Unexpected hydroxyl radical production in brewed tea under sunlight.

Tea is one of the world's most popular and widely consumed beverages. It is a common pastime to enjoy a cup of tea in the sunshine. However, little attention has been given to understanding the possible photochemical reactions occurring beneath the calm surface of brewed tea. Epigallocatechin gallate (EGCG), which is widely used in food and beverages, is the most significant active ingredient found in tea. In this study, we investigated the presence of free radicals in both an aqueous EGCG solution and brewed tea under simulated sunlight conditions. To our surprise, we unexpectedly observed the production of hydroxyl radicals (•OH) in brewed tea. It was found that sunlight irradiation played a critical role in the formation of •OH, independent of the presence of metal ions. Furthermore, we demonstrated that the •OH generated from the EGCG aqueous solution induced cell cytotoxicity and DNA damage in vitro. Considering the crucial role of •OH in various fields, including human health and the environment, it is important to further explore the practical implications of •OH production in brewed tea under sunlight. In summary, our study unveils the unexpected formation of •OH in brewed tea and emphasizes the significance of sunlight-induced reactions. The observed cytotoxic and DNA-damaging effects of •OH emphasize the importance of understanding the potential health consequences associated with tea consumption. Further research in this area will contribute to a better understanding of the broader implications of •OH production in brewed tea under sunlight.

Target Analysis of Polychlorinated Naphthalenes and Nontarget Screening of Organic Chemicals in Bovine Milk, Infant Formula, and Adult Milk Powder by High-Resolution Mass Spectrometry.

Infant formula is intended as an effective substitute for breast milk but is the main source of polychlorinated naphthalenes (PCNs) to nonbreastfed infants. We performed target and nontarget analyses to determine PCNs and identify other organic contaminants in infant formula. The mean PCN concentrations in infant formula, milk powder, and bovine milk were 106.1, 88.8, and 78.2 µg kg-1 of dry weight, respectively. The PCN congener profiles indicated that thermal processes and raw materials were probably the main sources of PCNs in infant formula. A health risk assessment indicated that PCNs in infant formula do not pose health risks to infants. Using gas chromatography-Orbitrap mass spectrometry, 352, 372, and 161 organic chemicals were identified in the infant formula, milk powder, and bovine milk samples, respectively. Phthalate esters were detected in all four plastic-packed milk powder samples. The results indicated milk becomes more contaminated with organic chemicals during manufacturing, processing, and packaging.

Global squid contamination by halogenated polycyclic aromatic hydrocarbons and its trade induced risk transfer.

Squid is traded globally as an important food resource. However, the occurrence of carcinogenic halogenated polycyclic aromatic hydrocarbons (HPAHs) in squid and the risk of their transfer through trade is little understood or recognized. Here, we comprehensively evaluated the occurrence and risk transfer by quantifying the congener-specific concentrations of HPAHs in 121 squid samples collected from the Pacific, Atlantic and Indian oceans. This was the first time that nine of the 36 target chlorinated and brominated PAH congeners had been detected in squid. The HPAHs exhibited growth-dilution effects in the squid. The lipid content of squid was the most significant factor influencing HPAH bioaccumulation, while differences in squid growth and local ocean contamination influenced by geographical distribution also affected HPAH bioaccumulation. The redistribution and risk transfers of HPAHs in squid as a food could be affected by international trading. The cancer risks from squid consumption in China and Mexico were increased by 50 % and 30 %, respectively, because of international squid trading.

[Characteristics of Organic Matter Composition and Oxidation Potential in Road Dust in Winter in Xi'an].

