UV-treated Samples Research Articles

Effects of Leachates from UV-Weathered Microplastic in Cell-Based Bioassays.

Standard ecotoxicological testing of microplastic does not provide insight into the influence that environmental weathering by, e.g., UV light has on related effects. In this study, we leached chemicals from plastic into artificial seawater during simulated UV-induced weathering. We tested largely additive-free preproduction polyethylene, polyethylene terephthalate, polypropylene, and polystyrene and two types of plastic obtained from electronic equipment as positive controls. Leachates were concentrated by solid-phase extraction and dosed into cell-based bioassays that cover (i) cytotoxicity; (ii) activation of metabolic enzymes via binding to the arylhydrocarbon receptor (AhR) and the peroxisome proliferator-activated receptor (PPARγ); (iii) specific, receptor-mediated effects (estrogenicity, ERα); and (iv) adaptive response to oxidative stress (AREc32). LC-HRMS analysis was used to identify possible chain-scission products of polymer degradation, which were then tested in AREc32 and PPARγ. Explicit activation of all assays by the positive controls provided proof-of-concept of the experimental setup to demonstrate effects of chemicals liberated during weathering. All plastic leachates activated the oxidative stress response, in most cases with increased induction by UV-treated samples compared to dark controls. For PPARγ, polyethylene-specific effects were partially explained by the detected dicarboxylic acids. Since the preproduction plastic showed low effects often in the range of the blanks future studies should investigate implications of weathering on end consumer products containing additives.

Influence of UV Irradiation and Cold Atmospheric Pressure Plasma on Zirconia Surfaces: An In Vitro Study

To compare the influence of ultraviolet (UV) irradiation and cold atmospheric pressure plasma (CAP) treatment on surface structure, surface chemistry, cytocompatibility, and cell behavior on zirconia in vitro. Zirconia samples (TZ-3YSBE) were treated by UV irradiation, oxygen plasma, or argon plasma for 12 minutes each and compared with the nontreated samples. Surface analysis was conducted using scanning electron microscopy, roughness analysis, and x-ray photoelectron spectroscopy. Cell proliferation, viability, and cell attachment as well as cytotoxicity were evaluated using MC3T3-E1 murine osteoblasts cultivated directly on the zirconia samples. Surface structure and roughness were not affected by the surface treatments. CAP and UV irradiation significantly reduced organic material and increased the surface oxidation on the zirconia samples. Furthermore, CAP and UV treatment significantly decreased the contact angle on the zirconia samples, indicating superhydrophilicity. Cell attachment was significantly increased on oxygen plasma-treated zirconia samples compared with the nontreated samples at all times (P < .001). After 24 and 48 hours, cell proliferation and viability (P < .001) were significantly increased on oxygen plasma-treated samples in comparison with the nontreated, UV-treated, and argon plasma-treated samples. Neither UV nor CAP treatment led to cytotoxicity. In vitro, surface treatment by UV irradiation or CAP causes a significant reduction of organic material, increases the hydrophilicity of zirconia, and improves the conditions for osteoblasts. Results stipulate that treatment of zirconia surfaces with oxygen plasma may favor cell proliferation.

Biomass Recovery Method for Adenosine Triphosphate (ATP) Quantification Following UV Disinfection

ABSTRACTA biomass recovery method was developed to monitor UV disinfection efficacy using adenosine triphosphate (ATP). Typically, disinfection monitoring at wastewater treatment facilities (WWTFs) involves quantifying fecal and total coliforms or colony forming units, the results of which take a minimum of 24 h to produce. ATP quantification immediately before and after UV treatment, which takes only minutes, shows little reduction and often an increase in the microbial population since UV irradiation results in cells that are viable (i.e., still producing ATP) but not culturable. To overcome this, our biomass recovery method incorporates an incubation step to encourage life cycling of microbes. Average log reductions in cellular ATP (cATP) were found to be −0.28 ± 0.19, −0.011 ± 0.153, −0.17 ± 0.32, and 0.065 ± 0.074 using direct ATP measurements on UV-treated samples from WWTFs A, B, C, and D, respectively, while those using the recovery method were correspondingly 0.17 ± 0.34, 1.8 ± 0.8, 0.20 ± 0.35, and 0.72 ± 0.26. The response of the biomass recovery-ATP method indicated a significant direct correlation to the microbial population reduction observed in heterotrophic plate count (HPC) and Colilert® methods using both pure Escherichia coli culture and secondary municipal wastewater effluent.

