A biospectral analysis was a medical scan to identify and verify organic and inorganic matter, including their bioelectric patterns.
In 2369 Data ran a biospectral analysis on the young quantum singularity lifeform who was trapped in the engine core of a Romulan warbird. (TNG: "Timescape")
In 2370, Ensign Martinez was ordered by Doctor Crusher to contact Doctor Selar and tell her she should perform a biospectral analysis on the dead body of Ned Quint. (TNG: "Sub Rosa")
Later that year, Lieutenant Barclay suggests a biospectral analysis on a solvent found dissolving a Bulkhead and Conduit in a Jefferies tube. The solvent turned out to be Worf's venom, as he was spraying it throughout the ship after becoming infected with Barclay's Protomorphosis Syndrome. (TNG: "Genesis")