Detection of flagellin by interaction with human recombinant TLR5 immobilized in liposomes

Digestive diseases caused by flagellated bacteria are a huge public health problem worldwide and rapid detection methods are needed for contaminated environments. In this study, we propose a method to detect patterns associated with pathogens based on the properties of the innate immune system. Specifically, we use Toll-like receptor 5 (TLR5), a transmembrane protein that specifically recognizes flagellin (the structural protein of bacterial flagella). TLR5, which was obtained by recombinant production in insect cells, was immobilized into liposomes to form TLR5-proteoliposomes. Through surface plasmon resonance (SPR) and competition flow cytometry assays, the sensitivity of proteoliposomes to recognize Escherichia coli and Salmonella typhimurium flagellin was evaluated. In addition, we compared the results obtained by immobilizing anti-flagellin antibodies into liposomes. The results of the flagellin-affinity tests, expressed as an SPR kinetic rate constant ratio in the equilibrium equation K _D?=?k _d/k _a, showed values of 13.8?×?10^?9 and 7.73?×?10^?9?M for the TLR5-proteoliposomes and anti-flagellin antibodies, respectively, against S. typhimurium. The anti-flagellin affinity results for E. coli showed K _D of 84.1?×?10^?8?M for SPR assays and K _D of 3.5?×?10^?8?M for competitive flow cytometry, which was used as a detection system without the immobilization of proteoliposomes. This research demonstrates the practical possibility of using proteoliposomes as recognition elements in the generation of systems for the rapid detection of flagellated bacteria, which could help avoid consumption of contaminated food by humans and thereby prevent intestinal infections.     

Part per trillion determination of atrazine in natural water samples by a surface plasmon resonance immunosensor

A new immunoassay for continuously monitoring atrazine in water has been developed. It uses a portable biosensor platform based on surface plasmon resonance (SPR) technology. This immunoassay is based on the binding inhibition format with purified polyclonal antibodies, with the analyte derivative covalently immobilized on a gold sensor surface. An alkanethiol self-assembled monolayer (SAM) was formed on the gold-coated sensor surface in order to obtain a reusable sensing surface. The low detection limit for the optimized assay, calculated as the concentration that produces a 10% decrease in the blank signal, is 20 ng/L. A complete assay cycle, including regeneration, is accomplished in 25 min. Additionally, a study of the matrix effects of different types of wastewater was performed. All measurements were carried out with the SPR sensor system (β-SPR) commercialised by the company Sensia, S.L. (Spain). The small size and low response time of the β-SPR platform would allow it to be used in real contaminated locations. The immunosensor was evaluated and validated by measuring the atrazine content of 26 natural samples collected from Ebro River. Solid-phase extraction followed by gas chromatography coupled to mass spectrometric detection (SPE–GC–MS) was used to validate the new immunoassay.     

On-line determination of 3,5,6-trichloro-2-pyridinol in human urine samples by surface plasmon resonance immunosensing

An immunochemical method for the analysis of 3,5,6-trichloro-2-pyridinol (TCP), a major urinary metabolite of chlorpyrifos, is developed using a surface plasmon resonance (SPR)-based biosensor. The stability of the assay was assessed by covalently linking the analyte derivative to a thin, gold-modified sensor surface. For optimization of analyte derivative immobilization, sensor chips were activated via alkanethiol monolayers with terminal amine or carboxyl groups. Binding inhibition tests were performed in untreated urine samples and compared to those obtained in distilled water and PBS was used as control. In all cases, similar detection limits, at the micrograms per litre level (0.1–0.24 μg L⁻¹), were attained for TCP assays independently of the dilution buffer. Reproducibility of measurements was studied throughout more than 130 regeneration cycles, which allowed the repeated use of the same immunosensor surface without significant variation of the SPR signal. All measurements were developed in real-time in only 10 min, using a SPR portable system. The device could be applied as a valuable analytical method to both environmental screening and clinic diagnostics.     

Nanophotonic lab-on-a-chip platforms including novel bimodal interferometers, microfluidics and grating couplers

One of the main limitations for achieving truly lab-on-a-chip (LOC) devices for point-of-care diagnosis is the incorporation of the "on-chip" detection. Indeed, most of the state-of-the-art LOC devices usually require complex read-out instrumentation, losing the main advantages of portability and simplicity. In this context, we present our last advances towards the achievement of a portable and label-free LOC platform with highly sensitive "on-chip" detection by using nanophotonic biosensors. Bimodal waveguide interferometers fabricated by standard silicon processes have been integrated with sub-micronic grating couplers for efficient light in-coupling, showing a phase resolution of 6.6 × 10(-4)× 2π rad and a limit of detection of 3.3 × 10(-7) refractive index unit (RIU) in bulk. A 3D network of SU-8 polymer microfluidics monolithically assembled at the wafer-level was included, ensuring perfect sealing and compact packaging. To overcome some of the drawbacks inherent to interferometric read-outs, a novel all-optical wavelength modulation system has been implemented, providing a linear response and a direct read-out of the phase variation. Sensitivity, specificity and reproducibility of the wavelength modulated BiMW sensor has been demonstrated through the label-free immunodetection of the human hormone hTSH at picomolar level using a reliable biofunctionalization process.     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.     

