The toxicology of indium tin oxide

Robust ZTO-reinforced Ag nanowire hybrid transparent conductive thin films with absorption-enhanced electromagnetic interference shielding property

Technological advances have accelerated the pursuit of transparent conducting thin films (TCFs) with superior mechanical properties, durability, efficient optoelectrical performance and substrate compatibility as a pivotal focus in the realm of flexible transparent electronics. Against this background, this work investigates the fabrication of multilayer silver nanowire (AgNW) thin films reinforced by zinc tin oxide (ZTO) thin film encapsulation on polycarbonate substrates by a combination of sputtering and spin-coating techniques. An investigation of the influence of AgNW percolation networks on the optoelectrical properties of ZTO/AgNW/ZTO hybrid thin films was carried out. The impact of ZTO protective layers on the enhancement of electrical properties, adhesivity, flexibility and environmental stability of the multilayer TCF was elucidated. Additionally, to explore the compatibility of the fabricated TCF in integrated device and stealth applications, its electromagnetic interference shielding properties were investigated. The hybrid TCF showed 99.47% EMI shielding efficiency with an absorption-dominant EMI shielding effectiveness of 22.7 dB in the x-band region.

Toxicokinetics and systematic responses of differently sized indium tin oxide (ITO) particles in mice via oropharyngeal aspiration exposure

Indium tin oxide (ITO) is an important semiconductor material, because of increasing commercial products consumption and potentially exposed workers worldwide. So, urgently we need to assess and manage potential health risks of ITO. Although the Occupational Exposure Limit (OEL) has been established for ITO exposure, there is still a lack of distinguishing the risks of exposure to particles of different sizes. Therefore, obtaining toxicological data of small-sized particles will help to improve its risk assessment data. Important questions raised in quantitative risk assessments for ITO particles are whether biodistribution of ITO particles is affected by particle size and to what extent systematic adverse responses is subsequently initiated. In order to determine whether this toxicological paradigm for size is relevant in ITO toxic effect, we performed comparative studies on the toxicokinetics and sub-acute toxicity test of ITO in mice. The results indicate both sized-ITO resided in the lung tissue and slowly excreted from the mice, and the smaller size of ITO being cleared more slowly. Only a little ITO was transferred to other organs, especially with higher blood flow. Two type of ITO which deposit in the lung mainly impacts respiratory system and may injure liver or kidney. After sub-acute exposure to ITO, inflammation featured by neutrophils infiltration and fibrosis with both dose and size effects have been observed. Our findings revealed toxicokinetics and dose-dependent pulmonary toxicity in mice via oropharyngeal aspiration exposure, also replenish in vivo risk assessment of ITO. Collectively, these data indicate that under the current OEL, there are potential toxic effects after exposure to the ITO particles. The observed size-dependent biodistribution patterns and toxic effect might be important for approaching the hazard potential of small-sized ITO in an occupational environment.

Trace Elements in the Large Population-Based HUNT3 Survey

The Nord-Trøndelag Health Study (The HUNT Study) is a large health survey population study in the county of Trøndelag, Norway. The survey has been repeated four times in about 10-year intervals. In the HUNT3 survey (2006-2008), we collected 28,000 samples for trace element analysis. Blood samples from 758 healthy persons without known occupational exposure were selected for multielement analysis of a small sample of blood (0.25 mL). The aim of the study was to determine the minimum blood volume that can be used for the analytical procedure and to compare our results with previously published results of similar surveys in healthy populations. Samples were digested and the concentration of selected trace elements was determined by ICP-MS. We report results on essential elements (B, Co, Cu, Mn, Se and Zn) as well as non-essential elements (As, Be, Br, Cd, Cs, In, La, Pb, Hg, Nd, Ni, Nb, Pd, Pt, Sm, Ta and Sn). Results are similar to previous studies on the HUNT3 population, and with a few exceptions, our data compares very well with results obtained in recent studies from other countries. We wanted to test a minimum volume of blood in a large-scale analytical program. For a number of nonessential elements, our results were below the limit of detection. We suggest that future studies using similar ICP-MS equipment as analytical tool should use at least 0.5 mL of blood.

Assessment of Occupational Exposure to Indium Dust for Indium-Tin-Oxide Manufacturing Workers

