Facile preparation of sisal-Fe/Zn layered double hydroxide bio-nanocomposites for the efficient removal of rifampin from aqueous solution: kinetic, equilibrium, and thermodynamic studies.

In the present study, sisal-Fe/Zn LDH bio-nanocomposite for efficiently removing rifampin was synthesized using a simple co-precipitation method. SEM, XRD, and FTIR analyses were applied to characterize the prepared composite. In the following, different factors that are affecting the adsorption of rifampin, including contact time, initial rifampin concentration, adsorbent dosage, and temperature were evaluated. Also, the kinetic, isotherm, and thermodynamic studies were investigated. The results indicated that Freundlich (R2 = 0.9976) was a suitable model for describing the adsorption equilibrium and adsorption kinetic showed that the data are in maximum agreement with the pseudo-second-order kinetic model (R2 = 0.9931). According to the Langmuir isotherm model, the maximum adsorption capacity of rifampin was found to be 40.00 mg/g. The main mechanisms for rifampin elimination were introduced as electrostatic attraction and physical adsorption. Moreover, the spontaneity and nature of the reaction were analyzed by elucidating thermodynamic factors that indicated the adsorption process was exothermic and spontaneous. Also, the batch process design indicated that for treating 10 L wastewater containing 100 mg/L rifampin with a removal efficiency of 96%, the needed amount of sisal-Fe/Zn LDH is 51.6 g. This study revealed that the sisal-Fe/Zn LDH bio-nanocomposites as a low-cost adsorbent have promising adsorption potential.

In this study, an innovative bio-nanocomposite (sisal­Fe/Zn layered double hydroxide) has been synthesized using a co-precipitation method for the first time and was used for the removal of pharmaceutical pollutants. Sisal­Fe/Zn LDH exhibited an excellent adsorption capacity of 40.00 mg/g to remove rifampin from the aqueous solution. The main mechanisms for rifampin elimination were introduced as electrostatic attraction and physical adsorption. Also, the batch process design showed that for treating 10 L wastewater containing 100 mg/L rifampin with a removal rate of 96%, the amount of sisal­LDH bio-nanocomposite required is about 51.6 g. Therefore, sisal­Fe/Zn layered double hydroxide as an eco-friendly biosorbent can be considered for future water treatment.

Natural deep eutectic solvent-decorated magnetic layered double hydroxide as a sorbent for the enrichment of organochlorine pesticides in environmental samples.

A newly designed magnetic layered double hydroxide composite modified with a natural deep eutectic solvent derived from choline chloride and sucrose was synthesized and applied as a sorbent for the enrichment of organochlorine pesticides. The magnetic solid phase extraction (MSPE) procedure was optimized via a small central composite design and response surface methodology. The MSPE method was able to preconcentrate the organochlorine residues in environmental samples prior to GC-MS analysis. Good analytical performance of the proposed method was observed with an enrichment factor of up to 158 and low limits of detection in the ranges of 0.002-0.015 µg·L-1 and 0.03-0.10 ng·g-1 for water and soil, respectively. Satisfactory recoveries for spiked water and soil samples were obtained in the ranges of 80.9-104.7% (RSDs<7.9) and 88.8-104.1% (RSDs<7.3), respectively. This finding highlights the role of natural deep eutectic solvents as modifying agents for magnetic layered double hydroxides, which enhance the efficiency of extraction of the target analytes. The developed MSPE/GC-MS procedure was sensitive and reliable for the determination of trace organochlorine residues in environmental samples.

Sources and levels of copper affect liver copper profile, intestinal morphology and cecal microbiota population of broiler chickens fed wheat-soybean meal diets.

