Direct electrochemistry and electrocatalysis of myoglobin immobilized on L-cysteine self-assembled gold electrode

Voltammetric sensor based on cobalt-poly(methionine)-modified glassy carbon electrode for determination of estriol hormone in pharmaceuticals and urine

A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine) (Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at +0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH = 7.0). Different voltammetric scan rates (10–200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R² = 0.996) and from 5.66 μmol/L to 9.90 μmol/L (R² = 0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Co-poly(Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%–103% and 98.7%–102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.

End Group Properties of Thiols Affecting the Self-Assembly Mechanism at Gold Nanoparticles Film As Evidenced by Water Infrared Probe

Water infrared probe has been employed for in situ monitoring of the detailed self-assembly processes of four thiol molecules with different end groups (-CH₃, -NH₂, -COOH, and -OH) on gold nanoparticles (Au NPs) film in aqueous solution. Based on the change of water IR signal, the significant influence of end group properties on the kinetics and thermodynamics of thiols self-assembly can be estimated. It is found that the assembly kinetics of thiols decreases with the increase of the hydrophobicity of the end groups. In addition, the charges carried by the end groups (-COOH and -NH₂ terminated thiols) will also slow down the self-assembly kinetics owing to the electrostatic repulsions. However, the isothermal adsorption is only affected by the wettability of the end groups of thiols. The higher hydrophilicity of the end groups results in larger equilibrium constant of the self-assembly process. Results show that water infrared probe offers an additional approach to the monitoring of thiols self-assembly processes with higher sensitivity and more detailed information as compared to traditional molecule fingerprints.

Effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin

In this work, we have studied the effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin (Mb), and by means of electrochemical techniques, we have shown that this reaction is undoubtedly affected following the interaction with the venom. Surface plasmon resonance, electrophoresis, UV-Vis, and circular dichroism showed that the interaction involves the attachment of some constituent of the venom to the protein, although not affecting its first and secondary structures. Mass spectra support this suggestion by showing the appearance of signals assigned to the Mb dimer and to a new species resulting from the interaction between Mb and the venom proteins. In addition, the mass spectra suggest the aromatic amino acids of myoglobin, mainly tryptophan and phenylalanine, are more exposed to the solvent medium upon the exposure to the venom solution. The results altogether indicate that the harmful effects of the venom of Crotalus basiliscus snake are likely connected to the blocking of the redox site of Mb.

Electrochemical nitric oxide biosensor based on amine-modified MoS2/graphene oxide/myoglobin hybrid

Nitric oxide (NO) is one of the most important molecules in living things due to its role as a signaling molecule in influencing pathological and physiological mechanisms including neurotransmission. In this study, the electrochemical biosensor based on the amine-modified molybdenum disulfide nanoparticles (MoS₂), graphene oxide (GO) and myoglobin (Mb) hybrid material (amine-modified MoS₂/GO/Mb hybrid) is developed to achieve the accurate detection of NO with electrochemical signal improvement. For the first time, the synthesis of MoS₂ accompanying the amine-modification of the surface of MoS₂ is done to hybridize with GO efficiently through the short linkage. After the amine-modification of MoS₂, it is enclosed with GO directly (amine-modified MoS₂/GO). Then, Mb which can induce the reduction of NO is immobilized on the amine-modified MoS₂/GO to fabricate the amine-modified MoS₂/GO/Mb hybrid for NO detection. The prepared hybrid shows the signal improved redox properties relative to the result of the electrode prepared without hybrid. Furthermore, upon addition of NO, the electrode prepared with hybrid shows the improved amperometric response compared with that of the electrode without hybrid. This amine-modified MoS₂/GO/Mb hybrid can be used in the development of the biosensor platform accompanying the electrochemical signal improvement and accurate detection of target materials.

