Voltammetric detection of vitamin D employing Au-MoS2 hybrid as immunosensing platform.

A voltammetric immunosensor based on molybdenum sulphide (MoS2) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D3 (25(OH)D3) is reported. Anti-vit D (Ab-25(OH)D3) was immobilized onto the cysteamine-modified MoS2 and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS2/FTO). The MoS2 sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS2/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS2/FTO which acts as a linker to covalently bind Ab-25(OH)D3. The Ab-25(OH)D3-immobilized Cys/Au/MoS2/FTO was used to detect 25(OH)D3 using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D3 and 25(OH)D3. The immunosensor shows linear response from 1 pg mL-1 to 100 ng mL-1 25(OH)D3 and a sensitivity of 189 µA [log (pg mL-1)]-1 cm-2 along with a low limit of detection (LOD) of 0.38 pg mL-1. The immunosensor is highly selective towards 25(OH)D3 and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15-3.22%).

Electrochemical biosensor for miRNA-21 based on gold-platinum bimetallic nanoparticles coated 3-aminopropyltriethoxy silane.

We report an electrochemical biosensor based on gold platinum bimetallic nanoparticles (AuPtBNPs)/3-aminopropyltriethoxy silane (APTS) nanocomposite coated fluorine-doped tin oxide (FTO) as a biosensing platform for hybridization-based detection of miRNA-21. Field Emission-Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and electrochemical measurements were carried out to ensure the successful construction of the biosensor. The amount of cDNA immobilized on electrode surface and hybridization time required for the miRNA-21 sensing were optimized. The biosensing platform showed detection limit of 0.63 fM with wide linear range i.e. 1 fM-100 nM for miRNA-21 detection. The biosensing strategy demonstrates a good recovery yield from 90.18% to 94.6% in serum samples. It offers good selectivity for its complementary miRNA compared to the non-complementary miRNAs. Other analytical features of the biosensor such as stability, reusability and reproducibility were also tested, providing appropriate results.

Gold-silver core-shell nanoparticle-based impedimetric immunosensor for detection of iron homeostasis biomarker hepcidin.

An impedimetric immunosensor based on gold-silver core-shell nanoparticles for hepcidin detection is reported. The core-shell nanoparticles were prepared by seed-mediated method and characterized by dynamic light scattering, UV-Vis, XRD, field emission-scanning electron micrograph imaging, energy dispersive spectroscopy, and atomic force microscopy. The immunosensor was fabricated with core-shell nanoparticles and cysteamine employing covalent chemistry (amide bond formation) strategy for ensuring proper orientation of anti-hepcidin antibody on to the amine-functionalized nanomaterial decorated electrodes. The hepcidin detection principle was based on the variation of charge transfer resistance (ΔRct) relative to the Fe(CN)64-/3- electrochemical probe in the presence of the biomarker. The frequency range was 10-1 to 105 Hz at the scan rate of 10 mV s-1and a potential of 0.1 V. Based on the antigen-antibody interaction in 40 min at pH 7.0, a linear relationship between ΔRct and hepcidin concentration was obtained in the range 0.01 to 100 ng/mL with a detection limit of 0.857 pg/mL. Furthermore, the designed immunosensor had acceptable reproducibility, stability, selectivity, and reusability. It was successfully applied to the detection of hepcidin in spiked human serum samples and acceptable recovery (90-95.9%) was obtained. Graphical abstract Gold-silver core-shell nanoparticle-based impedimetric immunosensor for detection of iron homeostasis biomarker hepcidin. The study focuses on the detection of iron regulatory protein hepcidin using gold-silver core-shell nanoparticles. This immunosensor was fabricated with core-shell nanoparticles and cysteamine employing covalent chemistry (amide bond formation) strategy. The sensor was sensitive in the range from 0.01 to 100 ng/mL, with a detection limit of 0.857 pg/mL.

A voltammetric hybridization assay for microRNA-21 using carboxylated graphene oxide decorated with gold-platinum bimetallic nanoparticles.

