Proton beam irradiation induces invisible modifications under the surface of painted parchment.

Ion beam analysis plays an important role in cultural heritage (CH) studies as it offers a combination of simultaneous and complementary analytical techniques (PIXE/PIGE/RBS) and spatially resolved mapping functions. Despite being considered non-destructive, the potential risk of beam-induced modifications during analysis is increasingly discussed. This work focuses on the impact of proton beams on parchment, present in our CH in form of unique historical manuscripts. Parchment is one of the organic, protein-based CH materials believed to be the most susceptible to radiation-induced changes. Various modification patterns, observed on parchment cross-sections by optical and electron microscopy are reported: discoloration (yellowing), formation of cavities and denaturation of collagen fibers. Considerable modifications were detected up to 100 µm deep into the sample for beam fluences of 4 µC/cm2 and higher. The presence of ultramarine paint on the parchment surface appears to increase the harmful effects of proton radiation. Based on our results, a maximum radiation dose of 0.5 µC/cm2 can be considered as 'safe boundary' for 2.3 MeV PIXE analysis of parchment under the applied conditions.

Study of the geometry of open channels in a layer-bed-type microfluidic immobilized enzyme reactor.

This paper aims at studying open channel geometries in a layer-bed-type immobilized enzyme reactor with computer-aided simulations. The main properties of these reactors are their simple channel pattern, simple immobilization procedure, regenerability, and disposability; all these features make these devices one of the simplest yet efficient enzymatic microreactors. The high surface-to-volume ratio of the reactor was achieved using narrow (25-75 µm wide) channels. The simulation demonstrated that curves support the mixing of solutions in the channel even in strong laminar flow conditions; thus, it is worth including several curves in the channel system. In the three different designs of microreactor proposed, the lengths of the channels were identical, but in two reactors, the liquid flow was split to 8 or 32 parallel streams at the inlet of the reactor. Despite their overall higher volumetric flow rate, the split-flow structures are advantageous due to the increased contact time. Saliva samples were used to test the efficiencies of the digestions in the microreactors.

Towards more reliable AFM force-curve evaluation: A method for spring constant selection, adaptive lever sensitivity calibration and fitting boundary identification.

This work discusses key issues regarding the atomic force microscopy (AFM) force-curve evaluation practice, which can affect the determined Young's modulus of the investigated sample. These issues are 1) the proper calibration of lever sensitivity and the effect of its variation between the measurements; 2) the selection of proper cantilever spring constant for the investigated sample; and 3) the selection of the fitting boundaries for the contact mechanics model-based force-curve evaluation. A method is proposed, which solves the above mentioned issues, namely, categorizes the obtained force-curves based on the relation between the elastic properties of the sample and the spring constant of the cantilever, and thus helps in the selection of the proper spring constant for the given surface; helps in the identification of the optimal model-fitting boundaries, and also, provides a way of adaptive lever sensitivity calibration. The method is demonstrated on PDMS (polydimethylsiloxane) samples, which were irradiated with various fluences of ion beams to control their elastic properties in the 4 MPa - 22 GPa range. Our proposed method, if applied correctly can significantly increase the reliability of AFM force-curve evaluation.

Enhanced growth of tellurium nanowires under conditions of macromolecular crowding.

An unprecedented rate enhancement was observed in the wet-chemical synthesis of tellurium nanowires under crowded conditions of inert macromolecules. The synthesis was carried out at 105 °C using solutions of sodium tellurite (Na2TeO3) as a precursor, hydrazine (N2H4) as a reducing agent, and polyvinylpyrrolidone (PVP) as both a stabilizing and crowding agent. The PVP concentration was systematically varied between the dilute and crowding regimes up to 166 g l-1. The growth of the nanowires was monitored by measuring their size-dependent optical properties in the UV-Vis spectrum characterizing the size and morphology evolution of the nanowires and a coexisting phase of amorphous tellurium nanoparticles. The observed growth characteristics were interpreted in terms of non-specific structural organization of the crowded media due to the entropic-driven effects of space compartmentalization.

Direct Trace Element Analysis of Liquid Blood Samples by In-Air Ion Beam Analytical Techniques (PIXE-PIGE).

There are various liquid materials whose elemental composition is of interest in various fields of science and technology. In many cases, sample preparation or the extraction can be complicated, or it would destroy the original environment before the analysis (for example, in the case of biological samples). However, multielement direct analysis of liquid samples can be realized by an external PIXE-PIGE measurement system. Particle-induced X-ray and gamma-ray emission spectroscopy (PIXE, PIGE) techniques were applied in external (in-air) microbeam configuration for the trace and main element determination of liquid samples. The direct analysis of standard solutions of several metal salts and human blood samples (whole blood, blood serum, blood plasma, and formed elements) was realized. From the blood samples, Na, P, S, Cl, K, Ca, Fe, Cu, Zn, and Br elemental concentrations were determined. The focused and scanned ion beam creates an opportunity to analyze very small volume samples (∼10 µL). As the sample matrix consists of light elements, the analysis is possible at ppm level. Using this external beam setup, it was found that it is possible to determine elemental composition of small-volume liquid samples routinely, while the liquid samples do not require any preparation processes, and thus, they can be analyzed directly. In the case of lower concentrations, the method is also suitable for the analysis (down to even ∼1 ppm level) but with less accuracy and longer measurement times.

