Edson G.R. Fernandes

Optimized architecture for Tyrosinase-containing Langmuir–Blodgett films to detect pyrogallol

The control of molecular architectures has been a key factor for the use of Langmuir–Blodgett (LB) films in biosensors, especially because biomolecules can be immobilized with preserved activity. In this paper we investigated the incorporation of tyrosinase (Tyr) in mixed Langmuir films of arachidic acid (AA) and a lutetium bisphthalocyanine (LuPc2), which is confirmed by a large expansion in the surface pressure isotherm. These mixed films of AA–LuPc2 + Tyr could be transferred onto ITO and Pt electrodes as indicated by FTIR and electrochemical measurements, and there was no need for crosslinking of the enzyme molecules to preserve their activity. Significantly, the activity of the immobilised Tyr was considerably higher than in previous work in the literature, which allowed Tyr-containing LB films to be used as highly sensitive voltammetric sensors to detect pyrogallol. Linear responses have been found up to 400 μM, with a detection limit of 4.87 × 10−2 μM (n = 4) and a sensitivity of 1.54 μA μM−1 cm−2. In addition, the Hill coefficient (h = 1.27) indicates cooperation with LuPc2 that also acts as a catalyst. The enhanced performance of the LB-based biosensor resulted therefore from a preserved activity of Tyr combined with the catalytic activity of LuPc2, in a strategy that can be extended to other enzymes and analytes upon varying the LB film architecture.

Immobilization of lutetium bisphthalocyanine in nanostructured biomimetic sensors using the LbL technique for phenol detection

This study describes the development of amperometric sensors based on poly(allylamine hydrochloride) (PAH) and lutetium bisphthalocyanine (LuPc(2)) films assembled using the Layer-by-Layer (LbL) technique. The films have been used as modified electrodes for catechol quantification. Electrochemical measurements have been employed to investigate the catalytic properties of the LuPc(2) immobilized in the LbL films. By chronoamperometry, the sensors present excellent sensitivity (20 nA μM(-1)) in a wide linear range (R(2)=0.994) up to 900 μM and limit of detection (s/n=3) of 37.5 × 10(-8)M for catechol. The sensors have good reproducibility and can be used at least for ten times. The work potential is +0.3 V vs. saturated calomel electrode (SCE). In voltammetry measurements, the calibration curve shows a good linearity (R(2)=0.992) in the range of catechol up to 500 μM with a sensitivity of 90 nA μM(-1) and LD of 8 μM.

Electrospinning of Hyperbranched Poly-L-Lysine/Polyaniline Nanofibers for Application in Cardiac Tissue Engineering

Electrospun polyaniline nanofibers are one of the most promising materials for cardiac tissue engineering due to their tunable electroactive properties. Moreover, the biocompatibility of polyaniline nanofibes can be improved by grafting of adhesive peptides during the synthesis. In this paper, we describe the biocompatible properties and cardiomyocytes proliferation on polyaniline electrospun nanofibers modified by hyperbranched poly-L-lysine dendrimers (HPLys). The microstructure characterization of the HPLys/polyaniline nanofibers was carried out by scanning electron microscopy (SEM). It was observed that the application of electrical current stimulates the differentiation of cardiac cells cultured on the nanofiber scaffolds. Both electroactivity and biocompatibility of the HPLys based nanofibers suggest the use this material for culture of cardiac cells and opens the possibility of using this material as a biocompatible electroactive 3-D matrix in cardiac tissue engineering.

A peroxidase biomimetic system based on Fe3O4 nanoparticles in non-enzymatic sensors

Magnetic nanoparticles have been applied in many areas of nanomedicine. Sensing platforms based on this type of nanoparticles have received attention due to the relative low cost and biocompatibility. Biosensor is the most widely investigated type of analytical device. This type of sensor combines the physicochemical transduction with the incorporation of biological sensing components. Among the biological components, enzymes are the most commonly used as sensitive elements. However, natural enzymes may exhibit serious disadvantages such as lack of stability and loss of catalytic activity after immobilization. The study of enzymatic biomimetic systems are of great interest. This study reports the development of a new sensor composed of Fe3O4@CTAB and poly(sodium 4-styrenesulfonate) (PSS) films assembled via Layer-by-Layer (LbL) technique and used as peroxidase mimetic systems. Magnetic nanoparticles (MNps) were synthesized using thermal decomposition method and further dispersed to aqueous medium by ligand modification reaction using cetyltrimethylammonium bromide (CTAB). The amperometric detection limit of H2O2 was found to be ca. 103 µmol L(-1). By chronoamperometry, the peroxidase biomimetic sensor exhibited a linear response for H2O2 in the range from 100 µmol L(-1) to 1.8 mmol L(-1) (R(2) = 0.994) with sensitivity of 16 nA mol(-1) L. The apparent Michaelis-Menten constant was 5.3 mmol L(-1), comparable with some biosensors based on peroxidase enzyme. Moreover, the sensor presented a reproducibility of ca. 7.7% (n = 4) and their response (response time: 90 s) is not significantly affected in the presence of some interferents including K(+), Na(+), Cl(-), Mg(2+), Ca(2+), and Uric Acid.

