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Amyloid-β 1-42 (Aβ1-42) aggregation is considered as an important process in the pathology of Alzheimer's disease (AD). Astaxanthin (ATX), a xanthophyll carotenoid, has a broad range of biological activities such as neuroprotective one. The present study aimed to elucidate the interaction of ATX with Aβ1-42, as well as its effect on Aβ1-42 aggregates under different conditions. Based on the surface plasmon resonance (SPR) results, ATX possessed a high affinity towards Aβ1-42 and the binding process was spontaneous, endothermic, and entropy-driven. Additionally, the binding affinity of ATX to Aβ1-42 was glucose and insulin concentration-dependent. Hydrophobic interactions may play an important role in the interaction between ATX and Aβ1-42. The results of SPR, thioflavin T (ThT), and transmission electron microscopy (TEM) analyses represented the dependency of the anti-amyloid activity of ATX on glucose, insulin, and ATX concentrations. Further, molecular docking results indicated the presence of some same binding sites on Aβ1-42 for ATX and glucose, as well as ATX and insulin, which suggests the possible competition between the molecules for Aβ1-42 binding. Furthermore, the MTT results confirmed that ATX effect on the viability of Aβ1-42-treated PC12 cells was dependent on glucose, insulin, and ATX concentrations. In general, the results provided further insights into the interaction between Aβ1-42 and ATX, as well as the effect of ATX on Aβ1-42 aggregates under various conditions., (Copyright © 2021. Published by Elsevier B.V.)

Surface plasmon resonance (SPR), as an optical technique, has widely been used for the detection of biomarkers. Various investigations have been conducted to address the impacts of SPR on the kinetics of biological interactions between the ligand and its cognate bio-element. Up until now, different biofunctionalized metal nanoparticles (NPs) have been used for the ultrasensitive detection of biomarkers in the enhanced SPR. The enhancement of plasmonic properties and refractive index by means of metal NPs in SPR-based biosensors have significantly improved the diagnosis and monitoring of molecular markers in different disesaes including malignancies. In all the enhanced SPR systems utilized for the direct/sandwich assay, each NP is covalently modified with the analyte molecules like antibody (Ab) or a nucleic acid such as DNA/RNA aptamer (Ap) capable of interaction with the related biomarker(s). The increasing of density near the gold surface and plasmonic coupling of gold film and NPs can provide a large shift in the refractive index enhancing the plasmonic resonance because the SPR response unit is sensitive to alteration of the refractive index and the mass shifting onto the chip surface. In this study, we review the potential applications of two major NPs for enhancing the SPR signals for the detection of molecular biomarkers, including gold and magnetic NPs., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Surface plasmon resonance (SPR) biosensors are most commonly applied for real-time dynamic analysis and measurement of interactions in bio-molecular studies and cell-surface analysis without the need for labeling processes. Up to present, SPR application in stem cell biology and biomedical sciences was underused. Herein, a very simple and sensitive method was developed to evaluate human mesenchymal stem cells trans-differentiation to endothelial lineage of over a period of 14 days based on VE-cadherin biomarker. The SPR signals increased with the increase of the amount of VE-cadherin expression on the cell surface during cell differentiation process. The method was able to detect ≈27 cells permm 2 . No significant effect was observed on the cell viability during the cell attachment to the surface of immune-reactive biochips and during the SPR analysis. Using this highly sensitive SPR method, it was possible to sense the early stage of endothelial differentiation on day 3 in label-free form, whereas flow cytometry and fluorescent microscopy methods were found unable to detect the cell differentiation at the same time. Therefore, the proposed method can rapidly and accurately detect cell differentiation in live cells and label-free manner without any need of cell breakage and has great potential for both diagnostic and experimental approaches., (Copyright © 2017. Published by Elsevier B.V.)

