Nowadays the development of stable and highly efficient Solid-Contact Ion-Selective Electrodes (SC-ISEs) attracts much attention in the research community because of the great expansion of portable analytical devices. In this work, we present highly stable Li+ all-solid-state ISEs exploiting noble metals nanostructures as ion-to-electron transducers. The detection of lithium is essential for therapeutic drug monitoring of bipolar patients. In addition, greater environmental exposure to this ion is occurring due to the large diffusion of lithium-ion batteries. However, only a limited number of SC Li+ ISEs already exists in literature based on Conductive Polymers (CPs) and carbon nanotubes. The use of noble metals for ion-to-electron transduction offers considerable advantages over CPs and carbon materials, including fast and conformal one-step deposition by electrochemical means, non-toxicity and high stability. We investigate for the first time the use of gold nanocorals obtained by means of a one-step electrodeposition process to improve sensor performance and we compare it to all-solid-state ISEs based on electrodeposited platinum nanoflowers. In addition, the effect of substrate electrode material, membrane thickness and conditioning concentration on the potentiometric response is carefully analysed. Scanning Electron Microscopy (SEM) and Current Reversal Chronopotentiometry (CRC) techniques are used to characterize the morphology and the electrochemical behaviour of the different ISEs. The use of nanostructured gold and platinum contacts allows the increase of the SC capacitance by one or two orders of magnitude, respectively, with respect to the flat metal, while the SC resistance is significantly reduced. We show that the microfabricated sensors offer Nernstian behaviour (58.7±0.8 mV/decade) in the activity range from 10-5 to 0.1 M, with short response time (∼15 s) and small potential drift during CRC measurements (dEdt=3×10-5±2×10-5 V/s). The exceptional response stability is verified also when no potential is applied. The sensor shows high selectivity towards all clinically important ions, with values very similar to conventional ISEs. Furthermore, to our knowledge, the selectivity towards Ca+2 is the best ever reported for SC-ISEs. In conclusion, the present study opens up new interesting perspectives towards the development of simple and reproducible fabrication protocols to obtain high-quality and high-stability all-solid-state ISEs.

The research on ion-measuring devices has seen a rapid expansion in the last years as a consequence of the growing interest in wearable sensors for biofluids analysis and in portable devices for remote or in-line water and food quality monitoring. As a result, an increasing number of researchers is approaching the field of ion-selective sensors. Despite the apparently simple transduction principle, the theory behind their working mechanism is far from trivial and a correct understanding is necessary for an optimal exploitation of the technology. In current literature, imprecise characterization procedures lead to the definition of misleading sensors parameters, which cannot be effectively used for comparisons. In fact, some unique definitions and procedures applies to this category of sensors, which significantly differ from the traditional ones applied in sensing research. This tutorial aims at highlighting the basic thermodynamic theory and the correct experimental practice for the accurate and reproducible characterization of potentiometric ion-sensors. The most important requirements and design considerations on hardware and software interfaces will also be discussed to give a complete overview of the various aspects of current technology to people approaching this promising area of sensing.

Lithium represents the main drug for the treatment of Bipolar Disorder (BD) as it acts as a mood stabilizer. However, because of its narrow therapeutic window, psychiatric patients are obliged to frequent tests in hospital to control their lithium blood concentration during therapy. In this paper, we fabricate for the first time a complete non-invasive system for the Therapeutic Drug Monitoring (TDM) of lithium in sweat in people suffering from BD. The wearable electrochemical sensing platform includes a paper fluidics and a stable Reference Electrode (RE). Lithium detection is based on the use of a potentiometric Ion-Selective Electrode (ISE) with a nanostructured solid contact in order to increase the potential stability of the sensor. A chemical chlorination combined with the use of a PVC membrane doped with an Ionic Liquid (IL) is used to minimize possible potential drifts of the RE. The Nernstian response (56.8±3.9 mV /decade) of the system in the range of clinical interest is then proved in aqueous solution and in sweat. The integration of the sensing platform with a paper fluidics transporting fresh sweat sample to the sensing area is also considered. The already tested sweat is collected in a reservoir made of slow adsorbing paper. The complete wearable system is then successfully tested in a simulated setup by using a mannequin. The measured potential is well compared to the predicted ones in the therapeutic window of lithium drug, proving the good sensing capability in artificial sweat.

Nanostructured materials have attracted considerable interest over the last few decades to enhance sensing capabilities thanks to their unique properties and large surface area. In particular, noble metal nanostructures offer several advantages including high stability, non-toxicity and excellent electrochemical behaviour. However, in recent years the great expansion of point-of-care (POC) and wearable systems and the attempt to perform measurements in tiny spaces have also risen the need of increasing sensors miniaturization. Fast constant potential electrodeposition techniques have been proven to be an efficient way to obtain conformal platinum and gold nanostructured layers on macro-electrodes. However, this technique is not effective on micro-electrodes. In this paper, we investigate an alternative one-step deposition technique of platinum nanoflowers on micro-electrodes by linear sweep voltammetry (LSV). The effective deposition of platinum nanoflowers with similar properties to the ones deposited on macro-electrodes is confirmed by morphological analysis and by the similar roughness factor (~200) and capacitance (~18 $\mathsf{\mu }$ F/mm ${}^2$ ). The electrochemical behaviour of the nanostructured layer is then tested in an solid-contact (SC) $L{i}^{+}$ -selective micro-electrode and compared to the case of macro-electrodes. The sensor offers Nernstian calibration with same response time (~15 s) and a one-order of magnitude smaller limit of detection (LOD) ( $2.6\times {10}^{-6}$ ) with respect to the macro-ion-selective sensors (ISE). Finally, sensor reversibility and stability in both wet and dry conditions is proven.

This work presents the design and the realization of a flexible front-end circuitry for electrochemical sensing with wearable devices. The hardware combines readout circuitry for amperometric and Open Circuit Potential (OCP) measurements. The sensing platforms are dedicated to lactate and lithium detection in sweat, hence allowing the monitoring of athletes under physical effort. The wearability of the system is ensured by the flexibility of the electronic substrate, its small dimensions that fit an armband case, and the wireless transmission through a Bluetooth Low Energy (BLE) module. The power consumption of the system has been evaluated to be 200mW, with 3.6V on board power supply.