A simple and sensitive methodology for voltammetric determination of valproic acid in human blood plasma samples using 3-aminopropyletriethoxy silane coated magnetic nanoparticles modified pencil graphite electrode.

In this work, we have prepared a nano-material modified pencil graphite electrode for the sensing of valproic acid (VA) by immobilization 3-aminopropyletriethoxy silane coated magnetic nanoparticles (APTES-MNPs) on the pencil graphite surface (PGE). Electrochemical studies indicated that the APTES-MNPs efficiently increased the electron transfer kinetics between VA and the electrode and the free NH2 groups of the APTES on the outer surface of magnetic nanoparticles can interact with carboxyl groups of VA. Based on this, we have proposed a sensitive, rapid and convenient electrochemical method for VA determination. Under the optimized conditions, the reduction peak current of VA is found to be proportional to its concentration in the range of 1.0 (±0.2) to 100.0 (±0.3) ppm with a detection limit of 0.4 (±0.1) ppm. The whole sensor fabrication process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods with using [Fe(CN)6]3-/4-as an electrochemical redox indicator. The prepared modified electrode showed several advantages such as high sensitivity, selectivity, ease of preparation and good repeatability, reproducibility and stability. The proposed method was applied to determination of valproic acid in blood plasma samples and the obtained results were satisfactory accurate.

Using gold nanostars modified pencil graphite electrode as a novel substrate for design a sensitive and selective Dopamine aptasensor.

For the first time, gold nanostars (GNS) were applied for electrostatic and covalent immobilizing a thiol modified Dopamine aptamer on the pencil graphite electrode and signal amplification. Dopamine aptamer was immobilized on the gold nanostars through electrostatic interaction between negatively charged phosphate groups of aptamer and positively charged gold nanostars and AuS well known covalent interaction. In the presence of Dopamine in the test solution, the charge transfer resistance (RCT) on the electrode surface increased with the increase of the Dopamine concentration due to specific interaction between Dopamine aptamer and Dopamine molecules, which made a barrier for electrons and inhibited the electron-transfer. So, the proposed approach showed a high sensitivity and a wide linearity to Dopamine in the range from 1.0 (±0.1) to 100.0 (±0.3) ngL-1 (ppt) with detection and quantification limits of 0.29 (±0.10) and 0.90 (±0.08) ngL-1 (ppt), respectively. Finally, the sensor was successfully used for determination of Dopamine in biological (human blood plasma and urine) samples. The results open up the path for manufacturing cost effective aptasensors for other biomedical applications.

Synergistic effect of magnetite and gold nanoparticles onto the response of a label-free impedimetric hepatitis B virus DNA biosensor.

A magnetite and gold nanoparticle modified carbon paste electrode (CPE) was prepared for the immobilization of a thiol modified Hepatitis B virus (HBV) probe DNA and determination trace amount of target HBV DNA. Indeed, the sensing platform integrated two nanoparticles that had previously been employed individually in the DNA biosensors. The proposed DNA biosensor could measure target HBV DNA virus concentration with a low detection limit of 3.1 (±0.1)×10-(13)M, which was greatly lower than the detection limit reported with gold or magnetite nanoparticles alone. The change of interfacial charge transfer resistance (RCT) was confirmed the hybrid formation between probe and target HBV DNA. The RCT difference (before and after hybridization with the target HBV DNA) was in a linear relationship with the logarithm of complementary oligonucleotide concentrations in the range of 8.3 (±0.1)×10(-13) to 6.4 (±0.2)×10(-7)M. In addition, the novel methodology for specific DNA sequence detection was highly selective, repeatable, and reproducible. Finally, this work was successfully utilized for the sensitive and label free impedimetric determination of HBV target DNA in the urine and blood plasma samples.

A novel morphine electrochemical biosensor based on intercalative and electrostatic interaction of morphine with double strand DNA immobilized onto a modified Au electrode.

