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Development of multifunctional nanomaterials, one of the most interesting and advanced research areas in the field of nanotechnology, is anticipated to revolutionize cancer diagnosis and treatment. Gold nanoparticles (AuNPs) are now being widely utilized in bio-imaging and phototherapy due to their tunable and highly sensitive optical and electronic properties (the surface plasmon resonance). As a new concept, termed "theranostics," multifunctional AuNPs may contain diagnostic and therapeutic functions that can be integrated into one system, thereby simultaneously facilitating diagnosis and therapy and monitoring therapeutic responses. In this review, the important properties of AuNPs relevant to diagnostic and phototherapeutic applications such as structure, shape, optics, and surface chemistry are described. Barriers for translational development of theranostic AuNPs and recent advances in the application of AuNPs for cancer diagnosis, photothermal, and photodynamic therapy are discussed.

We have investigated the spectral dispersion of real and imaginary parts of third-order nonlinear optical susceptibility of silver nanospherical particles in the aqueous solution using Z-scan and antiresonant ring interferometric nonlinear spectroscopic (ARINS) techniques by femtosecond pulses from the modelocked Ti:Sapphire laser over the spectral range of 720-820 nm. The observed characteristic of imaginary part shows a peak at similar to 766 nm which coincides with the peak of spectral dispersion of real part induced thermally. The observed peak in the dispersion of nonlinear absorption coefficient at similar to 766 nm is attributed to the two-photon absorption. This two-photon resonance peak is attributed to l =2 plasmon (quadrupolar mode) arising from the phase retardation effects in the spherical nanoparticles present in our polydispersed sample with their diameters (80 +/- 20 nm) beyond the quasi-static limit. (C) 2012 Elsevier B.V. All rights reserved.