Indium tin oxide synthesized by a low cost route as SEGFET pH sensor

2 atmosphere using a low-cost chemical vapor deposition (CVD) system. The films were evaluated as pH sensors in separative extended gate field-effect transistor (SEGFET) apparatus, exhibiting a sensitivity of 53 mV/pH, close to the expected Nernstian theoretical value for ion sensitive materials. The use of CVD process to synthesize ITO, as described here, may represent an alternative for fabrication of SEGFET pH sensors at low cost to be used in disposable biosensors since H + ions are the product of several oxireductase enzymes.

The Use of Le Bail Method to Analyze the Semicrystalline Pattern of a Nanocomposite Based on Polyaniline Emeraldine-Salt Form and α-Al2O3

Ceramic nanocomposites constituted by a matrix of α-Al2O3 microparticles reinforced by polyaniline emeraldine-salt form (PANI-ES) nanoparticles were prepared by in situ polymerization and characterized structural and morphologically. Peaks related to both materials were observed through XRD technique: PANI-ES presented peaks at = 8.9, 14.9, 20.8, 25.3, 27.1, and 30.0° and in α-Al2O3 phase peaks were found at = 25.6, 35.2, 37.9, 43.5, 52.6, 57.6, and 68.1°. Nanocomposite crystallinity percentage was estimated around 70%. SEM showed a polymerization of PANI-ES over alumina plates. By Le Bail method it was observed that PANI-ES and α-Al2O3 have crystallite average size around, respectively, 41 and 250 A. By FTIR analysis characteristic absorption bands of both materials were identified. Additional bands indicating new chemical bonds were not observed, suggesting that nanocomposite was formed by physical deposition. Nanocomposite DC electrical conductivity was found around 0.24 S/cm (against  S/cm for pure PANI-ES), showing an increase of about 1,300 times compared to the pure PANI-ES at room temperature. Thus, this paper showed that both materials have kept its original structural characteristics and exhibited high electrical conductivity when combined in nanocomposite form.

Nanocomposite based on polyaniline emeraldine-base and α-Al2O3: A structural characterization

Abstract A ceramic-matrix nanocomposite based on polyaniline emeraldine base and aluminum oxide (PANI-EB/α-Al2O3) was obtained by in-situ polymerization. X-ray diffraction pattern presented peaks related to both materials. The level of crystallinity was estimated at about 53%. The average crystallite sizes of PANI-EB and α-Al2O3 were found to be ∼40 Å and 570 Å, respectively. Scanning electron microscopy showed polymerization over ceramic particles. Fourier-transform infrared spectroscopy suggested physical deposition. The electrical conductivity of the PANI-EB/α-Al2O3 nanocomposite was decreased by a factor of 80 when compared with that of pure PANI-EB. Therefore, the polymeric reinforcement and the ceramic matrix maintained their original structural features, but the electrical conductivity in the nanocomposite was reduced.

Biosensors Based on Field-Effect Devices

This chapter brings an overview on the use of field-effect devices (FEDs) in biochemical sensors, emphasizing their advantages and specificity for biosensing, which is typical of such semiconductor-based device. Following the introductory sections on operation principles and comparison with field-effect transistors, we concentrate on different types of FEDs and their detection methods. In particular, we shall focus on ion-sensitive field-effect transistor (ISFET), electrolyte-insulator-semiconductor (EIS), light-addressable potentiometric sensor, extended-gate field-effect transistor (EGFET) and separative extended-gate field-effect transistor (SEGFET). Important contributions in the literature in biochemical sensors based on such devices are highlighted. A discussion is also provided on how the functionalization of these devices with nanostructured films can result in sensors with increased sensitivity and selectivity. Examples of modified devices containing polyelectrolytes, metallic nanoparticles, carbon nanotubes, and other compounds, used for detecting a variety of analytes, will be provided. We discuss the concepts involved in the operation principles and the particularity of different FEDs. The prospects for clinical diagnosis with such biosensors and environment monitoring are also addressed. Moreover, strategies to improve sensing properties through functionalization are placed on, particularly with synergistic combination of organic and inorganic materials. For example, nanostructured films containing carbon nanotubes exhibited enhanced performance in biosensing. It is expected that this chapter may provide researchers with an alternative sensing platform to study new biochemical sensors concepts for specific applications.