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Food safety control is a key issue in the food and agriculture industries. For such purposes, developing miniaturized analytical methods is critical for enabling the rapid and sensitive detection of food supplements, allergens, and pollutants. Here, a novel bioanalytical methodology based on DNA-functionalized gold nanoparticles (AuNPs) and colorimetric detection was developed to detect the presence of sesame (a major allergen) through sesame seed DNA as a target, in food samples. The presence of sesame DNA induces controlled nanoparticle aggregation/desegregation, resulting in a color change (from blue to red) proportional to sesame DNA concentration. The incorporation of multicomponent nucleic acid enzymes (MNAzymes) in this strategy has been carried out to perform an isothermal signal amplification strategy to improve the sensitivity of detection. Also, open-source software for color analysis was used to ensure an unbiased visual color-change detection, enhancing detection accuracy and sensitivity and opening the possibility of performing a simple and decentralized analyte detection. The method successfully detected the presence of sesame DNA in sesame seed, sesame oil, olive oil, and sunflower oil. In brief, the developed approach constitutes a simple and affordable alternative to perform a highly sensitive detection of DNA in food without complex methodologies or the requirement of expensive instrumentation.

One of the current challenges in medicine is to achieve a rapid and unequivocal detection and quantification of extremely low levels of disease biomarkers in complex biological samples. Here, we present the development and analytical evaluation of a low-cost smartphone-based system designed for ultrasensitive detection of the prostate-specific antigen (PSA) using two detection alternatives: electrochemical or optical, by coupling the smartphone with a portable potentiostat or magnifying lenses. An antibody tagged with gold nanoparticles (AuNPs), and indium tin oxide coated polyethylene terephthalate platform (ITO-PET) have been used to develop a sandwich-type immunoassay. Then, a controlled silver electrodeposition on the AuNPs surface is carried out, enhancing their size greatly. Due to such strong nanoparticle-size amplification (from nm to μm), the final detection can be dual, by measuring current intensity or the number of silver-enlarged microstructures generated. The proposed strategies exhibited limit detections (LOD) of 102 and 37 fg/mL for electrochemical and optical detection respectively. The developed immunosensor reaches excellent selectivity and performance characteristics to quantify biomarkers at clinically relevant values without any pretreatment. These proposed procedures could be useful to check and verify possible recurrence after clinical treatment of tumors or even report levels of disease serum biomarkers in early stages., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Guillermo Redondo-Fernández reports financial support was provided by Spanish Ministry of Science and Innovation. Guillermo Redondo-Fernández reports financial support was provided by Principado de Asturias GRUPIN, co-financed by the Feder Programme of the European Union. Guillermo Redondo-Fernández reports financial support was provided by University of Oviedo., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The almost-two-centuries history of spectrochemical analysis has generated a body of literature so vast that it has become nearly intractable for experts, much less for those wishing to enter the field. Authoritative, focused reviews help to address this problem but become so granular that the overall directions of the field are lost. This broader perspective can be provided partially by general overviews but then the thinking, experimental details, theoretical underpinnings and instrumental innovations of the original work must be sacrificed. In the present compilation, this dilemma is overcome by assembling the most impactful publications in the area of analytical atomic spectrometry. Each entry was proposed by at least one current expert in the field and supported by a narrative that justifies its inclusion. The entries were then assembled into a coherent sequence and returned to contributors for a round-robin review.

One of the most consumed foods is milk and milk products, and guaranteeing the suitability of these products is one of the major concerns in our society. This has led to the development of numerous sensors to enhance quality controls in the food chain. However, this is not a simple task, because it is necessary to establish the parameters to be analyzed and often, not only one compound is responsible for food contamination or degradation. To attempt to address this problem, a multiplex analysis together with a non-directed (e.g., general parameters such as pH) analysis are the most relevant alternatives to identifying the safety of dairy food. In recent years, the use of new technologies in the development of devices/platforms with optical or electrochemical signals has accelerated and intensified the pursuit of systems that provide a simple, rapid, cost-effective, and/or multiparametric response to the presence of contaminants, markers of various diseases, and/or indicators of safety levels. However, achieving the simultaneous determination of two or more analytes in situ, in a single measurement, and in real time, using only one working 'real sensor', remains one of the most daunting challenges, primarily due to the complexity of the sample matrix. To address these requirements, different approaches have been explored. The state of the art on food safety sensors will be summarized in this review including optical, electrochemical, and other sensor-based detection methods such as magnetoelastic or mass-based sensors.

Nanosized UiO66 are among the most studied MOF materials. They have been extensively applied in various areas, such as catalysis, gas absorption, electrochemistry, chemical sensing, and biomedical applications. However, the preparation of stable nano-sized UiO66 for drug delivery applications is challenging because of the high tendency of UiO66 to aggregate during storage. To address this issue, we coated UiO66 with oligomers made of crosslinked cyclodextrins. The coated UiO66 exhibited a good stability upon storage for more than three weeks, even for low quantities of coating materials. The resulting core-shell UiO66 were characterized using a set of complementary methods including microscopies, spectroscopies, X-ray diffraction, and thermogravimetric investigations. Size distribution was assessed by orthogonal methods. Cisplatin was loaded in the core-shell nanoparticles, followed by an in-depth analysis by asymmetric flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS). This method combines the extremely high elemental selectivity and ultratrace detection limits of mass spectrometry with the capacity of AF4 to differentiate the diverse populations present in the sample. Free cisplatin and UiO66-associated cisplatin could be well separated by AF4. AF4-ICP-MS/MS analysis provided the exact drug loading, without the need of separating the nanoparticles from their suspension media. These data suggest the potential of AF4-ICP-MS/MS in the optimization of drug delivery systems., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A major challenge in the 21st century is the development of point-of-care diagnostic tools capable to detect and quantify disease biomarkers in a straightforward, affordable, sensitive, and specific manner. The remarkable plasmonic properties of gold nanoparticles (AuNPs) have promoted their use for development of simple methodologies for nucleic acid detection in combination with a variety of oligonucleotides amplification techniques. Here, assemblies of AuNPs with Multicomponent Nucleic Acid enzymes (MNAzymes) has been successfully used in the design of a highly sensitive and simple bioassay for rapid spectroscopic detection and quantification of miRNA-4739 in blood samples. The miRNA selected is a doxorubicin chemoresistant biomarker in breast cancer which overexpression promotes the proliferation, progression, and survival of cancer cells. In this work, two alternatives experimental designs, based on use of MNAzymes and AuNPs, have been optimized and applied for sensitive miRNA-4739 quantification: one based on a traditional direct measurement of wavelength shift and a second non-conventional simple approach based on isolation and measurement of free nanoparticles absorbance. Improvement in sensitivity and, higher measurement accuracy and precision were achieved with the second approach. The developed bioassay provides a detection limit as low as 7 pmolL -1 for miRNA-4739 quantification and performed satisfactory selectivity and well practical applicability by analysis of the miRNA-4739 in blood, demonstrating that the proposed strategy is a promising and suitable spectroscopic method for breast cancer diagnosis thought liquid biopsy of circulating tumoral cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

MicroRNAs (miRNAs) represent a class of small noncoding RNAs that are considered a novel emerging class of disease biomarkers in a variety of afflictions. Sensitive detection of miRNA is typically achieved using hybridization-based methods coupled with genetic amplification techniques. Although their sensitivity has improved, amplification techniques often present erroneous results due to their complexity. In addition, the use of these techniques is usually linked to the application of protein enzymes, the activity of which is dependent on the temperature and pH of the medium. To address these drawbacks, an alternative genetic enzyme for the highly sensitive detection of miRNAs is proposed in this work. Multicomponent nucleic acid enzymes (MNAzymes), coupled with the use of DNA-functionalized gold nanoparticles (AuNPs), were used in this study to develop an isothermal signal amplification strategy for visual genetic detection. miR146a, a biomarker of bovine mastitis present in milk, was selected as a model analyte. The developed methodology is easily carried out in 80 min at 50 °C, generating a low visual limit of detection of 250 pM based on the observation of a color change. The methodology was successfully applied to the detection of miR146a in raw cow milk samples., (© 2023. The Author(s).)

