Sustainable agricultural production has the aim to maximise the yield and quality of harvests. For that, farmers need to monitor nutrient levels within soils to apply fertilizers accordingly and to prevent land degradation and soil exhaustion. Current methods involve time-consuming sampling and transport to a laboratory; and most farmers do not have the resources to measure frequently at multiple locations, limiting their sustainable production. In order to address this challenge, a paper-based analytical device (PAD) for the multiplexed detection of soil nutrients, i.e. phosphate, nitrate and pH, extracted with a cafetière-based method, is developed in this work. The compact and easy-to-use platform enables an accurate soil analysis in less than 20 min; 3 min for extraction and 15 min for readout. Two detection channels for nitrate and phosphate analysis, and one circular detection area for pH, including the selective reagents to each analyte, are defined within the PAD. Upon contact with the specific nutrients, the platform produces a colorimetric response that is easily readable by naked eye and smartphone camera. The detection reactions were optimized in the range 1 − 22.5 mg L⁻¹, 10 −100 mg L⁻¹ and 5.0 – 8.5 for phosphate, nitrate and pH, respectively, in agreement with the relevant levels in soils. The volume of water, the number of pushes of the plunger, the extraction time and the mass of soil were also optimized for the nutrient extraction method with the cafetière. The optimal workflow was validated with commercial soils and compared with the conventional UV-Vis method and the labels from the soil package, showing excellent agreement. This paper-based platform provides the possibility of a cheap, sensitive and specific monitoring of soil nutrients by minimally trained operators, such as farmers, enabling in-the-field analyses of multiple key soil nutrients in resource-limited settings and therefore addressing the challenge of routine monitoring for sustainable agriculture.

Lab on Printed Circuit Boards (Lab-on-PCB) technology has emerged as a promising platform, offering miniaturization, integration, and cost-effective fabrication for a wide range of sensing applications. This review explores the most common optical detection techniques implemented on printed circuit boards (PCBs), including absorbance, fluorescence, and chemiluminescence, discussing their working principles, advantages, and limitations in the context of PCB-based sensing. Additionally, evanescent wave generation is considered as an alternative optical approach with benefits for specific applications. Elements such as excitation sources, photodetectors, and the distinguishing characteristics of each method are analyzed to provide a comprehensive, but concise, overview of the field. Emphasis is placed on how the PCB platform influences the performance, sensitivity, and feasibility of these detection methods, highlighting relevant design considerations. This work aims to provide a solid foundation for researchers interested in optical sensing within this technology, serving as a reference for future developments and applications in PCB-based optical detection.

The nature and size of biological, pharmaceutical or environmental analytes complicates their extraction and detection outside of laboratories and near the site of interest by the current chromatographic methods because they require the combination of bulky extraction and detection methods. In order to solve this inefficient centralized control, a ground-breaking and miniaturized proof of concept platform is developed in this work. The platform integrates for the very first time an electro-membrane extraction process and an accurate analyte quantification method in the same device, by using electrochemical impedance spectroscopy (EIS) as analytical technique. The microfluidic flow cell, including the microfluidic components, is fabricated in polymeric materials by rapid prototyping techniques. It comprises a four-electrode platinum thin-film chip that enables the control of the microextraction and the full characterization of the process, i.e., extraction efficiency determination, at the same time. The microfluidic system has been simulated by using computational tools, enabling an accurate prediction of the effect of the different experimental conditions in the microextraction efficiency. The platform has been validated in the microextraction of the nonsteroidal anti-inflammatory drug ketoprofen in a range from 0.5 ppm to 6 ppm. The predicted microextraction efficiency values obtained by EIS were compared with those calculated from the high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD), showing an excellent agreement. This validates the high potential of this integrated and miniaturized platform for the simultaneous extraction by electro-membrane and also the analysis within the platform, solving one of the of most important limitations of current systems.

Dissolved inorganic carbon (DIC) levels in freshwaters play a key role in the equilibrium of the carbon cycle between the atmosphere, water and living beings. Standard classical methods for DIC determination generally involve bulky and expensive equipment used in centralized laboratories, resulting in time-consuming processes that do not allow for adequate monitoring in the field. In order to address this challenge, we have developed a distance-based paper analytical device (PAD) for on-site determination of DIC in water. The portable, cost-effective and easy-to-use device was based on the miniaturization and integration of a classical acid-base colorimetric titration on a paper channel, enabling an accurate determination of DIC in less than 20 min. The length of the blue colored line in the detection channel after being filled with the sample was related to the DIC concentration in the sample. The reagent solution used to modify the titration channel was optimized so that DIC concentrations in the range 50–1000 mg L⁻¹ could be measured. The long-term stability of the paper-based device was also evaluated, demonstrating a working stability for more than 70 days after their fabrication, an important characteristic for in-the-field analysis. Finally, the PAD was validated with different water samples, i.e. tap water, commercial bottled drinking water and water samples from a mine, with excellent agreement between the results obtained from the PAD and the standard method. This demonstrates the high potential of the proposed paper analytical device to quantify DIC in situ by minimally-trained personnel without the need for peripheral equipment, which represents an important advance compared to the current limited analysis systems.

Cardiovascular diseases cause a high number of deaths nowadays. To improve these statistics, new strategies to better understand the electrical and mechanical abnormalities underlying them are urgently required. This study focuses on the development of a sensor to measure tissue stretch in excised tissues, enabling improved knowledge of biomechanical properties and allowing greater control in real time. A system made of biocompatible materials is described, which is based on two cantilevered platforms that integrate an optical fiber inside them to quantify the amount of stretch the tissues are exposed to with a precision of mu m. The operating principle of the sensor is based on the variation of the optical path with the movement of the platforms onto which the samples are fixed. The conducted tests highlight that this system, based on a simple topology and technology, is capable of achieving the desired purpose (a resolution of similar to 1 mu m), enabling the tissue to be bathed in any medium within the system.