Simultaneous monitoring of glucose and lactate by an interference and cross-talk free dual electrode amperometric biosensor based on electropolymerized thin films

Multiplexed Immunosensor Based on the Amperometric Transduction for Monitoring of Marine Pollutants in Sea Water

Environmental pollutants vigilance is one of the main problems that the aquaculture industry has to face with the objective to ensure the quality of their products and prevent entrance in the food chain that finally may arrive to the consumer. Contaminants such as hormones, antibiotics or biocides are especially relevant due to their toxicity, pharmacological effect or hormonal activity that can be considered harmful for the final consumer. The contaminants can be detected in the environment where the food is growing, and their concentration can be found (i.e., seawater) in the range of µg·L⁻¹, ng·L⁻¹ or even in lower concentrations. Thus, sensitive and selective methods for their monitoring are required to avoid their arrival in the food chain. Here, the development of a multiplexed amperometric biosensor is described, based on the use of specific antibodies to reach the necessary detectability to measure the targeted contaminants directly in seawater. The multiplexed immunosensor allows the detection of four relevant pollutants, such as el Irgarol 1051, sulfapyridine, chloramphenicol and estradiol, reaching an IC₅₀ of 5.04 ± 0.29, 3.45 ± 0.29, 4.17 ± 0.44 and 5.94 ± 0.28 µg·L⁻¹, directly measured in seawater.

Simple Fabrication of Flexible Biosensor Arrays Using Direct Writing for Multianalyte Measurement from Human Astrocytes

Simultaneous measurements of glucose, lactate, and neurotransmitters (e.g., glutamate) in cell culture over hours and days can provide a more dynamic and longitudinal perspective on ways neural cells respond to various drugs and environmental cues. Compared with conventional microfabrication techniques, direct writing of conductive ink is cheaper, faster, and customizable, which allows rapid iteration for different applications. Using a simple direct writing technique, we printed biosensor arrays onto cell culture dishes, flexible laminate, and glass to enable multianalyte monitoring. The ink was a composite of PEDOT:PSS conductive polymer, silicone, activated carbon, and Pt microparticles. We applied 0.5% Nafion to the biosensors for selectivity and functionalized them with oxidase enzymes. We characterized biosensors in phosphate-buffered saline and in cell culture medium supplemented with fetal bovine serum. The biosensor arrays measured glucose, lactate, and glutamate simultaneously and continued to function after incubation in cell culture at 37 °C for up to 2 days. We cultured primary human astrocytes on top of the biosensor arrays and placed arrays into astrocyte cultures. The biosensors simultaneously measured glucose, glutamate, and lactate from astrocyte cultures. Direct writing can be integrated with microfluidic organ-on-a-chip platforms or as part of a smart culture dish system. Because we print extrudable and flexible components, sensing elements can be printed on any 3D or flexible substrate.

A Minimally Invasive Microsensor Specially Designed for Simultaneous Dissolved Oxygen and pH Biofilm Profiling

A novel sensing device for simultaneous dissolved oxygen (DO) and pH monitoring specially designed for biofilm profiling is presented in this work. This device enabled the recording of instantaneous DO and pH dynamic profiles within biofilms, improving the tools available for the study and the characterization of biological systems. The microsensor consisted of two parallel arrays of microelectrodes. Microelectrodes used for DO sensing were bare gold electrodes, while microelectrodes used for pH sensing were platinum-based electrodes modified using electrodeposited iridium oxide. The device was fabricated with a polyimide (Kapton^®) film of 127 µm as a substrate for minimizing the damage caused on the biofilm structure during its insertion. The electrodes were covered with a Nafion^® layer to increase sensor stability and repeatability and to avoid electrode surface fouling. DO microelectrodes showed a linear response in the range 0–8 mg L⁻¹, a detection limit of 0.05 mg L⁻¹, and a sensitivity of 2.06 nA L mg⁻¹. pH electrodes showed a linear super-Nernstian response (74.2 ± 0.7 mV/pH unit) in a wide pH range (pH 4−9). The multi-analyte sensor array was validated in a flat plate bioreactor where simultaneous and instantaneous pH and DO profiles within a sulfide oxidizing biofilm were recorded. The electrodes spatial resolution, the monitoring sensitivity, and the minimally invasive features exhibited by the proposed microsensor improved biofilm monitoring performance, enabling the quantification of mass transfer resistances and the assessment of biological activity.

