Benjamin Schazmann

A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration

We report a new method for the real-time quantitative analysis of sodium in human sweat, consolidating sweat collection and analysis in a single, integrated, wearable platform. This temporal data opens up new possibilities in the study of human physiology, broadly applicable from assessing high performance athletes to monitoring Cystic Fibrosis (CF) sufferers. Our compact Sodium Sensor Belt (SSB) consists of a sodium selective Ion Selective Electrode (ISE) integrated into a platform that can be interfaced with the human body during exercise. No skin cleaning regime or sweat storage technology is required as the sweat is continually wicked from the skin to a sensing surface and from there to a storage area via a fabric pump. Our results suggest that after an initial equilibration period, a steady-state sodium plateau concentration was reached. Atomic Absorption Spectroscopy (AAS) was used as a reference method, and this has confirmed the accuracy of the new continuous monitoring approach. The steady-state concentrations observed were found to fall within ranges previously found in the literature, which further validates the approach. Daily calibration repeatability (n = 4) was ±3.0% RSD and over a three month period reproducibility was ±12.1% RSD (n = 56). As a further application, we attempted to monitor the sweat of Cystic Fibrosis (CF) sufferers using the same device. We observed high sodium concentrations symptomatic of CF (∼60 mM Na+) for two CF patients, with no conclusive results for the remaining patients due to their limited exercising capability, and high viscosity/low volume of sweat produced.

Improved Nitrate Sensing using Ion Selective Electrodes Based on Urea–Calixarene Ionophores

Urea–calix[4]arenes 1 and 2 were synthesised and incorporated into ISE membranes for assessment as sensors for inorganic anions in water. 1 revealed a strong response to all anions following the Hofmeister selectivity order. For ISEs of 2, the response to a portion of the anion series was suppressed, increasing the margin of selectivity of nitrate over chloride, a common interferant of nitrate in fresh and marine water samples. The performance of ISEs containing 2 was compared to commercially available alkylammonium nitrate ion-exchange salts used for nitrate sensing. Our ISEs performed favourably in terms of sensitivity, linear range and LOD with an improved selectivity coefficient over chloride of log KNO3−Cl−pot of −3.4, an order of magnitude better than commercially available nitrate ISEs. The pre-conditioning of ISEs in non-primary chloride salt was essential for obtaining these results.

Wearable technology for bio-chemical analysis of body fluids during exercise

This paper details the development of a textile based fluid handling system with integrated wireless biochemical sensors. Such research represents a new advancement in the area of wearable technologies. The system contains pH, sodium and conductivity sensors. It has been demonstrated during on-body trials that the pH sensor has close agreement with measurements obtained using a reference pH probe. Initial investigations into the sodium and conductivity sensors have shown their suitability for integration into the wearable system. It is thought that applications exist in personal health and sports performance and training.

Development of a calix[4]arene sensor for soft metals based on nitrile functionality.

The current work is amongst the first to examine the potential usefulness of the nitrile functional group in potentiometric analytical sensors for soft metals. Nitrile functionality has hereby been incorporated into a calix[4]arene skeleton to give a series of new cation selective hosts. The analytical sensing behaviour of these hosts was examined by Ion Selective Electrode (ISE) based potentiometry. In all cases a preference for soft metals was observed, explained primarily in terms of soft–soft compatibility between calix[4]arene nitrile hosts and metal guests in combination with a classical ‘lock and key’ best fit mechanism. Hosts 2, 3 and 4 showed very strong responses towards Hg(II) ions, with Ag(I) being the main interferant. The introduction of electron delocalising aromaticity proximal to the nitrile functionality was thought to reduce the availability of negative charge for cation coordination, apparently affecting the Hg(II) cation in particular. An acute fall in Hg(II) response coupled with the emergence of Ag(I) as the primary ion was observed for 7 and 8.

