Desing of plasmomic nano-structures for SERS ultrasensitive spectroscopy: comparison between self-assembly and bioconjugation

En este trabajo, se presenta una estrategia sencilla para generar nanoestructuras plasmónicas por autoensamblado y bioconjugación de nanoesferas (NSs) de Au, para ser aplicadas como plataformas de espectroscopia Raman incrementada por superficie (SERS). Mediante el reconocimiento molecular altamente específico entre biotina y estreptavidina (STV) se generan dímeros con una distancia interpartícula de alrededor de 8 nm, mientras que en ausencia de STV la agregación no direccionada de la superficie de las NSs genera aglomerados compactos con distancia interpartícula de 5 nm debido a los puente hidrógeno que se establecen entre moléculas de biotina funcionalizadas. Ambos sustratos permiten detectar concentraciones de biotina picomolares (1x10-12 M). Sin embargo, los factores de incremento analíticos (AEF) son un orden de magnitud mayor en el caso de los dímeros (107) que en el caso de los aglomerados compactos (106). Utilizando los grandes incrementos de campo eléctrico se utilizaron estos sustratos para detectar un analito externo, Rodamina 6G (RH6G), y se determino que los dímeros generan incrementos de un orden de magnitud mayor (105) que el uso de aglomerados compactos (104). La dependencia de la longitud de onda y las diferencias en los AEF para los sustratos diméricos y los aglomerados compactos de NSs de Au se correlacionaron con simulaciones electrodinámicas rigurosas. Los dímeros generados son en sí un nuevo tipo de un sustrato SERS que puede ser autocalibrado donde selectivamente se puede “atrapar” moléculas biotiniladas por STV y situándolas en la zona de máximo incremento de campo electromagnético. Por otra parte, el estudio de las propiedades ópticas de los aglomerados compactos permitió el desarrollo de un procedimiento general para hacer una predicción cuantitativa de la respuesta SERS de este tipo de nanoestructuras.In this work, we report a simple strategy to obtain ultrasensitive SERS nanostructures by self-assembly and bioconjugation of Au nanospheres (NSs). Homodimer aggregates with an interparticle gap of around 8 nm are generated in aqueous dispersions by the highly specific molecular recognition of biotinylated Au NSs to streptavidin (STV), while compact-tight Au NS aggregates with a gap of 5 nm are formed in the absence of STV due to hydrogen bonding among biotinylated NSs. Both types of aggregates depict the capability to detect biotin concentrations lower than 1x10-12 M. Nevertheless, it was found that dimers are better SERS substrates as they generate enhancements one order of magnitude bigger than the compact-tight aggregates (107 and 106, respectively). Quite interesting, the AEF for an external analyte, Rhodamine 6G (RH6G), using the dimer aggregates is also 1 order of magnitude greater (105) than using compact-tight aggregates (around 104). The dependence on the wavelength and the differences of the AEF for Au random aggregates and dimers are rationalized with rigorous electrodynamic simulations. The dimers obtained afford a new type of an in situ self-calibrated and reliable SERS substrate where biotinylated molecules can selectively be “trapped” by STV and located in the nanogap enhanced plasmonic field. On the other hand, the study of the optical properties of compact-tight aggregates allow to develop a general procedure to make a quantitative prediction of the SERS response tight-compact clusters that is demonstrated to be quite general independent of the metal (Ag or Au) and size of the individual NSs of the cluster.Fil: Fraire, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Rift Valley Fever: An Economic Assessment of Agricultural and Human Vulnerability

This research focused on the assessment of the U.S. agricultural sector and human vulnerability to a Rift Valley Fever (RVF) outbreak and the implications of a select set of alternative disease control strategies. Livestock impact assessment is done by using an integrated epidemic/economic model to examine the extent of RVF spread in the Southeast Texas livestock population and its consequences plus the outcome of implementing two different control strategies: emergency vaccination and larvicide vector control separately plus when they are used simultaneously. Human impact assessment utilized an inferential procedure, which comprises of a cost of illness calculation to assess the dollar cost of human illnesses and deaths, as well as a Disability Adjusted Life Year calculation to give an estimate of the burden of disease on public health as a whole. Results indicate substantial potential losses to the U.S., where combined livestock and human national costs ranged from $121 million to$2.3 billion.Rift Valley Fever, Outbreak, Welfare, Vaccination, Larvicide., Environmental Economics and Policy, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Health Economics and Policy,

Distributed On-Demand Routing for LEO Mega-Constellations: A Starlink Case Study

The design and launch of large-scale satellite networks create an imminent demand for efficient and delay-minimising routing methods. With the rising number of satellites in such constellations, pre-computing all shortest routes between all satellites and for all times becomes more and more infeasible due to space and time limitations. Even though distributed on-demand routing methods were developed for specific LEO satellite network configurations, they are not suited for increasingly popular mega-constellations based on Walker Delta formations. The contributions of this paper are twofold. First, we introduce a formal model that mathematically captures the time-evolving locations of satellites in a Walker Delta constellation and use it to establish a formula to compute the minimum number of ISL hops between two given satellites. In the second part, we present an on-demand hop-count-based routing algorithm that approximates the optimal path while achieving superior performance compared to classical shortest-path algorithms like Dijkstra.Comment: This is an extended version of a paper published in ASMS/SPSC 2022 containing proofs and further detail