Modulation of proteins adsorption onto the surface of chitosan complexed with anionic copolymers. Real time analysis by surface plasmon resonance

The interpolyelectrolyte complex formation between chitosan and anionic polyacrylic derivatives, bearing sulfonic moieties, as well as the protein adsorption onto the chitosan/polyacrylic complexes were studied by surface plasmon resonance (SPR) optical biosensor. This unique technique allows a real time monitoring of different surface molecular interactions with very high sensitivity. The acrylic macromolecules are two families of copolymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and, respectively, 2-hydroxyethylmethacrylate (HEMA) and N,N'-dimethylacrylamide (DMAA). The complexation process was evaluated through the SPR measurements resulting from the flowing of polyacrylic aqueous solution over the sensor previously coated with chitosan. The SPR was able to differentiate strong ionic bonds from other weak and reversible interactions. By means of the coated sensors (uncomplexed and the whole series of complexed chitosan), SPR cold be used for a simple "in vitro" protein adsorption analysis, by flowing aqueous solutions of albumin and fibrinogen. While both proteins were adsorbed on the uncomplexed chitosan, the complexed coatings exhibited different and very promising behaviors. In particular, they showed no adsorption or only selective adsorption of albumin.     

Nanomechanics of the formation of DNA self-assembled monolayers and hybridization on microcantilevers

Biomolecular interactions over the surface of a microcantilever can produce its bending motion via changes of the surface stress, which is referred to nanomechanical response. Here, we have studied the interaction forces responsible for the bending motion during the formation of a self-assembled monolayer of thiolated 27-mer single-stranded DNA on the gold-coated side of a microcantilever and during the subsequent hybridization with the complementary nucleic acid. The immobilization of the single-stranded DNA probe gives a mean surface stress of 25 mN/m and a mean bending of 23 nm for microcantilevers with a length and thickness of about 200 microm and 0.8 microm, respectively. The hybridization with the complementary sequence could not be inferred from the nanomechanical response. The nanomechanical response was compared with data from well-established techniques such as surface plasmon resonance and radiolabeling, to determine the surface coverage and study the intermolecular forces between neighboring DNA molecules anchored to the microcantilever surface. From both techniques, an immobilization surface density of 3 x 10(12) molecules/cm(2) and a hybridization efficiency of 40% were determined. More importantly, label-free hybridization was clearly detected in the same conditions with a conventional sensor based on surface plasmon resonance. The results imply that the nanomechanical signal during the immobilization process arises mainly from the covalent attachment to the gold surface, and the interchain interactions between neighboring DNA molecules are weak, producing an undetectable surface stress. We conclude that detection of nucleic acid hybridization with nanomechanical sensors requires reference cantilevers to remove nonspecific signals, more sensitive microcantilever geometries, and immobilization chemistries specially addressed to enhance the surface stress variations.     

Small Angle X-ray Scattering,Molecular Modeling,and Chemometric Studies from a Thrombin-Like (Lmr-47) Enzyme of Lachesis m. rhombeata Venom

Introduction: Snakebite envenomation is considered a neglected tropical disease, and SVTLEs critical elements are involved in serious coagulopathies that occur on envenoming. Although some enzymes of this group have been structurally investigated, it is essential to characterize other proteins to better understand their unique properties such as the Lachesis muta rhombeata 47 kDa (Lmr-47) venom serine protease. Methods: The structure of Lmr-47 was studied in solution, using SAXS, DLS, CD, and in silico by homology modeling. Molecular docking experiments simulated 21 competitive inhibitors. Results: At pH 8.0, Lmr-47 has an Rg of 34.5 ± 0.6 Å, Dmax of 130 Å, and SR of 50 Å, according to DLS data. Kratky plot analysis indicates a rigid shape at pH 8.0. Conversely, the pH variation does not change the center of mass’s intrinsic fluorescence, possibly indicating the absence of fluorescent amino acids in the regions affected by pH variation. CD experiments show a substantially random coiled secondary structure not affected by pH. The low-resolution model of Lmr-47 presented a prolate elongated shape at pH 8.0. Using the 3D structure obtained by molecular modeling, docking experiments identified five good and three suitable competitive inhibitors. Conclusion: Together, our work provided insights into the structure of the Lmr-47 and identified inhibitors that may enhance our understanding of thrombin-like family proteins.