Herein, we introduce the first relative single-particle inductively coupled plasma mass spectrometry (spICP-MS) approach where size calibration is carried out using the target NP itself measured under different instrumental conditions without external dependence on the complex and prone-to-error determination of transport efficiency or mass flux calibrations, in contrast to most spICP-MS approaches. The simple approach proposed allows determining gold nanoparticle (AuNP) sizes, with errors ranging from 0.3 to 3.1% (corroborated by HR-TEM). It has been demonstrated that the changes observed in the single-particle histograms obtained for a suspension of AuNPs under different sensitivity conditions ( n = 5) are directly and exclusively related to the mass (size) of the target AuNP itself. Interestingly, the relative nature of the approach shows that once the ICP-MS system has been calibrated with a generic NP standard, it is no longer necessary to repeat the calibration for the size determination of different unimetallic NPs carried out along time (at least 8 months), independently of their size (16-73 nm) and even nature (AuNP or AgNP). Additionally, neither the NP surface functionalization with biomolecules nor protein corona formation led to significant changes (relative errors slightly increased 1.3- to 1.5-fold, up to 7%) in the NP size determination, in contrast to conventional spICP-MS approaches where relative errors increased 2- to 8-fold, up to 32%. This feature could be especially valuable for the analysis of NPs in real samples without the need of matrix-matched calibration.

In-depth characterization of functionalized nanomaterials is still a remaining challenge in nanobioanalytical chemistry. In this work, we propose the online coupling of Asymmetric Flow Field-Flow Fractionation (AF4) with UV/Vis, Multiangle Light Scattering (MALS) and Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) detectors to carry out, in less than 10 min and directly in the functionalization reaction mixture, the complete characterization of gold nanoparticles (AuNPs) functionalized with oligonucleotides and surface-modified with polyethylene glycol (PEG). AF4 separation provided full separation of the bioconjugates from the original AuNPs while P/Au and S/Au ICP-MS/MS ratios in the bioconjugate fractographic peaks could be used to compute the corresponding stoichiometries, oligonucleotide/AuNP and PEG/AuNPs. MALS detection clearly showed the coexistence of two distinct nanoparticulated populations in the bioconjugation mixture, which were demonstrated to be different not only in size but in functionality as well. The major bioconjugate population showed lower hydrodynamic ratios (18 nm) with higher and steadier oligonucleotides/AuNPs (92) and PEG/AuNPs (2350) stoichiometries, in comparison to the minor abundant population (54 nm, 51 and 1877, respectively). Moreover, the ratio between the absorbance signals measured at 520 nm and 650 nm reflects a lower AuNP aggregation in the major (10.5) than in the minor (4.5) population. Results obtained prove the benefits of a detailed characterization to find out if subsequent purification of functionalized AuNP-oligonucleotides is required to design more efficiently their final bioanalytical application., Competing Interests: Declaration of competing interest The authors declare no financial interests/personal relationships which may be considered as potential competing interests., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) frequently coexist in soils near industrial areas and sometimes in environmental compartments directly linked to feed (forage) and food (milk) production. However, the distribution of these pollutants along the dairy farm production chain is unclear. Here, we analyzed soil, forage, and milk samples from 16 livestock farms in Spain: several PTEs and PAHs were quantified. Farms were compared in terms of whether they were close to (<5 km) or far away from (>5 km) industrial areas. The results showed that PTEs and PAHs were enriched in the soils and forages from farms close to industrial areas, but not in the milk. In the soil, the maximum concentrations of PTEs reached 141, 46.1, 3.67, 6.11, and 138 mg kg -1 for chromium, arsenic, cadmium, mercury, and lead, respectively, while fluoranthene (172.8 µg kg -1 ) and benzo(b)fluoranthene (177.4 µg kg -1 ) were the most abundant PAHs. Principal component analysis of the soil PTEs suggested common pollution sources for iron, arsenic, and lead. In the forage, the maximum contents of chromium, arsenic, cadmium, mercury, and lead were 32.8, 7.87, 1.31, 0.47, and 7.85 mg kg -1 , respectively. The PAH found in the highest concentration in the feed forage was pyrene (120 µg kg -1 ). In the milk, the maximum PTE levels were much lower than in the soil or the feed forages: 74.1, 16.1, 0.12, 0.28, and 2.7 µg kg -1 for chromium, arsenic, cadmium, mercury, and lead, respectively. Neither of the two milk samples exceeded the 20 µg kg -1 limit for lead set in EU 1881/2006. Pyrene was the most abundant PAH found in the milk (39.4 µg kg -1 ), while high molecular weight PAHs were not detected. For PTEs, the results showed that soil-forage transfer factors were higher than forage-milk ratios. Our results suggest that soils and forages around farms near industries, as well as the milk produced from those farms, have generally low levels of PTE and PAH contaminants.

The prolific applicability of nanomaterials has made them a common citizen in biological systems, where they interact with proteins forming a biological corona complex. These complexes drive the interaction of nanomaterials with and within the cells, bringing forward numerous potential applications in nanobiomedicine, but also arising toxicological issues and concerns. Proper characterization of the protein corona complex is a great challenge typically handled with the combination of several techniques. Surprisingly, despite inductively coupled plasma mass spectrometry (ICP-MS) being a powerful quantitative technique whose application in nanomaterials characterization and quantification has been consolidated in the last decade, its application to nanoparticle-protein corona studies is scarce. Furthermore, in the last decades, ICP-MS has experienced a turning point in its capabilities for protein quantification through sulfur detection, hence becoming a generic quantitative detector. In this regard, we would like to introduce the potential of ICP-MS in the nanoparticle protein corona complex characterization and quantification complementary to current methods and protocols.

Adulterations of olive oil are performed by adding seed oils to this high-quality product, which are cheaper than olive oils. Food safety controls have been established by the European Union to avoid these episodes. Most of these methodologies require expensive equipment, time-consuming procedures, and expert personnel to execute. Near-infrared spectroscopy (NIRS) technology has many applications in the food processing industry. It analyzes food safety and quality parameters along the food chain. Using principal component analysis (PCA), the differences and similarities between olive oil and seed oils (sesame, sunflower, and flax oil) have been evaluated. To quantify the percentage of adulterated seed oil in olive oils, partial least squares (PLS) have been employed. A total of 96 samples of olive oil adulterated with seed oils were prepared. These samples were used to build a spectra library covering various mixtures containing seed oils and olive oil contents. Eighteen chemometric models were developed by combining the first and second derivatives with Standard Normal Variable (SNV) for scatter correction to classify and quantify seed oil adulteration and percentage. The results obtained for all seed oils show excellent coefficients of determination for calibration higher than 0.80. Because the instrumental aspects are not generally sufficiently addressed in the articles, we include a specific section on some key aspects of developing a high-performance and cost-effective NIR spectroscopy solution for fraud detection in olive oil. First, spectroscopy architectures are introduced, especially the Texas Instruments Digital Light Processing (DLP) technology for spectroscopy that has been used in this work. These results demonstrate that the portable prototype can be used as an effective tool to detect food fraud in liquid samples.