Roads are the main places where urban people are exposed to atmospheric particulate matter from outdoor activities, and certain oxidatively active substances contained in road particulate matter are important components that induce the generation of reactive oxygen species (ROS), which in turn endanger human health. Here, we explored the characteristics of organic matter composition in water-soluble (WSM) and methanol-soluble fractions (MSM) of road dust in Xi'an and its oxidation potential (OP). Additionally, we investigated the organic fractions and their distribution based on parallel factor analysis (PARAFAC) and analyzed the correlation between organic matter types and OP. The results showed that the water-insoluble fraction of road dust in Xi'an contained more chromophoric organic matter with an average total concentration of (4.71±1.27)×104 R.U., which was 12 times higher than that of WSM[(3.96±1.10)×103 R.U.], of which low-oxidizing humic-like substances (HULIS) were the main organic matter (34.8%-43.7% of the total organic matter). The results of cluster analysis showed that the important sources of organic matter in road dust in Xi'an were fuel combustion and industrial production. The mean value of dust oxidative toxicity was (0.34±0.08) pmol·(min·µg)-1, with the water-insoluble fraction providing 70% of the total oxidative toxicity of dust particles, which was 2.4 times higher than the water-soluble fraction. The main precursors of oxidative toxicity of dust particles were metal elements, and special types of organic substances were also one of the important oxidative toxicity precursors, among which chromophore organic matter was the main cause of OP production in the WSM fraction (r=0.35, P<0.01), and protein-like organic matter and highly oxidized HULIS in WSM may have been the main two types of organic substances for OP production. However, there was no significant correlation between organic matter concentration in MSM and water-insoluble OP (OPTotal-OPWSM) (r=-0.04, P>0.1), so the oxidative toxicity of the water-insoluble particulate matter fraction was mainly generated from non-organic matter.

Occurrences and spatial distributions of dioxin-like polychlorinated biphenyls in chlorobenzene and chloroethylene manufacturing processes in China.

As a group of pollutants listed in the Stockholm Convention, polychlorinated biphenyls (PCB) should be eliminated and their releases should be controlled. For this purpose, a complete PCB emission inventory is urgently required. Current unintentional releases of PCB were dominantly focused on waste incineration and non-ferrous metal production industries. The formation of PCB in chlorinated chemical manufacturing processes is poorly understood. In this study, occurrences and inventory of dioxin-like PCB (dl-PCB) in three typical chemical manufacturing processes, including chlorobenzene and chloroethylene production processes, were investigated. The bottom residues, which were high boiling point by-products after rectification tower, contained higher concentration of PCB than other stage samples in monochlorobenzene production and trichloroethylene production processes. The PCB concentrations were as high as 1.58 ng/mL and 152.87 ng/mL, respectively, which should be further concerned. The toxic equivalent quantities (TEQ) of dl-PCB in monochlorobenzene, trichloroethylene, and tetrachloroethylene products were 0.25 µg TEQ/t, 1.14 µg TEQ/t, and 5.23 µg TEQ/t, respectively. The mass concentration and TEQ of dl-PCB determined in this research can be used for the further development of dl-PCB emission inventory from these chemical manufacturing industries. In addition, temporal and spatial trends of PCB releases from typical chemical manufacturing processes from 1952 to 2018 in China were clarified. The releases increased rapidly in the latest two decades and presented an expansion tendency from the southeast coastal areas to northern and central areas. The continuing upward trend for the output and the high dl-PCB TEQ of chloroethylene indicated significant releases of PCB from chemical manufacturing processes and should receive more attention.

Industrial source identification of polyhalogenated carbazoles and preliminary assessment of their global emissions.

Polyhalogenated carbazoles (PHCZs) are emerging global pollutants found in environmental matrices, e.g., 3000 tonnes of PHCZs have been detected in the sediments of the Great Lakes. Recognition of PHCZ emissions from ongoing industrial activities worldwide is still lacking. Here, we identify and quantify PHCZ emissions from 13 large-scale industries, 12 of which previously have no data. Congener profiles of PHCZs from investigated industrial sources are clarified, which enables apportioning of PHCZ sources. Annual PHCZ emissions from major industries are estimated on the basis of derived emission factors and then mapped globally. Coke production is a prime PHCZ emitter of 9229 g/yr, followed by iron ore sintering with a PHCZ emission of 3237 g/yr. China, Australia, Japan, India, USA, and Russia are found to be significant emitters through these industrial activities. PHCZ pollution is potentially a global human health and environmental issue.

An updated global overview of the manufacture and unintentional formation of polychlorinated naphthalenes (PCNs).

