Synthesis and characterization of methacrylic microspheres for biomolecular recognition: Ultrasensitive biosensor for Dengue virus detection

Recognition of the interaction between the bioactive peptide Val-Pro-Pro and the minimal promoter region of genes SOD and CAT using QCM-D and docking studies

Bioactive peptides are biomolecules involved in very diverse mechanisms in vivo. It has been reported that bioactive peptides play a very important role in the regulation of physiological functions such as oxidative stress, hypertension, cancer and inflammation. It's been reported that the milk derived peptide (VPP) prevents the progress of hypertension in different animal models and human beings with mild hypertension. It has also been shown that oral administration of VPP produces an anti-inflammatory effect in adipose tissue of mouse models. Currently there are no reports on the possible interaction of VPP with the enzymes superoxide dismutase (SOD) and catalase (CAT), the main regulators of oxidative stress. This study analyzes the interaction between VPP and specific domains in the minimal promoter region of the genes SOD and CAT in blood samples of obese children using a QCM-D type piezoelectric biosensor. We also used molecular modeling (docking) to determine the interaction between the peptide VPP and the minimal promoter region of both genes. With QCM-D, we detected the interaction of VPP with the nitrogenous base sequences that comprise the minimal promoter regions of both genes CAT and SOD. These experimental interactions were explained at the atomic level by molecular docking simulations showing how the peptides are capable of reaching the DNA structures by means of hydrogen bonds with favored free energy values. It is possible to conclude that the combined use of docking and QCM-D allows for the determination of the interaction of small peptides (VPP) with specific sequences of genes.

Droplet Surface Immunoassay by Relocation (D-SIRe) for High-Throughput Analysis of Cytosolic Proteins at the Single-Cell Level

Enzyme-linked immunosorbent assay (ELISA) is a central analytic method in biological science for the detection of proteins. Introduction of droplet-based microfluidics allowed the development of miniaturized, less-consuming, and more sensitive ELISA assays by coencapsulating the biological sample and antibody-functionalized particles. We report herein an alternative in-droplet immunoassay format, which avoids the use of particles. It exploits the oil/aqueous-phase interface as a protein capture and detection surface. This is achieved using tailored perfluorinated surfactants bearing azide-functionalized PEG-based polar headgroups, which spontaneously react when meeting at the droplet formation site, with strained alkyne-functionalized antibodies solubilized in the water phase. The resulting antibody-functionalized inner surface can then be used to capture a target protein. This surface capture process leads to concomitant relocation at the surface of a labeled detection antibody and in turn to a drastic change in the shape of the fluorescence signal from a convex shape (not captured) to a characteristic concave shape (captured). This novel droplet surface immunoassay by fluorescence relocation (D-SIRe) proved to be fast and sensitive at 2.3 attomoles of analyte per droplet. It was further demonstrated to allow detection of cytosolic proteins at the single bacteria level.

Development of peptide biosensor for the detection of dengue fever biomarker, nonstructural 1

Dengue virus (DENV) nonstructural 1 (NS1) protein is a specific and sensitive biomarker for the diagnosis of dengue. In this study, an efficient electrochemical biosensor that uses chemically modified affinity peptides was developed for the detection of dengue virus NS1. A series of amino acid-substituted synthetic peptides was rationally designed, chemically synthesized and covalently immobilized to a gold sensor surface. The sensor performance was monitored via square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). Potential affinity peptides specific for NS1 were chosen according to the dynamic current decrease in SWV experiments. Using circular dichroism, the molar ellipticity of peptides (DGV BP1–BP5) was determined, indicating that they had a mostly similar in random coil structure, not totally identical. Using SWV, DGV BP1 was selected as a promising recognition peptide and limit of detection for NS1 was found to be 1.49 μg/mL by the 3-sigma rule. DGV BP1 showed good specificity and stability for NS1, with low signal interference. The validation of the sensor to detect NS1 proteins was confirmed with four dengue virus culture broth (from serotype 1 to 4) as proof-of-concept. The detection performance of our sensor incorporating DGV BP1 peptides showed a statistically significant difference. These results indicate that this strategy can potentially be used to detect the dengue virus antigen, NS1, and to diagnosis dengue fever within a miniaturized portable device in point-of-care testing.

