Abstract
<title>Abstract</title> <p>pH is a crucial indicator for assessing the acidity or alkalinity of a solution. In certain emerging testing scenarios, it is necessary to develop new detection methods to accommodate their specific testing environments.The synthesized carbon dots（CDs）derived from natural plant materials—scallion leaves, which exhibited excellent optical sensing performance under both acidic and alkaline conditions. The results showed that the carbon dots could detect pH values ranging from 2-6 and 8-12 respectively. The sensing mechanism may be attributed to protonation-deprotonation and aggregation effects. Satisfactory results were achieved when testing actual samples. It is applicable to pH measurement of trace solutions, biomass solutions and other special liquids with wide detection range, low cost, easy operation and favorable biocompatibility.</p>