Nucleic acid enzymes (NAzymes) are a class of nucleic acid molecules with catalytic activity, which can be modulated by the presence of different species such as metal ions, genetic biomarkers, small molecules or proteins, among others. NAzymes offer several important advantages for development of novel bioanalytical strategies, resulting from their functionality as specific recognition elements and as amplified analytical signal generators, making them ideal candidates for developing highly specific bioanalytical strategies for the detection of a wide variety of targets. When coupled with the exceptional features of inorganic nanoparticles (NPs), the sensitivity of the assays can be significantly improved, allowing the detection of targets using many different detection techniques including visual readout, spectrophotometry, fluorimetry, electrochemiluminescence, voltammetry, and single-particle inductively coupled plasma-mass spectrometry. Here we provide an overview of the fundamentals of novel strategies developed to achieve analytical signal amplification based on the use of NAzymes coupled with inorganic NPs. Some representative examples of such strategies for the highly sensitive detection of different targets will be presented, including metal ions, proteins, DNA- or RNA-based biomarkers, and small molecules or microorganisms. Furthermore, future prospective challenges will be discussed., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

Breast milk is an optimal food that covers all the nutritional needs of the newborn. It is a dynamic fluid whose composition varies with lactation period. The neonatal units of hospitals have human milk banks, a service that analyzes, stores, and distributes donated human milk. This milk is used to feed premature infants (born before 32 weeks of gestation or weighing less than 1500 g) whose mothers, for some reason, cannot feed them with their own milk. Here, we aimed to develop near-infrared spectroscopy (NIRS) measures for the analysis of breast milk. For this purpose, we used a portable NIRS instrument scanning in the range of 1396-2396 nm to collect the spectra of milk samples. Then, different chemometrics were calculated to develop 18 calibration models with and without using derivatives and the standard normal variate. Once the calibration models were developed, the best treatments were selected according to the correlation coefficients (r 2 ) and prediction errors (SECVs). The best results for the assayed macronutrients were obtained when no pre-treatment was applied to the NIR spectra of fat (r 2 = 0.841, SECV = 0.51), raw protein (r 2 = 0.512, SECV = 0.21), and carbohydrates (r 2 = 0.741, SECV = 1.35). SNV plus the first derivative was applied to obtain satisfactory results for energy (r 2 = 0.830, SECV = 9.60) quantification. The interpretation of the obtained results showed the richness of the NIRS spectra; moreover, the presence of specific bands for fat provided excellent statistics in quantitative models. These results demonstrated the ability of portable NIRS sensors in a methodology developed for the quality control of macronutrients in breast milk.

It is widely recognized that the toxicity of mercury (Hg) is attenuated by the simultaneous administration of selenium (Se) compounds in various organisms. In this study, we revealed the mechanisms underlying the antagonistic effect of sodium selenite (Na 2 SeO 3 ) on inorganic Hg (Hg 2+ ) toxicity in human hepatoma HepG2 cells. Observations by transmission electron microscopy indicated that HgSe (tiemannite) granules of up to 100 nm in diameter were accumulated in lysosomal-like structures in the cells. The HgSe granules were composed of a number of HgSe nanoparticles, each measuring less than 10 nm in diameter. No accumulation of HgSe nanoparticles in lysosomes was observed in the cells exposed to chemically synthesized HgSe nanoparticles. This suggests that intracellular HgSe nanoparticles were biologically generated from Na 2 SeO 3 and Hg 2+ ions transported into the cells and were not derived from HgSe nanoparticles formed in the extracellular fluid. Approximately 85% of biogenic HgSe remained in the cells at 72 h post culturing, indicating that biogenic HgSe was hardly excreted from the cells. Moreover, the cytotoxicity of Hg 2+ was ameliorated by the simultaneous exposure to Na 2 SeO 3 even before the formation of insoluble HgSe nanoparticles. Our data confirmed for the first time that HepG2 cells can circumvent the toxicity of Hg 2+ through the direct interaction of Hg 2+ with a reduced form of Se (selenide) to form HgSe nanoparticles via a Hg-Se soluble complex in the cells. Biogenic HgSe nanoparticles are considered the ultimate metabolite in the Hg detoxification process.

Mercury (Hg) is one of the most toxic environmental pollutants, and is biocondensed via the food chain. Selenium (Se) is an essential element that possesses an antagonistic property towards Hg in vivo. The antagonistic property is explained by the assumption that Hg and Se directly interact to form HgSe nanoparticles (HgSe NPs) in organs. It is presumed that the toxic effects of HgSe NPs are lower than that of ionic Hg; however, no precise evaluation has been conducted so far. In the present study, we evaluated the distribution of HgSe NPs ingested in Se-deficient rats. The recovery of serum selenoproteins from a deficient level was not observed in rats orally administered HgSe NPs. In addition, the excretion of Hg and Se via urine was not observed. Interestingly, the biosynthesis of selenoproteins and urinary selenometabolites would have required the production of selenide through the degradation of HgSe NPs. Therefore, it seems that selenide and Hg are not released from HgSe NPs in vivo. The administration of HgSe NPs did not increase Hg and Se concentrations in organs, and almost all HgSe NPs were recovered in feces, indicating no or low bioaccessibility of HgSe NPs even in Se-deficient rats. These results suggest that HgSe NPs are biologically inert and do not become a secondary environmental pollutant of Hg., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Inductively coupled plasma-mass spectrometry (ICP-MS) has been widely used in Life Sciences for the absolute quantification of biomolecules without specific standards, assuming the same response for generic compounds including complex biomolecules. However, contradictory results have been published on this regard. We present the first critical statistical comparison of the ICP-MS response factors obtained for 14 different relevant S-containing biomolecules (three peptides, four proteins, one amino acid, two cofactors, three polyethylene glycol (PEG) derivatives, and sulfate standard), covering a wide range of hydrophobicities and molecular sizes. Two regular flow nebulizers and a total consumption nebulizer (TCN) were tested. ICP-MS response factors were determined though calibration curves, and isotope dilution analysis was used to normalize the results. No statistical differences have been found for low-molecular-weight biocompounds, PEGs, and nonhydrophobic peptides using any of the nebulizers tested. Interestingly, while statistical differences were still found negligible (96-104%) for the proteins and hydrophobic peptide using the TCN, significantly lower response factors (87-40%) were obtained using regular flow nebulizers. Such differential behavior seems to be related mostly to hydrophobicity and partially to the molecular weight. Findings were validated using IDA in intact and digested bovine serum albumin solutions using the TCN (98 and 100%, respectively) and the concentric nebulizer (73 and 97%, respectively). Additionally, in the case of a phosphoprotein, results were corroborated using the P trace in parallel to the S trace used along the manuscript. This work seems to suggest that ICP-MS operated with regular nebulizers can offer absolute quantification using generic standards for most biomolecules except proteins and hydrophobic peptides.

A major challenge in the development of bioanalytical methods is to achieve a rapid and robust quantification of disease biomarkers present at very low concentration levels in complex biological samples. An immunoassay platform is presented herein for ultrasensitive and fast detection of the prostate-specific antigen (PSA), a well-recognized cancer biomarker. A sandwich type immunosensor has been developed employing a detection antibody labeled with inorganic nanoparticles acting as tags for further indirect quantification of the analyte. The required high sensitivity is then achieved through a controlled gold deposition on the nanoparticle surface, carried out after completing the recognition step of the immunoassay, thus effectively amplifying the size of the nanoparticles from nm to µm range. Due to such an amplification procedure, quantification of the biomolecule could be carried out directly on the immunoassay plates using confocal microscopy for measurement of the reflected light produced by gold-enlarged nanostructures. The high specificity of the immunoassay was demonstrated with the addition of a major abundant protein in serum (albumin) at much higher concentrations. An extremely low detection limit for PSA quantification (LOD of 1.1 fg·mL -1 PSA) has been achieved. Such excellent LOD is 2-3 orders of magnitude lower than the clinically relevant PSA levels present in biological samples (4-10 ng·mL -1 ) and even to monitor eventual recurrence after clinical treatment of a prostate tumor (0.1 ng·mL -1 ). In fact, the broad dynamic range obtained (4 orders of magnitude) would allow the PSA quantification of diverse samples at very different relevant levels.

