GPT and metabolic disease: In regards to medical diagnostics, the development of PADs has largely focused on quantifying small compounds related to the detection and quantification of metabolic disease-related compounds (e.g., glucose), antigens or enzymes (such as alanine transaminase (ALT), prostate-specific antigen (PSA), microorganisms (e.g., Mycobacterium tuberculosis), viruses (e.g., hepatitis C virus), nucleotide analysis, and even semen analysis [9,10,11,12,13,14,15,16,17,18,19,20,21,22].