Voltammetric Sensing of Chloride Based on a Redox-Active Complex: A Terpyridine-Co(II)-Dipyrromethene Functionalized Anion Receptor Deposited on a Gold Electrode.

A redox-active complex containing Co(II) connected to a terpyridine (TPY) and dipyrromethene functionalized anion receptor (DPM-AR) was created on a gold electrode surface. This host-guest supramolecular system based on a redox-active layer was used for voltammetric detection of chloride anions in aqueous solutions. The sensing mechanism was based on the changes in the redox activity of the complex observed upon binding of the anion to the receptor. The electron transfer coefficient (α) and electron transfer rate constant (k0) for the modified gold electrodes were calculated based on Cyclic Voltammetry (CV) experiments results. On the other hand, the sensing abilities were examined using Square Wave Voltammetry (SWV). More importantly, the anion receptor was selective to chloride, resulting in the highest change in Co(II) current intensity and allowing to distinguish chloride, sulfate and bromide. The proposed system displayed the highest sensitivity to Cl- with a limit of detection of 0.50 fM. The order of selectivity was: Cl- > SO42- > Br-, which was confirmed by the binding constants (K) and reaction coupling efficiencies (RCE).

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.

Redox-Active Monolayers Self-Assembled on Gold Electrodes-Effect of Their Structures on Electrochemical Parameters and DNA Sensing Ability.

The background: The monolayers self-assembled on the gold electrode incorporated transition metal complexes can act both as receptor ("host" molecules) immobilization sites, as well as transducer for interface recognitions of "guest" molecules present in the aqueous solutions. Their electrochemical parameters influencing the sensing properties strongly depend on the transition metal complex structures. The objectives: The electrochemical characterization of the symmetric terpyridine-M2+-terpyridine and asymmetric dipyrromethene-M2+-terpyridine complexes modified with ssDNA probe covalently attached to the gold electrodes and exploring their ssDNA sensing ability were the main aims of the research presented. The methods: Two transition metal cations have been selected: Cu2+ and Co2+ for creation of redox-active monolayers. The electron transfer coefficients indicating the reversibility and electron transfer rate constant measuring kinetic of redox reactions have been determined for all SAMs studied using: Cyclic Voltammetry, Osteryoung Square-Wave Voltammetry, and Differential Pulse Voltammetry. All redox-active platforms have been applied for immobilization of ssDNA probe. Next, their sensing properties towards complementary DNA target have been explored electrochemically. The results: All SAMs studied were stable displaying quasi-reversible redox activity. The linear relationships between cathodic and anodic current vs. san rate were obtained for both symmetric and asymmetric SAMs incorporating Co2+ and Cu2+, indicating that oxidized and reduced redox sites are adsorbed on the electrode surface. The ssDNA sensing ability were observed in the fM concentration range. The low responses towards non-complementary ssDNA sequences provided evidences for sensors good selectivity. The conclusions: All redox-active SAMs modified with a ssDNA probe were suitable for sensing of ssDNA target, with very good sensitivity in fM range and very good selectivity. The detection limits obtained for SAMs incorporating Cu2+, both symmetric and asymmetric, were better in comparison to SAMs incorporating Co2+. Thus, selection of the right transition metal cation has stronger influence on ssDNA sensing ability, than complex structures.

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.

Highly sensitive electrochemical biosensor based on redox - active monolayer for detection of anti-hemagglutinin antibodies against swine-origin influenza virus H1N1 in sera of vaccinated mice.

