious and time consuming bacterial growth assays At the same time this feature makes phage virions or RBPs an excellent choice for the development of probes capable of selectively capturing bacteria on solid surfaces with subsequent quick and automatic detection of the binding event This review focuses on the description of pathogen detection approaches based on immobilized phage virions as well as pure recombinant RBPs Specific advantages of RBP-based molecular probes are also discussed

A simple filter-based approach to surface enhanced Raman spectroscopy for trace chemical detection

Abstract: We demonstrate an extremely simple and practical surface enhanced Raman spectroscopy (SERS) technique for trace chemical detection. Filter membranes first trap silver nanoparticles to form a SERS-active substrate and then concentrate analytes from a mL-scale sample into a μL-scale detection volume. We demonstrate a significant improvement in detection limit as compared to colloidal SERS for the pesticide malathion and the food contaminant melamine. The measured SERS intensity exhibits low variation relative to traditional SERS techniques, and the data can be closely fit with a Langmuir isotherm. Thus, due to the simple procedure, the low-cost of the substrates, the quantitative results, and the performance improvement due to analyte concentration, our technique enables SERS to be practical for a broad range of analytical applications, including field-based detection of toxins in large-volume samples.

Optical mesosensors for monitoring and removal of ultra-trace concentration of Zn(II) and Cu(II) ions from water

Abstract: Optical captor design is necessary for the controlled development of a technique for detecting and removing heavy and toxic metals from drinking water with high flexibility and low capital cost. We designed chemical mesocaptors for optical separation/extraction and monitoring/detection of Cu(II) and Zn(II) ions from water even at trace concentration levels without a preconcentration process. The mesoporous aluminosilica carriers with three-dimensional (3D) structures, high aluminum content, natural surfaces, and active acid sites strongly induced H-bonding and dispersive interactions with organic moieties, thereby leading to the formation of stable captors without chromophore leaching during the removal assays of Cu(II) and Zn(II) ions. Using such a tailored mesocaptor design, the direct immobilization of these hydrophobic ligands (4,5-diamino-6-hydroxy-2-mercaptopyrimidine and diphenylthiocarbazone) into ordered pore-based aluminasilica monoliths enabled the easy generation and transduction of optical colour signals as a response to metal-to-ligand binding events, even at ultra-trace concentrations (∼10−9 mol dm−3) of Cu(II) and Zn(II) ions in drinking water, without the need for sophisticated instruments. Theoretical models have been developed to provide insights into the effect of active site surfaces on the enhancement of the optical removal process in terms of long-term stability, reversibility, and selectivity, hence allowing us to understand the role of mesoscopic geometry and nanoscale pore orientation of mesocaptors better. Generally, this ion-capture model enables the development of a simple and effective technique for effective wastewater treatment and management.