Fig. 3: State-of-the-art wearable biosensor techniques.

a Colorimetric wearable patch that allows the detection of CKD biomarkers (creatinine and urea). Reproduced with permission from ref. ⁴⁷, copyright (Royal Society of Chemistry, 2019). b An ISF-based cystatin C sensor for POC tests. Reproduced with permission from ref. ⁴⁸, copyright (Elsevier, 2022). c Schematic illustration of a microneedle-type sensor that can detect biomarkers through an ISF. d An example of the microneedle-based ISF sensors. Reproduced under the terms of CC-BY 4.0 from ref. ⁵⁹, copyright (Elsevier, 2017). e An ISF extraction method using reverse iontophoresis. Applied current enables analytes to be secreted electro-osmotically to the skin surface along with ISF. f A sweat induction method based on iontophoresis. A topical current is applied between hydrogels containing a sweat-stimulating drug. This allows the drug to be injected beneath the skin surface, which makes glands secrete sweat. g An example of a wearable patch capable of extracting both the ISF and sweat. h All-laser-engraved microfluidic channels allow accurate real-time sweat analysis. Reproduced with permission from ref. ⁹, copyright (Springer Nature, 2020). i Inclusion of a hydrophilic filler in the microfluidic channel enables a natural sweat collection without exercise, thermal or chemically induced methods. Reproduced under the terms of CC-BY 4.0 from ref. ¹⁰, copyright (Springer Nature, 2021). j The use of OECTs as a transducer allows significant signal amplification, facilitating a highly sensitive biosensor. Reproduced with permission from ref. ³³, copyright (AAAS, 2018).