Dengue virus: a review on advances in detection and trends - from conventional methods to novel biosensors

Dengue virus is an important arbovirus infection which transmitted by the Aedes female mosquitoes. The attempt to control and early detection of this infection is a global public health issue at present. Because of the clinical importance of its detection, the main focus of this review is on all of the methods that can offer the new diagnosis strategies. The advantages and disadvantages of reported methods have been discussed comprehensively from different aspects like biomarkers type, sensitivity, accuracy, rate of detection, possibility of commercialization, availability, limit of detection, linear range, simplicity, mechanism of detection, and ability of usage for clinical applications. The optical, electrochemical, microfluidic, enzyme linked immunosorbent assay (ELISA), and smartphone-based biosensors are the main approaches which developed for detection of different biomarkers and serotypes of Dengue virus. Future efforts in miniaturization of these methods open the horizons for development of commercial biosensors for early-diagnosis of Dengue virus infection. Graphical abstract Transmission of Dengue virus by the biting of an Aedes aegypti mosquito, the symptoms of Dengue hemorrhagic fever and the structure of Dengue virus and application of biosensors for its detection.

Robust immunosensing system based on biotin-streptavidin coupling for spatially localized femtogram mL-1 level detection of interleukin-6

Detection of a very low amount of cytokines such as interleukin-6 (IL-6) in clinical fluids is important in biomedical research and clinical applications. Here, we demonstrate spatially-localized ultrasensitive (femtogram mL^-1) level detection of IL-6 in serum and in cell culture media. Our approach is based on a sandwich immunosensor fabricated on the surface of an optical fibre. Firstly, the biotinylated IL-6 capture antibody was immobilized on the fibre surface by biotin-streptavidin coupling. Then the fabricated fibre was used for capturing IL-6 followed by exposure to detection antibody which was labeled with the fluorescent magnetic nanoparticles to report the signal. A linear relationship between IL-6 concentration and the fluorescence signal was obtained in the range from 0.4pgmL^-1 to 400pgmL^-1 of IL-6, with the limit of detection down to 0.1pgmL^-1. In addition, this optical fibre sensor was successfully applied for the localized detection of IL-6 with the spatial resolution of 200µm and a sample volume of 1µL. Finally, the performance of the fibre sensor was demonstrated by detection of IL-6 secreted by BV-2 cells with comparable performance of the conventional enzyme-linked immunosorbent assay (ELISA).

Low coherence digital holography microscopy based on the Lorenz-Mie scattering model

We demonstrate the use of low spatial and temporal coherence holography microscopy, based on the Lorenz-Mie model, using the standard tungsten-halogen lamp present in an inverted microscope. An optical model is put forward to incorporate the effect of spectral width and different incidence angles of the incident light determined by the aperture at the back focal plane of the condenser lens. The model is validated for 899 nm diameter polystyrene microspheres in glycerol, giving a resolution of 0.4% for the index of refraction and 2.2% for the diameter of the particles.

Polymethacrylate Coated Electrospun PHB Fibers as a Functionalized Platform for Bio-Diagnostics: Confirmation Analysis on the Presence of Immobilized IgG Antibodies against Dengue Virus

In this article, a combination of far field electrospinning (FFES) and free-radical polymerization has been used to create a unique platform for protein immobilization via the physical attachment of biomolecules to the surface of the fiber mats. The large specific surface area of the fibers with its tailored chemistry provides a desirable platform for effective analyte-surface interaction. The detailed analysis of protein immobilization on a newly developed bio-receptive surface plays a vital role to gauge its advantages in bio-diagnostic applications. We relied on scanning electron microscopy (SEM), diameter range analysis, and X-ray photoelectron spectroscopy (XPS), along with thermal gravimetric analysis (TGA), water-in-air contact angle analysis (WCA), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) to study our developed platforms and to provide valuable information regarding the presence of biomolecular entities on the surface. Detailed analyses of the fiber mats before and after antibody immobilization have shown obvious changes on the surface of the bioreceptive surface including: (i) an additional peak corresponding to the presence of an antibody in TGA analysis; (ii) extra FTIR peaks corresponding to the presence of antibodies on the coated fiber platforms; and (iii) a clear alteration in surface roughness recorded by AFM analysis. Confirmation analyses on protein immobilization are of great importance as they underlay substantial grounds for various biosensing applications.

