If you want to see state of the art 40 years ago there's Army M9 detector paper which is this concept applied to tape instead of fabric, and detecting multiple

If you want to see state of the art 40 years ago there's Army M9 detector paper which is this concept applied to tape instead of fabric, and detecting multiple chemical agents instead of lactate. Using pH to determine intensity is ingenious. My experience in the Army was 1) Supply is enough of a hassle under normal circumstances such that having to replace after it detects is a pain. 2) It was always unclear if a faint color change meant a minor exposure or some kind of contaminant laundry malfunction type thing.