This review updates information on the historical manufacture and unintentional production of polychlorinated naphthalenes (PCNs). The direct toxicity of PCNs as a result of occupational human exposure and through contaminated feed in livestock was recognised decades ago, making PCNs a precursor chemical for consideration in occupational medicine and occupational safety. This was confirmed by the listing of PCNs by the Stockholm Convention as a persistent organic pollutant in the environment, food, animals and humans. PCNs were manufactured globally between 1910 ∼ 1980, but reliable data on the volumes produced or national outputs are scarce. A total figure for global production would be useful for the purposes of inventory and control and it is clear that combustion related sources such as waste incineration, industrial metallurgy and use of chlorine are current major sources of PCNs to the environment. The upper bound estimate of total global production has been put at 400,000 metric tons but the amounts (at least, many 10 s of tonnes) that are currently emitted unintentionally every year through industrial combustion processes should also be inventoried along with estimates for emissions from bush and forest fires. This would however require considerable national effort, financing and co-operation from source operators. The historical (1910-1970 s) production and resulting emissions through diffusive/evaporative releases through usage, are still reflected in documented occurrence and patterns of PCNs in human milk in Europe and other locations worldwide. More recently, PCN occurrence in human milk from Chinese provinces has been linked to local unintentional emissions from thermal processes.

Integrated in silico-in vitro rational design of oncogenic EGFR-derived specific monoclonal antibody-binding peptide mimotopes.

Human epidermal growth factor receptor (EGFR) is strongly associated with malignant proliferation and has been established as an attractive therapeutic target of diverse cancers and used as a significant biomarker for tumor diagnosis. Over the past decades, a variety of monoclonal antibodies (mAbs) have been successfully developed to specifically recognize the third subdomain (TSD) of EGFR extracellular domain. Here, the complex crystal structures of EGFR TSD subdomain with its cognate mAbs were examined and compared systematically, revealing a consistent binding mode shared by these mAbs. The recognition site is located on the [Formula: see text]-sheet surface of TSD ladder architecture, from which several hotspot residues that significantly confer both stability and specificity to the recognition were identified, responsible for about half of the total binding potency of mAbs to TSD subdomain. A number of linear peptide mimotopes were rationally designed to mimic these TSD hotspot residues in different orientations and/or in different head-to-tail manners by using an orthogonal threading-through-strand (OTTS) strategy, which, however, are intrinsically disordered in Free State and thus cannot be maintained in a native hotspot-like conformation. A chemical stapling strategy was employed to constrain the free peptides into a double-stranded conformation by introducing a disulfide bond across two strand arms of the peptide mimotopes. Both empirical scoring and [Formula: see text]fluorescence assay reached an agreement that the stapling can effectively improve the interaction potency of OTTS-designed peptide mimotopes to different mAbs, with binding affinity increase by [Formula: see text]-fold. Conformational analysis revealed that the stapled cyclic peptide mimotopes can spontaneously fold into a double-stranded conformation that well threads through all the hotspot residues on TSD [Formula: see text]-sheet surface and exhibits a consistent binding mode with the TSD hotspot site to mAbs.

Emission reduction of PCDD/Fs by flue gas recirculation and activated carbon in the iron ore sintering.

One of the main sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment is the sintering of iron ore. Both flue gas recirculation (FGR) and activated carbon (AC), which have the impact of decreasing both PCDD/Fs and conventional pollutants (NOx, SO2, etc.), are significant technologies for the abatement of PCDD/Fs from the sintering exhaust gas. This work involved the first measurement of PCDD/Fs emissions during FGR and a thorough analysis of the impact of PCDD/Fs reduction following the coupling of FGR and AC technologies. According to the measured data, the ratio of PCDFs to PCDDs in the sintered flue gas was 6.8, indicating that during the sintering process, the PCDD/Fs were primarily produced by de novo synthesis. Further investigation revealed that FGR initially removed 60.7% of PCDD/Fs by returning it to the high temperature bed, and AC further removed 95.2% of the remaining PCDD/Fs through physical adsorption. While AC is better at removing PCDFs and can efficiently remove tetra-to octa-chlorinated homologs, FGR is more effective at removing PCDDs and has higher removal efficiency for hexa-to octa-chlorinated PCDD/Fs. Together, they complement each other with a removal rate of 98.1%. The study's findings are instructional for the process design of combining FGR and AC technologies to reduce PCDD/Fs in the sintered flue gas.

[Emission Characteristics and Control of Heavy Metals in Secondary Copper Smelting Process].

