Matrix augmentation as an efficient method for resolving interaction of bromocriptine with human serum albumin: trouble shooting and simultaneous resolution.

This work reports the results of an interesting study related to the investigation of interactions of bromocriptine (BCP) with human serum albumin (HSA) by mathematicall modelling of voltammetric and spectroscopic data into an augmented data matrix and its resolution by multivariate curve resolution-alternating least squares (MCR-ALS). The quality of the results obtained by MCR-ALS was examined by MCR-BANDS and its outputs confirmed the absence of rotational ambiguities in the MCR-ALS results. BCP-HSA interactions were also modeled by molecular docking methods to verify the results obtained from experimental sections and fortunately, they were compatible. Hard modeling of the experimental data by EQUISPEC helped us to calculate the binding constant of the complex formed from BCP-HSA interactions which was in a good agreement with that of calculated from direct analysis of the experimental data. Finally, with the help of two different amperometric measurements based on BCP-HSA interactions a novel electroanalytical method was developed for biosensing of HSA in serum samples.

Fabrication of a novel impedimetric biosensor for label free detection of DNA damage induced by doxorubicin.

In this work, a novel impedimetric biosensor has been fabricated for detection of DNA damage induced by doxorubicin (DX). Cytochrome P450 reductase (CPR) is required for electron transfer from nicotinamide adenine dinucleotide phosphate (NADPH) to cytochrome P450 (CP450) which causes DX to undergo a one-electron reduction of the p-quinone residue to form the semiquinone radical resulting in the generation of free hydroxyl radical which causes DNA damage. After modification of bare glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs) and chitosan (Ch), CPR and CP450 were co-immobilized onto the surface of Ch/MWCNTs/GCE by cross-linking CPR, CP450 and Ch through addition of glutaraldehyde. Then, the DNA was assembled onto the surface of CPRCP450/Ch/MWCNTs/GCE to fabricate the biosensor (DNA/CPRCP450/Ch/MWCNTs/GCE). Modifications applied to the bare GCE to fabricate the biosensor were characterized by CV, EIS and SEM. The DNA/CPRCP450/Ch/MWCNTs/GCE was treated in the damaging solution (DX + NADPH) which caused a significant DNA damage and the exposed DNA bases reduced the electrostatic repulsion of the negatively charged redox probe leading to Faradaic impedance changes. Performance of the biosensor for detection of DNA damage in the presence of Spinach extract was also examined and finally, an indirect impedimetric method was developed for determination of DX.

Simultaneous co-immobilization of three enzymes onto a modified glassy carbon electrode to fabricate a high-performance amperometric biosensor for determination of total cholesterol.

In this work, we have fabricated a novel amperometric cholesterol (CHO) biosensor because of the importance of determination of CHO levels in blood which is an important parameter for diagnosis and prevention of disease. To achieve this goal, cholesterol oxidase, cholesterol esterase and horseradish peroxidase were simultaneously co-immobilized onto a glassy carbon electrode (GCE) modified with gold nanoparticles/chitin-ionic liquid/poly(3,4-ethylenedioxypyrrole)/graphene-multiwalled carbon nanotubes-1,1'-ferrocenedicarboxylic acid-ionic liquid. Modifications applied to the bare GCE were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The biosensor detected CHO in linear ranges of 0.1-25 µM and 25-950 µM with a detection limit of 0.07 µM. The sensitivity of the biosensor was estimated to be 6.6 µA µM-1 cm-2, its response time was <5 s and Michaelis-Menten constant was calculated to be 0.12 µM. Results obtained in this study revealed that the biosensor was selective, sensitive, stable, repeatable and reproducible. Finally, the biosensor was successfully applied to the determination of CHO levels in rats plasma.

Chemometrics-assisted investigation of interactions of Tasmar with human serum albumin at a glassy carbon disk: Application to electrochemical biosensing of electro-inactive serum albumin.