BACKGROUND: In this work, we report an electrochemical biosensor for the detection of anti-hemagglutinin antibodies against the swine virus H1N1 present in mice sera immunized with mixture of His6-H1 HA in monomeric and oligomeric form. The oriented immobilization of the recombinant His-tagged hemagglutinin (His6-H1 HA) consists of: (i) formation of a mixed layer of 4-mercaptobutanol (MBT) and the thiol derivative of dipyrromethene (DPM); (ii) complexation of Cu (II) by DPM; (iii) immobilization of His6-H1 HA via coordination bonds between Cu (II) sites from DPM-Cu (II) complex and imidazole nitrogen atoms of a histidine tag; (iv) filling free spaces with bovine serum albumin. The interactions between recombinant His6- H1 HA covalently attached to the electrode surface and the anti-hemagglutinin H1 antibodies present in mice sera were explored with Osteryoung square-wave voltammetry. RESULTS: This analytical device was able to detect the antibodies present in vaccinated mice sera diluted from 1 × 109 to 1 × 108 fold. CONCLUSIONS: The unprecedented sensitivity of described biosensor is much better than widely use ELISA test and other analytical methods for determination of antibodies against the influenza A viruses. It has been proved that redox active DPM-Cu (II) monolayer is a universal platform suitable for stable and oriented immobilization of any His-tagged sensing elements. Thus, this universal layer could be a base of numerous analytical devices suitable for detection of antibodies against different viruses.

Highly Sensitive Electrochemical Sensor for the Detection of Anions in Water Based on a Redox-Active Monolayer Incorporating an Anion Receptor.

In the present work, gold electrodes were modified using a redox-active layer based on dipyrromethene complexes with Cu(II) or Co(II) and a dipodal anion receptor functionalized with dipyrromethene. These modified gold electrodes were then applied for the electrochemical detection of anions (Cl-, SO42-, and Br-) in a highly diluted water solution (in the picomolar range). The results showed that both systems, incorporating Cu(II) as well as Co(II) redox centers, exhibited highest sensitivity toward Cl-. The selectivity sequence found for both systems was Cl- > SO42- > Br-. The high selectivity of Cl- anions can be attributed to the higher binding constant of Cl- with the anion receptor and the stronger electronic effect between the central metal and anion in the complex. The detection limit for the determination of Cl- was found at the 1.0 pM level for both sensing systems. The electrodes based on Co(II) redox centers displayed better selectivity toward Cl- anion detection than those based on Cu(II) centers which can be attributed to the stronger electronic interaction between the receptor-target anion complex and the Co(II)/Co(III) redox centers in comparison to the Cu(II)/Cu(I) system. Applicability of gold electrodes modified with DPM-Co(II)-DPM-AR for the electrochemical determination of Cl- anions was demonstrated using the artificial matrix mimicking human serum.

Gold Electrodes Modified with Calix[4]arene for Electrochemical Determination of Dopamine in the Presence of Selected Neurotransmitters.

Here, we present an electrochemical sensor based on gold electrodes modified with calix[4]arene functionalized with carboxypiperidino groups at the upper rim. It has been demonstrated that these groups are involved in a complex formation with dopamine (DA) on the surface of gold electrodes. The supramolecular complex calix[4]arene-DA created on the gold electrode surface has been characterized electrochemically and the measuring conditions have been optimized. The presented sensor displayed a detection limit in the pM range. The DA determination was performed successfully in the presence of ascorbic acid, uric acid and selected neurotransmitters.

Electrochemical label-free and reagentless genosensor based on an ion barrier switch-off system for DNA sequence-specific detection of the avian influenza virus.

This paper concerns the development of genosensors based on redox-active monolayers incorporating (dipyrromethene)2Cu(II) and (dipyrromethene)2Co(II) complexes formed step by step on a gold electrode surface. They were applied for electrochemical determination of oligonucleotide sequences related to avian influenza virus (AIV) type H5N1. A 20-mer probe (NH2-NC3) was covalently attached to the gold electrode surface via a reaction performed in the presence of ethyl(dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide (EDC/NHS) between the amine group present in the probe and carboxylic groups present on the surface of the redox-active layer. Each modification step has been controlled with Osteryoung square-wave voltammetry. The genosensor incorporating the (dipyrromethene)2Cu(II) complex was able to detect a fully complementary single-stranded DNA target with a detection limit of 1.39 pM. A linear dynamic range was observed from 1 to 10 pM. This genosensor displays good discrimination between three single-stranded DNA targets studied: fully complementary, partially complementary (with only six complementary bases), and totally noncomplementary to the probe. When the (dipyrromethene)2Co(II) complex was applied, a detection limit of 1.28 pM for the fully complementary target was obtained. However, this genosensor was not able to discriminate partially complementary and totally noncomplementary oligonucleotide sequences to the probe. Electrochemical measurements, using both types of genosensors in the presence of different supporting electrolytes, were performed in order to elaborate a new mechanism of analytical signal generation based on an ion barrier "switch-off" system.

