Nowadays, wearable sensors such as heart rate monitors and pedometers are in common use. The use of
wearable systems such as these for personalized exercise regimes for health and rehabilitation is particularly interesting.
In particular, the true potential of wearable chemical sensors, which for the real-time ambulatory monitoring of bodily
fluids such as tears, sweat, urine and blood has not been realized. Here we present a brief introduction into the fields of
ionogels and organic electrochemical transistors, and in particular, the concept of an OECT transistor incorporated into a
sticking-plaster, along with a printable "ionogel" to provide a wearable biosensor platform.
In this work a mechanical optode mounting system for functional brain imaging with light is presented. The particular application here is a non-invasive optical brain computer interface (BCI) working in the near-infrared range. A BCI is a device that allows a user to interact with their environment through thought processes alone. Their most common use is as a communication aid for the severely disabled. We have recently pioneered the use of optical techniques for such BCI systems rather than the usual electrical modality. Our optical BCI detects characteristic changes in the cerebral haemodynamic responses that occur during motor imagery tasks. On detection of features of the optical response, resulting from localised haemodynamic changes, the BCI translates such responses and provides visual feedback to the user. While signal processing has a large part to play in terms of optimising performance we have found that it is the mechanical mounting of the optical sources and detectors (optodes) that has the greatest bearing on the performance of the system and indeed presents many interesting and novel challenges with regard to sensor placement, depth of penetration, signal intensity, artifact reduction and robustness of measurement. Here a solution is presented that accommodates the range of experimental parameters required for the application as well as meeting many of the challenges outlined above. This is the first time that a concerted study on optode mounting systems for optical BCIs has been attempted and it is hoped this paper may stimulate further research in this area.
Studies of neurovascular coupling (hemodynamic changes and neuronal activation) in the visual cortex using a time-domain single photon counting system have been undertaken. The system operates in near infrared (NIR) range of spectrum and allows functional brain monitoring to be done non-invasively. The detection system employs a photomultiplier and multi-channel scaler to detect and record emerging photons with sub-microsecond resolution (the effective collection time per curve point is ~ 200 ns). Localisation of the visual evoked potentials in the brain was done using knowledge obtained from electroencephalographic (EEG) studies and previous frequency-domain optical NIR spectroscopic systems. The well-known approach of visual stimulation of the human brain, which consists of an alternating black and white checkerboard pattern used previously for the EEG study of neural responses, is applied here. The checkerboard pattern is synchronized with the multi-channel scaler system and allows the analysis of time variation in back-scattered light, at different stimulation frequencies. Slow hemodynamic changes in the human brain due to Hb-HbO2 changes in the blood flow were observed, which is evidence of the system's capability to monitor these changes. Monocular visual tests were undertaken and compared with those done with an EEG system. In some subjects a fast optical response on a time scale commensurate with the neural activity associated with the visual cortex was detected. Future work will concentrate on improved experimental protocols and apparatus to confirm the existence of this important physiological signal.
This study investigates the feasibility of acquiring fast optical response signals from the peripheral nervous system (PNS) and specifically to obtain knowledge about the sensory response of the median nerve through comparing electrophysiological responses with those obtained with a single photon counting system. Nerve potentials have been well studied so the primary purpose of this investigation is to better understand the conditions required for recording the optical analogue of this signal. Such action potential-correlated optical signals have been termed 'fast optical evoked responses' and their measurement in-vivo has hitherto proved fraught with difficulty. As yet measurement of these signals has been confined to evoked potential studies in the brain and so far there is no repeatable, confirmed procedure for their robust acquisition. In this work it is suggested that perhaps an easier route to acquire these elusive optical signals is through evoked potential studies centred on the PNS as opposed to the brain. Preliminary results suggest it is possible to correlate both data and draw important information from it although the most important contribution of this paper is the principle of directing the search for robust fast optical signals to the peripheral nervous system as opposed to the brain.