An electrochemical hybridization assay is described for the determination of microRNA-21. Fluorine tin oxide (FTO) sheets were coated with carboxylated graphene oxide followed by deposition of gold-platinum bimetallic nanoparticles by using chronoamperometry at a potential of -0.2 V for 350 s. The capture probe was immobilized on the surface of the modified FTO sheets by biotin-avidin interaction. On exposure to microRNA-21, hybridization occurs, and that can be detected at a relatively low working potential of 0.25 V by using ferri/ferro-cyanide as an electrochemical probe. The various modifications of the FTO sheets were characterized by means of FE-SEM, FT-IR, contact angle studies and electrochemical techniques. The effects of pH value, EDC-NHS activation time, concentration of capture probe and incubation time were optimized. The sensor has a wide linear response that extends from 1 fM to 1 µM of microRNA-21, and the detection limit is 1 fM. The sensor is stable for about 15 days (by retaining 90% of its initial activity) and can be reused for about 3 times (85% of initial activity) after regeneration with 50 mM NaOH solution. The sensor was applied to the analysis of spiked human serum and gave recoveries between 90 and 111%. Graphical abstract Carboxylated graphene oxide (CGO) coated on a fluorine tin oxide (FTO) electrode was decorated with Au-Pt bimetallic nanoparticles (Au-PtBNPs). The Au-PtBNPs/CGO/FTO electrode surface was used for immobilizing streptavidin and biotinylated capture probe which can electrochemically detect microRNA-21 based on its sequence complementarity.

Ultrasensitive detection of holoTC for analysis of Vitamin B12 levels using Ag2MoO4 deposited PEDOT sensing platform.

Vitamin B12 is an essential micronutrient required for the proper functioning of the human body. Vitamin B12 deficiency is primarily causative of various neurolological disorders alongwith recurrence of oral ulcers and burning sensations which are early signs of condition such as pernicious anemia. Other complications associated with Vitamin B12 deficiency include risk of heart failure due to anemia, risk of developing autoimmune disorders and gastric cancer. Therefore, to obstruct these communal health issues, early detection of Vit B12 is highly needed. However, screening of vitamin B12 insufficiency is hindered by the low sensitivity of the conventional vitamin B12 test. Holotranscobalamin (holoTC) is an early indicator of the negative vitamin B12 balance as it is the first protein to decline in the serum. We report a novel impedimetric immunosensor based on flower-like poly (3,4-ethylenedioxythiophene) (PEDOT) nanostructural film impregnated with silver molybdate nanoparticles (Ag2MoO4 NPs) deposited on fluorine-doped tin oxide electrode. The prepared electrodes were characterized by Field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical studies. The activated anti-holoTC antibody was immobilized and optimized to capture the target in a response time of 15 min. The electrochemical performance of the sensor was carried out by using the electrochemical impedance spectroscopy technique (EIS) and a good linear relationship between ΔRct and holoTC was obtained in the range from 0.1 pg mL-1 to 100 ng mL-1 with a detection limit of 0.093 pg mL-1. The proposed sensor was successfully applied in human serum samples for holoTC detection. The experimental results showed that the immunosensor is highly selective towards holoTC and presented an acceptable stability of 20 days with reproducibility RSD ≤4%. To the best of our knowledge, this is the first developed electrochemical immunosensor for holoTC detection.

MC-Au/MSS-Z8 porous network assisted advanced electrochemical immunosensing of 25-hydroxyvitamin D3.

On-site monitoring of vitamin D levels is subject matter of immediate attention owing to the serious aftermath of its long standing deficiency. Therefore, a novel and efficient voltammetric immunosensing of 25-hydroxyvitamin D3 (25(OH)VD3) has been experimented based on an advanced sensing platform composed of meso-microporous silica-zeolitic imidazolate framework-8 (MSS-Z8) with highly enhanced surface area (SBET, MSS-Z8 (643.4 m2g-1) > SBET, MSS (49.95 m2g-1)), embedded with gold particles (mass loading of 82 µg), particularly of microcubic morphology (MC-Au). Further, the MC-Au/MSS-Z8/FTO platform was fashioned with antibody specific to 25(OH)VD3 via interaction between Au and abundant -SH groups present on the antibody surface. After optimization of operational parameters, the Ab/MC-Au/MSS-Z8/FTO immunosensor was employed for the determination of 25(OH)VD3 within 0.01-106 pg mL-1 concentration range through differential pulse voltammetry technique in [Fe(CN)6]3-/4-. Thus, 0.01 pg mL-1 concentration of 25(OH)VD3 was the experimental limit of detection of the immunosensor. Further, upon examination of various analytical parameters, it turns out that the immunosensor exhibited low theoretical LOD (0.23 pg mL-1) and LOQ (0.76 pg mL-1), wide linear range (0.01-106 pg mL-1), ultra-sensitivity (143.9 µA [log (pg mL-1)]-1 cm-2), adequate reproducibility (RSD ≤1.23%) and acceptable shelf life. Most importantly, the immunosensor presented proficient performance with spiked human serum samples (Recovery = 97.20-100.7%, RSD value < 5.6%), evincing the adequacy of present biosensing approach.