Temporary and permanent changes to the defect equilibrium due to ultraviolet exposure: Surface and bulk effects on ZnO nanostructures

We report on the influence of prolonged exposure of above band gap illumination (UV) on the surface electronic structure (core and valence band) and bulk defect equilibrium of ZnO nanorods. We investigated two samples (ZnO1 and ZnO2) of mutually contrasting surface electronic structure as well as photoluminescence responses. The changes due to the above gap exposure were juxtaposed of as-prepared, UV-treated and healed samples. As prepared samples consist of CC, COC and COOH groups at the surface. The intrinsic surface/defect mediated photocatalytic activity under UV-illumination regenerated the lattice oxygen, oxidized the excess zinc and increased the COC fraction. The surface of ZnO2 was catalytically more active than that of ZnO1 due to zinc interstitials (Znis) and extended Znis (ex-Znis). Also, we identify chemisorbed oxygeneous species, interstitial hydrogen (Hi+), multidentate complexes and disassociated O2 molecule at oxygen vacancies (VO). As a result of the catalytic activity severe changes occurred to the valance band (VB) edge and deeper-VB structure. After the course of healing, the VB edge for ZnO1 recovered to its pristine condition, unlike ZnO2. Additionally, we note increased fraction of O2s component for both the samples which, after healing did not recover to their as prepared condition. In the context of defect equilibrium the UV-treatment reduced the density of charged oxygen vacancy (VOδ) and the thickness of the depletion layer which we attribute to the desorption of some chemisorbed gases and reconstruction of lattice oxygen. For ZnO1, ex-Znis are induced after UV-treatment, which subdued to an extent in the course of healing. In sharp contrast, for ZnO2 the UV-treatment subdued the ex-Zni related emission, which slightly recovered after healing in addition to a further loss of VOδ related emission. The slow recovery and reorganization of intrinsic defects are attributed to the diffusivity of Hi+ and the associated lattice distortion, and Znis in the neighborhood of VOs. Furthermore, the non-Coulombic attractive interaction between neutral VOs and Znis mediate the migration of defects and subsequent stabilization on slower timescales. The changes due to UV illumination on the electronic structure and defect equilibrium enhance the applicability and understanding of ZnO nanostructures in optoelectronic applications.

Investigation of DNA transfer onto clothing during regular daily activities.

Low levels of DNA from an unidentified human source, often referred to as trace DNA, are ubiquitous, can be transferred onto objects by either direct or indirect methods and have an unknown longevity in situ. Clothing items from crime scenes are often submitted for trace DNA analysis, usually in attempt to identify a person of interest. This study examined the transfer of DNA onto three 10 × 10cm areas located on the front, back and shoulder of an individual's external clothing (n = 300) during a regular day's activity. After wearing for a day, the DNA quantity on all three areas increased approximately 8-fold, which usually corresponded with an increase in the endogenous DNA from the wearer on the front area of the shirt. However, the back area of the shirt was more likely to demonstrate mixtures of endogenous and extraneous DNA. An additional study was also carried out to examine whether domestic laundering is a possible mechanism for the transfer of foreign DNA onto freshly laundered items and revealed that 74% of UV-treated cotton swatch samples produced DNA profiles after laundry with household garments. In summary, this study highlights the ease of DNA transfer onto an individual's external clothing during a regular day, and that extraneous DNA may be already on the clothing item prior to it being worn. The study provides empirical data to assist in the interpretation of trace DNA profiles and support a Bayesian approach to estimate statistical likelihoods for the transfer of foreign DNA. Graphical abstract ᅟ.

