Polydimethylsiloxane doped with colloidal CdSe/CdS nanocrystals is proposed as high-luminescent and biocompatible nanocomposite. A physical mixing procedure has been adopted to realize the optically active material and spectral and time-resolved optical analysis has been carried out in order to proof that nanocrystals quantum properties are preserved into the polymeric host matrix. Biocompatibility tests have shown no cadmium release in water ambient and no differences have been observed in cell viability cultured on pure PDMS substrates and on nanocomposite films. The obtained results let us envision possible applications of the proposed material as luminescent substrate for label-free cell imaging compatible with the most common optical microscopy techniques.