Advances in High-Resolution Microscale Impedance Sensors

Sensors based on impedance transduction have been well consolidated in the industry for decades. Today, the downscaling of the size of sensing elements to micrometric and submicrometric dimensions is enabled by the diffusion of lithographic processes and fostered by the convergence of complementary disciplines such as microelectronics, photonics, biology, electrochemistry, and material science, all focusing on energy and information manipulation at the micro- and nanoscale. Although such a miniaturization trend is pivotal in supporting the pervasiveness of sensors (in the context of mass deployment paradigms such as smart city, home and body monitoring networks, and Internet of Things), it also presents new challenges for the detection electronics, reaching the zeptoFarad domain. In this tutorial review, a selection of examples is illustrated with the purpose of distilling key indications and guidelines for the design of high-resolution impedance readout circuits and sensors. The applications span from biological cells to inertial and ultrasonic MEMS sensors, environmental monitoring, and integrated photonics

Polyelectrolyte based sensors as key to achieve quantitative electronic tongues: Detection of triclosan on aqueous environmental matrices

This work was supported by the Project “Development of Nanostructures for Detection of Triclosan Traces on Aquatic Environments” (PTDC/FIS-NAN/0909/2014). The Center for Environmental and Sustainability Research CENSE and Centre of Physics and Technological Research CEFITEC,which is financed bynational funds from FCT/MEC (UID/AMB/04085/2019 and UID/FIS/00068/2019). This research was anchored by the RESOLUTION LAB, an infrastructure at NOVA School of Science and Technology. J. Pereira-da-Silva and P. Zagalo acknowledge their fellowships PD/BD/142768/2018, PD/BD/142767/2018 from RABBIT Doctoral Program, respectively. C. Magro acknowledges to Fundação para a Ciência e a Tecnologia for her PhD fellowship (SFRH/BD/114674/2016).Triclosan (TCS) is a bacteriostatic used in household items that promotes antimicrobial resistance and endocrine disruption effects both to humans and biota, raising health concerns. In this sense, new devices for its continuous monitoring in complex matrices are needed. In this work, sensors, based on polyelectrolyte layer-by-layer (LbL) films prepared onto gold interdigitated electrodes (IDE), were studied. An electronic tongue array, composed of (polyethyleneimine (PEI)/polysodium 4-styrenesulfonate (PSS))5 and (poly(allylamine hydrochloride/graphene oxide)5 LbL films together with gold IDE without coating were used to detect TCS concentrations (10−15–10−5 M). Electrical impedance spectroscopy was used as means of transduction and the obtained data was analyzed by principal component analysis (PCA). The electronic tongue was tested in deionized water, mineral water and wastewater matrices showing its ability to (1) distinguish between TCS doped and non-doped solutions and (2) sort out the TCS range of concentrations. Regarding film stability, strong polyelectrolytes, as (PEI/PSS)n, presented more firmness and no significant desorption when immersed in wastewater. Finally, the PCA data of gold IDE and (PEI/PSS)5 sensors, for the mineral water and wastewater matrices, respectively, showed the ability to distinguish both matrices. A sensitivity value of 0.19 ± 0.02 per decade to TCS concentration and a resolution of 0.13 pM were found through the PCA second principal component.publishersversionpublishe

Sub-Femto-Farad Resolution Electronic Interfaces for Integrated Capacitive Sensors: A Review

Capacitance detection is a universal transduction mechanism used in a wide variety of sensors and applications. It requires an electronic front-end converting the capacitance variation into another more convenient physical variable, ultimately determining the performance of the whole sensor. In this paper we present a comprehensive review of the different signal conditioning front-end topologies targeted in particular at sub-femtofarad resolution. Main design equations and analysis of the limits due to noise are reported in order to provide the designer with guidelines for choosing the most suitable topology according to the main design specifications, namely energy consumption, area occupation, measuring time and resolution. A data-driven comparison of the different solutions in literature is also carried out revealing that resolution, measuring time, area occupation and energy/conversion lower than 100 aF, 1 ms 0.1 mm2, and 100 pJ/conv. can be obtained by capacitance to digital topologies, which therefore allow to get the best compromise among all design specifications

Sensori elettrochimici stampati per la quantificazione di ioni nel sudore: principio di funzionamento e applicazioni

