Bioconjugation and photonic applications of metal nanoparticles obtained by laser ablation in liquid solution

Metal nanoparticles (MNP) have a notable role in nanotechnology, due to their surface plasmon absorption (SPA) and to their surface chemistry. Functionalization and/or bioconjugation are key points for MNP applications, and they depend on surface accessibility and on solvents compatibility with the functional molecules. Often, synthesis methods based on chemical reduction require long and expensive processes to obtain the desired MNP functionalization. An alternative is represented by laser ablation synthesis of metal nanoparticles in liquid solution (LASiS).[1-3] LASiS provides stable colloidal solutions in water or in organic solvents, without any ligand or stabilizing molecule. Therefore MNP surface is usually free and functionalization occurs directly in the same solvent where MNP are obtained. These methods proved to be suitable for the conjugation in one step of MNP with a wide range of organic- and bio-molecules, also allowing the real time monitoring of the surface coverage process by UV-Vis spectroscopy. By fitting the UV-Vis spectra with a model based on the Mie theory, also the average size of MNP can be obtained with good accuracy.[1-3] The size of MNP obtained by LASiS can be further manipulated by a chemical free laser techniques inspired by top down and bottom up approaches. Gold nanoparticles (AuNP) with average radii of 4.5 nm were obtained in this way, which allowed the sensing of AuNP bioconjugation with bovine serum albumin (BSA) down to a ratio of 10:1 for AuNP:BSA.[4] The conjugation of AuNP with the thermo-responsive polymer poly-N-isopropylacrylamide was exploited for the temperature controlled cellular uptake of AuNP and the photothermal therapy of AuNP loaded human breast adenocarcinoma MCF7 cells.[5] Non functionalized AuNP have been studied for nonlinear optical applications. AuNP synthesized by LASiS in water solution of sodium dodecylsuphate have been used for the optical doping of polystirene opals, which allowed the controlled red shift of the photonic pseudogap. The strong SPA of AuNP also allowed the switching of the photonic bandgap upon irradiation with 9 ns laser pulses at 532 nm.[6] A blend of zinc phthalocyanines (ZnPc) and gold nanoparticles obtained by LASiS in tetrahydrofuran showed enhanced optical limiting properties at 532 nm (9 ns) due to a photoinduced redox mechanism between AuNP and ZnPc. This mechanism allowed the self healing of gold nanoparticles during the optical limiting measurements, though the laser induced photo-fragmentation of AuNP at the base of the limiting process.[7] 1. V. Amendola, S. Polizzi, M. Meneghetti; J. Phys. Chem. B 2006, 110, 7232 – 7237. 2. V. Amendola, S. Polizzi, M. Meneghetti; Langmuir 2007, 23, 6766 – 6770. 3. V. Amendola, G. A. Rizzi, S. Polizzi, M. Meneghetti; J. Phys. Chem. B 2005, 109, 23125 – 23128. 4. V. Amendola, M. Meneghetti; J. Mater. Chem. 2007, 17, 4705-4710. 5. S. Salmaso, P. Caliceti, V. Amendola, M. Meneghetti, G. Pasparakis, A. Cameron; Submitted. 6. V. Morandi, F. Marabelli, V. Amendola, M. Meneghetti, D. Comoretto; Adv. Func. Mater. 2007, 17, 2779–2786. 7. V. Amendola, S. Polizzi, K. Kadish, D. Dini, M. Hanack, M. Meneghetti; In preparation.