Selective determination of non-organophosphorus insecticide using DNA aptamer-based single-use biosensors.

In the present study, we developed a disposable aptamer-based biosensor for rapid, sensitive, and reliable detection of acetamiprid (ACE). To improve the sensitivity of the aptasensor, poly-5-amino-2-mercapto-1,3,4-thiadiazole [P(AMT)] and gold nanoparticles (AuNPs) were progressively electrodeposited on the screen-printed electrode (SPE) surface by using cyclic voltammetry (CV) technique. For the determination of ACE, thiol-modified primary aptamer (Apt1) was selected by using the SELEX method and immobilized on the surface of the P(AMT) and AuNPs-modified SPE (SPE/P(AMT)/AuNPs) via AuS bonding. Then, the surface-bound aptamer was incubated with ACE for 45 Min. After that, the biotin-labeled aptamer 2 (Apt2) was interacted with the ACE, then the enzyme-labeled step was performed. In this step, alkaline phosphatase (ALP) was bound to the surface through the interaction between Apt2 labeled with biotin and streptavidin (strep)-ALP conjugate. The determination of ACE was achieved by measuring the oxidation signal of α-naphthol, which is formed on the electrode surface through the interaction of ALP with α-naphthyl phosphate. The working range of the developed aptasensor was determined as 5 × 10-12 -5 × 10-10  mol L-1 with a low limit of detection (1.5 pmol L-1 ). It was also found that the proposed aptasensor possessed great advantages such as low cost, good selectivity, and good reproducibility.

An electrochemical sandwich-type aptasensor for determination of lipocalin-2 based on graphene oxide/polymer composite and gold nanoparticles.

In this work, we reported an electrochemical aptasensor based on the poly-3-amino-1,2,4-triazole-5-thiol/graphene oxide composite (P(ATT)-GO) and gold nanoparticles (AuNPs) modified graphite screen-printed electrode (GSPE) (GSPE/P(ATT)-GO/AuNPs) for determination of lipocalin-2 (LCN2) (neutrophil gelatinase-associated lipocalin). A sandwich based strategy was utilized to enhance the electrochemical signal. First, a thiol tethered DNA aptamer was immobilized onto the composite electrode. Then, the LCN2 solution was incubated with the aptamer modified GSPE/P(ATT)-GO/AuNPs. Secondary aptamer (Apt2) peculiar to the LCN2 and labeled with biotin was interacted with the LCN2. A streptavidin-alkaline phosphatase conjugate was then applied to the surface. The determination of LCN2 was performed by using the electroactive property of α-naphthol which is acquired the product from the interaction between alkaline phosphatase and α-naphthyl phosphate. The constructed electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The aptamer modified GSPE/P(ATT)-GO/AuNPs showed the superior electrocatalytic performance towards the voltammetric determination of LCN2 with a wide linear range (1.0-1000.0 ng/mL) and a low limit of detection (LOD) (0.3 ng/mL). The proposed aptasensor revealed the excellent sensitivity, anti-interference ability and reproducibility which approved that the GSPE/P (ATT)-GO/AuNPs is a promising composite for the sensitive detection of LCN2. The fabricated aptasensor was applied for the determination of LCN2 in fetal bovine serum samples using the standard addition method and the recovery values were in the range of 99.2% and 103.22%.

Interaction of prednisone with dsDNA at silver nanoparticles/poly(glyoxal-bis(2-hydroxyanil))/dsDNA modified electrode and its analytical application.

