The present invention relates to compounds for and a method of detecting beta-lactamase activity in a sample. The sample is contacted with a nanoparticulate tag. The nanoparticulate tag comprises a metal or a combination of metals, or it comprises a nanotube of a metal, boron nitride and/or carbon. The respective metal is capable of forming one of a covalent bond, a coordinative bond and a non-covalent interaction with a thio or a seleno group. The sample is contacted with a compound of one of general formulas (I)-(III) and (VII)-(IX). At least one beta-lactam moiety of the compound is cleaved by the beta-lactamase activity in the sample. As a result a cleavage moiety Z-A-Z, Z-A-Z—R15, Z-A-Z—R16, Z-A-Z—R17, Z-A-Z—R18 or Z-G-N(R8)R9 is released that is immobilised on the surface of the nanoparticulate tag by a covalent bond via a Z atom. The presence of beta-lactamase activity is determined based on the presence of the cleavage moiety immobilized onto the surface of the nanoparticulate tag.