The impact of space environment in human physiology is one of the biggest hurdles for the success of long duration manned missions.¹ Traditionally, the impact of space environment is assessed by comparing different physiological parameters before and after deployment. For long duration missions (i.e Moon or Mars), sample return for a ground base analysis will be impractical and in-flight, portable analytical devices will be required. Additionally, the further crew travel from earth, the less feasible it is to rely on resupply of these portable analytical devices. One solution is to develop methodologies for manufacturing analytical devices on-demand and in an in-space environment. Electrochemical biosensors can serve as point-of-care (POC) analytical devices as they can be easily fabricated onto cheap, disposable substrates by printing nanomaterial-based electronic inks. Inkjet printing is a suitable deposition technique as it provides contactless deposition of material droplets (ink) in very precise coordinates (high spatial resolution), allowing the fabrication of complex features.² This offers a highly tailorable manufacturing process as the printed features are based on a easily adjustable/editable digital file. Also, this manufacture approach is amenable for an in-space environment fabrication due to its low dependence on an operator, fast manufacturing time with low waste generation, easily scalable, highly/easily tunable, ability to print a variety of electronic inks (conductors and insulators) with minimal chance of cross contamination between materials and different types of sensors can be manufactured using the same printer.^3,4 Inkjet printing has the added advantage of allowing POC devices to be manufacture on a demand basis, optimizing resource use.

Here we present the first steps of the development of a print-on-demand 3-electrode electrochemical biosensor for the detection of cortisol, a stress biomarker.⁵ For these devices, 3 types of inks were use: multi walled carbon nanotubes (MWCNT), silver nanoparticles (AgNP) and SU-8. First, AgNP ink was printed onto a kapton substrate to define the reference electrode (RE), electrical contact pads and electrical connections. Second, MWCNT ink was printed to generate the working electrode (WE) and the counter electrode (CE). Third, the SU-8 ink is used to encapsulate and insulate the AgNP electrical connectors. Lastly, the surface of the WE was modified with an antibody anti-cortisol using EDC/NHS coupling chemistry. The surface modification and detection of cortisol is identified through a measurable electrical change such as current and impedance, etc.⁶

(1) Demontis, G. C.; Germani, M. M.; Caiani, E. G.; Barravecchia, I.; Passino, C.; Angeloni, D. Human Pathophysiological Adaptations to the Space Environment. Front. Physiol. 2017, 8, 1–17.

(2) Raut, N. C.; Al-Shamery, K. Inkjet Printing Metals on Flexible Materials for Plastic and Paper Electronics. J. Mater. Chem. C 2018, 6 (7), 1618–1641.

(3) Li, J.; Rossignol, F.; Macdonald, J. Inkjet Printing for Biosensor Fabrication: Combining Chemistry and Technology for Advanced Manufacturing. Lab Chip 2015, 15 (12), 2538–2558.

(4) Khan, S.; Ali, S.; Bermak, A. Recent Developments in Printing Flexible and Wearable Sensing Electronics for Healthcare Applications. Sensors (Basel). 2019, 19 (5).

(5) Hellhammer, D. H.; Wüst, S.; Kudielka, B. M. Salivary Cortisol as a Biomarker in Stress Research. Psychoneuroendocrinology 2009, 34 (2), 163–171.

(6) Kimmel, D. W.; LeBlanc, G.; Meschievitz, M. E.; Cliffel, D. E. Electrochemical Sensors and Biosensors. Anal. Chem. 2012, 84, 685–707.