This paper reports the fabrication of an electrochemical DNA biosensor for the electrochemical determination of prednisone (PRD), which is a synthetic corticosteroid. For this purpose, silver nanoparticles (AgNPs) and a new polymer film poly(glyoxal-bis(2-hydroxyanil)) (P(GBHA)) were electrochemically deposited on a glassy carbon electrode (GCE), respectively. Then, an electrochemical DNA biosensor was prepared onto this electrode surface (GCE/AgNPs/P(GBHA)) by the immobilization of dsDNA using a chronoamperometry method. The proposed electrode was characterized by FESEM, XPS, and cyclic voltammetry (CV). The interaction between the PRD and dsDNA immobilized on the GCE/AgNPs/P(GBHA) electrode was investigated via a differential pulse voltammetry (DPV) method and UV-Vis spectrophotometry. The experimental factors affecting the interaction between the PRD concentration and dsDNA were optimized. The fabricated biosensor showed a wide linear response in a PRD concentration range of 1.0-50.0 µg mL-1 depending on both the adenine and guanine base signals. The detection limit based on the guanine and adenine signals was 0.3 µg mL-1 and 0.25 µg mL-1, respectively. The sensor exhibited excellent anti-interferential ability, good stability and reproducibility and was satisfactorily employed for the electrochemical assay of PRD in serum samples. The new DNA biosensor can be utilized for the sensitive, accurate and rapid analysis of PRD.

Electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) modified glassy carbon electrode for the determination of anticancer drug gemcitabine.

In this study, a simple methodology was used to develop a new electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) (P(PDCA)) modified glassy carbon electrode (GCE). This modified electrode was used to monitor for the electrochemical interaction between the dsDNA and gemcitabine (GEM) for the first time. A decrease in oxidation signals of guanine after the interaction of the dsDNA with the GEM was used as an indicator for the selective determination of the GEM via differential pulse voltammetry (DPV). The guanine oxidation peak currents were linearly proportional to the concentrations of the GEM in the range of 1-30mgL(‒1). Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.276mgL(‒1) and 0.922mgL(‒1), respectively. The reproducibility, repeatability, and applicability of the analysis to pharmaceutical dosage forms and human serum samples were also examined. In addition to DPV method, UV-vis and viscosity measurements were utilized to propose the interaction mechanism between the GEM and the dsDNA. The novel DNA biosensor could serve for sensitive, accurate and rapid determination of the GEM.

A sensitive electrochemical DNA biosensor for antineoplastic drug 5-fluorouracil based on glassy carbon electrode modified with poly(bromocresol purple).

This paper describes an electrochemical sensor for the first time based on poly(bromocresol purple) (P(BCP)) developed to observe the interaction between 5-fluorouracil (5-FU) and fish sperm double strand DNA (dsDNA). The P(BCP) film was electrosynthesized by cyclic voltammetry method on the glassy carbon electrode (GCE). The dsDNA was electrochemically immobilized on the surface of P(BCP) modified GCE and the DNA biosensor was prepared. The interaction mechanism of dsDNA with 5-FU was investigated by differential pulse voltammetry using this biosensor. A decrease in the guanine oxidation peak current of the biosensor was observed after the interaction of dsDNA and 5-FU in 0.5 mol L(-1) acetate buffer (pH 4.8) containing 0.02 mol L(-1) NaCl. The accumulation time and dsDNA concentration were optimized to obtain the best peak current response. Under optimum conditions, the linear response on the guanine signal decreasing curve was observed in the 5-FU concentration range of 1.0-50 mg L(-1). The interaction mechanism between dsDNA and 5-FU was further investigated by UV-vis spectroscopy and viscometer. The results reveal that intercalation is the primary mode of interaction between 5-FU and dsDNA.

Electrochemical glucose biosensor based on nickel oxide nanoparticle-modified carbon paste electrode.

In the present work, we designed an amperometric glucose biosensor based on nickel oxide nanoparticles (NiONPs)-modified carbon paste electrode. The biosensor was prepared by incorporation of glucose oxidase and NiONPs into a carbon paste matrix. It showed good analytical performances such as high sensitivity (367 µA mmolL(-1)) and a wide linear response from 1.9×10(-3) mmolL(-1) to 15.0 mmolL(-1) with a limit of detection (0.11 µmolL(-1)). The biosensor was used for the determination of glucose in human serum samples. The results illustrate that NiONPs have enormous potential in the construction of biosensor for determination of glucose.

A novel amperometric biosensor based on ZnO nanoparticles-modified carbon paste electrode for determination of glucose in human serum.