Background Differentiation between hemorrhagic and ischemic stroke is currently made by brain imaging or analyzing blood and cerebrospinal fluid (CSF) samples. After describing a new drainage route from brain to nasal mucosa, nasal exudate samples can be considered a new and promising source of biomarkers. Saliva can also be evaluated. Methods We determined iron in nasal exudate and saliva samples from patients of acute stroke during the first 48 h from onset. A simple, non-invasive sampling procedure was employed to obtain information from the brain. Samples were taken with a pre-weighed swab, solved in a 2% nitric acid solution and iron was measured by inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). Results A significant difference in the dispersion of results of iron concentration for both stroke subtypes was observed in nasal exudate samples. The interquartile range was 0.608 nmol mg-1 of iron for hemorrhagic strokes and only 0.044 nmol mg-1 for ischemic strokes. In saliva samples, however, the values were 0.236 vs. 0.157 nmol mg-1. A cut-off limit of 0.102 nmol of iron per mg of nasal exudate provides a methodology with a 90% of sensitivity and a 90% of specificity. The value of the area under (AUC) the receiver operating characteristic curve (ROC) for nasal exudate samples is 0.960, considered as very good in which regards to its predictive value. Conclusions Non-invasive samples of nasal secretion have allowed obtaining, for the first time, information from the brain. Determination of iron in nasal exudate by ICP-MS allowed differentiation between ischemic and hemorrhagic strokes.

Gold nanoparticles of different sizes have been synthesized and surface-functionalized with selected RNA probes in order to develop a rapid, low-cost and sensitive method for detection of microRNA146a (miR146a). The strategy is based on the change of colour that can be observed visually after aggregation of the RNA modified-gold nanoparticles (AuNPs) in presence of miR146a. Experimental conditions have been carefully selected in order to obtain a good sensitivity that allows to perform visual detection of microRNA at the nM level, achieving a detection limit of 5 nM. Good repeatability and selectivity versus other sequences that only differ from miR146a in 3 bases was achieved. miR146a has been described as one of the main microRNA involved in the immune response of bovine mastitis, being expressed in tissue, blood and milk samples. The method was successfully applied to the detection of miR146a in raw cow milk samples. The present scheme constitutes a rapid and low-cost alternative to perform highly sensitive detection of microRNA without the need of instrumentation and amplification steps for the early detection of bovine mastitis in the agrofood industry. Graphical abstract Schematic representation of the assay based on aggregation of RNA-modified gold nanoparticles (blue) in presence of microRNA146a generating a dark blue spot onto a solid support, versus a pink spot observed in absence of miR146a due to dispersed gold nanoparticles (red).

In this work, novel silver sulphide quantum dots (Ag 2 S QD) are electrochemically quantified for the first time. The method is based on the electrochemical reduction of Ag + to Ag 0 at -0.3 V on screen-printed carbon electrodes (SPCEs), followed by anodic stripping voltammetric oxidation that gives a peak of currents at +0.06 V which represents the analytical signal. The optimized methodology allows the quantification of water-stabilized Ag 2 S QD in the range of approximately 2 × 10 9 -2 × 10 12 QD·mL -1 with a good reproducibility (RSD: 5%). Moreover, as proof-of-concept of relevant biosensing application, Ag 2 S QD are evaluated as tags for Escherichia coli (E. coli) bacteria determination. Bacteria tagged with QD are separated by centrifugation from the sample solution and placed on the SPCE surface for quantitative analysis. The effect of two different Ag 2 S QD surface coating/stabilizing agents on both the voltammetric response and the bacteria sensing is also evaluated. 3-mercaptopropionic acid (3-MPA) is studied as model of short length coating ligand with no affinity for the bacteria, while boronic acid (BA) is evaluated as longer length ligand with chemical affinity for the polysaccharides present in the peptidoglycan layer on the bacteria cells surface. The biosensing system allows to detect bacteria in the range 10 -1 -10 3 bacteria·mL -1 with a limit of detection as low as 1 bacteria·mL -1 . This methodology is a promising proof-of-concept alternative to traditional laboratory-based tests, with good sensitivity and short time and low cost of analysis. Graphical abstractNovel silver sulphide quantum dots (Ag 2 S QD) are electrochemically quantified for the first time. Moreover, Ag 2 S QD are evaluated as tags for Escherichia coli bacteria determination. The effect of two different QD surface coating ligands is also evaluated.

The asymmetric flow field-flow fractionation (AF4) coupled on-line with elemental (inductively coupled plasma-mass spectrometry, ICP-MS) and molecular (fluorescence and UV) detection has been investigated as a powerful tool for the characterization of bioinorganic nano-conjugates. In this study, we described methods for the characterization of biotin-antibody complexes bioconjugated with streptavidin quantum dots (QDs-SA-b-Ab). Operating parameters of AF4 separation technique were optimized and two procedures are proposed using a channel thickness of 350 μm and 500 μm. The use of a 500 μm spacer allowed to achieve an efficient AF4 separation of the QDs-SA-b-Ab complexes from the excess of individual species used in the bioconjugation that was required for a proper characterization of the bioconjugates. Optimization of the AF4 allowed a separation resolution good enough to isolate the QDs-SA-b-Ab bioconjugates from the free excess of b-Ab and QD-SA. The efficiency of the bioconjugation process could be then calculated, obtaining a value of 86% for a 1 QDs-SA: 5 b-Ab bioconjugation ratio. In addition, sample recovery around 90% was achieved., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Introduction: Differential diagnosis between ischemic and hemorrhagic strokes in the acute stage is one of the major challenges of neurovascular research. Several biomarkers have been studied, but attempts to date have focused on determining their blood levels. Recently, cerebral lymphatic drainage toward the nostrils has been discovered, giving us the chance to study nasal exudate looking for biomarkers of neural damage. We sought to confirm whether iron levels in nasal exudate could identify the hemorrhagic nature of acute stroke., Methods: We studied iron nasal exudate levels in 32 ischemic and 43 hemorrhagic stroke patients. All patients underwent neurological examination assessed by the National Institutes of Health Stroke Scale (NIHSS), brain computed tomography to the differential diagnosis of stroke subtype, laboratory tests, and measurement of iron levels in nasal exudate., Results: The iron levels in nasal exudate were higher in hemorrhagic stroke patients. The area under the receiver operating characteristic curve for ischemic/hemorrhagic stroke discrimination was 0.896 (95% confidence interval 0.823-0.970) and cutoff point of 0.078 nmol/mg (sensitivity 93%, specificity 73%)., Conclusions: Our findings suggest that iron levels in nasal exudate may be useful in the acute stage for the differential diagnosis between ischemic and hemorrhagic damage in acute stroke patients. They also open a potential field to study other biomarkers in nasal exudate in several neurological disorders. Clinical studies must be performed to confirm our results., (© 2020 S. Karger AG, Basel.)

