Sensors in action: towards bespoke analytical devices

A sensor is a device that transforms physical/chemical information into a quantifiable signal, through optical or electrochemical transduction. Differently to analyses carried out in specialized laboratories, chemical sensors permit miniaturization, point-of-care medical diagnostics (e.g., glucometers), integrating analytical information into everyday objects (e.g. smartphones). In this scenario, this lecture aims at providing an overview of bespoke sensors technologies, enabling specific analytical applications in the field of diagnostics and environmental monitoring. Notably, printing methods allows for the reconfigurable preparation of such analysis platforms (see Figure 1).[1] At first, inkjet printing for is shown as suitable approach to dispense aqueous droplets of substrate and inhibitor (D-glucose and D-glucal) onto a glucose oxidase layer immobilized onto a solid silicon support, thereby enabling microarray‐based drug screening assays in picoliter scale droplets.[2] Then, protein ligands patterning via direct DNA directed immobilization coupled with Dip Pen Nanolitography on surfaces is demonstrated at scales smaller than those of individual cells to analyze sub‐cellular processes (e.g. receptor clustering, cell signalling) rather than whole‐cell scale patterning.[3] To demonstrate the proof of principle, EGFR (Epidermal growth factor receptor) proteins of the human breast adenocarcinoma cells (MCF-7) cluster on surfaces patterned with biotinylated EGF attached via the DNA directed immobilization. Aiming at producing a more complex platform, the fine control of droplets inkjet printing ejection at sizes smaller than subcellular scale compartments can produce artificial compartments mimicking certain functions of natural cells, such as selective permeability and compartmentalization of biochemical reactions.[4] Such knowledge framework for creating artificial biological systems by printing technologies could be a foundation to reconstruct the fundamental processes of life in simplified synthetic systems. Indeed, the resulting field of Printing Biology defines the ability to print artificial systems mimicking the control over the spatial organization of biomolecular components, crucial for orchestrating biochemical pathways.[5] When dealing with sensors, a crucial factor is to make the detection easy and scalable. To this aim, optical sensors can be complex and expensive but excel in applications where high precision, high resolution and accuracy are critical. Differently, electrical detection constitutes a more practical transduction approach in comparison to the optical one, resulting in highly sensitive, accurate, cost- effective, and miniaturized portable devices. Electrochemical sensors can also be mass-produced by employing different printing techniques such as screen-printing, inkjet printing, and also 3D printing To this aim, a shift toward detection for applications in mechanical sensing comprises integrating wet chemistry synthesized ZnO based materials within Printed Circuit Boards, ultimately making nanotechnology scalable and integrable into real-world piezoelectric wearable sensors.[6] Finally, coupled with enzyme immobilization. electrochemical sensors prepared by screen printing can provide a rapid (approx. two minutes per analysis) electrochemical impedance spectroscopy based analysis to differentiate and quantify microplastics (MPs) in aqueous suspension — specifically to distinguish MPs that have adsorbed Pb2+ ions from those that haven’t. As a result, the analytical detection of clean vs polluted MPs is done on the basis of higher double layer resistance which is quantified by the equivalent circuit model.[7] Finally, advancements in chemical sensors can be tailored to meet specific needs, moving the analysis from centralized laboratories to decentralized, real-time decision-making. Such innovation enables new capabilities, such as obtaining a predictive analytical tool – e.g. by using machine learning approaches. Finally, chemical sensors based on electrochemical detection can democratize chemical analysis, making it faster, cheaper, and more accessible, thereby solving problems in real time across medicine, environment, industry, and daily life.