We have developed uniform core/shell nanoparticles, consisting of a silica layer coating and pigments or magnetite core, using a water-in-oil microemulsion method. The nanoparticles are highly luminescent and photostable with the size ranging from 5 nm to 400 nm. Bioconjugation of these silica nanoparticles adds unique biofunctions with various molecules such as enzymes, antibodies, and DNA molecules. Significant advantages have been shown in using bioconjugated nanoparticles for biosensing and bioimaging, such as cell staining, DNA detection and separation, rapid single bacterium detection, and biotechnological application in DNA protection.

In this paper, we explore the possibility of using ultrasmall near-infrared (NIR) gold nanoclusters (AuNCs) as novel contrast imaging agents for tumor fluorescence imaging in vivo. The fluorescence imaging signal of the tail vein administrated AuNCs in living organisms can spectrally be well distinguished from the background with maximum emission wavelength at about 710 nm, and the high photostability of AuNCs promises continuous imaging in vivo. The uptake of AuNCs by the reticuloendothelial system is relatively low in comparison with other nanoparticle-based contrast imaging agents due to their ultrasmall hydrodynamic size (∼2.7 nm). Through the body weight change analysis, the results show that the body weight of the mice administrated with AuNCs has not been changed obviously in comparison with that of the control mice injected with PBS. Furthermore, using MDA-MB-45 and Hela tumor xenograft models, in vivo and ex vivo imaging studies show that the ultrasmall NIR AuNCs are able to be highly accumulated in the tumor areas, thanks to the enhanced permeability and retention (EPR) effects. And the tumor-to-background ratio is about 15 for 6 h postinjection. The results indicate that the ultrasmall NIR AuNCs appear as very promising contrast imaging agents for in vivo fluorescence tumor imaging.

The biodistribution and urinary excretion of different surface-modified silica nanoparticles (SiNPs) in mice were investigated in situ using an in vivo optical imaging system. Three types of surface-modified SiNPs, including OH-SiNPs, COOH-SiNPs, and PEG-SiNPs with a size of approximately 45 nm, have been prepared with RuBPY doped for imaging purposes. Intravenous (i.v.) injection of these SiNPs followed by fluorescence tracing in vivo using the Maestro in vivo imaging system indicated that OH-SiNPs, COOH-SiNPs, and PEG-SiNPs were all cleared from the systemic blood circulation, but that both the clearance time and subsequent biological organ deposition were dependent on the surface chemical modification of the SiNPs. Thus, for instance, the PEG-SiNPs exhibited relatively longer blood circulation times and lower uptake by the reticuloendothelial system organs than OH-SiNPs and COOH-SiNPs. More interestingly, in vivo real-time imaged dominant signal in bladder and urine excretion studies revealed that all three types of i.v.-injected SiNPs with a size of approximately 45 nm were partly excreted through the renal excretion route. These conclusions were further confirmed through ex vivo organ optical imaging and TEM imaging and energy-dispersed X-ray spectrum analysis of urine samples. These findings would have direct implications for the use of SiNPs as delivery systems and imaging tools in live animals. Furthermore, our results demonstrate that the in vivo optical imaging method is helpful for in vivo sensing the biological effects of SiNPs by using luminescent dye doped in the silica matrix as a synchronous signal.

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We have developed a novel method to protect DNA from cleavage using bioconjugated nanoparticles. Positively charged amino-modified silica nanoparticles have been directly prepared using water-in-oil microemulsion. Plasmid DNA can be easily enriched onto the positively charged nanoparticle surface, and the DNA strands are well protected from enzymatic cleavage. When incubated with nuclease enzyme for enzymatic cleavage, free plasmid DNA strands are completely cleaved, while those on the nanoparticle surfaces are intact. Our results clearly demonstrate unique properties of nanomaterials when combined with biomolecules. Our simple bionanotechnology will be highly useful in DNA separation, manipulation, and detection, and possibly in genetic engineering and gene therapy, as plasmid DNA can be protected in cellular environments without any change in its property.