Currently, available sleep monitoring systems use electrical recording where the electrodes make contact with the patient’s skin using a conducting gel. The electrode wires are connected to a processing recording system. The subject has to be in close proximity of these machines due to the direct electrical connections with the body and the machine. The conductive gel along with many wires connected to the biopotential electrodes makes them uncomfortable for the subject, with the result that recording and monitoring of the patient’s sleep patterns can become very difficult. The patient has to be in a sleep lab and/or a hospital at all times and at least one technician needs to watch the patient’s sleep behavior via video. The patient may not experience normal sleep patterns under such environments and as such, the diagnostic results are not really very conclusive. The commonly monitored biopotential electrodes are electrocardiogram, electroencephalogram, electromyogram, and electrooculogram. The electrodes used for monitoring these signals are Ag/AgCl and gold, which require skin preparation by means of scrubbing to remove the dead cells and application of electrolytic gel to reduce the skin contact resistance. The gel takes a role of reducing skin contact impedance in the conventional Ag/AgCl electrode and its usage is directly related to the sensitivity. However, the wet conventional Ag/AgCl electrode has some drawbacks such as difficulty in long time monitoring because the gel dries out after few hours and skin irritations. Usually, physiological parameters are monitored over an extended period of time during the patient’s normal daily life to diagnose a disease. In this case, the wet conventional Ag/AgCl cannot be used because of the dry-out of gel. The dry-out of gel increases the impedance between skin and electrode and it is reflected in the poor signal sensitivity. Also noises, such as motion artifact and baseline wander, are added to the biopotential signals as the electrode floats over the electrolytic gel during monitoring. To overcome these drawbacks, dry nanoelectrodes are proposed in this paper where the electrodes are held against the skin surface to establish contact with the skin without the need for electrolytic fluids or gels. The results are presented along with a wireless communication such that the proposed system is ideal for point-of-care diagnosis of the patient at home.

This research presents the development of neural recording electrodes with high sensitivity using nanotechnology and the evaluation of their electrochemical sensing properties. Neural electrodes with heterostructured IrO2/Au nanowires have been fabricated on a flexible needle probe using a polyimide substrate. The outer, functional layer of the nanoelectrodes was made with a thin iridium oxide layer on vertically aligned Au nanowire cores providing low impedance and high charge storage capacity, which can enhance neural sensing and stimulating efficiency. Acute recording from the hippocampus of a rat brain has confirmed the neural sensing functionality of the heterostructured nanowire electrodes.

This paper presents the fabrication of dual electrode ensembles for electrochemical sensing of dopamine. A new dual electrode ensemble consists of vertically aligned core nanowire electrodes and a shell electrode with a hemicylindrical nanocavity structure and submicron inter-electrode spacing between the two working electrodes. By using a 3-dimensional cavity structure of two working electrodes, collection efficiency in redox cycling of dopamine is enhanced. Initial measurement results show the ability to detect 200 mM concentration of dopamine with 69% collection efficiency on a dual electrode ensemble.

This research discusses the development of biosensors with vertically aligned nanowires, and the evaluation of their physical properties, electrochemical performance and biocompatibility. The developments include neurotransmitter (dopamine) sensors, glucose sensors for continuous monitoring, potassium ion sensors and integration of those sensors. A hemi-cylindrical nanocavity structure has been developed for dopamine sensing using redox cycling with radial diffusion within the cavities. By immobilization of enzymes in a conducting polymer matrix on vertically aligned nanowires, glucose sensing electrodes have been obtained with high sensitivity and selectivity. In addition, potassium sensing, potentially useful for monitoring changes of extracellular potassium concentration during myocardial ischemia, has been demonstrated using ion selective membranes (ISM) on nanowires. Sensor developments and measurement results are included in the presentation along with descriptions of top-down and bottom-up nano-/micro-fabrication technologies such as lithography and thin film deposition.

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