The sensitive monitoring of mercury (II) selenide nanoparticles (HgSe NPs) is of great potential relevance in environmental studies, since such NPs are believed to be the ultimate metabolic product of the lifesaving mechanism pathway of Hg detoxification in biological systems. In this context, we take advantage of using gold-nanostructured screen-printed carbon electrodes (SPCE-Au) for the rapid, simple and sensitive electrochemical quantification of engineered water-stable HgSe NPs, as an advantageous alternative to conventional elemental analysis techniques. HgSe NPs are first treated in an optimized oxidative/acidic medium for Hg 2+ release, followed by sensitive electrochemical detection by anodic stripping voltammetry (ASV). To the best of our knowledge, this is the first time that water-stable HgSe NPs are quantified using electrochemical techniques. The low limit of detection achieved (3.86 × 10 7 HgSe NPs/mL) together with the excellent repeatability (RSD: 3%), reproducibility (RSD: 5%) and trueness (relative error: 10%), the good performance in real sea water samples (recoveries of the analytical signal higher than 90%) and the simplicity/low cost of analysis make our method an ideal candidate for HgSe NPs monitoring in future environmental studies., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A current remaining challenge in nanotechnology is the fast and reliable determination of the ratios between engineered nanoparticles and the species attached to their surface after chemical functionalization. The approach proposed herein based on the online coupling of asymmetric flow field-flow fractionation (AF4) with inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) allows for the first time the direct determination of such ratios in CdSe/ZnS core-shell quantum dot:rat monoclonal IgG2a antibody (QD:Ab) conjugate mixtures in a single run without any previous sample preparation (i.e., derivatization). AF4 provides full recovery and adequate resolution of the resulting bioconjugate from the excess of nanoparticles and proteins used in the different bioconjugation mixtures (1:1, 2:1, and 3:1 QD:Ab molar ratios were assessed). The point-by-point determination by ICP-MS/MS of the metal to sulfur ratios along the bioconjugate fractographic peak allowed disclosing the mixture of the different species in the bioconjugated sample, providing not only the limits of the range of QD:Ab ratios in the different bioconjugate species resulting after functionalization but also a good estimation of their individual relative abundance in the mixture. Interestingly, a wide variety of compositions were observed for the different bioconjugate mixtures studied (QD:Ab molar ratios ranging from 0.27 to 4.6). The resulting weighted QD:Ab ratio computed in this way for each bioconjugate peak matches well with both the global (average) QD:Ab ratio experimentally obtained by the simpler peak area ratio computation and the theoretical QD:Ab molar ratios assayed, which internally validates the procedure developed.

Near infrared (NIR) emitting Ag 2 S quantum dots have been synthesized, characterized and evaluated for chemical sensing applications. After their optical characterization, it was observed that the Ag 2 S quantum dots present both, excitation and emission in the NIR region, and an excellent quantum yield of 33.2%. These features are of great value for many biological applications, since autofluorescence of biological tissues or cells is minimized, and also for environmental applications, where other fluorescent concomitant species with excitation and emission in the ultraviolet-visible region might be present. Different purification procedures were evaluated in order to obtain a stable and homogeneous population of nanoparticles, which is necessary to perform quantitative analysis (e.g.: mass spectrometry-based applications), as well as to obtain a narrow NIR emission spectrum for optical applications. Comprehensive characterization using X-ray diffraction, transmission electron microscopy, and asymmetric flow field flow fractionation coupled to inductively coupled plasma-mass spectrometry has been performed to obtain parameters not easily achieved and of great interest in different research areas, such as the nanoparticle concentration NIR-emitting nanoparticles, and the surface ligand density, which directly affects to the interactions of the nanoparticles with their close environment, including unspecific adsorptions, cellular uptake, macrophage interaction, etc. Finally, the capability for sensing analytes of environmental interest based on direct-interactions of a reactive compound with the surface of the nanoparticle has been also evaluated. Quenching of the NIR emission upon interaction of the Ag 2 S quantum dots with cyanide ions was observed. Hence, a rapid, selective and highly sensitive methodology was developed for the detection of cyanide in natural waters., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Inorganic nanoparticles are a fascinating class of materials which promise great potential in numerous fields, including optical (bio)sensing. Many different kinds of such nanoparticles have been widely used for fluorescent sensing and imaging due to the different merits of fluorescent nanoparticles compared to molecular fluorophores. Progress made in the rational design of nanomaterials also allowed the synthesis of hybrid phosphorescent nanoparticles, that finds growing applications in sensing due to the combination of the interesting size- and shape-dependent properties of nanomaterials with a phosphorescence-type emission. In this review, we intend to highlight some of progress made in this active research area and update the database of various phosphorescent nanoparticles-based sensors on the basis of different sensing targets of interest in environmental, industrial and biomedical areas. Following an introduction and a discussion of merits of the synergy between nanomaterials and phosphorescence detection as compared to molecular luminophores the article assesses the kinds and specific features of nanomaterials often used in phosphorescence sensing. Specific examples on the use of phosphorescence nanoparticles in chemical sensing and bioimaging are given next. A final section intends to provide an overview of the prospects of such type of nanomaterials in the design of future devices for analytical chemistry., (Copyright © 2018. Published by Elsevier B.V.)

The use of functionalized magnetic particles is increasing because they simplify the analytical process and yield promising results in a wide range of applications. Particularly, streptavidin-coated magnetic beads offer the possibility of rapid and very efficient grafting of biomolecules. Unfortunately, current methods to monitor and compute this grafting process are cumbersome and scarce. We describe herein a simple, rapid, and reliable chemiluminescent assay we have developed to check the grafting rate of functionalized magnetic beads. The power of the assay also relies on its ability to predict the amount of ligands required to obtain a precise grafting rate. In addition, results were correlated with a more general parameter in material functionalization characterization like surface ligand density. Finally, the assay was validated for a wide variety of biotinylated biomolecule sizes, ranging from small molecules (around 200 Da) to antibodies (around 150 kDa). This approach will allow a precise quantification and prediction of the functionalization of magnetic particles that is of enormous importance for quality control in many applications.

Carbon dots have demonstrated great potential as luminescent nanoparticles in bioapplications. Although such nanoparticles appear to exhibit low toxicity compared to other metal luminescent nanomaterials, today we know that the toxicity of carbon dots (C-dots) strongly depends on the protocol of fabrication. In this work, aqueous fluorescent C-dots have been synthesized from cinnamon, red chilli, turmeric and black pepper, by a one-pot green hydrothermal method. The synthesized C-dots were firstly characterized by means of UV-vis, fluorescence, Fourier transform infrared and Raman spectroscopy, dynamic light scattering and transmission electron microscopy. The optical performance showed an outstanding ability for imaging purposes, with quantum yields up to 43.6%. Thus, the cytotoxicity of the above mentioned spice-derived C-dots was evaluated in vitro in human glioblastoma cells (LN-229 cancer cell line) and in human kidney cells (HK-2 non-cancerous cell line). Bioimaging and viability studies were performed with different C-dot concentrations from 0.1 to 2 mg·mL -1 , exhibiting a higher uptake of C-dots in the cancer cultures compared to the non-cancerous cells. Results showed that the spice-derived C-dots inhibited cell viability dose-dependently after a 24 h incubation period, displaying a higher toxicity in LN-229, than in HK-2 cells. As a control, C-dots synthesized from citric acid did not show any significant toxicity in either cancerous or non-cancerous cells, implying that the tumour cell growth inhibition properties observed in the spice-derived C-dots can be attributed to the starting material employed for their fabrication. These results evidence that functional groups in the surface of the C-dots might be responsible for the selective cytotoxicity, as suggested by the presence of piperine in the surface of black pepper C-dots analysed by ESI-QTOF-MS.

