In Vitro Assessment of the Physiologically Relevant Oral Bioaccessibility of Metallic Elements in Edible Herbs Using the Unified Bioaccessibility Protocol.

In this work, the total content of seven metallic elements (Fe, Cu, Zn, Mg, Pb, Ni, and Co) in common edible herbs was determined and related to their bioaccessibility by an in vitro human digestion model. Specifically, the unified bioaccessibility protocol developed by the BioAccessibility Research Group of Europe (BARGE) was used to determine the release of each element during gastric and gastrointestinal digestion. The results show that Fe, Zn, and Mg are released during gastric digestion (34-57% Fe, 28-80% Zn, 79-95% Mg), but their overall bioaccessibility is reduced in the gastrointestinal tract (<30%). On the contrary, Cu is more bioaccessible during gastrointestinal digestion (38-60%). Pb, Ni, and Co exhibited similar bioaccessibility in both gastric and gastrointestinal fluids. Principle component analysis of the data shows that the classification of the nutritional value of herbs differs between the total and the gastrointestinal concentration, suggesting that the total concentration alone is not an adequate indicator for drawing secure conclusions concerning the nutritional benefits of edible plant species.

Analyte-mediated formation and growth of nanoparticles for the development of chemical sensors and biosensors.

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles' formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies.

Biothiol modulated growth and aggregation of gold nanoparticles and their determination in biological fluids using digital photometry.

This work describes a novel and easy to use method for the determination of biologically important thiols that relies on their ability to inhibit the catalytic enlargement of AuNP seeds in the presence of ACl4- ions and trigger their aggregation. UV-vis spectroscopic monitoring of the plasmon resonance bands of the formed AuNPs showed that the spectral and color transitions depend both on the concentration and the structure of biothiols. The colorimetric changes induced by biothiols were quantified in the concentration range from 5 to 300 µM in the RGB color system with digital photometry using a commercially available flatbed scanner as detector. On the basis of these results, the applicability of the method was tested to the determination of glutathione in red blood cells and cysteine in blood plasma with satisfactory recoveries (88.7-96.5%), low detection limits (1.0 µM), good selectivity against major biomolecules under physiologically relevant conditions and satisfactory reproducibility (<8%). The method requires minimum technical expertise, is easy to use and is performed without scientific equipment, holding promise as a simple assay of biothiol testing even by non-experts.

Development of a sequential extraction and speciation procedure for assessing the mobility and fractionation of metal nanoparticles in soils.

This study describes the development of a sequential extraction procedure for the evaluation of metal nanoparticle mobility and bioaccessibility in soils. The procedure, that was developed using gold nanoparticles (AuNPs) as model species, relies on the fractionation of nanoparticles by sequentially dissolving soil matrix components (carbonates, metal oxides, organic matter and mineral phases) in order to release the entrapped nanoparticle species in the extract solution. By summing up the concentration of AuNPs recovered in each fraction it was found that 93.5% of the spiked AuNP concentration could be recovered which satisfactorily represents the nominal AuNP concentration in the soil. The efficiency of the procedure was found to depend on several procedural artifacts related to the separation of AuNPs from soil colloids and the reactivity of the extraction reagents with AuNPs and their precursor metal ions. Based on the results obtained a protocol for the speciation of the AuNPs and Au ions in the soil sample was also developed. The results of the study show that both AuNPs and Au ions are mainly associated with soil organic matter, which significantly reduces their mobility, while a small amount (<10%) is associated with metal oxides which are more mobile and potentially bioaccessible. The developed procedure provides a springboard for further development of sequential extraction procedures of metal nanoparticles in soils that could be used to assess both the exposure and release of metal nanoparticles and their precursor metal ions in the environment (as total extractable concentration) as well as provide evidence regarding their bioaccessibility and potential bioavailability by determining the concentration of nanoparticles in each specific soil fraction.

