Effects of hydroxyl group variations on a flavonoid backbone toward modulation of metal-free and metal-induced amyloid-?? aggregation

Amyloid-?? (A??) and metal ions are suggested to be involved in the pathogenesis of Alzheimer???s disease(AD). Cu(II) and Zn(II) can interact with A?? and facilitate peptide aggregation producing toxic oligomeric peptide species. Additionally, redox-active metal-bound A?? is shown to generate reactive oxygen species(ROS). Although the interaction of metal ions with A?? and the reactivity of metal-associated A?? (metal-A??) are indicated, the relationship between metal-A?? and AD etiology is still unclear. Some naturally occurring flavonoids capable of redirecting metal-A?? peptides into nontoxic, off-pathway A?? aggregates have been presented as valuable tools for elucidating the role of metal-A?? in AD. The structural moieties of the flavonoids responsible for their reactivity toward metal-A?? are not identified, however. To determine a structure-interaction-reactivity relationship between flavonoids and metal-free A?? or metal-A??, four flavonoids (morin, quercetin, galangin, and luteolin) were rationally selected based on structural variations(i.e., number and position of hydroxyl groups). These four flavonoids could noticeably modulate metal-A?? aggregation over metal-free analogue to different extents. Moreover, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) studies reveal that the direct interactions of the flavonoids with metal-free and/or metal-bound A?? are distinct. Overall, our studies demonstrate that alternation of the hydroxyl groups on the B and C rings of flavonoids (structure) could differentiate their metal/metal-free A??/metal-A?? interactions (interaction) and subsequently direct their effects on metal-free A?? and metal-A?? aggregation in vitro and A??-/metal-A??-triggered toxicity in living cells (reactivity), suggesting a structure-interaction-reactivity relationship.open

ESTUDIO DE LA INFLUENCIA DE LA ESTRUCTURA DE ANILLO B DE FLAVONOLES EN SUS CONSTANTES DE ACIDEZ Y CAPACIDAD ANTIOXIDANTE

Cuatro flavonoles: Quercetina, Morina, Kaempferol y Miricetina con características estructurales similares pero con diferente número y posición de grupos OH en uno de sus anillos (anillo B) fueron estudiados con el fin de determinar su estabilidad, constantes de acidez, el orden de desprotonación y su actividad antioxidante en solución acuosa. Para analizar la estabilidad de estos compuestos y determinar las constantes de acidez se empleó espectrofotometría UV-Vis a diferentes valores de pH. Los mecanismos de desprotonación fueron calculados con la ayuda de la química computacional, usando la Teoría de los Funcionales de la Densidad. Los cálculos se realizaron en solución acuosa utilizando el modelo continuo SMD y los resultados fueron reportados como energías de desprotonación. Los resultados muestran que tanto la Quercetina como la Miricetina son altamente inestables a valores de pH básico. El Kaempferol, por otro lado, es mucho más estable y la Morina es el único entre los compuestos estudiados, que no se vio afectado por el valor de pH. A pesar de este inconveniente, sus constantes de acidez se estimaron mediante el análisis de su cinética de descomposición y se propone como consecuencia la corrección de los espectros. Se obtiene una correlación entre los valores de pKa y los observados experimentalmente y el ∆G calculado de las desprotonaciones sucesivas. Por otra parte se sintetizaron nanocristales de sulfuro de cadmio, se caracterizaron usando TEM y se observa como los flavonoles inhiben la fluorescencia de estas nanopartículas, proponiéndose así un método de determinación, selectivo a flavonoles. El porcentaje de inhibición depende de la estructura del compuesto y podría relacionarse con la actividad antioxidante. Por último se determinó la capacidad antioxidante usando el método del DPPH donde los resultados indican que la Miricetina es la más reactiva. Además se evidencia la regeneración del grupo catecol en Metanol. También se emplearon cálculos computacionales considerando todos los posibles mecanismos de reacción frente al radical OOH● donde se demuestra la importancia de considerar todos los posibles mecanismos de reacción y las fracciones molares de las especies a un determinado valor de pH, se analizó el mecanismo de transferencia electrónica donde la Miricetina sigue siendo la más reactiva. No obstante el mecanismo predominante frente al radical estudiado es el de transferencia de Hidrógeno obteniéndose que la Morina es la más reactiva por esta vía con una constante de velocidad limitada por difusión.Four flavonols namely: Quercetin, Morin, Kaempferol and Myricetin were studied using spectrophotometry UV/Vis, in aqueous solution. The study was performed varying the pH to analyze the stability of these compounds, and to estimate their acidity constants. In addition, the deprotonation mechanisms were studied using computational chemistry, within the Density Functional Theory framework. The calculations were performed in aqueous solution using the SMD continuum model and the results are reported as deprotonation energies. Our results show that both quercetin and myricetin are highly unstable at basic pH. Kaempferol, on the other hand, is much more stable; and morin is the only one, among the studied compounds, that was not affected by pH. In spite of this inconvenience, their acidity constants were estimated through analysis of their decomposition kinetics, correcting the spectra accordingly, and obtaining a correlation of values between the experimentally observed pKa and the calculated ∆G of successive deprotonations. On the other hand cadmium sulfide nanocrystals where synthesized and characterized using TEM. A fluorescence quenching of these nanoparticles was observed in the presence of flavonoids. This allows proposing a high selective method of determination for this kind of compounds. The percentage of inhibition depends on the structure of the compound and might be related to their antioxidant activity. The antioxidant capacity was estimated using the traditional DPPH method. The results indicate that Myricetin is the most reactive among all the studied flavonoids. Furthermore, regeneration of the catechol group in methanol was postulated. In addition computational calculations were also employed to estimate the antioxidant activity, considering different reaction mechanisms and reactions with the OOH radical. For the electron transfer mechanism the obtained trend is similar to that arising from the DPPH assay. However the predominant mechanism for the hydroperoxyl radical scavenging activity of these compounds is the hydrogen transfer. Morin was found to be the most reactive of the studied compounds via H transfer, with rate constant within the diffusion-limited regime. This methodology demonstrates the importance of considering the molar fraction of the chemical species at a fixed pH