Zinc oxide nanoparticles-(ZnONPs)modified carbon paste enzyme electrodes (ZnONPsMCPE) were developed for determination of glucose. The determination of glucose was carried out by oxidation of H2O2 at +0.4 V. ZnONPsMCPE provided biocompatible microenvironment for GOx and necessary pathway of electron transfer between GOx and electrode. The response of GOx/ZnONPsMCPE was proportional to glucose concentration and detection limit was 9.1 × 10(-3) mM. Km and Imax, were calculated as 0.124 mM and 2.033 µA. The developed biosensor exhibits high analytical performance with wide linear range (9.1 × 10(-3)-14.5 mM), selectivity and reproducibility. Serum glucose results allow us to ascertain practical utility of GOx/ZnONPsMCPE biosensor.

Amperometric carbon paste enzyme electrodes with Fe(3)O(4) nanoparticles and 1,4-benzoquinone for glucose determination.

Two new amperometric carbon paste enzyme electrodes including Fe(3)O(4) nanoparticles with and without 1,4-benzoquinone were developed for glucose determination. Electron transfer properties of unmodified and Fe(3)O(4) nanoparticles and/or 1,4-benzoquinone modified carbon paste electrodes were investigated in 0.1 M KCl support electrolyte containing Fe(CN)6(3-/4-) as redox probe by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe(3)O(4) nanoparticles increased electron transfer at solution/electrode interface. The parameters affecting the analytical performance of the enzyme electrode have been investigated in detail and optimized for Fe(3)O(4) nanoparticle modified enzyme electrode (Fe(3)O(4)-CPEE). Fe(3)O(4) nanoparticles and 1,4-benzoquinone modified enzyme electrode (BQ-Fe(3)O(4)-CPEE) exhibited linear response from 1.9 × 10(-7) M to 3.7 × 10(-6) M, from 7.2 × 10(-6) M to 1.5 × 10(-4) M and from 1.3 × 10(-3) M to 1.2 × 10(-2) M with an excellent detection limit of 1.9 × 10(-8) M. BQ-Fe(3)O(4)-CPEE was used for determination of glucose in serum samples and results were in good agreement with those obtained by spectrophotometric method.

An Fe3O4-nanoparticles-based amperometric biosensor for creatine determination.

An amperometric biosensor for the detection of creatine was designed, based on carbon paste electrode modified with Fe(3)O(4) nanoparticles. Electron transfer properties of unmodified and Fe(3)O(4)-nanoparticles-modified carbon paste electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe(3)O(4) nanoparticles increased the surface area and electric conductivity of the electrode, thus enhancing the sensitivity of the electrode. Optimum pH, buffer concentration, working potential and enzyme loading were selected as 7.0; 0.05 mol L(-1); +0.30 V and 2.0 Unit creatinase (CI), 1.0 Unit sarcosine oxidase (SO), respectively. The purposed biosensor exhibited linear response from 2.0 × 10(-7) mol L(-1) to 3.8 × 10(-6) mol L(-1) and from 9.0 × 10(-6) mol L(-1) to 1.2 × 10(-4) mol L(-1) with a detection limit of 2.0 × 10(-7) mol L(-1). Biosensor was used for determination of creatine in commercial creatine powder samples and showed a good sensing performance.

Novel creatine biosensors based on all solid-state contact ammonium-selective membrane electrodes.

Novel creatine bienzymatic potentiometric biosensors were prepared by immobilizing urease and creatinase on all solid-state contact PVC-containing palmitic acid and carboxylated PVC matrix membrane ammonium-selective electrodes without inner reference solution. Potentiometric characteristics of biosensors were examined in physiological model solutions at different creatine concentrations. The linear working range and long-term sensitivity of the biosensors were also determined. The creatine biosensors prepared by using the carboxylated PVC membrane electrodes showed more effective performance than those of the PVC containing palmitic acid membrane electrodes. Creatine assay in serum samples was successfully carried out by using the standard addition method.

Comparison of covalent and noncovalent immobilization of Malatya apricot pectinesterase (Prunus armeniaca L.).

