Eoghan McNamara

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.

Integrated flow analysis platform for the direct detection of nitrate in water using a simplified chromotropic acid method

This work describes the first use of a direct nitrate analyser using chromotropic acid. A simplified chromotropic acid method eliminating several steps previously associated with this method is employed in the platform. In a sulphuric acid medium, chromotropic acid reacts with nitrate ions and produces a characteristic yellow colour associated with an absorbance band in the visible region (λmax = 430 nm). The modified method allows for nitrate determination over the linear range 0.9–80 mg L−1 nitrate with a limit of detection of 0.73 μg L−1 nitrate. Validation was achieved by analysing water samples from various sources including groundwater, trade effluent and drinking water by the modified method and by ion chromatography. The method was implemented on a flow analysis platform incorporating a paired emitter–detector diode (PEDD) as the optical detector. An excellent correlation coefficient of 0.993 was obtained between the modified method and ion chromatography. The modified chromotropic acid method represents a rapid, simple, low cost technique for the direct determination of nitrate in water.

Photo-switchable microvalve in a reusable Lab-on-a-disc

This contribution describes for the first time the fabrication and the performance of a reversible ionogel microvalve in-situ photopolymerised into a reusable disc platform for fluid control. During storage and spinning, the swollen microvalve provides a permanent liquid barrier due to the special chemical characteristics of the ionogel. The microvalve is easy actuated using a white light LED allowing open of the channel at a desired time. The actuation mechanism is chemically reversible when an acid solution is provided to the microvalve. Here a perpendicular microchannel, connected to the valve from behind, is used to ensure the re-swelling of the ionogel and therefore reusability of the Lab-on-a-disc.