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

Sensors and Biosensors for the Determination of Small Molecule Biological Toxins

The following review of sensors and biosensors focuses on the determination of commonly studied small molecule biological toxins, including mycotoxins and small molecule neurotoxins. Because of the high toxicity of small molecule toxins, an effective analysis technique for determining their toxicity is indispensable. Sensors and biosensors have emerged as sensitive and rapid techniques for toxicity analysis in the past decade. Several different sensors for the determination of mycotoxins and other small molecule neurotoxins have been reported in the literature, and many of these sensors such as tissue biosensors, enzyme sensors, optical immunosensors, electrochemical sensors, quartz crystal sensors, and surface plasmon resonance biosensors are reviewed in this paper. Sensors are a practical and convenient monitoring tool in the area of routine analysis, and their specificity, sensitivity, reproducibility and analysis stability should all be improved in future work. In addition, accuracy field portable sensing devices and multiplexing analysis devices will be important requirement for the future.

Clinical evaluation of bionime rightest GM310 biosensors with a simplified electrode fabrication for alternative-site blood glucose tests

BACKGROUND

Most processes for fabricating biosensors applied to screen-printed carbon electrodes (SPCEs) are complex. This study presents a novel one-step process for manufacturing electrodes for injection-molding biosensors.

METHODS

During the sensor-fabrication process, barrel-plated gold electrodes were inserted into an injection-molded base. The electrode directly touched the electrical contact of a meter. We analyzed technical measurements for this biosensor, including tests of the measurement range, within-run imprecision, and between-meter imprecision. In clinical trials, experienced technicians tested 3 alternative sites (fingertip, palm, and arm). The results were simultaneously compared with plasma values obtained with the hexokinase method on the Olympus AU640 instrument. Analytical results were evaluated according to International Standards Organization 15197 (ISO 15197:2003) criteria and by Clarke error grid analysis (EGA), and CVs were calculated to evaluate within-run imprecision.

RESULTS

The glucose measurement range was 0.6- 33.3 mmol/L (y = 0.96x + 0.07 mmol/L; r(2) = 0.9977). The CVs in the within-run imprecision test were 1.7%-3.5%, and the overall CV was 2.1%, indicating good reproducibility of results. The Student t-tests of mean values from 5 meters revealed statistically insignificant differences (P > 0.05). In clinical trials, the agreement of the Rightest GM310 meter results with those of a laboratory method complied with ISO 15197:2003 criteria. In the EGA, 100% of the values were within the acceptable zones (A + B), and the proportion of values within zone A exceeded 95%.

CONCLUSIONS

The Bionime Rightest GM310 meter applied a simplified process for biosensor fabrication and displayed acceptable performance for monitoring glucose concentrations at alternative test sites.

Kinetic study of the decomposition of Prussian Blue electrocatalytic layer during cathodic reduction of hydrogen peroxide

Kinetic study on the decomposition of Prussian Blue electrocatalytic layer during electrochemical reduction of hydrogen peroxide has been studied in relation to biosensor application of this electrocatalyst. The decomposition has been shown to proceed as a nearly exponential decay process and the corresponding first-order rate coefficients were determined. It has been shown that the decomposition proceeds about 10 times faster in pH 7.3 buffer solution as compared to pH 5.5 buffer. A linear dependence of the decomposition rate on the concentration of hydrogen peroxide has been found.

Characterization and electrocatalytic properties of Prussian blue electrochemically deposited on nano-Au/PAMAM dendrimer-modified gold electrode

Gold electrode was modified with 3-mercaptopropionic acid (MPA) and further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) then attached the nano-Au to obtain films on which Prussian blue (PB) was electrochemically deposited to afford much wider pH adaptive range, much better electrochemical stability and excellent electrochemical response. The microstructure and electrochemical behavior of Au/MPA/PAMAM/nano-Au/PB electrode were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The electrochemical response of the Au/MPA/PAMAM/nano-Au/PB-modified electrode for the electrocatalytic reduction of hydrogen peroxide was investigated, and it was found that the sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au/PB-modified electrode and Au/MPA/PAMAM/PB electrode. Based on this, a new electrochemical sensor for determination of hydrogen peroxide has been developed.

