Cortisol Sensor for Soldier Stress and Fatigue Monitoring
The hormone cortisol, which is produced by the adrenal gland and is released in the body during stressed or agitated states, has gained widespread attention as the so-called "stress hormone." But this hormone is more than a simple marker of stress levels- it is necessary for the functioning of almost every part of the body. Excesses or deficiencies of this crucial hormone also lead to various physical symptoms and disease states. This compound has been studied as a biomarker for many diseases such as Cushing's disease, chronic fatigue syndrome and fibromyalgia, an autoimmune disorder. Cortisol has also been correlated with stress levels. It has been found that the level of salivary cortisol serves as a biochemical marker for post-traumatic psychological distress disorders and other conduct disorders. Thus, measurement of cortisol levels in the body can be an important diagnostic tool - both in clinical settings and during certain stress-intensive activities. For these reasons, the military has been interested in measuring the relative stress levels of their soldiers in combat situations. Clinical studies of different disorders as well as trials for drugs to treat cortisol related problems also have a need for these same measurements. However, cortisol levels in the body fluctuate throughout the day with levels being highest in the morning and lowest in the evening. Dietary intake and metabolic imbalances cause further fluctuations. To identify and allow for these different fluctuations, a real-time determination of cortisol levels is needed, without the use of costly and cumbersome laboratory equipment.
To address the demands of the Army's Land Warrior program, researchers at the Johns Hopkins Applied Physics Laboratory (JHU/APL) have combined molecularly imprinted polymer (MIP) technology and dynamic fluorescence measurement to develop a cortisol sensor for monitoring levels in the saliva. The JHU/APL polymer-based sensor is used to create a robust and completely synthetic immunoassay in order to monitor cortisol levels in real time. Although developed to determine a soldier's relative stress level in the field, this same technique could be used for many different applications. Molecularly imprinted polymers (MIP) have a specific transporting or penetrating path, pore or matrix through which only the desired substrate, cortisol, is able to pass. Specific receptor sites in polymeric membranes are introduced by the molecular imprinting technique. Molecular imprinting is a process for making selective recognition sites in synthetic polymers. The process employs a target molecule as the template. The template is surrounded by molecular compliments that possess polymerizable functionalities. The template complex is typically copolymerized with a matrix monomer and a cross-linking monomer in the presence of a suitable solvent. The cross-linking monomers add rigidity to the finished polymer and the solvent provides site accessibility. Removal of the template molecules leaves behind cavities that exhibit enhanced affinity for rebinding the target molecule – in this case, cortisol. A cortisol MIP sensor, for soldiers, could be integrated into their standard gear. The most likely target is the mouthpiece for hands free hydration systems. A sensor incorporated at this site would take measurements with each sip. The water could serve to flush, or reset the device between each reading. Options for devices to test less active subjects are unlimited because MIP sensor technology lends itself well to miniaturized, automated devices.
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