Adaptable Xerogel-Layered Amperometric Biosensor Platforms on Wire Electrodes for Clinically Relevant Measurements

Biosensing strategies that employ readily adaptable materials for different analytes, can be miniaturized into needle electrode form, and function in bodily fluids represent a significant step toward the development of clinically relevant in vitro and in vivo sensors. In this work, a general scheme for 1st generation amperometric biosensors involving layer-by-layer electrode modification with enzyme-doped xerogels, electrochemically-deposited polymer, and polyurethane semi-permeable membranes is shown to achieve these goals. With minor modifications to these materials, sensors representing potential point-of-care medical tools are demonstrated to be sensitive and selective for a number of conditions. The potential for bedside measurements or continuous monitoring of analytes may offer faster and more accurate clinical diagnoses for diseases such as diabetes (glucose), preeclampsia (uric acid), galactosemia (galactose), xanthinuria (xanthine), and sepsis (lactate). For the specific diagnostic application, the sensing schemes have been miniaturized to wire electrodes and/or demonstrated as functional in synthetic urine or blood serum. Signal enhancement through the incorporation of platinum nanoparticle film in the scheme offers additional design control within the sensing scheme. The presented sensing strategy has the potential to be applied to any disease that has a related biomolecule and corresponding oxidase enzyme and represents rare, adaptable, sensing capabilities.

Conducting Polymers, Hydrogels and Their Composites: Preparation, Properties and Bioapplications

This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- and nanostructures, and enhanced surface areas compared with those of conventionally prepared ICPs. Hydrogels, due to their defined porous structures and being filled with aqueous solution, offer the ability to increase the amount of immobilized chemical, biological or biochemical molecules. When other components are incorporated into ICPs, the materials form composites; in this particular case, they form conductive composites. The design and synthesis of conductive composites result in the inheritance of the advantages of each component and offer new features because of the synergistic effects between the components. The resulting structures of ICPs, conducting polymer hydrogels and their composites, as well as the unusual physicochemical properties, biocompatibility and multi-functionality of these materials, facilitate their bioapplications. The synergistic effects between constituents have made these materials particularly attractive as sensing elements for biological agents, and they also enable the immobilization of bioreceptors such as enzymes, antigen-antibodies, and nucleic acids onto their surfaces for the detection of an array of biological agents. Currently, these materials have unlimited applicability in biomedicine. In this review, we have limited discussion to three areas in which it seems that the use of ICPs and materials, including their different forms, are particularly interesting, namely, biosensors, delivery of drugs and tissue engineering.

Chemical and Biological Sensors for Food-Quality Monitoring and Smart Packaging

The growing interest in food quality and safety requires the development of sensitive and reliable methods of analysis as well as technology for freshness preservation and food quality. This review describes the status of chemical and biological sensors for food monitoring and smart packaging. Sensing designs and their analytical features for measuring freshness markers, allergens, pathogens, adulterants and toxicants are discussed with example of applications. Their potential implementation in smart packaging could facilitate food-status monitoring, reduce food waste, extend shelf-life, and improve overall food quality. However, most sensors are still in the development stage and need significant work before implementation in real-world applications. Issues like sensitivity, selectivity, robustness, and safety of the sensing materials due to potential contact or migration in food need to be established. The current development status of these technologies, along with a discussion of the challenges and opportunities for future research, are discussed.

Sensors for Fetal Hypoxia and Metabolic Acidosis: A Review

This article reviews existing clinical practices and sensor research undertaken to monitor fetal well-being during labour. Current clinical practices that include fetal heart rate monitoring and fetal scalp blood sampling are shown to be either inadequate or time-consuming. Monitoring of lactate in blood is identified as a potential alternative for intrapartum fetal monitoring due to its ability to distinguish between different types of acidosis. A literature review from a medical and technical perspective is presented to identify the current advancements in the field of lactate sensors for this application. It is concluded that a less invasive and a more continuous monitoring device is required to fulfill the clinical needs of intrapartum fetal monitoring. Potential specifications for such a system are also presented in this paper.

