Previous cancer chemoprevention studies from our laboratories and by other investigators have demonstrated that the extract of red beetroot (Beta vulgaris L.), the FDA approved red food color E162, can be effective in suppressing the development of multi-organ tumors in experimental animals. To further explore this finding, we have compared the cytotoxic effect of the red beetroot extract with anticancer drug, doxorubicin (adriamycin) in the androgen-independent human prostate cancer cells (PC-3) and in the well-established estrogen receptor-positive human breast cancer cells (MCF-7). This red colored anticancer antibiotic was selected for comparative cytotoxic study because its chemical structure with a planar configuration of an aromatic chromophore attached to a sugar molecule is remarkably similar to that of betanin, the beetroot extract constituent primarily responsible for its red color. Both doxorubicin and the beetroot extract exhibited a dose-dependent cytotoxic effect in the two cancer cell lines tested. Although the cytotoxicity of the beetroot extract was significantly lower when compared to doxorubicin, it continued to decrease the growth rate of the PC-3 cells (3.7% in 3 days vs. 12.5% in 7 days) when tested at the concentration of 29 µg/ml. In contrast, doxorubicin, at the same concentration level, completely inhibited the growth of the PC-3 cells in three days. Similarly, comparative studies in the normal human skin FC and liver HC cell lines showed that the beetroot extract had significantly lower cytotoxic effect than doxorubicin (8.6% vs. 100%, respectively, at 29 µg/ml concentration of each, three-day test period). The results suggest that betanin, the major betacyanin constituent, may play an important role in the cytotoxicity exhibited by the red beetroot extract. Further studies are needed to evaluate the chemopreventive potentials of the beetroot extract when used alone or in combination with doxorubicin to mitigate the toxic side-effects of the latter.

Numerical simulations of the frequency modulation atomic force microscope, including the whole dynamical regulation by the electronics, show that the cantilever dynamics is conditionally stable and that there is a direct link between the frequency shift and the conservative tip-sample interaction. However, a soft coupling between the electronics and the nonlinearity of the interaction may significantly affect the damping. A resonance between the scan speed and the response time of the system can provide a simple explanation for the spatial shift and contrast inversion between topographical and damping images, and for the extreme sensitivity of the damping to a tip change. DOI: 10.1103/PhysRevLett.89.146104 PACS numbers: 68.37.Ef, 07.79.Lh, 87.64.Dz The rapid advance in nanoscale physics has constantly triggered innovative refinement of tools for detecting novel atomic scale phenomena. Scanning tunneling microscopy (STM) [1] exploits the exponential distance decay of the tip-sample tunneling current, and its confinement to the foremost atoms of the tip can provide atomically resolved images of conducting surfaces. Atomic force microscopy (AFM) [2] was devised to extend these capabilities to more general surfaces but the tip-sample contact area is often too large to permit atomic resolution. To remedy the situation, the amplitude modulation (AM) technique [3] (also known as tapping mode), where the change in amplitude of a vibrating cantilever due to the interaction is used for imaging the sample, has been adapted for AFM. However, the nonlinearity of the tipsample force can lead to a complicated dynamical behavior [4] because two stable oscillation states coexist in many situations of interest.Frequency modulation (FM) AFM [5] (also called noncontact AFM) has achieved the long-standing goal of true atomic resolution with AFM in UHV [6,7], as well as the direct measurement of the covalent bonding between the tip apex and sample atoms [8]. In FM-AFM, the dynamical system is more complicated because the oscillation amplitude of the cantilever is kept constant and the separation is regulated by measuring the change in the resonance frequency of the cantilever caused by the interaction force. Because the cantilever motion is highly sinusoidal, the measured frequency shift can be related to the interaction using perturbation theory [9][10][11].In FM-AFM, the amount of excitation necessary to keep the oscillation amplitude constant (damping signal) can also be used as an imaging signal [12 -17], but its magnitude and characteristics have been more difficult to quantify and interpret than the frequency shift. In principle, the damping signal could unleash important information about the surface such as that related to the phonon local density of states in complete analogy with STM [18,19], although preliminary studies indicate that its magnitude is small compared to those reported in experiments. A number of mechanisms such as adhesion hysteresis [10,20 -22] or Joule dissipation have been proposed to account for the...

We experimentally reveal that the short-range attractive force between a Si tip and a Si(111)-7 7 surface is enhanced at specified bias voltages; we conduct force spectroscopy based on noncontact atomic force microscopy with changing bias voltage at a fixed separation. The spectra exhibit prominent peaks and a broad peak, which are attributed to quantum mechanical resonance as the energy levels of sample surface states are tuned to those of the tip states by shifting the Fermi level through changing bias voltage, and to the resonating states over a lowered tunneling barrier, respectively. DOI: 10.1103/PhysRevLett.93.256101 PACS numbers: 68.37.Ps, 73.20.-r, 81.05.Cy The adhesive force between two solid bodies at close separations is one of the most fundamental interactions in condensed matter, which involve chemical bond, metallic bond, van der Waals force, electrostatic force, and so on. For a simple case of chemical covalent bonding between two isolated atoms, Pauling successfully introduced the concept of quantum mechanical resonance between their electronic states at close energy levels [1]. By extending this concept of the resonance to condensed matter, the force interaction between two bodies at small separations can be regarded as the resonating overlap of their electron wave functions.Since the advent of scanning tunneling microscopy (STM) [2] and atomic force microscopy (AFM) [3], the adhesive force and the tunneling conductance between two bodies have simultaneously been examined by bringing a tip closer to a sample, i.e., by taking force-distance curves [4]. For the correlation between the force and the tunneling current, Chen theoretically evaluated it on the basis of the quantum mechanical resonance between the surface electronic states of both tip and sample through the tunneling barrier [5]. The force and the tunneling conductance can be derived from the overlapping of their wave functions at close energy levels through a tunneling barrier: the Bardeen's matrix element, which is used to evaluate the tunneling current, is fundamentally equal to the Heisenberg's resonance energy E, corresponding to the covalent bonding. The correlation between the force and the tunneling current has been shown experimentally for metals [6 -8], but it is still under debate: the decay length of force is larger than that of typical chemical interactions, and the patched charges around a tip may change the interaction.It is noted that the energy level of the surface electronic state in one body of condensed matter can be shifted relatively with respect to the other by changing bias voltage, corresponding to the Fermi level shift. Since the resonance occurs between the electronic states having closer energy levels, the quantum mechanical resonance is expected to be enhanced by tuning the energy levels of surface electronic states in the two bodies through the Fermi level shift. Thus, the interaction between two bodies should be analyzed by force spectroscopy with a capability of changing bias voltage.The noncontact (n...

No abstract