ARAMENDIA Pedro Francisco
congresos y reuniones científicas
Interaction of gold nanoparticles with photochemically active molecules
Congreso; XI Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2012
Interaction of gold nanoparticles with photochemically activemoleculesSimoncelli, Sabrina1; Roberti, María Julia1; Aramendía, Pedro F.11INQUIMAE y DQIAyQF. FCEN. UBA. Ciudad Universitaria. Buenos Aires.simoncelli@qi.fcen.uba.arThe interaction of gold nanoparticles (NP) with photochemically active molecules hasbeen extensively studied in recent years not only for the basic interest of understanding theinteraction modes between nanostructure and molecule but also for the practical possibilitiesof increasing the detection limit in microscopy, to prolong the imaging time, and to improvesensor development. The aim of this work is to explore the influence of Au NP plasmon in theisomerization rate of photochromic systems.The influence of Au NP in the isomerization rate of photochromic systems was studiedby using pulsed excitation and measurements from the ps to ms timescales. Experimentswere performed in three systems: a push-pull azobenzene, a carbocyanine, and a spiropyran,as representative of systems with different expected influence on the isomerization rate. Flashphotolysis experiments monitoring the back thermal reaction rate of 4-(dimethylamino)-4´-(nitro)-azobenzene, n-DAB, when increasing nanoparticle concentration were performed.Laser pulse energy, temperature, pH and Au NP diameter where taken into consideration. Theresults suggest that nanoparticles with diameters higher than 30 nm, increase the decay rate.To study the effect of NP in the efficiency of 1,1, -dimethyloxadicarbocyanine iodide (DODCI)isomerization ()ISO), the lifetime of the excited singlet state,WS1, and fluorescence lifetime, WF,as a function of NP concentration were studied. Experiments using time-resolved fluorescenceshowed a decrease in WF when increasing the (NP) / (DODCI) ratio. In addition, experienceswith ultra-fast kinetics in the presence of NP resulted in a slight lifetime decrease of the WS1.Finally, the merocyanine (MC) photoisomer of 1,3?,3?-trimethyl-6-nitrospiro-[2H-1-benzopyran-2,2?-indoline], overlaps its absorption band with the plasmon of spherical Au NP of 40 to 100nm diameter. Thus its weak fluorescence can be enhanced by the presence of NP, thereforefacilitating their detection. Since the lifetime of the MC form is in the order of minutes, theirevolution over time was followed by fluorescence imaging sequences and an increase in theMC lifetime was observed, Figure 1.80006000400020000Figure 1.- Left: Wide field fluorescence microscopy image of a thin PPMA film containing SPspin coated onto a glass coverslip functionalized with 80 nm Au NP after irradiation with UVlight. Right: Typical thermal decay of MC to SP alone (round) and over a NP (triangles).These results suggest that a highly polarizable structure, such as NP, can in principleaccelerate or slow down the isomerization lifetime of dyes which have a great dipole momentchange between the stable form and the transition state of the isomerization.