>The new method detects a unique sequence of atoms that bind the constituent molecules of the external membranes of living bacteria and eukarya cells. These constitute the vast majority of biological matter on Earth and include the kinds of lifeforms the scientists would also expect to find beyond our planet.

Yay!

>Once an organism dies, its IPL bonds disintegrate within hours, after which time they can no longer be detected, and a spike no longer appears in the instrument readout.

Boo!

So, you need lots of life to have a chance of seeing any alive. In which case, you probably can tell there's life already. Barring that, maybe a rover can zap rock patina and take a whiff.