Gold-coated Sensor Research Articles

Enzymatic Plasmonic Optical Fiber Biosensor for Uric Acid Detection

Uric acid plays important roles in the body, acting as an antioxidant, contributing to the elimination of metabolic waste, and helping to combat some infections. Alterations in uric acid concentration can be important indicators of disease and their real-time and point-of-care monitoring is of extreme importance, for instance in primary care facilities. Optical fibre biosensors are a promising option, allowing real-time detection, quantification, and monitoring of uric acid concentrations in blood plasma or urine. In this work, enzymatic plasmonic sensors were developed for the detection of uric acid using multimode optical fibres composed of a 400 µm silica core and a polymer cladding. To prepare the sensors, the coating and cladding were removed from a section at the fibre tip, and nano film of gold was deposited on their surface, obtaining gold-coated sensors at the fibre tips (Au-tips). Initially, the sensor was characterized to bulk refractive index, exhibiting a sensitivity of 1420.7 ± 59.8 nm/RIU. The Au-tip was biofunctionalized with the enzyme uricase and detection tests were carried out. Uric acid detection tests revealed a response consistent with the Michaelis-Menten function, which was employed to assess the enzymatic kinetics of uricase immobilized on the Au-tips.

High-speed nanoscale tribology enabled by combined QCM/AFM

Forming a fundamental understanding of tribological processes on the atomic scale has the potential to revolutionize the control of friction and wear in macroscopic mechanical systems. On the other hand, methods such as atomic force microscopy (AFM) that provide nanoscale spatial resolution are severely limited in terms of scanning speed when compared with macroscopic mechanical processes, leading to a “speed gap” between fundamental and applied tribology that spans several orders of magnitude. Here, we propose a new method combining AFM experiments with simultaneous quartz crystal microbalance (QCM) measurements for high-speed nanoscale tribology. In particular, scanning speed and vibration amplitude are controlled by QCM whereas normal loads are controlled by AFM. Complementary data are simultaneously recorded in the form of nanoscale, two-dimensional maps of frequency shifts and lateral forces provided by the QCM and AFM, respectively. Proof-of-principle results are presented on a gold-coated QCM sensor surface patterned with a graphene array, whereby stick and partial slip regimes are observed as a function of sliding speed.

Surface Plasmon Resonance-Based Gold-Coated Hollow-Core Negative Curvature Optical Fiber Sensor.

The hollow-core fiber-based sensor has garnered high interest due to its simple structure and low transmission loss. A new hollow-core negative-curvature fiber (HC-NCF) sensor based on the surface plasmon resonance (SPR) technique is proposed in this work. The cladding region is composed of six circular silica tubes and two elliptical silica tubes to reduce fabrication complexity. Chemically stable gold is used as a plasmonic material on the inner wall of the sensor structure to induce the SPR effect. The proposed sensor detects a minor variation in the refractive indices (RIs) of the analyte placed in the hollow core. Numerical investigations are carried out using the finite element method (FEM). Through the optimization of structural parameters, the maximum wavelength sensitivity of 6000 nm/RIU and the highest resolution of 2.5 × 10-5 RIU are achieved in the RI range of 1.31 to 1.36. In addition, an improved figure of merit (FOM) of 2000 RIU-1 for Y-polarization and 857.1 RIU-1 for X-polarization is obtained. Because of its simple structure, high sensitivity, high FOM, and low transmission loss, the proposed sensor can be used as a temperature sensor, a chemical sensor, and a biosensor.

Experimental Evaluation of Quantum Dots and Antibodies Conjugation by Surface Plasmon Resonance Spectroscopy.

