**2.2. Synthesis of plasmonic-fluorescent and fluorescent-magnetic hybrid nanostructures**

Plasmonic-fluorescent hybrid nanostructures have seen a renewed interest in photocatalytic degradation of organic contaminants and photocatalytic water splitting.[4] Banin et al.[1, 3] synthesized various classes of these materials via photodeposition of metals on semiconductors. Au/CdSe/CdS hybrid nanorods were synthesized through growing Au precursors on the reactive facets exposed tips of the seeded rods.[23] Under UV excitation, large Au domains were exclusively deposited at one end of the seeded CdSe/CdS rod because of electron migration to one of the reactive facets of the tips. The strong Au-Se coordination allowed Au precursors at high concentration to grow further on the side facets of the seeds. Au-CdSe pyramids were obtained by growth and reductive transformation of a gold shell around a CdSe pyramid under electron beam irradiation. The deposition of the Au clusters along the anisotropic semiconductors was strongly influenced by reaction temperature and ligand-mediated defect sites. Decreasing the amount of surfactant allowed the Au tips to interact and coalesce, forming disordered networks of the fused hybrid nanostructures. The selective growth of the Au precursors on the tips of the CdSe rod, tetrapod, pyramid exhibited a significant modification of the optical property compared to the corresponding singe components.

**Figure 3** shows Au-CdSe rod- and pyramid-shaped hybrids synthesized by Klinke et al.[24] via growth and reductive transformation of the Au shell around the pyramidal CdSe nanocrystals in the presence of chlorine under either electron beam irradiation or addition of reducing agent. The size of the deposited Au dots can be tuned from 1.4 to 3.9 nm by varying the synthesis conditions, such as ligands and shape of the CdSe. The shape rod and pyramid were thermodynamically favored for the size-controlled growth of Au precursors

**nanostructures** 

the corresponding singe components.

nitrate (Co(NO3)2·6H2O or Ni(NO3)2·6H2O) in octadecylamine used as both solvent and surfactant. The formation of the hybrid structures was illustrated by metal-induced reduction process namely, octadecylamine-supplied electron cloud surrounded Au atoms reduced transition metal ions to form the nanohybrids. The strong magnetism of the plasmonic-magnetic nanohybrids and the CO superior catalytic activity of the Au-Co coreshells were showed as a result of incorporating magnetic heterometals into gold particles. The authors [22] also synthesized bifunctional Au-Fe3O4 nanohybrids through the conjugation of Au particles to thiol-modified Fe3O4 nanoparticles. Lysine contained both amino and carboxylic groups played dual roles as both linker and capping agent in attaching metals on Fe2O3 particles. The hybrid nanostructures can be used for magnetic separation of biosubstances and for protein separation. The authors [27] also synthesized hexagonal pyramid-like shaped Au-ZnO nanohybrids based on the growth of ZnO particles derived from a mixture of zinc acetate/oleylamine/dodecanol on Au seeds. The nanopyramids composed of Au particles as the tip and hexagonal ZnO pyramid as the tail. The Au-ZnO hybrid nanopyramids with homogeneous composition and controlled

morphology showed better photocatalytic efficiency than ZnO nanocrystals.

**2.2. Synthesis of plasmonic-fluorescent and fluorescent-magnetic hybrid** 

Plasmonic-fluorescent hybrid nanostructures have seen a renewed interest in photocatalytic degradation of organic contaminants and photocatalytic water splitting.[4] Banin et al.[1, 3] synthesized various classes of these materials via photodeposition of metals on semiconductors. Au/CdSe/CdS hybrid nanorods were synthesized through growing Au precursors on the reactive facets exposed tips of the seeded rods.[23] Under UV excitation, large Au domains were exclusively deposited at one end of the seeded CdSe/CdS rod because of electron migration to one of the reactive facets of the tips. The strong Au-Se coordination allowed Au precursors at high concentration to grow further on the side facets of the seeds. Au-CdSe pyramids were obtained by growth and reductive transformation of a gold shell around a CdSe pyramid under electron beam irradiation. The deposition of the Au clusters along the anisotropic semiconductors was strongly influenced by reaction temperature and ligand-mediated defect sites. Decreasing the amount of surfactant allowed the Au tips to interact and coalesce, forming disordered networks of the fused hybrid nanostructures. The selective growth of the Au precursors on the tips of the CdSe rod, tetrapod, pyramid exhibited a significant modification of the optical property compared to