Wearable sensors for monitoring sports performance and training

Textile based devices for biochemical analysis of body fluids represent a new development in the area of wearable sensors. This paper outlines the development of a fluid handling system and wireless sensors for the real-time analysis of sweat pH and sodium levels during exercise. Liquid is drawn into the system using a moisture wicking material and passive pump. The sensor then displays pH induced colorimetric changes, which are recorded using an optical detection system. The device has been tested under laboratory conditions and can easily detect increments of 0.2 pH units. At present, changes in sodium content are determined using a specially constructed classic ion selective electrode and reference electrode, combined to form a single probe. This is placed in contact with the fabric of the fluid handling system in order to obtain a real-time potentiometric sodium measurement. Both devices have successfully been used for the investigation of sweat composition during on-body trials.

Covalent attachment of functional side-groups to polyaniline nanofibres

Polyaniline (PAni) is an example of a conducting polymer that can be switched between an insulating and a conductive state. This switching is accompanied by a colour change. Recently, interest has developed in the nanofibre form of PAni as these low dimensional structures have a very high surface area, thus enabling a faster response time. We investigate how the surface chemistry of these nanofibres can be modified by covalently attaching functional side-groups. In particular, we demonstrate the attachment of both amide and carboxylic acid groups. This can be achieved using a simple reflux technique. The modified material retains its nanomorphology and the intrinsic electrochemical, spectroscopic and redox properties of PAni are also preserved. Both acid and amine side-groups are interesting in that they provide a template, which could be further altered to enhance the selectivity of PAni. Acid terminated chains can also be used to introduce self-doping behaviour to PAni.

Wearable technology for the real-time analysis of sweat during exercise

Textile based sensors which can be used to measure the chemical composition of bodily fluids represents a major advancement in the area of wearable technology. BIOTEX is an EU funded project aiming to develop such sensors with a particular interest in monitoring perspiration. A textile based fluid handling system has been developed for sample collection and transport. Sodium, conductivity and pH sensors have also been developed. This paper details the integration and testing of these sensors. Results show that the developed system can collect and analyze sweat in real time during exercise and transmit this data wirelessly to a remote receiver.

Identification and Recovery of an Asymmetric Calix[4]arene Tetranitrile Derivative using Liquid Chromatography and Mass Spectrometry

A simple analytical liquid chromatography mass spectrometry (LC-MS) method and associated instrumentation has been adapted for use by the organic chemist to yield milligram quantities of target compound from a reaction mixture. Calix[4]arene 3 was identified as representing 51% of total peak area of a reaction mixture containing no less than 10 components, using LC-MS. This peak corresponded to a mass of 878.8, equivalent to a complex of 3 and an ammonium cation. Molecular models further rationalize this observation by showing that the asymmetric binding cavity of 3 is suitable for binding tetrahedral guests such as the ammonium ion. By scaling up the LC method, using analytical instrumentation, 55 mg of 98% pure 3 was isolated with a recovery yield of 90% in 1 h. The current method represents a powerful and easily adapted tool for monitoring a challenging synthesis that combines identification, efficient separation and partial characterization for reaction mixture components using readily available instrumentation and methods.

5',6-Dichloro-1',3',3'-trimethyl-spiro-[2H-1-benzopyran-2,2'-indoline].

In the crystal structure of the title compound, C19H17Cl2NO, the indoline and benzopyran ring systems are approximately perpendicular to each other. The indoline ring is in an envelope conformation with the spiro C atom as the flap. The N atom of the indoline ring forms a pyramidal environment, the sum of the angles at this atom being 352.46°.

An ionic liquid-based sensor for diclofenac determination in water

ABSTRACT This paper details a miniaturised, solid state ion-selective electrode selective for diclofenac. The sensor comprises a novel ionic liquid electroactive material – an imidazolium–diclofenac ion associate. The ion associate is present in a plasticised poly(vinyl chloride) (PVC) membrane on planar carbon electrodes, with an intermediate poly(3,4-ethylenedioxythiophene) layer. The sensitivity and selectivity of the sensor were determined using chronopotentiometric methods. In response to diclofenac, a slope of −53.3 ± 3.6 mV/dec was observed. A limit of detection of 2.90 × 10−3 g L−1 is reported, with a linear range of 3.18 × 10−3 g L−1 to 3.18 g L−1. The sensors show good selectivity towards diclofenac against pertinent interferent molecules, with a response time of <15 s.