Sustainable beeswax modified cellulose paper for the determination of tricyclic antidepressants in biofluids.

This article describes the synthesis of sorptive phases for bioanalysis based on the modification of cellulose paper with natural beeswax as sorbent, resulting in a substrate completely renewable and sustainable. The preparation of the sorptive phases consisted of the dissolution of beeswax in hexane, followed by its drop-casting on cellulose paper and subsequent evaporation of the solvent. The beeswax modification of paper renders it hydrophobic, enabling the extraction of the target analytes, i.e., imipramine, desipramine, amitriptyline and trimipramine, via hydrophobic interactions. The main variables affecting the extraction performance were investigated (e.g., pH, ionic strength, extraction time, eluent composition, agitation speed). The analytical workflow combines a straightforward sampling, simultaneous extraction of 30 samples in 1 h, and the rapid (<2 min) determination of the analytes via direct infusion mass spectrometry. The method provided limits of detection in the range 2.0 and 3.2 µg L-1, and the precision, expressed as relative standard deviation, was better than 5.4 % and 8.5 % for intra and inter-day analyses, respectively. The accuracy, in terms of relative recovery, ranged from 90 % to 121 % using saliva as model biofluid.

Icosahedral gold nanoparticles decorated with hexon protein: a surrogate for adenovirus serotype 5.

The development of synthetic particles that emulate real viruses in size, shape, and chemical composition is vital to the development of imprinted polymer-based sorbent materials (molecularly imprinted polymers, MIPs). In this study, we address surrogates for adenovirus type 5 (Adv 5) via the synthesis and subsequent modification of icosahedral gold nanoparticles (iAuNPs) decorated with the most abundant protein of the Adv 5 (i.e., hexon protein) at the surface. CTAB-capped iAuNPs with dimensions in the range of 40-90 nm were synthesized, and then CTAB was replaced by a variety of polyethylene glycols (PEGs) in order to introduce suitable functionalities serving as anchoring points for the attachment of the hexon protein. The latter was achieved by non-covalent linking of the protein to the iAuNP surface using a PEG without reactive termination (i.e., methoxy PEG thiol, mPEG-SH, Mn=800). Alternatively, covalent anchoring points were generated by modifying the iAuNPs with a bifunctional PEG (i.e., thiol PEG amine, SH-PEG-NH2) followed by the addition of glutaraldehyde. X-ray photoelectron spectroscopy (XPS) confirmed the formation of the anchoring points at the iAuNP surface. Next, the amino groups present in the amino acids of the hexon protein interacted with the glutaraldehyde. iAuNPs before and after PEGylation were characterized using dynamic light scattering (DLS), XPS, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV-Vis spectroscopy, confirming the CTAB-PEG exchange. Finally, the distinct red shift obtained in the UV-Vis spectra of the pegylated iAuNPs in the presence of the hexon protein, the increase in the hydrodynamic diameter, the change in the zeta potential, and the selective binding of the hexon-modified iAuNPs towards a hexon-imprinted polymer (HIP) confirmed success in both the covalent and non-covalent attachment at the iAuNP surface.

Portable Raman Spectrometer as a Screening Tool for Characterization of Iberian Dry-Cured Ham.

Dry-cured Iberian ham is officially classified into different commercial categories according to the pig's breed and feeding regime. These reach very different prices, thus promoting labelling fraud and causing great damage to the food sector. In this work, a method based on Raman spectroscopy was explored as a rapid in situ screening tool for Iberian ham samples. A total of 110 samples were analyzed to assess the potential of this technique to differentiate purebred, crossbred, acorn-fed and feed-fed dry-cured Iberian ham. A continuous signal probably due to sample fluorescence was obtained, which hid the Raman scattering signal. Therefore, chemometric treatment was applied in order to extract non-apparent information. High validated classification rates were obtained for feeding regime (83.3%) and breed (86.7%). In addition, an interlaboratory study was carried out to confirm the applicability of the method with 52 samples, obtaining a validated rate above 80%.

Recent developments on gold nanostructures for surface enhanced Raman spectroscopy: Particle shape, substrates and analytical applications. A review.

