This thesis presents new results on searches for lepton-flavour-violating particle decays, performed in the LHCb experiment at CERN. Two analyses are discussed in detail. The first one concerns the B(s,d)->e mu decay. No evidence of signal is observed and two upper limits are set, respectively for the Bd and Bs mesons: BF(Bd -> e mu) < 1.0(1.3)x10^(-9) and BF(Bs -> e mu) < 6.0(7.2)x10^(-9). The second analysis concerns the baryon sector: the Lambdab -> Lambda e mu decay is searched. This study is currently under review in the LHCb collaboration. The whole procedure is described here in detail and its final results will be added when available. Furthermore, the present thesis contains a description and the results of the quality assurance process for the production of mats of scintillating fibres for the SciFi, a new tracker for the LHCb detector developed in view of the Run III of LHC.