Coupling of asymmetric flow field-flow fractionation (AF4) to an on-line elemental detection (inductively coupled plasma-mass spectrometry, ICP-MS) has been recently proposed as a powerful diagnostic tool for characterization of the bioconjugation of CdSe/ZnS core-shell Quantum Dots (QDs) to antibodies. Such approach has been used herein to demonstrate that cap exchange of the native hydrophobic shell of core/shell QDs with the bidentate dihydrolipoic acid ligands directly removes completely the eventual side nanoparticulated populations generated during simple one-pot synthesis, which can ruin the subsequent final bioapplication. The critical assessment of the chemical and physical purity of the surface-modified QDs achieved allows to explain the transmission electron microscopy findings obtained for the different nanoparticle surface modification assayed., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Herein, high-quality Mn-doped ZnS quantum dots (QDs) have been synthesized using a facile approach directly in aqueous media. The surface of the obtained QDs was further modified by cap-exchange of the native cysteine shell with dihydrolipoic acid (DHLA) ligands resulting in nanocrystals with high water-stability having an intense phosphorescent signal. Covalent bioconjugation of the DHLA-coated nanoparticles with an anti-IgG antibody was then carried out. Interestingly the QD immunoprobe (QD-labelled antibodies) maintained an intense phosphorescence emission, without any significant spectral-shift (as compared to the free QDs). Coupling of an asymmetric flow field flow fractionation technique to an elemental mass spectrometry detection enabled the accurate determination of the efficiency of the bioconjugation reaction. The obtained nanoparticle-antibody bioconjugate was then applied to develop a quantitative sandwich-type phosphorescent immunoassay for Prostate Specific Antigen (PSA), and a limit of detection (LOD) of 17 pg mL -1 of PSA was achieved and allow to quantify such biomarker in samples within clinically relevant levels. Finally, the assay was validated for the quantification of PSA in the cellular media of prostate cancer cells. Obtained results proved the robustness of the proposed immunoassay based on long-lived phosphorescence measurements against eventual photoluminescent interferences significantly affecting the conventional short-lived fluorescence detection., (Copyright © 2017. Published by Elsevier B.V.)

Colloidal Mn 2+ -doped ZnS quantum dots (QDs) were synthesized, surface modified, and thoroughly characterized using a pool of complementary techniques. Cap exchange of the native l-cysteine coating of the QDs with dihydrolipoic acid (DHLA) ligands is proposed as a strategy to produce nanocrystals with a strong phosphorescent-type emission and improved aqueous stability. Moreover, such a stable DHLA coating can facilitate further bioconjugation of these QDs to biomolecules using established reagents such as cross-linker molecules. First, a structural and morphological characterization of the l-cysteine QD core was performed by resorting to complementary techniques, including X-ray powder diffraction (XRD) and microscopy tools. XRD patterns provided information about the local structure of ions within the nanocrystal structure and the number of metal atoms constituting the core of a QD. The judicious combination of the data obtained from these complementary characterization tools with the analysis of the QDs using inductively coupled plasma-mass spectrometry (ICP-MS) allowed us to assess the number concentration of nanoparticles in an aqueous sample, a key parameter when such materials are going to be used in bioanalytical or toxicological studies. Asymmetric flow field-flow fractionation (AF4) coupled online to ICP-MS detection proved to be an invaluable tool to compute the number of DHLA molecules attached to the surface of a single QD, a key feature that is difficult to estimate in nanoparticles and that critically affects the behavior of nanoparticles when entering the biological media (e.g., cellular uptake, biodistribution, or protein corona formation). This hybrid technique also allowed us to demonstrate that the elemental composition of the nanoparticle core remains unaffected after the ligand exchange process. Finally, the photostability and robustness of the DHLA-capped QDs, critical parameters for bioanalytical applications, were assessed by molecular luminescence spectroscopy.

Antimony is a metalloid that affects biological functions in humans due to a mechanism still not understood. There is no doubt that the toxicity and physicochemical properties of Sb are strongly related with its chemical state. In this paper, the interaction between Sb(III) and Sb(V) with bovine serum albumin (BSA) was investigated in vitro by fluorescence spectroscopy, and circular dichroism (CD) under simulated physiological conditions. Moreover, the coupling of the separation technique, asymmetric flow field-flow fractionation, with elemental mass spectrometry to understand the interaction of Sb(V) and Sb(III) with the BSA was also used. Our results showed a different behaviour of Sb(III) vs. Sb(V) regarding their effects on the interaction with the BSA. The effects in terms of protein aggregates and conformational changes were higher in the presence of Sb(III) compared to Sb(V) which may explain the differences in toxicity between both Sb species in vivo. Obtained results demonstrated the protective effect of GSH that modifies the degree of interaction between the Sb species with BSA. Interestingly, in our experiments it was possible to detect an interaction between BSA and Sb species, which may be related with the presence of labile complex between the Sb and a protein for the first time., Competing Interests: The authors have declared that no competing interests exist.

Absolute protein quantification methods based on molecular mass spectrometry usually require stable isotope-labeled analogous standards for each target protein or peptide under study, which in turn must be certified using natural standards. In this work, we report a direct and accurate methodology based on capLC-ICP-QQQ and online isotope dilution analysis for the absolute and sensitive quantification of intact proteins. The combination of the postcolumn addition of 34 S and a generic S-containing internal standard spiked to the sample provides full compound independent detector response and thus protein quantification without the need for specific standards. Quantitative recoveries, using a chromatographic core-shell C4 column for the various protein species assayed were obtained (96-100%). Thus, the proposed strategy enables the accurate quantification of proteins even if no specific standards are available for them. In addition, to the best of our knowledge, we obtained the lowest detection limits reported in the quantitative analysis of intact proteins by direct measurement of sulfur with ICPMS (358 fmol) and protein (ranging from 7 to 15 fmol depending on the assayed protein). The quantitative results for individual and simple mixtures of model proteins were statistically indistinguishable from the manufacturer's values. Finally, the suitability of the strategy for real sample analysis (including quantitative protein recovery from the column) was illustrated for the individual absolute quantification of the proteins and whole protein content in a venom sample. Parallel capLC-ESI-QTOF analysis was employed to identify the proteins, a prerequisite to translate the mass of quantified S for each chromatographic peak into individual protein mass.

Optical analysis based on fluorescence labeling has been extensively used for the selective tagging of a wide range of biomedical important targets or for sensing purposes. Fluorescent nanoparticles (NPs) offer interesting properties as labels, as they can be also used as active labels that change their properties upon changes in the environment, such as pH- or distance-dependent fluorescence. In case NPs are not intrinsically fluorescent, they can be made fluorescent by attaching fluorophores to their volume and/or surface. Dye-labelled NPs can produce a highly amplified optical signal compared to a single dye molecule, as there are many dye molecule attached to each NP, providing a great improvement in analytical sensitivity. However, an appropriate control to quantify the fluorophore/NP ratio is required to succeed in the preparation of quantitative platforms matching the required application. Here a methodology to determine such parameter, the fluorophore/NP ratio, is presented. The methodology combines data obtained from UV/Vis absorption spectroscopy for determination of the dye concentration and inductively coupled plasma-mass spectrometry (ICP-MS) analysis for determination of the NP concentration. To validate the approach, it has been applied to the analysis of different sets of fluorophore-NP conjugates prepared using diverse fluorescent dyes (i.e. fluorophores with different structures and emissions) and several types of NPs (i.e. PbS QDs, Au NPs and FePt NPs). The fluorophore-NP conjugates hereby were designed to incorporate the dye directly into an amphiphilic polymer coating. The developed methodology allows for quantification of fluorophore-NP coupling, and therefore, opens up the possibility of selecting controlled conjugates.