A biosensor based on electroactive dipyrromethene-Cu(II) layer deposited onto gold electrodes for the detection of antibodies against avian influenza virus type H5N1 in hen sera.

This paper describes the development of a biosensor for the detection of anti-hemagglutinin antibodies against the influenza virus hemagglutinin. The steps of biosensor fabrications are as follows: (i) creation of a mixed layer containing the thiol derivative of dipyrromethene and 4-mercapto-1-butanol, (ii) complexation of Cu(II) ions, (iii) oriented immobilization of the recombinant histidine-tagged hemagglutinin, and (iv) filling free spaces with bovine serum albumin. The interactions between recombinants hemagglutinin from the highly pathogenic avian influenza virus type H5N1 and anti-hemagglutinin H5 monoclonal antibodies were explored with Osteryoung square-wave voltammetry. The biosensor displayed a good detection limit of 2.4 pg/mL, quantification limit of 7.2 pg/mL, and dynamic range from 4.0 to 100.0 pg/mL in buffer. In addition, this analytical device was applied for the detection of antibodies in hen sera from individuals vaccinated and non-vaccinated against the avian influenza virus type H5N1. The limit of detection for the assay was the dilution of sera 1: 7 × 10(6), which is about 200 times better than the enzyme-linked immunosorbent assay.

Ion-channel genosensor for the detection of specific DNA sequences derived from Plum Pox Virus in plant extracts.

A DNA biosensor for detection of specific oligonucleotides sequences of Plum Pox Virus (PPV) in plant extracts and buffer is proposed. The working principles of a genosensor are based on the ion-channel mechanism. The NH2-ssDNA probe was deposited onto a glassy carbon electrode surface to form an amide bond between the carboxyl group of oxidized electrode surface and amino group from ssDNA probe. The analytical signals generated as a result of hybridization were registered in Osteryoung square wave voltammetry in the presence of [Fe(CN)6]3-/4- as a redox marker. The 22-mer and 42-mer complementary ssDNA sequences derived from PPV and DNA samples from plants infected with PPV were used as targets. Similar detection limits of 2.4 pM (31.0 pg/mL) and 2.3 pM (29.5 pg/mL) in the concentration range 1-8 pM were observed in the presence of the 22-mer ssDNA and 42-mer complementary ssDNA sequences of PPV, respectively. The genosensor was capable of discriminating between samples consisting of extracts from healthy plants and leaf extracts from infected plants in the concentration range 10-50 pg/mL. The detection limit was 12.8 pg/mL. The genosensor displayed good selectivity and sensitivity. The 20-mer partially complementary DNA sequences with four complementary bases and DNA samples from healthy plants used as negative controls generated low signal.

Voltammetric detection of S100B protein using His-tagged receptor domains for advanced glycation end products (RAGE) immobilized onto a gold electrode surface.

In this work we report on an electrochemical biosensor for the determination of the S100B protein. The His-tagged VC1 domains of Receptors for Advanced Glycation End (RAGE) products used as analytically active molecules were covalently immobilized on a monolayer of a thiol derivative of pentetic acid (DPTA) complex with Cu(II) deposited on a gold electrode surface. The recognition processes between the RAGE VC1 domain and the S100B protein results in changes in the redox activity of the DPTA-Cu(II) centres which were measured by Osteryoung square-wave voltammetry (OSWV). In order to verify whether the observed analytical signal originates from the recognition process between the His6-RAGE VC1 domains and the S100B protein, the electrode modified with the His6-RAGE C2 and His6-RAGE VC1 deleted domains which have no ability to bind S100B peptides were applied. The proposed biosensor was quite sensitive, with a detection limit of 0.52 pM recorded in the buffer solution. The presence of diluted human plasma and 10 nM Aß(1-40) have no influence on the biosensor performance.