Negli ultimi anni l’interesse verso i sensori elettrochimici ha avuto un grande sviluppo. Infatti, essi hanno rivoluzionato i metodi di analisi, soprattutto nel settore medicale in diagnostica e per il monitoraggio continuo, e di ricerca. Un’importante rivoluzione è stata la stampa, una nuova tecnica di fabbricazione con cui si possono ottenere sensori miniaturizzati su substrati polimerici flessibili e biocompatibili. Grazie a ciò si possono realizzare dispositivi maneggevoli e indossabili, rendendo l’analisi facile e veloce, anche per non esperti. Un’applicazione interessante di essi è l’analisi non invasiva della concentrazione degli ioni nel sudore, che permette di ottenere delle indicazioni utili sullo stato di salute del paziente. In particolare, vengono molto utilizzati in questo ambito i sensori elettrochimici impedenziometrici e potenziometrici stampati. In questo elaborato vengono discusse la loro struttura e le loro caratteristiche metrologiche. Infine, viene riportata un’esperienza di calibrazione di due sensori, uno impedenziometrico e uno potenziometrico, entrambi stampati

Development of an impedance based biosensor for studies of spheroids formation

Three-dimensional (3D) multicellular spheroids are exceptional in vitro cell models for their ability to accurately mimic real cell-cell interaction processes. However, the challenges in producing well-defined spheroids with controlled size together with the deficiency of techniques to monitor them significantly restrict their use. Herein, a novel device to study spheroid formation in real time is presented. By exploiting electrochemical impedance spectroscopy, a multi-electrode array (MEA) attached to a calcium alginate scaffold is able to monitor the behaviour of 36 different hydrogel wells. The scaffold contains inverted shape pyramidal microwells, which guide the aggregation of cells into spheroids with controlled dimensions. Preliminar studies on calcium alginate, optimisation of fabrication strategy are shown, together with testing of the device in the presence and the absence of the hydrogel. Lastly, the device was tested for its intended aim, i.e. to monitor the formation of a spheroid, proving its potential as an impedance biosensor

Micro- and Nanofluidics for Bionanoparticle Analysis

Bionanoparticles such as microorganisms and exosomes are recoganized as important targets for clinical applications, food safety, and environmental monitoring. Other nanoscale biological particles, includeing liposomes, micelles, and functionalized polymeric particles are widely used in nanomedicines. The recent deveopment of microfluidic and nanofluidic technologies has enabled the separation and anslysis of these species in a lab-on-a-chip platform, while there are still many challenges to address before these analytical tools can be adopted in practice. For example, the complex matrices within which these species reside in create a high background for their detection. Their small dimension and often low concentration demand creative strategies to amplify the sensing signal and enhance the detection speed. This Special Issue aims to recruit recent discoveries and developments of micro- and nanofluidic strategies for the processing and analysis of biological nanoparticles. The collection of papers will hopefully bring out more innovative ideas and fundamental insights to overcome the hurdles faced in the separation and detection of bionanoparticles

Portable impedance-sensing device for microparticle characterization

À ce jour, quelques biocapteurs ont été proposés pour mesurer rapidement et facilement les caractéristiques et les propriétés des microrganismes individuels membres d'une population hétérogène, mais aucune de ces approches ne s'est avérée être adéquate pour effectuer des mesures directement sur le terrain. Les biocapteurs pour les organismes microscopiques nécessitent généralement une sensibilité ou une spécificité extrême, qui sont difficiles à combiner avec un dispositif général portatif. Cette étude propose un dispositif portatif basé sur la cytométrie de flux d'impédance qui peut détecter et quantifier le diamètre de microbilles de tailles supérieure à 50 µm directement sur le terrain, tout en présentant un faible coût, une taille réduite, une basse consommation de puissance, et une simplicité de conception et d'opération qui maximise le potentiel de l'impression 3D et de la fabrication industrielle de circuits imprimés. Un exemple est offert afin de démontrer les capacités du capteurs pour de larges échantillons, avec un jeu de données contenant 2380 microbilles détectées de tailles entre 50 µm et 90 µm.To this day, a couple of biosensors have been proposed to quickly and easily measure the features and properties of individual microorganisms member of an heterogeneous population, but none of these approaches were adequate candidates to perform measurements directly in the field. Biosensors for micron-scale organisms generally require extreme sensitivity or specificity, which are difficult to combine with a portable general device. This study proposes a portable device based on Impedance Flow-Cytometry that can detect and quantify directly in the fields the size and velocity of microbeads of size bigger than 50 µm, while boasting a low cost, low size, low power, and simplicity of design and operation utilizing the potential of 3D-printing and industrial PCB fabrication. An example is provided for a Big Data application from a sampled dataset containing 2380 successfully detected microbeads of sizes between 50 µm and 90 µm