The development of new methods and concepts to visualize massive amounts of data holds the promise to revolutionize the way scientific results are analyzed, especially when tasks such as ...classification and clustering are involved, as in the case of sensing and biosensing. In this paper we employ a suite of software tools, referred to as PEx-Sensors, through which projection techniques are used to analyze electrical impedance spectroscopy data in electronic tongues and related sensors. The possibility of treating high dimension datasets with PEx-Sensors is advantageous because the whole impedance vs. frequency curves obtained with various sensing units and for a variety of samples can be analyzed at once. It will be shown that non-linear projection techniques such as Sammon's Mapping or IDMAP provide higher distinction ability than linear methods for sensor arrays containing units capable of molecular recognition, apparently because these techniques are able to capture the cooperative response owing to specific interactions between the sensing unit material and the analyte. In addition to allowing for a higher sensitivity and selectivity, the use of PEx-Sensors permits the identification of the major contributors for the distinguishing ability of sensing units and of the optimized frequency range. The latter will be illustrated with sensing units made with layer-by-layer (LbL) films to detect phytic acid, whose capacitance data were visualized with Parallel Coordinates. Significantly, the implementation of PEx-Sensors was conceived so as to handle any type of sensor based on any type of principle of detection, representing therefore a generic platform for treating large amounts of data for sensors and biosensors.
Venous thromboembolism (VTE) is a serious clinical condition which early and accurate diagnosis may contribute to the reduction of associated morbidity and mortality. VTE occurs when a blood clot ...(thrombus) blocks the vein blood flow causing deep vein thrombosis (DVT) and, when it migrates to the lungs, it may clog the pulmonary arteries characterizing pulmonary embolism (PE). Analysis using fibrin degradation products or D-dimer and coagulation factor VIII may assist early diagnosis of VTE. Thus, two immunosensors were built using layer-by-layer (LbL) films technique, one containing the anti-D-dimer immobilized on polyethylene imine (PEI) and another the anti-FVIII on silk fibroin (SF). Immunosensor response, the antigen-antibody specific interaction, was investigated using cyclic voltammetry. When immunosensors, PEI/anti-D-dimer and SF/anti-FVIII, were exposed to antigens, D-dimer and Factor VIII, the voltammograms area and current were significantly increased with increasing specific antigen concentration. The specific interaction was confirmed with control experiments, electrodes containing only PEI or SF, that no significant changes in the voltammogram responses were observed and principal component analysis confirmed these results. The films formation and response were verified using scanning electronic microscopy (SEM). The developed immunosensor seems to be a promising and effective early complementary exam to assist in the VTE diagnosis, through the combined response of two biomarkers very sensible.
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•Simultaneous detection of D-dimer and Factor VIII to support Venous Thromboembolism (VTE) detection.•The antibodies against D-dimer and Factor VIII were immobilized on polyethylene imine and silk fibroin, respectively.•Immunosensor seems be a promising to assist in the VTE diagnosis, through the combined response of two biomarkers.
Immunosensors based on electrical impedance spectroscopy (EIS) are increasingly being used as a fast and potentially low cost method for clinical diagnostics. In this work we fabricated immunosensors ...by depositing layer-by-layer (LbL) films made with an antigenic peptide (p17-1) sequence (H2N-LSGGELDRWEKIRLRPGG-OH) and lignin on interdigitated gold electrodes, which could detect anti-p17 (HIV, human immune deficiency virus) antibodies (Ab) in phosphate buffered solutions (PBS). The molecular recognition interaction between the peptide (p17-1) and the specific Ab (anti-p17) yielded substantial changes in morphology of the with LbL films, with increased roughness according to atomic force microscopy data. This interaction is behind the high sensitivity of the immunosensor. Indeed, from the EIS results, we noted that the capacitance increased significantly with the specific Ab concentration, before getting close to saturation of available peptide sites at high concentrations. Concentrations of specific antibodies as low as 0.1ng/mL could be detected and the immunosensors had their activity preserved for two months at least. The selectivity of the immunosensor was confirmed with two types of control experiments. First, no changes in impedance were observed when the lignin/peptide LbL immunosensor was immersed into a PBS solution containing the non-specific Ab (anti-HCV for Hepatitis C) antibodies. Furthermore, for sensing units made LbL films of lignin only, the electrical response was not affected by adding specific antibodies into the PBS buffer. The successful immunosensing for HIV with antigenic peptides in a lignin matrix is also relevant for valorization of lignin, which is an important biomass component in the sugar and ethanol industry, and brings the prospect for all-organic, biocompatible sensors if implantation is ever required.
•Immunosensors have been developed with nanostructured films for detecting HIV.•The immunosensors were highly sensitive and selective when the impedance spectroscopy data are treated with information visualization methods.•Antigenic peptides were used, which warranted long life times for the immunosensors.•The sensing units were made with nanostructured films where lignin served as matrix for immobilizing the peptides.•Valorization of lignin is achieved with a noble application.
A direct, low-cost method to determine the concentration of lactose is an important goal with possible impact in various types of industry. In this study, a biosensor is reported that exploits the ...specific interaction between lactose and the enzyme β-galactosidase (β-Gal) normally employed to process lactose into glucose and galactose for lactose-intolerant people. The biosensor was made with β-Gal immobilized in layer-by-layer (LbL) films with the polyelectrolyte poly(ethylene imine) (PEI) and poly(vinyl sufonate) (PVS) on an indium tin oxide (ITO) electrode modified with a layer of Prussian Blue (PB). With an ITO/PB/(PEI/PVS)1(PEI/β-Gal)30 architecture, lactose could be determined with an amperometric method with sensitivity of 0.31 μA mmol–1 cm–2 and detection limit of 1.13 mmol L–1, which is sufficient for detecting lactose in milk and for clinical exams. Detection occurred via a cascade reaction involving glucose oxidase titrated as electrolytic solution in the electrochemical cell, while PB allowed for operation at 0.0 V versus saturated calomel electrode, thus avoiding effects from interfering species. Sum-frequency generation spectroscopy data for the interface between the LbL film and a buffer containing lactose indicated that β-Gal lost order, which is the first demonstration of structural effects induced by the molecular recognition interaction with lactose.
