Multi-element fingerprinting of waters to evaluate connectivity among depressional wetlands

Establishing the connectivity among depressional wetlands is important for their proper management, conservation and restoration. In this study, the concentrations of 38 elements in surface water and porewater of depressional wetlands were investigated to determine chemical and hydrological connectivity of three hydrological types: recharge, flow-through, and discharge, in the Prairie Pothole Region of North America. Most element concentrations of porewater varied significantly by wetland hydrologic type (p \u3c 0.05), and increased along a recharge to discharge hydrologic gradient. Significant spatial variation of element concentrations in surface water was observed in discharge wetlands. Generally, higher element concentrations occurred in natural wetlands compared to wetlands with known disturbances (previous drainage and grazing). Electrical conductivity explained 42.3% and 30.5% of the variation of all element concentrations in porewater and surface water. Non-metric multidimensional scaling analysis showed that the similarity decreased from recharge to flowthrough to discharge wetland in each sampling site. Cluster analysis confirmed that element compositions in porewater of interconnected wetlands were more similar to each other than to those of wetlands located farther away. Porewater and surface water in a restored wetland showed similar multi-element characteristics to natural wetlands. In contrast, depressional wetlands connected by seeps along a deactivated drain-tile path and a grazed wetland showed distinctly different multi-element characteristics compared to other wetlands sampled. Our findings confirm that the multi-element fingerprinting method can be useful for assessing hydro-chemical connectivity across the landscape, and indicate that element concentrations are not only affected by land use, but also by hydrological characteristics

Towards highly sensitive and multiplexed nanoplasmonic biosensors

En esta tesis se ha abordado la caracterización de sensores LSPR refractométricos desde diferentes puntos de vista. En primer lugar, se presenta un análisis teórico y experimental de nanocápsulas cilíndricas (nanorods) de oro, comparando su capacidad sensora con sensores SPP convencionales. El estudio ha conducido al hallagzo de una región espectral con rendimiento sensor optimizado, y a la que se puede acceder llevando a cabo un diseño preciso y detallado de las nanoestructuras. Por otro lado, el análisis desvela un rendimiento superior de los LSPR comparado con los convencionales SPP, con atisbos de mejoras adicionales si se superan ciertos inconvenientes inherentes a estas plataformas biosensoras. De cara a identificar y suprimir estos inconvenientes, se han empleado matrices de nanodiscos de oro como nanoestructura modelo. En primer lugar, se han analizado las influencias negativas que se derivan de las finas capas metálicas de adhesión y de los altos índices de refracción del sustrato que soporta a los nanodiscos. Se ha demostrado que la elección adecuada del material y del espesor de estas capas de adhesión mejora significativamente la relación señal-ruido. Además, mediante la colocación de los nanodiscos sobre nanopilares dieléctricos, alejándolos del sustrato, se han obtenido incrementos significativos de sensibilidad, proporcionando así una estrategia que se puede extender fácilmente a otros sistemas plasmónicos. Se ha demostrado, por otro lado, que estas matrices de nanodiscos soportan un modo guiado, que, además de otras aplicaciones nanofotónicas interesantes, provoca un cambio en la radiación en campo lejano de estas estructuras que causa mejoras en sensibilidad y en la relación señal-ruido. Por último, se han combinado todos los conocimientos adqueridos y resultados obtenidos para esbozar la creación de un biosensor LSPR con funciones de multiplexado y con microfluídica integrada.In this dissertation, different aspects of refractometric nanoplasmonic sensors are discussed. First, a theoretical and experimental sensing performance assessment is made of Localized Surface Plasmon Resonance (LSPR) sensors based on single gold nanorods, by directly comparing them to conventional thin film Surface Plasmon Polariton (SPP) sensors. Besides the discovery of a material-specific optimized spectral sensing region that can be accessed via precise nanoparticle engineering, this work reveals a better biosensing performance for LSPR sensors that can be further improved if certain - inherent - drawbacks are overcome. For this, arrays of gold nanodisks are used to identify and suppress such drawbacks. First, negative influences that stem from thin metal adhesion layers and the high refractive indices of the supporting substrate are analyzed. It is shown that the right choice of material and thickness for these adhesion layers, significantly improves the signal-to-noise ratio (S/N)-values of these biosensors. Besides, by placing the nanodisks on nanopillars, thereby distancing them from the substrate, much higher sensitivities can be obtained, providing a strategy that can be easily expanded to other plasmonic systems. Next, it is demonstrated that the employed arrays of gold nanodisks support a guided mode that besides other interesting nanophotonics applications, alters the far-field radiation of these nanoplasmonic structures in such a manner, that both enhanced sensitivities and improved S/N-ratios are obtained. Finally, combining all gathered knowledge, a road map is sketched towards the creation of a LSPR sensor with multiplexing capabilities and integrated microfluidics