Fabrication of Prussian Blue modified ultramicroelectrode for GOD imaging using scanning electrochemical microscopy

A Prussian Blue (PB) film modified disk ultramicroelectrode (UME) was fabricated by electrochemical deposition technique on a Pt-disk UME. The electrocatalytical reductions of hydrogen peroxide derived from glucose oxidase (GOD) on this modified UME were investigated. The enzymatic biochemical reactivity was imaged by scanning electrochemical microscopy (SECM) utilizing the PB film modified UME. It is evident that sensitivity and spatial resolution for hydrogen peroxide measurement were improved obviously. SECM images obtained clearly revealed the concentration profile of the reaction products around the enzymes. The PB film modified microelectrode is in the nature of simple preparation, high catalytic activity on hydrogen peroxide and substrate selectivity for SECM etc.

Enzyme-functionalized gold nanowires for the fabrication of biosensors

Gold nanowires were prepared by an electrodeposition strategy using nanopore polycarbonate (PC) membrane, with the average diameter of the nanowires about 250 nm and length about 10 microm. The nanowires prepared were dispersed into chitosan (CHIT) solution and stably immobilized onto glassy carbon electrode (GCE) surface. The electrochemical behavior of gold nanowire modified electrode and its application to the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)) were investigated. The modified electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. Moreover, the good biocompatibility of nanometer-sized gold, the vast surface area of the nanowire-structure make it ideal for adsorption of enzymes for the fabrication of biosensors. Glucose oxidase was adsorbed onto the nanowire surface to fabricate glucose biosensor as an application example. The detection of glucose was performed in phosphate buffer (pH 6.98) at -0.2 V. The resulting glucose biosensor exhibited sensitive response, with a short response time (<8 s), a linear range of 10(-5)-2 x 10(-2) M and detection limit of 5 x 10(-6) M.

Electrochemical Sensor for Tryptophan Determination Based on Copper-cobalt Hexacyanoferrate Film Modified Graphite Electrode

In this work, the development of a tryptophan sensor and its application to milk are described. The mixed metal (copper and cobalt) hexacynoferrates are electrodeposited on the graphite electrode, and this film exhibits an electrocatalytic activity towards for the oxidation of tryptophan. The experimental conditions, including the scan cycles, the ratio of copper(II) and cobalt(II), pH value, applied potential, are investigated in detail. At the optimal conditions, the eletctrocatalytic response is a linear relationship with the concentration of tryptophan in the range of 10 μM and 900 μM, with a detection limit of about 6 μM. This modified electrode was also successfully used to detect the tryptophan concentration in milk.

Amperometric glucose biosensors based on layer-by-layer assembly of chitosan and glucose oxidase on the Prussian blue-modified gold electrode

A glucose biosensor based on layer-by-layer (LBL) self-assembling of chitosan and glucose oxidase (GOD) on a Prussian blue film was developed. First, Prussian blue was deposited on a cleaned gold electrode then chitosan and GOD were assembled alternately to construct a multilayer film. The resulting amperometric glucose biosensor exhibited a fast response time (within 10 s) and a linear calibration range from 6 microM to 1.6 mM with a detection limit of 3.1 microM glucose (s/n = 3). With the low operating potential, the biosensor showed little interference to the possible interferents, including ascorbic acid, acetaminophen and uric acid, indicating an excellent selectivity.

Part I: recent developments in nanoelectrodes for biological measurements

Biosensors are a type of analytical device that use biological molecules to monitor biorecognition events and interactions. Coupled with the progress in nanotechnologies over recent years, the development of a nanobiosensor based on individual nanoelectrodes and nanoelectrode arrays or nanoelectrode ensembles offers unprecedented avenues for screening and detection at ultrahigh sensitivities. These capabilities provide the basis for a paradigmatic change in biomedical diagnostics and treatment. In this review, we highlight recent developments in nanoelectrode platforms and their suitability for integrating with biological components for the fabrication of ultrasensitive nanobiosensors.

