Vincent Raimbault

Aquatic ecosystems need accurate observation to understand its trajectory in a context of increasing anthropogenic pressure and climate change. These environments are however undersampled in many areas (Brewin et al. 2017, Kirchner et al. 2004): acquiring essential variables at relevant spatial and temporal resolution is often not compatible with traditional methods of sample collection followed by laboratory analysis, but field-deployable or in-situ systems are either too expensive, too complicated to be used by non-trained users or even non-existent. In an effort to propose an alternative in-situ measurement system for biogeochemical and physicochemical measurement in marine and continental waters, we developed a multiparameter probe that measures 7 parameters for a very modest bill-of-materials cost (around 300 € for a single prototype). The performance of this probe is sufficient for most water bodies, both in terms of range and sensitivity, and its replication is facilitated by the use of rapid-prototyping methods. The Openprobe multiparameter (Fig. 1) is able to measure conductivity, temperature, pressure (depth or water level above), dissolved oxygen, turbidity, chlorophyll a, photosynthetically active radiation (PAR) as well as water color. These parameters were chosen based on a compromise between their relevance and our capability to measure them at a scientifically appropriate standard using low-cost components, an approach which resonates with the definition of the Standard Observations in eLTER (Zacharias et al. 2021). The electronic architecture is based around an Adafruit Feather M0 microcontroller board, an Adafruit Adalogger microSD-card logger with a Real-Time-Clock, and two custom Printed Circuit Boards (PCBs) that hosts the different sensors. Housing of the probe uses a Blue Robotics 2" diameter enclosure tubes. The sensor's PCBs are integrated in end-caps fabricated by stereolithography (SLA), using a desktop Formlabs Form 3 SLA printer with Black V4 resin. Compared to conventional fused-deposition modelling 3D printing (FDM), SLA is an isotropic printing technique which delivers fully dense and watertight parts. The higher resolution of SLA also allows to create o-ring grooves with appropriate tolerance, and has shown to be a valid fabrication technique even for the challenging pressures encountered in deep-sea science (Karp et al. 2023, Phillips et al. 2019). Atop of that, the 3D printed end-cads ensures auto-alignment of the optical elements (LEDs, photodiodes) and optical filters. The assembly/disassembly can be done manually without any tool, for easy access to the electronics, the battery, or the micro SD card on the field. Polydimethylsiloxane (PDMS), a silicone-based material with good transparency in the VIS-IR, is used within the end-caps to create optical ports, and also acts similarly to a potting material to ensure watertightness. The first PCB is integrated at the top of the probe, and contains the CTD (Conductivity, Depth, Temperature) as well as the PAR sensor. The conductivity sensor is based around a two-electrode cell on a ceramic substrate connected to an impedance analyzer integrated circuit (IC). Intercomparison with a Decagon CTD-10 and an Atlas Scientific EZO sensor showed that our sensor offered a better sensitivity, together with a smaller cost and a lower power consumption. Pressure and temperature sensors are based around the same IC used by Blue Robotics pressure and temperature sensors, and as such as been validated in many conditions (Poulsen et al. 2022). We worked on their integration on a custom PCB, with special care taken in minimizing the thermal inertia around the temperature sensor to reduce its response time when performing profiling analysis. The PAR sensor completes this part of the probe. It is based around the AMS AS7341, modified with a diffuser cut precisely with the xurography technique (Bartholomeusz et al. 2005), and intercompares with a+/- 5% confidence interval versus an Apogee SQ-512-SS sensor (Fig. 2), a value commonly exceeded when comparing different commercial sensors (Long et al. 2012). The second PCB, located at the opposite end of the probe, contains a chlorophyll a fluorometer, an oxygen optode, and a turbidity sensor. The chlorophyll a fluorometer uses synchronous detection: this approach allows efficient ambient light rejection, and captures the weak fluorescence signals observed due to the small fluorescence yield of in-vivo chl.a (Morrison 2003). The oxygen otpode uses PreSens Pst3 oxygen sensor spots, paired with a custom optoelectronic readout architecture. A DDS (Direct Digital Synthesizer) generates a sine wave to excite the Pst3 luminophore, and an I/Q demodulator measures the phase shift between excitation and the emitted fluorescence. The fluorescence signal is quenched in the presence of oxygen, which translates to a decrease of the fluorescence decay and in-fine by a phase shift . This is similar to the operating principle of Aanderaa optodes, commonly found in the Biogeochemical Argo floats. Our optode is intercompared with a benchtop PreSens Fibox 4 system and shown good accuracy (Fig. 3). Finally, the turbidity sensor implements 90° nephelometry as well as 180° backscattering measurements to cover a broad range of turbidity. Its architecture is based around an Analog Devices ADPD1080, an IC usually found in smartwatches for the measurement of photoplethysmography (PPG). The Openprobe multiparameter probe could be a very valuable tool in order to increase spatial and temporal resolution in aquatic ecosystem monitoring. Through the use of advanced, yet affordable electronic components initially developed for the Internet Of Things market, we created a frugal tool without compromising on accuracy.

The move toward sophisticated sensor networks in ecological applications requires a substantial amount of energy. Energy storage solutions based simply on batteries are often not sufficient to cover the energy needs, so a standalone power supply using solar energy harvesting is generally required. However, designing an appropriate solar power supply without oversizing and avoiding output power disruption all year long is not a trivial task. This paper provides a set of guidelines as well as useful information and advice for environmental researchers and other non-experts to select the right components when designing their own autonomous solar power supply for a range between 10 mW and 10 W. The design steps are compiled into a comprehensive document, free of irrelevant information yet still presenting a general overview of the solar power supply design process, in order to make this task more accessible and understandable for non-experts. The methodology for simple initial dimensioning was carried out and applied to a real-life use case by using the estimated or measured daily consumption combined with free meteorological data of the deployment site provided by various websites. Next, an hourly simulation completed the first sizing. A year of experimental results validated the methodology.