Secondary copper smelting is an important source of heavy metal emission. Flue gas samples were collected from different stages in secondary copper smelters to study the emission characteristics and control of particulate matters (PM) and heavy metals such as Cd, Cr, As, Pb, Sn, and Sb. The mass concentrations of heavy metals in flue gas and fly ash were determined using inductively coupled plasma-mass spectrometry. The emission factors of heavy metals were estimated. The results showed that the mass concentrations of heavy metals and PM in the flue gas were high in the cooling stage. After passing through a series of air pollution control devices, such as a bag filter and adsorption tower, the heavy metals and PM were simultaneously removed with a removal efficiency of 80%-99%. The concentration order of heavy metals in the stack gas from different anode furnace stages followed feeding-fusion>oxidation≈deoxidization. In general, the mass concentrations of heavy metals and PM in the stack gas could meet the industry emission standards. The average emission factors of As, Pb, Cr, Sn, Sb, and Cd were 2.6×103, 2.4×103, 2.7×103, 5.6×102, 34.1, and 9.8 mg·t-1, respectively. This could provide data support for estimating the annual emission amounts of heavy metals from the secondary copper industry and establishing the emission inventories. The fly ash contained high concentrations of Cu and Zn, which can be recycled as raw materials for recycling the valuable metals.

Framework of the Integrated Approach to Formation Mechanisms of Typical Combustion Byproducts─Polyhalogenated Dibenzo-p-dioxins/Dibenzofurans (PXDD/Fs).

Understanding the mechanisms through which persistent organic pollutants (POPs) form during combustion processes is critical for controlling emissions of POPs, but the mechanisms through which most POPs form are poorly understood. Polyhalogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs) are typical toxic POPs, and the formation mechanisms of PXDD/Fs are better understood than the mechanisms through which other POPs form. In this study, a framework for identifying detailed PXDD/Fs formation mechanisms was developed and reviewed. The latest laboratory studies in which organic free radical intermediates of PXDD/Fs have been detected in situ and isotope labeling methods have been used to trace transformation pathways were reviewed. These studies provided direct evidence for PXDD/Fs formation pathways. Quantum chemical calculations were performed to determine the rationality of proposed PXDD/Fs formation pathways involving different elementary reactions. Many field studies have been performed, and the PXDD/Fs congener patterns found were compared with PXDD/Fs congener patterns obtained in laboratory simulation studies and theoretical studies to mutually verify the dominant PXDD/Fs formation mechanisms. The integrated method involving laboratory simulation studies, theoretical calculations, and field studies described and reviewed here can be used to clarify the mechanisms involved in PXDD/Fs formation. This review brings together information about PXDD/Fs formation mechanisms and provides a methodological framework for investigating PXDD/Fs and other POPs formation mechanisms during combustion processes, which will help in the development of strategies for controlling POPs emissions.

Formation and Inventory of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans and Other Byproducts along Manufacturing Processes of Chlorobenzene and Chloroethylene.

Chlorinated organic chemicals are produced and used extensively worldwide, and their risks to the biology and environment are of increasing concern. However, chlorinated byproducts [e.g., polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)] formed during the commercial manufacturing processes and present in organochlorine products are rarely reported. The knowledge on the occurrences and fate of unintentional persistent organic chemicals in the manufacturing of organochlorine chemical is necessary for accurate assessment of the risks of commercial chemicals and their production. Here, PCDD/Fs were tracked throughout chlorobenzene and chloroethylene production processes (from raw materials to final products) by target analysis. Other byproducts that can further transform into PCDD/Fs were also identified by performing non-target screening. As a result, the PCDD/F concentrations were mostly the highest in bottom residues, and the octachlorinated congeners were dominant. Alkali/water washing stages may cause the formation of oxygen-containing byproducts including PCDD/Fs and acyl-containing compounds, so more attention should be paid to these stages. PCDD/Fs were of 0.17 and 0.21-1.2 ng/mL in monochlorobenzene and chloroethylene products, respectively. Annual PCDD/F emissions (17 g toxic equivalent in 2018) during chlorobenzene and chloroethylene production were estimated using PCDD/F emission factors. The results can contribute to the improvement of PCDD/F inventories for the analyzed commercial chemicals.

Concentrations, congener patterns, and correlations of unintentional persistent organic pollutants in cement kilns co-processing hazardous waste.

