Morphology and photoluminescence properties of silicon nanoparticles deposited in helium-nitrogen mixtures maintained at low residual pressures

We elaborated a technique of pulsed laser ablation in gas mixtures (He-N2), maintained under residual pressures of 0.5–5 Torr to deposit silicon (Si)-based nanostructured films on a substrate. We show that the deposited films can exhibit strong photoluminescence (PL) emission with the position of peaks depending on the pressure of ambient gas and the ratio of gases in the mixture. Nanostructured films prepared in pure He gas exhibited a strong band in the infrared range (around 760 nm) and a weak band in the green range (550 nm), which were attributed to quantum-confined excitonic states in small Si nanocrystals and radiative transitions via the localized electronic states in silicon suboxide coating, respectively. In contrast, nanostructured films prepared in He-N2 mixtures exhibited more intense “green-yellow” PL band centered at 580 nm, which was attributed to a radiative recombination in amorphous oxynitride (a-SiNxOy) coating of Si nanocrystals. We also present a detailed analysis of morphology of nanostructures Si-based films prepared by laser ablation. Finally, we show that the nanocrystals can be removed from the substrate and milled by ultrasound to form aqueous solutions of colloidal Si nanopartiles. The fabricated Si-based nanocrystals present a promising object for theranostics, combining imaging functionality based on PL emission and a series of therapy functionalities (photo and radiofrequency hyperthermia, photodynamic therapy).

Secondary Analysis on Malaria RDTs in WHO Product Testing from Round 5 to 8 on False Negative Results in Testing Sample

Background with the widespread use of malaria rapid diagnostic tests (RDTs) in clinical practice, they also show their own challenges. Compared with most of the attention focusing on false positive results in WHO product testing, the same important false negative results attract insufficient focus. Method data of 129 malaria RDTs in the summary of WHO rounds 5 to 8 product testing was secondary analyzed in 5 aspects including low parasite density, improper RDTs storage, operation and interpretation, P. falciparum (Pf) with pfhrp2/3 genes deletion, inter-lot variation. Results First, the percentage of tests that achieved a panel detection score (PDS) < 80% at a low parasite density was 20-25% for Pf, and substantially higher for P. vivax (Pv). Second, Some Pv- and Pf- detecting products showed an increasing deterioration with increase of storage temperature. Third, approximately 20-27% products’ performances were unsatisfied in blood safety and instruction quality; and 30-35% test bands of the RDTs for Pf were barely visible, and the ones for Pv returned a higher proportion of weak band intensity. Fourth, different Lots of each test products may produce inconsistent results. Fifth, many malaria RDTs obtained a low PDS (< 50%) and a high false negative rate (> 50%) when testing Pf with deletion of pfhrp2/3 gene. Conclusion the malaria RDTs currently widely used were overestimated and could cause false negative results in practice. The clinicians should be aware of these shortcomings in order to draw more accurate diagnosis and treatment.

Study on the Development of a Cyclohexane Based Tripodal Molecular Device as "OFF-ON-OFF" pH Sensor and Fluorescent Iron Sensor

