Analysis of microneedles used for diagnosis in the scientific literature. (i) Classification based on a) type of microneedle used for diagnosis, b) type of biomarker for diagnosis, and c) testing environment. (ii) The different types of biomarkers identified for each type of microneedle: a) dissolvable, b) coated, c) hollow and d) solid. (iii) The different types of microneedles identified for each type of biomarker: a) collection of physiological parameters, b) collection of fluid, and c) collection of biomarker.