Can ELISA be used to detect a plant enzyme? Creating assay for a new enzyme
I want to add something on top of Chris answer.

The production of an antibody it is usually a quite slow (and expensive) process, an alternative that worth to consider is phage display (https://en.wikipedia.org/wiki/Phage_display). Once you find the phage that effectively bind your protein of interest, you can use it instead of an antibody in what is called a Phage-ELISA assay.
However, mind that the ELISA (or Phage-ELISA) will give you information about the presence and the concentration of the enzyme, it will not give you any hint about its activity.