Studying the polymerization efficiency of photosensitive compositions by using the surface plasmon resonance method

In a real-time scale, it has been investigated the polymerization process in photosensitive compositions based on oligourethanacrylates with various concentrations of photoinitiators by using the method of surface plasmon resonance. Experimentally determined were the speed of polymerization and induction period for the studied samples of photopolymerization compositions as well as their optimum ratio of components for the chosen illumination wavelength 407 nm. It has been ascertained that with increasing the concentration of photoinitiators Irgacure 651 and Irgacure 819 from 1 up to 2% the speed of polymerization is increased by 3 and 7 times, respectively, while the induction period is decreased by almost 2 and 10 times, respectively. The presence of Irgacure 819 in these compositions provides the highest polymerization speed and the lowest induction period, which is related with the optimal choice of the illumination source wavelength inside the absorption spectrum of initiator, and the competitive absorption in other components of the photopolymer composition is minimal. These investigations are useful for developing optimal compositions of the studied materials for using them in various branches of industry.

Towards shifted position-diffuse reflectance imaging of anatomically correctly scaled human microvasculature

Due to significant advantages, the trend in the field of medical technology is moving towards minimally or even non-invasive examination methods. In this respect, optical methods offer inherent benefits, as does diffuse reflectance imaging (DRI). The present study attempts to prove the suitability of DRI—when implemented alongside a suitable setup and data evaluation algorithm—to derive information from anatomically correctly scaled human capillaries (diameter: $$10\,\upmu \hbox {m}$$ 10 μ m , length: $$45\,\upmu \hbox {m}$$ 45 μ m ) by conducting extensive Monte–Carlo simulations and by verifying the findings through laboratory experiments. As a result, the method of shifted position-diffuse reflectance imaging (SP-DRI) is established by which average signal modulations of up to 5% could be generated with an illumination wavelength of $$\lambda =424\,\hbox {nm}$$ λ = 424 nm and a core diameter of the illumination fiber of $$50\,\upmu \hbox {m}$$ 50 μ m . No reference image is needed for this technique. The present study reveals that the diffuse reflectance data in combination with the SP-DRI normalization are suitable to localize human capillaries within turbid media.

SAMSON: Spectral Absorption-fluorescence Microscopy System for ON-site-imaging of algae

This paper presents SAMSON, a Spectral Absorption-fluorescenceMicroscopy System for ON-site-imaging of algae within a watersample. Designed to be portable and low-cost for on-site use,the optical sub-system of SAMSON consists of a mixture of low-cost optics and electronics, designed specifically to capture bothfluorescent and absorption responses from a water sample. Thegraphical user interface (GUI) sub-system of SAMSON was de-signed to enable flexible visualisation of algae in the water samplein real-time, with the ability to perform fine-grained exposure con-trol and illumination wavelength selection. We demonstrate SAM-SON’s capabilities by equipping the system with two fluorescentillumination sources and seven absorption illumination sources toenable the capture of multispectral data from six different algaespecies (three from the Cyanophyta phylum (blue-green algae) andthree from the Chlorophyta phylum (green algae)). The key benefitof SAMSON is the ability to perform rapid acquisition of fluores-cence and absorption data at different wavelengths and magnifica-tion levels, thus opening the door for machine learning methods toautomatically identify and enumerate different algae in water sam-ples using this rich wealth of data.

Quantum efficiency of the photo-induced electronic transfer in dye–TiO2 complexes

The quantum efficiency of charge transfer in a dye–titania complex is calculated as a function of illumination wavelength.

Photoconductive behavior of binary porphyrin crystalline assemblies

The mechanism of photoconductivity in a crystalline photoconductor synthesized from 1:1 ratio of meso-tetra(4-pyridyl)porphyrin (TPyP) and meso-tetra(4-sulfonatophenyl)porphyrin (TSPP) ionic tectons was examined. The rod-like crystals of TPyP:TSPP insulate in the dark but become photoconducting on illumination and a portion of the photoinduced current persists after the laser light is turned off. This persistent photoconductivity (PPC) is investigated as a function of laser illumination wavelength, laser power, and sample temperature. The primary charge carriers in the TPyP:TSPP upon photoexcitation are electrons and the charge recombination mechanism follows monomolecular kinetics. The number of electrons contributing to the photocurrent is directly proportional to the number of photons absorbed thus, the mechanisms of the photoconductivity resulting from excitations within the Soret band and the Q-band are the same. The PPC is interpreted to be the result of the formation of photoinduced metastable defects that allow for Miller–Abrahams-like hopping conductivity. The TPyP:TSPP has an incommensurately modulated crystal lattice and its proposed model structure is based on both ionic and neutral porphyrin tectons. The thermogravimetric analysis shows that the porphyrin crystals undergo dehydration on heating (˜50 ∘C) by losing water molecules located in the crystalline channels. Temperature dependent XRD indicates that dehydration causes irreversible changes to the crystal structure. The loss of crystallinity observed with heating the TPyP:TSPP crystals above 90 ∘C causes approximately 25% loss in photoconductivity but has little effect on the lifetime associated with the persistent photoconductivity.