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Glucose oxidase (GOD) has been immobilized in Layer-by-Layer (LbL) films, adsorbed alternately with poly(allylamine) hydrochloride (PAH) layers, onto an ITO substrate modified with a Prussian Blue (PB) layer. The ITO/PB/GOD-PAH heterostructures were tested in amperometric glucose biosensors, with a high sensitivity of 16 μA mmol-1 l cm-2 and a limit of detection of 0.20 mmol l-1 being achieved. This high sensitivity is attributed to the ultrathin nature of the film in addition to the low operating potentials that could be used due to the efficient catalysis of H2O2 produced in the enzymatic reaction in the presence of Prussian Blue. The biosensors are highly selective to glucose, as demonstrated by the lack of interference from possible interferents such as ascorbic and uric acids and acetominophen. The stability of the biosensors was checked by observing an almost constant sensitivity for a period of approximately 20 days, thus indicating a stable adsorption of GOD. [Copyright &y& Elsevier]

Abstract: Sophisticated molecular architectures can be produced with the layer-by-layer (LbL) method, which may combine distinct materials on the same film. In this study, we take advantage of this capability to produce cholesterol amperometric biosensors from LbL films containing hemoglobin (Hb) and cholesterol oxidase in addition to the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(ethylene imine) (PEI). Following an optimization procedure, we found that an LbL film deposited onto ITO substrates, with the architecture ITO(PEI/Hb)5(PEI/COx)10, yielded a sensitivity of 93.4μAμmolL−1 cm−2 for cholesterol incorporated into phospholipid liposomes, comparable to state-of-the-art biosensors. Hb acted as efficient electron mediator and did not suffer interference from phospholipids. Significantly, cholesterol could also be detected in real samples from chicken egg yolk, with no effects from potential interferents, including phospholipids. Taken together these results demonstrate the possible fabrication of low cost, easy-to-use cholesterol amperometric biosensors, whose sensitivity can be enhanced by further optimizing the molecular architectures of the LbL films. [Copyright &y& Elsevier]

In this work nanostructured film composites of the monoamine oxidase B (MAO-B) enzyme, free or encapsulated in liposomes, were fabricated by the layer-by-layer (LbL) self-assembly technique, employing polyethylene imine (PEI) as polycation. Initially, the MAO-B enzyme was incorporated into liposomes in order to preserve its enzymatic structure ensuring their activity and catalytic stability. The LbL film growth was monitored by surface plasmon resonance (SPR) by gold resonance angle shift analysis after each bilayer deposition. Subsequently, the films were applied as amperometric biosensors for dopamine detection using Prussian Blue (PB) as the electron mediator. The biosensor fabricated by MAO-B incorporated into liposomes composed of DPPG:POPG in the ratio (1:4) ( w / w ) showed the best performance with a sensitivity of 0.86 (μA cm − 2 )/(mmol L − 1 ) and a detection limit of 0.33 mmol L − 1 . [ABSTRACT FROM AUTHOR]

Abstract: In this paper we discuss the detection of glucose and triglycerides using information visualization methods to process impedance spectroscopy data. The sensing units contained either lipase or glucose oxidase immobilized in layer-by-layer (LbL) films deposited onto interdigitated electrodes. The optimization consisted in identifying which part of the electrical response and combination of sensing units yielded the best distinguishing ability. It is shown that complete separation can be obtained for a range of concentrations of glucose and triglyceride when the interactive document map (IDMAP) technique is used to project the data into a two-dimensional plot. Most importantly, the optimization procedure can be extended to other types of biosensors, thus increasing the versatility of analysis provided by tailored molecular architectures exploited with various detection principles. [Copyright &y& Elsevier]

Abstract: Amperometric biosensors based on the physical immobilization of phytase (PhyA) into polypyrrole (PPy) films were prepared in aqueous medium. The PPy/PhyA films were characterized by cyclic voltammetry, and surface and structural characterization techniques, SEM and FTIR. Both voltammetric and amperometric transduction methods were used in order to detect phytic acid in acetate buffer at pH 5.5 at room temperature. The biosensors exhibited a detection limit of 0.15mmolL−1 and a linear range of phytic acid content from 0.5 to 2.0mmolL−1, which are adequate values for typical analyses of phytic acids in most seeds, grains, and vegetables. [Copyright &y& Elsevier]