Nano-lantern on paper for smartphone-based ATP detection

ATP-driven bioluminescence relying on the D-luciferin-luciferase reaction is widely employed for several biosensing applications where bacterial ATP detection allows to verify microbial contamination for hygiene monitoring in hospitals, food processing and in general for cell viability studies. Several ATP kit assays are already commercially available but an user-friendly ATP biosensor characterized by low-cost, portability, and adequate sensitivity would be highly valuable for rapid and facile on site screening. Thanks to an innovative freeze-drying procedure, we developed a user-friendly, ready-to-use and stable ATP sensing paper biosensor that can be combined with smartphone detection. The ATP sensing paper includes a lyophilized \u201cnano-lantern\u201d with reaction components being rapidly reconstituted by 10 \u3bcL sample addition, enabling detection of 10 1214 mol of ATP within 10 min. We analysed urinary microbial ATP as a biomarker of urinary tract infection (UTI), confirming the capability of the ATP sensing paper to detect the threshold for positivity corresponding to 105 colony-forming units of bacteria per mL of urine

Freestanding laser-induced two dimensional heterostructures for self-contained paper-based sensors

The production of 2D/2D heterostructures (HTs) with favorable electrochemical features is challenging, particularly for semiconductor transition metal dichalcogenides (TMDs). In this studies, we introduce a CO2 laser plotter-based technology for the realization of HT films comprising reduced graphene oxide (rGO) and 2D-TMDs (MoS2, WS2, MoSe2, and WSe2) produced via water phase exfoliation. The strategy relies on the Laser-Induced production of HeterosTructures (LIHTs), where after irradiation the nanomaterials exhibit changes in the morphological and chemical structure, becoming conductive easily transferable nanostructured films. The LIHTs were characterized in detail by SEM, XPS, Raman and electrochemical analysis. The laser treatment induces the conversion of GO into conductive highly exfoliated rGO decorated with homogeneously distributed small TMD/TM-oxide nanoflakes. The freestanding LIHT films obtained were employed to build self-contained sensors onto nitrocellulose, where the HT works both as a transducer and sensing surface. The proposed nitrocellulose-sensor manufacturing process is semi-automated and reproducible, multiple HT films may be produced in the same laser treatment and the stencil-printing allows customizable design. Excellent performance in the electroanalytical detection of different molecules such as dopamine (a neurotransmitter), catechin (a flavonol), and hydrogen peroxide was demonstrated, obtaining nanomolar limits of detection and satisfactory recovery rates in biological and agrifood samples, together with high fouling resistance. Considering the robust and rapid laser-induced production of HTs and the versatility of scribing desired patterns, the proposed approach appears as a disruptive technology for the development of electrochemical devices through sustainable and accessible strategies