Emissions from two typical cement kilns co-processing different kind of hazardous waste were analyzed for 143 congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls, polychlorinated naphthalenes, polybrominated dibenzo-p-dioxins and dibenzofurans, and polybrominated diphenyl ethers. The congener distributions in different process stages were investigated. One of the plants co-processed waste chemical reagents from laboratories. The emission factor (TEQ basis) for the plant was 2.09 ng WHO2005 TEQ/t, with the kiln head and the kiln back end contributing 1.18, 0.91 ng WHO2005 TEQ/t, respectively. The other plant co-processed municipal waste incineration fly ash. The emission factor for the plant was 0.12 ng WHO2005 TEQ/t, with the kiln head and the kiln back end contributing 0.022, and 0.10 ng WHO2005 TEQ/t. These results indicate that co-processing of waste containing reagents from laboratories may lead to higher emission levels than co-processing of other types of waste. The congener patterns of persistent organic pollutants (POPs) in ash samples from the humidifier tower were similar to those in samples from the bag filter at the kiln back end. The correlation coefficients of five pollutants between the humidifier and bag filters samples were generally high, which indicated that conditions in those two stages similarly favored the formation of these POPs. Comparison of the concentrations for different process stages suggested that the main stage for formation of unintentional POPs was the humidifier tower. These results improve our understanding of emission characteristics and could be used for simultaneous control of multiple POPs.

Free radical mechanism of toxic organic compound formations from o-chlorophenol.

Organic free radical intermediates are pivotal to our understanding of toxic chemicals formation from chlorophenols that widely exist in thermal processes. However, in most cases, multiple free radical intermediates exist and produce complex spectra that are hard to deconvolute. Identification of free radical intermediates is the current difficulty for detailed formation mechanisms of toxic products from chlorophenols. In this study, a universal bottom-up method was developed to identify the organic free radical intermediates. Candidate organic free radicals were firstly speculated according to the critical parameters obtained from experimental electron paramagnetic resonance (EPR) spectra and the calculated bond dissociation energies of precursors. Their theoretical spectra were then used retrospectively to justify the accordance with the experimental EPR spectra. Identification of the organic free radicals provides straightforward evidence for the formation pathways of pollutants from chlorophenol. Internal factors influencing formation of radical intermediates and the toxic products were also studied, including the ortho effect of the precursor, spin densities of the organic free radical intermediates, and steric hindrance effects of the molecular intermediates. In combination of the experimental results and theoretical calculations, detailed formation mechanisms of toxic pollutants intermediating by organic free radicals from thermal oxidation of chlorophenol were strongly evidenced.

Man-made reactive oxygen species as green disinfectants.

Image 1.

Tuning the Carrier Transfer Behavior of Coaxial ZnO/ZnS/ZnIn2 S4 Nanorods with a Coherent Lattice Heterojunction Structure for Photoelectrochemical Water Oxidation.

Invited for this month's cover is the group of Feng Li at the Ningxia University. The image shows how the coherent lattice heterojunction interface can play a role in the efficient separation of photogenerated carriers of ZnO-based photoanode for photoelectrochemical water splitting. The Research Article itself is available at 10.1002/cssc.202201469.

Tuning the Carrier Transfer Behavior of Coaxial ZnO/ZnS/ZnIn2 S4 Nanorods with a Coherent Lattice Heterojunction Structure for Photoelectrochemical Water Oxidation.

Serious degradation and the short photogenerated carrier lifetime for the wide-bandgap semiconductor ZnO have become prominent issues that negatively affect photoelectrochemical (PEC) water splitting. Herein, a novel electron transport pathway was constructed by simple but effective coaxial growth of ZnO/ZnS/ZnIn2 S4 heterostructure nanoarrays to increase the carrier separation efficiency. This new photoanode fulfilled the requirements of both favorable band alignment and stability, achieving a stable photocurrent density of 1.146 mA cm-2 at 1.2 VRHE , which was approximately twice that of pristine ZnO. Detailed experimental studies revealed that the improved PEC activity was due to the lattice-matching interface coherency that activated the carrier transport pathway, giving rise to an optimized interfacial electronic structure for promoted charge separation by the built-in electric field and strengthened water oxidation activity. This design may provide a new approach to fabricating various efficient lattice-matching coherent interface photoanodes for PEC water splitting.

Metal-Catalyzed Formation of Organic Pollutants Intermediated by Organic Free Radicals.

