Gold Nanoparticle Probes Display Efficient Photoluminescence

Investigators at Boston College in Chestnut Hill, Mass., suggest that gold nanoparticles are attractive substitutes for fluorophores or semiconductor nanoparticles as labels in the imaging of microscopic biological structures. In a study published in Nano Letters online May 18, they report that multiphoton-absorption-induced luminescence in 2.5- to 125-nm-diameter gold nanoparticles offers comparable emission intensities to and higher quantum efficiencies than fluorophores and better short- and long-term photostability than semiconductor nanoparticles.

To measure the response of the gold nanoparticles, the researchers excited thin films of uncoated and silica-coated samples using a homebuilt Ti:sapphire laser that produced sub-100-fs pulses of 790-nm radiation at a repetition rate of 76 MHz. An inverted microscope with a 1.3 NA, 40× objective, both from Carl Zeiss GmbH of Jena, Germany, served as the optical setup. Single-photon-counting avalanche photodiodes and a fiber optic spectrometer collected luminescence data and emission spectra, respectively.

Logarithmic plots of the emission intensity versus laser power showed that the excitation is a three-photon process, enabling strong emission from relatively weak excitation pulses. Employing synthesis techniques to produce gold nanoparticles with the desired asymmetries to exhibit electric field enhancements in the near-IR, the metal structures promise to enable in vivo imaging at the single-molecule level, the researchers suggest.