The interaction of bovine serum albumin (BSA) with various drugs, such as antibiotics, due to the importance of BSA in drug delivery has attracted increasing research attention at present. Therefore, the aim of this study was investigation of BSA interaction with rifampicin using surface plasmon resonance (SPR) and molecular docking methods under the imitated physiological conditions ( pH = 7.4 ). BSA immobilization on carboxymethyl dextran hydrogel chip has been carried out after activation with N-hydroxysuccinimide/N-ethyl-N-(3-diethylaminopropyl) carbodiimide. The dose-response sensorgrams of BSA upon increasing concentration of refampicin were attained in SPR analysis. The high affinity of rifampicin to BSA was demonstrated by a low equilibrium constants ( K D ) value ( 3.46 × 10 ? 5 at 40°C). The process of kinetic values changing shows that affinity of BSA to rifampicin decreased with rising temperature. The positive value of both enthalpy change ( ? H ) and entropy change ( ? S ) showed that hydrophobic force plays major role in the BSA interaction with rifampicin. The positive value of ? G was indicative of nonspontaneous and enthalpy-driven binding process. In addition, according to the molecular docking study, hydrogen binding has some contributions in the interaction of rifampicin with BSA.

Propyl gallate (PG) and tert-butylhydroquinone (TBHQ) are examples of phenolic antioxidant agents, which have widespread uses in food industry. In this study, for the first time, we report on the interaction of PG and TBHQ with bovine serum albumin (BSA) using surface plasmon resonance (SPR). In order to modify Au slide with carboxyl functional group, 11-mercaptoundecanoic acid (MUA) was used. After activation of carboxylic groups, BSA was immobilized onto the MUA through both covalent amide bond and electrostatic binding formation. The SPR analysis showed dose-response sensograms of BSA upon increasing concentration of PG and TBHQ. At pH 4.5, the equilibrium dissociation constant or affinity unit (KD) for PG and TBHQ were 1.89e(-10) and 1.49e(-10) and at pH 7.5 were 4.74e(-10) and 1.83e(-9), respectively. The smaller amount of KD demonstrated high food additive molecules affinity to BSA. Based on these findings, it can be concluded that PG and TBHQ molecules can interact with BSA and effectively distributed within the body. Besides, SPR can be considered as useful automatic tool for quantification of PG and TBHQ interaction with serum albumin and it can deliver precise real-time kinetic data., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Introduction: Beta-Boswellic acid (BBA) is a pentacyclic terpene which has been obtained from frankincense and its beneficial effects on neurodegenerative disorders such as Alzheimer's disease (AD) have been addressed. Methods: In the present study, thermodynamic and kinetic aspects of BBA interaction with Tau protein as one of the important proteins involved in AD in the absence and presence of glucose has been investigated using surface plasmon resonance (SPR) method. Tau protein was immobilized onto the carboxy methyl dextran chip and its binding interactions with BBA were studied at physiological pH at various temperatures. Glucose interference with these interactions was also investigated. Results: Results showed that BBA forms a stable complex with Tau (KD=8.45×10-7 M) at 298 K. Molecular modeling analysis showed a hydrophobic interaction between BBA and HVPGGG segment of R2 and R4 repeated domains of Tau. Conclusion: The binding affinity increased by temperature enhancement, while it decreased significantly in the presence of glucose. Both association and dissociation of the BBA-Tau complex were accompanied with an entropic activation barrier; however, positive enthalpy and entropy changes revealed that hydrophobic bonding is the main force involved in the interaction. [ABSTRACT FROM AUTHOR]

Introduction: The detection of micrometer-sized particles like cells is limited by surface plasmon resonance (SPR) biosensors because of having a depth of evanescent wave <500 nm. In this study, for the first time, we exhibited the use of streptavidin-functionalized gold nanorods (GNRs) as intensification labels for detection of cell surface markers in SPR-based biosensors. Methods: The GNRs (ʎ max: 735 nm) were modified with streptavidin using EDC/NHS coupling method and human umbilical vein endothelial cells (HUVECs) were selected as the cell model for detecting VE-cadherin on cell surface using real-time SPR device in the 785 nm wavelength of the laser source. Results: The investigations revealed that the plasmonic field extension produced from the gold layer and GNRs resulted in multiple enhancement of SPR signals when the wavelength of laser source in SPR instrument was matched with the wavelength of maximum absorbance in GNRs. Moreover, the results showed that the growth of ΔRU value in specific and non-specific bindings for various cell number injections were produced with increasing the cell number. Conclusion: The results displayed that cell detection can be performed in real-time form without any need to a time-consuming process used in conventional methods like immunocytochemistry, flow cytometry, and western blotting. [ABSTRACT FROM AUTHOR]