Surface enhanced Raman spectroscopy (SERS) is a powerful technique for sensitive analysis which is attracting great attention in the last decades. In this review, different gold nanostructures that have been exploited for SERS analysis are described, ranging from gold nanospheres to anisotropic and complex-shaped gold nanostructures, in which the presence of high aspect ratio features leads to an increment of the electromagnetic field at the surface of the nanomaterial, resulting in enhanced SERS response. In addition to the shape of the nanostructure, the interparticle nanogaps play a prominent role in the SERS efficiency. In this sense, different approaches such as nanoaggregation and formation of assemblies and ordered structures lead to the creation of the so-called hot spots. SERS measurements may be performed in solution, while usually the nanostructures are deposited building a SERS substrate, which can be created via attachment of chemically prepared gold nanostructures, as well as via top-down physical methods. Among the classical supports for creating the SERS substrates, in the last years there is a trend towards the development of flexible supports based on polymers as well as paper. Finally, some recent applications of gold nanostructures-based SERS substrates within the analytical field are discussed to spotlight the potential of this technique in real-world analytical scenarios.

Photocatalytic Cellulose-Paper: Deepening in the Sustainable and Synergic Combination of Sorption and Photodegradation.

Clean water is one of the sustainable development goals set by the United Nations for 2030. The development of effective but worldwide affordable strategies is essential to guarantee this achievement. Photocatalysis technology fulfills these criteria whenever the photocatalyst is sustainable and nontoxic. In this article, a cellulose-paper modified with a polyamide-titanium dioxide (TiO2) nanocomposite by dip-coating is evaluated to degrade estrogens efficiently under solar light. The study deepens on the synergic combination of the sorptive capacity of the polyamide and the activity of TiO2. The photocatalytic performance was studied under artificial and sunlight in a miniaturized experimental setup (batch of six reactors). Also, the effects of the dispersed/immobilized catalyst, irradiation time, and adsorption evaluation were studied under kinetic conditions. The photocatalyst composition, considering the polyamide (nylon-6) and TiO2 amounts and the dipping cycles, was studied by a response surface methodology, and the reusability of the photocatalytic cellulose-paper was investigated. The LED source provided removal efficiencies of 65, 62, and 52% (for estrone, 17ß-estradiol, and estriol, respectively) after 420 min of light exposure. Under sunlight, the efficiency increased up to 99.5% for estrone and 17ß-estradiol and 98.5% for estriol after 180 min of irradiation. The sustainable character of the cellulosic substrate, the low toxicity of the nanocomposite ingredients, and its performance under sunlight make the material attractive for in-field application.

Hybrid Gold Nanoparticle-Polyoxovanadate Matrices: A Novel Surface Enhanced Raman/Surface Enhanced Infrared Spectroscopy Substrate.

Bare gold nanoparticles were embedded into an iron-polyoxovanadate matrix and used to enhance both the infrared and Raman signatures of a model analyte. A detailed characterization of the matrix-embedded nanoparticles revealed that they retained a plasmon resonance at 564 nm. The enhancement of vibrational signatures of the model analyte crystal violet using bare and embedded gold nanoparticles was compared for both surface enhanced infrared (SEIRA) spectroscopy and surface enhanced Raman spectroscopy (SERS) yielding enhancement factors of 2.2 for SEIRA and 77 for SERS. In contrast, the bare gold nanoparticles revealed significantly lower enhancements (1.6 for SEIRA; 20 for SERS). Hence, it was shown that embedding nanoparticles within an inorganic polyoxometalate-based matrix is an innovative strategy to amplify their signal enhancement properties in vibrational spectroscopies.

Gold Nanoparticles Synthesis Using Stainless Steel as Solid Reductant: A Critical Overview.

Gold nanoparticles (AuNPs) were produced using stainless steel as a solid reductant to assist the synthesis of metal NPs, using HAuCl4 as a precursor. This method is very easy, quick, and cost-effective, allowing the synthesis of highly stable NPs without additional capping agents. However, the reaction mechanism is still under debate. In order to contribute to the investigation of the synthesis of AuNPs using stainless steel, different experimental conditions were tested. Cl- concentration, pH of the precursor solution, as well as stainless steel composition were systematically changed. The syntheses were performed recording the open circuit potential to potentiometrically explore the electrochemical properties of the system, under operando conditions. Spectroscopic and morphological characterizations were carried out along with potentiometric monitoring, aiming at correlating the synthesis parameters with the AuNPs characteristics. As a result, an overview of the process features, and of its most reasonable mechanism were obtained.

Toxicity evaluation of barium ferrite nanoparticles in bacteria, yeast and nematode.