Generic Assay of Sulfur-Containing Compounds Based on Kinetics Inhibition of Gold Nanoparticle Photochemical Growth.

This work describes a new, equipment-free, generic method for the determination of sulfur-containing compounds that is based on their ability to slow down the photoreduction kinetics of gold ions to gold nanoparticles. The method involves tracking the time required for a red coloration to appear in the tested sample, indicative of the formation of gold nanoparticles, and compare the measured time relative to a control sample in the absence of the target analyte. The method is applicable with minimal and simple steps requiring only two solutions (i.e., a buffer and a gold solution), a source of light (UV or visible), and a timer. The method responds to a large variety of sulfur-containing compounds including thiols, thioesters, disulfides, thiophosphates, metal-sulfur bonds, and inorganic sulfur and was therefore applied to the determination of a variety of compounds such as dithiocarbamate and organophosphorous pesticides, biothiols, pharmaceutically active compounds, and sulfides in different samples such as natural waters and wastewater, biological fluids, and prescription drugs. The analytical figures of merit of the method include satisfactory sensitivity (quantitation limits at the low µM levels), good recoveries (from 93 to 109%), and satisfactory reproducibility (from 4.8 to 9.8%). The method is easily adoptable to both laboratory settings and nonlaboratory conditions for quantitative and semiquantitative analysis, respectively, is user-friendly even for the minimally trained user, and can be performed with limited resources at low cost.

Determination of gold nanoparticles in environmental water samples by second-order optical scattering using dithiotreitol-functionalized CdS quantum dots after cloud point extraction.

This work presents a new method for the sensitive and selective determination of gold nanoparticles in water samples. The method combines a sample preparation and enrichment step based on cloud point extraction with a new detection motif that relies on the optical incoherent light scattering of a nano-hybrid assembly that is formed by hydrogen bond interactions between gold nanoparticles and dithiotreitol-functionalized CdS quantum dots. The experimental parameters affecting the extraction and detection of gold nanoparticles were optimized and evaluated to the analysis of gold nanoparticles of variable size and surface coating. The selectivity of the method against gold ions and other nanoparticle species was also evaluated under different conditions reminiscent to those usually found in natural water samples. The developed method was applied to the analysis of gold nanoparticles in natural waters and wastewater with satisfactory results in terms of sensitivity (detection limit at the low pmolL-1 levels), recoveries (>80%) and reproducibility (<9%). Compared to other methods employing molecular spectrometry for metal nanoparticle analysis, the developed method offers improved sensitivity and it is easy-to-operate thus providing an additional tool for the monitoring and the assessment of nanoparticles toxicity and hazards in the environment.

In-situ suspended aggregate microextraction of gold nanoparticles from water samples and determination by electrothermal atomic absorption spectrometry.

This work describes a new method for the extraction and determination of gold nanoparticles in environmental samples by means of in-situ suspended aggregate microextraction and electrothermal atomic absorption spectrometry. The method relies on the in-situ formation of a supramolecular aggregate phase through ion-association between a cationic surfactant and a benzene sulfonic acid derivative. Gold nanoparticles are physically entrapped into the aggregate phase which is separated from the bulk aqueous solution by vacuum filtration on the surface of a cellulose filter in the form of a thin film. The film is removed from the filter surface and is dissociated into an acidified methanolic solution which is used for analysis. Under the optimized experimental conditions, gold nanoparticles can be efficiently extracted from water samples with recovery rates between 81.0-93.3%, precision 5.4-12.0% and detection limits as low as 75femtomolL(-1) using only 20mL of sample volume. The satisfactory analytical features of the method along with the simplicity indicate the efficiency of this new approach to adequately collect and extract gold nanoparticle species from water samples.

Paper-based assay of antioxidant activity using analyte-mediated on-paper nucleation of gold nanoparticles as colorimetric probes.