A great body of evidence unveiled the existence of different stem cell types in various tissues with efficient capability for self-renewal and differentiation. Characterization and enumeration of a specific stem cell population seem difficult because these cells consist of a small percentage of cells within different milieu. As such, due to lack of accuracy provided by convenient methods, biosensing techniques are at the center of attention to improve stem cells characterization with high rate of sensitivity and specificity. In line with this statement, bio-sensing, as a sensitive analytical method, opens novel avenues in biological aspects. Physicochemical signals produced by the interaction of analyte-ligands could be applicable for a wide range of scientific fields such as chemical, biochemical, pharmaceutical and immunological purposes. Noninvasive and label free monitoring methods without need to stain, fix, lyse, or fluorescent-tags are desirable in basic stem cell technology and therapeutic applications of cells. We, here, highlighted basic concepts and terms associated with label free biosensor technology for measuring cell entity, evaluating cell surface marker, and peculiarly in the field of stem cell biology. Furthermore, different aspects and methodologies concerning with bio-sensing techniques, including photonic-based detection systems like Surface Plasmon Resonance (SPR) assays, Impedance-based method , Quartz Crystal Microbalance (QCM) and paper based detection of lateral flow biosensor (LFB) were discussed. [ABSTRACT FROM AUTHOR]

Introduction: The interactions between biomacromolecules such as serum albumin (SA) and various drugs have attracted increasing research attention in recent years. However, the study of SA with those drugs that have relatively high hydrophilicity and a lower affinity for SA could be a challenging issue. At the present study, the interaction of bovine SA (BSA) with neomycin as a hydrophilic drug has been investigated using surface plasmon resonance (SPR) and molecular docking methods. Methods: BSA was immobilized on the carboxymethyl dextran hydrogel sensor chip after activation of carboxylic groups through NHS/EDC and, then, the neomycin interaction with BSA at different concentrations (1-128 µM) was investigated. Results: Dose-response sensorgrams of BSA upon increasing concentration of neomycin has been shown through SPR analysis. The small KD value (4.96 e-7 at 40°C) demonstrated high affinity of neomycin to BSA. Thermodynamic parameters were calculated through van't Hoff equation at 4 different temperatures. The results showed that neomycin interacts with BSA via Van der Waals interactions and hydrogen bonds and increase of KD with temperature rising indicated that the binding process was entropy driven. Molecular docking study confirmed that hydrogen bond was the major intermolecular force stabilizing neomycin-BSA complex. Conclusion: The attained results showed that neomycin molecules can efficiently distribute within the body after interaction with BSA in spite of having hydrophilic properties. Besides, SPR can be considered as a useful instrument for study of the interaction of hydrophilic drugs with SA. [ABSTRACT FROM AUTHOR]

Here, we reported the development of a label-free and real-time surface plasmon resonance (SPR) based biosensor for cancer stem cells (CSCs) detection using cell surface biomarker; CD133. The fabricated biosensor was used for detection of this marker in some acute myeloid leukemia (AML) patients and the results were compared with those obtained from flow cytometry (FC) method. CD133 antibody was immobilized on the gold chip surface via EDC/NHS coupling method and binding of the candidate cells to the modified gold sensor surface was monitored after isolation of mononuclear cells from bone marrow of the patients. The method was validated in terms of various parameters such as CD133- antibody concentration and cell density. The CD133-marked cells were investigated in seven AML patients. All SPR results were compared with those obtained from FC method. A very good correlation (R2 = 0.96) was obtained between SPR and FC responses related to CD133-marked cells densities. In conclusion, in this study, a label-free and real-time SPR cytometry method was developed to detect CD133 and it was successfully applied to follow this cancer stem cell biomarker in AML patients. Unlabelled Image • SPR-based method was developed for detection of CD133+ cancer stem cells in patients with AML. • SPR was validated by using CD133 antibody concentrations and cell density. • A strong correlation was obtained between SPR and flow cytometry responses. [ABSTRACT FROM AUTHOR]