Super dosing copper (Cu) has long been used as an alternative to antibiotic growth-promoters in broiler chickens' diet to improve gut health. This study was designed to compare nutritional and growth-promoting levels of Cu hydroxychloride (CH) with CuSO4 on gut health bio-markers and liver mineral profile of broiler chickens. Ross 308 chicks (n = 864) were randomly assigned to eight treatments, as basal diet containing no supplemental Cu; the basal diet with 15 or 200 mg/kg Cu as CuSO4; or 15, 50, 100, 150 or 200 mg/kg Cu from CH. The highest liver Cu content was observed in birds fed the diets with 200 mg/kg CuSO4 (P < 0.01). Serum FITC-d concentration as the leaky gut marker, and liver malondialdehyde concentration were not affected. Copper level or source had no effect on cecal short chain fatty acid and the mRNA expression of five jejunal genes involved in gut integrity. Negative linear responses of Cu were observed on Lactobacillus (P = 0.032), Bacteroides (P = 0.033), and Enterobacteriaceae (P = 0.028) counts. The jejunal villus height increased in birds fed CH at 200 and 100 mg/kg (P < 0.05). Increasing Cu levels, linearly and quadratically (P < 0.001), increased Cu excretion.

Reversible Chemosensor for Bioimaging and Biosensing of Zn(II) and hpH in Cells, Larval Zebrafish, and Plants with Dual-Channel Fluorescence Signals.

Zinc/Zn(II) is an essential trace element for humans and acts as an important substance that maintains the normal growth, development, and metabolism of the body. Excess or deficient Zn(II) can cause abnormal metabolism in the human body, leading to a series of diseases. Moreover, biosystems have complex homeostasis systems, especially harsh pH (OH-) environments. Thus, investigating the variation in the levels of Zn(II) and OH- is extremely important in clinical, medical, and environmental testing. Nevertheless, the lack of practical and convenient fluorescence imaging tools limits the tracing of Zn(II) and OH- in biosystems. In this work, a well-designed dual-channel fluorescent signal response chemosensor (DACH-fhba) was assembled for selective sensing of Zn(II) and OH- in the biosystem using a fluorescence turn-on strategy. On encountering Zn(II), the chemosensor emitted a blue fluorescence signal (455 nm). Meanwhile, the bright green fluorescence signal (530 nm) increased with OH- addition simultaneously. With the blue/green dual fluorescence response of DACH-fhba, the sensor exhibited high stability and reversibility. Notably, the bioimaging revealed that DACH-fhba successfully tracked Zn(II) and OH- in live cells, larval zebrafish, and plants. Further results implied that DACH-fhba can be used to achieve visual detection of Zn(II) and OH- in organisms. Altogether, this work is conducive to the monitoring of Zn(II) and OH- in organisms and promotes the understanding of the function of Zn(II) and OH- in biosystems.

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California.

We investigated rock varnish, a thin, manganese- and iron-rich, dark surface crust, on basaltic lava flows and petroglyphs in the Owens and Rose Valleys (California) by portable X-ray fluorescence (pXRF) and femtosecond laser-ablation inductively-coupled-plasma mass spectrometry (fs-LA-ICPMS). The major element composition of the varnish was consistent with a mixture of Mn-Fe oxyhydroxides and clay minerals. As expected, it contained elevated concentrations of elements that are typically enriched in rock varnish, e.g., Mn, Pb, Ba, Ce, and Co, but also showed unusually high enrichments in U, Cu, and Th. The rare earth and yttrium (REY) enrichment pattern revealed a very strong positive cerium (Ce) anomaly and distinct negative europium (Eu) and Y anomalies. The light rare earth elements (REE) were much more strongly enriched than the heavy REY. These enrichment patterns are consistent with a formation mechanism by leaching of Mn and trace elements from aeolian dust, reprecipitation of Mn and Fe as oxyhydroxides, and scavenging of trace elements by these oxyhydroxides. We inferred accumulation rates of Mn and Fe in the varnish from their areal densities measured by pXRF and the known ages of some of the lava flow surfaces. The areal densities of Mn and Fe, as well as their accumulation rates, were comparable to our previous results from the desert of Saudi Arabia. There was a moderate dependence of the Mn areal density on the inclination of the rock surfaces, but no relationship to its cardinal orientation. We attempted to use the degree of varnish regrowth on the rock art surfaces as an estimate of their age. While an absolute dating of the petroglyphs was not possible because of the lack of suitable calibration surfaces and a considerable amount of variability, the measured degree of varnish regrowth on the various petroglyphs was consistent with chronologies based on archeological and other archaeometric techniques. In particular, our results suggest that rock art creation in the study area continued over an extended period of time, possibly starting around the Pleistocene/Holocene transition and extending into the last few centuries.

