Small interfering RNA (siRNA) is potentially a promising tool in influencing gene expression with a high degree of target specificity. However, its poor intracellular uptake, instability in vivo, and non-specific immune stimulations impeded its effect in clinical applications. In this study, carbon nanotubes (CNTs) functionalized with two types of phospholipid-polyethylene glycol (PEG) have shown capabilities to stabilize siRNA in cell culture medium during the transfection and efficiently deliver siRNA into neuroblastoma and breast cancer cells. Moreover, the intrinsic optical properties of CNTs have been investigated through absorption and fluorescence measurements. We have found that the directly-functionalized groups play an important role on the fluorescence imaging of functionalized CNTs. The unique fluorescence imaging and high delivery efficiency make CNTs a promising material to deliver drugs and evaluate the treatment effect simultaneously.
DNA translocase SpoIIIE protein is a kind of motor proteins, which transports DNA from one side of
the membrane to the other side, so it plays an important role in cell division. In experiment, λDNA is
labeled on one end with biotin and the other with digoxigenin. In this work we study kinetics of DNA
translocase SpoIIIE by means of dual optical tweezers. In our experiment, λDNA is tethered between
streptavidin-coated polystyrene bead and antidigoxigenin-coated polystyrene bead held by dual optical
tweezers. One trap is immovable, and the other is movable. When SpoIIIE protein transports DNA, the
length of DNA changes. The length change can be calculated according to the displacement of the
trapped bead, which is detected by quadrant photodiode. When SpoIIIE transports DNA, DNA is
shortened by up to about 500nm, then as the translocation stops, the DNA returns to its normal length,
and this process repeats time and time again. The most probable speed that SpoIIIE transports DNA is
In the force measurement of protein-protein interaction, proteins are usually attached to microbeads, so the coated beads serve as both handles and force transducers. Due to the short interaction distance between proteins, the beads are usually close enough to each other. When dual-beam optical tweezers and quadrant photodiode detector are used to investigate the interaction of proteins, it is found that the signal of detected beads is greatly affected by adjacent beads. Analysis reveals that the contribution of two beads to the quadrant detector signal is independent. A method for extracting the real interaction signal from a disturbed one is presented. Based on this method, interaction between microtubules and AtMAP65-1 is measured. The results show that this method is useful for measuring short-distance interaction with the precision of piconewton and nanometer scales.
In force calibration, when triangular-wave input is exerted on the piezoelectric-driven substage, there is a damped oscillation superposed on the square-wave movement of the trapped bead in our experiments. This will bring about instability for well trapping bead and become the noise source of the bead signal. Consequently, the superposed vibration will influence the precision and the range of force that can be calibrated. In order to analyze derivation of the oscillation and solve it, a model of equivalent oscillator is put forward. Based on this model, we calculate the initial amplitude of oscillation and frequency spectra of the movement of trapped bead, which is well in agreement with the experimental one. We apply sinusoidal-wave input substituted for triangular one to the substage, as a result, oscillation disturbance is avoided effectively, so the trapping stability of optical trap increases and the range of calibrated force has been extended greatly.