In this work, voltammetric data recorded by a glassy carbon electrode (GCE) was used to investigate the interactions of tolcapone (Tasmar, TAS) with human serum albumin (HSA) at the electrode surface. The recorded voltammetric data was also combined with spectroscopic data to construct an augmented data matrix which was analysed by multivariate curve resolution-alternating least squares (MCR-ALS) as an efficient chemometric tool to obtain more information about TAS-HSA interactions. The results of MCR-ALS confirmed formation of one complex species (HSA-TAS2) and application of MCR-BANDS to the results of MCR-ALS confirmed the absence of rotational ambiguities and existing unambiguous and reliable results. Binding of TAS to HSA was also modeled by molecular docking and the results showed that the TAS was bound to sub-domain IIA of HSA which were compatible with the ones obtained by recording experimental data. Hard-modeling of combined voltammetric and spectroscopic data by EQUISPEC helped us to compute binding constant of HSA-TAS2 complex species which was compatible with the binding constant value obtained by direct analysis of experimental data. Finally, a new electroanalytical method was developed based on TAS-HSA interactions for determination of HSA in two ranges of 0-541 nM and 541-1200 nM with a limit of detection of 0.04 nM and a sensitivity of 0.02 µA nM-1.

Fabrication of a novel enzymatic electrochemical biosensor for determination of tyrosine in some food samples.

In this work, fabrication of a novel and ultrasensitive electrochemical biosensor based on immobilization of tyrosine hydroxylase onto palladium-platinum bimetallic alloy nanoparticles/chitosan-1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide/graphene-multiwalled carbon nanotubes-IL/glassy carbon electrode for determination of L-tyrosine in some high tyrosine foods including cheese, egg and yogurt was reported. Immobilization of tyrosine hydroxylase onto the surface of the biosensor was performed by cross-linking tyrosine hydroxylase and chitosan through the addition of glutaraldehyde. Enzymatic biosensors employ the affinity and selectivity of catalytically active proteins towards their target molecules and here, the tyrosine hydroxylase selectively catalyzes the conversion of tyrosine to levodopa which can be oxidized at lower potentials than tyrosine. The modifications were characterized by electrochemical impedance spectroscopy, cyclic voltammetry, energy dispersive X-ray spectroscopic and scanning electron microscopy. Under optimal conditions, the biosensor detected tyrosine in concentration ranges of 0.01 × 10-9 to 8.0 × 10-9 mol L-1 and 8.0 × 10-9 to 160.0 × 10-9 mol L-1 with a limit of detection of 0.009 × 10-9 mol L-1. The biosensor was able to selective determination of tyrosine even in the presence of common interferents therefore, the biosensor was highly selective. The biosensor also showed good operational stability, antifouling properties, sensitivity, repeatability and reproducibility.

Developing a novel paper-based enzymatic biosensor assisted by digital image processing and first-order multivariate calibration for rapid determination of nitrate in food samples.

For the first time, a novel analytical method based on a paper based enzymatic biosensor assisted by digital image processing and first-order multivariate calibration has been reported for rapid determination of nitrate in food samples. The platform of the biosensor includes a piece of Whatman filter paper impregnated with Griess reagent (3-nitroaniline, 1-naphthylamine and hydrochloric acid) and nitrate reductase. After dropping a distinct volume of nitrate solution onto the biosensor surface, nitrate reductase selectively reduces nitrate to nitrite and then the Griess reagent selectively reacts with nitrite to produce a red colored azo dye. Therefore, the color intensity of the produced azo dye is correlated with nitrate concentration. After image capture, the images were processed and digitized in the MATLAB environment by the use of an image processing toolbox and the vectors produced by the digital image processing step were used as inputs of the first-order multivariate calibration algorithms. Several multivariate calibration algorithms and pre-processing techniques have been used to build multivariate calibration models for verifying which technique offers the best predictions towards nitrate concentrations in synthetic samples and the best algorithm has been chosen for nitrate determination in potato, onion, carrot, cabbage and lettuce samples as real cases.