Ammonia plasma-treated electrospun polyacrylonitryle nanofibrous membrane: the robust substrate for protein immobilization through glutaraldhyde coupling chemistry for biosensor application

The surface of polyacrylonitrile electrospun nanofibrous membrane (PAN NFM) was aminated by the ammonia plasma treatment. The content of amine groups has been estimated for different time of plasma treatment. The newly generated amine groups were successfully activated by glutaraldehyde (Ga) for the covalent attachment of the protein molecules on the NFM surface. Bio-functionalization of ammonia plasma treated PAN NFM was carried out by the primary antibodies (Ab) immobilization as a protein model through Ga coupling chemistry. For comparison, the immobilization of Ab was also performed through physical interactions. Attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) was used for the characterization of surface functional groups of PAN NFM after different modifications. The surface morphology of the NFM after immobilization was characterized using scanning electron microscope (SEM). The efficacy of Ab immobilization was estimated by enzyme-linked immuno sorbent assay (ELISA) method. X- Ray photoelectron spectroscopy (XPS) was performed to confirm the covalent immobilization of Ab on the modified PAN NFM. Results show that ammonia plasma treatment effectively increased the amount of Ab immobilization through Ga coupling chemistry. Our findings suggest that this is a versatile model for the preparation of stable bio-functionalized NFM which is applicable in different field of biomedical science.

Microsphere integrated microfluidic disk: synergy of two techniques for rapid and ultrasensitive dengue detection

The application of microfluidic devices in diagnostic systems is well-established in contemporary research. Large specific surface area of microspheres, on the other hand, has secured an important position for their use in bioanalytical assays. Herein, we report a combination of microspheres and microfluidic disk in a unique hybrid platform for highly sensitive and selective detection of dengue virus. Surface engineered polymethacrylate microspheres with carefully designed functional groups facilitate biorecognition in a multitude manner. In order to maximize the utility of the microspheres' specific surface area in biomolecular interaction, the microfluidic disk was equipped with a micromixing system. The mixing mechanism (microballoon mixing) enhances the number of molecular encounters between spheres and target analyte by accessing the entire sample volume more effectively, which subsequently results in signal amplification. Significant reduction of incubation time along with considerable lower detection limits were the prime motivations for the integration of microspheres inside the microfluidic disk. Lengthy incubations of routine analytical assays were reduced from 2 hours to 5 minutes while developed system successfully detected a few units of dengue virus. Obtained results make this hybrid microsphere-microfluidic approach to dengue detection a promising avenue for early detection of this fatal illness.

Polymethacrylate coated electrospun PHB fibers: An exquisite outlook for fabrication of paper-based biosensors

Electrospun polyhydroxybutyrate (PHB) fibers were dip-coated by polymethyl methacrylate-co-methacrylic acid, poly(MMA-co-MAA), which was synthesized in different molar ratios of the monomers via free-radical polymerization. Fabricated platfrom was employed for immobilization of the dengue antibody and subsequent detection of dengue enveloped virus in enzyme-linked immunosorbent assay (ELISA). There is a major advantage for combination of electrospun fibers and copolymers. Fiber structre of electrospun PHB provides large specific surface area available for biomolecular interaction. In addition, polymer coated parts of the platform inherited the premanent presence of surface carboxyl (-COOH) groups from MAA segments of the copolymer which can be effectively used for covalent and physical protein immobilization. By tuning the concentration of MAA monomers in polymerization reaction the concentration of surface -COOH groups can be carefully controlled. Therefore two different techniques have been used for immobilization of the dengue antibody aimed for dengue detection: physical attachment of dengue antibodies to the surface and covalent immobilization of antibodies through carbodiimide chemistry. In that perspective, several different characterization techniques were employed to investigate the new polymeric fiber platform such as scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA) measurement and UV-vis titration. Regardless of the immobilization techniques, substantially higher signal intensity was recorded from developed platform in comparison to the conventional ELISA assay.