Hyphenation of asymmetric flow field-flow fractionation (AF4) to an on-line elemental detection (inductively coupled plasma-mass spectrometry, ICP-MS) is proposed as a powerful diagnostic tool for quantum dots bioconjugation studies. In particular, conjugation effectiveness between a "model" monoclonal IgG antibody (Ab) and CdSe/ZnS core-shell Quantum Dots (QDs), surface-coated with an amphiphilic polymer, has been monitored here by such hybrid AF4-ICP-MS technique. Experimental conditions have been optimized searching for a proper separation between the sought bioconjugates from the eventual free reagents excesses employed during the bioconjugation (QDs and antibodies). Composition and pH of the carrier have been found to be critical parameters to ensure an efficient separation while ensuring high species recovery from the AF4 channel. An ICP-MS equipped with a triple quadropole was selected as elemental detector to enable sensitive and reliable simultaneous quantification of the elemental constituents, including sulfur, of the nanoparticulated species and the antibody. The hyphenated technique used provided nanoparticle size-based separation, elemental detection, and composition analysis capabilities that turned out to be instrumental in order to investigate in depth the Ab-QDs bioconjugation process. Moreover, the analytical strategy here proposed allowed us not only to clearly identify the bioconjugation reaction products but also to quantify nanoparticle:antibodies bioconjugation efficiency. This is a key issue in future development of analytical and bioanalytical photoluminescent QDs applications., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A generic strategy based on the use of CdSe/ZnS Quantum Dots (QDs) as elemental labels for protein quantification, using immunoassays with elemental mass spectrometry (ICP-MS), detection is presented. In this strategy, streptavidin modified QDs (QDs-SA) are bioconjugated to a biotinylated secondary antibody (b-Ab2). After a multi-technique characterization of the synthesized generic platform (QDs-SA-b-Ab2) it was applied to the sequential quantification of five proteins (transferrin, complement C3, apolipoprotein A1, transthyretin and apolipoprotein A4) at different concentration levels in human serum samples. It is shown how this generic strategy does only require the appropriate unlabeled primary antibody for each protein to be detected. Therefore, it introduces a way out to the need for the cumbersome and specific bioconjugation of the QDs to the corresponding specific recognition antibody for every target analyte (protein). Results obtained were validated with those obtained using UV-vis spectrophotometry and commercial ELISA Kits. As expected, ICP-MS offered one order of magnitude lower DL (0.23 fmol absolute for transferrin) than the classical spectrophotometric detection (3.2 fmol absolute). ICP-MS precision and detection limits, however turned out to be compromised by procedural blanks. The full analytical performance of the ICP-MS-based immunoassay proposed was assessed for detection of transferrin (Tf), present at the low ng mL(-1) range in a complex "model" synthetic matrix, where the total protein concentration was 100 μg mL(-1). Finally, ICP-MS detection allowed the quantitative control of all the steps of the proposed immunoassay, by computing mass balances obtained, and the development of a faster indirect immunoassay format where the plate wells were directly coated with the whole protein mixture sample., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A one-step synthesis of near infrared fluorescent platinum nanoclusters (PtNCs) in aqueous medium is described. The proposed optimized procedure for PtNC synthesis is rather simple, fast and it is based on the direct metal reduction with NaBH4. Bidentated thiol ligands (lipoic acid) were selected as nanoclusters stabilizers in water media. The structural characterization revealed attractive features of the PtNCs, including small size, high water solubility, near-infrared luminescence centered at 680 nm, long-term stability and the highest quantum yield in water reported so far (47%) for PtNCs. Moreover, their stability in different pH media and an ionic strength of 0.2 M NaCl was studied and no significant changes in fluorescence emission were detected. In brief, they offer a new type of fluorescent noble metal nanoprobe with a great potential to be applied in several fields, including biolabeling and imaging experiments.

The performance of radiofrequency (rf) millisecond pulsed glow discharge (PGD) coupled to a fast orthogonal time-of-flight mass spectrometer (TOFMS) for chemical characterization and quantification of organic volatile compounds was investigated by using two different GD chamber designs. The designs investigated had substantial differences in the way that the volatile organic compound is introduced into the GD and the distance between the cathode and the sampling cone of the mass spectrometer. Bromochloromethane was selected as the model analyte because of the practical interest of determining trihalomethanes at low concentrations, and also because of both its low boiling point (to avoid problems associated with condensations in the interface) and the fact that it has two different heteroatoms, making the fragmentation patterns easier to follow. Pulse shapes of element, fragment, and molecular parent ions obtained by using the two GD chambers under investigation were critically compared. Results revealed the critical effect of the GD chamber geometry in obtaining the three types of chemical information, temporally discriminated. The spectra of the gaseous samples and of a polymer containing TBBPA (solid sample) were also compared. Detection limits for bromochloromethane in the order of low ng L(-1), and the required high tolerance of the plasmas to the introduction of organic vapours, were achieved using one of the proposed GD designs. The capability of the designed system for the analysis of other volatile compounds, for example dimethyl disulfide and dimethyl selenide, was also successfully evaluated, making use of the analytical potential of the information obtained from the different pulse time regions.

A reliable and robust direct screening methodology based on a quantum dot (QD) fluorescent immunoassay has been developed to detect trace levels of different antibiotic species from the family of the tetracyclines (e.g., oxytetracycline, tetracycline, chlortetracycline, and doxycycline) in contaminated bovine muscle tissues. First, the synthesis and characterization of a new immunoprobe (oxytetracycline-bovine serum albumin-QD) has been carried out for its further application in the development of a competitive fluorescent QD-immunoassay. The developed fluoroimmunoassay provides sensitive and binary "yes/no" responses being appropriate for the screening of this family of antibiotics above or below a preset concentration threshold. The detection limit achieved with this strategy, 1 μg/L in aqueous media and 10 μg/kg in bovine muscle samples, is 10-fold lower than the maximum level concentration allowed by International Legislation in muscle tissue, enabling suitable and efficient screening of the antibiotics.

A one-step aqueous synthesis of highly fluorescent water-soluble copper nanoclusters (CuNCs) is here described, based on direct reduction of the metal precursor with NaBH4 in the presence of bidentate ligands (made of lipoic acid anchoring groups, appended with a poly(ethylene glycol) short chain). A complete optical and structural characterization was carried out: the optical emission was centred at 416 nm, with a luminescence quantum yield in water of 3.6% (the highest one reported so far in water for this kind of nanocluster). The structural characterization reveals a homogeneous size distribution (of 2.5 nm diameter) with spherical shape. The CuNCs obtained offer long-term stability (the luminescence emission remained unaltered after more than two months) under a broad range of chemical conditions (e.g., stored at pH 3-12 or even in a high ionic strength medium such as 1 M NaCl) and high photostability, keeping their fluorescence emission intact after more than 2 h of daylight and UV-light exposition. All those advantageous features warrant synthesized CuNCs being promising fluorescent nanoprobes for further developments including (bio)applications.

A critical comparison between Elemental Mass Spectrometry (ICP-MS) and molecular fluorescence, as detection techniques for CdSe/ZnS Quantum Dots (QDs)-based immunoassays is presented here. Using a QDs-based progesterone immunoassay as "model" analytical system the features of both detection modes has been investigated. Minimal changes, compared to the previously developed fluorescent approach, were necessary to build the corresponding inhibition curve for the progesterone immunoassay using ICP-MS detection of cadmium (contained in the QDs core). Adequate agreement between results obtained using both elemental and molecular techniques for the determination of progesterone in cow milk has been obtained. Moreover, results from the comparison showed that fluorescence detection of the QDs is simpler, less time consuming and less expensive, but ICP-MS detection affords alternative and useful information unattainable using luminescence detection. First of all, ICP-MS allowed mass balances to be carried out (all along the sample preparation) providing an internal validation of the immunoassay procedure. Secondly, matrix-independent quantification as provided by ICP-MS enabled a direct determination of progesterone in raw milk without any further sample preparation (dilution) step. As a matter of fact, ICP-MS results showed that the quenching matrix effect suffered on bioconjugated QDs fluorescence emission (e.g. when the immunoassay was carried out directly in whole milk without any dilution) could be unequivocally attributed to nonspecific interactions between the matrix of the whole milk and the QDs surface. Finally, better sensitivity could be obtained with ICP-MS detection, IC(10)=0.028 ng/mL, versus 0.11 ng/mL using conventional fluorimetric detection, just by using lower reagents concentrations., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A new prototype based on a microsecond pulsed glow discharge ion source coupled to a time-of-flight mass spectrometer was recently designed, constructed and analytically evaluated in our laboratory for simultaneous collection of elemental and molecular information, and as a gas-chromatographic detector of compounds of environmental concern. To investigate further the analytical capabilities of such a new setup, its capability for the determination of element ratios in volatile organic halogenated compounds has been explored. Moreover, compound-independent calibration has been carried out with the prototype as well. The results demonstrated that the intensity ratios (analyte to internal standard) were linear with the corresponding ratio of concentrations. Both for chlorine and bromine (measured in the prepeak) and for BrC (measured in the plateau) the slope was 1 and the intercept was 0. Moreover, detection limits were improved by more than 1 order of magnitude as compared with using external calibration. The applicability of the proposed approach has been demonstrated for the straightforward determination of chloroform in drinking and river waters.