Barium ferrite nanoparticles (BaFeNPs) are a permanent magnetic nanomaterial widely used in electrical energy storage, recording media or in the improvement of the magnetic properties of other nanoparticles (NPs). However, the information about the toxicity of BaFeNPs is almost non-existent. Thus, in the present work, the antimicrobial effect of BaFeNPs was evaluated for the first time in gram-negative and gram-positive bacteria and yeast showing neither antibacterial nor antifungal activity at moderate concentrations. On the other hand, in order to assess the in vivo toxicity of BaFeNPs the model organism Caenorhabditis elegans was used and ingestion, survival, reproduction and ROS production were evaluated in worms treated with different concentrations of BaFeNPs. Our results show that worms ingest these NPs through the digestive system affecting survival, reproduction and ROS production.

Magnetic Graphene Oxide Composite for the Microextraction and Determination of Benzophenones in Water Samples.

Magnetite nanoparticles (Fe3O4) functionalized with graphene oxide (GO) have been synthesized through a silanization process of the magnetic nanoparticles with tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane and further coupling of GO. The synthesized nanomaterials have been characterized by several techniques, such as transmission electron microscopy (TEM), and infrared and Raman spectroscopy, which enabled the evaluation of the different steps of the functionalization process. The hybrid nanomaterial has been employed for the extraction of five benzophenones (benzophenone-1, benzophenone-3, 4-hydroxybenzophenone, benzophenone-6 and benzophenone-8) in aqueous samples by dispersive micro-solid phase extraction, combining the magnetic properties of magnetite nanoparticles with the excellent sorption capacity of graphene oxide via hydrophobic interactions with the analytes. The subsequent separation and quantification of the analytes was performed by liquid chromatography with tandem mass spectrometric detection, achieving limits of detection (LODs) in the range 2.5 to 8.2 µg·L-1, with relative standard deviations ranging from 1.3-9.8% and relative recovering in the range 86 to 105%. Positive swimming pool water samples analysed following the developed method revealed the presence of benzophenones in from 14.3 to 39 µg·L-1.

Infrared attenuated total reflection and 2D fluorescence spectroscopy for the discrimination of differently aggregated monoclonal antibodies.

Antibody aggregates may occur as undesirable by-products during the manufacturing process of biopharmaceutical proteins since parameters such as pH, temperature, ionic strength, protein concentration, oxygen, and shear forces can lead to aggregate formation. These aggregates have to be detected, quantified and removed cost extensively, since they may reduce the safety and efficacy of the product. Protein aggregates can range from small soluble dimers up to large visible agglomerates. Differently aggregated antibody samples were characterized for their soluble and insoluble aggregate concentration by size exclusion chromatography and fluorescence microscopy, respectively. The samples exhibited a high diversity of protein aggregates, which varied in amount, size and shape. For secondary structure characterization, infrared attenuated total reflection (IR-ATR) and two-dimensional fluorescence (2D-FL) spectroscopy were applied. Using direct spectroscopy, only marginal differences of various antibody aggregates were evident. However, using appropriate chemometric strategies, the evaluation of IR-ATR and 2D-FL spectra yielded the discrimination of differently aggregated antibody samples with yet unprecedented precision.

Surface analysis of sheep menisci after meniscectomy via infrared attenuated total reflection spectroscopy.

Menisci are very important fibrocartilaginous tissue, which maintain biomechanical functions and physiological stabilization of knee joint. Meniscectomy is known as a surgery to recover partial functions from acute meniscus tears. However, the late consequences of total or partial meniscectomy include signs of osteoarthritis and even ligament instability. Infrared attenuated total reflection (IR-ATR) spectroscopy is a very useful technique, which can reveal molecular characteristics via the analysis of vibrational bands. The present study has employed IR-ATR spectroscopy to investigate sheep menisci samples after meniscectomy in a label-free fashion. Several differences of peak absorbance change and peak shift were observed between the native healthy samples and the meniscectomy samples in distinct IR wavenumber regions, such as amide I band, amide II band, C-H bending band as well as the sugar band region. Combining the results from the collagen protein IR spectra, it can be speculated that six months after meniscectomy collagen fibrils on the incision lose its ordered arrangement and a decrease in the triple helical structure of collagen fibril is observed. In addition, the collagen fibrils and proteoglycan content might also be slight varied after meniscectomy.

Analysis of human menisci degeneration via infrared attenuated total reflection spectroscopy.

