Luiza A. Mercante

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.

Molecularly Imprinted Polymer-Decorated Magnetite Nanoparticles for Selective Sulfonamide Detection

Sulfonamides are known not only to be antimicrobial drugs that lead to antimicrobial resistance but also to be chemotherapeutic agents that may be allergenic and potentially carcinogenic, which represents a potentially hazardous compound once present in soil or water. Herein, a hybrid material based on molecularly imprinted polymer (MIP)-decorated magnetite nanoparticles for specific and label-free sulfonamide detection is reported. The composite has been characterized using different spectroscopic and imaging techniques. The magnetic properties of the composite are used to separate, preconcentrate, and manipulate the analyte which is selectively captured by the MIP onto the surface of the composite. Screen printed electrodes have been employed to monitor the impedance levels of the whole material, which is related to the amount of the captured analyte, via electrochemical impedance spectroscopy. This composite-based sensing system exhibits an extraordinary limit of detection of 1 × 10(-12) mol L(-1) (2.8 × 10(-4) ppb) (S/N = 3), which is close to those obtained with liquid chromatography and mass spectrometry, and it was demonstrated to screen sulfamethoxazole in a complex matrix such as seawater, where according to the literature sulfonamides content is minimum compared with other environmental samples.

Graphene-based Janus micromotors for the dynamic removal of pollutants

Persistent organic pollutants (POPs) are ubiquitous in the environment as a result of modern industrial processes. We present an effective POPs decontamination strategy based on their dynamic adsorption at the surface of reduced graphene oxide (rGO)-coated silica (SiO2)–Pt Janus magnetic micromotors for their appropriate final disposition. While the motors rapidly move in a contaminated solution, the adsorption of POPs efficiently takes place in a very short time. Characterization of the micromotors both from the materials and from the motion point of view was performed. Polybrominated diphenyl ethers (PBDEs) and 5-chloro-2-(2,4-dichlorophenoxy) phenol (triclosan) were chosen as model POPs and the removal of the contaminants was efficiently achieved. The rGO-coated micromotors demonstrated superior adsorbent properties with respect to their concomitant GO-coated micromotors, static rGO-coated particles and dynamic silica micromotors counterparts. The extent of decontamination was studied over the number of micromotors, whose magnetic properties were used for their collection from environmental samples. The adsorption properties were maintained for 4 cycles of micromotors reuse. The new rGO-coated SiO2 functional material-based micromotors showed outstanding capabilities towards the removal of POPs and their further disposition, opening up new possibilities for efficient environmental remediation of these hazardous compounds.

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.

Detection of trace levels of organophosphate pesticides using an electronic tongue based on graphene hybrid nanocomposites

Organophosphate (OP) compounds impose significant strains on public health, environmental/food safety and homeland security, once they have been widely used as pesticides and insecticides and also display potential to be employed as chemical warfare agents by terrorists. In this context, the development of sensitive and reliable chemical sensors that would allow in-situ measurements of such contaminants is highly pursued. Here we report on a free-enzyme impedimetric electronic tongue (e-tongue) used in the analysis of organophosphate pesticides comprising four sensing units based on graphene hybrid nanocomposites. The nanocomposites were prepared by reduction of graphene oxide in the presence of conducting polymers (PEDOT:PSS and polypyrrole) and gold nanoparticles (AuNPs), which were deposited by drop casting onto gold interdigitated electrodes. Impedance spectroscopy measurements were collected in triplicate for each sample analyzed, and the electrical resistance data were treated by Principal Component Analysis (PCA), revealing that the system was able to discriminate OPs at nanomolar concentrations. In addition, the electronic tongue system could detect OPs in real samples, where relations between the principal components and the variation of pesticides in a mixture were established, proving to be useful to analyze and monitor mixtures of OP pesticides. The materials employed provided sensing units with high specific surface area and high conductivity, yielding the development of a sensor with suitable stability, good reproducibility, and high sensitivity towards pesticide samples, being able to discriminate concentrations as low as 0.1nmolL-1. Our results indicate that the e-tongue system can be used as a rapid, simple and low cost alternative in the analyses of OPs pesticide solutions below the concentration range permitted by legislation of some countries.

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.

Solution blow spun PMMA nanofibers wrapped with reduced graphene oxide as an efficient dye adsorbent

Nanotechnology has provided innovative solutions to guarantee sustainable energy and maintain a clean environment for the future. In this regard, 1D nanostructured materials, such as nanofibers, are very attractive, especially for the development of economic and environmentally friendly approaches for wastewater treatment. Recently, Solution Blow Spinning (SBS) has appeared as a powerful fiber forming technique with several advantages compared to the traditional electrospinning method. Herein, we present the fabrication of composite membranes using solution blow spun poly(methylmethacrylate) nanofibers wrapped with reduced graphene oxide (PMMA-rGO) to adsorb methylene blue (MB), which is a typical dye used in the printing and dyeing industry. The dye adsorption kinetics and isotherm follow the pseudo-second-order and the Langmuir models, respectively. The π–π stacking interactions were considered to be the major driving force for the spontaneous adsorption of MB and the maximum adsorption capacity was 698.51 mg g−1 according to Langmuir fitting. The developed nanocomposite shows great potential for decolorizing dyeing wastewater aimed at industrial and environmental remediation applications.

An electronic tongue based on conducting electrospun nanofibers for detecting tetracycline in milk samples

The development of novel and portable chemical sensors aimed at the food industry is of prime importance for food safety issues, and nanomaterial science can greatly contribute to this task. In this context, a careful choice of the sensing material is essential for achieving high performance sensor arrays, such as those employed in nanostructured electronic tongues (e-tongues). In the current work, an impedimetric e-tongue based on gold interdigitated microelectrodes (IDEs) modified with polyamide 6/polyaniline (PA6/PANI) electrospun nanofibers was developed, characterized and used to detect tetracycline (TC) residue in fat and skimmed milk samples. By analyzing the electrical resistance data collected by the e-tongue, which were treated by Principal Component Analysis (PCA), the e-tongue was able to identify the presence of TC residues (from 1 to 300 ppb) in fat and skimmed milk samples. The results obtained demonstrate the ability of the approach of modifying IDEs with conducting electrospun nanofibers to be used as sensing units in the e-tongue, aiming to analyze complex matrices such as milk without any prior pre-treatment.

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.

Fluorescent and Colorimetric Electrospun Nanofibers for Heavy-Metal Sensing

The accumulation of heavy metals in the human body and/or in the environment can be highly deleterious for mankind, and currently, considerable efforts have been made to develop reliable and sensitive techniques for their detection. Among the detection methods, chemical sensors appear as a promising technology, with emphasis on systems employing optically active nanofibers. Such nanofibers can be obtained by the electrospinning technique, and further functionalized with optically active chromophores such as dyes, conjugated polymers, carbon-based nanomaterials and nanoparticles, in order to produce fluorescent and colorimetric nanofibers. In this review we survey recent investigations reporting the use of optically active electrospun nanofibers in sensors aiming at the specific detection of heavy metals using colorimetry and fluorescence methods. The examples given in this review article provide sufficient evidence of the potential of optically electrospun nanofibers as a valid approach to fabricate highly selective and sensitive optical sensors for fast and low-cost detection of heavy metals.