A bioanalytical method for HIV detection based on surface-enhanced Raman scattering (SERS) is described. The assay targeted the peptide p17-1. This peptide sequence is present in the protein p17, a ...structural protein essential in the life cycle of the human immunodeficiency retrovirus (HIV). The antibody anti-p17 was immobilized in a planar gold surface using self-assembled techniques. This planar platform was used to capture the target analyte (p17-1 peptide). The peptide detection was carried out using specially designed SERS probes, consisting of gold nanoparticles coated with a Raman reporter molecule (Nile Blue A) and functionalized with anti-p17. This sandwich assay led to the successful detection of the peptide p17-1 at 40.8 ng/mL levels. The sandwich assay described here demonstrated that the SERS technique can rival more common fluorescence methods, such as ELISA, in the detection HIV-type virus.
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High molecular weight Chi modulates the orientation of SF groups (Try and Try).Chi and SF LbL films were successfully used as template for phytase immobilization.The matrix ...improved the performance of phytic acid biosensing.
In this paper, we show that chitosan may induce conformation changes in silk fibroin (SF) in layer-by-layer (LbL) films, which were used as matrix for immobilization of the enzyme phytase to detect phytic acid. Three chitosan (CH) samples possessing distinct molecular weights were used to build CH/SF LbL films, and a larger change in conformation from random coils to β-sheets for SF was observed for high molecular weight chitosan (CHH). The CHH/SF LbL films deposited onto interdigitated gold electrodes were coated with a layer of phytase, with which phytic acid could be detected down to 10⿿9M using impedance spectroscopy as the principle of detection and treating the data with a multidimensional projection technique. This high sensitivity may be ascribed to the suitability of the CHH/SF matrix, thus indicating that the molecular-level interactions between chitosan and SF may be exploited in other biosensors and biodevices.
The peptide NS5A-1 (PPLLESWKDPDYVPPWHG), derived from hepatitis C virus (HCV) NS5A protein, was immobilized into layer-by-layer (LbL) silk fibroin (SF) films. Deposition was monitored by UV–vis ...absorption measurements at each bilayer deposited. The interaction SF/peptide film induced secondary structure in NS5A-1 as indicated by fluorescence and circular dichroism (CD) measurements. Voltammetric sensor (SF/NS5A-1) properties were observed when the composite film was tested in the presence of anti-HCV. The peptide–silk fibroin interaction studied here showed new architectures for immunosensors based on antigenic peptides and SF as a suitable immobilization matrix.
Several countries, as Brazil, have public policies for periconceptional folic acid supplementation (FAS) in order to prevent unfavorable outcomes. Our aim was to evaluate the FAS situation in a ...public reference hospital from Southern Brazil. This study included all mothers who had children born at the Hospital Materno Infantil Presidente Vargas, RS, Brazil, in a 1-year period. Data collection was conducted through interviews with application of a clinical protocol and analysis of the patients' records. FAS was defined as the use of folic acid in any period of the periconceptional period, irrespective of the duration and amount. We also classified those mothers who correctly followed the national recommendation proposed by the Health Ministry of Brazil. The sample consisted of 765 mothers evaluated soon after childbirth. Their ages ranged from 12 to 45 years (mean 25.2 years). The overall level of FAS was 51.5%, and the use according to the national recommendation occurred in only 1.6%. Factors associated with non-FAS consisted of lower maternal age (p = .009) and maternal schooling (p = .023), higher number of pregnancies (p = .003), fewer prenatal visits (p = .050) and later prenatal care onset (p = .037). Periconceptional FAS in our midst seems to be very far from the ideal goal. Susceptible groups appeared to be mothers who were younger, less educated, multiparous, and had inadequate prenatal care. We believe that efforts of education and awareness should be especially targeted for these groups. These recommendations should also be strengthened among those who prescribe the FAS.
Melanin in liposomes (A) and LbL films (B). A much stronger adsorption occurred for the film with immobilized liposomes, denoted by the darker color in PEI/DPPG
+
melanin.
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► Liposomes ...protect the melanin in aqueous solution ► Melanin incorporated into liposome may be immobilizated in layer-by-layer films
The use of melanin in bioinspired applications is mostly limited by its poor stability in solid films. This problem has been addressed here by incorporating melanin into dipalmitoyl phosphatidyl glycerol (DPPG) liposomes, which were then immobilized onto a solid substrate as an LbL film. Results from steady-state and time-resolved fluorescence indicated an increased stability for melanin incorporated into DPPG liposomes. If not protected by liposomes, melanin looses completely its fluorescence properties in LbL films. The thickness of the liposome-melanin layer obtained from neutron reflectivity data was 4.1
±
0.2
nm, consistent with the value estimated for the phospholipid bilayer of the liposomes, an evidence of the collapse of most liposomes. On the other hand, the final roughness indicated that some of the liposomes had their structure preserved. In summary, liposomes were proven excellent for encapsulation, thus providing a suitable environment, closer to the physiological conditions without using organic solvents or high pHs.
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