Nanophotonic label-free biosensors for environmental monitoring

The field of environmental monitoring has experienced a substantial progress in the last years but still the on-site control of contaminants is an elusive problem. In addition, the growing number of pollutant sources is accompanied by an increasing need of having efficient early warning systems. Several years ago biosensor devices emerged as promising environmental monitoring tools, but their level of miniaturization and their fully operation outside the laboratory prevented their use on-site. In the last period, nanophotonic biosensors based on evanescent sensing have emerged as an outstanding choice for portable point-of-care diagnosis thanks to their capability, among others, of miniaturization, multiplexing, label-free detection and integration in lab-on-chip platforms. This review covers the most relevant nanophotonic biosensors which have been proposed (including interferometric waveguides, grating-couplers, microcavity resonators, photonic crystals and localized surface plasmon resonance sensors) and their recent application for environmental surveillance

The Optical Property of Core-Shell Nanosensors and Detection of Atrazine Based on Localized Surface Plasmon Resonance (LSPR) Sensing

Three different nanosensors with core-shell structures were fabricated by molecular self-assembly and evaporation techniques. Such closely packed nanoparticles exhibit fine optical properties which are useful for biochemical sensing. The refractive index sensitivity (RIS) of nanosensors was detected by varying the refractive index of the surrounding medium and the decay length of nanosensors was investigated using a layer-by-layer polyelectrolyte multilayer assembly. The results showed that the thickness of the Au shell plays an important role in determining the RIS and the decay length. A system based on localized surface plasmon resonances (LSPR) sensing was constructed in our study. The core-shell nanosensors can detect 10 ng/mL atrazine solutions and are suitable for pesticide residue detection

The Optical Property of Core-Shell Nanosensors and Detection of Atrazine Based on Localized Surface Plasmon Resonance (LSPR) Sensing

Three different nanosensors with core-shell structures were fabricated by molecular self-assembly and evaporation techniques. Such closely packed nanoparticles exhibit fine optical properties which are useful for biochemical sensing. The refractive index sensitivity (RIS) of nanosensors was detected by varying the refractive index of the surrounding medium and the decay length of nanosensors was investigated using a layer-by-layer polyelectrolyte multilayer assembly. The results showed that the thickness of the Au shell plays an important role in determining the RIS and the decay length. A system based on localized surface plasmon resonances (LSPR) sensing was constructed in our study. The core-shell nanosensors can detect 10 ng/mL atrazine solutions and are suitable for pesticide residue detection