**Figure 3** shows Au-CdSe rod- and pyramid-shaped hybrids synthesized by Klinke et al.[24] via growth and reductive transformation of the Au shell around the pyramidal CdSe nanocrystals in the presence of chlorine under either electron beam irradiation or addition of reducing agent. The size of the deposited Au dots can be tuned from 1.4 to 3.9 nm by varying the synthesis conditions, such as ligands and shape of the CdSe. The shape rod and pyramid were thermodynamically favored for the size-controlled growth of Au precursors

**Figure 3.** Growth of Au shell around pyramidal CdSe nanocrystals. (a) Scheme of the Au growth process onto CdSe nanocrystals. (b) Incubation of CdSe with Au-tetra-*n*-butylammonium borohydride/dodecyltrimethylammonium bromide led to Au clusters positioned at apexes of the CdSe pyramids. (c) STEM image of Au/CdSe hybrids with sharp angles as reactive sites for the nucleation of Au particles. Reproduced with permission from ref. [24]. Copyright 2010, The Royal Society of Chemistry.

on the corners and tips of the CdSe nanocrystals through the suitable choice of the metal precursor and the surface ligand concentration. The pyramid structure provided relatively sharp angles which were highly reactive sites for the nucleation of the gold particles. Banin et al.[25] also synthesized cage-shaped Ru/Cu2S nanohybrids by adding Ru(acac)3 to Cu2S seed suspension in octadecylamine. Metallic Ru selectively grew on the crystal edges of the Cu2S nanocages to form a symmetrical cage around a Cu2S core. The cage formation could be due to the capping of thiol ligands on the Cu2S facets to block the growth of these crystal facets. These Ru/Cu2S nanocages were used as an excellent electrocatalyst for H2O2 sensing with catalytic activity higher than Cu2S electrode.

The recent progress made in the synthesis of magnetic-fluorescent nanohybrids with combined magneto-transport properties has been reported. Cozzoli et al.[26] reported the two-step seeded-growth for the selective synthesis of Co-tipped CdSe/CdS core-shell nanorods. A two-step procedure consisted of injection of tri-n-octyl phosphine sulphide/CdSe seeds to Cd-surfactant complexes and heated at 350-380 °C to form CdSe/CdS core-shells. Co clusters were then attached with the CdSe/CdS seeds by injecting Co2(CO)8 solution into octadecene solvent containing CdSe/CdS seeds at 200-240 °C under inert atmosphere. An excess volume of oleic acid was added to the growing mixture to stabilize the hybrid nanostructures formed after reaction completion. The formation of the

nanohybrids with matchstick-like topology was predicted by crystal-oriented-attachment occurred the directional fusion of the generated Co nanocrystals to the nanorod tips. These Co-tipped CdSe/CdS heterostructures exhibited unusual room-temperature ferromagnetism and uorescent emission despite photoexcited charge transfer from the semiconductor to the metal domain. Talapin et al.[27] synthesized FePt/PbS and FePt/PbSe nanohybrids with magneto-transport properties by coupling ferromagnetic FePt particles with either PbS or PbSe in form of core-shells or dumbbells. The formation of the hybrid products by injecting bis(trimethylsilyl) sulfide to reaction mixture containing FePt nanoparticles, oleic acid, Pboleate complex dissolved in octadecene at 120-150 °C. The nanohybrid shape was controlled by capping of the ligand on the surface of the FePt seeds and the reaction temperature. These magnet-in-the-semiconductor hybrid nanostructures showed semiconductor-type transport properties with magnetoresistance characteristic of combining the advantages of both functional components. The maghemite-metal sulphide (ZnS, CdS, HgS) nanohybrids were synthesized by adding sulphur and appropriate metallorganic precursors to the Fe2O3 particles followed by heating treatment.[28] In other reports, the large lattice mismatch between Fe2O3 and metal sulphide resulted in the formation of non-centrosymmetric nanostructures. The formations of trimers and oligomers were observed for ZnS and dimers for CdS and HgS nanocomposites. Alloy-cadmium selenide core-shells including FePt/CdSe, NiPt/CdSe, FePt/CdSe, NiPt/CdSe were synthesized by hydrolysis of cadmium stearate in oleylamine, hexadecylamine/octyl ether, 1,2-hexadecandiol in the presence of alloy seeds.[29]