Trends and challenges of refractometric nanoplasmonic biosensors : a review

Motivated by potential benefits such as sensor miniaturization, multiplexing opportunities and higher sensitivities, refractometric nanoplasmonic biosensing has profiled itself in a short time span as an interesting alternative to conventional Surface Plasmon Resonance (SPR) biosensors. This latter conventional sensing concept has been subjected during the last decades to strong commercialization, thereby strongly leaning on well-developed thin-film surface chemistry protocols. Not surprisingly, the examples found in literature based on this sensing concept are generally characterized by extensive analytical studies of relevant clinical and diagnostic problems. In contrast, the more novel Localized Surface Plasmon Resonance (LSPR) alternative finds itself in a much earlier, and especially, more fundamental stage of development. Driven by new fabrication methodologies to create nanostructured substrates, published work typically focuses on the novelty of the presented material, its optical properties and its use - generally limited to a proof-of-concept - as a label-free biosensing scheme. Given the different stages of development both SPR and LSPR sensors find themselves in, it becomes apparent that providing a comparative analysis of both concepts is not a trivial task. Nevertheless, in this review we make an effort to provide an overview that illustrates the progress booked in both fields during the last five years. First, we discuss the most relevant advances in SPR biosensing, including interesting analytical applications, together with different strategies that assure improvements in performance, throughput and/or integration. Subsequently, the remaining part of this work focuses on the use of nanoplasmonic sensors for real label-free biosensing applications. First, we discuss the motivation that serves as a driving force behind this research topic, together with a brief summary that comprises the main fabrication methodologies used in this field. Next, the sensing performance of LSPR sensors is examined by analyzing different parameters that can be invoked in order to quantitatively assess their overall sensing performance. Two aspects are highlighted that turn out to be especially important when trying to maximize their sensing performance, being (1) the targeted functionalization of the electromagnetic hotspots of the nanostructures, and (2) overcoming inherent negative influence that stem from the presence of a high refractive index substrate that supports the nanostructures. Next, although few in numbers, an overview is given of the most exhaustive and diagnostically relevant LSPR sensing assays that have been recently reported in literature, followed by examples that exploit inherent LSPR characteristics in order to create highly integrated and high-throughput optical biosensors. Finally, we discuss a series of considerations that, in our opinion, should be addressed in order to bring the realization of a stand-alone LSPR biosensor with competitive levels of sensitivity, robustness and integration (when compared to a conventional SPR sensor) much closer to reality

Metamirrors Based on Arrays of Silicon Nanowires with Height Gradients

Arrays of silicon nanowires with height gradients fabricated using metal-assisted chemical etching act as tunable metamirrors enabling light focusing the reflected light in arbitrary shapes. Metamirrors with non-cylindrical nanowires can simultaneously focus the reflected light and induce strong polarization conversion effect

Molecular inversion probe-based SPR biosensing for specific, label-free and real-time detection of regional DNA methylation

DNA methylation has the potential to be a clinically important biomarker in cancer. This communication reports a real-time and label-free biosensing strategy for DNA methylation detection in the cancer cell line. This has been achieved by using surface plasmon resonance biosensing combined with the highly specific molecular inversion probe based amplification method, which requires only 50 ng of bisulfite treated genomic DNA