Near-infrared (NIR) fluorescent probes offer advantages of high photon penetration, reduced light scattering and minimal autofluorescence from living tissues, rendering them valuable for noninvasive mapping of molecular events, assessment of therapeutic efficacy, and monitoring of disease progression in animal models. This review provides an overview of the recent development of the design and optical property of the different classes of NIR fluorescent nanoprobes associated with in vivo imaging applications.

Transparent bicontinuous nanostructured polymeric materials have been synthesized via the polymerization of bicontinuous microemulsions of appropriate formulations. The use of polymerizable zwitterionic betaine surfactant of (acryloyloxy)undecyldimethylammonio acetate (AUDMAA) and cationic surfactant (acryloyloxy)undecyltrimethylammonium bromide (AUTMAB) is the key factor to the success of the stable polymerization. The nanostructures (pores) of polymeric materials were characterized by SEM, thermoporometry, and membrane-filtration of poly(ethylene glycol) having different molecular weights. The pore size or the width of the polymerized bicontinuous microemulsions (transparent solid polymers) increased substantially from about 20 to 100 nm with the increase of the water content (20−60 wt %) or NaCl concentration (0−2 wt %) in precursor microemulsions. In contrast, the incorporation of 12 wt % HEMA in the precursor microemulsion reduced the pore size drastically to about 2 nm. This total polymerization (except water) approach enables one to synthesize various bicontinuous nanostructures (2−150 nm) of transparent polymeric materials by simply adjusting the concentrations of water, HEMA, polymerizable surfactant, and electrolyte in precursor bicontinuous microemulsions.

An effective photochemical route is reported here for size-controlled synthesis of nonaqueous colloidal gold particles in a highly polar and viscous medium, formamide in the presence of poly(vinylpyrrolidone). The effective photoreduction of AuCl4 -in the nonaqueous system is attributed to the higher degree of dissociation of AuCl4 -in formamide and the direct reduction by the photogenerated free radicals from the coordinated formamide molecules. Evident photochemical formation of gold particles was not achieved in dimethylformamide because AuCl4 -cannot be dissociated in dimethylformamide, having no amino group but an aldehyde group as in formamide. Under similar conditions, uniform gold particles were prepared much more easily in formamide than in water, and the photoreduction of AuCl4 -was also carried out much more completely in formamide than in water. A Coulomb staircase was clearly observed at room temperature on the nonaqueously grown uniform gold particles of 12 nm, but this behavior did not occur on the aqueously grown gold particles of similar size. This new photochemical route is also very effective to produce other uniform transition-metal particles such as silver, palladium, and platinum.