Ruthenium Purple-Mediated Microelectrode Biosensors Based on Sol−Gel Film

Ruthenium Purple (RP), an analogue of Prussian Blue, has potentially advantageous electrochemical characteristics. We now demonstrate its use in microelectrode biosensors for the first time. An RP layer was grown on, and remained stably anchored to, the surface of gold microelectrodes at physiological pH ranges. Crucially, it retained its electrochemical activity in sodium-based phosphate buffers. The RP microelectrodes displayed electrocatalytic reduction of hydrogen peroxide at 0 to -50 mV (vs Ag/AgCl). To fabricate biosensors on the RP microelectrodes, we used a sol-gel film electrodeposition technique to create ATP and hypoxanthine biosensors as examples of the methodology. These RP-mediated biosensors displayed excellent performance including the following: high selectivity against interferences such as 5HT, ascorbic acid, urate, and acetaminophen; high sensitivity with wide linear calibration range; and good stability. These attractive characteristics demonstrate that RP can be universally employed as an electron mediator in fabrication of highly selective oxidase-based microelectrode biosensors. Furthermore, given their ability to operate in the presence of physiological levels of Na+, the RP-mediated biosensors can be potentially applied to the in vitro and in vivo measurement of physiological signaling substances.

Synthesis and characterization of copper hexacyanoferrate nanoparticles for building up long-term stability electrochromic electrodes

Nanoparticles of a Prussian blue (PB) analogue, copper hexacyanoferrate, were synthesized by using ultrasonic radiation and characterized by spectroscopic and electrochemical techniques. The nanoparticles (ca. 10 nm diameter) were immobilized onto transparent indium tin oxide electrodes by electrostatic layer-by-layer deposition. These modified electrodes showed interesting electrochromic properties, changing the coloration during the redox process from brown to orange when oxidized. The nanostructured electrode presented high stability, in contrast to that observed for PB nanoparticles; this fact must be related to the maintenance of the electrostatic assembly because the oxidized compound, CuII/FeIII(CN)6, still possesses a negative excess of charge due to the high number of cyanide groups that link the nanoparticles with the polycation, assuring the integrity of the whole electrostatic assembled film.

Flow injection analysis of blood l-lactate by using a Prussian Blue-based biosensor as amperometric detector

An amperometric l-lactate biosensor was fabricated by confining lactate oxidase in a Prussian Blue-modified electrode with a Nafion membrane. The detector was assembled in a flow injection apparatus and operated at -0.1 V. Conditions for optimal electrode response were determined by investigating the influence of the amount of immobilized enzyme, the sample volume, and the flow rate. At the established operational conditions, the biosensor exhibited negligible response from interfering species usually present in biological fluids. The stability of the biosensor was also investigated, and its sensitivity was maintained unchanged at certain experimental conditions. l-Lactate was determined in blood samples, and the influence of physical exercise on the results was clearly evidenced, demonstrating that the proposed amperometric detector is suitable for monitoring changes in the l-lactate levels in biological fluids.

Fabrication and electrochemical investigation of layer-by-layer deposited titanium phosphate/Prussian blue composite films

Composite films of titanium phosphate (TiPS)/Prussian blue (PB) were fabricated by the alternative deposition of TiPS layer and PB nanocrystals. The layer of TiPS was fabricated by adsorption of hydrated titanium from aqueous Ti(SO4)2 solution and subsequent reaction with phosphate groups. The layer of PB nanocrystals was fabricated by sequential adsorption of FeCl3 solution and K4[Fe(CN)6] solution. Regular deposition of TiPS/PB composite films were verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. The successful fabrication of the TiPS/PB composite films was further confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Instead of producing films of TiPS layers alternating with PB nanocrystal layers, the TiPS/PB composite films have a structure in which the interstices of the PB nanocrystal films are filled with TiPS component. TiPS/PB composite films show enhanced electrochemical properties and improved stability in comparison with pure PB films prepared by the multiple sequential adsorption process. TiPS/PB composite films have the capability to catalyze the electrochemical reduction of H2O2 and can be used as a biosensor for detecting H2O2.