Photoinduced fluorescence enhancement of colloidal quantum dots (QDs) is a hot topic addressed in many studies due to its great influence on the bioanalytical performance of such nanoparticles. However, understanding of this process is not a simple task, and it cannot be explained by a general mechanism as it greatly depends on the QDs' nature, solubilization strategies, surrounding environment, etc. In this vein, we have critically compared the behavior of CdSe QDs (widely used in bioanalytical applications) with different surface modifications (ligand exchange and polymer coating), in different controlled experimental conditions, in the presence-absence of the ZnS layer and in different media when exposed for long times to intense UV irradiation. Thus six different types of colloidal QDs were finally studied. This research was carried out from a novel perspective, based on the analysis of the dynamic behavior of the photoactivation process (of great interest for further applications of QDs as labels in biomedical applications). The results showed a different behavior of the studied colloidal QDs after UV irradiation in terms of their photoluminescence characteristics, potential toxicity due to metal release to the environment, nanoparticle stability and surface coating degradation.

The use of semiconductor quantum dots (QDs) as fluorescent labels to develop a competitive immunoassay for sensitive detection and quantification of progesterone in cow's milk is described. Colloidal water-soluble CdSe/ZnS QDs are conjugated to an antigen derivative (progesterone-BSA conjugate) and a simple methodology is optimised to determine the antigen concentration in the final bioconjugate. The obtained QD-linked antigens were then employed together with unlabelled anti-progesterone monoclonal antibodies, as the biological recognition elements, in the development of the quantitative QDs-based fluorescent immunoassay for progesterone in bovine milk. After optimization, the developed immunoassay proved to cover a progesterone concentration range from 0.3 to 14.5 ng/mL in cow milk. Milk samples were just diluted 10-fold with deionised water and directly analysed with the proposed immunoassay, without additional sample pre-treatment or analyte extraction. The minimum detectable level (IC(10)) of the developed immunoassay turned out to be 0.1 ng/mL of progesterone in bovine milk. The sensitivity (IC(50)) achieved was 2.2 ng/mL with a reproducibility of 3.5% RSD as obtained from the results of the analysis of the triplicate of same samples but in three different days. Applicability of the proposed methodology was evaluated by analyzing cow's milk samples enriched with known concentrations of progesterone and recoveries better than 90% were achieved., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The synthesis and characterization of a novel water-compatible microsized material, based on fluorescent conjugated polymers (CPs), and its applicability for optical sensing of inorganic ions of environment interest (copper and cyanide) in water media is here described. Polyfluorene-based fluorescent CPs were synthesized and functionalized with imidazole moieties (selective recognition element) and a terminal double bond (covalently linked to an organic matrix) through a postfunctionalization strategy. Further, microspheres of the novel imidazole-functionalized fluorescent CPs, able to work in water media, were synthesized via a microemulsion and polymerization procedure. The synthesized imidazole-functionalized CP microspheres were then evaluated as fluorescence "turn-Off" sensing materials for Cu(2+) detection in aqueous media. Analyte detection was based on the quenching effect of the Cu(2+), selectively recognized by the imidazole group, on the polymer fluorescence emission. The developed optosensor exhibits a detection limit of 1 μg/L for the determination of Cu(2+) in water with a reproducibility of 4%. The synthesized microsized material was also evaluated for the "turn-on" optosensing of cyanide in water, measuring the recovery of the emission signal from the CP that has been previously deactivated by the presence of quencher species. The "turn-On" optosensor allows the selective determination of free cyanide in aqueous solution with high sensitivity (detection limit of 18 μg/L), obtaining a reproducibility of 2.9%. A high sample throughput (between 7 and 12 samples per hour) was achieved in both cases. Analytical applicability of the fluorescent CP microsphere materials has been successfully demonstrated by tap and mineral water analysis.

Herein, we demonstrate that both qualitative molecular and quantitative elemental data obtained from size exclusion chromatography coupled online for the first time to both molecular fluorescence and elemental mass spectrometry, respectively, turned out to be critical to evaluate the quality of coatings of quantum dots. Moreover, such an instrumental approach also allowed us to study quantitatively the appropriated bioconjugation of quantum dots to antibodies, a critical step for QDs future use in quantitative fluorescence immunoassays.

A fluorescent quantum dot-based antibody array, used in sandwich format, has been developed to detect Escherichia coli O157:H7. Numerous parameters such as solid support, optimal concentration of immunoreagents, blocking reagents, and assay time were optimized for array construction. Quantum dot-conjugated anti-IgG was used as the detecting system. The array allows the detection of E. coli O157:H7 at concentrations below 10 CFU mL(-1) without sample enrichment, exhibiting an increase of three orders of magnitude in the limit of detection compared to ELISA. The interference caused by Gram (+) and Gram (-) bacteria was negligible at low concentrations of bacteria.

Chemical speciation studies are commonly accomplished by resorting to hyphenated analytical techniques, consisting of a powerful chromatographic separation technique coupled to a highly sensitive elemental spectrometric detector. However, in addition to this element-selective information, complementary molecular spectrometric tools are often required for a complete identification of macromolecules. Therefore, there is an increased research effort focused towards the development of integrated instruments to carry out the complete chemical speciation within a sample using a single instrument. An outline of recent developments in plasma-based mass spectrometric instrumentation for such comprehensive chemical speciation studies is here presented and their pros and cons detailed. In this context, the use of complementary techniques operating in parallel after splitting to a single chromatographic separation (dual sources) providing simultaneously elemental and molecular information is critically reviewed. Also, instrumental developments involving the use of stationary plasma sources operated in non-traditional modes (e.g. low pressure and low power) are also discussed. Moreover, the capabilities of tunable plasma-based ionization sources (allowing different ionization processes and, so, quasi-simultaneously providing elemental and molecular information with a single instrument) as a relatively simple and cheap approach are revised.

Optical labelling reagents (dyes and fluorophores) are an essential component of probe-based biomolecule detection, an approach widely employed in a variety of areas including environmental analysis, disease diagnostics, pharmaceutical screening, and proteomic and genomic studies. Recently, functional nanomaterials, as a new generation of high-value optical labels, have been applied to molecular detection. The great potential of such recent optical labels has paved the way for the development of new biomolecule assays with unprecedented analytical performance characteristics, related to sensitivity, multiplexing capability, sample throughput, cost-effectiveness and ease of use. This review aims to provide an overview of recent advances using different nanoparticles (such as quantum dots, rare earth doped nanoparticles or gold nanoparticles) for analytical genomics and proteomics, with particular emphasis on the outlook for different strategies of using nanoparticles for bioimaging and quantitative bioanalytical applications, as well as possibilities and limitations of nanoparticles in such a growing field.