Simple and Cost-effective "Turn-on" Fluorescence Sensor for the Determination of Xanthine.

A simple and selective 'turn-on' fluorescence sensor have been developed for the determination of xanthine (XA) based on glutathione (GSH) capped copper nanoclusters (CuNCs) as the fluorescent probe. The proposed sensor possess several advantages such as sensitivity, short analysis time and requires no sample pretreatment. The conditions for the performances of the sensor have been optimized and good linear relationship was obtained between concentration and relative fluorescence intensity in the concentration range 9.0[Formula: see text]10-3 M to 8.0[Formula: see text]10-5 M with a detection limit 6.0[Formula: see text]10-6 M. The mechanism behind the fluorescence enhancement may be ascribed to the binding of XA on the surface of GSH CuNCs. The sensor have been successfully applied to determine XA in spiked physiological samples.

Copper nanoclusters: an efficient fluorescence sensing platform for quinoline yellow.

Fluorescence quenching behavior of artificial food colorant quinoline yellow (QY), on interaction with l-cysteine stabilized copper nanoclusters (l-Cys-CuNCs) is investigated in this work. For this purpose, l-cysteine stabilized CuNCs were synthesized and characterized using various analytical techniques. Results demonstrated that the synthesized probe (size ~2 nm) had very promising optical features such as bright blue fluorescence, significant quantum yield and excellent photostability. l-Cys-CuNCs can function as a fluorescence sensor by selectively sensing QY among other yellow colorants, giving a detection limit as low as 0.11 µM. The developed sensor exhibited a linear concentration range from 5.50 to 0.20 µM. The developed fluorescence assay was successfully applied for testing commercial samples, thereby making this sensing strategy significant for quality control of food stuffs.

Electrochemical Biosensor for the Detection of Glycated Albumin.

BACKGROUND: Alzheimer's disease (AD) is the most common form of dementia. The process of AD can begin 20 years before any symptom of cognitive loss. Thus, the development of systems for early diagnosis and prevention is very important. The mechanism of AD is still under debate. Nevertheless, higher levels of glycated albumin in cerebrospinal fluid and plasma are observed in AD patients. Therefore, glycated albumin could be a biomarker of AD development. METHODS: Electrochemical biosensor for direct determination of glycated albumin was based on thiol derivative of pentetic acid (DTPA) complex with Cu(II) created on gold electrode surface. His-tagged domains of Receptors for Advanced Glycation End Products (RAGE) were applied as analytical active element for glycated albumin recognition. The binding of glycated albumin by His6- RAGE domains was monitored using Osteryoung square - wave voltammetry. RESULTS: Electrodes modified with His6 - RAGE VC1 natural domain generated decrease of Cu(II) redox currents in the presence of glycated albumin. Human albumin, Aß 1-40 and S100B protein caused negligible influence on biosensors responses towards glycated albumin. The detection limits were: 2.3 pM, 1.1 pM, 2.9 pM and 3.1 pM in the presence of: buffer, buffer + albumin, buffer + S100B, buffer + Aß1-40 , respectively. CONCLUSION: The presented electrochemical biosensor was successfully applied for the determination of glycated albumin. Considering analytical parameters such as good selectivity and sensitivity in pM range, biosensor could be recommended as an analytical tool for medical samples analysis.

An immunosensor based on antibody binding fragments attached to gold nanoparticles for the detection of peptides derived from avian influenza hemagglutinin H5.

This paper concerns the development of an immunosensor for detection of peptides derived from avian influenza hemagglutinin H5. Its preparation consists of successive gold electrode modification steps: (i) modification with 1,6-hexanedithiol and gold colloidal nanoparticles; (ii) immobilization of antibody-binding fragments (Fab') of anti-hemagglutinin H5 monoclonal antibodies Mab 6-9-1 via S-Au covalent bonds; and (iii) covering the remaining free space on the electrode surfaces with bovine serum albumin. The interactions between Fab' fragments and hemagglutinin (HA) variants have been explored with electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)6](3-/4-) as an electroactive marker. The immunosensor was able to recognize three different His-tagged variants of recombinant hemagglutinin from H5N1 viruses: H1 subunit (17-340 residues) of A/swan/Poland/305-135V08/2006, the long HA (17-530 residues) A/Bar-headed Goose/Qinghai/12/2005 and H1 subunit (1-345 residues) of A/Vietnam/1194/2004. The strongest response has been observed for the long variant with detection limit of 2.2 pg/mL and dynamic range from 4.0 to 20.0 pg/mL.