With the increasing interest in the health benefits arising from the consumption of dietary products rich in antioxidants, there exists a clear demand for easy-to-use and cost-effective tests that can be used for the identification of the antioxidant power of food products. Paper-based analytical devices constitute a remarkable platform for such expedient and low-cost assays with minimal external resources but efforts in this direction are still scarce. In this work we introduce a new paper-based device in the form of a sensor patch that enables the determination of antioxidant activity through analyte-driven on-paper formation of gold nanoparticles. The principle of detection capitalizes, for the first time, on the on-paper nucleation of gold ions to its respective nanoparticles, upon reduction by antioxidant compounds present in an aqueous sample. The ensuing chromatic transitions, induced on the paper surface, are used as an optical "signature" of the antioxidant strength of the solution. The response of the paper-based sensor was evaluated against a large variety of antioxidant species and the respective dose response curves were constructed. On the basis of these data, the contribution of each species according to its chemical structure was elucidated. For the analysis of real samples, a concentration-dependent colorimetric response was established against Gallic acid equivalents over a linear range of 10 µM-1.0 mM, with detection limits at the low and ultra-low µM levels (i.e. <1.0 µM) and satisfactory precision (RSD=3.6-12.6%). The sensor has been tested for the assessment of antioxidant activity in real samples (teas and wines) and the results correlated well with commonly used antioxidant detection methods. Importantly, the sensor performed favorably for long periods of time when stored at moisture-free and low temperature conditions without losing its activity thus posing as an attractive alternative to the assessment of antioxidant activity without specialized equipment. The use of the sensor by non-experts for a rapid assessment of natural products in field testing is envisioned. Importantly, we demonstrate for the first time that analyte-mediated growth of nanomaterials directly on the paper surface could open new opportunities in paper-based analytical devices.

Rhodium nanoparticle-modified screen-printed graphite electrodes for the determination of hydrogen peroxide in tea extracts in the presence of oxygen.

In this work we describe the fabrication of nanostructured electrocatalytic surfaces based on polyethyleneimine (PEI)-supported rhodium nanoparticles (Rh-NP) over graphite screen-printed electrodes (SPEs) for the determination of hydrogen peroxide in the presence of oxygen. Rh-NP, electrostatically stabilized by citrate anions, were immobilized over graphite SPEs, through coulombic attraction on a thin film of positively charged PEI. The functionalized sensors, polarized at 0.0 V vs. Ag/AgCl/3 M KCl, exhibited a linear response to H2O2 over the concentration range from 5 to 600 µmol L(-1) H2O2 in the presence of oxygen. The 3σ limit of detection was 2 µmol L(-1) H2O2, while the reproducibility of the method at the concentration level of 10 µmol L(-1) H2O2 (n=10) and between different sensors (n=4) was lower than 3 and 5%, respectively. Most importantly, the sensors showed an excellent working and storage stability at ambient conditions and they were successfully applied to the determination of H2O2 produced by autooxidation of polylphenols in tea extracts with ageing. Recovery rates ranged between 97 and 104% suggesting that the as-prepared electrodes can be used for the development of small-scale, low-cost chemical sensors for use in on-site applications.

Programming fluid transport in paper-based microfluidic devices using razor-crafted open channels.

Manipulating fluid transport in microfluidic, paper-based analytical devices (µPADs) is an essential prerequisite to enable multiple timed analytical steps on the same device. Current methods to control fluid distribution mainly rely on controlling how slowly the fluid moves within a device or by activating an on/off switch to flow. In this Article, we present an easy approach for programming fluid transport within paper-based devices that enables both acceleration as well as delay of fluid transport without active pumping. Both operations are programmed by carving open channels either longitudinally or perpendicularly to the flow path using a craft-cutting tool equipped with a knife blade. Channels are crafted after µPADs fabrication enabling the end user to generate patterns of open-channels on demand by carving the porous material of the paper without cutting or removing the paper substrate altogether. Parameters to control the acceleration or delay of flow include the orientation, length, and number of open channels. Using this method, accelerated as well as reduced fluid transport rates were achieved on the same device. This methodology was applied to µPADs for multiple and time-programmable assays for metal ion determination.