Influence of Sumac Extract on the Physico-chemical Properties and Oxidative Stability of Some Cold Pressed Citrus Seed Oils.

The acidity values changed between 1.03 mgKOH/100g (control) and 1.11 mgKOH/100g (0.1% extract) for orange oil, 1.06 mgKOH/100g (0.5% extract) and 1.13 mgKOH/100g (0.1% extract) and 1.25 mgKOH/100g (0.5% extract) and 1.31 mgKOH/100g (control) for mandarin oil. The peroxide values were determined between1.37 meqO2/kg (0.5% extract) and 1.43 meqO2/kg (0.1% extract) for orange oil, between 1.24 meqO2/kg (control) and 1.27 meqO2/kg (0.1% extract) for lemon and 1.60 meqO2/kg (0.5% extract) and 1.71 meqO2/kg (control) in mandarin oil samples. The viscosity values of samples changed between 0.051 Pa.S (control) and 0.065 Pa.S (0.5% extract) for orange, 0.051 Pa.S (control) and 0.067 Pa.S (0.5% extract) lemon and 0.044 Pa.S (control) and 0.057 Pa.S (0.5% extract) in mandarin oil samples. At the end of storage study (28th day), the acidity values significantly changed, and their values ranged between 2.28 mgKOH/100g (0.5% extract) and 3.64 mgKOH/100g (control) in orange, 1.67 mgKOH/100g (0.5% extract) and 2.28 mgKOH/100g (control) in lemon and 1.74 mgKOH/100g (0.5% extract) and 2.36 mgKOH/100g (control) in mandarin oil samples. While peroxide values vary between 11.68 meqO2/kg (0.5% extract) and 32.57 meqO2/kg (control) for orange, 12.55 meqO2/kg (0.5% extract) and 34.63 meqO2/kg (control) for lemon and between 17.56 meqO2/kg (0.5% extract) and 37.81 meqO2/kg (control) for mandarin oils, viscosity values after 28 day storage changed between 0.123 Pa.S (0.5% extract) and 0.675 Pa.S (control) in orange, 0.257 Pa.S (0.5% extract) and 0.697 Pa.S (control) in lemon and 0.215 Pa.S (0.5% extract) and 0.728 Pa.S (control) in mandarin oil samples.

Adsorption of aromatic carboxylic acids on carbon nanotubes: impact of surface functionalization, molecular size and structure.

A large quantity of emerging contaminants are ionizable, and the ionized compounds display different adsorption behaviors than their neutral counterparts. In particular, a strong intermolecular force, negative charge assisted hydrogen bonding ((-)CAHB), was recently identified, which explains the unusually strong adsorption of negatively charged compounds on carbon nanotubes with oxygen-containing functional groups. However, most previous studies only probed molecules with one benzene ring. The adsorption of ionizable compounds with more than one benzene ring and additional functional groups has not been examined. This study investigated the effect of surface functionalization, molecular size and structure of six aromatic carboxylic acids on their adsorption on multi-walled carbon nanotubes (MWNTs) in batch reactors. In addition, the short-range interactions of the neutral acids with MWNTs were calculated to evaluate the effect of aromaticity and bulkiness. Hydrophobicity and electrostatic interactions dominate the intermolecular forces between ionized contaminants and MWNT surfaces. pH dependent octanol/water partitioning coefficient (Dow) is a more precise indicator of the adsorption of ionizable compounds on MWNTs. (-)CAHB is a significant force only for compounds with one benzene ring. Hydroxyl and carboxyl functional groups displayed similar capacity to form (-)CAHB, as indicated by the release of hydroxide ions.