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.

Single electrode genosensor for simultaneous determination of sequences encoding hemagglutinin and neuraminidase of avian influenza virus type H5N1.

The duo-genosensor consisting of two different oligonucleotide probes immobilized covalently on the surface of one gold electrode via Au-S bond formation was used for simultaneous determination of two different oligonucleotide targets. One of the probes, decorated on its 5'-end with ferrocene (SH-ssDNA-Fc), is complementary to the cDNA representing a sequence encoding part of H5 hemagglutinin from H5N1 virus. The second probe, decorated on its 5'-end with methylene blue (SH-ssDNA-MB), is complementary to cDNA representing the fragment of N1 neuraminidase from the same virus. The presence of both probes on the surface of gold electrodes was confirmed with Osteryoung square-wave voltammetry (OSWV). The changes in redox activity of both redox active complexes before and after the hybridization process were used as analytical signal. The peak at +400 ± 2 mV was observed in the presence of 40 nM ssDNA used as a target for SH-ssDNA-Fc probe. This peak increased with the increase of concentration of target ssDNA. It indicates the "signal on" mode of analytical signal generation. The peak at -250 ± 4 mV, characteristic for SH-ssDNA-MB probe, was decreasing with the increase of the concentration of the complementary ssDNA target starting from 8 to 100 nM. This indicates the generation of electrochemical signal according to the "signal off" mode. The proposed duo-genosensor is capable of simultaneous, specific, and good sensitivity probing for the sequences derived from genes encoding two main markers of the influenza virus, hemagglutinin and neuraminidase.

Oriented immobilization of His-tagged protein on a redox active thiol derivative of DPTA-Cu(II) layer deposited on a gold electrode--the base of electrochemical biosensors.

This paper concerns the development of an electrochemical biosensor for the determination of Aß(16-23') and A(ß1-40) peptides. The His-tagged V and VC1 domains of Receptor for Advanced Glycation end Products (RAGE) immobilized on a gold electrode surface were used as analytically active molecules. The immobilization of His6-RAGE domains consists of: (i) formation of a mixed layer of N-acetylcysteamine (NAC) and the thiol derivative of pentetic acid (DPTA); (ii) complexation of Cu(II) by DPTA; (iii) oriented immobilization of His6-RAGE domains via coordination bonds between Cu(II) sites from DPTA-Cu(II) complex and imidazole nitrogen atoms of a histidine tag. Each modification step was controlled by cyclic voltammetry (CV), Osteryoung square-wave voltammetry (OSWV), and atomic force microscopy (AFM). The applicability of the proposed biosensor was tested in the presence of human plasma, which had no influence on its performance. The detection limits for Aß(1-40) determination were 1.06 nM and 0.80 nM, in the presence of buffer and human plasma, respectively. These values reach the concentration level of Aß(1-40) which is relevant for determination of its soluble form in human plasma, as well as in brain. This indicates the promising future application of biosensor presented for early diagnosis of neurodegenerative diseases.

Surface plasmon resonance based biosensors for exploring the influence of alkaloids on aggregation of amyloid-ß peptide.

The main objective of the presented study was the development of a simple analytical tool for exploring the influence of naturally occurring compounds on the aggregation of amyloid-ß peptide (Aß(40)) in order to find potential anti-neurodegenerative drugs. The gold discs used for surface plasmon resonance (SPR) measurements were modified with thioaliphatic acid. The surface functionalized with carboxylic groups was used for covalent attaching of Aß(40) probe by creation of amide bonds in the presence of EDC/NHS. The modified SPR gold discs were used for exploring the Aß(40) aggregation process in the presence of selected alkaloids: arecoline hydrobromide, pseudopelletierine hydrochloride, trigonelline hydrochloride and α-lobeline hydrochloride. The obtained results were discussed with other parameters which govern the phenomenon studied such as lipophilicity/hydrophilicy and Aß(40)-alkaloid association constants.

Immunosensor incorporating half-antibody fragment for electrochemical monitoring of amyloid-ß fibrils in artificial blood plasma.