The application of antibody-functionalized quantum dots (QDs) in different areas has been widely described in the literature. However, a standard routine method for obtaining information on the conjugation efficiency of QDs with antibodies in terms of the interaction of the functionalized QDs with a specific antigen is still lacking. Herein, surface plasmon resonance (SPR) spectroscopy is proposed for this purpose. Gold-coated SPR sensor disks were modified with a self-assembled monolayer of 11-mercaptoundecanoic acid, and carbodiimide cross-linker chemistry was used to covalently immobilize the CD44 biomarker on the premodified surface (Au/CD44). Meanwhile, QDs functionalized with amine-derivatized polyethylene glycol (PEG) (QDs-NH2) were chosen for conjugation with antibodies because of their low non-specific adsorption on the Au/CD44 surface. Prior to conjugation, the surface binding capacity (Bmax) and equilibrium dissociation constant (KD) of the specific antibodies against CD44 (anti-CD44) were found to be 263.32 ± 2.44 m° and 1.00 × 10−7 ± 2.29 × 10−9 M, respectively. QDs-NH2 and anti-CD44 were conjugated at their initial molar ratios of 1:3, 1:5, 1:10 and 1:12. SPR measurements showed that the conjugates (QDs-anti-CD44) prepared using 1:10 and 1:12 molar ratios interacted comparably with immobilized CD44 biomarkers. The equilibrium angles in the case of 10- and 12-fold concentrations of anti-CD44 were calculated to be 60.43 ± 4.51 and 61.36 ± 4.40 m°, respectively. This could be explained by the QDs-NH2 and anti-CD44 having a similar surface loading (about four molecules per QDs-NH2) and similar hydrodynamic diameters, which were 46.63 ± 3.86 and 42.42 ± 0.80 nm for the 1:10 and 1:12 ratios, respectively. An initial QDs-NH2: anti-CD44 molar ratio of 1:10 was chosen as being optimal. SPR spectroscopy proved to be the right choice for QDs-anti-CD44 conjugation optimization, and can be used for the evaluation of conjugation efficiency for other nanostructures with various bio-recognition molecules.

Chitosan mediated layer-by-layer assembly based graphene oxide decorated surface plasmon resonance biosensor for highly sensitive detection of β-amyloid

Alzheimer's disease (AD), and its consequent effect primarily clinical dementia, Parkinson’s disease dementia, etc. currently bring potential avenues for diagnosis centered on identification of beta-amyloid1–42 (Aβ1–42). Unfortunately, techniques engaged in AD core biomarker (Aβ1–42) detection are majorly suffering from poor sensitivity and selectivity. Thus, we fabricated graphene oxide (GO) surface decorated chitosan (CS) mediated layer-by-layer (LbL) assembly based surface plasmon resonance (SPR) biosensor for highly sensitive and selective recognition of Aβ1–42. Briefly, silver nanoparticles (AgNPs) and GO synthesis were achieved through a greener approach. LbL assembly was designed using CS and polystyrene sulphonate (PSS) on surface of AgNPs (AgNPs-CS-PSS-CS) and then antibodies of Aβ (anti-Aβ) were fixed on LbL assembly (AgNPs-CS-PSS-CS@anti-Aβ). Herein, amine functionality of CS offers a plethora of sites for anti-Aβ antibody immobilization that gives specific direction, high selectivity, and an adequate amount of antibody immobilization. For fabrication, synthesized GO was immobilized on an amine-modified gold-coated sensor chip via carbodiimide chemistry followed by AgNPs-CS-PSS-CS@anti-Aβ immobilization on an activated GO surface. Inimitable features of LbL assembly showed improved selectivity towards Aβ peptide whereas utilization of affinity biotransducer with a combination of plasmonic and non-plasmonic nanomaterial improved sensitivity and selectivity. Consequently, linearity range and limit of detection (LOD) of Aβ1–42 antigens were found to be 2 fg/mL to 400 ng/mL and 1.21 fg/mL, respectively. Moreover, analysis of Aβ1–42 in AD-induced rats confirmed the real-time-applicability of the designed SPR biosensor. Hence, GO surface decorated AgNPs-CS-PSS-CS@anti-Aβ mediated SPR biosensor would provide a novel approach for exceptionally sensitive and selective Aβ detection.