Novel protocol for integration of object inside stereolithography-based chips and proof-of-concepts: bacteria imaging, blue energy and in-flow cell capture.

Fluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating impinging jets have been shown to improve heat transfer compared to steady jets. In this study, special focus is given to these characteristics as a preparation for a subsequent thermal study that will evaluate the performance of these pulsed jets against steady jets. The functioning of the device in response to different operating and design parameters is first considered. It was shown that a transition between different operating modes is possible, depending on both the inlet mass flowrate and the width of the feedback channel of the device. This was followed by a study of the velocity fields of the pulsed jets produced by the device. More specifically, attention is given to the developing characteristics and flow structures of the pulsating free jets of air which are then compared to equivalent steady jets. Finally, by taking advantage of the periodic aspect of the flow, the phase-averaged velocity field was reconstructed. Vortex dipoles were detected, tracked and their convection velocity computed from the same data and compared to a theoretical value from the literature. A proper orthogonal decomposition (POD) of the synchronized raw data was then performed to further highlight the presence of these vortex structures and other flow instabilities.

Turbidity is a commonly used indicator of water quality in continental and marine waters and is mostly caused by suspended and colloidal particles such as organic and inorganic particles. Many methods are available for the measurement of turbidity, ranging from the Secchi disk to infrared light-based benchtop or in situ turbidimeters as well as acoustic methods. The operational methodologies of the large majority of turbidity instruments involve the physics of light scattering and absorption by suspended particles when light is passed through a sample. As such, in the case of in situ monitoring in water bodies, the measurement of turbidity is highly influenced by external light and biofouling. Our motivation for this project is to propose an open-source, low-cost in situ turbidity sensor with a suitable sensitivity and operating range to operate in low-to-medium-turbidity natural waters. This prototype device combines two angular photodetectors and two infrared light sources with different positions, resulting in two different types of light detection, namely nephelometric (i.e., scattering) and attenuation light, according to the ISO 7027 method. The mechanical design involves 3D-printed parts by stereolithography, which are compatible with commercially available waterproof enclosures, thus ensuring easy integration for future users. An effort was made to rely on mostly off-the-shelf electronic components to encourage replication of the system, with the use of a highly integrated photometric front-end commonly used in portable photoplethysmography systems. The sensor was tested in laboratory conditions against a commercial benchtop turbidimeter with Formazin standards. The monitoring results were analyzed, obtaining a linear trendline from 0 to 50 Nephelometric Turbidity Unit (NTU) and an accuracy of +/−0.4 NTU in the 0 to 10 NTU range with a response time of less than 100 ms.

This paper presents an experimental platform allowing in situ measurement in an aqueous medium using an acoustic Love wave sensor. The aim of this platform, which includes the sensor, a test cell for electrical connections, a microfluidic chip, and a readout electronic circuit, is to realize a first estimation of water quality without transportation of water samples from the field to the laboratory as a medium-term objective. In the first step, to validate the ability of such a platform to operate in the field and in Amazonian water, an isolated and difficult-to-access location, namely, the floodplain Logo Do Curuaï in the Brazilian Amazon, was chosen. The ability of such a platform to be transported, installed on site, and used is discussed in terms of user friendliness and versatility. The response of the Love wave sensor to in situ water samples is estimated according to the physical parameters of Amazonian water. Finally, the very good quality of the acoustic response is established, potential further improvements are discussed, and the paper is concluded.

The different biosensing strategies with microring resonators consist in quantifying the resonance shift under the presence of biological or chemical agents. These strategies lead to the measurement of a wavelength shift or an output power variation correlated to the analyte concentration. The design guidelines to enhance the sensitivity have been already studied and reviewed over the past decade. However, very few studies have been published addressing ring resonator performance used as absorption micro-spectrometer, which can be explored with colorimetric chemistry and microfluidic handling. In this work, a sensitivity model for the operation of absorptive based ring resonators is presented. Such a model is proposed to provide a guideline to optimize ring resonator design and parameters. Finally, 2.5 FDTD simulations of different ring geometries are presented and compared to the results obtained with the model.

Cancer is a leading cause of death worldwide and actual analytical techniques are restrictive in detecting it. Thus, there is still a challenge, as well as a need, for the development of quantitative non-invasive tools for the diagnosis of cancers and the follow-up care of patients. We introduce first the overall interest of electronic nose or tongue for such application of microsensors arrays with data processing in complex media, either gas (e.g., Volatile Organic Compounds or VOCs as biomarkers in breath) or liquid (e.g., modified nucleosides as urinary biomarkers). Then this is illustrated with a versatile acoustic wave transducer, functionalized with molecularly-imprinted polymers (MIP) synthesized for adenosine-5′-monophosphate (AMP) as a model for nucleosides. The device including the thin film coating is described, then static measurements with scanning electron microscopy (SEM) and electrical characterization after each step of the sensitive MIP process (deposit, removal of AMP template, capture of AMP target) demonstrate the thin film functionality. Dynamic measurements with a microfluidic setup and four targets are presented afterwards. They show a sensitivity of 5 Hz·ppm⁻¹ of the non-optimized microsensor for AMP detection, with a specificity of three times compared to PMPA, and almost nil sensitivity to 3′AMP and CMP, in accordance with previously published results on bulk MIP.