Continuous molecular monitoring of human dermal interstitial fluid with microneedle-enabled electrochemical aptamer sensors.

The ability to continually collect diagnostic information from the body during daily activity has revolutionized the monitoring of health and disease. Much of this monitoring, however, has been of physical "vital signs", with the monitoring of molecular markers having been limited to glucose, primarily due to the lack of other medically relevant molecules for which continuous measurements are possible in bodily fluids. Electrochemical aptamer sensors, however, have a recent history of successful in vivo demonstrations in rat animal models. Herein, we present the first report of real-time human molecular data collected using such sensors, successfully demonstrating their ability to measure the concentration of phenylalanine in dermal interstitial fluid after an oral bolus. To achieve this, we used a device that employs three hollow microneedles to couple the interstitial fluid to an ex vivo, phenylalanine-detecting sensor. The resulting architecture achieves good precision over the physiological concentration range and clinically relevant, 20 min lag times. By also demonstrating 90 days dry room-temperature shelf storage, the reported work also reaches another important milestone in moving such sensors to the clinic. While the devices demonstrated are not without remaining challenges, the results at minimum provide a simple method by which aptamer sensors can be quickly moved into human subjects for testing.

A Simple Non-Contact Optical Method to Quantify In-Vivo Sweat Gland Activity and Pulsation.

OBJECTIVE: Most methods for monitoring sweat gland activity use simple gravimetric methods, which merely measure the average sweat rate of multiple sweat glands over a region of skin. It would be extremely useful to have a method which could quantify individual gland activity in order to improve the treatment of conditions which use sweat tests as a diagnostic tool, such as hyperhidrosis, cystic fibrosis, and peripheral nerve degeneration. METHODS: An optical method using an infrared camera to monitor the skin surface temperature was developed. A thermodynamics computer model was then implemented to utilize these skin temperature values along with other environmental parameters, such as ambient temperature and relative humidity, to calculate the sweat rates of individual glands using chemically stimulated and unstimulated sweating. The optical method was also used to monitor sweat pulsation patterns of individual sweat glands. RESULTS: In this preliminary study, the feasibility of the optical approach was demonstrated by measuring sweat rates of individual glands at various bodily locations. Calculated values from this method agree with expected sweat rates given values found in literature. In addition, a lack of pulsatile sweat expulsion was observed during chemically stimulated sweating, and a potential explanation for this phenomenon was proposed. CONCLUSION: A simple, non-contact optical method to quantify sweat gland activity in-vivo was presented. SIGNIFICANCE: This method allows researchers and clinicians to investigate several sweat glands simultaneously, which has the potential to provide more accurate diagnoses and treatment as well as increase the potential utility for wearable sweat sensors.