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Detection of leishmaniasis is important in clinical diagnoses. In the present study, identification of Leishmania parasites was performed by a label-free, PCR-free and signal-on ultrasensitive electrochemical DNA biosensor. Gold nanoleaves were firstly electrodeposited by an electrodeposition method using spermidine as a shape directing agent. The biosensor was fabricated by immobilization of a Leishmania major specific DNA probe onto gold nanoleaves, and methylene blue was employed as a marker. Hybridization of the complementary single stranded DNA sequence with the biosensor under the selected conditions was then investigated. The biosensor could detect a synthetic DNA target in a range of 1.0×10 −10 to 1.0×10 −19 mol L −1 with a limit of detection of 1.8×10 −20 mol L −1 , and genomic DNA in a range of 0.5–20 ng μL −1 with a limit of detection of 0.07 ng μL −1 . The biosensor could distinguish Leishmania major from a non-complementary-sequence oligonucleotide and the tropica species with a high selectivity. The biosensor was applicable to detect Leishmania major in patient samples. [ABSTRACT FROM AUTHOR]

Precise and sensitive identification methods of Leishmania are required for efficient treatment of leishmaniasis. Detection of Leishmania species approves the efficiency of the applied therapy. Current diagnosis methods, such as culture and microscopy methods, are time-consuming and have limited sensitivity, and are laborious when encountering lots of samples. Although molecular methods can identify Leishmania species, their diagnosis depends on individual responsiveness. Therefore, rapid, sensitive and low-cost methods are required for identification of Leishmania species. In this study, a new method was developed based on hybridization of gold nanoparticles linked a specific single stranded DNA probe from non-protein coding region ( AB678349.1 ) of Leishmania major minicircle kinetoplast DNA (kDNA). Dispersion or aggregation of the gold nanoparticles-probe conjugates in the presence or absence of a complementary DNA sequence leads to an obvious and sensitive change in the UV–vis spectra and the solution color. The results indicated that this method is useful for diagnosis of Leishmania major from other non- Leishmania species with a detection limit of 7.0 pg μL −1 . The efficacy of the present PCR-free assay was evaluated to identify genomic DNA extracted from Leishmania major and clinical samples. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles were potentiostatically electrodeposited on a gold surface at a highly negative potential. The nanostructure, as a transducer, was utilized to immobilize a Brucella -specific probe and the process of immobilization and hybridization was detected by electrochemical methods. The proposed method for detection of the complementary sequence and a non-complementary sequence was applied. The fabricated genosensor was evaluated for the assay of the bacteria in the cultured and human samples with and without PCR. The genosensor could detect the complementary sequence with a sensitivity of 0.02 μA dm 3 mol −1 , a linear concentration range of 1.0 × 10 −12 to 1.0 × 10 −19 mol dm −3 , and a detection limit of 2.7 × 10 −20 mol dm −3 . [ABSTRACT FROM AUTHOR]

Introduction The causative agents of brucellosis from genus Brucella can infect a variety of animal species and human. However, conventional methods for the detection of Brucella are time-consuming and the handling of microorganism is hazardous for laboratory personnel. In this study, a nanobiosensor based on gold nanoparticles (AuNPs) and oligonucleotide probe was designed for the visual detection of Brucella spp. Methods A specific oligonucleotide probe from IS711 gene region was functionalized with AuNPs (AuNP-probe). Then, AuNP-probe was exposed to target (complementary) and non-target (non-complementary) DNA for the hybridization. Also, hybridization conditions were analyzed in the presence of Brucella genomic DNA and extracted DNA from clinical samples. Results Upon acid addition, a red color for the samples containing complementary DNA was observed, whereas in the samples without complementary DNA, AuNP-probe turned blue-purple. The results were investigated visually and also by UV–vis spectroscopic measurements. This method detected up to 1.09 pg μL −1 of unamplified Brucella genomic DNA. Since Brucella is a facultative intracellular bacteria, clinical samples were amplified by PCR, and colorimetric detections were performed. The results showed high sensitivity and selectivity for the amplified clinical samples. Conclusion To the best of our knowledge, this developed assay is highly specific, and this is the first assay that can be used with low cost, and as a method of rapid, direct and visual detection of Brucella spp. [ABSTRACT FROM AUTHOR]

Abstract: A nanocomposite of cobalt hexacyanoferrate/reduced graphene oxide was synthesized by a facile precipitation route. The nanocomposite morphology was characterized by scanning electron microscopy. A nanocomposite-modified carbon paste electrode was then fabricated and its redox behavior was characterized. In the voltammograms of the modified electrode recorded in phosphate buffer solution, pH 7.4, two quasi-reversible redox transitions appeared related to the Co(II)/Co(III) and Fe(II)/Fe(III) transitions. The diffusion of the counter cation into the nanocomposite and the charge transfer kinetics across the electrode/electrolyte interface were studied. The modified electrode showed an efficient electrocatalytic activity toward the electrooxidation of captopril. In the presence of captopril, the anodic peak current of the Fe(II)/Fe(III) transition increased and the cathodic one decreased, while, the peak currents of the Co(II)/Co(III) transition remained almost constant. This indicates that captopril was oxidized on the modified electrode surface through a surface mediated electron transfer (an electrocatalytic reaction). The catalytic rate constant and the electron transfer coefficient for the electrooxidation process and the captopril diffusion coefficient were reported. A sensitive and time-saving amperometric method was developed for the analysis of captopril. Based on the developed method, captopril was determined with a detection limit of 0.331μM. The proposed amperometric method was also applied to the analysis of captopril in tablets. [Copyright &y& Elsevier]

