An amperometric glucose biosensor based on poly(o-aminophenol) and Prussian blue films at platinum electrode

Prussian blue nanocubes with peroxidase-like activity for polyphenol detection in commercial beverages

The present study describes an efficient method for the determination of polyphenol content in beverages based on a composite material of graphene oxide decorated with Prussian blue nanocubes (rGO/PBNCs). In this method, rGO/PBNCs act as a nanoenzyme with peroxidase-like catalytic activity and produce a colorimetric product in the presence of hydrogen peroxide and tetramethylbenzidine (TMB). To verify the effectiveness of the method, we used two model standards for antioxidants: gallic acid (GA) and tannic acid (TA). The method validation included a comparison of the performance of a natural enzyme and an artificial one (rGO/PBNCs) and two polyphenols in the analysis of commercial beverage samples. After optimization, a pH of 4, ambient temperature (22 °C), a reaction time of 2 minutes and an rGO/PBNCs concentration of 0.01 μg mL-1 were found to be the most favorable conditions. The detection limits obtained were 5.6 μmol L-1 for GA and 1.5 μmol L-1 for TA. Overall, rGO/PBNCs offer advantages over natural enzymes in terms of stability, versatility, scalability and durability, making them attractive candidates for a wide range of catalytic and sensory applications.

A bimetallic nanocoral Au decorated with Pt nanoflowers (bio)sensor for H2O2 detection at low potential

In this work, we have developed for the first time a method to make novel gold and platinum hybrid bimetallic nanostructures differing in shape and size. Au-Pt nanostructures were prepared by electrodeposition in two simple steps. The first step consists of the electrodeposition of nanocoral Au onto a gold substrate using hydrogen as a dynamic template in an ammonium chloride solution. After that, the Pt nanostructures were deposited onto the nanocoral Au organized in pores. Using Pt (II) and Pt (IV), we realized nanocoral Au decorated with Pt nanospheres and nanocoral Au decorated with Pt nanoflowers, respectively. The bimetallic nanostructures showed better capability to electrochemically oxidize hydrogen peroxide compared with nanocoral Au. Moreover, Au-Pt nanostructures were able to lower the potential of detection and a higher performance was obtained at a low applied potential. Then, glucose oxidase was immobilized onto the bimetallic Au-Pt nanostructure using cross-linking with glutaraldehyde. The biosensor was characterized by chronoamperometry at +0.15V vs. Ag pseudo-reference electrode (PRE) and showed good analytical performances with a linear range from 0.01 to 2.00mM and a sensitivity of 33.66µA/mMcm². The good value of K_m^app (2.28mM) demonstrates that the hybrid nanostructure is a favorable environment for the enzyme. Moreover, the low working potential can minimize the interference from ascorbic acid and uric acid as well as reducing power consumption to effect sensing. The simple procedure to realize this nanostructure and to immobilize enzymes, as well as the analytical performances of the resulting devices, encourage the use of this technology for the development of biosensors for clinical analysis.

Poly(o-aminophenol) prepared by Cu(ii) catalyzed air oxidation and its use as a bio-sensing architecture

A novel procedure for the preparation of organosoluble poly(o-aminophenol) is described.

Design and Characterization of a Sensorized Microfluidic Cell-Culture System with Electro-Thermal Micro-Pumps and Sensors for Cell Adhesion, Oxygen, and pH on a Glass Chip

We combined a multi-sensor glass-chip with a microfluidic channel grid for the characterization of cellular behavior. The grid was imprinted in poly-dimethyl-siloxane. Mouse-embryonal/fetal calvaria fibroblasts (MC3T3-E1) were used as a model system. Thin-film platinum (Pt) sensors for respiration (amperometric oxygen electrode), acidification (potentiometric pH electrodes) and cell adhesion (interdigitated-electrodes structures, IDES) allowed us to monitor cell-physiological parameters as well as the cell-spreading behavior. Two on-chip electro-thermal micro-pumps (ETμPs) permitted the induction of medium flow in the system, e.g., for medium mixing and drug delivery. The glass-wafer technology ensured the microscopic observability of the on-chip cell culture. Connecting Pt structures were passivated by a 1.2 μm layer of silicon nitride (Si3N4). Thin Si3N4 layers (20 nm or 60 nm) were used as the sensitive material of the pH electrodes. These electrodes showed a linear behavior in the pH range from 4 to 9, with a sensitivity of up to 39 mV per pH step. The oxygen sensors were circular Pt electrodes with a sensor area of 78.5 μm(2). Their sensitivity was 100 pA per 1% oxygen increase in the range from 0% to 21% oxygen (air saturated). Two different IDES geometries with 30- and 50-μm finger spacings showed comparable sensitivities in detecting the proliferation rate of MC3T3 cells. These cells were cultured for 11 days in vitro to test the biocompatibility, microfluidics and electric sensors of our system under standard laboratory conditions.

