Vitamin B-12 (VB12) as a biomolecule was successfully applied to modify the as -synthesized ZnO nanoparticles (NPs). VB12-ZnO conjugate was fabricated by a solution based method, the phase component of which was independent of the modification process, as shown by X-ray diffraction (XRD) analysis. The amount of loaded VB12 on ZnO NPs was measured by thermal gravimetry (TGA) to be 25 wt.%. Fourier transform infrared (FTIR) spectroscopy was used to probe the interaction of ZnO NPs with VB12. Although the sensitization process did not cause the appearance of any intense new peak in the FTIR results, the traces of a new band at 756 cm(-1) and also the intensification of the peak at 3411 cm(-1) (in comparison to ZnO spectrum) confirmed the formation of some new bands between NPs and VB12 molecules. The UV-vis spectroscopy revealed that VB12-ZnO conjugate absorbed light irradiation at around 272, 380 and 454 nm. The third one is situated in the visible light region, originating from the conjugation between ZnO NPs and the functional ring of VB12. The photoluminescence (PL) behavior was affected by the sensitization process, shifting the PL peak of ZnO NPs toward a higher wavelength and increasing its intensity. (C) 2016 Elsevier Ltd. All rights reserved.