Towards absolute calibration of optical tweezers

Aiming at absolute force calibration of optical tweezers, following a critical review of proposed theoretical models, we present and test the results of MDSA (Mie-Debye-Spherical Aberration) theory, an extension of a previous (MD) model, taking account of spherical aberration at the glass/water interface. This first-principles theory is formulated entirely in terms of experimentally accessible parameters (none adjustable). Careful experimental tests of the MDSA theory, undertaken at two laboratories, with very different setups, are described. A detailed description is given of the procedures employed to measure laser beam waist, local beam power at the transparent microspheres trapped by the tweezers, microsphere radius and the trap transverse stiffness, as a function of radius and height in the (inverted microscope) sample chamber. We find generally very good agreement with MDSA theory predictions, for a wide size range, from the Rayleigh domain to large radii, including the values most often employed in practice, and at different chamber heights, both with objective overfilling and underfilling. The results asymptotically approach geometrical optics in the mean over size intervals, as they should, and this already happens for size parameters not much larger than unity. MDSA predictions for the trapping threshold, position of stiffness peak, stiffness variation with height, multiple equilibrium points and `hopping' effects among them are verified. Remaining discrepancies are ascribed to focus degradation, possibly arising from objective aberrations in the infrared, not yet included in MDSA theory.Comment: 15 pages, 20 figure

Ocorrência e identificação de vespas predadoras (Hymenoptera: vespidae) em cafezal orgânico em formação (Coffea arabica L) e sua relação com a predação do bicho mineiro, Leucoptera coffeella (GUÉR.-MÈNEV., 1942)(Lepidoptera: Lyonetiidae).

Muitos estudos têm mostrado que o movimento de artrópodes benéficos das margens de entorno para dentro das plantações e maiores níveis de controle biológico são geralmente observados em culturas que são vizinhas a vegetação nativa. O objetivo deste trabalho foi observar a ocorrência de vespas (Hymenoptera: Vespidae) presentes em cafezal orgânico (Coffea arabica L.), sua identificação e relação com a predação do bicho-mineiro (Leucoptera coffeella (Guér.-Mènev., 1942)) (Lepidoptera: Lyonetiidae), através de coletas mensais, nos mesmos pontos, de folhas de cafeeiro para contagem de minas predadas e de vespas em armadilhas adesivas amarelas. Os resultados parciais obtidos entre 2004 (segundo ano de formação do cafezal) e 2006 mostraram que o total de vespas capturadas foi significativamente correlacionado linearmente com as minas predadas (P<0,01), indicando que o método de coleta de vespas com as armadilhas adesivas amarelas é recomendável para os estudos de vespas predadoras do bicho-mineiro em cafezais. Também podemos afirmar que Brachygastra augusti (de Saussure, 1854), Polybia occidentalis (Olivier, 1791) e Polybia paulista Ihering, 1986, foram as espécies de vespas que apresentaram correlação linear mais significativa em relação ao número de minas predadas, indicando que estas devem ser predadoras mais específicas do bicho-mineiro e talvez as mais importantes em cafezais orgânicos em formação

Absence of light exposure increases pathogenicity of Pseudomonas aeruginosa pneumonia-associated clinical isolates

Pseudomonas aeruginosa can alter its lifestyle in response to changes in environmental conditions. The switch to a pathogenic host-associated lifestyle can be triggered by the luminosity settings, resorting to at least one photoreceptor which senses light and regulates cellular processes. This study aimed to address how light exposure affects the dynamic and adaptability of two P. aeruginosa pneumonia-associated isolates, HB13 and HB15. A phenotypic characterization of two opposing growth conditions, constant illumination and intensity of full-spectrum light and total absence of light, was performed. Given the nature of P. aeruginosa pathogenicity, distinct fractions were characterized, and its inherent pathogenic potential screened by comparing induced morphological alterations and cytotoxicity against human pulmonary epithelial cells (A549 cell line). Growth in the dark promoted some virulence-associated traits (e.g., pigment production, LasA proteolytic activity), which, together with higher cytotoxicity of secreted fractions, supported an increased pathogenic potential in conditions that better mimic the lung microenvironment of P. aeruginosa. These preliminary findings evidenced that light exposure settings may influence the P. aeruginosa pathogenic potential, likely owing to differential production of virulence factors. Thus, this study raised awareness towards the importance in controlling light conditions during bacterial pathogenicity evaluation approaches, to more accurately interpret bacterial responses.FCT -Fundação para a Ciência e a Tecnologia(SFRH/BD/98558/2013)info:eu-repo/semantics/publishedVersio

Design of a disposable µPAD for on-hand quantification of urinary creatinine

In this work, a new microfluidic paper-based analytical device (μPAD) was developed for on-hand creatinine quantification in urine samples. This is clinically significant since creatinine monitorization in urine is an indicator of health condition, as kidney-failure [1]. When compared with conventional methods, this innovative μPAD approach is more accessible, portable, providing low-cost analysis and applicable to non-invasive biological fluids [2]. Additionally, the μPAD is environmentally friendly, as it uses small amounts of reagents, results in low waste production, and is disposal by incineration. The developed μPAD configuration consisted in two layers of filter paper discs (9.5 mm of diameter) staked into a hydrophilic unit and aligned into a laminated plastic pouch (hydrophobic zone), with 3 mm holes for the standard/sample insertion. The top layer served as a reservoir and the bottom layer contained the reagent (alkaline picrate). After the standard/sample loading, creatinine reacts with picric acid in alkaline conditions, forming an orange/red complex. The colour was registered by scanning the μPAD and the image processed in ImageJ software to obtain the colour intensity values then used to calculate the absorbance. A linear correlation was established between the creatinine concentration and the calculated absorbance values. The μPAD operational parameters were studied to attain the best sensitivity (calibration curve slope) for creatinine determination within the dynamic range of 2.20 - 35.0 mg/dL with a limit of detection (LOD) of 0.66 mg/dL and a limit of quantification (LOQ) of 2.2 mg/dL. Finally, the method was validated by analysing several urine samples with the developed μPAD and comparing the results with a comparative batchwise process, and it was demonstrated that there were no statistically significant differences between them.info:eu-repo/semantics/publishedVersio

Análise estrutural de aduela prefabricada em betão reforçado com fibras para o revestimento de túneis

A presente comunicação descreve a investigação desenvolvida no âmbito da análise estrutural de aduelas prefabricadas em betão reforçado com fibras (BRFA), com comportamento melhorado ao fogo, para os casos de carga a que estão sujeitas durante a sua vida útil. Os ensaios necessários à caracterização das propriedades do BRFA desenvolvido são descritos e os resultados obtidos são apresentados

Cephalic secretion of Arapaima gigas: sex steroids, peptides and proteins suggest roles in chemical communication and parental care.

Adults of the Amazon fish Arapaima gigas secrete a fluid from the cephalic canals of the lateral line system, whose biological role(s) along the reproductive cycle are unclear. Up-todate, the biochemical composition of this fluid has been poorly investigated in A. gigas as well as other teleosts. Hence, this study aimed to (1) investigate the potential pheromone release through this cephalic fluid, and (2) to characterise its proteome and peptidome by comparing males and females during and outside the parental care phase