According to recent research, indium nanoparticles (NPs) are more toxic than micro-sized particles. While cases of indium lung disease have been reported worldwide, very little research has been conducted on the occupational exposure to indium NPs. Recently, an indium-related lung disease was reported in Korea, a global powerhouse for display manufacturing. In this study, we conducted an assessment ofoccupational exposure at an indium tin oxide (ITO) powder manufacturing plant, where the first case of indium lung disease in Korea occurred. Airborne dustwas obtained from a worker's breathing zone, and area sampling in the workplace environment was conducted using real-time monitoring devices. Personal samples were analyzed for the indium concentrations in total dust, respirable dust fraction, and NPs using personal NPs respiratory deposition samplers. The total indium concentration of the personal samples was lower than the threshold limit value recommended by the American Conference of Governmental Industrial Hygienists (ACGIH TLV), which was set as occupational exposure limit (OEL). However, the respirable indium concentration exceeded the recently set ACGIH TLV for the respirable fraction of indium dust. The concentration of indium NPs ranged between 0.003 and 0.010 × 10-2 mg/m3, accounting for only 0.4% of the total and 2.7% of the respirable indium particles. This was attributed to the aggregating of NPs at the µm sub-level. Given the extremely low fraction of indium NPs in the total and respirable dust, the current OEL values, set as the total and respirable indium concentrations, do not holistically represent the occupational exposure to indium NPs or prevent health hazards. Therefore, it is necessary to set separate OEL values for indium NPs. This study covers only the process of handling ITO powder. Therefore, follow-up studies need to be conducted on other ITO sputtering target polishing and milling processes, which typically generate more airborne NPs, to further investigate the effects of indium on workers and facilitate the necessary implementation of indium-reducing technologies.

The toxicology of gallium oxide in comparison with gallium arsenide and indium oxide

Gallium arsenide (GaAs) and indium oxide (In₂O₃) are used in electronic industries at high and increasing tonnages since decades. Gallium oxide (Ga₂O₃) is an emerging wide-bandgap transparent conductive oxide with as yet little industrial use. Since GaAs has received critical attention due to the arsenic ion, it seemed reasonable to compare its toxicology with the respective endpoints of Ga₂O₃ and In₂O₃ toxicology in order to find out if and to what extent arsenic contributes. In addition, the toxicology of Ga₂O₃ has not yet been adequately reviewed, Therefore, this review provides the first evaluation of all available toxicity data on Ga₂O₃. The acute toxicity of all three compounds is rather low. Subchronic inhalation studies in rats and mice revealed persistent pulmonary alveolar proteinosis (PAP) and/or alveolar histiocytic infiltrates down to the lowest tested concentration in rats and mice, i.e. 0.16 mg Ga₂O₃/m³. These are also the predominant effects after GaAs and In₂O₃ exposure at similarly low levels, i.e. 0.1 mg/m³ each. Subchronic Ga₂O₃ exposure caused a minimal microcytic anemia with erythrocytosis in rats (at 6.4 mg/m³ and greater) and mice (at 32 and 64 mg/m³), a decrease in epididymal sperm motility and concentration as well as testicular degeneration at 64 mg/m³. At comparable concentrations the hematological effects and male fertility of GaAs were much stronger. The stronger effects of GaAs are due to its better solubility and presumed higher bioavailability. The database for In₂O₃ is too small and subchronic testing was at very low levels to allow conclusive judgements if blood/blood forming or degrading and male fertility organs/tissues would also be targets.

Low serum indium levels induce expression disorders of some inflammatory factors

OBJECTIVES

It has been reported that occupational exposure to indium compounds, including indium-tin oxide, can induce pulmonary inflammation resulting in serious indium lung disease. However, whether there is an early effect of indium exposure on inflammatory factor expression remains unclear.

METHODS

Twenty indium-tin oxide processing workers and 15 healthy volunteers were recruited to measure serum indium levels, respiratory symptoms, pulmonary function, and serum inflammatory factor levels.

RESULTS

Although low serum indium was detected in workers, lung abnormalities were not increased, compared with healthy population. However, serum G-CSF, IL-4, IL-5, TNF-alpha, and TNF-beta levels were significantly increased, while IL-16 and TIMP-1 were obviously down-regulated in indium-tin oxide processing workers. These inflammatory factor levels showed a significant correlation with serum indium levels.

CONCLUSIONS

Basing on our findings, we speculate that low serum indium levels may induce inflammatory responses, which may be an adaptive response or may cause lung diseases. Therefore, further experiments or follow-up is needed. However, better safeguard procedures and indium exposure reduction should be considered in ITO industry.

Anticandidal and In vitro Anti-Proliferative Activity of Sonochemically synthesized Indium Tin Oxide Nanoparticles

The present work demonstrates the synthesis, characterization and biological activities of different concentrations of tin doped indium oxide nanoparticles (Sn doped In2O3 NPs), i.e., (Sn/In = 5%, 10% and 15%). We have synthesized different size (38.11 nm, 18.46 nm and 10.21 nm) of Sn doped In2O3 NPs. by using an ultra-sonication process. The Sn doped In2O3 NPs were characterized by by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) which confirmed the successful doping of tin (Sn) with Indium oxide (In2O3). Anticandidal activity was performed by standard agar dilution method using Candida albicans for the study. The minimum inhibitory/fungicidal concentration (MIC/MFC) values recorded were, 8 & >8 mg/ml for pure In2O3 NPs, 4 & 8 mg/ml for 5%, 2 & 8 mg/ml for 10%, whereas 1 & >4 mg/ml for 15% Sn doped In2O3 NPs, respectively. The topographical alteration caused by Sn doped In2O3 NPs on Candida cells, was clearly observed by SEM examination. A significant enhancement in anticandidal activity was seen, when Candida cells were exposed to (Sn/In = 5%, 10% and 15%). Moreover, we have also evaluated the impact of Sn-In2O3 NPs on human colorectal carcinoma cells (HCT-116). The results demonstrated that Sn-In2O3 NPs (Sn/In = 5%, 10% and 15%), caused dose dependent decrease in the cancer cell viability as the low dosage (2.0 mg/mL) showed 62.11% cell viability, while 4.0, 8.0, 16.0, 32.0 mg/mL dosages showed 20.45%, 18.25%, 16.58%, and 15.58% cell viability. In addition, the treatment of Sn-In2O3 NPs also showed significant cellular and anatomical changes in cancer cells as examined by microscopes. We have also examined the impact of Sn-In2O3 NPs (5%, 10%, 15%) on normal cells (HEK-293) and the results demonstrate that Sn-In2O3 NPs did not reduce the cell viability of normal cells.