Impedance spectroscopy has been proven a powerful tool for reaching high sensitivity in sensor arrays made with nanostructured films in the so-called electronic tongue systems, whose distinguishing ability may be enhanced with sensing units capable of molecular recognition. In this study we show that for optimized sensors and biosensors the dielectric relaxation processes involved in impedance measurements should also be considered, in addition to an adequate choice of sensing materials. We used sensing units made from layer-by-layer (LbL) films with alternating layers of the polyeletrolytes, poly(allylamine) hydrochloride (PAR) and poly(vinyl sulfonate) (PVS), or LbL films of PAR alternated with layers of the enzyme phytase, all adsothed on gold interdigitate electides. Surprisingly, the detection of phytic acid was as effective in the PVS/PAR sensing system as with the PAH phytase system, in spite of the specific interactions of the latter. This was attributed to the dependence of the relaxation processes on nonspecific interactions such as electrostatic cross-linking and possibly on the distinct film architecture as the phytase layers were found to grow as columns on the LbL film, in contrast to the molecularly thin PAH/PVS films. Using projection techniques, we were able to detect phytic acid at the micromolar level with either of the sensing units in a data analysis procedure that allows for further optimization. [ABSTRACT FROM AUTHOR]

Abstract: The preserved activity of immobilized biomolecules in layer-by-layer (LbL) films can be exploited in various applications, including biosensing. In this study, cholesterol oxidase (COX) layers were alternated with layers of poly(allylamine hydrochloride) (PAH) in LbL films whose morphology was investigated with atomic force microscopy (AFM). The adsorption kinetics of COX layers comprised two regimes, a fast, first-order kinetics process followed by a slow process fitted with a Johnson–Mehl–Avrami (JMA) function, with exponent ~2 characteristic of aggregates growing as disks. The concept based on the use of sensor arrays to increase sensitivity, widely employed in electronic tongues, was extended to biosensing with impedance spectroscopy measurements. Using three sensing units, made of LbL films of PAH/COX and PAH/PVS (polyvinyl sulfonic acid) and a bare gold interdigitated electrode, we were able to detect cholesterol in aqueous solutions down to the 10−6 M level. This high sensitivity is attributed to the molecular-recognition interaction between COX and cholesterol, and opens the way for clinical tests to be made with low cost, fast experimental procedures. [Copyright &y& Elsevier]

Abstract: Phytase (myo-inositol hexaphosphate phosphohydrolase) and phytic acid (myo-inositol hexaphosphate) play an important environmental role, in addition to being a health issue in food industry. Phytic acid is antinutritional due to its ability to chelate metal ions and may also react with proteins decreasing their bioavailability. In this work, we produced biosensors with phytase immobilized in Layer-by-Layer (LbL) films, which could detect phytic acid with a detection limit of 0.19mmolL−1, which is sufficient to detect phytic acid in seeds of grains and vegetables. The biosensosrs consisted of LbL films containing up to eight bilayers of phytase alternated with poly(allylamine) hydrochloride (PAH) deposited onto an indium–tin oxide (ITO) substrate modified with Prussian Blue. Amperometric detection was conducted in an acetate buffer solution (at pH 5.5) at room temperature, with the biosensor response attributed to the formation of phosphate ions. In subsidiary experiments with the currents measured at 0.0V (vs. SCE), we demonstrated the absence of effects from some interferents, pointing to a good selectivity of the biosensor. [Copyright &y& Elsevier]

[Display omitted] • Gold nanoparticles were synthesized by cysteamine stabilization. • Gold nanoparticles functionalized with Creatine Phosphate (Pcrea) CK-MB. • CK-MB was successfully detected by Surface Plasmonic Resonance (SPR). • Low cost and rapid time of analysis achieved by the biosensor. • A sensitivity comparable with others biosensors was achieved. In this paper, we report a new biosensor for detection of the cardiac biomarker Creatine Kinase (CK-MB) using Surface Plasmon Surface (SPR) technique, with the purpose of the diagnosis of Acute Myocardial Infarction (AMI). For this, we employed gold nanoparticles (AuNP) stabilized with Cysteamine (Cys), and functionalized with Creatine Phosphate (Pcrea), which promote an increase in the sensitivity and accuracy for creatine kinase (CK-MB) detection in saliva and urine samples. The characteristics of the electronic transfer of the sensor could be observed by Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV), that showed significant redox peaks on electrode surface evidencing the high electron exchange process and low resistance charge transfer between the electrolyte solution and the modified surface. The morphological characteristics were confirmed by Atomic Force Microscopy (AFM), micro-Raman and Contact Angle (CA), as well as the adsorption and interaction processes between the materials, which could be observed by Surface Plasmon Resonance (SPR). The SPR analytical curve, ranged from 5.0 ng mL−1 to 100.0 ng mL−1, provided some important parameters, such as limit of detection (LOD) of 0.209 ng mL−1, limit of quantification (LOQ) of 0.696 ng mL−1, and sensitivity of 8.67 × 10–3 ± 0.17 × 10–3 (°) mL ng−1. The specific interaction between functionalized substrate and CK-MB demonstrates a high affinity of 15.14 ng mL−1 based on the Michaelis-Menten fitting. [ABSTRACT FROM AUTHOR]