Degeneration of human meniscal tissue induces impairment of normal knee functions, and is a highly relevant etiology of knee joint tears and osteoarthritis. Currently, the grading scale of meniscus degeneration is conventionally derived from evaluating meniscal morphology and histological staining. However, mid-infrared attenuated total reflectance (IR-ATR) spectroscopy is a particularly useful technique that may analyze the biomolecular composition at a sample surface, and provide information on the intra- and/or inter-molecular chemical bonds. In the present study, 61 lyophilized human menisci samples at different grades of degeneration were analyzed via IR-ATR spectroscopy in a label-free fashion, and the data were evaluated via Gaussian peak fitting and 2D correlation analysis. During increasing meniscal degeneration (i.e., grade 1 to 4) along with calcification at grade 4, an evident blue shift of the amide I band (1700-1600 cm-1) was observed in the associated IR spectra. In addition, Gaussian peak fitting revealed significant area variance of the fitted sub-peaks. 2D correlation spectra provided further access to detailed changes of the amide I band during the degeneration process. Derived from this multi-tiered data analysis taking into account the protein secondary structure information within the amide I band, and the triple helical structure of meniscal collagen, the blue shift and peak area changes during meniscus degeneration are indicative of collagen fibril formation during evolving degeneration. Furthermore, a degradation of the water-binding proteoglycan and collagen network especially for degenerated menisci with calcification was observed. Results were compared with a collagen-chondroitin sulphate mixture model, confirming the observed changes in collagen fibrils and proteoglycans. In summary, this study confirms the utility of IR-ATR spectroscopy as a versatile tool providing access to meniscal tissue degeneration processes at molecular level detail, and may in future evolve into a useful diagnostic instrument for analyzing cartilage degeneration.

Gold-nanostar-based SERS substrates for studying protein aggregation processes.

Aggregation of proteins has been related to some neurodegenerative diseases such as Alzheimer's and Parkinson's among others. Raman spectroscopy is a useful technique for the investigation of protein conformation and of changes in their secondary structure. In this study, a surface enhanced Raman spectroscopy (SERS) substrate based on the immobilization of plasmonic gold nanostars on a glass slide via silanization of the surface has been prepared and characterized. Gold nanostars were synthesized via a seed-growth method using gold nanoparticles as seeds obtained via stainless steel as the reducing agent. The plasmonic substrate provided an enhancement of 5.7 × 102 fold, as shown for the Raman signal of crystal violet. Using this SERS-active substrate, the investigation of aggregation processes of bovine serum albumin (BSA) and myoglobin proteins upon temperature and solvent modification has been enabled with enhanced sensitivity. Both curve fitting and deconvolution of the amide I band, as well as 2D correlation analysis, were employed for the evaluation of the changes in the SERS spectra of the protein samples. The amide I band within the SERS spectra of the BSA protein revealed a decrease in the α-helix structures within the secondary structure of the protein while the presence of ß-sheet structures increased with temperature and solvent concentration.

Monolithic Solid Based on Single-Walled Carbon Nanohorns: Preparation, Characterization, and Practical Evaluation as a Sorbent.

A monolithic solid based solely on single walled carbon nanohorns (SWNHs) was prepared without the need of radical initiators or gelators. The procedure involves the preparation of a wet jelly-like system of pristine SWNHs followed by slow drying (48 h) at 25 °C. As a result, a robust and stable porous network was formed due to the interaction between SWNHs not only via π-π and van der Waals interactions, but also via the formation of carbon bonds similar to those observed within dahlia aggregates. Pristine SWNHs and the SWNH monolith were characterized by several techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), confocal laser scanning microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen intrusion porosimetry. Taking into account the efficiency of carbon nanoparticles in sorption processes, the potential applicability of the SWNH-monolith in this research field was explored using toluene; m-, p-, and o-xylene; ethylbenzene; and styrene, as target analytes. Detection limits were 0.01 µg·L-1 in all cases and the inter-day precision was in the interval 7.4⁻15.7%. The sorbent performance of the nanostructured monolithic solid was evaluated by extracting the selected compounds from different water samples with recovery values between 81.5% and 116.4%.

Ion beam sputtering deposition of silver nanoparticles and TiOx/ZnO nanocomposites for use in surface enhanced vibrational spectroscopy (SERS and SEIRAS).