DNA probe modified with 3-iron bis(dicarbollide) for electrochemical determination of DNA sequence of Avian Influenza Virus H5N1.

In this work, we report on oligonucleotide probes bearing metallacarborane [3-iron bis(dicarbollide)] redox label, deposited on gold electrode for electrochemical determination of DNA sequence derived from Avian Influenza Virus (AIV), type H5N1. The oligonucleotide probes containing 5'-terminal NH2 group were covalently attached to the electrode, via NHS/EDC coupling to 3-mercaptopropionic acid SAM, previously deposited on the surface of gold. The changes in redox activity of Fe(III) centre of the metallacarborane complex before and after hybridization process was used as analytical signal. The signals generated upon hybridization with targets such as complementary or non-complementary 20-mer ssDNA or various PCR products consisting of 180-190 bp (dsDNA) were recorded by Osteryoung square-wave voltammetry (OSWV). The developed system was very sensitive towards targets containing sequence complementary to the probe with the detection limit estimated as 0.03 fM (S/N=3.0) and 0.08 fM (S/N=3.0) for 20-mer ssDNA and for dsDNA (PCR product), respectively. The non-complementary targets generated very weak responses. Furthermore, the proposed genosensor was suitable for discrimination of PCR products with different location of the complementarity region.

Association constants of pyridine and piperidine alkaloids to amyloid beta peptide determined by electrochemical impedance spectroscopy.

Amyloid beta(1-40) peptide was immobilized on an Au-colloid modified gold electrode and an electrochemical impedance spectroscopy (EIS) system was elaborated for determining the association constants, K(a), between small molecular ligands and the peptide. The changes in the resistance of the modified electrode layer with deposited Abeta(1-40) peptide were measured with EIS in relation to a series of concentrations of the ligands studied. The association constants were calculated from Langmuir isotherms. The method is sensitive, reproducible and consumes only very little amounts of interacting species. The method was applied to determine the affinity of a series of pyridine and piperidine derivatives, mainly alkaloids of a known ability, to cross the blood-brain barrier. Along with nicotine and its main metabolite cotinine, the following agents were taken for the study: anabasine, arecoline, coniine, lobeline, pseudopelletierine, trigonelline, as well as pyridine and piperidine themselves. For the sake of comparison, two vitamins were also subjected to the study: ascorbic acid and pyridoxine. There was no association of these vitamins, which were tested as a negative control. For the compounds studied, a strong association with Abeta(1-40) was determined with K(a) ranging from 1.7 x 10(7) M(-1) for (+/-)-anabasine to 2.3 x 10(8) M(-1) for arecoline hydrobromide. As a positive control, a well known amyloid specific binder, Congo Red, was tested, displaying K(a) equal to 3.7 x 10(8) M(-1).

Electrochemical biosensor for pesticides based on acetylcholinesterase immobilized on polyaniline deposited on vertically assembled carbon nanotubes wrapped with ssDNA.

An electrochemical biosensor for the determination of pesticides: methyl parathion and chlorpyrifos, two of the most commonly used organophosphorous insecticides in vegetable crops, is described. The self-assembled monolayers (SAMs) of single walled carbon nanotubes (SWCNT) wrapped by thiol terminated single strand oligonucleotide (ssDNA) on gold was utilized to prepare nano size polyaniline matrix for acetylcholinesterase (AChE) enzyme immobilization. The key step of this biosensor was AChE-acetylcholine enzymatic reaction which causes the small changes of local pH in the vicinity of an electrode surface. The pesticides were determined through inhibition of enzyme reaction. The dynamic range for the determination of methyl parathion and chlorpyrifos was found to be in between 1.0x10(-11) and 1.0x10(-6) M (0.6

Iron (III) porphyrin bearing 2,6-di-tert-butylphenol pendants deposited onto gold electrodes for amperometric determination of L-histidine.