Synthesis of mucin type core 3 and core 5 structures and their interaction analysis with sugar chips

For the functional analysis of mucin related glycan, we synthesized core 3 and 5 structures of mucin type O-glycan and investigated their binding interaction with lectins using sugar chip technology. The construction of Tn antigen moiety containing α-N-acetylgalactosamine residue was achieved by α-selective glycosylation of 2-azido-6-tert-butyldiphenylsilyl-3,4-di-O-chloroacetyl-2-deoxy-galctopyranosyl imidate and glucose moiety, which acts as a hydrophilic spacer when immobilized on a gold-coated sensor chip. Core 3 and core 5 structures were synthesized by the glycosylation of appropriate N-acetylglucosamine and N-galactosamine donors, respectively, and were converted into sugar-chain ligand conjugates according to the method reported. The interaction analysis of lectins with sugar chips coated with ligand conjugates was performed with a surface plasmon resonance (SPR) biosensor. The specific interaction was observed between the core 3 structure and Jacalin (JAC) and kinetic parameters were estimated as ka = 1.5 × 104, kd = 5.8 × 10−3, and KD = 3.8 × 10−7.

Highly sensitive gold-coated surface plasmon resonance photonic crystal fiber sensor in near-infrared region

In this research paper, we propose a highly sensitive yet simple design hexagonal photonic crystal fiber (PCF) core-based surface plasmon resonance (SPR) refractive index (RI) sensor. The unknown target analyte and the plasmonic material, gold (Au) are placed at the exterior of the sensor surface for the feasibility of the operation. Twelve purely circular air-holes in two rings constitute PCF structure which makes the fabrication process realizable and practical. Numerical investigations are carried out utilizing the full-vector finite element method (FEM) to obtain the sensing performance of the PCF-SPR structure. After optimizing the structural parameters, the proposed PCF-SPR sensor obtains the highest wavelength sensitivity of 36000 nm/RIU and the highest amplitude sensitivity of 642.53 RIU-1, for an analyte RI range of 1.395 to 1.420 in the near-infrared wavelength regime (800 nm − 1200 nm). Aside from that, the sensor attained the maximum wavelength resolution and amplitude resolution of 2.77×10-6 RIU and 1.55×10-5RIU-1 respectively to assure excellent detection accuracy of smallest RI changes. Furthermore, the sensor achieved the highest Figure of Merit of 257.14 RIU-1. Thus, the proposed PCF-SPR sensor has the potential to detect unknown RI in a variety of applications including biosensing.

SSM-based electrophysiology, a label-free real-time method reveals sugar binding & transport events in SGLT1

Here, we present a solid-supported membrane (SSM)-based electrophysiological approach to study sugar binding and Na+/glucose cotransport by SGLT1 in membrane vesicles. SSM-based electrophysiology delivers a cumulative real-time current readout from numerous SGLT1 proteins simultaneously using a gold-coated sensor chip.In contrast to conventional techniques, which mainly operate with voltage steps, currents are triggered by sugar or sodium addition. Sugar concentration jumps in the presence of sodium lead to transport currents between 5 and 10 nA. Remarkably, in the absence of sodium (i.e. no transport), we observed fast pre-steady-state (PSS) currents with time constants between 3 and 10 ms. These PSS currents mainly originate from sugar binding. Sodium binding does not induce PSS currents. Due to high time resolution, PSS currents were distinguished from transport and eventually correlated with conformational transitions within the sugar translocation pathway.In addition, we analyzed the impact of driving forces on transport and binding currents, showing that membrane voltage and sodium concentration gradients lead to an increased transport rate without affecting sugar binding kinetics. We also compared Na+/sugar efflux with physiologically relevant influx and found similar transport rates, but lower affinity in efflux mode.SSM-based electrophysiology is a powerful technique, which overcomes bottlenecks for transport measurements observed in other techniques such as the requirement of labels or the lack of real-time data. Rapid solution exchange enables the observation of substrate-induced electrogenic events like conformational transitions, opening novel perspectives for in-depth functional studies of SGLT1 and other transporters.

