Disclosed herein are isotopically labeled calcofluor derivatives and uses of such to detect fungi, such as filamentous fungi, including Aspergillus species, such as by positron emission tomography (PET) scanning. In some examples, the disclosed compounds have a formula of wherein R1 is an amine, a hydroxyl group, a sulfide, a carboxylic acid, an amide, an alkyl, or aryl; R2 is —NHC(O)—R3—L or —C(O)NH—R3—L, wherein R3 is an aryl or an aliphatic group (such as alkyl); each R4 independently may be selected from halogen, aliphatic (such as alkyl), aryl, amine, hydroxyl, haloalkyl, carboxylic acid, amide, aralkyl, cyano, ester, thiol, thioether, or alkoxy; each R5 independently may be selected from hydrogen, aralkyl, alkyl, or aryl, with any one of the aralkyl, alkyl, or aryl groups optionally being substituted with any one of the substituents provided for R4; each n independently is 1, 2, 3, 4, or 5; and L is 18F or a chelator capable of chelating a radiolabel (such as chelators for [18F]AlF, 64Cu, 68Ga),1,4,7,10-tetraazacyclododecane-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-triacetic acid (NOTA).