In this report, an electrochemical immunosensor for the selective and sensitive monitoring of Aß1-42 fibrils is presented. The sensing platform was prepared by the formation of a 4,4'-thiobisbenzenethiol (TBBT) self-assembled monolayer on a clean gold surface followed by the covalent entrapment of gold nanoparticles (AuNPs). The half-antibody fragments of the Anti-Amyloid Fibrils antibody were immobilized on AuNPs via S-Au covalent bonds. Each step of immunosensor fabrication was characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The biosensor was successfully used for the sensing of Aß1-42 fibrils in both phosphate saline buffer (PBS) and artificial blood plasma (ABP). The immunosensor sensitivity estimated based on calibration slopes was better in the presence of APP in the comparison to PBS. The LOD values obtained for both measuring media were of 0.6 pM level. The moderate response towards Aß1-42 oligomers demonstrated the immunosensor selectivity.

Silver or gold? A comparison of nanoparticle modified electrochemical genosensors based on cobalt porphyrin-DNA.

We applied a cobalt-porphyrin modified DNA as electrochemical marker, which was attached to nanoparticles, to detect specific DNA sequences. We compare the performance of gold and silver NPs in oligonucleotide sensors to determine if a change in metal will lead to either higher sensitivity or different selectivity, based on the redox behaviour of silver vs. gold. Surprisingly, we find that using either gold or silver NPs yields very similar overall performance. The electrochemical measurements of both types of sensors show the same redox behaviour which is dominated by the cobalt porphyrin, indicating that the electron pathway does not include the NP, but there is direct electron transfer between the porphyrin and the electrode. Both sensors show a linear response in the range of 5 × 10-17-1 × 10-16 M; the limit of detection (LOD) is 3.8 × 10-18 M for the AuNP sensor, and 5.0 × 10-18 M for the AgNP sensor, respectively, which corresponds to the detection of about 20-50 DNA molecules in the analyte. Overall, the silver system results in a better DNA economy and using cheaper starting materials for the NPs, thus shows better cost-effectivness and could be more suitable for the mass-production of highly sensitive DNA sensors.

Ultrasensitive electrochemical genosensor for direct detection of specific RNA sequences derived from avian influenza viruses present in biological samples.

An electrochemical genosensor based on an epoxy-phenanthroline-Fe(III)-NH2-ssDNA layer for the detection of RNA derived from Avian Influenza is presented. The biosensor preparation consists of: (I) modification of gold electrodes with aminoethanethiol, (II) modification of the self-assembled monolayer of aminoethanethiol with 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline using "click" chemistry, (III) a first step of complexation of Fe(III) by 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline, (IV) a second step of complexation of Fe(III) by 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline, (V) immobilization of the single stranded amino-DNA probe via "click" chemistry between epoxy and amino groups. The interactions between the ssDNA probe and RNA targets were explored with Osteryoung Square Wave Voltammetry. The genosensor showed a remarkable detection limit of 3 copies/µL (5 aM) for RNA extracted from A/swan/Poland/305/06 (H5N1) containing a fully complementary sequence. A linear dynamic range for this sequence was observed from 3.0×103 to 3.0×105 [copies/µl]. RNA extracted from A/mallard/Poland/446/09 (H7N7), containing a non-complementary sequence, generated a much weaker response. Moreover, the developed genosensor allows to distinguish RNA present in biological samples having 2, 3 and 4 mismatches. This biosensing approach can become a potential alternative tool for detecting RNA samples in biomedical research and early clinical diagnosis of avian influenza viruses.

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.

Approaching single DNA molecule detection with an ultrasensitive electrochemical genosensor based on gold nanoparticles and cobalt-porphyrin DNA conjugates.

We describe an ultrasensitive electrochemical genosensor based on gold nanoparticles and cobalt-porphyrin functionalised ssDNA probes. The sensitivity at the attomolar concentration level arises from an increased density of redox labels on the electrode surface compared to sensors without NP modification. The electrode detects as few as 23 DNA molecules, approaching single molecule detection.