The toxicology of indium oxide

Indium oxide (In₂O₃) is a technologically important semiconductor essentially used, doped with tin oxide, to form indium tin oxide (ITO). It is poorly soluble in all so far tested physiologic media. After repeated inhalation, In₂O₃ particles accumulate in the lungs. Their mobilization can cause significant systemic exposure over long periods of time. An increasing number of cases of severe lung effects (characterized by pulmonary alveolar proteinosis, emphysema and/or interstitial fibrosis) in workers of the ITO industry warrants a review of the toxicological hazards also of In₂O₃. The database on acute and chronic toxicity/carcinogenicity/genotoxicity/reproductive toxicity as well skin/eye irritation and sensitization is very limited or even lacking. Short-term and subchronic inhalation studies in rats and mice revealed persistent alveolar proteinosis, inflammation and early indicators of fibrosis in the lungs down to concentrations of 1 mg/m³. Epidemiological and medical surveillance studies, serum/blood indium levels in workers as well as data on the exposure to airborne indium concentrations indicate a need for measures to reduce exposure at In₂O₃ workplaces.

New interplay between interstitial and alveolar macrophages explains pulmonary alveolar proteinosis (PAP) induced by indium tin oxide particles

Occupational exposure to indium tin oxide (ITO) particles has been associated with the development of severe lung diseases, including pulmonary alveolar proteinosis (PAP). The mechanisms of this lung toxicity remain unknown. Here, we reveal the respective roles of resident alveolar (Siglec-F^high AM) and recruited interstitial (Siglec-F^low IM) macrophages contributing in concert to the development of PAP. In mice treated with ITO particles, PAP is specifically associated with IL-1α (not GM-CSF) deficiency and Siglec-F^high AM (not Siglec-F^low IM) depletion. Mechanistically, ITO particles are preferentially phagocytosed and dissolved to soluble In³⁺ by Siglec-F^low IM. In contrast, Siglec-F^high AM weakly phagocytose or dissolve ITO particles, but are sensitive to released In³⁺ through the expression of the transferrin receptor-1 (TfR1). Blocking pulmonary Siglec-F^low IM recruitment in CCR2-deficient mice reduces ITO particle dissolution, In³⁺ release, Siglec-F^high AM depletion, and PAP formation. Restoration of IL-1-related Siglec-F^high AM also prevented ITO-induced PAP. We identified a new mechanism of secondary PAP development according to which metal ions released from inhaled particles by phagocytic IM disturb IL-1α-dependent AM self-maintenance and, in turn, alveolar clearance.

Solubility of indium-tin oxide in simulated lung and gastric fluids: Pathways for human intake

From being a metal with very limited natural distribution, indium (In) has recently become disseminated throughout the human society. Little is known of how In compounds behave in the natural environment, but recent medical studies link exposure to In compounds to elevated risk of respiratory disorders. Animal tests suggest that exposure may lead to more widespread damage in the body, notably the liver, kidneys and spleen. In this paper, we investigate the solubility of the most widely used In compound, indium-tin oxide (ITO) in simulated lung and gastric fluids in order to better understand the potential pathways for metals to be introduced into the bloodstream. Our results show significant potential for release of In and tin (Sn) in the deep parts of the lungs (artificial lysosomal fluid) and digestive tract, while the solubility in the upper parts of the lungs (the respiratory tract or tracheobronchial tree) is very low. Our study confirms that ITO is likely to remain as solid particles in the upper parts of the lungs, but that particles are likely to slowly dissolve in the deep lungs. Considering the prolonged residence time of inhaled particles in the deep lung, this environment is likely to provide the major route for uptake of In and Sn from inhaled ITO nano- and microparticles. Although dissolution through digestion may also lead to some uptake, the much shorter residence time is likely to lead to much lower risk of uptake.

Characteristics of an oxide/metal/oxide transparent conducting electrode fabricated with an intermediate Cu–Mo metal composite layer for application in efficient CIGS solar cell

CIGS solar cells fabricated with different types of AZO/metal/AZO (AZO/Cu/AZO, AZO/Mo/AZO and AZO/Cu–Mo/AZO) transparent conducting electrodes.