Tilt angle dependent three-dimensional position detection of a trapped cylindrical particle in a focused laser beam

We investigated theoretically the applicability of an optically trapped cylindrical particle as a local probe in photonic force microscopy. To do this we calculated the far-field scattering from a subwavelength-sized dielectric cylinder in a highly focused laser field. From this we obtained interferometric three-dimensional-position detection signals and compared these to signals calculated for a spherical particle. We have calculated the accuracy to which the position of an optically trapped cylinder can be determined, as a function of the cylinder’s orientational fluctuations. The position accuracy is better than a few nanometers for tilt angle fluctuations up to several degrees. Our study is relevant for trapping experiments, where the influence of angle fluctuations needs to be estimated

Control of relative radiation pressure in optical traps : application to phagocytic membrane binding studies

We show how to control the relative radiation pressure and thereby the stable trap position of an optically trapped bead by variation of the mean incident axial photon momentum. The thermal position fluctuations of a trapped bead are recorded by a three-dimensional back focal plane interferometry. The interferometric detection signals are in agreement with predictions based on an extended Mie theory. Depending on the application, the unique and the linear range of such a detection system can be optimized by controlling the trap position of the bead. We use this method to investigate in three dimensions the binding of beads to membranes of living cells during phagocytosis. We found that independent of the bead coating (IgG, complement, LPS, avidin) the most frequent initial mechanical response of the cell was a downward pulling of the bead into the cell. The time delay between binding and response was on average 2 seconds

Estrogen dependent expression of the receptor tyrosine kinase axl in normal and malignant human breast

Summary Background: Axl, a member of a family of receptor tyrosine kinases characterized by an extracellular domain resembling cell adhesion molecules and an intracellular conserved tyrosine kinase domain has been reported to induce cell proliferation and transformation. In mice, axl is expressed in the normal mammary gland and over-expressed in aggressive mammary tumors. Patients and methods: We have investigated the expression of axl immunohistochemically in 23 normal human breast samples and in 111 consecutive breast carcinomas. Expression of axl was correlated with tumour characteristics (lymph node involvement, stage, grade) and immunohistochemical expression of ER, PR, Ki-67 and c-erbB-2. Results: In normal tissue, axl localizes to the membrane of breast epithelial cells. Axl protein shows membrane associated staining in high correlation (P = 0.004) with the expression of the estrogen receptor (ER). Axl expression was found in a subset of breast carcinomas and was also correlated with high significance (P < 0.0001) with the presence of ER. Conclusion: Our results suggest that axl may serve as a mediator of estrogen stimulation preventing the completion of the breast epithelial life cycle and that estrogen induced axl expression may give a survival signal to cancerous cells, preventing them from dying through apoptosi

An optically actuated surface scanning probe

We demonstrate the use of an extended, optically trapped probe that is capable of imaging surface topography with nanometre precision, whilst applying ultra-low, femto-Newton sized forces. This degree of precision and sensitivity is acquired through three distinct strategies. First, the probe itself is shaped in such a way as to soften the trap along the sensing axis and stiffen it in transverse directions. Next, these characteristics are enhanced by selectively position clamping independent motions of the probe. Finally, force clamping is used to refine the surface contact response. Detailed analyses are presented for each of these mechanisms. To test our sensor, we scan it laterally over a calibration sample consisting of a series of graduated steps, and demonstrate a height resolution of ∼ 11 nm. Using equipartition theory, we estimate that an average force of only ∼ 140 fN is exerted on the sample during the scan, making this technique ideal for the investigation of delicate biological samples

Grazing Endophyte Infested Tall Fescue and Changes in Bovine Blood Components and Gain

Tall fescue (Festuca arundinacea) is utilized on more than 15 million ha of pasture in the eastern USA and over 80% of the plants in this area are infested with the endophyte Neotyphodium coenophialum. Tall fescue toxicosis results from consumption of the infested (E+) grass host and is an important problem that causes considerable economic loss to producers. However, the agronomic attributes of tall fescue make it an attractive forage because of its ability to withstand cool temperatures, drought, poor soil conditions and intensive defoliation. There is need to understand mechanisms of animal physiology that are affected by the alkaloids produced by the endophyte/grass association. Blood serum samples were collected from steers (Bos taurus) grazing either E+ or endophyte free (E-) tall fescue in spring and summer during three consecutive years and were related to animal performance. Consistent and significant changes associated with E+ tall fescue were noted for daily gain, prolactin, albumin/globulin ratio, alanine aminotransferase, cholesterol, creatinine, globulin, total bilirubin, total serum protein, copper, red blood cells, mean corpuscular volume, mean corpuscular hemoglobin, and eosinophils. Thus, repeatable changes that occur in serum biochemical and blood cellular values of cattle grazing E+ tall fescue were identified and will aid in understanding the pathogenesis of the toxicosis

Potential use of sorghum in school feeding programs

To encourage the cultivation of sorghum, which is more drought tolerant than maize, it is desirable to replace a portion of the maize used in school feeding programmes with sorghum. The immediate constraint was the acceptability of sorghum among school children. A set of sensory taste trials were established to evaluate the acceptability of sorghum in breakfast porridge (uji) and stiff porridge (ugali) used for lunches at three schools in Tanzania. A sample of 106 children participated in the trials. Each received uji made from both dehulled and hulled grain. On a different day each received ugali made from both dehulled and hulled grain. Almost 98% of children found the sorghum acceptable as a replacement for maize in breakfast and lunch meals. It is hoped to substitute 10% of the maize used in the school feeding programme with sorghum rising to 50% in the next years