Claudio Zuliani

An integrated sensing and wireless communications platform for sensing sodium in sweat

The ability to non-invasively monitor sodium levels in sweat is of significant importance. Sodium is one of the preferred markers to diagnose and track the progression of cystic fibrosis, and knowledge of sodium levels could potentially enable personalised hydration strategies to be implemented for athletes or people working under severe environmental conditions. Herein we present a novel approach for the realisation of disposable potentiometric strips that allow for real-time monitoring of sodium in sweat. Our platform consists of a Solid-Contact Ion-Selective Electrode (SC-ISE) for Na+ detection and of a liquid-junction-free Reference Electrode (RE), combined together on a dual screen-printed substrate. Different poly-3,4-ethylenedioxythiophene (PEDOT) based films were tested as solid-contact, showing a significant impact on sensor characteristics such as sensitivity (i.e. differing from sub-Nernstian to Nernstian), dynamic range (i.e. 10−5 to 10−2.5 or 10−5 to 10−1aNa+), and especially within-batch reproducibility. The SC-ISE/RE combination was integrated into a microfluidic chip that was tested and optimised via on-bench trials. The Potentiometric Microfluidic Chip (PotMicroChip) was then connected to a wireless electronic platform to realise a wearable device whose performance was assessed during real-time stationary cycling sessions.

Formation and Growth of Oxide Layers at Platinum and Gold Nano- and Microelectrodes

The construction and characterization of platinum and gold disk electrodes with minimum radii of 7 nm (platinum) and 500 nm (gold) is reported. The electrodes were prepared with a micropipet puller using a two step procedure and have been characterized using scanning electron microscopy, scanning electrochemical microscopy, high speed chronoamperometry, and cyclic voltammetry. The formation and growth of platinum and gold oxide layers, on the electrodes at time scales from microseconds to seconds, is reported. Significantly, the apparent microscopic area as determined by forming and subsequently reducing an oxide layer in acidic electrolyte using cyclic voltammetry depends dramatically on the scan rate. While conventional roughness factors between 1.8 and 3 are observed on average for scan rates above 5 V s(-1), the apparent roughness can exceed 30 for scan rates less than 0.5 V s(-1). Chronoamperometry, conducted on the microsecond to millisecond time scale, is used to probe the dynamics of monolayer and multilayer oxide formation as well as the reversibility of the oxide formation and removal. The latter study suggests that (at least for platinum) the growth of the oxide layer proceeds with a lower constant rate after an oxide monolayer is formed.

A liquid-junction-free reference electrode based on a PEDOT solid-contact and ionogel capping membrane.

Liquid-junction-free reference electrodes have been prepared on screen printed substrates using poly-3,4-ethylenedioxythiophene (PEDOT) as solid-contact and novel ionogels as capping membrane. The chemico-physical properties of the PEDOT layer were tuned by changing the electropolymerization media and the electrodeposition technique. Electrodepositing PEDOT films potentiostatically or potentiodynamically were found to have a significant impact on the stability of the electrodes during the conditioning step. Optimization of the capping membrane formulation, e.g., acrylate monomers, ionic liquid, cross-linkers and photo-initiators, produced electrodes with properties almost equivalent with a commercial reference electrode. Thus, calibration plots of Na(+) ion-selective electrodes against the optimized solid-contact ionogel reference electrodes (SCI-REs) or against a double-liquid junction Ag/AgCl electrode did not present any significant difference. Such SCI-REs may provide an effective route to the generation of future low-cost components for potentiometric sensing strips.

Single nanocavity electrodes: fabrication, electrochemical and photonic properties

Nanosphere lithography has been used to create spherical recessed electrodes of nanometre dimensions capable of enhancing fluorescent signals.

Distributed Environmental Monitoring

With the increasingly ubiquitous use of web-based technologies in modern society, autonomous sensor networks represent the future in large-scale information acquisition for applications ranging from environmental monitoring to in-vivo sensing. This chapter presents a range of on-going projects with an emphasis on environmental sensing; relevant literature pertaining to sensor networks is reviewed, validated sensing applications are described and the contribution of high-resolution temporal data to better decision-making is discussed.

Recent progress in disposable ion-selective sensors for environmental applications

Solid-contact Ion Selective Electrodes (SC-ISEs) for the detection of lead are prepared on screen printed substrates in order to have low-cost and disposable sensors which may be useful in long-term environmental monitoring. It is shown that the materials used as solid contact layer, the deposition techniques and their thickness affect greatly the performances of the sensors. Poly(3-octylthiophene-2,5-diyl) (POT) and poly-3,4-ethylenedioxithiophene (PEDOT) are employed in this investigation. A trend showing an optimum is found for sensors prepared with POT as the batch reproducibility depends on the amount drop-cast, i.e., thickness. In case of PEDOT which is grown amperometrically the trend is more complex but an optimum for the batch reproducibility is again found depending on the current density. In the latter case, the film thickness and the overoxidation degree of the polymer probably concur in determining a more complex relationship.

Properties and Customization of Sensor Materials for Biomedical Applications

Low-power chemo- and biosensing devices capable of monitoring clinically important parameters in real time represent a great challenge in the analytical field because the issue of sensor calibration pertaining to keeping the response within an accurate calibration domain is particularly significant. Diagnostics, personal health, and related costs will also benefit from the introduction of sensors technology. In addition, with the introduction of Registration, Evaluation, Authorization, and Restriction of Chemical Substances regulation, unraveling the cause–effect relationships in epidemiology studies will be of outmost importance in order to help establish reliable environmental policies aimed at protecting the health of individuals and communities. For instance, the effect of low concentration of toxic elements is seldom investigated as physicians do not have means to access the data.