Pectinesterase isolated from Malatya apricot pulp was noncovalently and covalently immobilized onto bentonite and glutaraldehyde-containing amino group functionalized porous glass beads surface at pH 8.0 and pH 9.0, respectively. The effect of various parameters such as pH, temperature, activation energy, heat and storage stability on immobilized enzyme were investigated. The optimum temperature of covalently and noncovalently immobilized PE was 50°C. This value was 60°C for free PE. Although optimum pH of covalently-immobilized PE was 8.0, this parameter was 9.0 for free and covalently-immobilized PE. The noncovalently immobilized enzyme exhibited better thermostability than the free and covalently immobilized PE.

Amperometric enzyme electrodes for xanthine determination with different mediators.

Two new amperometric carbon paste enzyme electrodes were developed for xanthine determination. 1,4-benzoquinone and poly(vinylferrocene) (PVF) were investigated as mediators. The parameters affecting the analytical performance of the enzyme electrode have been investigated in detail and optimized for modified enzyme electrodes. 1,4-benzoquinone modified enzyme electrode (BQ-CPEE) exhibited linear response from 1.9 × 10-7 M to 5.5 × 10-6 M and from 5.2 × 10-5 M to 8.2 × 10-4 M with a good detection limit of 1.0 × 10-7 M. The linear working range of the PVF modified enzyme electrode was between 1.9 × 10-7-2.1 × 10-6 M, 1.9 × 10-6-1.0 × 10-5 M and 1.1 × 10-4-8.8 × 10-4 M with a detection limit of 1.0 × 10-7 M. Hypoxanthine response of the electrodes was also determined. Modified enzyme electrodes were used for xanthine determination in real samples and good recoveries were obtained.

Noncovalent immobilization of Pectinesterase (Prunus armeniaca L.) onto bentonite.

In this work, pectinesterase isolated from Malatya apricot was immobilized onto acid-treated bentonite surface by simple adsorption at pH 9.0. The properties of free and immobilized enzyme were defined. The effect of various factors such as pH, temperature, heat, and storage stability on immobilized enzyme were investigated. Optimum pH and temperature were determined to be 9.0 and 50 degrees C, respectively. Kinetic parameters of the immobilized enzyme (Km and Vmax values) were also determined as 0.51 mM of the Km and 14.6 micromol min(-1) mg(-1) of the Vmax. No drastic change was observed in the Km value after immobilization. The Vmax value of immobilized enzyme was 8.4-fold bigger than those of free enzyme. Thermal and storage stability experiments were carried out. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. The properties of the immobilized enzyme were compared to those of the free enzyme.

Purification and biochemical characteristics of pectinesterase from Malatya apricot (Prunus armeniaca L.).

Pectinesterase (PE) in Malatya apricot pulp (Prunus armeniaca L.) was extracted and purified through (NH(4))(2)SO(4) precipitation, dialysis, and DEAE-Sephadex gel filtration chromatography. The samples obtained from the dialysis procedure, named partially purified enzyme, were used for characterization of the apricot pectinesterase. The effect of various factors such as pH, temperature, heat, and storage stability on the partially purified apricot PE enzyme was investigated. Optimum pH value was 9.0 for PE with 1% pectin in 0.1 N NaCl (w/v). The optimum temperature for apricot PE was found to be 60 degrees C on standard analysis conditions. Heat inactivation studies showed a decrease in enzymatic activity at temperatures above 70 degrees C. Km and V(max) values were 0.77 mM and 1.75 micromol min(-1) mg(-1) for apricot PE. Five inhibitors were tested in the study; the most effective inhibitor was found to be sodium carbonate (100% inhibition). The order of inhibitory effectiveness was: Na(2)CO(3), iodine, lauril sulphate, AgNO(3), EDTA. Thermal inactivation data indicated that apparent activation energy with pectin substrate was 2.96 kcal mol(-1) for the enzyme. Ascorbic acid, CaCl(2), and KCl showed activatory effect on the apricot PE enzyme.

A new potentiometric ammonium electrode for biosensor construction.