Algal DNA Repair Kinetics Support Culture-Based Enumeration for Validation of Ultraviolet Disinfection Ballast Water Treatment Systems

To mitigate the potential spread of invasive species and pathogens, the International Maritime Organization and U.S. Coast Guard (USCG) adopted discharge performance standards for ballast water management that will take full effect in 2017. The USCG requires staining methods for enumerating ballast water treatment system (BWTS) efficacy. These stains do not detect DNA damage, the primary mechanism for ultraviolet (UV) disinfection, and neglect potential DNA repair after discharge. These factors necessitate investigation of enumeration methods for accurate validation and approval of UV-based BWTSs. To molecularly assess DNA damage and repair kinetics, UV-induced DNA lesions were quantified by an enzyme-linked immunosorbent assay in Tetraselmis suecica control and UV-treated samples that were cultured and tested over time. Most DNA repair occurred within 6 h, was essentially complete within 24 h, and was insensitive to light or nutrient conditions during incubation. Asymptotic repair kinetics indicated a ma...

Effect of Ultraviolet Irradiation on the Osseointegration of a Titanium Alloy with Bone.

Introduction:Attempt has been made to analyze the potential of titanium (Ti) alloy for osteointegration by the effect of surface photo functionalization in different aspects as follows: in Ringer's solution, in vitro cell growth, and in vivo study on rabbit. The present study was aimed to investigate the influence of ultraviolet (UV) light on surface topography, corrosion behavior, and bioactivity of indigenously manufactured samples of Ti alloy mini-implant.Materials and Methods:The study includes surface modification of Ti samples by UV treatment, corrosion testing of the specimens using Potentiostat (GAMRY System), qualitative examination of modified surface topography using scanning electron microscope, and cellular viability test on Ti alloy surface (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ASSAY). To find the effect of UV light on implant bone integration, biochemical test was performed on the femur of rabbits.Results and Discussion:Corrosion resistance of untreated Ti alloy in Ringer's solution was found to be less, whereas corrosion rate was more. Corrosion resistance of UV-treated samples was found to increase significantly, thereby lowering the corrosion rate. Cell growth in UV-treated specimen was observed to be higher than that in untreated samples. It is important to mention that cell growth was significantly enhanced on samples which were UV treated for longer duration of time.Conclusions:There was a marked improvement in cell growth on UV-treated Ti alloy samples. Hence, it is expected that it would enhance the process of osseointegration of Ti with bone. Another important finding obtained was that the removal torque values of UV-treated implants were higher than that of untreated implants. The overall result reveals that UV treatment of implants does help us in speeding up the osseointegration process.

The influence of incubation time on adenovirus quantitation in A549 cells by most probable number

Cell culture based assays used to detect waterborne viruses typically call for incubating the sample for at least two weeks in order to ensure that all the culturable virus present is detected. Historically, this estimate was based, at least in part, on the length of time used for detecting poliovirus. In this study, we have examined A549 cells infected with human adenovirus type 2, and have found that a three week incubation of virus infected cells results in a higher number of detected viruses by quantal assay than what is seen after two weeks of incubation, with an average 955% increase in Most Probable Number (MPN) from 2 weeks to 3 weeks. This increase suggests that the extended incubation time is essential for accurately estimating viral titer, particularly for slow-growing viruses, UV treated samples, or samples with low titers of virus. In addition, we found that for some UV-treated samples, there was no detectable MPN at 2 weeks, but after 3 weeks, MPN values were obtained. For UV-treated samples, the average increase in MPN from 2 weeks to 3 weeks was 1401%, while untreated samples averaged a change in MPN of 674%, leading us to believe that the UV-damaged viral DNA may be able to be repaired such that viral replication then occurs.

Effect of ultraviolet photofunctionalisation on the cell attractiveness of zirconia implant materials.

Ultraviolet (UV) light treatment of implant surfaces has been demonstrated to enhance their bioactivity significantly. This study examined the effect of UV treatment of different zirconia surfaces on the response of primary human alveolar bone-derived osteoblasts (PhABO). Disks of two zirconia-based materials with two different surface topographies (smooth, roughened) were exposed to UV light. Qualitative and quantitative assessment of PhABO on zirconia surfaces, by means of immunofluorescence, scanning electron microscopy and DNA quantification at 4 and 24 h revealed a higher number of initially attached osteoblasts on UV-treated surfaces. Cell area and perimeter were significantly larger on all UV-treated surfaces (p<0.05). The proliferation activity was significantly higher on both roughened UV-treated surfaces than on untreated samples at day 3 of culture (p<0.05). The expression levels of collagen I, osteopontin and osteocalcin at day 14 and alkaline phosphatase activity at day 7 and 14 of culture period were similar among UV-treated and untreated surfaces. Alizarin-Red-Staining at day 21 demonstrated significantly more mineralised nodules on UV-treated samples than on untreated samples. Contact angle measurements and X-ray photoelectron spectroscopy showed that UV light transformed zirconia surfaces from hydrophobic to (super-) hydrophilic (p<0.05) and significantly reduced the atomic percentage of surface carbon. The results showed that UV light pre-treatment of zirconia surfaces changes their physicochemical properties and improves their attractiveness against PhABO, primarily demonstrated by an augmented cell attachment and spreading. This may result in faster healing and better bone-to-implant contact of zirconia implants in vivo following such a pre-treatment.

