Jian-Long Xiao

Dynamics of cancer cell filopodia characterized by super-resolution bright-field optical microscopy

We explore the dynamics of cancer cell filopodia of diameters around 200 nm by using super-resolution bright-field optical microscopy. The high contrast required by the super-resolution image-restoration process is from the nanometer topographic sensitivity of non-interferometric widefield optical profilometry, rather than fluorescence labeling. Because the image-acquisition rate of this bright-field system is 20 frames/min, fast cellular dynamics can be captured and then analyzed. We successfully observe the growth and activities of the filopodia of a CL1-0 lung cancer cell. In the culturing condition, we measure that the filopodia exhibit an average elongation rate of 90 nm/sec, and an average shrinkage rate of 75 nm/sec. With the treatment of epidermal growth factor, the elongation and shrinkage rates increase to 110 nm/sec and 100 nm/sec respectively. We also find that the treatment of epidermal growth factor raises the number of filopodia by nearly a factor of 2, which implies enhancement of cell motility.

Using optical profilometry to characterize cell membrane roughness influenced by amyloid-beta 42 aggregates and electric fields

Abstract. The membrane roughness of Neuro-2a neroblastoma cells is measured by using noninterferometric wide-field optical profilometry. The cells are treated with the fibril and oligomer conformers of amyloid-beta (Aβ) 42, which is a peptide of 42 amino acids related to the development of Alzheimer’s disease. We find that both the Aβ42 fibrils and Aβ42 oligomers reduced the cell membrane roughness, but the effect of Aβ42 oligomers was faster and stronger than that of the fibrils. We also apply direct-current electric field (dcEF) stimulations on the cells. A dcEF of 300  mV/mm can increase the membrane roughness under the treatment of Aβ42. These results suggest that Aβ42 can decrease the membrane compliance of live neuroblastoma cells, and dcEFs may counteract this effect.

Motion of cancer-cell lamellipodia perturbed by laser light of two wavelengths

We employ 405 and 1064 nm laser light to perturb the motions of lung cancer cell lamellipodia. The 405 nm light causes lamellipodial retractions while the 1064 nm light enhances protrusions. With the observation of actin distributions in the lamellipodia, we find that the 1064 nm laser light increases the density of actin near the illuminated site, while the 405 nm light reduces the actin distribution.

Guiding the migration of adherent cells by using optical micropatterns

We employed static and dynamic optical patterns to guide the motion of adherent cells. With the illumination intensity of 0.2 W/cm2 and propelling patterns moving at a speed of 2.8 μm/h, nearly 70% of the tested cells could be guided along a static optical pattern. We also demonstrated the cell guidance in an L-shaped optical channel. Comparing the result with only the static optical channel and that with both the static channel and moving optical pushes, we ascertained that the optical pushes placed at the start and turning points are necessary for effective optical cell guidance.

Optically micropatterned culture of adherent cells

We used a liquid-crystal spatial light modulator to project 473 nm light patterns surrounding a region of adherent cells and achieved an arbitrarily micropatterned cell culture. For a group of ∼60 cells, the cell boundaries fit the pattern of light within 15% deviation of the side length. We also demonstrated a wound-healing experiment with a definite starting temporal point by using this technique. While observing mitochondrial structures in the illuminated cells, we found that the 473 nm light damaged the integrity of mitochondria and thus prohibited cell proliferation in the illuminated region.

Three-dimensional tracking and temporal analysis of liposomal transport in live cells using bright-field imaging.

Gold nanoparticles (AuNPs) confined in liposomes of diameters around 200 nm produce strong scattering signal owing to surface plasmon resonance, and therefore bright‐field optical tracking of the AuNP‐encapsulating liposomes can be conducted in living cells. Using an optical profiling technique called noninterferometric wide‐field optical profilometry and a bright‐field tracking algorithm, the polynomial‐fit Gaussian weight method, we analyze three‐dimensional (3D) motion of such liposomes in living fibroblasts. The positioning accuracy in three dimensions is nearly 20 nm. We tag the liposome membranes with fibroblast growth factor‐1 and reveal the intracellular transportation processes toward or away from the nucleus. On the basis of a temporal analysis of the intracellular 3D trajectories of AuNP‐encapsulating liposomes, we identify directed and diffusive motions in the transportation processes. Microsc. Res. Tech., 2010.

Measurement of membrane rigidity on trapped unilamellar phospholipid vesicles by using differential confocal microscopy

We use optical tweezers to trap a unilamellar phospholipid vesicle and measure the out-of-plane thermal fluctuations by using differential confocal microscopy. Bending moduli of the lipid membranes are calculated directly from the mean-square values of the fluctuation amplitudes. Owing to the refractive index contrast between the inner and outer solutions of the vesicle, optical tweezers trap the vesicle laterally and improve the reliability of the measured fluctuation amplitudes along the optical axis. Bending moduli of membranes in gel or fluid phases obtained by the combination of differential confocal microscopy and optical tweezers are close to those reported previously. We also obtain the bending modulus of sphingomyelin membranes in the gel phase, which was not reported previously.

Cell migration guidance by using optical micropatterns

We used static and dynamic optical micropatterns to guide the migration of adherent cells. With 0.2 W/cm2 intensity and a 2.8 μm/h pattern speed, 70% of the tested cells were guided along an optical pattern.

Optical measurement on membrane roughness of neuroblastoma cells treated with amyloid-beta peptide and electric fields

We measured the membrane roughness of neuroblastoma cells by non-interferometric wide-field optical profilometry. We found that the peptide related to Alzheimers disease, Amyloid-beta 42, reduces membrane roughness, but direct-current electrical fields recover this effect.

Gold-coated polystyrene bead array and the investigation of their plasmon coupling abilities

Many of SERS nanoparticles took advantage of the surface roughness for the significant improvement of their Raman sensing ability. Nevertheless, few papers analyzed the characteristics of surface roughness nanostructures that contribute to the SERS. Thus, this paper investigates the characteristics of the corrugated polystyrene bead (PSB) array etched by a series of oxygen plasma etching time for giving a criterion to fabricate appropriate SERS-active nanoparticles. Three factors were considered in this paper: (1) the effect of plasma coupling among neighboring particles, (2) the vertical surface roughness of nanocorrugations, and (3) the pitch size, the lateral surface roughness, of nanocorrugations. By the analysis of SEM and AFM images, those factors were quantifiable. The correlation coefficient between each factor and SERS Raman enhancement was also investigated to verify that the pitch size of nanocorrugations (ranging from ~6 nm to ~12 nm on the surface of PSBs) dominates the SERS enhancement. Therefore, the maximum improvement of Raman intensity that derives from surface roughness treatment is 12 times compared to smooth surface. Moreover, it has a high enhancement factor of ~106.