New ammonium-selective membrane electrode based on poly(vinyl chloride) (PVC) membrane containing palmitic acid (a long-chain fatty acid) and nonactin as an ammonium ionophore for the determination of ammonium ions in the 10(-7) - 10(-1) mol/L concentration range was prepared and compared to those of the electrode prepared by using carboxylated PVC. Sebacate was used as a plasticiser for both of the ammonium sensor membranes. The analytical characteristics of the ammonium electrodes was investigated. The effect of pH, buffer concentration, temperature and stirring rate on the response to ammonium electrode was investigated. The linear working range and sensitivity of the electrodes were also determined. Ammonium electrodes give Nernstian response (52-58 mV/p[NH4+]) throughout the ammonium ion concentration range of 10(-1) to 10(-6)M with detection limits of 10(-6)M ammonium ions. The ammonium-selective electrodes prepared by using the PVC membranes containing palmitic acid showed more effective performance than those of the carboxylated PVC. The ammonium ion sensor has potential application in the analysis of ammonium ions for biosensor construction.

Determination of creatine in commercial creatine powder with new potentiometric and amperometric biosensors.

New potentiometric and amperometric biosensors were developed for the determination of creatine. The potentiometric creatine biosensor was prepared by immobilizing urease and creatinase on poly(vinylchloride) (PVC) ammonium membrane electrode containing palmitic acid prepared by using nonactine as an ammonium-ionophore. The linear working range of the biosensor was 1.0 x 10(-5) - 1.0 x 10(-3) M and the response time was about 60 s. The optimum pH, temperature, and buffer concentration were found to be 7.0, 20 degrees C, and 5 mM, respectively. The slope of the electrode was 49.2 mV/p[creatine]. The storage stabilization of the biosensor was investigated and 40-45% decrease in the response was detected after 2 months. The amperometric creatine biosensor was prepared by immobilizing creatinase (CI) and sarcosine oxidase (SO) in a poly(vinylferrocenium) matrix onto the surface of a platinum working electrode by crosslinking with glutaraldehyde (GA) and bovine serum albumine (BSA). Determination of creatine was performed by the oxidation of enzymatically generated H2O2 at +0.7 V vs. Ag/AgCl. The linear working range of the biosensor was 2.0 x 10(-5) - 3.2 x 10(-4) M and the response time was about 50 s. The effects of pH, temperature, enzyme ratio and buffer concentration were investigated and optimum parameters were found to be 7.5, 37 degrees C, 2.5:1 (CI:SO) and 0.05 M, respectively. The determination of creatine in commercial creatine powder was successfully carried out with these creatine biosensors by using the standard addition and calibration curve methods. The results were in good agreement with those obtained from Jaffé method at 95% confidence level.

An amperometric enzyme electrode for creatine determination prepared by the immobilization of creatinase and sarcosine oxidase in poly(vinylferrocenium).

A new enzyme electrode for the determination of creatine was developed by immobilizing creatinase (CI) and sarcosine oxidase (SO). The enzymes were co-immobilized in a poly(vinylferrocenium) matrix onto the surface of a platinum working electrode. Crosslinking with glutaraldehyte (GA) and bovine serum albumin (BSA) was selected as the best immobilization method for the enzymatic system. Determination of creatine was performed by the oxidation of enzymatically generated H2O2 at + 0.7 V vs. Ag/AgCl. The linear working range of the electrode was 2.0 x 10(-5) - 3.2 x 10(-4) M and the response time was about 50 s. The effects of pH, temperature, enzyme ratio and buffer concentration were investigated and optimum parameters were found to be 7.5, 37 degrees C, 2.5:1 (CI:SO) and 0.05 M, respectively. The stability and reproducibility of the enzyme electrode have been also studied.

Urea biosensors based on PVC membrane containing palmitic acid.

A new urea biosensor was prepared by immobilizing urease with four different procedures on poly(vinylchloride) (PVC) ammonium membrane electrode containing palmitic acid by using nonactine as an ammonium-ionophore. The analytical characteristics were investigated and were compared those of the biosensor prepared by using carboxylated PVC. The effect of pH, buffer concentration, temperature, urease concentration, stirring rate and enzyme immobilization procedures on the response to urea of the enzyme electrode were investigated. The linear working range and sensitivity of the biosensor were also determined. The urea biosensor prepared by using the PVC membranes containing palmitic acid showed more effective performance than those of the carboxylated PVC based biosensors. Additionally, urea assay in serum was successfully carried out by using the standard addition method.