Multiparameter Water Quality Monitoring System for Continuous Monitoring of Fresh Waters

This paper presents an economical multiparameter water quality monitoring system for continuous monitoring of fresh waters. It is based on a sensor node that integrates turbidity, temperature, conductivity sensors, a miniature eighteen-channel spectrophotometer, and a sensor for the detection of thermotolerant coliforms, which is a major novelty of the system. Due to the influence of water impurities on the measurement of thermotolerant coliforms, a heuristic method has been developed to mitigate this effect. Moreover, the sensor is low-power and with an integrated LoRaWAN module, it comprises a system that is wireless sensor network (WSN) ready and can send data to a dedicated server. In addition, the system is submersible, capable of long-term field operation, and significantly cheaper in comparison to existing solutions. The purpose of the system is to give early warning of incidental pollution situations, thus enabling authorities to fast respond by taking a water sample for laboratory analysis for confirmation, analyze the source of contamination, and take action regarding further prevention of such occasions

Nanomembrane-Enabled MEMS Sensors: Case of Plasmonic Devices for Chemical and Biological Sensing

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Functionalization of Artificial Freestanding Composite Nanomembranes

Artificial nanomembranes may be defined as synthetic freestanding structures with a thickness below 100 nm and a very large aspect ratio, of at least a few orders of magnitude. Being quasi-2D, they exhibit a host of unusual properties useful for various applications in energy harvesting, sensing, optics, plasmonics, biomedicine, etc. We review the main approaches to nanomembrane functionalization through nanocompositing, which ensures performance far superior to that of simple nanomembranes. These approaches include lamination (stacking of nanometer-thin strata of different materials), introduction of nanoparticle fillers into the nanomembrane scaffold, nanomembrane surface sculpting and modification through patterning (including formation of nanohole arrays and introduction of ion channels similar in function to those in biological nanomembranes). We also present some of our original results related to functionalization of metal matrix composite nanomembranes

Adsorption-desorption noise in plasmonic chemical/biological sensors for multiple analyte environment

We investigated intrinsic noise in plasmonic sensors caused by adsorption and desorption of gaseous analytes on the sensor surface. We analyzed a general situation when there is a larger number of different analyte species. We applied our model to calculate various analyte mixtures, including some environmental pollutants, toxic and dangerous substances. The spectral density of mean square refractive index fluctuations follows a dependence similar to that of generation-recombination noise in photodetectors, flat at lower frequencies and sharply decreasing at higher. Some of the calculated noise levels are well within the detection range of conventional surface plasmon resonance sensors. An AD noise peak is observed in temperature dependence of mean square refractive index fluctuations, thus sensor operating temperature may be optimized to obtain larger signal to noise ratio. A significant property of AD noise is its rise with the decreasing plasmon sensor area, which means that it will be even more pronounced in modern nanoplasmonic devices. Our consideration is valid both for conventional surface plasmon resonance devices and for general nanoplasmonic devices

Performance limits to the operation of nanoplasmonic chemical sensors: noise-equivalent refractive index and detectivity

We considered figures of merit for chemical and biological sensors based on plasmonic structures and utilizing adsorption/desorption mechanism. The operation of these devices in general is limited by noise determining the minimum detectable refractive-index change. We dedicated our work to the intrinsic noise mechanisms connected with the plasmonic process itself. In contrast, most of the available literature is almost exclusively dedicated to the external noise sources (illumination source and photodetector). Reviewing the refractive-index fluctuations caused by thermal, adsorption-desorption and 1/f noise, we observed a striking analogy between the qualitative behavior of noise in (nano) plasmonic devices and that in semiconductor infrared detectors. The power spectral densities for noise in both of these have an almost identical shape; the adsorption-desorption noise corresponds to generation-recombination processes in detectors, while the other two mechanisms exist in the both types of the devices. Thus the large and mature existing apparatus for infrared detector noise analysis may be applied to the plasmonic sensors. Based on the observed analogy, we formulated the noise-equivalent refractive-index and the specific detectivity as the figures of merit to analyze the ultimate performance of plasmon sensors. The approach is valid for conventional surface plasmon resonance sensors, but also for nanoplasmonic and metamaterial-based devices

A consideration of optical noise figures of adsorption-based nanophotonic sensors

We consider some intrinsic noise mechanisms appearing in nanophotonic sensors based on plasmonic structures and surface plasmon-polaritons. We analyze the photonic Johnson-Nyquist fluctuations and the adsorption and desorption (AD) of analyte molecules at the sensing interface, as reflected through the refractive index and electromagnetic field changes. In some situations AD noise is especially large and may significantly influence the performance of nanoplasmonic sensors

Adsorption-Desorption Noise in Plasmonic Chemical/Biological Sensors in Multiple Analyte Environment

We analyzed the intrinsic noise of plasmonic sensors caused by the adsorption-desorption of gaseous analytes on the sensor surface. We analyzed a general situation when there is a larger number of different species in the environment. We developed our model and applied it to calculate various analyte mixtures, including some environmental pollutants, toxic and dangerous substances. The spectral density of mean square refractive index fluctuations follows a dependence similar to that of generation-recombination noise in photodetectors, flat at lower frequencies and sharply decreasing at higher. Some of the calculated noise levels are well within the detection range of conventional surface plasmon resonance sensors. One of the obvious conclusions is that AD noise may be an important limiting factor in monitoring process kinetics by nanoplasmonic sensors. An AD noise peak is observed in temperature dependence of mean square refractive index fluctuations, thus sensor operating temperature may be optimized to obtain larger signal to noise ratio. A significant property of AD noise is its increase with the plasmon sensor area decrease, which means that it will be even more pronounced in modern nanoplasmonic devices. Our consideration is valid both for conventional surface plasmon resonance devices and for general nanoplasmonic devices. This research could be of importance in diverse areas such as environmental sensing, homeland security, forensic applications, life sciences, etc

Performance limits to the operation of nanoplasmonic chemical sensors: noise-equivalent refractive index and detectivity

We considered figures of merit for chemical and biological sensors based on plasmonic structures and utilizing adsorption/desorption mechanism. The operation of these devices in general is limited by noise determining the minimum detectable refractive-index change. We dedicated our work to the intrinsic noise mechanisms connected with the plasmonic process itself. In contrast, most of the available literature is almost exclusively dedicated to the external noise sources (illumination source and photodetector). Reviewing the refractive-index fluctuations caused by thermal, adsorption-desorption and 1/f noise, we observed a striking analogy between the qualitative behavior of noise in (nano) plasmonic devices and that in semiconductor infrared detectors. The power spectral densities for noise in both of these have an almost identical shape; the adsorption-desorption noise corresponds to generation-recombination processes in detectors, while the other two mechanisms exist in the both types of the devices. Thus the large and mature existing apparatus for infrared detector noise analysis may be applied to the plasmonic sensors. Based on the observed analogy, we formulated the noise-equivalent refractive-index and the specific detectivity as the figures of merit to analyze the ultimate performance of plasmon sensors. The approach is valid for conventional surface plasmon resonance sensors, but also for nanoplasmonic and metamaterial-based devices