Adriana Pavinatto

Electrospun Polyamide 6/Poly(allylamine hydrochloride) Nanofibers Functionalized with Carbon Nanotubes for Electrochemical Detection of Dopamine

The use of nanomaterials as an electroactive medium has improved the performance of bio/chemical sensors, particularly when synergy is reached upon combining distinct materials. In this paper, we report on a novel architecture comprising electrospun polyamide 6/poly(allylamine hydrochloride) (PA6/PAH) nanofibers functionalized with multiwalled carbon nanotubes, used to detect the neurotransmitter dopamine (DA). Miscibility of PA6 and PAH was sufficient to form a single phase material, as indicated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), leading to nanofibers with no beads onto which the nanotubes could adsorb strongly. Differential pulse voltammetry was employed with indium tin oxide (ITO) electrodes coated with the functionalized nanofibers for the selective electrochemical detection of dopamine (DA), with no interference from uric acid (UA) and ascorbic acid (AA) that are normally present in biological fluids. The response was linear for a DA concentration range from 1 to 70 μmol L(-1), with detection limit of 0.15 μmol L(-1) (S/N = 3). The concepts behind the novel architecture to modify electrodes can be potentially harnessed in other electrochemical sensors and biosensors.

Electrostatic interactions are not sufficient to account for chitosan bioactivity.

Recent studies involving chitosan interacting with phospholipid monolayers that mimic cell membranes have brought molecular-level evidence for some of the physiological actions of chitosan, as in removing a protein from the membrane. This interaction has been proven to be primarily of electrostatic origin because of the positive charge of chitosan in low pH solutions, but indirect evidence has also appeared of the presence of hydrophobic interactions. In this study, we provide definitive proof that model membranes are not affected merely by the charges in the amine groups of chitosan. Such a proof was obtained by comparing surface pressure and surface potential isotherms of dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG) monolayers incorporating either chitosan or poly(allylamine hydrochloride) (PAH). As the latter is also positively charged and with the same charged functional group as chitosan, similar effects should be observed in case the electrical charge was the only relevant parameter. Instead, we observed a large expansion in the surface pressure isotherms upon interaction with chitosan, whereas PAH had much smaller effects. Of particular relevance for biological implications, chitosan considerably reduced the monolayer elasticity, whereas PAH had almost no effect. It is clear therefore that chitosan action depends strongly either on its functional uncharged groups and/or on its specific conformation in solution.

Improving the electrochemical properties of polyamide 6/polyaniline electrospun nanofibers by surface modification with ZnO nanoparticles

Heterostructured nanomaterials have attracted increasing interest because of their novel and distinct optical and electrical properties, finding applications in devices and chemical sensors. Here we report a new electrochemical platform based on the modification of fluorine doped tin oxide (FTO) electrodes with polyamide 6/polyaniline (PA6/PANI) electrospun nanofibers decorated with ZnO nanoparticles. The nanoparticles were synthesized by a co-precipitation method, followed by hydrothermal treatment; the route was optimized in order to obtain particles of small average diameter (45 nm). Polymeric nanofibers were obtained by the electrospinning technique and further subjected to ZnO modification by nanoparticle impregnation. SEM images confirmed the uniform distribution of ZnO nanoparticles adsorbed onto the nanofiber surface, the amount of which was estimated to be 4% w/w, according to thermal gravimetric analysis (TGA). According to the electrochemical characterization, an improvement in electron transfer kinetics and increase in electroactive area was observed for the ZnO-modified FTO electrode. The modified electrode was employed for monitoring hydrazine, and yielded a detection limit of 0.35 μmol L−1. Our results indicate that the novel sensing platform based on the adsorption of ZnO nanoparticles onto the surface of electrospun nanofibers can be potentially harnessed for electrochemical sensor and biosensor applications.