New faces of porous Prussian blue: interfacial assembly of integrated hetero-structures for sensing applications

Prussian blue (PB), the oldest synthetic coordination compound, is a classic and fascinating transition metal coordination material. Prussian blue is based on a three-dimensional (3-D) cubic polymeric porous network consisting of alternating ferric and ferrous ions, which provides facile assembly as well as precise interaction with active sites at functional interfaces. A fundamental understanding of the assembly mechanism of PB hetero-interfaces is essential to enable the full potential applications of PB crystals, including chemical sensing, catalysis, gas storage, drug delivery and electronic displays. Developing controlled assembly methods towards functionally integrated hetero-interfaces with adjustable sizes and morphology of PB crystals is necessary. A key point in the functional interface and device integration of PB nanocrystals is the fabrication of hetero-interfaces in a well-defined and oriented fashion on given substrates. This review will bring together these key aspects of the hetero-interfaces of PB nanocrystals, ranging from structure and properties, interfacial assembly strategies, to integrated hetero-structures for diverse sensing.

Template synthesis of highly ordered Prussian blue array and its application to the glucose biosensing

In this paper, we propose a strategy to form nanoelectrode arrays by electrochemical deposition of the Prussian blue (PB) through highly ordered porous anodic alumina (PAA) membrane. The structure and morphology of the nanoarrays were characterized by scanning electron microscopy (SEM). As the highly ordered PB arrays can behave as an ensemble of closely spaced but isolated nanoelectrodes, the nanostructured PB arrays are successfully applied to improve the analytical performances of glucose by electrocatalytic reduction enzymatically liberated H(2)O(2). The resulting PB based nanoelectrode arrays show a wide linear calibration range over three orders of magnitude of glucose concentrations (5.0 x 10(-6) to 8.0 x 10(-3)M) and a low detection limit of 1 microM. Moreover, the biosensor exhibits other good characteristics, such as short response time, high selectivity, excellent operation stability. In addition, effects of the glucose oxidase (GOx) loading, applied potential and pH on the biosensor performance were also discussed.

An electrochemical method for simultaneous detection and identification of Escherichia coli, Staphylococcus aureus and Salmonella choleraesuis using a glucose oxidase-peroxidase composite biosensor

Quantification of bacterial pollution by amperometric detection at 0.0 V of glucose consumption at a graphite-Teflon-glucose oxidase-peroxidase-ferrocene composite biosensor under flow injection conditions is reported. Using Escherichia coli as the model bacterium, the composition of the growing medium was optimized. A constant glucose concentration of 4.0 x 10(-4) M was added to the culture medium. The relative response to glucose, expressed as the ratio between the amperometric signal and the signal at incubation time t = 0 multiplied by 100, as a function of E. coli concentration, showed a typical behaviour. Limits of detection of 6.5 x 10(2) or 6.5 cfu mL(-1) were achieved after 3 or 7 h of incubation, respectively, with no pre-concentration step. The detection of bacteria did not affect the lifetime of the biosensor. The feasibility of the detection of Staphylococcus aureus and Salmonella choleraesuis throughout the glucose consumption measurement at the composite biosensor is also demonstrated. The capability of bacterial identification by evaluation of bacterial growth in the culture medium containing the antibiotics polymyxin B, vancomycin, erythromycin, bacitracin, chloramphenicol, tetracycline and ciprofloxacin, was investigated. Each micro-organism tested exhibited a different antibiotic susceptibility profile, thus suggesting the possibility of bacteria differentiation. A rapid methodology for screening of bacteria is proposed.

Amperometric choline biosensors prepared by layer-by-layer deposition of choline oxidase on the Prussian blue-modified platinum electrode

An amperometric choline biosensor was developed by immobilizing choline oxidase (ChOx) in a layer-by-layer (LBL) multilayer film on a platinum (Pt) electrode modified with Prussian blue (PB). 6-O-Ethoxytrimethylammoniochitosan chloride (EACC) was used to prepare the ChOx LBL films. The choline biosensor was used at 0.0V versus Ag/AgCl to detect choline and exhibited good characteristics such as relative low detection limit (5x10(-7)M), short response time (within 10s), high sensitivity (88.6muAmM(-1)cm(-2)) and a good selectivity. The results were explained based on the ultrathin nature of the LBL films and the low operating potential that could be due to the efficient catalytic reduction of H(2)O(2) by PB. In addition, the effects of pH, temperature and applied potential on the amperometric response of choline biosensor were evaluated. The apparent Michaelis-Menten constant was found to be (0.083+/-0.001)x10(-3)M. The biosensor showed excellent long-term storage stability, which originates from a strong adsorption of ChOx in the EACC multilayer film. When the present choline biosensor was applied to the analysis of phosphatidylcholine in serum samples, the measurement values agreed satisfactorily with those by a hospital method.