Functional Inorganic Nanohybrids for Biomedical Diagnosis 319

The nanohybrid colloids could be soluble in water by adsorbing amphiphilic polymers onto hydrophobic molecules-capped nanohybrids. The amphiphilic polymer adsorption are carried out through hydrophobic interaction of hydrocarbon chains and van der Waals force between the molecules. The desorption of polymer molecules from the nanoparticles is usually prevented because numerous contact points formed from the interactions of organic linkers and polymer chains. Advantage of this approach is mainly not dependent on the types of the inorganic hybrid cores and the organic linkers, and the physiochemical surface properties of the coated particles are significantly unchanged. A popular example is the gold particles in aqueous media prepared by citrate reduction. Citrate ions adsorbed on the gold surface resulted in their negative charge and colloidal stability within several years by electrostatic repulsion. The citrate layer was replaced by stronger-binding ligands of mercaptocarboxylic acids. The surface modification of the particles with mercaptocarboxylic acids allowed for achieving concentrated particle solutions, that can precipitate out of particles by salt-induced aggregation and redissolved in low-salt buffers.[30] The surface functionalization of TOP/TOPO-capped CdSe/ZnS quantum dots was substituted phosphine-based hydrophobic ligands with hydrophilic mercaptocarboxylic acid molecules.[31] The quantum dots in aqueous solution stabilized with mercaptoacetic acid

Polyethylene glycol (PEG) is a linear polymer consisted of ethylene oxide units and well soluble in water. PEG is high biocompatibility due to its inertness and non-toxic properties.[32] Apart from the post-modification approach by covalent chemistry, PEGmodified nanoparticles can be obtained by PEG-contained ligand molecules with functional group that can bind to the particle surface.[33] Owing to the solubility of PEG itself, the PEG-coated particles can also be dispersed in polar organic solvents.[34] **Figure 4** shows the modular design toward The synthesis of the amphiphilic polymer of poly(maleic anhydridealt-1-octadecene) (PMAO)-polyethylene glycol was carried out through reaction between maleic anhydride and primary amine-terminated polyethylene glycol methyl ethers and subsequent coating of PMAO-polyethylene glycol amphiphilic polymer with hydrophobic ligand-capped quantum dots.[35] The functionalized materials dissolved in water had the same optical spectra and quantum yield as those pre-synthesized quantum dots. The watersoluble encapsulated nanoparticles contain free carboxylic acid groups for conjugating anti-Her2 antibody to the polyethylene glycol-coated nanoparticles. The antibody-conjugated quantum dots were used as a probe to recognize human breast cancer cells with Her2 receptor with nonspecific binding of polyethylene glycol with cell receptors on the particle surface. Mattoussi et al.[33] achieved the capping of water-soluble ligand of mixed dihydrolipoic acid (DHLA) and poly(ethylene glycol) (PEG) on quantum dots. These ligands are consist of a poly(ethylene glycol) (PEG) segment attached anchoring DHLA group on one end to drive binding to the quantum dot. Cap exchange with these hydrophilic ligands made quantum dots to be stabilized in water over extended periods of time and over a broad pH range. The quantum dots capped with DHLA-PEG-biotin interacted with streptavidin coupled to proteins which were subsequently taken up by live cells. Yu et al.

were modified by co-adsorption of polyethylene glycol and peptides.

**3.1. Polymer adsorption** 