Ultratrace determination of silver, gold, and iron oxide nanoparticles by micelle mediated preconcentration/selective back-extraction coupled with flow injection chemiluminescence detection.

A new method has been developed for the ultrasensitive determination of silver, gold, and iron oxide nanoparticles in environmental samples. Cloud point extraction was optimized and used as a means to extract and preconcentrate all nanoparticle species simultaneously from the same sample. The extracted nanoparticles were sequentially isolated from the surfactant-rich phase by a new selective back-extraction procedure and dissociated into their precursor metal ions. Each ion solution was injected in a flow injection analysis (FIA) manifold, accommodating the chemiluminogenic oxidation of luminol, in order to amplify chemiluminescence (CL) emission in a manner proportional to its concentration. Under the optimum experimental conditions, the detection limits were brought down to the picomolar and femtomolar concentration levels with satisfactory analytical features in terms of precision (2.0-13.0%), selectivity against dissolved ions, and recoveries (74-114%). The method was successfully applied to the determination of iron oxide, silver, and gold nanoparticles in environmental samples of different complexity, ranging from unpolluted river water to raw sewage. The developed method could also serve as a basis for future deployment of molecular spectrometry detectors for the selective determination and speciation analysis of nanoparticles in environmental applications.

Determination of dissolved organic matter based on UV-light induced reduction of ionic silver to metallic nanoparticles by humic and fulvic acids.

We describe a novel solution-based method for the determination of dissolved organic matter (DOM) relying on the formation of silver nanoparticles (AgNPs) via photo-stimulated reduction of silver ions by humic and fulvic acids. The method is based on natural driven formation of nanoscale materials yielding a direct relationship between DOM concentration and AgNPs formation. The aqueous dispersion of the formed AgNPs show strong and uniform UV-Vis absorption bands between 450 and 550 nm irrespectively of DOM nature and properties (i.e. humic or fulvic acids). The ensuing chromatic shift accompanying the appearance of the new absorption bands is easily conceivable by a simple spectrophotometer and the bare eye, holding great promise for the on-site, instrumental-free screening of DOM levels. Under the optimum experimental conditions the determination of DOM was successfully demonstrated to various water samples with high sensitivity (<1.0 mg L(-1)), satisfactory recoveries (87.5-123.5%) and reproducibility (5.87-6.73%).

Ligand-free gold nanoparticles as colorimetric probes for the non-destructive determination of total dithiocarbamate pesticides after solid phase extraction.

In this work, we describe a simple and sensitive non-destructive method for the determination of the total concentration of dithiocarbamate fungicides (DTCs) in real samples. The proposed method combines for the first time the benefits of an extraction method for sample clean-up and preconcentration with a sensitive colorimetric assay based on gold nanoparticle probes. In this two-step procedure, the target DTCs are isolated from the matrix and preconcentrated by solid phase extraction onto commercially available C18 sorbents. Following elution, the extract containing the target dithiocarbamates, free from most interferences and matrix components, is delivered into an aqueous dispersion of plain citrate-capped gold nanoparticles (AuNPs) which aggregate in response to DTCs coordination on AuNPs surface through multiple gold thiolate bonds. This aggregation is evidenced by changes in the spectral properties of the solution involving a decrease in the original absorbance of Au nanoparticles at 522 nm and the appearance of a new absorption band above 700 nm. An ensuing chromatic shift of the solution from wine-red to purple-blue is observed which is visual by naked eye at concentrations as low as 50 µg L(-1). Further improvement in the detection limits can be accomplished by scaling-down the method to micro-volume conditions alleviating the need to preconcentrate larger sample volumes. Overall, by combining sample clean-up and preconcentration with the strong affinity of DTC thiol group for the gold surface, the total concentration of dithiocarbamate pesticides was successfully determined in various water samples at the low and ultra-low µg L(-1) levels without resorting to destructive techniques, sophisticated instrumentation or post-synthetic modification of gold nanoparticles. Method application in real samples showed good analytical features in terms of recoveries (81.0-94.0%), precision (5.6-8.9%) and reproducibility (~9%) rendering the method as an attractive alternative to current methodologies for the determination of DTC fungicide residues in samples of environmental interest.