Metal compounds play important roles in the formation of organic pollutants during thermal-related processes. However, the metal-catalyzed predominant organic pollutants have not previously been characterized nor have any detailed catalytic mechanisms been clarified. Here, we preciously distinguished the multiple organic free radical intermediates on metal catalyst surfaces during the organic pollutant formation through laboratory and theoretical studies. Differences between the organic free radical intermediate species, concentrations, and formation mechanisms under the catalysis of different metal compounds were investigated. The results were verified mutually with the differed characteristics of organic pollutant products. CuO predominantly catalyzed the formation of highly chlorinated phenoxy radical intermediates and dioxins. High proportions of semiquinone radicals and oxygen-containing derivatives were found on ZnO surfaces. Differently, methyl-substituted phenoxy radicals and long-chain products formed on Al2O3 surfaces. The results will be instructive for the target emission control of priority organic pollutants during thermal-related processes rich in different metal compounds.

Variation in the formation characteristics of PBDD/F, brominated PAH, and PBDE congeners along the secondary copper smelting processes.

Simultaneous determination of 58 congeners of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), brominated polycyclic aromatic hydrocarbons (Br-PAHs), and polybrominated diphenyl ethers (PBDEs) from multiple stages of industrial-scale secondary copper smelting plants was conducted with the aim of understanding their variations and control. In addition to the historical manufacture of PBDEs as brominated flame retardants, this study confirmed that PBDEs can be unintentionally produced and released from the secondary copper industry. The average mass emission factors of PBDD/Fs, PBDEs, and Br-PAHs from different sources were 10.0, 5.21 × 103, and 7.24 × 103 µg t-1, respectively. Therefore, the emission of brominated persistent organic pollutants (POPs) in the secondary copper industry should be of concern. The concentration of brominated POPs increased from the gas cooling stage to stack outlet due to the possible "memory effect" and the regenerated POPs were mainly low-brominated homologs. A comparison of brominated POPs with corresponding chlorinated analogs in the same process indicated that the formation pathway of Br-PAHs was consistent with that of chlorinated PAHs. However, unlike chlorinated dioxins and furans, PBDD/Fs can also be formed from PBDEs as precursors, leading to obvious increases in highly brominated furans. Therefore, inhibiting the unintentional formation of PBDEs is important for controlling brominated POPs emissions.

Can Daytime Transcranial Direct Current Stimulation Treatment Change the Sleep Electroencephalogram Complexity of REM Sleep in Depressed Patients? A Double-Blinded, Randomized, Placebo-Controlled Trial.

Study Objectives: The purpose of this study was to determine the effects of daytime transcranial direct current stimulation (tDCS) on sleep electroencephalogram (EEG) in patients with depression. Methods: The study was a double-blinded, randomized, controlled clinical trial. A total of 37 patients diagnosed with a major depression were recruited; 19 patients (13 females and 6 males mean age 44.79 ± 15.25 years) received tDCS active stimulation and 18 patients (9 females and 9 males; mean age 43.61 ± 11.89 years) received sham stimulation. Ten sessions of daytime tDCS were administered with the anode over F3 and the cathode over F4. Each session delivered a 2 mA current for 30 min per 10 working days. Hamilton-24 and Montgomery scales were used to assess the severity of depression, and polysomnography (PSG) was used to assess sleep structure and EEG complexity. Eight intrinsic mode functions (IMFs) were computed from each EEG signal in a channel. The sample entropy of the cumulative sum of the IMFs were computed to acquire high-dimensional multi-scale complexity information of EEG signals. Results: The complexity of Rapid Eye Movement (REM) EEG signals significantly decreased intrinsic multi-scale entropy (iMSE) (1.732 ± 0.057 vs. 1.605 ± 0.046, P = 0.0004 in the case of the C4 channel, IMF 1:4 and scale 7) after tDCS active stimulation. The complexity of the REM EEG signals significantly increased iMSE (1.464 ± 0.101 vs. 1.611 ± 0.085, P = 0.001 for C4 channel, IMF 1:4 and scale 7) after tDCS sham stimulation. There was no significant difference in the Hamilton-24 (P = 0.988), Montgomery scale score (P = 0.726), and sleep structure (N1% P = 0.383; N2% P = 0.716; N3% P = 0.772) between the two groups after treatment. Conclusion: Daytime tDCS changed the complexity of sleep in the REM stage, and presented as decreased intrinsic multi-scale entropy, while no changes in sleep structure occurred. This finding indicated that daytime tDCS may be an effective method to improve sleep quality in depressed patients. Trial registration This trial has been registered at the ClinicalTrials.gov (protocol ID: TCHIRB-10409114, in progress).