High-throughput flow-injection analysis of glucose and glutamate in food and biological samples by using enzyme/polyion complex-bilayer membrane-based electrodes as the detectors

A Novel Polyurethane-Based Polyion Complex Material with Tunable Selectivity against Interferents for Selective Dopamine Determination

Polyion complex (PIC) materials have been widely used in biosensors due to their molecular selectivity. However, achieving both widely controllable molecular selectivity and long-term solution stability with traditional PIC materials has been challenging due to the different molecular structures of polycations (poly-C) and polyanions (poly-A). To address this issue, we propose a novel polyurethane (PU)-based PIC material in which the main chains of both poly-A and poly-C are composed of PU structures. In this study, we electrochemically detect dopamine (DA) as the analyte and L-ascorbic acid (AA) and uric acid (UA) as the interferents to evaluate the selective property of our material. The results show that AA and UA are significantly eliminated, while DA can be detected with a high sensitivity and selectivity. Moreover, we successfully tune the sensitivity and selectivity by changing the poly-A and poly-C ratios and adding nonionic polyurethane. These excellent results were employed in the development of a highly selective DA biosensor with a detection range from 500 nM to 100 μM and a 3.4 μM detection limit. Overall, our novel PIC-modified electrode has the potential to advance biosensing technologies for molecular detection.

Re-evaluation of glutamic acid (E 620), sodium glutamate (E 621), potassium glutamate (E 622), calcium glutamate (E 623), ammonium glutamate (E 624) and magnesium glutamate (E 625) as food additives

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of glutamic acid-glutamates (E 620-625) when used as food additives. Glutamate is absorbed in the intestine and it is presystemically metabolised in the gut wall. No adverse effects were observed in the available short-term, subchronic, chronic, reproductive and developmental studies. The only effect observed was increased kidney weight and increased spleen weight; however, the increase in organ weight was not accompanied by adverse histopathological findings and, therefore, the increase in organ weight was not considered as an adverse effect. The Panel considered that glutamic acid-glutamates (E 620-625) did not raise concern with regards to genotoxicity. From a neurodevelopmental toxicity study, a no observed adverse effect level (NOAEL) of 3,200 mg monosodium glutamate/kg body weight (bw) per day could be identified. The Panel assessed the suitability of human data to be used for the derivation of a health-based guidance value. Although effects on humans were identified human data were not suitable due to the lack of dose-response data from which a dose without effect could be identified. Based on the NOAEL of 3,200 mg monosodium glutamate/kg bw per day from the neurodevelopmental toxicity study and applying the default uncertainty factor of 100, the Panel derived a group acceptable daily intake (ADI) of 30 mg/kg bw per day, expressed as glutamic acid, for glutamic acid and glutamates (E 620-625). The Panel noted that the exposure to glutamic acid and glutamates (E 620-625) exceeded not only the proposed ADI, but also doses associated with adverse effects in humans for some population groups.

Gold nanoparticle modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine for potential use as a biosensing material

Gold nanoparticle (AuNP) modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2) was used as the biosensing platform for glucose analysis. Electrochemical measurements were carried out by following the consumed oxygen due to the enzymatic reaction of glucose oxidase (GOx) at -0.7V vs Ag/AgCl. Optimisation of pH, enzyme loading, stability experiments were carried out. Effect of NP was investigated by monitoring the signal responses at different AuNP sizes and amounts. A linear relation of y=1.597x+0.264 (R(2)=0.993) was found for glucose concentrations between 0.002 and 5.0mM. The analytical characteristics of the system were also evaluated for glucose determination in flow injection analysis (FIA) mode. Finally, the system was checked for glucose detection on real samples.

Stable and sensitive flow-through monitoring of phenol using a carbon nanotube based screen printed biosensor

A stable and sensitive biosensor for phenol detection based on a screen printed electrode modified with tyrosinase, multiwall carbon nanotubes and glutaraldehyde is designed and applied in a flow injection analytical system. The proposed carbon nanotube matrix is easy to prepare and ensures a very good entrapment environment for the enzyme, being simpler and cheaper than other reported strategies. In addition, the proposed matrix allows for a very fast operation of the enzyme, that leads to a response time of 15 s. Several parameters such as the working potential, pH of the measuring solution, biosensor response time, detection limit, linear range of response and sensitivity are studied. The obtained detection limit for phenol was 0.14 x 10(-6) M. The biosensor keeps its activity during continuous FIA measurements at room temperature, showing a stable response (RSD 5%) within a two week working period at room temperature. The developed biosensor is being applied for phenol detection in seawater samples and seems to be a promising alternative for automatic control of seawater contamination. The developed detection system can be extended to other enzyme biosensors with interest for several other applications.

