Defining the ability of simian virus 40 (SV40) to transform human cells has become of even greater importance with the increased understanding that this virus may play a role in some human malignancies. This report documents the requirement for viral small-t (ST) antigen in large-T (LT)-driven transformation of primary fibroblasts, a requirement that cannot be met by a well-known oncogene, c-Ha-ras (EJ-ras), which can cooperate with LT in rodent systems. The cellular gene telomerase is not essential for transformation, although transformed clones are not immortal without it. Similarly, an immortal mesothelial cell line has been developed using LT and telomerase. Immortalized mesothelial cells are morphologically normal, but can be transformed by introduction of ST, or ST + ras, but not by ras alone. It is likely that ST will be required along with LT for transformation of most human cell types.

Tip-enhanced Raman spectroscopy (TERS) has recently become one of the most important tools for analyzing advanced nano-devices and nano-materials, because it allows strong enhancement of weak Raman signal from the nanometric volume of a sample. However, consistent enhancement in TERS is still an issue and scientists have been struggling to fabricate good tips for reliable, strong and reproducible enhancement. There is a strong need to study the morphology and the arrangement of metal nanostructures near the tip apex for efficient plasmonic enhancement in TERS. Here, we present a study on the metal grains attached to the tip surface for producing higher and much consistent enhancement in TERS. Our study shows that the plasmonic enhancement strongly depends on the number of grains and on the their separations. We found through simulations that multiple grains arranged closely but discretely on a dielectric probe act as an efficient plasmonic antenna and that enhancement in TERS is maximum for an optimized number of grains. The number of grains and the nano-gap between them are crucial for reproducible enhancement. This promising result, which we also demonstrate and prove by experiments, will bring TERS to a new level, where it can be utilized with more confidence of large reproducible enhancement for those nano-sized samples that have extremely weak Raman scattering.

There have been increasing interests in applying gold nanoparticles in biological research, drug delivery, and therapy. As the interaction of gold nanoparticles with cells relies on properties of nanoparticles, the cytotoxicity is complex and still under debating. In this work, we investigate the cytotoxicity of gold nanoparticles of different encapsulations, surface charge states, sizes and shapes to both human HEp-2 and canine MDCK cells. We found that cetyltrimethylammonium-bromide- (CTAB-) encapsulated gold nanorods (GNRs) were relatively higher cytotoxic than GNRs undergone further polymer coating and citrate stabilized gold nanospheres (GNSs). The toxicity of CTAB-encapsulated GNRs was mainly caused by CTAB on GNRs' surface but not free CTAB in the solution. No obvious difference was found among GNRs of different aspect ratios. Time-lapse study revealed that cell death caused by GNRs occurred predominately within one hour through apoptosis, whereas cell death by free CTAB was in a time- and dose-dependent manner. Both positively and negatively surface-charged polymer-coated GNRs (PSS-GNRs and PAH-PSS-GNRs) showed similar levels of cytotoxic, suggesting the significance of surface functionality rather than surface charge in this case.

Abstract. Two-photon luminescence ͑TPL͒ from gold nanorods shows considerable potential in biological imaging. We study the imaging of gold nanorods in MadinDarby canine kidney ͑MDCK͒ cells using fluorescence lifetime imaging microscopy ͑FLIM͒. FLIM provides images with better contrast and sensitivity than intensity imaging. The characteristic fluorescence lifetime of gold nanorods is found to be less than 100 ps, which can be used to distinguish gold nanorods from other fluorescent labels and endogenous fluorophores in lifetime imaging. Gold nanorods are of great interest for optical imaging due to their remarkable absorption and scattering in the visible and near-infrared ͑NIR͒ regions enhanced by surface plasmon resonance ͑SPR͒.1,2 NIR band absorption between 700 and 900 nm, a spectral window that permits photons to penetrate biological tissues with relatively high transmission, induces two-photon luminescence with strong intensity.3,4 Two-photon luminescence ͑TPL͒ from gold nanorods has been found to be sensitive to the polarization of the incident excitation.4,5 All these properties make gold nanorods attractive probes for invitro and in-vivo imaging. 4,6,7 But so far, most related work has utilized traditional microscopy methods such as confocal microscopy and near-field optical microscopy imaging. [8][9][10][11][12] In contrast to traditional imaging methods based on fluorescence intensity, fluorescence lifetime imaging microscopy ͑FLIM͒ provides contrast according to the fluorescence decay time, with the term "fluorescence" usually being associated with aromatic dye molecules. Here we have an inorganic system for which the term "luminescence" is usually applied. Lifetime imaging can be integrated with confocal microscopy, two-photon excitation microscopy, and other microscope systems. The luminescence ͑or fluorescence͒ decay time is the average time a fluorophore remains in the excited state after excitation. It does not change on intensity variations, and therefore lifetime measurements are not dependent on the local concentration of fluorophores, bleaching, the optical path of the microscope, the local excitation light intensity, or on the local luminescence detection efficiency. Also, the fluorescence decay time for aromatic molecules usually depends usefully on the intrinsic characteristics of the fluorophore and local environment ͑the local viscosity, pH, or refractive index [13][14][15] ͒ as well as interactions with other molecules, such as collisional or energy transfer quenching.16,17 Thus, as well as being able to distinguish spectrally overlapping fluorophores, 18 imaging of the fluorescence lifetime can be used to probe the surroundings and dynamical processes of a fluorophore. 19,20 Unlike electron microscopy, fluorescence/ luminescence techniques can be used in situ.In this work, we use FLIM to visualize gold nanorods taken up by Madin-Darby canine kidney ͑MDCK͒ cells. A very short luminescence decay time of TPL from gold nanorods is observed. Compared with the lifetime of 4Ј-6-diamidino-2-...

We report a fluorescent probe for mRNA detection. It consists of a gold nanorod (GNR) functionalized with fluorophore-labeled hairpin oligonucleotides (hpDNA) that are complementary to the mRNA of a target gene. This nanoprobe was found to be sensitive to a complementary oligonucleotide, as indicated by significant changes in both fluorescence intensity and lifetime. The influence of the surface density of hpDNA on the performance of this nanoprobe was investigated, suggesting that high hybridization efficiency could be achieved at a relatively low surface loading density of hpDNA. However, steady-state fluorescence spectroscopy revealed better overall performance, in terms of sensitivity and detection range, for nanoprobes with higher hairpin coverage. Time-resolved fluorescence lifetime spectroscopy revealed significant lifetime changes of the fluorophore upon hybridization of hpDNA with targets, providing further insight on the hybridization kinetics of the probe as well as the quenching efficiency of GNRs.