Influence of ultraviolet photofunctionalization on the surface characteristics of zirconia-based dental implant materials

ObjectivesTo examine the effect of ultraviolet light (UV) treatment on the surface characteristics of two acid-etched zirconia-based dental implant materials. MethodsDiscs of two zirconia-based materials (Zr1 and Zr2) with smooth (m) and roughened (r) surfaces were treated by UV light for 15min. The surface topography was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface elemental composition of all samples was determined by X-ray photoelectron spectroscopy (XPS), the crystalline property by X-ray diffraction (XRD) and the hydrophilic status by contact angle (CA) measurements of a water droplet. ResultsSEM and AFM revealed quantitative and qualitative differences between the roughened and smooth surfaces. UV treatment did not induce any topographic changes of the tested surfaces (p>0.05). All UV-treated samples showed a significant surface elemental content change with a decrease of carbon by 43–81%, an increase of oxygen by 19–45%, and an increase of zirconia by 9–41%. Upon UV treatment, a 19–25% increase of the crystalline monoclinic phase was observed on surfaces of material Zr1, whereas a slight increase on the smooth Zr2 surface (+3%) and a decrease on the roughened Zr2 surface by 20% was observed. For all samples, the hydrophilic status changed significantly from hydrophobic to hydrophilic by UV treatment (p<0.0001). The average contact angles were between 56.4° and 69° before and 2.5° and 14.1° after UV-light treatment. SignificanceUV treatment altered the physicochemical properties of the two zirconia implant surfaces investigated. The mechanism by which such changes are induced requires further investigation.

Improved osteoblast response to UV-irradiated PMMA/TiO2 nanocomposites with controllable wettability.

Osteoblast response was evaluated with polymethylmethacrylate (PMMA)/titanium dioxide (TiO2) nanocomposite thin films that exhibit the controllable wettability with ultraviolet (UV) treatment. In this study, three samples of PMMA/TiO2 were fabricated with three different compositional volume ratios (i.e., 25/75, 50/50, and 75/25) followed by UV treatment for 0, 4, and 8h. All samples showed the increased hydrophilicity after UV irradiation. The films fabricated with the greater amount of TiO2 and treated with the longer UV irradiation time increased the hydrophilicity more. The partial elimination of PMMA on the surface after UV irradiation created a durable hydrophilic surface by (1) exposing higher amount of TiO2 on the surface, (2) increasing the hydroxyl groups on the TiO2 surface, and (3) producing a mesoporous structure that helps to hold the water molecules on the surface longer. The partial elimination of PMMA on the surface was confirmed by Fourier transform infrared spectroscopy. Surface profiler and atomic force microscopy demonstrated the increased surface roughness after UV irradiation. Both scanning electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that particles containing calcium and phosphate elements appeared on the 8h UV-treated surface of PMMA/TiO2 25/75 samples after 4days soaking in Dulbecco's Modified Eagle Medium. UV treatment showed the osteoblast adhesion improved on all the surfaces. While all UV-treated hydrophilic samples demonstrated the improvement of osteoblast cell adhesion, the PMMA/TiO2 25/75 sample after 8h UV irradiation (n=5, P value=0.000) represented the best cellular response as compared to other samples. UV-treated PMMA/TiO2 nanocomposite thin films with controllable surface properties represent a high potential for the biomaterials used in both orthopedic and dental applications.

OBSERVATION OF REDUCTION IN CASIMIR FORCE WITHOUT CHANGE OF DIELECTRIC PERMITTIVITY

Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au -coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.

