Walter M. de Azevedo

Bio: Walter M. de Azevedo is an academic researcher from Federal University of Pernambuco. The author has contributed to research in topics: Polyaniline & Thermoluminescence. The author has an hindex of 14, co-authored 59 publications receiving 726 citations.

Tb3+→Eu3+ Energy Transfer in Mixed-Lanthanide-Organic Frameworks

Abstract: In this work, we report a theoretical and experimental investigation of the energy transfer mechanism in two isotypical 2D coordination polymers, ∞[(Tb1–xEux)(DPA)(HDPA)], where H2DPA is pyridine 2,6-dicarboxylic acid and x = 0.05 or 0.50. Emission spectra of ∞[(Tb0.95Eu0.05)(DPA)(HDPA)] and ∞[(Tb0.5Eu0.5)(DPA)(HDPA)], (1) and (2), show that the high quenching effect on Tb3+ emission caused by Eu3+ ion indicates an efficient Tb3+→Eu3+ energy transfer (ET). The kET of Tb3+→ Eu3+ ET and rise rates (kr) of Eu3+ as a function of temperature for (1) are on the same order of magnitude, indicating that the sensitization of the Eu3+ 5D0 level is highly fed by ET from the 5D4 level of Tb3+ ion. The ηET and R0 values vary in the 67–79% and 7.15 to 7.93 A ranges. Hence, Tb3+ is enabled to transfer efficiently to Eu3+ that can occupy the possible sites at 6.32 and 6.75 A. For (2), the ET processes occur on average with ηET and R0 of 97% and 31 A, respectively. Consequently, Tb3+ ion is enabled to transfer energy to E...

Glucose biosensor using glucose oxidase immobilized in polyaniline.

Abstract: A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose with a response time of 2.5-4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for use as a support in optical sensor for clinical application.

Enzyme immobilization on anodic aluminum oxide/polyethyleneimine or polyaniline composites

Abstract: Anodic aluminum oxide (AAO) membranes were coated with either polyethyleneimine (PEI) or polyaniline (PANI) and used as supports for enzyme immobilization. The AAO–PEI composite was prepared by cross-flow filtration of the polymer solution through the membrane, whereas AAO–PANI was synthesized using surface chemical polymerization, where MnO 2 was used as oxidizing agent for aniline polymerization. After glutaraldehyde activation, horseradish peroxidase and trypsin were immobilized on the composites. The immobilized enzyme activities were determined either in a batch mode or flow-through system. The AAO–PEI–trypsin derivative yielded filtering membrane catalytically active with initial velocities of 2.95 nmol min −1 and 3.8 nmol min −1 measured in batch mode and flow-through system (0.46 mL min −1 ), respectively. Furthermore, AAO–PEI–trypsin prepared with membranes of different porosities showed that the enzymatic activity increased as the inside diameter of the pore enlarged. Additionally, it was demonstrated that covalent coupling presents higher activity as compared to attachment by adsorption on a membrane without PEI functionalities, which had 2.9 times less activity. Horseradish peroxidase was successfully immobilized onto the AAO–PANI and retained 74% of its initial activity after five batch cycles and 98% following 24 min under continuous flow. It was also observed by electron microscopy that membrane pores remained unclog after polyaniline coating. Therefore, these results showed the viability of these composites as attractive nano-structured matrices for biotechnological applications.

Conjugated polymer-based chemical sensors.

Abstract: When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Gas Sensors Based on Conducting Polymers

Abstract: The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Abstract: Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...