Nowadays, there is a high demand for sensitive and selective real-time analytical methods suitable for a wide range of applications, from personalized telemedicine, drug discovery, food safety, and quality control, to defense, security, as well as environmental monitoring. Biosensors are analytical devices able to detect bio-chemical analytes (e.g., neurotransmitters, cancer biomarkers, bio-molecules, and ions), through the combination of a bio-recognition element and a bio-transduction device. The use of customized bio-recognition elements such as enzymes, antibodies, aptamers, and ion-selective membranes facilitates achieving high selectivity. Among the different bio-transduction devices currently available, electrolyte-gated field-effect transistors, in which the dielectric is represented by an ionic liquid buffer solution containing the targeted analyte, are gaining increasing attention. Indeed, these biotransduction devices are characterized by superior electronic properties and intrinsic signal amplification that allow the detection of a wide rangeofbiomolecules with high sensitivity (down to pM concentration). A promising semiconducting material for bio-transduction devices is represented by carbon nanotubes, due to their unique electrical properties, nanosize, bio-compatibility, and their simple low-cost processability. This work provides acomprehensive and critical review of electrolyte-gated carbon nanotube field-effect transistor-based biosensors. First, an introduction to these bio-sensing devices is given. Next, the device configurations and operating principles are presented, and the most used materials and processes are reviewed with a particular focus on carbon nanotubes as the active material. Subsequently, different functionalization strategies reported in the literature, based on enzymes, antibodies, aptamers, and ion-selective membranes, are analyzed critically. Finally, present issues and challenges faced in the area are investigated,theconclusions are drawn, and a perspective outlook over the field of bio-sensing technologies, in general, is provided.

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Nitrate (NO 3 – ) contamination is becoming a major concern due to the negative effects of an excessive NO 3 – presence in water which can have detrimental effects on human health. Sensitive, real-time, low-cost, and portable measurement systems able to detect extremely low concentrations of NO 3 – in water are thus becoming extremely important. In this work, we present a novel method to realize a low-cost and easy to fabricate amperometric sensor capable of detecting small concentrations of NO 3 – in real water samples. The novel fabrication technique combines printing of a silver (Ag) working electrode with subsequent modification of the electrode with electrodeposited copper (Cu) nanoclusters. The process was tuned in order to reach optimized sensor response, with a high catalytic activity toward electroreduction of NO 3 – (sensitivity: 19.578 μA/mM), as well as a low limit of detection (LOD: 0.207 nM or 0.012 μg/L) and a good dynamic linear concentration range (0.05 to 5 mM or 31 to 310 mg/L). The sensors were tested against possible interference analytes (NO 2 – , Cl – , SO 4 2– , HCO 3 – , CH 3 COO – , Fe 2+ , Fe 3+ , Mn 2+ , Na + , and Cu 2+ ) yielding only negligible effects [maximum standard deviation (SD) was 3.9 μA]. The proposed sensors were also used to detect NO 3 – in real samples, including tap and river water, through the standard addition method, and the results were compared with the outcomes of high-performance liquid chromatography (HPLC). Temperature stability (maximum SD 3.09 μA), stability over time (maximum SD 3.69 μA), reproducibility (maximum SD 3.20 μA), and repeatability (maximum two-time useable) of this sensor were also investigated.

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Inkjet printing is a promising low-cost fabrication technique capable of depositing functional materials with micrometer resolution, making this technique attractive for the fabrication of deformable sensors. Despite all the possible promising applications, no examples of inkjet-printed strain sensors array able to map substrate surface deformation have been proposed yet. On the base of these premises, it is here presented the development and characterization of an all-inkjetprinted resistive strain sensors array, highlighting the criteria adopted in the design phase. Initially, the strain sensing behavior of the printed CNTs percolation matrix was investigated by fabricating and electromechanically characterizing a single sensor. The proposed single sensor featured a sensitivity of 7.2 ± 2 up to 2.5% strain, demonstrating that the proposed sensing material is suitable for the fabrication of an inkjet-printed strain sensors array. Moreover, the fabricated sensors array was characterized through a confined electromechanical tensile test in which a non-homogeneous strain state was applied. Results showed the mapping capability of inkjet-printed deformable sensors array that is able to measure different local strains on the substrate surface. This work paves the way for using inkjetprinting technique for the realization of sensors with a larger number of interesting applications.

Aptamers are chemically synthesized single-stranded DNA or RNA oligonucleotides widely used nowadays in sensors and nanoscale devices as highly sensitive biorecognition elements. With proper design, aptamers are able to bind to a specific target molecule with high selectivity. To date, the systematic evolution of ligands by exponential enrichment (SELEX) process is employed to isolate aptamers. Nevertheless, this method requires complex and time-consuming procedures. In silico methods comprising machine learning models have been recently proposed to reduce the time and cost of aptamer design. In this work, we present a new in silico approach allowing the generation of highly sensitive and selective RNA aptamers towards a specific target, here represented by ammonium dissolved in water. By using machine learning and bioinformatics tools, a rational design of aptamers is demonstrated. This “smart” SELEX method is experimentally proved by choosing the best five aptamer candidates obtained from the design process and applying them as functional elements in an electrochemical sensor to detect, as the target molecule, ammonium at different concentrations. We observed that the use of five different aptamers leads to a significant difference in the sensor’s response. This can be explained by considering the aptamers’ conformational change due to their interaction with the target molecule. We studied these conformational changes using a molecular dynamics simulation and suggested a possible explanation of the experimental observations. Finally, electrochemical measurements exposing the same sensors to different molecules were used to confirm the high selectivity of the designed aptamers. The proposed in silico SELEX approach can potentially reduce the cost and the time needed to identify the aptamers and potentially be applied to any target molecule.

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