Evaluation of liver specific ionizable lipid nanocarrier in the delivery of siRNA.

Hepcidin, a key regulator of iron homeostasis, has been implicated in the pathogenesis of various iron-related diseases. Although small interfering RNA (siRNA) are potent to modulate the expression of hepcidin, their bioavailability remains a major issue. The ß-galactopyranoside-conjugated liposomes (GAL-liposome) targeting liver synthesized hepcidin were prepared by thin lipid film hydration method to encapsulate siRNA and the conjugation of ß-galactopyranoside to the lipid nanocarrier was achieved by covalent chemistry. The prepared siRNA loaded GAL-lip were spherical with around 50 nm radius in size as observed by HR-TEM. The zeta potential and polydispersity index of the prepared liposomes were - 19.9 ± 0.96 mV and 0.44 ± 0.05, respectively. The encapsulation efficiency as determined by dialysis bag method was around 91.76 ± 1.74%. The cell viability and cellular uptake analysis was examined in HepG2 cells by MTT assay and flow cytometry, respectively. The stability and cumulative release of siRNA was also assessed. The hepcidin mRNA expression on administration of siRNA loaded GAL-lip was determined in HepG2 cells and in lipopolysaccharide-induced mice model followed by examining itsin vivo biodistribution by fluorescence microscopy. The results suggested thatsiRNA loaded GAL-lip reduced the hepcidin levels, thus, highlighting a novel ligand conjugated ionizable lipid-based nanocarrier for inducing RNA interference.

Iron disorders and hepcidin.

Iron is an essential element due to its role in a wide variety of physiological processes. Iron homeostasis is crucial to prevent iron overload disorders as well as iron deficiency anemia. The liver synthesized peptide hormone hepcidin is a master regulator of systemic iron metabolism. Given its role in overall health, measurement of hepcidin can be used as a predictive marker in disease states. In addition, hepcidin-targeting drugs appear beneficial as therapeutic agents. This review emphasizes recent development on analytical techniques (immunochemical, mass spectrometry and biosensors) and therapeutic approaches (hepcidin agonists, stimulators and antagonists). These insights highlight hepcidin as a potential biomarker as well as an aid in the development of new drugs for iron disorders.

Electrochemical detection of hepcidin based on spiegelmer and MoS2NF-GNR@AuNPs as sensing platform.

Spiegelmers, mirror image L- RNA oligonucleotides, possesses high plasma stability and non-immunogenicity. Herein, a novel spiegelmer based impedimetric biosensor grafted with Au nanoparticles and molybdenum disulfide nanoflowers/graphene nanoribbons nanocomposite has been designed to detect hepcidin in spiked-in human serum sample. Firstly, molybdenum disulfide nanoflowers/graphene nanoribbons (MoS2NF-GNR) hybrid was drop-casted onto the FTO electrode followed by electro deposition of Au nanoparticles (AuNPs). Hepcidin specific thiolated spiegelmer was then immobilized on the MoS2NF-GNR@AuNPs for hepcidin detection. Electrochemical impedance spectroscopy was used to assess the performance of the sensing platform based on the variation of charge transfer resistance (ΔRct) relative to the Fe(CN)64-/3- electrochemical probe in the presence of hepcidin. The impedance signals were recorded at the frequency range of 10-1 to 105 Hz and potential was set as 0.18 V. Under optimized conditions, the limit of detection of spiegelmer based sensor for hepcidin was 0.173 pgmL-1 within a wide linear range of 0.005-10 ngmL-1. The biosensor possesses selectivity, acceptable reproducibility with RSD as 4.76% and stability for up to 20 days. The satisfactory recovery result (89.8-103.1 %) in human serum indicates that the sensor has applicability in clinical monitoring of hepcidin.