Synthese von Kern@Schale hoch-k Nanopartikeln

In den letzten Jahren haben Kern@Schale Nanopartikel stark an Bedeutung in Forschung und Entwicklung neuartiger funktionaler Materialien gewonnen, da hier die Möglichkeit besteht, verschiedene Funktionalitäten zu kombinieren und die Eigenschaften durch Zusammensetzung, Dicke des Kerns und der Hülle und Partikelgröße gezielt zu beeinflussen. Als Kern Materialien kommen hierbei unter anderem Halbleiter, Metalle, magnetische Oxide und gekapselte Moleküle zum Einsatz. Die Schale kann den Kern vor Umwelteinflüssen schützen, die Agglomeration vermindern, die Stabilität und Dispergierbarkeit erhöhen, z. B. die kernoberfläche lassen sich funktionalisieren, dadurch wird ein homogenes Einbringen anorganischer Kernpartikel in eine organische Matrix möglich. BaTiO3 ist ein sehr bekanntes dielektrisches Material und wird als Dielektrikum in Kondensatoren verwendet aufgrund seiner hohen und frequenzunabhängigen relativen Permittivität mit niedriger dielektrischen Verluste. Der Fokus der Arbeit liegt auf der Synthese und Charakterisierung von BaTiO3 Nanopartikeln und die Verwendung von BaTiO3- Nanopartikeln zur Herstellung von verschiedenen Kern@Schale Nanopartikel: BaTiO3@SiO2 und Ag@BaTiO3. Für die Herstellung von BaTiO3 Nanopartikeln wird eine umfangreiche, kosteneffiziente und umweltverträgliche “Organosol” Synthese bei niedrigen Temperaturen entwickeln. Diese einfache, schnelle und schonende Synthese bietet viele Möglichkeiten, auf das gewünschte Produkt Einfluss zu nehmen. Hinzu kommt die einfache Skalierbarkeit und die genaue Kontrolle der Partikelgröße. Des Weiteren wird die Herstellung von BaTiO3@SiO2 Nanopartikel mit Kern@Schale-Struktur über inverse Mikroemulsion als Reaktionsmedium gezeigt. Die inverse Mikroemulsionslösung (W/O) besteht aus Triton X-100, n-Hexanol, Cyclohexan und einer wässrigen Phase. Bei diesem Verfahren werden aus einem Tetraalkylorthosilicat (TEOS) durch eine Ammoniak-katalysierte Hydrolyse-Kondensationsreaktion in einer inversen Mikroemulsion SiO2 beschichtete BaTiO3 Nanopartikel, wobei die SiO2 schale eine Dicke im Bereich von 3 nm bis 20 nm aufweist, erzeugt. Mikrostrukturanalysen, so wie TEM-EDS-Elementverteilungsbilder, zeigen SiO2 auf der BaTiO3 Nanopartikel-Oberfläche gebildet wird. Der dritte Teil der Arbeit befasst sich mit der Synthese und Charakterisierung von Ag@BaTiO3 Nanopartikel. Die Herstellung erfolgt in zwei Schritten: (1) Herstellung eines Ag Organo-sols, (2) anschließend Einbringen des hergestellten Ag Organosols in ein BaTiO3 “Organosol” Precursor. UV/Vis-Spektroskopie ermöglicht die Untersuchung der Bildung und Aggregation von Ag und Ag@BaTiO3 Nanopartikel. Die spektrale Lage der Plasmonresonanz wird von mehreren Faktoren beeinflusst, z.B. dem umgebenden Medium, auch der BaTiO3 Schichtdicke. Es zeigt sich eine erhebliche Veränderung der spektralen Lage von Ag@BaTiO3 Nanopartikeln mit einer ultradünnen Schale von weniger als 5 nm. Es entsteht ein breites spektrum, wenn sie alles auffallende Licht fast vollständig absorbieren. Die zukünftige Arbeit konzentriert sich auf die angestrebte homogene Einbettung unserer hergestellten Nanopartikeln mit Kern@Schale-Struktur in Polymermatrizes zur Anwendung und Entwicklung zukünftiger organischer Solarzellen.In recent years, the development of core@shell structured nanoparticles has received great research attention because of the combination of different properties in one particle based on different compositions of the core and the shell. The core often shows the relevant property (e.g. semiconductors, metals, magnetic oxides, encapsulated molecules), while the shell can not only avoid the aggregation and oxidation of the particles, but also can alter the dispersion characteristics of the particles by surface modification, so that the possibility is given to blend the core@shell particles into the polymer matrices. BaTiO3 is one of well-known dielectric materials that is also used in a variety of semiconductor devices owing to its high and frequency-independent permittivity with low dielectric loss. In this work, we aspire to develop a versatile, cost efficient, environmental friendly, and easy-to-scale up method for synthesizing BaTiO3 nanoparticles and BaTiO3-based different types of core@shell nanoparticles: BaTiO3@SiO2 and Ag@BaTiO3 with the core@shell structure. The “Organosol” sythesis is proposed to produce hydrophobic BaTiO3 nanoparticles at temperatures as low as room temperature. The advantages of this method are a high yield, a simple but precise control of the size of the particles, low process temperature, short reaction time, as well as low cost of reagents. BaTiO3@SiO2 compsite nanoparticles with tunable thickness from 3 nm to 20 nm are successfully prepared by a reverse microemulsion method. Specifically, the formation of BaTiO3@SiO2 is performed by using hydrophobic BaTiO3 nanoparticles as seeds in a Triton X-100/n-hexanol/cyclohexane/water reverse microemulsion (W/O). The shell is formed by hydrolysis and condensation of tetraethyl-orthosilicate (TEOS) on the surface of the BaTiO3 particles. The TEM and EDS elemental mapping images clearly show that the BaTiO3@SiO2 compsite nanoparticles have a core@shell structure. Ag@BaTiO3 composite nanoparticles with tunable optical properties were formed in two steps: (1) the synthesis of a Ag organosol, (2) followed by its incorporation with BaTiO3 “organosol” precursor to prepare Ag@BaTiO3 composite nanoparticles. A controllable nanolayer of BaTiO3 on the surface of Ag was formed at different Ag/Ba molar ratios. The UV-vis results reveal changes in the optical features of the Ag and Ag@BaTiO3 composite nanoparticles corresponding to the medium where the nanoparticles are embedded in and the thickness of the BaTiO3 shell. It was found that the ultrathin BaTiO3 shell with a thickness less than 5 nm in composite significantly alters the optical feature and results in almost complete absorption of light in broad spectrum. The future work will be focused on the preparation of polymer-based nanocomposites homogeneously incorporating our synthesized colloidal core@shell nanoparticles for development of organic photovoltaic devices