Toward a Hybrid Biosensor System for Analysis of Organic and Volatile Fatty Acids in Fermentation Processes

Monitoring of organic acids (OA) and volatile fatty acids (VFA) is crucial for the control of anaerobic digestion. In case of unstable process conditions, an accumulation of these intermediates occurs. In the present work, two different enzyme-based biosensor arrays are combined and presented for facile electrochemical determination of several process-relevant analytes. Each biosensor utilizes a platinum sensor chip (14 × 14 mm2) with five individual working electrodes. The OA biosensor enables simultaneous measurement of ethanol, formate, d- and l-lactate, based on a bi-enzymatic detection principle. The second VFA biosensor provides an amperometric platform for quantification of acetate and propionate, mediated by oxidation of hydrogen peroxide. The cross-sensitivity of both biosensors toward potential interferents, typically present in fermentation samples, was investigated. The potential for practical application in complex media was successfully demonstrated in spiked sludge samples collected from three different biogas plants. Thereby, the results obtained by both of the biosensors were in good agreement to the applied reference measurements by photometry and gas chromatography, respectively. The proposed hybrid biosensor system was also used for long-term monitoring of a lab-scale biogas reactor (0.01 m3) for a period of 2 months. In combination with typically monitored parameters, such as gas quality, pH and FOS/TAC (volatile organic acids/total anorganic carbonate), the amperometric measurements of OA and VFA concentration could enhance the understanding of ongoing fermentation processes.

Analytical Parameters of an Amperometric Glucose Biosensor for Fast Analysis in Food Samples

Amperometric biosensors based on the use of glucose oxidase (GOx) are able to combine the robustness of electrochemical techniques with the specificity of biological recognition processes. However, very little information can be found in literature about the fundamental analytical parameters of these sensors. In this work, the analytical behavior of an amperometric biosensor based on the immobilization of GOx using a hydrogel (Chitosan) onto highly ordered titanium dioxide nanotube arrays (TiO₂NTAs) has been evaluated. The GOx–Chitosan/TiO₂NTAs biosensor showed a sensitivity of 5.46 μA·mM⁻¹ with a linear range from 0.3 to 1.5 mM; its fundamental analytical parameters were studied using a commercial soft drink. The obtained results proved sufficient repeatability (RSD = 1.9%), reproducibility (RSD = 2.5%), accuracy (95–105% recovery), and robustness (RSD = 3.3%). Furthermore, no significant interferences from fructose, ascorbic acid and citric acid were obtained. In addition, the storage stability was further examined, after 30 days, the GOx–Chitosan/TiO₂NTAs biosensor retained 85% of its initial current response. Finally, the glucose content of different food samples was measured using the biosensor and compared with the respective HPLC value. In the worst scenario, a deviation smaller than 10% was obtained among the 20 samples evaluated.

Wearable Microsystem for Minimally Invasive, Pseudo-Continuous Blood Glucose Monitoring: The e-Mosquito

This paper presents a wearable microsystem for minimally invasive, autonomous, and pseudo-continuous blood glucose monitoring, addressing a growing demand for replacing tedious fingerpricking tests for diabetic patients. Unlike prevalent solutions which estimate blood glucose levels from interstitial fluids or tears, our design extracts a whole blood sample from a small lanced skin wound using a novel shape memory alloy (SMA)-based microactuator and directly measures the blood glucose level from the sample. In vitro characterization determined that the SMA microactuator produced penetration force of 225 gf, penetration depth of 3.55 mm, and consumed approximately 5.56 mW·h for triggering. The microactuation mechanism was also evaluated by extracting blood samples from the wrist of four human volunteers. A total of 19 out of 23 actuations successfully reached capillary vessels below the wrists producing blood droplets on the surface of the skin. The integrated potentiostat-based glucose sensing circuit of our e-Mosquito device also showed a good linear correlation (R² = 0.9733) with measurements using standard blood glucose monitoring technology. These proof-of-concept studies demonstrate the feasibility of the e-Mosquito microsystem for autonomous intermittent blood glucose monitoring.