An electrochemical aptasensor for analysis of MUC1 using gold platinum bimetallic nanoparticles deposited carboxylated graphene oxide.

A simple electrochemical strategy has been designed for the analysis of MUC1 using electrodeposited gold platinum bimetallic nanoparticles (Au-PtBNPs) on the surface of carboxylated graphene oxide (CGO)/FTO electrode as a signal amplification platform. The carboxylic groups of CGO were activated with EDS-NHS linker and subsequently immobilized with streptavidin for further deposition of biotin labelled aptamer. All the modification steps were characterized by FE-SEM, EDS mapping, FT-IR, contact angle measurements and electrochemical methods. After incubating with target protein MUC1, the aptaelectrode produced some concentration dependent responses which were measured electrochemically by DPV assay. The prepared aptasensor exhibits wide linear range from 1 fM-100 nM with detection limit of 0.79 fM under optimal experimental conditions. The performance of this aptaelectrode was also evaluated showing good selectivity, storage stability (15 days), reproducibility and reusability (up to 3 times). Furthermore, the applicability of the aptasensor for spiked serum samples showed recovery range from 92% to 97%.

Polyaniline based nucleic acid sensor.

Twenty-bases long NH2-modified DNA and PNA probes specific to a pathogen (Mycobacterium tuberculosis) were covalently immobilized onto a polyaniline (PANI)/Au electrode to detect nucleic acid hybridization with complementary, one-base mismatch and noncomplementary targets within 30 s using Methylene Blue. The PNA-PANI/Au electrode exhibits improved specificity (1000 times) and detection limit (0.125 x 10(-18) M) as compared to that of the DNA-PANI/Au electrode (2.5 x 10(-18) M). These PNA-PANI/Au electrodes can be utilized for detection of hybridization with the complementary sequence in 5 min sonicated M. tuberculosis genomic DNA within 1 min of hybridization time. These DNA-PANI/Au and PNA-PANI/Au electrodes can be used 6-7 and 13-15 times, respectively.

Nucleic acid sensor for M. tuberculosis detection based on surface plasmon resonance.

Cysteine modified NH(2)-end peptide nucleic acid (PNA) (24-mer) probe and 5'-thiol end labeled deoxyribonucleic acid (DNA) probes specific to Mycobacterium tuberculosis have been immobilized onto BK-7 gold coated glass plates for the detection of complementary, one-base mismatch, non-complementary targets and complementary target sequence in genomic DNA of Mycobacterium tuberculosis using a surface plasmon resonance (SPR) technique. The DNA/Au and PNA/Au bio-electrodes have been characterized using contact angle, atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) techniques, respectively. It is revealed that there is a 252 millidegrees SPR angle change in the case of PNA immobilization and 205 millidegrees for DNA immobilization, indicating increased amount of immobilized PNA molecules. Hybridization studies reveal that there is no binding of the non-complementary target to DNA/Au and PNA/Au electrode. Compared to the DNA/Au bioelectrode, PNA/Au electrode has been found to be more efficient for detection of one-base mismatch sequence. The PNA/Au bioelectrode shows better detection limit (1.0 ng ml(-1)) over the DNA-Au bioelectrode (3.0 ng ml(-1)). The values of the association (k(a)) and dissociation rate constant (k(d)) for the complementary sequence in case of the PNA/Au bioelectrode have been estimated as 8.5 x 10(4) m(-1) s(-1) and 3.6 x 10(-3) s(-1), respectively.

Effect of redox status of peripheral blood on immune signature of circulating regulatory and cytotoxic T cells in streptozotocin induced rodent model of type I diabetes.