Biosensors as analytical tools in food fermentation industry

The food industries need rapid and affordable methods to assure the quality ofproducts and process control. Biosensors, combining a biological recognition element and a sensitive transducer, are versatile analytical tools that offer advantages as classical analytical methods due to their inherent specificity, selectivity and simplicity. This paper reviews the recent trends in the development and applications of biosensors used in food fermentation industry, focusing on amperometric enzymatic and microbial sensors.

DNA–Cu(II) poly(amine) complex membrane as novel catalytic layer for highly sensitive amperometric determination of hydrogen peroxide

A novel hydrogen peroxide biosensor was fabricated by using a DNA-Cu(II) complex as a novel electrocatalyst for the reduction of hydrogen peroxide (H2O2). A polyion complex (PIC) membrane composed of DNA and poly(allylamine) (PAA) functioned as a support matrix for immobilization of electrocatalytic element-copper ion. The circular dichroism (CD) spectrum of the DNA-Cu(II)/PAA membrane in wet state showed that the DNA exists in B-like form within the membrane. Electrochemical measurements of the DNA-Cu(II)/PAA membrane-modified glassy carbon (GC) electrode revealed that the copper ion embedded in the DNA/PAA layer exhibits good electrochemical behaviors, and the electrochemical rate constant between the immobilized copper ion and the GC electrode surface was estimated to be 26.4 s(-1). The resulting DNA-Cu(II)/PAA/GC electrode showed an excellent electrocatalytic activity for the H2O2 reduction. The sensitivity of the sensor for the determination of H2O2 was affected by the amount of each component, such as copper ion, DNA and PAA in the DNA-Cu(II)/PAA membrane. Effects of applied potential, pH, temperature, ionic strength and buffer concentrations upon the response currents of the sensor were also investigated for an optimum analytical performance. Even in the presence of dissolved oxygen, the sensor exhibited highly sensitive and rapid (response time, less than 5 s) response to H2O2. The steady-state cathodic current responses of the sensor obtained at -0.2 V versus Ag/AgCl in air-saturated 50 mM phosphate buffer (pH 5.0) increased linearly up to 135 microM with the detection limit of 50 nM. Interference by ascorbic acid and uric acid due to the reduction of Cu(II) was effectively cancelled by further modification of outermost layer of polyion complex film. In addition, the sensor exhibited good reproducibility and stability.

The application of biosensors to fresh produce and the wider food industry

The inherent specificity, selectivity, and adaptability of biosensors make them ideal candidates for use throughout the food industry. Potential applications within the supply chain range from testing of foodstuffs for maximum pesticide residue verification through to the routine analysis of analyte(s) concentrations, such as, glucose, sucrose, alcohol, etc., which may be indicators of food quality/acceptability. Biosensor formats include simple "one-shot" disposable devices that can be used either in the field or integrated into more sophisticated laboratory instruments. Until now, the main impact of these devices has been in the medical diagnostics field. However, with ongoing technical development, the food industry will be one of the prime beneficiaries of biosensor technology in the future. This report assesses the current and future trends in the application of biosensors to fresh produce and the wider food industry, focusing on both potential and current target analytes that are fundamental to fresh produce quality, traceability, and safety.

Automated enzymatic assays in a renewable fashion using the multisyringe flow injection scheme with soluble enzymes

In this paper, a novel flowing stream scheme based upon the multisyringe flow injection (MSFI) technique is presented as a powerful tool to perform automated enzymatic assays. The exploitation of enzymes in homogeneous phase circumvents typical drawbacks associated with the commonly used packed-bead or open tubular permanent columns, namely, malfunctions of the reactor, carryover effects, flow resistance, loss of binding sites, large reagent consumption, and use of harmful organic solvents during immobilization procedures. The proposed MSFI system is able to handle minute volumes of soluble enzymes and accommodate reactions with divergent kinetic and pH demands, as demonstrated via the indirect chemiluminescence determination of trace levels of glucose. The procedure is based on the on-line glucose oxidase-catalyzed oxidation of beta-glucose in homogeneous phase to beta-glucono-delta-lactone and hydrogen peroxide. Subsequently, the generated oxidant merges downstream with an alkaline slug of 3-aminopthalhydrazide and a metal-catalyst zone (viz., Co(II)) at a total flow rate as high as 72 mL/min aiming to warrant maximum light collection from the fast CL reaction. Under optimum conditions for both sequentially occurring reactions, a glucose concentration as low as 90 microg/L may be easily detected at a 1000-fold photomultiplier gain. A second-order polynomial regression equation of light emission versus substrate concentration is found over the range 90 microg/L-2.7 mg/L glucose, although a maximum concentration of 180 mg/L may be determined by suitable gain selection without requiring manifold reconfiguration. An injection throughput of 20 h(-1), a repeatability better than 2.5% at the 1 mg/L level, and a 3sigma detection limit of 72 microg/L are the analytical features of the designed analyzer. The proposed approach was applied to the analysis of ultralow glucose content soft drinks as well as fruit juices suitable for diabetic consumers. The accuracy was assessed using the spectrophotometric batch glucose-Trinder method as an external reference methodology for the determination of the target species in parenteral solutions.