Background: Iron is an essential transition metal which is indispensable for life processes like oxygen transport and metabolism, electron transfer etc. However, misregulated iron is responsible for disease like anemia, hemochromatosis, Alzheimer’s and Parkinson’s disease. In order to encounter these diseases, a better understanding is needed of its role in misregulation. Fluorescent iron sensors could help provide this information. The new chemosensor developed by linking a cyclohexane unit with three 8-hydroxyquinoline provides selective detection of iron in numerous biological and environmental samples. Methods: The Uv-visible and fluorescence spectroscopy in combination with pH measurements will mainly be used for the study. Theoretical studies at DFT level will be used to validate the method and explain the theory behind the experiments. Results: The study of electronic spectra of the chelator, HQCC, reveals the appearance of a band at 262 nm along with a weak band at 335 nm due to π- π* and n- π* transitions respectively. Upon excitation with 335 nm, the ligand fluoresces at 388 nm wavelength. The intensity of the emission was affected in presence of metal ions, with maximum deviation for Fe(III). Selectivity studies showed that Fe(III) is more selective as compared to the biologically relevant metal ions viz., Al(III), Fe(III), Cr(III), Co(II), Fe(II), Ni(II), Zn(II), Cu(II), Mn(II) and Pb(II). pH dependent studies implied that the fluorescence intensity was highest at pH ~8.0, whereas maximum quenching for iron-HQCC system was observed at pH 7.4. The binding studies from the B-H plot confirms the formation of 1:1 complex with association constant of 5.95 × 106. The results obtained from experiments were in agreement with that obtained from the DFT and TD-DFT studies. Conclusion: A novel tripodal chelator based on 8-hydroxyquinoline and symmetric cyclohexane scaffold was successfully developed. In addition to the excellence of the ligand to be employed as a promising sensitive fluorescent probe for easy detection of Fe3+ions at the physiological pH with very low concentration (7.5 x 10-5 molL-1), the new ligand can be used as an OFF-ON-OFF pH sensor. Fe(III) encapsulation along with 1:1 ML-complexation formation have been established. Theoretical studies confirm a d-PET mechanism for the fluorescence quenching. DFT studies revealed that the neutral form of the ligand is less reactive than its protonated or the deprotonated form.

Kinetics of Cross-Linking Reaction of Epoxy Resin with Hydroxyapatite-Functionalized Layered Double Hydroxides

The cure kinetics analysis of thermoset polymer composites gives useful information about their properties. In this work, two types of layered double hydroxide (LDH) consisting of Mg2+ and Zn2+ as divalent metal ions and CO32− as an anion intercalating agent were synthesized and functionalized with hydroxyapatite (HA) to make a potential thermal resistant nanocomposite. The curing potential of the synthesized nanoplatelets in the epoxy resin was then studied, both qualitatively and quantitatively, in terms of the Cure Index as well as using isoconversional methods, working on the basis of nonisothermal differential scanning calorimetry (DSC) data. Fourier transform infrared spectroscopy (FTIR) was used along with X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to characterize the obtained LDH structures. The FTIR band at 3542 cm−1 corresponded to the O–H stretching vibration of the interlayer water molecules, while the weak band observed at 1640 cm−1 was attributed to the bending vibration of the H–O of the interlayer water. The characteristic band of carbonated hydroxyapatite was observed at 1456 cm−1. In the XRD patterns, the well-defined (00l) reflections, i.e., (003), (006), and (110), supported LDH basal reflections. Nanocomposites prepared at 0.1 wt % were examined for curing potential by the Cure Index as a qualitative criterion that elucidated a Poor cure state for epoxy/LDH nanocomposites. Moreover, the curing kinetics parameters including the activation energy (Eα), reaction order, and the frequency factor were computed using the Friedman and Kissinger–Akahira–Sunose (KAS) isoconversional methods. The evolution of Eα confirmed the inhibitory role of the LDH in the crosslinking reactions. The average value of Eα for the neat epoxy was 54.37 kJ/mol based on the KAS method, whereas the average values were 59.94 and 59.05 kJ/mol for the epoxy containing Zn-Al-CO3-HA and Mg Zn-Al-CO3-HA, respectively. Overall, it was concluded that the developed LDH structures hindered the epoxy curing reactions.

Encapsulation of Turmeric Crude Extracted in Chitosan Hydrogel Beads for Antimicrobial in Animal Health Care Applications

Hydrogel is very popular used in medicinal materials due to their properties. The aim of study is to investigate the development of chitosan (CS) hydrogel beads to extend drug-releasing time and enhance the stability of hydrogel beads from decomposition due to surrounding temperature. Gentamicin (GM) is using as a drug model for loading and releasing from hydrogel beads. For this purpose, the effects of ionic gelation of CS and tripolyphosphate (TPP) on various concentrations (1, 3, 5, and 7%w/v) are emphasized. Scanning electron microscopy (SEM) has revealed that CS hydrogel beads are roughly surface with decreasing of the %CS content. The Fourier transform infrared (FT-IR) spectra show a weak band of hydroxyl stretching at 2878 cm-1 of chitosan, the absorption band of the carbonyl stretching of the secondary amide at 1651 cm-1. The releasing solution of CS hydrogel beads exhibit an antimicrobial activity against 4 type of bacterias compared to Chloramphenical. For this reason, indicating that CS hydrogel beads are an appropriate for controlled drug release system to turmeric crude extract.