Experimental Evaluation of On-Board Contact-Graph Routing Solutions for Future Nano-Satellite Constellations

Hardware processing performance and storage capability for nanosatellites have increased notably in recent years. Unfortunately, this progress is not observed at the same pace in transmission data rate, mostly limited by available power in reduced and constrained platforms. Thus, space-to-ground data transfer becomes the operations bottleneck of most modern space applications. As channel rates are approaching the Shannon limit, alternative solutions to manage the data transmission are on the spot. Among these, networked nano-satellite constellations can cooperatively offload data to neighboring nodes via frequent inter-satellite links (ISL) opportunities in order to augment the overall volume and reduce the end-to-end data delivery delay. Nevertheless, the computation of efficient multi-hop routes needs to consider not only present satellite and ground segments as nodes, but a non-trivial time dynamic evolution of the system dictated by orbital dynamics. Moreover, the process should properly model and rely on considerable amount of available information from node’s configuration and network status obtained from recent telemetry. Also, in most practical cases, the forwarding decision shall happen in orbit, where satellites can timely react to local or in-transit traffic demands. In this context, it is appealing to investigate on the applicability of adequate algorithmic routing approaches running on state-of-the-art nanosatellite on-board computers. In this work, we present the first implementation of Contact Graph Routing (CGR) algorithm developed by the Jet Propulsion Laboratory (JPL, NASA) for a nanosatellite on-board computer. We describe CGR, including a Dijkstra adaptation operating at its core as well as protocol aspects depicted in CCSDS Schedule-Aware Bundle Routing (SABR) recommended standard. Based on JPL’s Interplanetary Overlay Network (ION) software stack, we build a strong baseline to develop the first CGR implementation for a nano-satellites. We make our code available to the public and adapt it to the GomSpace toolchain in order to compile it for the NanoMind A712C on-board flight hardware based on a 32-bit ARM7 RISC CPU processor. Next, we evaluate its performance in terms of CPU execution time (Tick counts) and memory resources for increasingly complex satellite networks. Obtained metrics serve as compelling evidence of the polynomial scalability of the approach, matching the predicted theoretical behavior. Furthermore, we are able to determine that the evaluated hardware and implementation can cope with satellite networks of more than 120 nodes and 1200 contact opportunities

Empowering the Tracking Performance of LEO PNT by Means of Meta-Signals

Global Navigation Satellite Systems (GNSSs) are by far the most widespread technology for Position Navigation and Timing (PNT). They have been traditionally deployed exploiting Medium Earth Orbit (MEO) or Geostationary Earth Orbit (GEO) satellite constellations. To meet future demands and overcome MEO and GEO limitations, GNSSs based on Low Earth Orbit (LEO) constellations have been investigated as a radical system change. Although characterized by a higher Doppler effect, a PNT service supplied by means of LEO satellites can provide received signals that are about 30 dB stronger. Moreover, existing LEO constellations and the forthcoming mega-constellations, which are designed for broadband internet coverage, can be exploited to provide a piggybacked PNT service. With this cost-effective solution, a secondary PNT service might be subject to an economical use of resources, which may result in substantial bandwidth limitations. At the same time, the introduction of meta-signals in the GNSS literature has brought a new receiver signal processing strategy, particularly effective in terms of available bandwidth exploitation. It allows to increase the positioning accuracy exploiting a wideband processing approach, which might be challenging under severe Doppler conditions. A narrowband implementation of the meta-signal concept, namely Virtual Wideband (VWB) can tolerate harsh Doppler conditions while also reducing the processed bandwidth. It is thus more effective when addressing a secondary PNT service, where a limited frequency occupation might be an essential requirement. The aim of this work is to show the applicability of a VWB receiver architecture on signals provided by a piggybacked PNT service, hosted on a broadband LEO constellation. We demonstrate the capability of this implementation to bear high Doppler conditions while empowering the potential of LEO PNT

Space-Terrestrial Integrated Internet of Things: Challenges and Opportunities

Large geographical regions of our planet remain uncovered by terrestrial network connections. Sparse and dense constellations of near-Earth orbit satellites can bridge this gap by providing Internet of Things (IoT) connectivity on a world-wide scale in a flexible and cost-effective manner. This paper presents a novel space-terrestrial integrated IoT network architecture spanning direct- and indirect-to-satellite access from IoT assets on the surface. Framed on the identified requirements, we analyze NB-IoT and LoRa/LoRaWAN features to put these technologies forward as appealing candidates for future satellite IoT deployments. Finally, we list and discuss the key open research challenges to be addressed in order to achieve a successful space-terrestrial IoT integration