Design and analysis of highly sensitive solid core gold-coated hexagonal photonic crystal fiber sensor based on surface plasmon resonance

A surface plasmon-based hexagonal photonic crystal fiber sensor is numerically computed and studied covering a large span of analyte refractive index from 1.33 to 1.40. Structural design parameters are optimized to improve the sensor performance. Investigation of sensor sensitivity has been performed by analyzing the electromagnetic behavior of light using finite element method-based mode solver. The studied sensor yields the maximum amplitude sensitivity of 3958.84 RIU − 1 at analyte RI of 1.39 and moderate wavelength sensitivity of 8000 nm RIU − 1 at analyte RI of 1.40. The observed results are also presented by changing the gold layer thickness, lattice period, and air hole diameter. The reported plasmonic sensor is an appealing aspirant in the field of biochemical sensing, biomolecule detection, and biological sample recognition.

Highly birefringent gold-coated SPR sensor with extremely enhanced amplitude and wavelength sensitivity

In this manuscript, we present a unique and simply designed surface plasmon resonance-based PCF biosensor that shows high sensing performance. The numerical technique finite element method is utilized to evaluate the fiber's guiding characteristics. Our design has a thin layer of gold (Au) surrounding the fiber, which is a stable plasmonic material. The strategic arrangement of the circular-shaped airholes inside the fiber enhances the overall performance of the sensor. After precise investigation of the various fiber parameters, the maximum amplitude sensitivity was found to be 3.35 × 103 RIU−1 for x-polarization and 5.00 × 103 RIU−1 for y-polarization in a sensing range of refractive index 1.33–1.41. The sensor exhibited a maximum birefringence of 2.23 × 10–3 and a maximum wavelength sensitivity of 3.00 × 104 nm/RIU and 3.25 × 104 nm/RIU for x- and y-polarization, respectively. The sensor resolution (amplitude) is found to be 2.98 × 10–6 for x-polarization and 2.00 × 10–6 for y-polarization, whereas the sensor resolution (wavelength) is 3.33 × 10–6 and 3.08 × 10–6 for x-polarization and y-polarization, respectively. Moreover, we obtained a high figure of merit of 4.48 × 102 RIU−1 for x-polarization and 4.44 × 102 RIU−1 for y-polarization. For its simplicity in design and high performance, this biosensor has a wide range of applications in the field of sensing unknown biomolecules and organic substances.

High adhesion ability of anammox granular microbes directly revealed by QCM-D technique

Anammox bacteria are widely found to grow in bioaggregates form, but the reason for their high aggregation ability remains elusive. In this study, four kinds of sludge, i.e., anammox granules, anaerobic granules, aerobic granules, and partial nitrification flocs, were studied and compared to investigate their differences in adherence properties. We directly explored the adherence properties of sludge samples before and after extracellular polymeric substances (EPS) extraction, using quartz-crystal microbalance technique with dissipation monitoring technique. Results showed that EPS indeed stimulated the adherence properties of all sludge samples. The most striking feature here is that anammox consortia had the highest adhesion rate and mass, and formed the most compact layer on the gold-coated sensor surfaces both before and after EPS extraction among the four sludge samples, indicating their inherent high adhesion ability. The composition and spectral characteristics of EPS samples were also investigated, and it reveals that the relatively high extracellular proteins/polysaccharides ratio of anammox granules (3.2 ± 0.4) rather than total EPS concentration had contributed to their high adhesion ability. The findings are helpful for understanding the adherence properties of anammox bacteria, and will serve as a guide for further researches to exploring the aggregation process of anammox bacteria.

Molecularly imprinted polymer nanogel-based fluorescence sensing of pork contamination in halal meat extracts