Thin-film amperometric multibiosensor for simultaneous determination of lactate and glucose in wine

An amperometric multi-biosensor based on lactate and glucose oxidases has been developed for determination of lactate and glucose in wine. Gold thin-film amperometric electrodes were used as multi-transducers. Analytical characteristics of the multi-biosensor developed were studied. The minimum detectable concentration was 5×10(-6) mol/l for both glucose and lactate. High reproducibility and storage stability of the multi-biosensor are demonstrated in this paper. Lactate and glucose were determined in wine, and a good correlation was obtained with concentrations determined using high-performance liquid chromatography (correlation coefficient for glucose R(2)=0.998, for lactate R(2)=0.718).

Biosensors based on electrochemical lactate detection: A comprehensive review

Lactate detection plays a significant role in healthcare, food industries and is specially necessitated in conditions like hemorrhage, respiratory failure, hepatic disease, sepsis and tissue hypoxia. Conventional methods for lactate determination are not accurate and fast so this accelerated the need of sensitive biosensors for high-throughput screening of lactate in different samples. This review focuses on applications and developments of various electrochemical biosensors based on lactate detection as lactate being essential metabolite in anaerobic metabolic pathway. A comparative study to summarize the L-lactate biosensors on the basis of different analytical properties in terms of fabrication, sensitivity, detection limit, linearity, response time and storage stability has been done. It also addresses the merits and demerits of current enzyme based lactate biosensors. Lactate biosensors are of two main types – lactate oxidase (LOD) and lactate dehydrogenase (LDH) based. Different supports tried for manufacturing lactate biosensors include membranes, polymeric matrices-conducting or non-conducting, transparent gel matrix, hydrogel supports, screen printed electrodes and nanoparticles. All the examples in these support categories have been aptly discussed. Finally this review encompasses the conclusion and future emerging prospects of lactate sensors.

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Different enzymes used in lactate bio sensing have been studied.

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Support used for fabrication biosensors have been discussed.

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The linearity range, response time, detection limit, etc. have been studied.

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Merits and demerits of different supports are also discussed.

Biofabrication Using Pyrrole Electropolymerization for the Immobilization of Glucose Oxidase and Lactate Oxidase on Implanted Microfabricated Biotransducers

The dual responsive Electrochemical Cell-on-a-Chip Microdisc Electrode Array (ECC MDEA 5037) is a recently developed electrochemical transducer for use in a wireless, implantable biosensor system for the continuous measurement of interstitial glucose and lactate. Fabrication of the biorecognition membrane via pyrrole electropolymerization and both in vitro and in vivo characterization of the resulting biotransducer is described. The influence of EDC-NHS covalent conjugation of glucose oxidase with 4-(3-pyrrolyl) butyric acid (monomerization) and with 4-sulfobenzoic acid (sulfonization) on biosensor performance was examined. As the extent of enzyme conjugation was increased sensitivity decreased for monomerized enzymes but increased for sulfonized enzymes. Implanted biotransducers were examined in a Sprague-Dawley rat hemorrhage model. Resection after 4 h and subsequent in vitro re-characterization showed a decreased sensitivity from 0.68 (±0.40) to 0.22 (±0.17) µA·cm^-2·mM^-1, an increase in the limit of detection from 0.05 (±0.03) to 0.27 (±0.27) mM and a six-fold increase in the response time from 41 (±18) to 244 (±193) s. This evidence reconfirms the importance of biofouling at the bio-abio interface and the need for mitigation strategies to address the foreign body response.

Lactate biosensors: current status and outlook

Many research efforts over the last few decades have been devoted to sensing lactate as an important analytical target in clinical care, sport medicine, and food processing. Therefore, research in designing lactate sensors is no longer in its infancy and now is more directed toward viable sensors for direct applications. In this review, we provide an overview of the most immediate and relevant developments toward this end, and we discuss and assess common transduction approaches. Further, we critically describe the pros and cons of current commercial lactate sensors and envision how future sensing design may benefit from emerging new technologies.

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H2O2) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed "diaphragms" that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H2O2 relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3mg GOD per 1mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H2O2, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6s), broad detection range (10μM to 10mM), high sensitivity (143.5μAmM(-1)cm(-2)) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1μM to 0.83mM, sensitivity of 494.9μAmM(-1)cm(-2), and detection limit of 0.02μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors.