An innovative immunosensor for detection of tumor suppressor protein p53 in unprocessed human plasma and cancer cell lysates

An innovative mediator-free electrochemical immunosensor for quantitation of p53 tumor suppressor protein based on signal amplification strategy was fabricated. In this work, biotin conjugated p53-antibody (anti-p53) was immobilized onto a green and biocompatible nanocomposite containing poly l-cysteine (P-Cys) as conductive matrix and 3D gold nanoparticles (GNPs) as signal amplification element. Therefore, a novel nanocomposite film based on P-Cys and GNPs was exploited to develop a highly sensitive immunosensor for detection of p53 protein. Importantly, GNPs prepared by sonoelectrodeposition method which lead to compact morphology. Fully electrochemical methodology was used to prepare a new transducer on a gold surface which provided a high surface area to immobilize a high amount of the anti-p53. The surface morphology of electrode was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDX). The immunosensor was employed for the detection of p53 in physiological pH using square wav voltammetry and differential pulse voltammetry (DPVs) techniques. Under optimized condition the calibration curve for p53 concentration by SWV and DPV was linear in 0.0369-50pM and 0.018-2.5pM with lower limit of quantification of 48fM and 18fM, respectively. The method was successfully applied assay of the p53 in unprocessed human plasma samples. Also, the method was applied to the assay of p53 in human plasma sample and normal and malignant cell line lysates such as (L929 normal cell Line from mouse C3H (L929), colon cancer cell-HCT, prostate cancer cell line PC-3, and human breast adenocarcinoma cell line-MCF7).

Highly sensitive immunosensing of prostate specific antigen using poly cysteine caped by graphene quantum dots and gold nanoparticle: A novel signal amplification strategy

A mediator-free electrochemical immunosensor for quantitation of prostate specific antigen (PSA) based on dual signal amplification strategy was fabricated. In this work, PSA-antibody (anti-PSA) was immobilized onto a green and biocompatible nanocomposite containing poly l-cysteine (P-Cys) as conductive matrix and graphene quantum dots (GQDs)/gold nanoparticles (GNPs) as dual signal amplification elements. Therefore, a novel multilayer film based on P-Cys, GQDs, and GNPs was exploited to develop a highly sensitive amperometric immunosensor for detection of PSA. Fully electrochemical methodology was used to prepare a new transducer on a gold surface which provided a high surface area to immobilize a high amount of the anti-PSA. Importantly, GNPs prepared by soft template synthesized method lead to compact morphology was achieved. The surface morphology of electrode surface was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDX). Chemical compositions of the gold nanoparticles were analysed by an EDX. The immunosensor was employed for the detection of PSA in physiological pH. Under optimized condition the calibration curve for PSA concentration was linear up to 2-9pgmL^-1 with lower limit of quantification of 1.8pgmL^-1.

Single gold nanowire electrodes and single Pt@Au nanowire electrodes: electrochemistry and applications

Single Au nanowire electrodes and single Pt@Au nanowire electrodes have been prepared and used to investigate electrochemical properties, fabricate an E-DNA sensor and study the oxygen reduction reaction.

Preparation, electrochemical responses and sensing application of Au disk nanoelectrodes down to 5 nm

Single Au nano-disk nanoelectrodes with the radii down to 5 nm have been prepared, which can be used to measure ferritin molecules in the amount of ∼3900 molecules or 6.1 zmol.

Electrochemistry, surface plasmon resonance, and quartz crystal microbalance: an associative study on cytochrome c adsorption on pyridine tail-group monolayers on gold

Quartz crystal microbalance (QCM), surface plasmon resonance (SPR), and electrochemistry techniques were used to study the electron-transfer (ET) reaction of cytochrome c (Cyt c) on gold surfaces modified with thionicotinamide, thioisonicotinamide, 4-mercaptopyridine, 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol, 5-phenyl-1,3,4-oxadiazole-2-thiol, 4,4'-bipyridine, and 4,4'-dithiopyridine. The electrochemical results showed that the ET process is complex, being chiefly diffusional with steps depending on the orientation of the pyridine or phenyl tail group of the modifiers. The correlation between the electrochemical results and those acquired by SPR and QCM indicated the presence of an adlayer of Cyt c adsorbed on the thiolate SAMs. This adlayer, although being not electroactive, is essential to assess the ET reaction of Cyt c in solution. The results presented in this work are consistent with the statement (Feng, Z. Q.; Imabayashi, S.; Kakiuchi, T.; Niki, K. J. Electroanal. Chem. 1995, 394, 149-154) that the ET reaction of Cyt c can be explained in terms of the through-bond tunneling mechanism.