Modifying the Casimir force between indium tin oxide film and Au sphere

We present complete results of the experiment on measuring the Casimir force between an Au-coated sphere and an untreated or, alternatively, UV-treated indium tin oxide (ITO) film deposited on a quartz substrate. Measurements were performed using an atomic force microscope in a high vacuum chamber. The measurement system was calibrated electrostatically. Special analysis of the systematic deviations is performed, and respective corrections in the calibration parameters are introduced. The corrected parameters are free from anomalies discussed in the literature. The experimental data for the Casimir force from two measurement sets for both untreated and UV-treated samples are presented. The random, systematic, and total experimental errors are determined at a 95$%$ confidence level. It is demonstrated that the UV treatment of an ITO plate results in a significant decrease in the magnitude of the Casimir force (from 21$%$ to 35$%$ depending on separation). However, ellipsometry measurements of the imaginary parts of dielectric permittivities of the untreated and UV-treated samples did not reveal any significant differences. The experimental data are compared with computations in the framework of the Lifshitz theory. It is found that the data for the untreated sample are in a very good agreement with theoretical results taking into account the free charge carriers in an ITO film. For the UV-treated sample the data exclude the theoretical results obtained with account of free charge carriers. These data are in very good agreement with computations disregarding the contribution of free carriers in the dielectric permittivity. According to the hypothetical explanation provided, this is caused by the phase transition of the ITO film from metallic to dielectric state caused by the UV treatment. Possible applications of the discovered phenomenon in nanotechnology are discussed.

OBSERVATION OF REDUCTION IN CASIMIR FORCE WITHOUT CHANGE OF DIELECTRIC PERMITTIVITY

Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.

Material properties of matrix lipids determine the conformation and intermolecular reactivity of diacetylenic phosphatidylcholine in the lipid bilayer.

Photopolymerizable phospholipid DC(8,9)PC (1,2-bis-(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) exhibits unique assembly characteristics in the lipid bilayer. Because of the presence of the diacetylene groups, DC(8,9)PC undergoes polymerization upon UV (254 nm) exposure and assumes chromogenic properties. DC(8,9)PC photopolymerization in gel-phase matrix lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monitored by UV-vis absorption spectroscopy occurred within 2 min after UV treatment, whereas no spectral shifts were observed when DC(8,9)PC was incorporated into liquid-phase matrix 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Liquid chromatography-tandem mass spectrometry analysis showed a decrease in the amount of DC(8,9)PC monomer in both DPPC and POPC environments without any change in the matrix lipids in UV-treated samples. Molecular dynamics (MD) simulations of DPPC/DC(8,9)PC and POPC/DC(8,9)PC bilayers indicate that the DC(8,9)PC molecules adjust to the thickness of the matrix lipid bilayer. Furthermore, the motions of DC(8,9)PC in the gel-phase bilayer are more restricted than in the fluid bilayer. The restricted motional flexibility of DC(8,9)PC (in the gel phase) enables the reactive diacetylenes in individual molecules to align and undergo polymerization, whereas the unrestricted motions in the fluid bilayer restrict polymerization because of the lack of appropriate alignment of the DC(8,9)PC fatty acyl chains. Fluorescence microscopy data indicates the homogeneous distribution of lipid probe 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lissamine rhodamine B sulfonyl ammonium salt (N-Rh-PE) in POPC/DC(8,9)PC monolayers but domain formation in DPPC/DC(8,9)PC monolayers. These results show that the DC(8,9)PC molecules cluster and assume the preferred conformation in the gel-phase matrix for the UV-triggered polymerization reaction.

Why Mechanical Properties of Collagen Scaffolds Should Be Tested in a Pseudo-Physiological Environment?

Collagen gels constitute an adequate scaffold for supporting the adhesion, proliferation and tissue regeneration of vascular cells inside a bioreactor. However, their mechanical properties should be enhanced not only for their manipulation but also to resist the mechanical constraints applied in the bioreactor. Actually, assessing the mechanical properties of a hydrogel requires many precautions since they are very sensitive to the environmental conditions (temperature, ionic strength, aqueous environment, etc). Whereas mechanical properties are usually measured directly in the air, the aim of this work was to evaluate the effects of a pseudo-physiological environment (PPE) on the mechanical properties of collagen gels. Furthermore, reinforcement was also tested using UV treatments (λ = 254 nm, 20 J/cm2), known to induce crosslinking. Irradiated samples were more resistant to enzymatic degradation and swelling tests showed that the crosslink density was increased by a factor of 30. This increase was thereafter correlated to the mechanical properties. Results showed that the UV-treated samples were stiffer and more brittle than the non-treated ones when tested in air. However, a 20% decrease and 40% increase were respectively measured on the linear modulus and strain at rupture when the gels were tested in the PPE. In the perspective of vascular tissue regeneration, these results show that the mechanical properties of a hydrogel should be performed in PPE in order to take into account the plasticization phenomenon that will occur in a bioreactor.