Tilted pillar array fabrication by the combination of proton beam writing and soft lithography for microfluidic cell capture: Part 1 Design and feasibility.

Design, fabrication, integration, and feasibility test results of a novel microfluidic cell capture device is presented, exploiting the advantages of proton beam writing to make lithographic irradiations under multiple target tilting angles and UV lithography to easily reproduce large area structures. A cell capture device is demonstrated with a unique doubly tilted micropillar array design for cell manipulation in microfluidic applications. Tilting the pillars increased their functional surface, therefore, enhanced fluidic interaction when special bioaffinity coating was used, and improved fluid dynamic behavior regarding cell culture injection. The proposed microstructures were capable to support adequate distribution of body fluids, such as blood, spinal fluid, etc., between the inlet and outlet of the microfluidic sample reservoirs, offering advanced cell capture capability on the functionalized surfaces. The hydrodynamic characteristics of the microfluidic systems were tested with yeast cells (similar size as red blood cells) for efficient capture.

Air-stable, heme-like water-soluble iron(II) porphyrin: in situ preparation and characterization.

Preparation of the water-soluble, kinetically labile, high-spin iron(II) tetrakis(4-sulfonatophenyl)porphyrin, Fe(II)TPPS(4-), has been realized in neutral or weakly acidic solutions containing acetate buffer. The buffer played a double role in these systems: it was used for both adjusting pH and, via formation of an acetato complex, trapping trace amounts of iron(III) ions, which would convert the iron(II) porphyrins to the corresponding iron(III) species. Fe(II)TPPS(4-) proved to be stable in these solutions even after saturation with air or oxygen. In the absence of acetate ions, however, iron(II) ions play a catalytic role in the formation of iron(III) porphyrins. While the kinetically inert iron(III) porphyrin, Fe(III)TPPS(3-), is a regular one with no emission and photoredox properties, the corresponding iron(II) porphyrin displays photoinduced features which are typical of sitting-atop complexes (redshifted Soret absorption and blueshifted emission and Q absorption bands, photoinduced porphyrin ligand-to-metal charge transfer, LMCT, reaction). In the photolysis of Fe(II)TPPS(4-) the LMCT process is followed by detachment of the reduced metal center and an irreversible ring-opening of the porphyrin ligand, resulting in the degradation of the complex. Possible oxygen-binding ability of Fe(II)TPPS(4-) (as a heme model) has been studied as well. Density functional theory calculations revealed that in solutions with high acetate concentration there is very little chance for iron(II) porpyrin to bind and release O(2), deviating from heme in a hydrophobic microenvironment in hemoglobin. In the presence of an iron(III)-trapping additive that is much less strongly coordinated to the iron(II) center than the acetate ion, Fe(II)TPPS(4-) may function as a heme model.

A heme-like, water-soluble iron(II) porphyrin: thermal and photoinduced properties, evidence for sitting-atop structure.

Water-soluble ferrous porphyrin (Fe(II)TPPS) was prepared by complexation reaction of free base porphyrin (H2TPPS) with iron(II) ions in the presence of iron(III)-trapping acetate buffer; the catalytic and photoinduced properties of this air-stable complex proved unambiguously its sitting-atop structure.

Degradation of surfactants by hydroxyl radicals photogenerated from hydroxoiron(III) complexes.

The Fe(III)-photoinduced oxidation of anionic lauryl sulfate (LS-) and cationic cetyltrimethylammonium (CTA+) surfactants has been investigated in aqueous solution. Competition experiments using 2-propanol showed that the initial rate of disappearance is proportional to the concentration of the photogenerated HO* radicals scavenged by the surfactants (the degradation of lauryl sulfate involves attack by HO* only) and no direct photoinduced charge-transfer reaction occurs between the Fe(III) species and the surfactant ions. Ageing of the Fe(III) solution did not significantly influence the efficiency of photodegradation in air-saturated systems. Conversion of Fe(III) to Fe(II) in aerated solution reached a steady-state level of ca. 50% after 2 h irradiation. In nitrogen-saturated systems, the rate of surfactant oxidation decreased due to the total reduction of Fe(III). Addition of H2O2 doubled the quantum yield of the disappearance of both detergents as a result of the photo-Fenton reaction. The photoinduced oxidation of both surfactants was most efficient in acidic solutions of pH 2-3, without H2O2, and for the photo-Fenton system; the quantum yields are phi(NaLS) = 0.011, phi(CTAB) = 0.012 without H2O2, and phi(NaLS) = 0.024, phi(CTAB) = 0.027 in the photo-Fenton system with irradiation at 366 nm. For the disappearance of 4 x 10(-4) M detergent, due to the first oxidation step, 4 h of irradiation (at pH 2.6) is sufficient, whereas 100% mineralization of the total organic carbon content requires prolonged photolysis for at least 10 h. The formation of carbon dioxide dramatically accelerated after a 2 h induction period (1 h in the photo-Fenton system), indicating the cleavage of the long hydrocarbon chains to shorter intermediates in the first stage of the mechanism. The following step is total mineralization of these smaller compounds, which were identified as mostly hydroxy acids via GC-MS.