Simple and inexpensive flow L-glutamate determination using pumpkin tissue

This work refers to a very easy to implementate flow injection system with potentiometric detection for l-glutamate determination in food samples. The proposed procedure is based on measurement of carbon dioxide produced by decarboxylation of l-glutamate catalyzed by l-glutamate decarboxylase (E.C. 4.1.1.1.5) from Cucurbita maxima (pumpkin). The FI potentiometric system includes an enzymatic reactor with a length of 8 cm and thickness of 5 mm packed with 200 mg of a C. maxima outer layer cut in to small pieces. The proposed procedure allowed l-glutamate determinations in the concentration interval of 10-100 mmol L(-1) for an injected sample volume of 50 microL. A phosphate buffer (0.1 mol L(-1), pH 5.5) solution flowing at 1.4 mL min(-1) was used as the carrier solution in the system. The results obtained in the analysis of food samples revealed a relative error lower than 5% when compared with those provided by the spectrophometric reference procedure. The immobilized reactor retained its initial activity for 21 days. It was possible to measure 40 samples/h with the flow system proposed.

Reproducible fabrication of miniaturized glucose sensors: preparation of sensing membranes for continuous monitoring

The immobilization process of glucose oxidase(GOx) in the poly(1,3-diaminobenzene) (poly(1,3-DAB)) network was closely investigated in situ using an electrochemical quartz crystal microbalance(EQCM). GOx captured in approximately 50 nm thick poly-1,3-DAB layer causes a 514 Hz frequency increase, corresponding to 541 ng, and distributes mostly in the outer part of the polymer film. The presence of poly-L-lysine and glutaraldehyde during electropolymerization of poly(1,3-DAB) improves sensitivity by raising the amount of GOx immobilized. Adding a protective membrane on to the enzyme layer from poly(tetrafluoroethylene) (PTFE) dispersed in aqueous media lets the entire fabrication procedure finish perfectly without nonaqueous solvent. The finalized needle-type glucose sensors show competent functions in sensitivity, stability, biocompatibility, lifetime, interference and reproducibility.

Flow-through chemiluminescence sensor using immobilized oxidases for the selective determination of L-glutamate in a flow-injection system

A selective and sensitive chemiluminometric flow sensor for the determination of L-glutamate in serum, based on immobilized oxidases such as glutamate oxidase (GOD), uricase (UC) and peroxidase (POD), is described herein. The principle for the selective chemiluminometric detection for L-glutamate is based on coupled reactions of four sequentially aligned immobilized oxidases, UC/POD/GOD/POD in a flow cell. The immobilized UC was employed to decompose urate, which is one of the major interfering components in serum for a luminol-H2O2 chemiluminescence reaction. The H2O2 produced from the UC reaction readily reacted with reducing components, such as ascorbate and glutathione, and then the excess H2O2 was decomposed by the immobilized POD. L-Glutamate in the sample plug was enzymatically converted to H2O2 with immobilized GOD. Subsequently, the peroxide reacts with luminol on the immobilized POD to produce chemiluminescence, proportional to glutamate concentration. The enzymes were immobilized on tresylated poly(vinyl alcohol beads). The immobilized enzymes were packed into TPFE tube (1.0 mm i.d. x 60 cm), in turn, and used as a flow cell. The sampling rate was 30 h-1. The calibration graph for L-glutamate is linear for 20 nM-5 microM; the detection limit (signal-to-noise = 3) is 10 nM.

Thin-film glucose biosensor based on plasma-polymerized film: simple design for mass production

We propose a simple thin-film glucose biosensor based on a plasma-polymerized film. The film is deposited directly onto the substrate under dry conditions. The resulting films are extreme thin, adhere well onto the substrate (electrode), and have a highly cross-linked network structure and functional groups, such as amino groups, which enable a large amount of enzyme to be immobilized. Since this design allows fabrication through a dry process, with the exception of the enzyme immobilization, which is the last stage of the process, the chip fabrication can be designed as a full-wafer process to achieve mass production compatibility. The resulting sensors produced using this film are more reproducible, exhibit lower noise, and reduce the effect of interference to a greater degree than sensors made using conventional immobilization methods, e.g., via 3-(aminopropyl)triethoxysilane. The obtained film is a good interfacial design between enzyme and electrode; enzyme two-dimensionally locates very close to the electrode in a manner that is quite reproducible. Therefore, a wide dynamic range (up to 60 mM) and rapid response time (11.5+/-0.8 s) were obtained. Because of its highly cross-linking network structure, the amperometric response due to interferences such as ascorbic acid and acetaminophen was reduced by size discrimination of plasma-polymerized films.