Determination of rimantadine in human urine by HPLC using a monolithic stationary phase and on-line post-column derivatization.

In the present study, we propose the first HPLC method coupled to postcolumn derivatization for the determination of rimantadine in human urine samples. The analyte and amantadine (internal standard) were isocratically separated using an RP monolithic stationary phase (100 × 4.6 mm id) with a mobile phase consisting of CH3OH/phosphate buffer (25 mmol/L, pH 3.0) at a volume ratio of 50:50. Postcolumn derivatization involved on-line reaction with o-phthalaldehyde (20 mmol/L) and N-acetyl-cysteine (5 mmol/L) at alkaline medium (100 mmol/L borate pH 11.0). Spectrofluorimetric detection at λ(ex)/λ(em) = 340/455 nm enabled the selective and sensitive determination of rimantadine in urine samples at a range of 50-500 ng/mL with an LOD of 5 ng/mL. Human urine samples were analyzed successfully after SPE using hydrophilic-lipophilic balanced RP cartridges (30 mg/mL, Oasis HLB). Recoveries ranged between 89.7 and 102.7%.

Development of a generic assay for the determination of total trihydroxybenzoate derivatives based on gold-luminol chemiluminescence.

A selective assay for the determination of one of the most important class of phenolic compounds, namely trihydroxybenzoates (monomeric and polymeric compounds having at least one gallate moiety) based on their enhancing effect on the chemiluminogenic reaction between gold ions and luminol is described for the first time. In the presence of trihydroxybenzoate derivatives, the light emission generated when alkaline luminol is oxidized by gold ions is amplified several orders of magnitude compared to other common phenolic compounds which exhibit minor reactivity or no reactivity at all (e.g. hydroxycinnamates, flavonols, benzenediols). Based on this property, the experimental conditions were optimized in order to enable the determination of total trihydroxybenzoates in complex mixtures without resorting to separation techniques. The method was applied to samples of different composition (teas, herbal infusions and wines) with satisfactory analytical features yielding detection limits at the 10(-7) mol L(-1) level, intra-day precision of 3.1%, inter-day precision less than 10% and recoveries between 88.7 and 97.6%. The strengths and weaknesses of the method were identified and discussed in relation to its application in real samples.

Dispersive micro-solid phase extraction of ortho-phosphate ions onto magnetite nanoparticles and determination as its molybdenum blue complex.

A direct microextraction method, employing dispersive micro-solid phase extraction (µ-SPE) of ortho-phosphate (o-PO(4)(3-)) anions onto ferromagnetic nanoparticles (MNPs) is described in this work for the first time. The method exploits the complexation of phosphate ions on the surface of positively charged magnetite nanoparticles through the formation of an inner sphere complex, which are separated from the bulk aqueous phase with the application of an adscititious magnetic field. Phosphates are eluted with sodium bicarbonate and determined spectrophotometrically as their phosphomolybdenum blue complex. The method is generally free from common interferences, likely to affect the measurement of phosphate, since it alleviates their presence already from the extraction step, thus they are absent during detection. The detection limits are as low as 0.01 µM with very satisfactory precision ranging from 3.68% (intra-day) to 8.5% (inter-day) and accuracy between 91.5% and 104.8%.

Multivariate chemometric discrimination of cigarette tobacco blends based on the UV-Vis spectrum of their hydrophilic extracts.