Molecular structure and properties of wool fiber surface-grafted with nano-antibacterial materials

Wool fiber was modified by ultraviolet irradiation (UV) and functionalized by grafting antibacterial agent. The structure and properties of antibacterial wool fiber were discussed in detail. The secondary structure changes and crystal structure were analyzed based on Fourier Transformation Raman Spectrometry (FTR) and X-ray diffraction (XRD). The results show that the disordered degree of UV-treated sample was increased and the antibacterial sample became more oriented. Compared with parent wool fiber, the antibacterial wool fiber was improved in mechanical property. The force, tensile strength and elongation were increased by 18%, 16%, and 7%, respectively. Also, the anti-shrinkage performance was increased because of the decrease in the directional frictional effect (DFE).

Degradation of aflatoxin B1 in aqueous medium through UV irradiation

Mutagenesis and cytotoxicity were assessed after exposure to different concentrations of AFB1 and the mixtures of photodegradation products in water (Pw). The Ames test, employing Salmonella typhimurium tester strains TA98 and TA100, was employed to evaluate the residual toxicity of Pw, and the results indicated that the mutagenic activity of UV-treated samples was lower compared with that of untreated samples, but not eliminate absolutely. After exposure of the HepG2 cells to these compounds for different times and concentrations, the cytotoxicity of Pw decreased approximately 40% compared to AFB1, and a small amount of cells were observed dead by the inverted phase-contrast microscope. The results of the Ames and in vitro cytotoxicity assay, providing clues to the assessment of safety issues of UV method applied in AFB1 decontamination, indicate that Pw are less toxic than AFB1, which can be explained by the differences in the chemical nature of the test compounds.

Photodegradation of Aflatoxin B1 in peanut oil

A photodegradation study of aflatoxin B1 (AFB1) in peanut oil was performed under UV irradiation at different AFB1 initial concentrations and UV irradiation intensities. The UV intensity and the irradiation duration on the AFB1 photodegradation ratio is more effective, when compared with AFB1 initial concentration, and AFB1 with initial concentration of 2 mg/kg can be degraded thoroughly within 30 min under the intensity of 800 μw/cm2. The photodegradation of AFB1 between the selected ranges of concentrations was proved to follow first-order reaction kinetics well (R2 ≥ 0.99). The Ames test, employing Salmonella typhimurium tester strains TA98 and TA100, was employed to evaluate the residual toxicity of the AFB1 subproducts in peanut oil, and the results indicated that the mutagenic activity of UV-treated samples (800 μw/cm2 × 30 min) was completely lost compared with that of untreated samples, providing clues to the assessment of safety issues of UV method applied in AFB1 decontamination.

Photocurrent Study of Oxygen-Mediated Doping States in Pentacene Thin-Film Transistors

We have measured and analyzed the gate-bias dependence of the photocurrent in pentacene organic field-effect transistors which have been doped using a UV-ozone treatment and compared these to the response of identical devices produced with no air or ozone exposure. The wavelength-dependent photocurrent spectrum shows intensified photocurrent peaks in oxygen-doped samples in the range of 350-480 nm, which corresponds to energy transitions (2.66, 2.76, 2.95, and 3.15 eV) larger than the pentacene HOMO-LUMO gap. These peaks are attributed to the formation of excitons and improved dissociation into electrons and holes, owing to the trap states formed at the interface between the UV-treated dielectric and the pentacene, which also account for positively shifted threshold voltage in the UV-treated sample. Our results are consistent with the trap-and-release transport model for pentacene. The gate-bias-dependent photocurrent spectrum shows that the photocurrent intensity is proportional to the mobility in the linear region, and this mobility relationship was confirmed via simultaneous transport measurement in the device.