Low molecular-weight chitosans are stronger biomembrane model perturbants

The influence from the chitosan molecular weight on its interaction with cell membrane models has been studied. A low molecular weight chitosan (LMWChi) adsorbed from the subphase expanded the surface pressure-area and surface potential-area isotherms of dimyristoyl phosphatidic acid (DMPA) monolayers and decreased the compressional modulus. The expansion in the monolayers and the decrease in the compressional modulus were larger for LMWChi than for a high molecular weight chitosan (Chi). The polymeric nature is still essential for the interaction though, which was demonstrated by measuring negligible changes in the mechanical properties of the DMPA monolayer when the subphase contained glucosamine and acetyl-glucosamine. The results were rationalized in a model through which chitosan interacted with the membrane via electrostatic and hydrophobic interactions, with the smaller chains of LMWChi having less steric hindrance to be accommodated in the membrane. In summary, the activity based on membrane interactions depends on the distribution of molar mass, with lower molecular weight chitosan more likely to have stronger effects.

Electronic tongue based on nanostructured hybrid films of gold nanoparticles and phthalocyanines for milk analysis

The use of gold nanoparticles combined with other organic and inorganic materials for designing nanostructured films has demonstrated their versatility for various applications, including optoelectronic devices and chemical sensors. In this study, we reported the synthesis and characterization of gold nanoparticles stabilized with poly(allylamine hydrochloride) (Au@PAH NPs), as well as the capability of this material to form multilayer Layer-by-Layer (LbL) nanostructured films with metal tetrasulfonated phthalocyanines (MTsPc). Film growth was monitored by UV-Vis absorption spectroscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). Once LbL films have been applied as active layers in chemical sensors, Au@PAH/MTsPc and PAH/MTsPc LbL films were used in an electronic tongue system for milk analysis regarding fat content. The capacitance data were treated using Principal Component Analysis (PCA), revealing the role played by the gold nanoparticles on the LbL films electrical properties, enabling this kind of system to be used for analyzing complex matrices such as milk without any prior pretreatment.

Acylated Carrageenan Changes the Physicochemical Properties of Mixed Enzyme–Lipid Ultrathin Films and Enhances the Catalytic Properties of Sucrose Phosphorylase Nanostructured as Smart Surfaces

Control over the catalytic activity of enzymes is important to construct biosensors with a wide range of detectability and higher stability. For this, immobilization of enzymes on solid supports as nanostructured films is a current approach that permits easy control of the molecular architecture as well as tuning of the properties. In this article, we employed acylated carrageenan (AC) mixed with phospholipids at the air-water interface to facilitate the adsorption of the enzyme sucrose phosphorylase (SP). AC stabilized the adsorption of SP at the phospholipid monolayer, as detected by tensiometry, by which thermodynamic parameters could be inferred from the surface pressure-area isotherm. Also, infrared spectroscopy applied in situ over the monolayer showed that the AC-phospholipid system not only permitted the enzyme to be adsorbed but also helped conserve its secondary structure. The mixed monolayers were then transferred onto solid supports as Langmuir-Blodgett (LB) films and investigated with transfer ratio, quartz crystal microbalance, fluorescence spectroscopy, and atomic force microscopy. The enzyme activity of the LB film was then determined, revealing that although there was an expected reduction in activity in relation to the homogeneous environment the activity could be better preserved after 1 month, revealing enhanced stability.

Chemical sensors based on hybrid nanomaterials for food analysis

Abstract Hybrid nanostructured materials possess appealing features such as a high surface area/volume ratio and size- dependent optical and electrical properties, which are highly desirable for designing chemicals sensors with optimized properties. Reliable, cheap, and sensitive portable chemical sensors have been highly pursued for applications in food analysis and food safety, allowing monitoring of the chemical composition, taste and smell, and contamination by microorganisms including bacteria and fungus, among other applications. In this chapter we give an overview on distinct nanostructured materials and the molecular architectures employed as active layers for chemical sensors, including thin films of conjugated polymers, nanofibers, metallic nanoparticles, carbon nanotubes, and enzymes. Such materials can drastically improve both sensitivity and limit of detection of sensors, including conventional potentiometric sensors, biosensors, electronic tongue and electronic nose sensors.