Fluorescent monolayer protected gold nanoparticles – Preparation and structure elucidation

A novel N-substituted 4-methoxy-1,8-naphthalimide (NAFTA 8) especially designed for fluorescent labeling of gold nanoparticles has been synthesized. NAFTA 8 bears a long methylene chain at the imide N atom and has a terminal SH group, which enables its chemical binding to gold nanostructures. The longest wavelength absorption maximum of NAFTA 8 in chloroform is at 370 nm, the fluorescent maximum is at 430 nm and the fluorescent quantum yield is 0.95. The newly synthesized fluorophore is applied for functionalization of gold nanoparticles with diameter 1.5 ± 0.5 nm prepared through chemical reduction. The obtained Monolayer Protected Clusters are characterized by elemental analysis, TEM, XPS, FT-IR, absorption and fluorescence spectroscopy. The performed investigations provide evidence for the formation of chemical bond between the thiol ligand and the gold surface. They also show that the obtained metal/dielectric 3D structures are highly fluorescent

Functionalized Au/Ag nanocages as a novel fluorescence and SERS dual probe for sensing

We obtained chitosan-protected Au/Ag nanocages (NCs), i.e., hollow and porous metallic nanoparticles, by galvanic replacement reaction. Subsequently, we functionalized the NCs with a fluorescent derivative of 4-methoxy-1,8-naphtalimide (NAFTA6). The plasmonic properties of these structures, which exhibit an extinction maximum in the 700–800 nm range, allowed their use as SERS active substrates for excitation at 785 nm and an efficient identification of the vibrational bands of NAFTA6, in spite of the low ligand concentration (<10-5 M). Furthermore, NAFTA6 could also be identified from its fluorescence emission. The proposed functionalization with fluorescent compounds opens the way to the application of metal NCs using double-wavelength detection. Namely, Raman spectroscopy in the near infrared and fluorescence emission in the visible region, with considerable potential especially for in vivo medical applications, as the plasmonic band is centered in the visible light region where biological fluids and tissues are transparent