Wearable sweat sensors are emerging as promising platforms for personalized and real-time tracking of evolving health and fitness parameters. While most wearable sweat sensors focus on tracking biomarker concentration profiles, sweat secretion rate is a key metric with broad implications for assessing hydration, cardiac, and neural conditions. Here we present a wearable microfluidic sensor for continuous sweat rate measurement. A discrete impedimetric sensing scheme relying on interdigitated electrodes within a microfluidic sweat collector allows for precise and selective sweat rate measurement across a broad physiological range. Integration of a manually activated pressure pump to expel sweat from the device prevents sensor saturation and enables continuous sweat rate tracking over hours. By enabling broad range and prolonged sweat rate measurement, this platform tackles a key obstacle to realizing meaningful and actionable sweat sensing for applications in exercise physiology and medicine.

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Manufacturing of microfluidic based diagnostic devices requires small tolerances and uniform quality to guarantee reliable and repeatable test results. This work describes characterization of morphological changes that occur to a hot embossed PMMA microfluidic channel after solvent lamination with a PMMA lid. A noncontact cross-sectional analysis of the lidded microfluidic device was performed by optical coherence tomography (OCT). The solvent induced morphology change led to a porous structure in bottom corners of hot-embossed channels, which allowed a fluid to absorb in the material. The measurements of solvent diffusion showed faster diffusion rate at the corners of the channel, in which the accumulated stress during the embossing process was the highest. The stress profile was verified by simulation of von Mises stresses during a molding phase of a hot embossing process. The porous structure with increased fluid diffusion has an unwanted effect on bioassay result, e.g. when detection molecules leak into the substrate thus leading to unspecific signal on chip. OCT was found to be a valuable, non-destructive imaging method to monitor solvent diffusion process and lamination process quality.

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We have developed a microfluidics based sampling system for tissue analytics. The proof-of-concept of the sampling system was demonstrated by extracting lipid samples from tissue biopsies. The sample collection system consists of a disposable silicon based multiport microneedle integrated with polymer microfluidics. The polymethyl methacrylate polymer microfluidic chip has a 10 μl sample reservoir and actuation membranes for liquid pumping. A special automated robotic system was developed to control the positioning of the needle and the sampling procedure on preselected spots on the tissue. Real breast cancer tissue samples were used to test the feasibility of the sampling system. We successfully measured indicative cancer biomarkers from the tissue surface. Phosphatidylcholine and phosphoethanolamine were extracted from the tissue membrane with methyl tert-butyl ether solvent and detected by mass spectrometry. In the future, this tool could be used in characterization of preoperative biopsies and tumour tissues removed during surgery.