Abstract: Electrocatalytic oxidation of acetylcholine (ACh) on different nickel-based composites was investigated. Cyclic voltammetry, steady-state polarization measurements and chronoamperometry were employed to study the mechanism and kinetics of the oxidation process. The results showed that ACh was irreversibly oxidized on nickel nanoshells-carbon microparticles-Nafion nanocomposite with an excellent catalytic activity. The catalytic rate constant and the transfer coefficient for the electrocatalytic oxidation of ACh and the diffusion coefficient of ACh were obtained using cyclic voltammetry, steady-state polarization measurements and chronoamperometry. A sensitive and time-saving hydrodynamic amperometry method was developed for the determination of ACh. The nanocomposite showed a high sensing performance with a sensitivity of 48.58±0.52mAM−1 cm−2 and a limit of detection of 49.33nM. The nanocomposite represented many advantages as an ACh biosensor such as simple preparation method without using any specific enzyme or reagent, excellent catalytic activity, high sensitivity, long-term stability, and antifouling property toward ACh and its oxidation product(s). Sensitivity and detection limit of the present biosensor are better than all of the reports appeared in the literature. [Copyright &y& Elsevier]

Recently, enterococci have been introduced as a major nosocomial infection that resist to conventional therapies. A nano-genosensor was designed here by immobilization of a specific oligonucleotide from 16s rRNA gene sequence of Enterococcus faecalis on the surface of gold nanoparticles. It was followed by hybridization assays with synthetic target, genomic target, or PCR products of genomic DNA samples extracted from patients. This genosensor had advantages such as visual detection, short and fast reading of the results and also economical aspects. The genosensor had detection limits of 18.6 and 83.3 pg μL −1 for detection of synthetic target and genomic DNA sequences, respectively (based on spectrophotometic detections). The practical quantitation limits were obtained as 0.31 and 0.34 ng μL −1 for the visual detection of the synthetic target and genomic DNA, respectively. [ABSTRACT FROM AUTHOR]

Bacteria, parasites and viruses are found widely in the environment as potential pathogens, and can be the source of infections. Therefore, sensitive and rapid methods for identification of the pathogens are required to achieve a better quality of life. Enterococcus faecalis commonly colonizes and threatens human health. In the present study, we demonstrate the fabrication of a novel electrochemical DNA biosensor based on electrodeposited gold nanostructures as a transducer substrate combined with toluidine blue (TB) as a redox marker. Binding of TB with the single and double stranded DNA (ssDNA and dsDNA) was shortly investigated, and based on the results, TB could discriminate between ssDNA and dsDNA. A specific thiolated ssDNA sequence was immobilized on the transducer substrate, and DNA hybridization was followed by differential pulse voltammetry. The DNA biosensor showed excellent performances with high sensitivity and good selectivity. The DNA biosensor was applied to detect a synthetic target in a linear range of 1.0 × 10 −17 –1.0 × 10 −10  mol L −1 with a limit of detection (LOD) of 4.7 × 10 −20  mol L −1 . In addition, LOD of the DNA biosensor for the detection of genomic DNA was found to be 30.1 ng μL −1 . [ABSTRACT FROM AUTHOR]

Meso/macroporous cobalt (II) oxide nanoflakes were electrodeposited in a one-step process in the presence of N -methylpyrrolidone. On the surface of nanoflakes, a specific single stranded DNA sequence from the genome of influenza A subtype was then immobilized to fabricate an electrochemical biosensor. Hybridization of the biosensor with complementary, non-complementary and base-mismatch sequences was electrochemically detected. The biosensor was also employed to detect complementary DNA of viral RNA in culture and human samples. The biosensor could detect the complementary sequence with a detection limit of 86.4 amol L −1 and a linear concentration range of 1.0 fmol L −1 to 1.0 nmol L −1 . It also detected a complementary DNA sequence converted from viral RNA with a detection limit of 0.28 ng μL −1 in a linear concentration range of 0.5–10 ng μL −1 . Low detection limit, simple method of preparation of the transducer and no needing any DNA strand modification and tag are the principal advantages of the biosensor. [ABSTRACT FROM AUTHOR]

Recently, convergence of nanotechnology, medicine, biology and chemistry has provided novel solutions for efficient diagnosis systems for disease markers. A detection method of troponin I (TnI), as the gold standard of acute myocardial infarction biomarker, was investigated and a novel aptasensor was presented for this biomarker. An array of gold nanodumbbells was firstly synthesized using putrescine as the shape directing agent at a surface. It was then applied as a transducer for the immobilization of a 76-mer TnI aptamer to fabricate a simple electrochemical TnI aptasensor. Using the aptasensor, TnI was detected in a linear range of 0.05–500 ng mL −1 with a limit of detection of 8.0 pg mL −1 . The aptasensor showed a diagnostic sensitivity of 100% and a diagnostic specificity of 85% when challenged with blood serum samples of 89 individuals. [ABSTRACT FROM AUTHOR]