Skin in the diagnostics game: Wearable biosensor nano- and microsystems for medical diagnostics

The skin, as the largest and most accessible organ in the human body, contains biofluids rich in biomarkers useful not only in diagnosis and monitoring of diseases, but also in profiling an individual's wellbeing. Advancements in micro- and nanotechnology research have underpinned the development of multifunctional wearable sensing devices. Those sensors may allow monitoring of physiological parameters from different skin sections such as epidermis, dermis and hypodermis by sampling various bodily fluids. Our review summarizes current advances in wearable biosensors for on-skin analysis of sweat, transdermal monitoring of interstitial fluid and analysis of subcutaneous fluids via implanted devices. The review is divided into three main parts describing biosensors acting on the different skin sections. Each part focuses on recent scientific and technological advancements in the wearable biosensing field by highlighting critical challenges as well as providing information on how these barriers are being addressed by the research community.