The only compact solution I know of is a one-off device that creates a voltage pulse using a slab of piezo crystal and a layer of plastic explosive. This has been used.
You asked for science-based, so you get other stuff. Most life is not particularly EMP sensitive. The Carrington event fried telegraph and telephone services over the whole world, but nobody noticed apart from the lights in the sky. Look for something else. If this life-form is artificial, maybe it was made with some 'backdoor' vulnerability to keep it safe in the lab, such as being sensitive to green light.