A colorimetric probe for the real-time naked eye detection of cyanide and hydroxide ions in tap water: experimental and theoretical studies.

Herein, a colorimetric sensor (L) based on a naphthyl derivative bearing hydrazone receptors was synthesized via a one-step reaction process, and its recognition properties towards biologically important anions in an acetonitrile-water mixture were investigated by naked-eye observation and UV-Vis and 1H NMR spectroscopy. The molar addition of anions, such as TBAF-, TBAOH-, TBACN- and TBAAcO-, induced a significant red shift in the charge transfer band (Δλ = 73 nm, from 337 nm to 410 nm), in agreement with visible "naked eye" detectable colorimetric activities; in addition, soaked-in-L paper strips were prepared, which could significantly discriminate cyanide (KCN) and hydroxide (NaOH) ions dissolved in tap water via the litmus test method. This study was complemented by density functional theory computations to gain more insight into the interaction between L and anions.

Metabolomic Coverage of Chemical-Group-Submetabolome Analysis: Group Classification and Four-Channel Chemical Isotope Labeling LC-MS.

Chemical isotope labeling (CIL) liquid chromatography mass spectrometry (LC-MS) is a powerful technique for in-depth metabolome analysis with high quantification accuracy. Unlike conventional LC-MS, it analyzes chemical-group-based submetabolomes and uses the combined results to represent the whole metabolome. Due to analysis time and cost constraint, not all submetabolomes can be profiled and thus knowledge of chemical group classification is important in guiding submetabolome selection. Herein we report a study of determining the distribution of functional groups of compounds in a database and then examine how well we can experimentally analyze the major chemical groups in two representative samples (i.e., human plasma and yeast). We developed a computer algorithm to classify chemical structures according to their functional groups. After removing lipids which are targeted molecules in lipidomic analysis, inorganic species and other molecules that are unique to drug, food, plant, and environmental origins, five groups (i.e., amine, phenol, hydroxyl, carboxyl, and carbonyl) are found to be the dominant classes. In the databases of MCID (2683 filtered metabolites), HMDB (5506), KEGG (11598), YMDB (1107), and ECMDB (1462), 94.7%, 85.7%, 86.4%, 85.7%, and 95.8% of the filtered metabolites belong to one or more of the five groups, respectively. These groups can be analyzed in four-channel CIL LC-MS where hydroxyls (H), amines and phenols (A), carboxyls (C), and carbonyls or ketones/aldehydes (K) are separately profiled as individual channels using dansyl and DmPA labeling reagents. A total of 7431 peak pairs were detected with 6109 unique-mass pairs from plasma, while 5629 pairs with 4955 unique-mass pairs were detected in yeast. Compared to group distributions of database compounds, hydroxyl-containing metabolites were severely underdetected, which might indicate that the current method is less than optimal for analyzing this group of metabolites. As a result, the overall experimental coverage is likely significantly lower than the database-derived coverage. In short, this study has shown that high metabolome coverage is theoretically attainable by analyzing only the H, A, C, and K submetabolomes and the group classification information should be helpful in guiding future analytical method development and choices of submetabolomes to be analyzed.

Mg-Al-CO3 layered double hydroxide reinforced polymer inclusion membrane as an extractant phase for thin-film microextraction of cyanide from environmental water samples.

In this paper, a flexible and efficient nano-reinforced polymer inclusion membrane (PIM) was fabricated and used for cyanide (CN-) extraction from water samples. Aliquat 336 (a liquid anion exchanger) was embedded in poly(vinyl chloride) (PVC) support as the extractant. Mg-Al-CO3 layered double hydroxide (LDH) with high surface area and anion exchange ability was applied to promote the extraction efficiency of PIM. A PIM comprising 56% PVC, 40% Aliquat 336, and 4% Mg-Al-CO3 LDH showed the best extraction efficiency. A single beam ultraviolet-visible spectrophotometer was used for the detection of cyanide. Surface morphology of the PIM was studied by field emission scanning electron microscopy. The experimental parameters influencing the extraction process were investigated and optimized. The intra- and inter-day relative standard deviations at two different concentrations were in the range of 2.8-7.6%. The dynamic range of the method was in the range of 5-500 µg L-1, and the detection limit was 1.4 µg L-1. The LDH reinforced PIM showed proper characteristics for the extraction of cyanide from real water and wastewater samples with recoveries between 82 and 115%.