Toward high precision XCO2 retrievals from TanSat observations

&lt;p&gt;TanSat is the 1&lt;sup&gt;st&lt;/sup&gt; Chinese carbon dioxide measurement satellite, launched in 2016. Preliminary TanSat XCO&lt;sub&gt;2&lt;/sub&gt; retrievals have been introduced in previous studies based on the 1.6 m weak CO&lt;sub&gt;2&lt;/sub&gt; band. In this study, the University of Leicester Full Physics (UoL-FP) algorithm is implemented for TanSat nadir mode XCO&lt;sub&gt;2&lt;/sub&gt; retrievals. We develop a spectrum correction method to reduce the retrieval errors by an online fitting of an 8&lt;sup&gt;th&lt;/sup&gt; order Fourier series. The model and a priori is developed by analyzing the solar calibration measurement. This correction provides a significant improvement to the O&lt;sub&gt;2&lt;/sub&gt; A band retrieval. Accordingly, we extend the previous TanSat single CO&lt;sub&gt;2&lt;/sub&gt; weak band retrieval to a combined O&lt;sub&gt;2&lt;/sub&gt; A and CO&lt;sub&gt;2&lt;/sub&gt; weak band retrieval. A Genetic Algorithm (GA) has been applied to determine the threshold values of post-screening filters. In total, 18.3% of the retrieved data is identified as high quality compared. The same quality control parameters have been used in the bias correction due to the stronger correlation with the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval error. A footprint independent multiple linear regression is applied to determine the sounding XCO&lt;sub&gt;2&lt;/sub&gt; retrieval error and bias correction. Twenty sites of the Total Column Carbon Observing Network (TCCON) have been selected to validate our new approach of the TanSat XCO&lt;sub&gt;2&lt;/sub&gt; retrieval. We show that our new approach produces a significant improvement of the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval accuracy and precision when compared with TCCON with an average bias and RMSE of -0.08 and 1.47 ppm respectively. The methods used in this study, such as continuum correction, can help to improve the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval from TanSat and subsequently the Level-2 data production, and hence will be applied in the TanSat operational XCO&lt;sub&gt;2&lt;/sub&gt; processing.&lt;/p&gt;

Рентгенолюминесценция тетраподов ZnO, выращенных в присутствии примеси Сu и Au в исходной шихте

The morphology and luminescent properties of ZnO tetrapod powders with Cu and Au impurities obtained by pyrolytic carbothermal synthesis were studied. The X-ray luminescence spectrum of the samples is dominated by a broad band in the range from 450 to 650 nm. A weak band-edge luminescence band with a maximum at 391 nm is also registered. Measurements of the decay kinetics showed the presence of both fast (~ 1 ns) and slow (~ 850 ns) luminescence components, where the fast one generally did not exceed 1% of the integrated intensity. It is shown that with the used doping method, the incorporation of Cu and Au impurities into the ZnO lattice does not occur. In this case, the presence of Cu with a concentration of up to 9% does not affect the morphology and luminescent properties of tetrapods, while Au has an effect even at a concentration close to 1%.