The intercalative and electrostatic interaction of morphine with double-stranded DNA (ds-DNA), which was immobilized onto mercapto-benzaldehyde-modified Au electrode, was employed for designing a sensitive biosensor. The interaction of morphine with the immobilized ds-DNA onto the electrode surface has been studied by differential pulse voltammetry (DPV). Under the optimum conditions, a linear dependence for the morphine concentration in the range of 0.05-500 µmol L(-1) and its oxidation signal were observed and a detection limit of 0.01 µmol L(-1) for the morphine was obtained. The reproducibility and applicability of the analysis to real samples were also investigated and results demonstrated that this DNA biosensor could be utilized for the sensitive, rapid, simple, and cost effective determination of morphine in urine and blood plasma samples.

A novel optical DNA biosensor for detection of trace amounts of mercuric ions using gold nanoparticles introduced onto modified glass surface.

In this work we report a DNA spectrophotometric biosensor for detection of Hg2+ ions in which a pair of oligonucleotides with four thymine-thymine (T-T) mismatched bases was immobilized onto modified glass surface. Firstly, glass surface modified with 3-(mercaptopropyl) trimethoxysilane (MSPT) and gold nano-particles respectively and then one oligonucleotide (P1) modified with hexanthiol at 5-terminal was immobilized on gold nano-particles via self-assembly and inserted in methylene blue. Methylene blue can intercalate on single strand DNA (ss-DNA) and its absorption peak can measure spectrophotometrically. Then the other oligonucleotide was able to hybridize with P1 by forming thymine-Hg2+-thymine (T-Hg2+-T) complexes in the presence of Hg2+, and absorption signal of methylene blue reduced upon Hg2+ increasing concentration because inaccessibility of guanine base in DNA duplex. However, when Hg2+ was absent, the two oligonucleotides could not hybridize due to the T-T mismatched bases, and P2 could not be fixed on the modified glass surface and any change in absorption peak of methylene blue takes place. The UV-Vis spectrum showed a linear correlation between the absorption peak of methylene blue and the concentration of Hg2+ over the range from 10 nM to 10 µM (R2=0.9985) with a detection limit of 6 nM. This spectrophotometric biosensor could be widely used for selective detection of Hg2+.

A new methodology for electrostatic immobilization of a non-labeled single strand DNA onto a self-assembled diazonium modified gold electrode and detection of its hybridization by differential pulse voltammetry.

In this work, a self-assembled diazonium modified gold electrode (D-MGE) was used for the fabrication of an electrochemical DNA biosensor. For preparation of D-MGE, initially 2-amino-5-mercapto-1, 3, 4-thiadiazole (AMT) self-assembled on gold electrode and a simple diazonation reaction was used to prepare D-MGE. Then, non-labeled single strand DNA (NL-ssDNA) directly was immobilized on D-MGE through electrostatic interaction. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) characterized the DNA biosensor fabrication process with the use of ferro-ferric cyanide as an electrochemical redox indicator. The hybridization capacity of the developed biosensor was monitored with differential pulse voltammetry using [Fe (CN)(6)](4-) as an indicating probe. A wide dynamic detection range (7.9 × 10(-11)-1.2 × 10(-7) mol L(-1)) and a low detection limit (1.4 × 10(-11) mol L(-1)) were achieved for the complementary sequence. In addition, the hybridization specificity experiments showed that the sensing system could accurately discriminate complementary sequence from non-complementary sequences.

Used gold nano-particles as an on/off switch for response of a potentiometric sensor to Al(III) or Cu(II) metal ions.

The potentiometric response of a carbon paste electrode modified with silica sol-gel and mercaptosuccinic acid (MSA) in the presence and absence of gold nano-particles was studied. The results showed that the electrode with gold nano-particles was responded to Al(3+) ions as a hard metal ion. On the other hand, the electrode without gold nano-particles was responded to copper ions as a soft metal ion. The electrodes without and with gold nano-particles exhibits a Nernstian slope of 29.1 and 19.2 mV decade(-1) for copper and aluminum ions over a wide concentration range of 4.3×10(-7)-1.0×10(-2) and 4.5×10(-7)-1.6×10(-3) mol L(-1), respectively. The detection limits of electrodes were 4.0×10(-7) and 1.6×10(-7) mol L(-1) for copper and aluminum ions, respectively.