The application of UV-Vis spectrophotometry as an alternative or complementary approach to the classification of tobacco products is presented in this work for the first time. Two hundred fifty samples from five different cigarette brands composed of single and mixed tobacco blends were examined for that purpose on the basis of the UV-Vis spectrum of their aqueous extracts. Data transformation based on the normalization of absorbance intensities as a function of sample weight was employed in order to account for differences in the relative intensities of each sample. Principal components analysis (PCA) was used to extract outlier cases and sample classification was then pursued with the aid of discriminant analysis (DA) suggesting that a reduced number of variables (thirteen out of seven hundred initially available) could provide perfect classification (100% correct assignations) of samples containing single tobacco species or different blends and a fair classification of samples with similar composition (80% correct assignations) yielding an overall 95.7% correct classification. To this pursue, classification and regression trees were found to afford perfect classification of all samples using only a few logic rules based on appropriate split conditions at the expense of inserting 15 variables in the model.

Synthetic membranes (vesicles) in inorganic ion analysis: a review.

Vesicles are structures of amphiphile molecules occurring through a self-aggregation process at the molecular or nano scale level with a large structural variety and diverse properties providing a reaction environment for chemical reactions that resembles that of natural systems. Their high versatility and recognized utility in various applications have triggered a interdisciplinary scientific endeavor over their formation, characterization and potential applications with impressive results. However, in the vastness of applications surrounding vesicular structures, their utility in analytical chemistry has only received minor attention. Notwithstanding, studies demonstrating their potential as colorimetric or fluorescence sensors, extraction solvents of inorganic ions or their chelates and stationary phase modifiers in liquid chromatography have appeared. To this end, this article aims to present for the first time the analytical chemistry aspects behind the use of vesicle media with special emphasis on the detection and determination of inorganic ions and encourage further research on this promising field of analytical science.

Monitoring and classification of wastewater quality using supervised pattern recognition techniques and deterministic resolution of molecular absorption spectra based on multiwavelength UV spectra deconvolution.

A field flow approach for the in situ monitoring of wastewater quality is developed and assessed in this work, based on a combination of methods employing deconvolution of molecular absorption spectra and in situ/on-line analysis of wastewater effluent of various origin. The approach involves in situ immersion probes to monitor basic physicochemical parameters followed by UV spectrum deconvolution in order to provide a rapid estimate of organic matter, suspended solids and nitrate and on-line analysis of phosphates in a fully automated setup. The collected data are then treated with a series of supervised pattern recognition techniques in order to classify wastewater effluent according to their origin in three major categories namely municipal, industrial and hospital. The results suggest that the method affords a good approximation of realistic concentrations, as determined by reference methods, while it affords a good classification among various wastewater effluents of different origin. In that manner, the method enables a rapid inference of treated wastewater quality and a robust assessment of treatment process state, especially with regards to violations of effluent quality parameters.

Alkaline earth metal effect on the size and color transition of citrate-capped gold nanoparticles and analytical implications in periodate-luminol chemiluminescence.

Citrate-modified gold nanoparticles were found to undergo size and color transition upon interaction with alkaline earth metals. At low concentrations, metal ions coordinate with AuNPs via citrate boding inducing aggregation which results in size increase as evidenced by the decrease in their plasmon bandwidth. As the concentration increases further, color transition from red to blue is observed which is no longer attributed to aggregation but to specific ion adsorption phenomena. The response of gold nanoparticles to these changes linearly depends on cation concentration in both the UV and Vis regions, a feature that was exploited for the assessment of alkaline earth metal concentrations in water samples. Based on these findings, the modification of the surface properties of metal-coated AuNPs were investigated with regard to their potential influence on the catalytic oxidation of luminol by periodate. Interestingly, a significant amplification of the CL emission signal was recorded when metal ions were associated with AuNPs, even for chemiluminescence "inert" cations like calcium and magnesium. The analytical implications of these findings for the improvement of CL sensitivity and its potential analytical applications are also discussed.