Pork contamination is a serious concern for the global halal food market because many manufacturers commonly use pork instead of beef to reduce production costs. In this study, a highly sensitive fluorescent molecularly imprinted polymer nanogel (F-MIP-NG)-based sensor was developed for rapid porcine serum albumin (PSA) detection to investigate pork contamination in halal meat extracts. F-MIP-NGs were prepared via molecular imprinting and conjugation with ATTO 647N as the fluorescent reporter molecule for the post-imprinting modification (PIM) and then immobilized on gold-coated sensor chips. For achieving rapid and easy measurement, the fluorescence response was measured using a custom-made liquid handling robot equipped with a fluorescence microscope. The fluorescence response increased with increasing PSA concentration. Under optimal conditions, the F-MIP-NG-based sensors exhibited high sensitivity, a detection limit of 40 pM, a linear range of 0.25–5 nM, and excellent affinity and selectivity towards PSA, compared to potentially interfering proteins. Moreover, it was more efficient to detect beef contamination in 1 wt% pork contamination compared to the real-time polymerase chain reaction. Collectively the good analytical performance, high rates of recovery in real meat extract samples, fast detection, and a low detection limit of pork contamination (0.1 wt%) indicated the potential of the proposed sensor for detecting PSA as a marker of pork contamination in halal meat samples. The proposed sensing system based on the MIPs would open a way to establish highly sensitive and rapid sensing systems (<5 min/sample) for food analysis.

Multicore bi-layer gold-coated SPR-based sensor for simultaneous measurements of CFC and HCFC

Global warming is an alarming issue in our daily life. As we know that CFCs and HCFCs have a great impact on ozone depletion and global warming process. So, there must be a cheaper way to detect CFCs and HCFCs from refrigerant products like refrigerator, aerosols, air-conditioner, etc. So, for the very first time, this paper proposes a novel highly sensitive dual-core bi-layer gold-coated surface plasmon resonance (DB-SPR)-based photonic crystal fiber (PCF) for sensing CFCs and HCFCs in the field of chemical and biosensing. The analysis is assumed at 20[Formula: see text]C (293 K) for the concentration level of CFCs and HCFCs ranging between 20% and 80%. The entire numerical evaluation process is done by using finite element method (FEM) with a full vectorial software named COMSOL V-5.1 by examining the number of mesh elements of 228,120 which has better flexibility in the fabrication process. The proposed model can prove itself better than any other models by the justification of the major optical parameters, such as birefringence (B[Formula: see text]), coupling length (L[Formula: see text]), confinement loss ([Formula: see text]), transmittance (T[Formula: see text]), transmittance variance (T[Formula: see text]), power fraction (P[Formula: see text]), amplitude sensitivity (S[Formula: see text]), wavelength sensitivity (S[Formula: see text]), figure of merit (FOM), resolution (Rl[Formula: see text]), resonance (R2), etc. which respectively corresponds to their maximum performance profiles of 0.038, 40 [Formula: see text]m, 1140 dB/cm, −180 dB, 410 dB/RIU, 51%, −3200 RIU[Formula: see text], 30450.43 nm/RIU, 1300, 1.25[Formula: see text]×[Formula: see text]10[Formula: see text], 0.98712. So, it is evident that proposed SPR PCF can be a tough competitor in the field of biosensing and chemical sensing as well as gas sensing.

Adsorption of Amyloidogenic Peptides to Functionalized Surfaces Is Biased by Charge and Hydrophilicity.

Surfaces are abundant in living systems, such as in the form of cellular membranes, and govern many biological processes. In this study, the adsorption of the amyloidogenic model peptides GNNQQNY, NNFGAIL, and VQIVYK as well as the amyloid-forming antimicrobial peptide uperin 3.5 (U3.5) were studied at low concentrations (100 μM) to different surfaces. The technique of a quartz crystal microbalance with dissipation monitoring (QCM-D) was applied as it enables the monitoring of mass binding to sensors at nanogram sensitivity. Gold-coated quartz sensors were used as unmodified gold surfaces or functionalized with self-assembled monolayers (SAMs) of alkanethiols (terminated as methyl, amino, carboxyl, and hydroxyl) resulting in different adsorption affinities of the peptides. Our objective was to evaluate the underlying role of the nature and feature of interfaces in biological systems which could concentrate peptides and impact or trigger peptide aggregation processes. In overall, the largely hydrophobic peptides adsorbed with preference to hydrophobic or countercharged surfaces. Further, the glycoprotein lubricin (LUB) was tested as an antiadhesive coating. Despite its hydrophilicity, the adsorption of peptides to LUB coated sensors was similar to the adsorption to unmodified gold surfaces, which indicates that some peptides diffused through the LUB layer to reach the underlying gold sensor surface. The LUB protein-antiadhesive is thus more effective as a biomaterial coating against larger biomolecules than small peptides under the conditions used here. This study provides directions toward a better understanding of amyloid peptide adsorption to biologically relevant interfaces, such as cellular membranes.