Hybrids consisting of silver nanoparticles (in varying fractions) and of TiOx/ZnO were prepared via top-down ion beam sputtering (IBS) deposition on silicon substrates. The deposited nanomaterials were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. It is shown that such composites represent a viable substrate for use in both surface enhanced Raman spectroscopy (SERS) and surface enhanced infrared absorption spectroscopy (SEIRAS), as exemplarily shown for crystal violet as the model analyte. The C-H bending mode at about 1181 cm-1 and the C-N vibration at 1361 cm-1 observed in the SERS and SEIRAS spectra, respectively, have been used as analytical signal. The substrate consisting of TiOx NPs with 33% fraction of silver provides the strongest enhancement in SERS (up to 10,000-fold), while TiOx/AgNPs with thickness of 2 and 1 nm in ion beam sputtering, respectively, provides the best sensitivity in SEIRAS. The substrates also display photocatalytic activity as shown by the degradation of adsorbed crystal violet under ultraviolet irradiation. Graphical abstract Schematic of the preparation of hybrid substrates consisting of Ag and TiOx/ZnO nanoparticles via ion beam sputtering deposition. They were applied in both surface enhanced Raman and surface enhanced infrared absorption spectroscopies using crystal violet as model analyte, showing enhancements up to >10,000-fold in Raman.

Surface enhanced infrared absorption spectroscopy based on gold nanostars and spherical nanoparticles.

Plasmonic anisotropic nanoparticles possess a number of hot spots on their surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the nanostructures. In this paper, we explore different plasmonic nanostructures, including anisotropic gold nanostars (AuNSts) and spherical gold nanoparticles, in surface-enhanced infrared absorption spectroscopy (SEIRAS) in an attenuated total reflection (ATR) configuration. In our experiments, we observed up to 10-times enhancement of the infrared (IR) absorption of thioglycolic acid (TGA) and up to 2-times enhancement of signals for bovine serum albumin (BSA) protein on plasmonic nanostructure-based films deposited on a silicon (Si) internal reflection element (IRE) compared to bare Si IRE. The dependence of the observed enhancement on the amount of AuNSts present at the surface of the IRE has been demonstrated. Quantitative studies with both, TGA and BSA were performed, observing that the SEIRA signal can be correlated to the concentration of analyte molecules present within the evanescent field. The calibration curves in the presence of the AuNSts showed enhanced sensitivity as compared with the bare Si IRE. We finally compare efficiencies of anisotropic AuNSts and spherical citrate-capped and "bare" laser-synthesized gold nanoparticles as SEIRAS substrates for the detection of TGA and BSA. The signal obtained from AuNSts was at least 2 times higher for TGA molecules in comparison with spherical gold nanoparticles, which was explained by a more efficient generation of hot spots on anisotropic surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the AuNSts.

Mid-infrared spectroscopy for protein analysis: potential and challenges.

Mid-infrared (MIR) spectroscopy investigates the interaction of MIR photons with both organic and inorganic molecules via the excitation of vibrational and rotational modes, providing inherent molecular selectivity. In general, infrared (IR) spectroscopy is particularly sensitive to protein structure and structural changes via vibrational resonances originating from the polypeptide backbone or side chains; hence information on the secondary structure of proteins can be obtained in a label-free fashion. In this review, the challenges for IR spectroscopy for protein analysis are discussed as are the potential and limitations of different IR spectroscopic techniques enabling protein analysis. In particular, the amide I spectral range has been widely used to study protein secondary structure, conformational changes, protein aggregation, protein adsorption, and the formation of amyloid fibrils. In addition to representative examples of the potential of IR spectroscopy in various fields related to protein analysis, the potential of protein analysis taking advantage of miniaturized MIR systems, including waveguide-enhanced MIR sensors, is detailed.

Determination of nanoparticles in biological matrices.

Human exposure to nanoparticles has increased considerably due to anthropogenic activities dominated by coal and diesel oil fuel combustion. Not only the inhalation of nanoparticles, which nowadays is considered to be the most significant via of exposure to nanomaterials, but also the gradually more employment of nanoparticles in products such as cosmetics, deodorants, textiles, or even food is broadening the exposure to those materials. Developing the previous applications will obviously require the use of analytical methodologies to analyse biological matrices in order to assess potential risks in their use and take appropriate corrective actions. This chapter describes a general overview of the most important analytical techniques for the analysis of nanoparticles in biological matrices.