Nanoparticles as biochemical sensors

There is little doubt that nanoparticles offer real and new opportunities in many fields, such as biomedicine and materials science. Such particles are small enough to enter almost all areas of the body, including cells and organelles, potentially leading to new approaches in nanomedicine. Sensors for small molecules of biochemical interest are of critical importance. This review is an attempt to trace the use of nanomaterials in biochemical sensor design. The possibility of using nanoparticles functionalized with antibodies as markers for proteins will be elucidated. Moreover, capabilities and applications for nanoparticles based on gold, silver, magnetic, and semiconductor materials (quantum dots), used in optical (absorbance, luminescence, surface enhanced Raman spectroscopy, surface plasmon resonance), electrochemical, and mass-sensitive sensors will be highlighted. The unique ability of nanosensors to improve the analysis of biochemical fluids is discussed either through considering the use of nanoparticles for in vitro molecular diagnosis, or in the biological/biochemical analysis for in vivo interaction with the human body.

Improved glucose electrochemical biosensor by appropriate immobilization of nano-ZnO

We constructed the transferred ZnO biosensor and the grown ZnO biosensor by two different nano-ZnO immobilization approaches. And the influence of different assembly processes on the biosensor performance has been systematically investigated and compared. An enhanced sensitivity of the grown ZnO biosensor is found to be 52% higher than that of the transferred ZnO biosensor. Correspondingly, the other properties are also better in the grown ZnO biosensor, including the response time, the detection limit and the linear range. These results are well consistent with the fact that more glucose oxidase is immobilized on the well-aligned ZnO arrays, which have higher specific surface area and more direct electron communication path, in the grown sensor than the randomly distributed and stacked ZnO nanorods in the transferred sensor. The nano-ZnO grown directly has been demonstrated more desirable for enzymatic immobilization and signal transduction in the high performance biosensors.

Continuous-flow multi-analyte biosensor cartridge with controllable linear response range

This article presents the design and fabrication of a microfluidic biosensor cartridge for the continuous and simultaneous measurement of biologically relevant analytes in a sample solution. The biosensor principle is based on the amperometric detection of hydrogen peroxide using enzyme-modified electrodes. The low-integrated and disposable cartridge is fabricated in PDMS and SU-8 by rapid prototyping. The device is designed in such a way that it addresses two major challenges of biosensors using microfluidics approaches. Firstly, the enzymatic membrane is deposited on top of the platinum electrodes via a microfluidic deposition channel from outside the cartridge. This decouples the membrane deposition from the cartridge fabrication and enables the user to decide when and with what mixture he wants to modify the electrode. Secondly, by using laminar sheath-flow of the sample and a buffer solution, a dynamic diffusion layer is created. The analyte has to diffuse through the buffer solution layer before it can reach the immobilized enzyme membrane on the electrode. Controlling of the thickness of the diffusion layer by variation of the flow-rate of the two layers enables the user to adjust the sensitivity and the linear region of the sensor. The point where the buffer and sample stream join proved critical in creating the laminar sheath-flow. Results of computational simulations considering fluid dynamics and diffusion are presented. The consistency of the device was investigated through detection of glucose and lactate and are in accordance with the CFD simulations. A sensitivity of 157+/-28 nA/mM for the glucose sensor and 79+/-12 nA/mM for the lactate sensor was obtained. The linear response range of these biosensors could be increased from initially 2 mM up to 15 mM with a limit of detection of 0.2 mM.

Enzyme immobilization strategies and electropolymerization conditions to control sensitivity and selectivity parameters of a polymer-enzyme composite glucose biosensor

In an ongoing programme to develop characterization strategies relevant to biosensors for in-vivo monitoring, glucose biosensors were fabricated by immobilizing the enzyme glucose oxidase (GOx) on 125 μm diameter Pt cylinder wire electrodes (Pt(C)), using three different methods: before, after or during the amperometric electrosynthesis of poly(ortho-phenylenediamine), PoPD, which also served as a permselective membrane. These electrodes were calibrated with H(2)O(2) (the biosensor enzyme signal molecule), glucose, and the archetypal interference compound ascorbic acid (AA) to determine the relevant polymer permeabilities and the apparent Michaelis-Menten parameters for glucose. A number of selectivity parameters were used to identify the most successful design in terms of the balance between substrate sensitivity and interference blocking. For biosensors electrosynthesized in neutral buffer under the present conditions, entrapment of the GOx within the PoPD layer produced the design (Pt(C)/PoPD-GOx) with the highest linear sensitivity to glucose (5.0 ± 0.4 μA cm(-2) mM(-1)), good linear range (K(M) = 16 ± 2 mM) and response time (< 2 s), and the greatest AA blocking (99.8% for 1 mM AA). Further optimization showed that fabrication of Pt(C)/PoPD-GOx in the absence of added background electrolyte (i.e., electropolymerization in unbuffered enzyme-monomer solution) enhanced glucose selectivity 3-fold for this one-pot fabrication protocol which provided AA-rejection levels at least equal to recent multi-step polymer bilayer biosensor designs. Interestingly, the presence of enzyme protein in the polymer layer had opposite effects on permselectivity for low and high concentrations of AA, emphasizing the value of studying the concentration dependence of interference effects which is rarely reported in the literature.