A Novel Approach to Realizing Low-Cost Plasmonic Optical Fiber Sensors: Light-Diffusing Fibers Covered by Thin Metal Films

We have investigated, in a numerical and experimental way, a refractive index (RI) sensor based on surface plasmon resonance (SPR) in a silver-coated light-diffusing fiber (LDF). The experimental tests were conducted using water-glycerine mixtures with refractive indices ranging from 1.332 to 1.388. In the considered refractive index range, the experimental results show a sensitivity of the SPR wavelength to the outer medium’s RI ranging from ~2600 to ~4700 nm/RIU, which is larger than the sensitivity recently reported for a gold-coated LDF sensor (~1200 to ~4000 nm/RIU). The silver-coated sensor is also shown to ensure a higher signal-to-noise ratio (SNR) compared to the gold-coated sensor.

Gold Enhanced Hemoglobin Interaction in a Fabry–Pérot Based Optical Fiber Sensor for Measurement of Blood Refractive Index

A Fabry–Perot based optical fiber sensor to measure the oxygen concentration through monitoring the change of refractive index in red blood cells is reported. The optical fiber sensor with a diameter of 220 μm is made entirely of fused silica glass fibers, which can be integrated within standard brachytherapy seed delivery needle to be used in vivo . Isopropanol solution and pig blood are prepared to produce refractive index in the range 1.344–1.365. Gold is coated to a thickness of 100 nm at the tip of the sensor to enhance the interaction between hemoglobin and light. A fast Fourier transform algorithm is used to analyze the phase angle from the reflected output spectrum. The gold-coated sensor has up to almost ten times higher sensitivity to hemoglobin concentration in blood solutions compared to isopropanol solutions. A sensitivity of 9.82 rad/RIU with a refractive index resolution of 2.09 × 10–3 RIU is achieved for the sensor with a 16 μm thickness diaphragm.

SPR sensor for detection of heavy metal ions: Manipulating the EM waves polarization modes

Water contamination by heavy metals is a common issue encountered in many countries due to industrial and urban wastes in water resources which give health and socio-economic impacts. This work is carried out to investigate the effect of EM wave polarization modes on the sensing properties of surface plasmon resonance (SPR) sensor in detecting heavy metal ions namely mercury (Hg) and plumbum (Pb). Three types of polarization modes such as p-polarized, s-polarized and circular-polarized light were introduced. Gold and silver thin films with thicknesses of 50nm were deposited on top of SPR layer system to excite surface plasmon polaritons (SPPs). The SPR curves were analyzed by studying the FWHM, Q-factor and angle shifting characteristics. We manage to prove theoretically that the SPR phenomena able to be created by using not only the p-polarized light, yet by employing a circular-polarized light. The sensor shows positive respond for both polarization modes, where the troughs were red-shifted about 23.78% as Pb was introduced on the top of the gold-coated SPR sensor. The SPR angles were shifted about 24.45% as the sensor was exposed with Hg metal ions. Different response due to the presence of different analytes exhibits an excellent criteria of high selectivity sensor. In conclusion, the combination of p-polarized light or circular-polarized light and gold thin film able to accentuate the significant role of SPR sensor in detecting heavy metal ions.

Oriented, molecularly imprinted cavities with dual binding sites for highly sensitive and selective recognition of cortisol.

