Figure 3.

a) Sweat and blood glucose correlation in the same subject. b) Various biomarkers in biofluids, such as sweat, saliva, and tears. c) Scheme of pH and temperature sensors. d) Stretchable pH sensors on PDMS substrate. e) Tattoo‐based ammonium sensor. f) Enzymatic glucose sensor. a) Adapted with permission.^{[ 120 ]} Copyright 2019, ACS. c) Aadapted with permission.^{[ 141 ]} Copyright 2017, ACS. d) Reproduced with permission.^{[ 139 ]} Copyright 2018, Elsevier. e) Reproduced with permission.^{[ 152 ]} Copyright 2013, Royal Society of Chemistry. f) Reproduced with permission.^{[ 153 ]} Copyright 2019, Wiley‐VCH.