Diabetes mellitus is an autoimmune chronic inflammatory disease manifested by hyperglycemia and associated with imbalance in redox status and inflammatory response. Oxidative stress has been reported to affect functions of T cell repertoire- regulatory T cells (Tregs) and cytotoxic lymphocytes (CTLs). Tregs are involved in prevention against autoreactive T cells and controlling inflammation while CTLs are major mediators of tissue injury. Hence the present study is novel as it contemplates to understand oxidative stress in diabetes vis-à-vis T cells. Comparative analysis was carried out between two groups, i.e., healthy Sprague Dawley (SD) and Streptozotocin (STZ) induced SD rat model of type1 diabetes (T1D). Various hematological, biochemical and oxidative stress parameters were assessed in plasma samples in the study. Peripheral blood mononuclear cells (PBMCs), Tregs and CTLs were evaluated for intracellular oxidative stress using 2',7'-dichlorofluorescin diacetate (DCFDA), mitochondrial ROS using Mitosox-red, mitochondrial membrane potential using JC-1 in PBMCs. Treg populations expressing IL-4, IL-6 and IL-10 and CTLs expressing αß-T cell receptor (αß -TCR), interferon- γ (IFN-γ), perforin and granzyme were also considered. We found decreased activity of enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and reduced glutathione(GSH) and increased lipid peroxidation (LPO) in plasma indicated altered redox state in diabetic animals. Elevated intracellular reactive oxygen species (ROS) and mitochondrial superoxide was observed in T1D group confirming oxidative stress in cell specific manner. Cell population with hyperpolarized mitochondrial membrane potential was found to be elevated in T1D group. We found a decrease in Treg population in T1D group in comparison to healthy group. Treg population expressing IL-4, IL-6 were increased and those expressing IL-10 were found to be reduced in diabetic group. The CTL numbers were dropping whereas αß-TCR, IFN-γ, perforin and granzyme expressing CTLs were on the rise in diabetic group. Our finding suggested an increased oxidative stress in Tregs and CTLs which might be responsible for progressive inflammatory environment built up due to persistent hyperglycemia. This was fortified by the statistical analyses where strong correlation between LPO and CTLs expressing TCR, IFN-γ, perforin and granzyme was noted. Lipid peroxidation was also found to be correlated to intracellular ROS in Tregs and CTLs along with other important revelations. The present study gives important insights into the significance of oxidative stress on immune system and its mediators in diabetes.

Ultrasensitive DNA hybridization biosensor based on polyaniline.

Ultrasensitive DNA hybridization biosensor based on polyaniline (PANI) electrochemically deposited onto Pt disc electrode has been fabricated using biotin-avidin as indirect coupling agent to immobilize single-stranded 5'-biotin end-labeled polydeoxycytidine (BdC) probes and 5'-biotin end-labeled 35 base-long oligonucleotide probe (BdE) to detect complementary target, using both direct electrochemical oxidation of guanine and redox electroactive indicator methylene blue (MB), respectively. These polyaniline-based disc electrodes have been characterized using differential pulse voltammetry (DPV), Fourier transform infrared spectroscopy (FT-IR), impedance measurements and scanning electron microscopy (SEM) techniques, respectively. Compared to direct electrochemical oxidation of guanine, hybridization detection using MB results in the enhanced detection limit by about 100 times. These DNA immobilized PANI electrodes have hybridization response time of about 60 s.

Electrochemical determination of M. tuberculosis antigen based on Poly(3,4-ethylenedioxythiophene) and functionalized carbon nanotubes hybrid platform.

An electrochemical DNA aptasensor for the detection of Mycobacterium tuberculosis (M. tb) antigen MPT64, was developed using Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes (CNTs). The biotinylated aptamer was immobilized onto streptavidin attached to -COOH functionalized CNTs via streptavidin-biotin interaction. Various characterization studies as FT-IR, FE-SEM, EIS and DPV were done to validate each fabrication step of the aptasensor. Optimization studies related to aptamer concentration and response time were performed. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically by differential pulse voltammetry in the presence of [Fe(CN)6]3-/4- as a redox probe. The aptasensor exhibited limit of detection of 0.5±0.2fgmL-1 within 15min with stability of 27 days at 4°C and reusability of 7 times after repeated regeneration with 50mM NaOH. The potential application of the aptasensor was established by spike-in studies to obtain recovery in between (88-95)%.

Chitosan-iron oxide nanocomposite based electrochemical aptasensor for determination of malathion.

An electrochemical aptasensor based on chitosan-iron oxide nanocomposite (CHIT-IO) film deposited on fluorine tin Oxide (FTO) was developed for the detection of malathion. Iron oxide nanoparticles were prepared by co-precipitation method and characterized by Transmission electron microscopy and UV-Visible spectroscopy. The biotinylated DNA aptamer sequence specific to the malathion was immobilized onto the iron oxide doped-chitosan/FTO electrode by using streptavidin as linking molecule. Various characterization studies like Field Emission-Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FT-IR), and Electrochemical studies were performed to attest the successful fabrication of bioelectrodes. Experimental parameters like aptamer concentration, response time, stability of electrode and reusability studies were optimized. Aptamer immobilized chitosan-iron oxide nanocomposite (APT/SA/CHIT-IO/FTO) bioelectrodes exhibited LOD of about 0.001 ng/mL within 15 min and spike-in studies revealed about 80-92% recovery of malathion from the lettuce leaves and soil sample.

