The National Institute of Standards and Technology is researching this cool technique for detecting alien life by exploiting the handedness of organic molecules.
Many organic molecules such as amino acids and sugars have two versions which are symmetrical, have the same basic atomic composition, but have structures which are mirror images of each other, referred to as right-handed or left-handed. Only one of the mirror images can play its role in organic processes. A preponderance of the right-handed or left-handed version of a given molecule is a marker of organic activity.
An aggregation of organic matter reflects light differently based on the proportion of right-handed or left-handed molecules.
This is pretty exciting, if in fact this signature can be detected at galactic scale. It sounds as though, so far, this is a lab trick at very short distances.