One-Step Laser Nanostructuration of Reduced Graphene Oxide Films Embedding Metal Nanoparticles for Sensing Applications

The combination of two-dimensional materials and metal nano-particles (MNPs) allows the fabrication of novel nanocomposites with unique physical/chemical properties exploitable in high-performance smart devices and biosensing strategies. Current methods to obtain graphene-based films decorated with noble MNPs are cumbersome, poorly reproducible, and difficult to scale up. Herein, we propose a straightforward, versatile, surfactant-free, and single-step technique to produce reduced graphene oxide (rGO) conductive films integrating "naked" noble MNPs. This method relies on the instantaneous laser-induced co-reduction of graphene oxide and metal cations, resulting in highly exfoliated rGO nanosheets embedding gold, silver, and platinum NPs. The production procedure has been optimized, and the obtained nanomaterials are fully characterized; the hybrid nanosheets have been easily transferred onto lab-made screen-printed electrodes preserving their nanoarchitecture. The Au@rGO-, Ag@rGO-, and Pt@ rGO-based electrodes have been challenged to detect caffeic acid, nitrite, and hydrogen peroxide in model solutions and real samples. The sensors yielded quantitative responses (R2 >= 0.997) with sub-micromolar limits of detections (LODs <= 0.6 mu M) for all the analytes, allowing accurate quantification in samples (recoveries >= 90%; RSD <= 14.8%, n = 3). This single-step protocol which requires low cost and minimal equipment will allow the fabrication of free-standing, MNP-embedded rGO films integrable into a variety of scalable smart devices and biosensors

Laser Reduced Graphene Oxide Electrode for Pathogenic Escherichia coli Detection

Graphene-based materials are of interest in electro-chemical biosensing due to their unique properties, such as high surface areas, unique electrochemical properties, and biocompatibility. However, the scalable production of graphene electrodes remains a challenge; it is typically slow, expensive, and inefficient. Herein, we reported a simple, fast, and maskless method for large-scale, low-cost reduced graphene oxide electrode fabrication; using direct writing (laser scribing and inkjet printing) coupled with a stamp-transferring method. In this process, graphene oxide is simultaneously reduced and patterned with a laser, before being press-stamped onto polyester sheets. The transferred electrodes were characterized by SEM, XPS, Raman, and electrochemical methods. The biosensing utility of the electrodes was demonstrated by developing an electrochemical test for Escherichia coli. These biosensors exhibited a wide dynamic range (917-2.1 x 107 CFU/mL) of low limits of detection (283 CFU/ mL) using just 5 mu L of sample. The test was also verified in spiked artificial urine, and the sensor was integrated into a portable wireless system driven and measured by a smartphone. This work demonstrates the potential to use these biosensors for real-world, point-of-care applications. Hypothetically, the devices are suitable for the detection of other pathogenic bacteria

Tutorial: design and fabrication of nanoparticle-based lateral-flow immunoassays

Lateral-flow assays (LFAs) are quick, simple and cheap assays to analyze various samples at the point of care or in the field, making them one of the most widespread biosensors currently available. They have been successfully employed for the detection of a myriad of different targets (ranging from atoms up to whole cells) in all type of samples (including water, blood, foodstuff and environmental samples). Their operation relies on the capillary flow of the sample throughout a series of sequential pads, each with different functionalities aiming to generate a signal to indicate the absence/presence (and, in some cases, the concentration) of the analyte of interest. To have a user-friendly operation, their development requires the optimization of multiple, interconnected parameters that may overwhelm new developers. In this tutorial, we provide the readers with: (i) the basic knowledge to understand the principles governing an LFA and to take informed decisions during lateral flow strip design and fabrication, (ii) a roadmap for optimal LFA development independent of the specific application, (iii) a step-by-step example procedure for the assembly and operation of an LF strip for the detection of human IgG and (iv) an extensive troubleshooting section addressing the most frequent issues in designing, assembling and using LFAs. By changing only the receptors, the provided example procedure can easily be adapted for cost-efficient detection of a broad variety of targets