As the focus on healthcare shifts from centralized hospital-based treatment to home-based management, there are growing needs for developing reliable, wearable healthcare monitoring systems.1,2 Such on-body (non-invasive or minimally-invasive) physiological monitoring devices are also of considerable interest for defense or sport applications. Integrating sensors and biosensors directly into clothing should thus have major advantages for future healthcare and soldier monitoring systems...

We have illustrated the direct screen-printing of amperometric carbon sensors onto clothing and the favorable electrochemical behavior of such textile-based sensors. Convenient measurements of hydrogen peroxide and NADH have been documented. Mechanical stress studies, relevant to the wearer's daily activity, have indicated that textile-based printed sensors survive large deformations. Both bending and stretching of the textile substrate have minimal detrimental effect upon the electrochemical measurements, and in some instances (e.g., for measurements of hydrogen peroxide) even lead to enhanced signals...

Future efforts in this direction will also include the incorporation of a chemically-selective layer (e.g., permselective coating or enzyme layer) and assessment of the role of the clothing deformation upon the performance and stability of such layers towards textile-based healthcare and soldier monitoring systems. Particularly attractive will be dehydrogenase- and oxidase-based enzyme sensors for ethanol and lactate, respectively, in connection with monitoring alcohol consumption in drivers or performance/stress of soldiers/athletes. Unlike glucose sweat levels, the concentration of alcohol or lactate in sweat has a significant clinical relevance. The large surface area of clothing could be used for integrating the necessary supporting electronic, display, power and communication functions (without external devices) and hence for communicating relevant health parameters. While clothing-integrated electrochemical sensors hold considerable promise for future healthcare, military or sport applications, such non-invasive textile-based sensing requires proper attention to key challenges of sample delivery to the electrode surface and of sensor calibration and interconnection.

SF fans are already used to the idea of underwear and clothing that monitors the physical characteristics of the wearer. In his 1988 novel Wetware, Rudy Rucker introduces the heartshirt:

Della's first present was an imipolex sweatshirt called a heartshirt…The heartshirt was an even dark blue, except for a few staticky red spots drifting about.

"It can feel your heartbeat … look." Sure enough there was a big red spot on the plastic shirt just over her heart..."
(Read more about the heartshirt)

Update 01-Jun-2020: An even better reference has turned up; take a look at the electric diaper from the classic 1928 story The Psychotronic Nurse by Dr. David Keller:

In every diaper there is a fine copper wire. When that becomes wet a delicate current is sent - you understand I mean an electrical current, not a watery one - to an amplifier and a certain sound is made...
(Read more about the Dr. David Keller's electric diaper)

End update.