Nuevas estrategias para el desarrollo de biosensores ópticos aplicados al análisis de micotoxinas y hongos toxigénicos en alimentos

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Analítica, leída el 15-07-2019Mycotoxins are a diverse group of low molecular weight compounds produced as secondary metabolites by numerous species of filamentous fungi. This assemblage is chemically and toxigenically rather heterogeneous, but generally these toxins are known to cause disease and death in human and other vertebrates even at low concentrations. Mycotoxigenic fungi grow on a wide range of conditions and they can produce mycotoxins into the matrices on which they grow, often food intended for human consumption or animal feed. As a result of the ubiquitous nature of mycotoxigenic fungi, particularly in temperate and tropical regions of the world, mycotoxin contamination is often inevitable, and some calculations have estimated that approximately 25–50% of world crops are contaminated with these toxins. Although the awareness related to the hazards of mycotoxins as food and feed contaminants is growing, there are no absolute measures available for eliminating mycotoxins from agricultural products. While mycotoxin occurrence in the field can be decreased by good agronomic practices and planting resistant varieties, in the end, analytical methods capable of detecting mycotoxins and toxigenic fungi even at low concentration are of key importance for ensuring food safety...Las micotoxinas son metabolitos secundarios tóxicos producidos por algunas cepas de hongos que contaminan alimentos, especialmente cereales y hortalizas. Estos compuestos de bajo peso molecular son químicamente y toxigénicamente heterogéneos; sin embargo, muchas de estas toxinas pueden originar enfermedades, y en ocasiones la muerte, tanto en humanos como en otros vertebrados. Los hongos toxigénicos crecen en muchas condiciones muy diversas, lo que puede dar lugar a la aparición de micotoxinas en los alimentos destinados tanto al consumo humano como al animal. Los hongos toxigénicos están ampliamente distribuidos por todo el mundo, particularmente en las regiones templadas y tropicales, por lo que la contaminación natural por micotoxinas es casi inevitable. De hecho, se estima que aproximadamente el 25–50% de los cultivos mundiales están contaminados por estas toxinas, y la preocupación sobre los peligros asociados a su presencia en alimentos es cada día mayor. Actualmente, no existen alternativas viables para su eliminación en los productos agrícolas; aunque el empleo de buenas prácticas agrícolas o la plantación de variedades resistentes a los hongos, pueden ayudar a mejorar este problema. En cualquier caso, se requieren métodos analíticos sensibles y selectivos para la detección de micotoxinas y hongos toxigénicos, a bajas concentraciones, afin de garantizar la seguridad alimentaria...Depto. de Química AnalíticaFac. de Ciencias QuímicasTRUEunpu