Tech Briefs

Identifying new biomarkers to help monitor cognition and stress in the human body could enhance human performance.

Researchers are identifying new biomarkers to help monitor cognition and stress in the human body and enhance human performance. Traditional biomarkers like heart rate, temperature, oxygen partial pressure, blood glucose, electrolyte concentration, and others have been correlated with cognition and stress states. However, the correlation is indirect. Molecular biomarkers with stronger and more specific links are preferred.

Molecular biomarkers can be more specific to cognition states and typically take the form of bioactive molecules including steroids, proteins, carbohydrates, lipids, and nucleic acids. The tools available to quantify molecular biomarkers during their discovery are sensitive and selective, but also have significant drawbacks. In particular, these tools are inconvenient in a variety of ways and prohibit real time monitoring. As medical researchers identify new molecular biomarkers of importance, medical professionals need wearable sensor systems to take full advantage of their discovery. The plan is to develop a modular wearable biosensor patch to provide non-invasive, continuous monitoring of sweat based biomarkers.

Initial microfluidic reservoir trial designs for four different volumes with detail of CBV features.

During this research, the feasibility of subsystems needed to realize a complete chronological sweat analysis and collection device was demonstrated. Sweat control including aggregation, transition to a microfluidic system, and sequential filling of reservoirs was demonstrated at the bench level using synthetic eccrine sweat driven by a syringe pump.

Design of the microfluidics included a study of multiple valve/control mechanisms before selection of capillary burst valves (CBV) as the primary flow control element. CBVs enable flow control without the need for cumbersome or bulky external drivers such as pneumatic pressure. Evaluation microfluidic devices were fabricated from polydimethylsiloxane (PDMS) for its flexibility and compatibility with aqueous systems like sweat and human skin contact.

Sequential filling was demonstrated over six approximately 100 μL reservoirs and evaluated multiple reservoir designs to target reliable and full filling. Sweat aggregation through a porous/breathable adhesive layer to a concentrated outlet point was demonstrated as a subsystem, as well as with partial integration to a simple microfluidic channel to show transitions from sweat source, through an adhesive layer, and into the microfluidic sweat sensing and collection device.

An electronic circuit was designed and demonstrated for measurement of nanoamp current signals and integration as part of the sweat sensing and collection device. The circuit using a 24-bit analog to digital converter (ADC) was demonstrated in a breadboard configuration to resolve currents in microampere to nanoampere ranges, suitable for advanced sensors such as organic field effect transistors (OFET) as well as other types of sensors including electrochemical, potentiostatic, and resistive. The electronic measurement circuit demonstrated the ability to detect a sub-microamp signal from an OFET device when exposed to synthetic eccrine sweat.

Design efforts for an initial prototype design were conducted, producing models showing device integration from skin application to measurement electronics.

This work was done by Dr. Brian E. Henslee and Frank M. Zalar of Cornerstone Research Group, Inc. for the Army Medical Research Acquisition Activity. ARL-0218

This Brief includes a Technical Support Package (TSP).

Modular Biosensor Patch (reference ARL-0218) is currently available for download from the TSP library.

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