Novel, molecularly imprinted polymers (MIPs) were developed for the highly sensitive and selective recognition of the stress marker cortisol. Oriented, homogeneous cavities with two binding sites for cortisol were fabricated by surface-initiated atom transfer radical polymerization, using a cortisol motif template molecule (TM1) which consists of a polymerizable moiety attached at the 3-carbonyl group of cortisol via an oxime linkage and an adamantane carboxylate moiety coupled with the 21-hydroxyl group. TM1 was orientationally immobilized on a β-cyclodextrin (β-CD)-grafted gold-coated sensor chip by inclusion of the adamantane moiety of TM1, followed by copolymerization of a hydrophilic comonomer, 2-methacryloyloxyethyl phosphorylcholine, with or without a cross-linker, N,N′-methylenebisacrylamide. Subsequent cleavage of the oxime linkage leaves the imprinted cavities that contain dual binding sites—namely, the aminooxy group and β-CD—capable of oxime formation and hydrophobic interaction, respectively. As an application, MIP-based picomolar level detection of cortisol was demonstrated by a competitive binding assay using a fluorescent competitor. Cross-linking of the MIP imparts rigidity to the binding cavities, and improves the selectivity and sensitivity significantly, reducing the limit of detection to 4.8 pM. In addition, detection of cortisol in saliva samples was demonstrated as a feasibility study.

Endothelial cells' biophysical, biochemical, and chromosomal aberrancies in high-glucose condition within the diabetic range.

To date, many studies have been conducted to find out the underlying mechanisms of hyperglycemia-induced complications in diabetes mellitus, attributed to the cellular pathologies of different cells-especially endothelial cells. However, there are still many ambiguities and unresolved issues to be clarified. Here, we investigated the alteration in biophysical and biochemical properties in human umbilical vein endothelial cells exposed to a high-glucose concentration (30mM), comparable to glucose content in type 2 diabetes mellitus, over a course of 120hours. In addition to a reduction in the rate of cell viability and induction of oxidative stress orchestrated by the high-glucose condition, the dynamic of the fatty acid profile-including polyunsaturated, monounsaturated, and saturated fatty acids-was also altered in favor of saturated fatty acids. Genetic imbalances were also detected at chromosomal level in the cells exposed to the abnormal concentration of glucose after 120hours. Moreover, the number of tip cells (CD31+ /CD34+ ) and in vitro tubulogenesis capability negatively diminished in comparison to parallel control groups. We found that diabetic hyperglycemia was associated with a decrease in the cell-cell tight junction and upregulation in vascular endothelial cadherin and zonula occludens (ZO)-1 molecules after 72 and 120hours of exposure to the abnormal glucose concentration, which resulted in a profound reduction in transendothelial electrical resistance. The surface plasmon resonance analysis of the human umbilical vein endothelial cells immobilized on gold-coated sensor chips confirmed the loosening of the cell to cell intercellular junction as well as stable attachment of each cell to the basal surface. Our findings highlighted the disturbing effects of a diabetic hyperglycemia on either biochemical or biophysical properties of endothelial cells.

Optimizing the Mass-Specific Activity of Bilirubin Oxidase Adlayers through Combined Electrochemical Quartz Crystal Microbalance and Dual Polarization Interferometry Analyses.

Two surface analysis techniques, dual polarization interferometry (DPI) and analysis by an electrochemical quartz crystal microbalance with dissipation capability (E-QCM-D), were paired to find the deposition conditions that give the highest and most stable electrocatalytic activity per adsorbed mass of enzyme. Layers were formed by adsorption from buffered solutions of bilirubin oxidase from Myrothecium verrucaria at pH 6.0 to planar surfaces, under high enzyme loading (≥1 mg mL(-1)) for contact periods of up to 2 min. Both unmodified and carboxylate-functionalized gold-coated sensors showed that a deposition solution concentration of 10-25 mg mL(-1) gave the highest activity per mass of adsorbed enzyme with an effective catalytic rate constant (k(cat)) of about 60 s(-1). The densification of adsorbed layers observed by DPI correlated with reduced bioactivity observed by parallel E-QCM-D measurements. Postadsorption changes in thickness and density observed by DPI were incorporated into Kelvin-Voigt models of the QCM-D response. The modeled response matched experimental observations when the adlayer viscosity tripled after adsorption.