In the first research, the pulsed-laser ablation (PLA) method was used as a facile and green approach to prepare oxide-free copper nanoparticles (Cu ), and was performed by laser ablation of a copper target in aqueous solutions of DNA bases (adenine, cytosine, and thymine). The structural analyses reveal that the in situ adsorption of the cytosine and thymine molecules on the surface of Cu , although improving the stability of the colloids, cannot prevent the interaction of Cu with the dissolved oxygen. However, the nanoparticles obtained in the aqueous solution of adenine are free from an oxide layer, indicating the high stabilizing effect of adenine molecules on the copper nanoparticles. FT-IR spectroscopy was used to study the mode of interaction of the DNA bases with the Cu . Our results show that the participation of the nitrogen atoms of the DNA bases in the coordination to the Cu surface has a significant effect on the stabilization of the Cu . In the case of adenine, the FT-IR spectra reveal that the excellent stabilizing effect originates from the ability of adenine to protect the laser-generated Cu through its –NH2 group and imidazole nitrogen atoms. Thymine has no such nitrogen atoms and the NH2 group of cytosine cannot significantly participate in the coordination to the Cu surface. To the best of our knowledge, this is the first report on the preparation of oxide-free copper nanoparticles by the laser ablation of bulk copper in aqueous solutions containing small neutral biomolecules. The synthesized Cu /adenine shows effective antibacterial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. In the second research, a stable colloidal solution of gold nanoparticle–3,4-dihydroxyphenylalanine (DOPA) zwitterion conjugates (Au NP–z-DOPA) was prepared using nanosecond-laser ablation of a gold target in an aqueous solution of zwitterionic DOPA (z-DOPA). The produced Au NP–z-DOPA conjugates were characterized by spectroscopic methods and transmission electron microscopy. The spectroscopic data revealed that the Au strongly interact with z-DOPA, which lead to a significant change in the electronic structure of z-DOPA. The results showed that the adsorbed z-DOPA is highly stable against the oxidation in the aqueous solution for a long period of time (at least two weeks), indicating a significant stabilizing e?ect of the Au surface on this zwitterion. To obtain more insight into the interaction of DOPA with the surface of Au , the electronic structures and geometries of z-DOPA and the other forms of DOPA (including uncharged (u-DOPA), cationic (c-DOPA), and anionic (a-DOPA) forms) adsorbed on the Au(111) nanosurface were determined using the ONIOM calculations. The geometry and electronic structure of each DOPA form are significantly affected by the surface upon the adsorption process. The analysis of the frontier orbitals confirmed the significant stabilizing effect of the Au on z-DOPA. In addition, the calculations are consistent with the variations observed in the recorded absorption spectra of the z-DOPA due to its interaction with the Au . One of the important findings of our calculations is that the Au nanosurface does not necessarily have a stabilizing effect on all DOPA forms. Finally, the in vitro cytotoxicity of the free z-DOPA and the Au NP–z-DOPA conjugates against the Jurkat T-cells was evaluated using an MTT assay. In comparison to the free z-DOPA with an IC50 165 ?g/mL, the Au NP–z-DOPA conjugates (containing only 0.6 ?g/mL adsorbed z-DOPA) exhibit a potent anticancer activity against the Jurkat T-cells with an IC50 value of 8.3 ± 2 ?g/mL. In the third research, a ?uorescent-superparamagnetic nanocomposite was prepared by decoration of silica-coated Fe3O4 nanoparticles with highly ?uorescent gold nanoparticles (Au ). The nanocomposite was embedded in a poly(ethylene glycol)-diacrylate (PEG-DA) layer. The outer polyethylene glycol layer not only e?ectively enhanced the stability of the nanocomposite but also provided a convenient and versatile functional groups to readily conjugate KH1C12 aptamer onto the nanocomposite to get cell accessibility. The nanocomposite was fully characterized by different spectroscopic techniques, including X-ray di?raction, energy dispersive analysis using X-rays, transmission electron microscopy, ?eld-emission scanning electron microscopy, and magnetic measurements. The nanocomposite was successfully used for specific recognition and magnetic removal of HL-60 cells from a homogeneous mixture of HL-60 and K562 cells.