Amperometric biosensor based on Prussian Blue-modified screen-printed electrode for lipase activity and triacylglycerol determination

Lipase activity against triacylglycerols has been measured using an amperometric enzyme biosensor based on glycerol dehydrogenase/NADH oxidase. A Prussian Blue modified screen-printed electrode was selected as substrate for the two immobilised-enzyme systems due to their higher operative stability reported in previous works. Various parameters such as cofactor (flavin mononucleotide FMN) concentration (1 mM), NAD+ coenzyme concentration (2 mM), pH effect (phosphate buffer pH 6 to 8, Tris buffer pH 8-10) response time and storage stability were evaluated and optimised. The glycerol biosensor was then investigated for lipase activity. The system was challenged against an olive or sunflower oil real samples in order to detect fatty acids and the results were compared with those provided either by the manufacture or reference methods with good agreement.

Enzymatic Spectrophotometric Method for Aflatoxin B Detection Based on Acetylcholinesterase Inhibition

A new method for aflatoxin B (AFB) determination is proposed. The AFB determination is based on acetylcholinesterase (AChE) inhibition, and the AChE residual activity is determined using the colorimetric method (Ellman's method). Cholinesterases (ChEs) from various sources were tested using AFB1 as reference aflatoxin. AChE from electric eel has shown the highest sensitivity to AFB1, and it was chosen for the rest of the work. To select and optimize the analytical procedures, an investigation on the type of AChE inhibition by AFB1 was carried out. The AChE degree of inhibition by AFB1 was independent of the incubation time and the enzyme concentrations, showing the reversibility of the inhibition. This reversibility of the inhibition permits a rapid analysis of AFB1, requiring only 3 min. For the development of the AFB1 assay, the pH, the time of reaction, temperature, and substrate concentration were evaluated and optimized. The linear range of 10-60 ng mL-1 was determined. To evaluate the selectivity of this method, the cross-reactivity with other aflatoxins such as aflatoxin B2, aflatoxin G1, aflatoxin G2, and aflatoxin M1 was investigated. Finally, the suitability of the assay for AFB1 quantification in barley was evaluated. This study shows a new approach to detect aflatoxins based on enzyme inhibition and has advantages such as the ease of use, rapidity, and cost effectiveness. Thus, it could find a possible use as a screening method for this type of mycotoxins.

The region ion sensitive field effect transistor, a novel bioelectronic nanosensor

A novel type of bioelectronic region ion sensitive field effect transistor (RISFET) nanosensor was constructed and demonstrated on two different sensor chips that could measure glucose with good linearity in the range of 0-0.6mM and 0-0.3mM with a limit of detection of 0.1 and 0.04 mM, respectively. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. For glucose measurements, negatively charged gluconate ions were gathered between the sensing electrodes. The signal current response was measured using a low-noise pico ammeter (pA). Two different sizes of the RISFET sensor chips were constructed using conventional electron beam lithography. The measurements are done in partial volumes mainly restricted by the working distance between the sensing electrodes (790 and 2500 nm, respectively) and the influence of electrical fields that are concentrating the ions. The sensitivity was 28 pA/mM (2500 nm) and 830 pA/mM (790 nm), respectively. That is an increase in field strength by five times between the sensing electrodes increased the sensitivity by 30 times. The volumes expressed in this way are in low or sub femtoliter range. Preliminary studies revealed that with suitable modification and control of parameters such as the electric control signals and the chip electrode dimensions this sensor could also be used as a nanobiosensor by applying single enzyme molecule trapping. Hypotheses are given for impedance factors of the RISFET conducting channel.

Bi-functionalization of a patterned Prussian blue array for amperometric measurement of glucose via two integrated detection schemes