Polyaniline Langmuir-Blodgett film based aptasensor for ochratoxin A detection.

Ochratoxin A (OTA) produced by Aspergillus Ochraceus and Penicillium verrucosum is a very dangerous toxin due to its toxic effects in human beings and its presence in a wide range of food products and cereals. A Langmuir-Blodgett (polyaniline (PANI)-stearic acid (SA)) film based highly sensitive and robust impedimetric aptasensor has been developed for ochratoxin A (OTA) detection. DNA Aptamer (Apt-DNA) specific to OTA has been covalently immobilized onto mixed Langmuir-Blodgett (LB) monolayer comprising of PANI-SA deposited onto indium tin-oxide (ITO) coated glass plates. This Apt-DNA/PANI-SA/ITO aptaelectrode has been characterized using scanning electron microscopy, Fourier transform-infrared spectroscopy, contact angle measurements, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The Apt-DNA/PANI-SA/ITO aptasensor shows detection of OTA by electrochemical impedance spectroscopy in the linear range of 0.0001 µg/ml (0.1 ng/ml) to 0.01 µg/ml (10 ng/ml) and 1 µg/ml-25 µg/ml with detection limit of 0.1 ng/ml in 15 min. The Apt-DNA/PANI-SA/ITO aptasensor can be reused ∼13 times. The binding or affinity constant (K(a)) of aptamer with OTA, calculated using Langmuir adsorption isotherm, is found be 1.21×10(7) M(-1).

Nucleic acid sensor for insecticide detection.

Nucleic acid sensor based on polyaniline (PANI) has been fabricated by covalently immobilizing double stranded calf thymus (dsCT) DNA onto perchlorate (ClO(-) (4))-doped PANI film deposited onto indium-tin-oxide (ITO) glass plate using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) chemistry. These dsCT-DNA-PANI-ClO(4)/ITO and PANI-ClO(4)/ITO electrodes have been characterized using square wave voltammetry, electrochemical impedance, scanning electron microscopy (SEM) and Fourier-transform-infrared (FTIR) measurements. This disposable dsCT-DNA-PANI-ClO(4)/ITO bioelectrode, stable for about 4 months, can be used to detect cypermethrin (0.005 ppm) and trichlorfon (0.01 ppm) in 30 and 60 s, respectively.

Self-assembled monolayer for toxicant detection using nucleic acid sensor based on surface plasmon resonance technique.

Double stranded calf thymus deoxyribonucleic acid (dsCT-DNA) has been covalently immobilized onto self-assembled monolayer (SAM) of beta-merceptoethanol (MCE) on gold substrates via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide chemistry for fabrication of the surface plasmon resonance (SPR) based biosensing device. The dsCT-DNA-MCE-SAM/Au bioelectrode has been characterized using electrochemical impedance spectroscopy, cyclic voltammetry, contact angle measurements and atomic force microscopy, respectively. This biosensing device has been utilized for detection of cypermethrin (0.0005 ppm) using electrochemical and SPR techniques, respectively. The mechanism of interaction of cypermethrin with dsCT-DNA immobilized onto MCE-SAM has been proposed.

Escherichia coli genosensor based on polyaniline.

Avidin-modified polyaniline (PANI) electrochemically deposited onto a Pt disk electrode has been utilized for direct detection of Escherichia coli by immobilizing a 5'-biotin-labeled E. coli probe (BdE) using a differential pulse voltammetric technique in the presence of methylene blue as a DNA hybridization indicator. Depending on the target sample and the sonication time, this BdE-avidin-PANI bioelectrode can be utilized to electrochemically detect a complementary target probe (0.009 ng/microL), E. coli genomic DNA (0.01 ng/microL) and 11 E. coli cells/mL in 60 s to 14 min (hybridization time) without using PCR and can be used 5-7 times at temperatures of 30-45 degrees C.