The infrared bands of polycyclic aromatic hydrocarbons in the 1.6–1.7 μm wavelength region

Context. The 3.3 μm aromatic C–H stretching band of polycyclic aromatic hydrocarbon (PAH) molecules seen in a wide variety of astrophysical regions is often accompanied by a series of weak satellite bands at ∼3.4–3.6 μm. One of these sources, IRAS 21282+5050, a planetary nebula, also exhibits a weak band at ∼1.68 μm. While the satellite features at ∼3.4–3.6 μm are often attributed to the anharmonicities of PAHs, it is not clear whether overtones or combination bands dominate the 1.68 μm feature. Aims. In this work, we examine the anharmonic spectra of eight PAH molecules, including anthracene, tetracene, pentacene, phenanthrene, chrysene, benz[a]anthracene, pyrene, and perylene, to explore the origin of the infrared bands in the 1.6–1.7 μm wavelength region. Methods. Density functional theory (DFT) in combination with the vibrational second-order perturbation theory (VPT2) was used to compute the anharmonic spectra of PAHs. To simulate the vibrational excitation process of PAHs, the Wang–Landau random walk technique was employed. Results. All the dominant bands in the 1.6–1.7 μm wavelength range and in the 3.1–3.5 μm C–H stretching region are calculated and tabulated. It is demonstrated that combination bands dominate the 1.6–1.7 μm region, while overtones are rare and weak in this region. We also calculate the intensity ratios of the 3.1–3.5 μm C–H stretching features to the bands in the 1.6–1.7 μm region, I3.1 − 3.5/I1.6 − 1.7, for both ground and vibrationally excited states. On average, we obtain ⟨I3.1 − 3.5/I1.6 − 1.7⟩≈12.6 and ⟨I3.1 − 3.5/I1.6 − 1.7⟩≈17.6 for PAHs at ground states and at vibrationally excited states, respectively.

Repeat HIV testing of individuals with discrepant HIV self-test results in Central Uganda

Background According to the user instructions from the manufacturer of OraQuick HIV self-test (HIVST) kits, individuals whose kits show one red band should be considered to be HIV-negative, no matter how weak the band is. However, recent reports show potential for a second false weak band after storage, thereby creating confusion in the interpretation of results. In this study, we re-tested individuals whose results were initially non-reactive but changed to weak reactive results to determine their true HIV status. Methods This study was nested within a large, cluster-randomized HIVST trial implemented among pregnant women attending antenatal care and their male partners in central Uganda between July 2016 and February 2017. Ninety-five initially HIV-negative respondents were enrolled into this study, including 52 whose kits developed a second weak band while in storage and 43 whose kits were interpreted as HIV-positive by interviewers at the next follow-up interview. Respondents were invited to return for repeat HIVST which was performed under the observation of a trained nurse counsellor. After HIVST, respondents underwent blood-based rapid HIV testing as per the national HIV testing algorithm (Determine (Abbot Laboratories), STAT-PAK (Chembio Diagnostic Systems Inc.) and Unigold (Trinity Biotech plc.) and dry blood spots were obtained for DNA/PCR testing. DNA/PCR was considered as the gold-standard HIV testing method. Results After repeat HIVST, 90 (94.7%) tested HIV-negative; 2 (2.1%) tested HIV-positive; and 3 (3.2%) had missing HIV test results. When respondents were subjected to blood-based rapid HIV testing, 97.9% (93/95) tested HIV-negative while 2.1% (2/95) tested HIV-positive. Finally, when the respondents were subjected to DNA/PCR, 99% (94/95) tested HIV-negative while 1.1% (1/95) tested HIV-positive. Conclusions Nearly all initially HIV-negative individuals whose HIVST kits developed a second weak band while in storage or were interpreted as HIV-positive by interviewers were found to be HIV-negative after confirmatory DNA/PCR HIV testing. These findings suggest a need for HIV-negative individuals whose HIVST results change to false positive while under storage or under other sub-optimal conditions to be provided with an option for repeat testing to determine their true HIV status.

The Bone Black Pigment Identification by Noninvasive, In Situ Infrared Reflection Spectroscopy

Two real case studies, an oil painting on woven paper and a cycle of mural paintings, have been presented to validate the use of infrared reflection spectroscopy as suitable technique for the identification of bone black pigment. By the use of the sharp weak band at 2013 cm−1, it has been possible to distinguish animal carbon-based blacks by a noninvasive method. Finally, an attempt for an eventual assignment for the widely used sharp band at 2013 cm−1 is discussed.