Optical tweezers in a new light

Abstract

Optical tweezers were invented in the mid-1980s by Arthur Ashkin and co-workers at the Bell Telephone Laboratories. Since then there has been a steady stream of developments and applications, particularly in the biological field. In the last five years, work using optical tweezers has increased significantly and they are becoming a mainstream tool within biological and nanotechnological fields. This introductory article seeks to explain the underpinning mechanism behind optical tweezers, present some recent technological advances and speculate on future applications within both biological and non-biological fields.     

Time series shapelets: a novel technique that allows accurate, interpretable and fast classification

Classification of time series has been attracting great interest over the past decade. While dozens of techniques have been introduced, recent empirical evidence has strongly suggested that the simple nearest neighbor algorithm is very difficult to beat for most time series problems, especially for large-scale datasets. While this may be considered good news, given the simplicity of implementing the nearest neighbor algorithm, there are some negative consequences of this. First, the nearest neighbor algorithm requires storing and searching the entire dataset, resulting in a high time and space complexity that limits its applicability, especially on resource-limited sensors. Second, beyond mere classification accuracy, we often wish to gain some insight into the data and to make the classification result more explainable, which global characteristics of the nearest neighbor cannot provide. In this work we introduce a new time series primitive, time series shapelets, which addresses these limitations. Informally, shapelets are time series subsequences which are in some sense maximally representative of a class. We can use the distance to the shapelet, rather than the distance to the nearest neighbor to classify objects. As we shall show with extensive empirical evaluations in diverse domains, classification algorithms based on the time series shapelet primitives can be interpretable, more accurate, and significantly faster than state-of-the-art classifiers.     

Expression of the brain creatine kinase gene in rat RT4 peripheral neurotumor cell lines and its modulation by cell confluence

Creatine kinases (CK) catalyze the reversible transfer of a high energy phosphate group between creatine phosphate and ADP to regenerate ATP in cell types where the requirements for ATP are extensive and/or sudden. Previously, we have shown in primary rat brain cell cultures that brain CK (CKB) mRNA levels are highest in astrocytes and oligodendrocytes and much lower in neuronal cells. However, little is known of the factors which regulate CKB expression in the central nervous system and peripheral nervous system. To begin to investigate these factors, we asked in this report (1) if this pattern of CKB expression was also characteristic of some established glial and neuronal cell lines derived from the PNS; (2) whether CKB expression could be rapidly modulated by culture conditions, and (3) if CKB is expressed in cells with characteristics of glial cell progenitors. In subconfluent cells, CKB mRNA and enzyme activity were found to be high in both the rat RT4 peripheral neurotumor stem cell RT4-AC36A and its glial cell derivative RT4-D6. Conversely, CKB mRNA and activity were 5- and 8-fold lower, respectively, in the neuronal derivative RT4-E5 and, more dramatically, CKB was undetectable in neuronal RT4-B8 cells. Maintaining RT4-D6 glial cells at confluence rapidly increased CKB enzyme activity by 7-fold, such that D6 cells contained about 25% of the CKB level in lysates prepared from either whole adult rat brain or primary cultures of rat brain astrocytes. The levels of CKB mRNA and immunoreactive protein were also correspondingly increased in confluent D6 cells. These confluence-mediated increases in CKB appeared to be due to cell-cell contact and not the depletion of serum growth factors or an increase in intracellular cAMP. This study indicates that CKB expression is highest in cells displaying glial properties and can be rapidly modulated by appropriate culture conditions. The results are discussed in relation to the factors which may regulate CKB expression in vivo.     

Factors influencing the small‐scale melt spinning of poly(ε‐caprolactone) monofilament fibres

Some of the main factors affecting the small‐scale melt spinning of poly(ε‐caprolactone), PCL, monofilament fibres have been studied. These factors included spinning temperature, extrusion rate, take‐up rate and draw ratio. The underlying influence of the polymer's own characteristic properties, in particular its chemical structure, transition temperatures (T_g, T_m) and crystallizability, were also interpreted within the context of the melt spinning process. Physically, the as‐spun fibres obtained were uniform in diameter and smooth in surface appearance. They were also semi‐crystalline (>50%) in morphology. Mechanically, however, they were still very weak and highly extensible. Subsequent off‐line cold‐drawing at room temperature introduced the required degree of molecular orientation to reinforce the fibres, yielding tensile strengths of approaching 300 MPa. PCL fibres of precisely controlled physical dimensions and matrix morphology are attracting increasing interest for use in biomedical applications. This paper describes how this control can be achieved through the processing operation. Copyright © 2003 Society of Chemical Industry     

Relative efficiency of tumor cell killing in vitro by two enzyme-prodrug systems delivered by identical adenovirus vectors

Enzyme-prodrug therapy for the treatment of cancer is an experimental procedure that is under intensive investigation. However, the relative merits of the various systems for use under specific conditions are still being determined. We have compared the efficacy of cell killing by the herpesvirus thymidine kinase (HSVTK)/ganciclovir and the purine nucleoside phosphorylase (PNP)/9-(beta-M-2-deoxy-erythropentofuranosyl)6-methylpurine enzyme/prodrug systems. These were chosen because of their differential dependence on DNA replication for their mechanism of action. The HSVTK and PNP genes, expressed from the identical prostate-specific antigen promoter, were transduced into human prostate and breast cancers cells using the same human adenovirus vector. The kinetics of cell killing in the presence of the respective prodrugs was monitored using a nondestructive assay that measured total cell bioactivity. The PNP/9-(beta-D-2-deoxy-erythropentofuranosyl)6-methylpurine system was clearly superior in its ability to cause cell death in vitro. Cells were killed in about half the time and at a 5-10-fold lower input of virus relative to the HSVTK/ganciclovir system. The PNP system may offer advantages for the treatment of slow-growing tumors in which the daily proliferative rate is low or in situations in which gene delivery or expression is inefficient.     

Effect of selenium status and supplementation with high-selenium yeast on plasma homocysteine and B vitamin concentrations in the UK elderly

The level of plasma total homocysteine (tHcy), long known to be B vitamin dependent, has recently been shown to be inversely associated with plasma selenium (Se) concentration in human subjects. We therefore, chose to investigate the interaction between Se, tHcy and B vitamins in a double-blind, placebo-controlled trial where 501 healthy UK elderly volunteers were randomly allocated to receive 100, 200, or 300 microg Se/day as high-Se-yeast, or placebo-yeast for 6 months. Plasma Se, tHcy, folate, vitamin B-12, pyridoxal-5'-phosphate (PLP) and its catabolite, 4-pyridoxic acid, were measured in all participants at baseline and in samples from the placebo, 100 and 300 microg Se/day groups, at follow-up. At baseline, Se was inversely correlated with tHcy but only in males (p < 0.001). Before supplementation, tHcy concentration was significantly lower in the highest compared to the lowest Se tertile in males (p < 0.05), and in females when folate concentrations were also in the top tertile (p < 0.05). The effect of folate, PLP and vitamin B-12 concentrations on plasma tHcy correlated with Se concentration at baseline. After 6 months of Se supplementation, only Se concentration had changed significantly. Supplementation with Se does not affect tHcy concentration in the UK elderly population.