Sensor and biosensor preparation, optimisation and applications of Prussian Blue modified electrodes

Being one of the most commonly used electrochemical mediators for analytical applications, Prussian Blue has found a wide use in the biosensor field during the last years. Its particular characteristic of catalysing hydrogen peroxide reduction has been applied in the construction of a large number of oxidase enzyme-based biosensors for clinical, environmental and food analysis. By modifying an electrode surface with Prussian Blue, it is in fact possible to easily detect hydrogen peroxide at an applied potential around 0.0 V versus Ag/AgCl, thus making possible coupling with oxidase enzymes while also avoiding or reducing electrochemical interferences. Papers dealing with glucose, lactate, cholesterol and galactose biosensors that are based on the use of Prussian Blue have recently appeared in the most important analytical chemistry journals. Another recent trend is the use of a choline probe based on choline oxidase for pesticide determination to exploit the inhibition of acetylcholinesterase by these compounds. In addition, the use of Prussian Blue in the development of biosensors for food analysis has captured the interest of many research groups and led to improved methods for the detection of glutamate, galactose, alcohol, fructosyl amine, formate, lysine and oxalate. This review will focus on the biosensing aspects of Prussian Blue-based sensors giving a general overview of the advantages provided by such mediator as well as its drawbacks. A comprehensive bibliographic reference list is presented together with the most up to date research findings in this field and possible future applications. The commercial potential of sensors based on this mediator will also be discussed.

An amperometric hydrogen peroxide sensor based on immobilization of hemoglobin in poly(o-aminophenol) film at iron–cobalt hexacyanoferrate-modified gold electrode

A series of hybrid iron-cobalt hexacyanoferrate (FeCoHCF) films were electrodeposited on gold electrodes from solutions containing 6mM Fe(CN)(6)(3-) with different concentrations of Co(2+) and Fe(3+). FeCoHCF films deposited from solutions with different molar ratios of iron were studied by cyclic voltammetry, and their solid states were characterized by Fourier transform infrared spectroscopy. The kind of FeCoHCF film that deposited from a solution with a molar ratio of iron of 0.4 showed the largest response current to H(2)O(2) and was characterized by energy-dispersive X-ray spectroscopy. Therefore, the optimized FeCoHCF film was combined with nonconducting poly(o-aminophenol) (POAP) film that entrapped the hemoglobin (Hb) to construct hydrogen peroxide biosensor. The response current of the Hb/POAP/FeCoHCF/Au electrode (29.8 nA) was nearly 40 and was 1.5 times that of the Hb/POAP/Au (0.7 nA) and POAP/FeCoHCF/Au (20 nA) electrodes, respectively. The Michaelis-Menten constant of Hb in the Hb/POAP/FeCoHCF/Au film was 9.31 mM. These results show that the immobilized Hb in the Hb/POAP/FeCoHCF/Au film exhibits higher catalytic activity and larger response current to H(2)O(2) by the mediation of FeCoHCF. In addition, effects of applied potential, solution pH, and electroactive interferent on the response current of the Hb/POAP/FeCoHCF/Au electrode were investigated in detail.

Electrochemical characteristics of a platinum electrode modified with a matrix of polyvinyl butyral and colloidal Ag containing immobilized horseradish peroxidase

A new hydrogen peroxide biosensor was constructed, which consisted of a platinum electrode modified by a matrix of polyvinyl butyral (PVB) and nanometer-sized Ag colloid containing immobilized horseradish peroxidase (HRP), and using Co(bpy)3(3+) as mediator in the hydrogen peroxide solution. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The modified process was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The sensor displays excellent electrocatalytic response to the reduction of H2O2. Analytical parameters such as pH and temperature were also studied. Linear calibration for H2O2 was obtained in the range of 1x10(-5) to 1x10(-2) M under optimized conditions. The sensor was highly sensitive to H2O2, with a detection limit of 2x10(-6) M, and the sensor achieved 95% of steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability.

An Amperometric Glucose Biosensor Based on Glucose Oxidase Immobilized in Electropolymerized Poly(o-aminophenol) and Carbon Nanotubes Composite Film on a Gold Electrode

An amperometric glucose biosensor is developed that is based on immobilization of glucose oxidase (GOD) in a composite film of poly(o-aminophenol) (POAP) and carbon nanotubes (CNT), which are electrochemically co-polymerized at a gold (Au) electrode. Because of the high surface per volume ratio and excellent electrical conductivity of CNT, the biosensor based on an Au/POAP/CNT/GOD electrode has lower detection limit (0.01 mM), larger maximum response current (0.24 mA cm(-2)) and higher sensitivity (11.4 mA M(-1) cm(-2)) than the values of the biosensor based on an Au/POAP/GOD electrode. Additionally, the biosensor shows fast response time, large response current, and good anti-interferent ability for ascorbic acid, uric acid and acetaminophen. Good reproducibility and stability of the biosensor are also observed.