Protein-protein interactions are involved in many biological processes and cellular functions and they are interesting therapeutic targets is several diseases for drug design and development. In the present study, the possible effects of caffeine (CF) as mostly consumed psychoactive substances in the modern life on tau-tau interactions were studied by localized surface plasmon resonance (LSPR) method. The obtained data indicated that tau monomers have high affinity to bind to the immobilized tau proteins on the surface of LSPR sensor chip of the gold nanoparticles (LSPR-AuNPs) and the LSPR peak was red-shifted from 598 ± 1.5 nm to 629 ± 0.1 nm. However, it was shown that the binding affinity of CF-tau complex was remarkably reduced. These results revealed that the binding of CF molecules on free tau monomers could potentially interrupt the interaction of tau-tau proteins. Circular dichroism (CD) and FTIR spectroscopy was applied to analyze the secondary structure of tau protein in the absence or presence of different amounts of CF. The results showed that CF can induce more random coil structure to the protein and also increase its structural stability. Docking studies and molecular dynamics simulations elucidated that CF not only can possibly provide a molecular and physical barrier for tau-tau interaction by binding to the microtubule binding domain, but also it decreases the stability of tau dimer, which were supported by experimental data. [Display omitted] • Tau proteins were immobilized covalently on the surface of LSPR sensor chip of the gold nanoparticles (LSPR-AuNPs). • Caffeine (CF) can reduce the binding affinity of tau monomers to the immobilized tau proteins on the surface of LSPR-AuNPs. • CF molecules could potentially interrupt the interaction of tau-tau proteins. • CF is able to induce more random coil on the secondary structure of tau protein and also increase its structural stability. [ABSTRACT FROM AUTHOR]

Alzheimer's is a progressive neurodegenerative disease in which extracellular precipitation of amyloid fibrils of the β peptides and the accumulation of phosphorylated tau in neurofibrillary tangles play major roles. There is some indirect evidence indicating the potential of donepezil to interact with tau protein. In the present study, various aspects of donepezil binding to tau protein have been investigated using surface plasmon resonance (SPR) and molecular modeling methods. Tau protein was immobilized on Au chip using 11-mercaptoundecanoic acid (MUA) and the interaction of various concentrations of donepezil with the immobilized tau was evaluated by SPR at different temperatures. Besides, to have a better understanding of this interaction, molecular docking approach was also performed. The equilibrium constant decreased following increasing the temperature in the presence of various concentrations of donepezil, which indicates that donepezil binding to tau protein increases upon rising temperature. The calculated thermodynamic parameters showed that the main force involved in the interaction is van der Waals and hydrogen bonding. Finally, the molecular modeling analysis showed that donepezil bind to a cavity on R2 region- microtubule binding domain of tau monomer. • Donepezil interaction with tau protein was investigated. • Dose-response sensorgrams attained upon donepezil interaction with tau protein. • Hydrogen bond and van der Waals force has role in donepezil interaction with tau. • Donepezil binds to a cavity on R2 region- microtubule binding domain of tau monomer. [ABSTRACT FROM AUTHOR]

The architecture of the immunosensor and the working principle for the detection of CD133. • AuNSs@g-CN nanosheets was used as an ECL emitter. • AuNSs@g-CN nanosheets offers an obviously enhanced ECL intensity. • This immunosensor exhibited favorable ECL performance to CD133 peptide detection. • This immunosensor is a candidate to create a low-cost, highly sensitive ECL sensor. Gold nanostars (AuNSs) demonstrate an intense electromagnetic field around tip of branches. In this research, we employed AuNSs-enhanced electrochemiluminescence (ECL) emission from graphitic carbon nitride nanosheets (g-CN nanosheets) to detect CD133 peptide as a cancer stem cell membrane biomarker. In this biosensor, the g-CN nanosheets were decorated with AuNSs (AuNSs@g-CN nanosheets). AuNSs@g-CN nanosheets exhibited strong and stable cathodic ECL emission compared to that of pure g-CN nanosheets. The ECL intensity from the AuNSs@g-CN nanosheets was over 30% higher than that of spherical gold nanoparticles (spherical AuNPs) decorated g-CN nanosheets. The additional ECL enhancement of AuNSs was due to the localized surface plasmon resonance (LSPR) effect located around multiple branch tips of AuNSs. The RSD of ECL curves intensities, obtained from successive potential scans for 10 cycles, were less than 4%, indicating the superior stability of the AuNSs@g-CN nanosheets. Under optimum conditions, the ECL intensity of GCE/AuNSs@g-CN nanosheets/anti-CD133 decreased linearly with CD133 peptide concentration in the range of 0.05–100 ng mL−1. The LOD achieved was 0.257 ng mL−1 (S/N = 3). The applicability of the designed biosensor in real samples was examined through the determination of CD133 peptide in spiked serum samples, from which satisfactory results were obtained. [ABSTRACT FROM AUTHOR]