Potential environmental risks of nanopesticides: Application of Cu(OH)2 nanopesticides to soil mitigates the degradation of neonicotinoid thiacloprid.

Cu(OH)2 nanopesticides and organic insecticides are continuously applied to soil at a temporal interval, while knowledge about the impact of Cu(OH)2 nanopesticides on organic insecticides degradation is currently scarce, resulting in poorly comprehensive evaluation of the potential environmental risks of Cu(OH)2 nanopesticides. Herein, a commercial Cu(OH)2 nanopesticide formulation (NPF), the active ingredient of NPF (AI-NPF), the prepared Cu(OH)2 nanotubes (NT) with comparable morphology and size to AI-NPF, and CuSO4 were respectively applied to soil at normal doses (0.5, 5 and 50 mg/kg), followed by an application of neonicotinoid thiacloprid after an interval of 21 d, showing that NPF at doses of 5 and 50 mg/kg significantly (p < 0.05) mitigated thiacloprid degradation compared to control and CuSO4. Furthermore, AI-NPF was the primary component that contributed to the mitigation effect of NPF, which was also validated by the NT. Large differences in the degradation efficiency of thiacloprid in sterilized and unsterilized soils with Cu(OH)2 nanopesticides suggested that biodegradation was the primary process responsible for thiacloprid degradation, especially as chemical degradation was negligible. Besides a decrease of thiacloprid bioavailability due to adsorption by Cu(OH)2 nanopesticides, we demonstrated that Cu(OH)2 nanopesticides changed soil microbial communities, reduced nitrile hydratase activity and down-regulated thiacloprid-degradative nth gene abundance, which thus mitigated thiacloprid biodegradation. Clearly, this study shed light on the potential environmental risks of Cu(OH)2 nanopesticide.

Formation of high crystalline LDH sludge for removing Cu and Zn from wastewater by controlled double-jet precipitation.

In order to improve the heavy metal wastewater treatment by avoiding formation of amorphous sludge phase, we develop a faster formation of high crystalline layered double hydroxide (LDH) sludge to remove Cu and Zn from wastewater by controlled double-jet precipitation (CDJP) without hydrothermal or heat aging post-treatment. A series of experimental procedures are conducted to determine the optimal parameters. Results show that the optimal adding rate, pH value, and stirring rate is 0.5 mL min-1, 9.0, and 500 rpm, respectively. The CuZnAl-LDH phase sludge is formed in a well-crystallized hexagonal platelet, which assembled into a flower-like architecture. Comparative studies show that the formation of amorphous LDH sludge in conventional precipitation (CP) could be divided roughly into two stages-from the mixed copper hydroxide, zinc hydroxide, and scarbroite to the mixed low crystallinity CuAl-LDH and ZnAl-LDH. However, in CDJP method, the high crystalline LDH sludge evolved from a new four-step evolution process that is the formation of an amorphous (quasi-)multinary metastable ternary CuZnAl-LDH phase, followed by the indiffusion of cations and substitution of anions to fabricate crystalline LDH, the integrated LDH hexagonal platelets assembled into a flower-like architecture by the screw dislocation growth mechanism, the coarsening growth of each ternary LDH platelet, respectively. Thereinto, the formation of (quasi-)multinary metastable LDH phase instead of metal hydroxide in initial stage would be an obvious advantage of the CDJP method compared to CP method due to the former skipping the sequential precipitation.

Ultraviolet Absorption Cross Sections of KOH and KCl for Nonintrusive Species-Specific Quantitative Detection in Hot Flue Gases.