A sensitive amperometric sensor for determination of L-histidine was developed using gold electrode modified with Fe(III)-porphyrin bearing three 2,6-di-tert-butylphenol groups and one palmitoyl chain. Two methods of electrode modification were applied: direct chemisorption and embedment into dodecanethiol monolayer. Both types of electrodes were used for detection of L-histidine using Osteryoung square-wave voltammetry. The sensitivity of sensors presented towards L-histidine depends on the method of electrode modification. The detection limits observed for the electrodes incorporating with Fe(III)-porphyrin host by embedment and chemisorption were in 1 and 100 nM ranges, respectively. In addition, the determination of L-histidine with electrode modified by embedment technique was more precise, in comparison to that obtained by the direct chemisorption. Applicability of gold electrodes modified with Fe(III)-porphyrin for the direct electrochemical determination of L-histidine was demonstrated using the artificial matrix mimicking human serum.

A Voltammetric Biosensor Based on Glassy Carbon Electrodes Modified with Single-Walled Carbon Nanotubes/Hemoglobin for Detection of Acrylamide in Water Extracts from Potato Crisps.

The presence of toxic acrylamide in a wide range of food products such as potato crisps, French fries or bread has been confirmed by Swedish scientists from Stockholm University. The neurotoxicity, possible carcinogenicity of this compound and its metabolites compels us to control them by quantitative and qualitative assays. Acrylamide forms adduct with hemoglobin (Hb) as a result of the reaction the -NH2 group of the Nterminal valine with acrylamide. In this work we present the use of glassy carbon electrodes coated with single-walled carbon nanotubes (SWCNTs) and Hb for voltammetric detection of acrylamide in water solutions. The electrodes presented a very low detection limit (1.0×10-9 M). The validation made in the matrix obtained by water extraction of potato crisps showed that the electrodes presented are suitable for the direct determination of acrylamide in food samples.

Electrochemical impedance spectroscopy for study of amyloid beta-peptide interactions with (-) nicotine ditartrate and (-) cotinine.

Immobilization of amyloid beta (Abeta) (1-40) peptide on Au-colloid modified gold electrodes has been studied. Colloidal Au was self-assembled onto gold electrodes through the thiol groups of 1,6-hexanedithiol monolayer. Next, buffered aqueous solution of Abeta (1-40) peptide existing in the beta-sheet structure in the acidic media was dropped on the electrode surface. Each step of electrode modification has been confirmed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The changes of the resistance of the layer with deposited Abeta (1-40) peptide, occurred under stimulation by different concentration of (-) nicotine ditartrate and (-) cotinine were measured with EIS and were used for the calculation of association constants. The gentle measuring conditions applied in electrochemical impedance spectroscopy, together with suitable environment for biomolecules immobilization created by Au-colloid, might be recommended as the analytical tool for assessing the effectiveness of potential drugs used in Alzheimer's disease (AD) therapy.

Novel voltammetric biosensor for determining acrylamide in food samples.

Recent findings showing that acrylamide is formed in heat-treated foods rich in asparagine and reducing sugars such as glucose, have accelerated the needs for the development of new analytical methods to determine this potential human carcinogen. Acrylamide forms adduct with hemoglobin (Hb) as a result of the reaction with the alpha-NH2 group of N-terminal valine of Hb. This interaction is the basis of a new voltammetric biosensor to detect acrylamide. The biosensor was constructed using a carbon-paste electrode modified with hemoglobin (Hb), which contains four prosthetic groups of heme--Fe(III). Such an electrode displays a reversible reduction/oxidation process of Hb-Fe(III)/Hb-Fe(II). Interaction between Hb and acrylamide was observed through decreasing of the peak current of Hb-Fe(III) reduction. The electrodes presented a very low detection limit (1.2 x 10(-10)M). The validation made in the matrix obtained by water extraction of potato chips showed that the electrodes presented are suitable for the direct determination of acrylamide in food samples.