• An SPR based DNA biosensor has been developed for detection of donkey meat marker. • Gold nanostars was used as enhanced label in the sandwich hybridization assay. • Target DNA could be detected with the LLOQ of 1.0 nM and RSD of 0.85%. • The detection of 1% and 5% values of donkey meat adulteration was successfully done. Herein, a surface plasmon resonance (SPR) enhanced DNA biosensor has been developed for real-time detection of donkey meat marker using biotinylated reporter and streptavidin functionalized gold nanostars (Stre@GNSs). Compared to the direct detection assay, this sandwich format for the enhancement of the signal, resulted in 6-folds orders increase in the sensitivity. Target DNA could be detected with the lower limit of quantification (LLOQ) of 1.0 nM with a relative standard deviation (RSD, n = 3) of 0.85%. In addition, the fabricated SPR sensor showed good selectivity for the target analyte over full complementary, single-base mismatch, three base-mismatch and non-complementary oligonucleotides. Finally, the proposed sensor was successfully applied for detection of donkey meat adulteration with various percentages in homemade beef sausage, as a real sample. The results indicated that the proposed biosensor provides a high specificity, easy, good sensitivity and fast approach for identification of donkey meat adulteration in food samples. [ABSTRACT FROM AUTHOR]

• The interaction between three anti-c-Met scFvs (ES1, ES2, and ES3) and this peptide was studied using SPR technique. • Kinetic parameters showed that ES1 has the highest affinity toward c-Met peptide. • Hydrophobic forces play major role in the interaction of c-Met with ES1 and the binding procedure was endothermic. Mesenchymal epithelial transition factor (c-Met) has been recently regarded as an attractive target for the treatment of cancer. Our previous study showed that c-Met-specific single chain fragment variables (scFvs) can be considered as a promising therapy for cancer, however, their molecular interaction with c-Met protein have not been assessed. Accordingly, in the current study we aim to evaluate the kinetic and thermodynamic properties of c-Met interaction with these scFvs as anticancer agents by means of surface plasmon resonance (SPR) technique. Phage-scFvs were immobilized on the 11-mercaptoundecanoic acid gold chips after carboxylic groups activation by N-ethyl-N-(3-diethylaminopropyl) carbodiimide/N-hydroxysuccinimide and, then the c-Met binding to each scFvs (ES1, ES2, and ES3) at different concentrations (ranging from 20 to 665 μM) was explored. Kinetic studies revealed that ES1 has the highest affinity (K D = 3.36 × 10−8) toward its target at 25°C. Calculation of thermodynamic parameters also showed positive values for enthalpy and entropy changes, which was representative of hydrophobic forces between c-Met and ES1. Furthermore, the positive value of Gibbs free energy indicated that c-Met binding to ES1 was enthalpy-driven. Taken together, we concluded that produced ES1 can be applied as promising scFv-based therapy for diagnosis or targeting of c-Met in various cancers. [ABSTRACT FROM AUTHOR]

The current study investigated the binding of BSA and piperacillin at multifarious concentrations (1–128 μM) along with four different temperatures. To do this, three sensitive methods were employed including surface plasmon resonance (SPR), fluorescence spectroscopy and molecular docking (MD). In the SPR method, BSA immobilized on the carboxymethyl dextran (CMD) hydrogel sensor chip through NHS/EDC activation. The Van't Hoff equation was applied for thermodynamic parameters determination at four distinct temperatures. Fluorescence spectroscopy results showed that binding constants decrease upon BSA interaction with piperacillin by rising temperature, which is indicative of BSA-piperacillin's complex formation and fluorescence quenching mechanism of BSA induced by piperacillin is via both static and dynamic quenching process. The SPR analysis showed dose-response sensorgrams of BSA as piperacillin concentration increased. In this regard, piperacillin demonstrated a higher affinity to BSA that was concluded via a smaller amount of equilibrium constants (K D). Besides, docking results indicated that IB and IIIA subdomains of BSA are the most favorable sites for piperacillin binding. Therefore, the attained results showed that piperacillin interaction with BSA could be changed from van der Waals interactions to hydrogen bonds depending on the BSA subdomains. • Piperacillin interaction with BSA was studied using various methods. • Dose-response sensorgrams confirmed the formation of the piperacillin–BSA complex. • Van der Waals and hydrogen bonds have role in the interaction of BSA with piperacillin. • The most favorable binding sites of piperacillin on the BSA were IB and IIIA. [ABSTRACT FROM AUTHOR]