An understanding of potassium chemistry in energy conversion processes supports the development of complex biomass utilization with high efficiency and low pollutant emissions. Potassium exists mainly as potassium hydroxide (KOH), potassium chloride (KCl), and atomic potassium (K) in combustion and related thermochemical processes. We report, for the first time, the measurement of the ultraviolet (UV) absorption cross sections of KOH and KCl at temperatures between 1300 K and 1800 K, using a newly developed method. Using the spectrally resolved UV absorption cross sections, the concentrations of KOH and KCl were measured simultaneously. In addition, we measured the concentrations of atomic K using tunable diode laser absorption spectroscopy, both at 404.4 and 769.9 nm. The 404.4 nm line was utilized to expand the measurement dynamic range to higher concentrations. A constant amount of KCl was seeded into premixed CH4/air flames with equivalence ratios varied from 0.67 to 1.32, and the concentrations of KOH, KCl, and atomic K in the hot flue gas were measured nonintrusively. The results indicate that these techniques can provide comprehensive data for quantitative understanding of the potassium chemistry in biomass combustion/gasification.

Triple-Interpenetrated Lanthanide-Organic Framework as Dual Wave Bands Self-Calibrated pH Luminescent Probe.

pH value is a key parameter in reflecting the health status, reaction process, and water quality. The construction of highly sensitive pH luminescent ratiometric is important but challenging. Herein we designed and synthesized a unique triple-interpenetrated luminescent lanthanide-organic framework {[Eu(PPTA)0.5(NO3)(DMF)2]·H2O} n(V104) based on an amphoteric ligand 4,4',4'',4'''-(1,4-phenylenebis(pyridine-4,2,6-triyl))tetrabenzoic acid (H4PPTA). Compound V104 possesses high solvent and acid/alkaline stabilities. Luminescent investigations reveal that V104 exhibits dual emission peaks at 390 and 480 nm, and these two peaks can separately detect OH- and H+ among various anions and cations. Importantly, V104 can serve as a self-calibrated pH ratiometric to quantitatively detect pH value, and the sensitivity can reach 403.2% per pH for OH-, and 129.5% per pH for H+. Furthermore, by encapsulating magnetic γ-Fe2O3 nanoparticles in V104, the pH sensor can be readily separated from the analyte by external magnet and recycled at least four times, suggesting as-synthesized γ-Fe2O3@V104 has potential for monitoring pH fluctuations in water. To our knowledge, this is the first self-calibrated ratiometric pH-sensor based on two responsive wave bands which can separately detect OH- and H+.

Printed Colorimetric Arrays for the Identification and Quantification of Acids and Bases.

Solid supported colorimetric sensing arrays have the advantage of portability and ease of use when deployed in the field, such as crime scenes, disaster zones, or in war zones, but many sensor arrays require complex fabrication methods. Here, we report a practical method for the fabrication of 4 × 4 colorimetric sensor arrays, which are printed on nylon membranes, using a commercially available inkjet printer. In order to test the efficacy of the printed arrays, they were exposed to 43 analytes at concentrations ranging from 0.001 to 3.0 M for a total of 559 samples of inorganic and organic acids or bases including hydrochloric, acetic, phthalic, malonic, picric, and trifluoroacetic acid, ammonium hydroxide, sodium hydroxide, lysine, and water as the control. Colorimetric data from the imaged arrays was analyzed with linear discriminant analysis and k-nearest neighbors to determine the analyte and concentration with ∼88-90% accuracy. Overall, the arrays have impressive analytical power to identify a variety of analytes at different concentrations while being simple to fabricate.

Assuring precision and calibration linearity in ultrasensitive suppressed ion chromatography by using deliberately contaminated hydroxide eluent.

EXPERIMENTAL: and theoretical studies were conducted to investigate low and non-linear responses in sub-micro molar-level suppressed ion chromatography with a hydroxide eluent. A calculated response was derived using experimentally determined detector effluent ion composition data and compared with measured experimental responses. The calibration curve was non-linear, and its slope varied considerably with different instrumental setups and operating conditions. The non-linearity of the solution conductivity response was determined by two acid-base equilibria of water and carbonic acid, and fluoride ion. By using eluent contaminated with para-toluene sulfonate at micro molar level, the non-linear response was greatly alleviated.