Development of a novel, sensitive amperometric-FIA glucose biosensor by packing up the amperometric cell with glucose oxidase modified anion exchange resin

In this work, the anion exchange resin (AER) was modified with a layer of glucose oxidase (GOD) and poly(diallyldimethylammonium chloride) (PDDA), respectively, via layer-by-layer electrostatic self-assembling strategy. The PDDA and GOD modified AER (PDDA/GOD/AER) was then packed into a home-made amperometric cell for flow injection analysis (FIA) of glucose. This design simplified the setup by integrating the enzyme reactor into the amperometric cell. And the AER in the cell behaved bifunctional, it was not only the support of enzymes, but also an anti-interference tool due to its retention effect toward ascorbic acid (AA) and uric acid (UA). A platinum modified porous titanium (Pt/PTi) electrode was utilized in the cell as the working electrode (WE), due to its large effective surface area it could increase the response by 8.3 times as compared with the planar pure platinum electrode. The proposed biosensor was very sensitive (22.4 microA cm(-2) mM(-1)) in glucose quantification, and the linear range was from 1 micromol L(-1) to 2 mmol L(-1) with the detection limit of 0.8 micromol L(-1). The biosensor was used for serum glucose determination, and the result obtained was satisfying. This work may have provided a reference design of the amperometric cell which could be adopted in other enzymatic-FIA biosensors.

A lactate biosensor based on lactate dehydrogenase/nictotinamide adenine dinucleotide (oxidized form) immobilized on a conducting polymer/multiwall carbon nanotube composite film

An amperometric lactate biosensor was developed based on a conducting polymer, poly-5,2'-5',2''-terthiophene-3'-carboxylic acid (pTTCA), and multiwall carbon nanotube (MWNT) composite on a gold electrode. Lactate dehydrogenase (LDH) and the oxidized form of nicotinamide adenine dinucleotide (NAD(+)) were subsequently immobilized onto the pTTCA/MWNT composite film. The modified electrode was characterized by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), and electrochemical experiments. The detection signal was amplified by the pTTCA/MWNT assembly onto which a sufficient amount of enzyme was immobilized and stabilized by the covalent bond formation between the amine groups of enzyme and the carboxylic acid groups of the pTTCA/MWNT film. Experimental parameters affecting the sensor responses, such as applied potential, pH, and temperature, were assessed and optimized. Analytical performances and dynamic ranges of the sensor were determined, and the results showed that the sensitivity, stability, and reproducibility of the sensor improved significantly using pTTCA/MWNT composite film. The calibration plot was linear (r(2)=0.9995) over the range of 5 to 90 microM. The sensitivity was approximately 0.0106 microA/microM, with a detection limit of 1 microM, based on a signal/noise ratio of 3. The applicability of the sensor for the analysis of l-lactate concentration in commercial milk and human serum samples was demonstrated successfully.

Assembling Amperometric Biosensors for Clinical Diagnostics

Clinical diagnosis and disease prevention routinely require the assessment ofspecies determined by chemical analysis. Biosensor technology offers several benefits overconventional diagnostic analysis. They include simplicity of use, specificity for the targetanalyte, speed to arise to a result, capability for continuous monitoring and multiplexing,together with the potentiality of coupling to low-cost, portable instrumentation. This workfocuses on the basic lines of decisions when designing electron-transfer-based biosensorsfor clinical analysis, with emphasis on the strategies currently used to improve the deviceperformance, the present status of amperometric electrodes for biomedicine, and the trendsand challenges envisaged for the near future.