A novel amperometric sensor that integrates two independent measurement schemes into a single chip for detection of glucose is fabricated. The sensor uses micro-patterned Prussian blue (PB) and ferrocene modified glucose oxidase covered by a thin Nafion membrane. We have developed an amperometric sensor for the detection of glucose that integrates two measurement schemes into a single chip. For fabrication of the sensing interface, micro-contact printing was used to transfer a self-assembled monolayer template onto a gold substrate, allowing selective electrochemical deposition of a PB array. The protective layer of the PB array was subsequently removed and replaced with a layer of redox-functionalized glucose oxidase (GOx), while the entire surface was finally covered with a perm-selective GOx-Nafion membrane. A variety of surface analytical techniques, including atomic force microscopy, surface plasmon resonance imaging and spectroscopic ellipsometry were employed to characterize the composite PB array electrode. The hybrid sensing interface allowed amperometric measurements of glucose to be carried out with two independent schemes at different potentials. The cathodic current was obtained with the PB array functioning as the electrocatalyst, while the anodic current was measured at a higher potential via a mediation mechanism using the ferrocene-modified GOx. For the quantitative detection of glucose, flow-injection analysis was used, and both the operating conditions and the design parameters were optimized. Linear responses were obtained for both anodic and cathodic signals over a concentration range from 0.1 to 50 mM, with a detection limit of 75 microM. The specificity of the sensor was demonstrated with respect to ascorbic and lactic acid. The implementation of integrated detection mechanisms allows the independent measurement of amperometric signals at two separate potentials. This improves the information gathering and opens up new avenues for developing novel methods that potentially eliminate false signal readings.

Structural and Magnetic Diversity in Cyano-Bridged Bi- and Trimetallic Complexes Assembled from Cyanometalates and [M(rac-CTH)]n+ Building Blocks (CTH = d,l-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane)

Seven new cyano-bridged heterometallic systems have been prepared by assembling [M'(rac-CTH)]n+ complexes (M' = CrIII, NiII, CuII), which have two cis available coordination positions, and [M(CN)6]3- (M = FeIII, CrIII) and [Fe(CN)2(bpy)2]+ cyanometalate building blocks. The assembled systems, which have been characterized by X-ray crystallography and magnetic investigations, are the molecular squares (meso-CTH-H2)[{Ni(rac-CTH)}2{Fe(CN)6)}2].5H2O (2) and [{Ni(rac-CTH)}2{Fe(CN)2(bpy)2}2](ClO4)4.H2O (5), the bimetallic chain [{Ni(rac-CTH)}2{Cr(CN)6)}2Ni(meso-CTH)].4H2O (3), the trimetallic chain [{Ni(rac-CTH)}2{Fe(CN)6)}2Cu(cyclam)]6H2O (4), the pentanuclear complexes [{Cu(rac-CTH}3{Fe(CN)6}2].2H2O (6) and [{Cu(rac-CTH)}3{Cr(CN)6)}2].2H2O (7), and the dinuclear complex [Cr(rac-CTH)(H2O)Fe(CN)6].2H2O (8). With the exception of 5, all compounds exhibit ferromagnetic interaction between the metal ions (JFeNi = 12.8(2) cm-1 for 2; J1FeCu= 13.8(2) cm-1 and J2FeCu= 3.9(4) cm-1 for 6; J1CrCu= 6.95(3) cm-1 and J2CrCu= 1.9(2)cm-1 for 7; JCrFe = 28.87(3) cm-1 for 8). Compound 5 exhibits the end of a transition from the high-spin to the low-spin state of the octahedral FeII ions. The bimetallic chain 3 behaves as a metamagnet with a critical field Hc = 300 G, which is associated with the occurrence of week antiferromagnetic interactions between the chains. Although the trimetallic chain 4 shows some degree of spin correlation along the chain, magnetic ordering does not occur. The sign and magnitude of the magnetic exchange interaction between CrIII and FeIII in compound 8 have been justified by DFT type calculations.

Band Gap Variation in Prussian Blue via Cation-Induced Structural Distortion

The charge-transfer band gap of the iron cyanide framework material Prussian Blue and its dependence on the type and location of the charge-compensating interstitial cations (K(+), Rb(+), Cs(+)) are investigated via periodic density functional (DF) calculations. The calculated variation in the band gap magnitude with respect to cation type confirms recent experimental results on cation-induced spectral shifts. The role of both the cation interaction with the framework and the cation-induced lattice expansion are examined with respect to their influence on the band gap. The gap magnitude is related to the cation type but is found to be more strongly affected by cation-induced lattice distortion as the cation passes through the material. Our results support the possibility of engineering the electronic structure of Prussian Blue type materials through guest-induced host-framework distortion.