Foliar Exposure of Cu(OH)2 Nanopesticide to Basil ( Ocimum basilicum): Variety-Dependent Copper Translocation and Biochemical Responses.

In this study, low and high anthocyanin basil ( Ocimum basilicum) varieties (LAV and HAV) were sprayed with 4.8 mg Cu/per pot from Cu(OH)2 nanowires, Cu(OH)2 bulk (CuPro), or CuSO4 and cultivated for 45 days. In both varieties, significantly higher Cu was determined in leaves of CuSO4 exposed plants (691 and 672.6 mg/kg for LAV and HAV, respectively); however, only in roots of HAV, Cu was higher, compared to control ( p ≤ 0.05). Nanowires increased n-decanoic, dodecanoic, octanoic, and nonanoic acids in LAV, but reduced n-decanoic, dodecanoic, octanoic, and tetradecanoic acids in HAV, compared with control. In HAV, all compounds reduced eugenol (87%), 2-methylundecanal (71%), and anthocyanin (3%) ( p ≤ 0.05). In addition, in all plant tissues, of both varieties, nanowires and CuSO4 reduced Mn, while CuPro increased chlorophyll contents, compared with controls ( p ≤ 0.05). Results suggest that the effects of Cu(OH)2 pesticides are variety- and compound-dependent.

Contact lens to measure individual ion concentrations in tears and applications to dry eye disease.

Dry eye disease (DED) affects millions of individuals in the United States and worldwide, and the incidence is increasing with an aging population. There is widespread agreement that the measurement of total tear osmolarity is the most reliable test, but this procedure provides only the total ionic strength and does not provide the concentration of each ionic species in tears. Here, we describe an approach to determine the individual ion concentrations in tears using modern silicone hydrogel (SiHG) contact lenses. We made pH (or H3O+, hydronium cation,/OH-, hydroxyl ion) and chloride ion (two of the important electrolytes in tear fluid) sensitive SiHG contact lenses. We attached hydrophobic C18 chains to water-soluble fluorescent probes for pH and chloride. The resulting hydrophobic ion sensitive fluorophores (H-ISF) bind strongly to SiHG lenses and could not be washed out with aqueous solutions. Both H-ISFs provide measurements which are independent of total intensity by use of wavelength-ratiometric measurements for pH or lifetime-based sensing for chloride. Our approach can be extended to fabricate a contact lens which provides measurements of the six dominant ionic species in tears. This capability will be valuable for research into the biochemical processes causing DED, which may improve the ability to diagnose the various types of DED.

Significant OH production under surface cleaning and air cleaning conditions: Impact on indoor air quality.

We report measurements of hydroxyl (OH) and hydroperoxy (HO2 ) radicals made by laser-induced fluorescence spectroscopy in a computer classroom (i) in the absence of indoor activities (ii) during desk cleaning with a limonene-containing cleaner (iii) during operation of a commercially available "air cleaning" device. In the unmanipulated environment, the one-minute averaged OH concentration remained close to or below the limit of detection (6.5×105  molecule cm-3 ), whilst that of HO2 was 1.3×107  molecule cm-3 . These concentrations increased to ~4×106 and 4×108  molecule cm-3 , respectively during desk cleaning. During operation of the air cleaning device, OH and HO2 concentrations reached ~2×107 and ~6×108  molecule cm-3 respectively. The potential of these OH concentrations to initiate chemical processing is explored using a detailed chemical model for indoor air (the INDCM). The model can reproduce the measured OH and HO2 concentrations to within 50% and often within a few % and demonstrates that the resulting secondary chemistry varies with the cleaning activity. Whilst terpene reaction products dominate the product composition following surface cleaning, those from aromatics and other VOCs are much more important during the use of the air cleaning device.