## 3 Printing Technologies to Deliver Disposable and Miniaturised Devices  
Printing techniques have revolutionized electrochemistry because the classical working, reference and counter electrodes with dimensions of few cm have been replaced with flexible printed working, reference and counter electrodes with dimensions of few mm, requiring only few uL of sample. In addition, the cost largely decreases from ca. 500 \(\upxi\) to about 1 \(\upxi\). Without doubt, printed biosensors have improved the life of diabetic patients, thanks to the printed electrochemical biosensor analysing their glucose in the blood at home with a simple finger prick, instead of going to hospital for more invasive analyses [26]. A butylcholinesteraseerase biosensor based on a screen-printed electrode was developed by our group for the detection of nerve agents in the liquid and gas phases using a portable potentiostat. In detail, screen-printed electrodes were modified with Prussian Blue to detect thiocholine, the enzymatic by-product of butylcholinesteraseerase at +200 mV vs. Ag/AgCl pseudoreference. Being the butylthiocholine hygroscopic, the stability of the substrate was studied by investigating the effect of nitrogen flow in delivering a stable room temperature substrate. The optimized biosensor was tested using a portable potentiostat that is commercially available with Sarin and VX standard solutions, showing detection limits of 10 ppb and 18 ppb, respectively. Furthermore, this biosensor demonstrated the capability of measuring Sarin in the gas phase by exposing the wet biosensor with phosphate buffer to Sarin gas. The effect of incubation time was evaluated by studying the incubation time from 30 s up to 10 min at concentrations of 0.1 mg/m\({}^{3}\) and 0.5 mg/m\({}^{3}\) of Sarin gas, demonstrating that only 30 s of incubation time are needed to detect Sarin at the concentration of 0.1 mg/m\({}^{3}\)[27]. This biosensor was also configured to be embedded with a sampling prototype constituted of an electrochemical cell, a little fan for sampling air, and an electronic circuit for applying the potential, registering the current, turning on-off the fan, and giving an alarm if the signal decreases by 20%, delivering a smart lab on a chip (Figure 3B). In detail, the biosensor was inserted in the cell by adding the substrate by a syringe. The detection of nerve agents in the gas phase was accomplished because the fan is able to sample 20-25 L of air/min by flowing the air into the electrochemical cell and enriching the working solution by nerve agents. This prototype encompasses an electronic circuit that is able to manage the fan and the miniaturized potentiostat by using (i) an analogic section for applying the potential (+200 mV) followed by an input I/V amplifier for converting the input current signal into the output voltage signal and a low-pass filter to exclude the transient frequency disturbs, (ii) a digital section with an A/D converter for an input stage of the microcontroller. Paraoxon was used as a simulant and was tested at a concentration of 1 ppm for 12 times, always giving the switch-on of the alarm. Furthermore, blank solution did not cause any alarm, thus demonstrating the suitability of the device [28]. Screen-printed electrodes were also used to evaluate the sensitivity of different biocomponents, namely recombinant, electric eel, and bovine erythrocytes origin acetylcholinesterasedisease, observing that human recombinant acetylcholinesteraseinesterase seemed to be the most sensitive toward the inhibition by Sarin with a limit detection of 0.45 \(\times\) 10\({}^{-8}\) mol/L [29]. The same group developed a biosensing system using a platinum screen-printed electrode and acetylcholinesteraseinesterase from electric eel in a solution to test Sarin, Soman, Tabun, and VX with the limits of detection of 7.41 \(\times\) 10\({}^{-12}\) mol/L for Sarin, 6.31 \(\times\) 10\({}^{-12}\) mol/L for Soman, 6.17 \(\times\) 10\({}^{-11}\) mol/L for Tabun, and 2.19 \(\times\) 10\({}^{-11}\) mol/L for VX, respectively [30].