• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Multicolor biomass based carbon nanodots for bacterial imaging

    2022-06-18 03:00:24WenboZhaoYongWangKaikaiLiuRuiZhouChongxinShan
    Chinese Chemical Letters 2022年2期

    Wenbo Zhao, Yong Wang, Kaikai Liu, Rui Zhou, Chongxin Shan

    Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Materials Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China

    ABSTRACT Biomass-based carbon nanodots (CNDs) are becoming promising fluorescent materials due to their superior optical properties and excellent biocompatibility.However, most fluorescent CNDs are prepared under high temperatures with artificial chemicals as precursors.In this work, multicolor biomass-based CNDs have been prepared by employing natural biomass as precursors through an ultrasonic-assisted method at room temperature.The multicolor biomass-based CNDs can be prepared within 10 min, and cavitation produced by ultrasound in solution contributes to the polymerization of biomolecules into nanodots.The emission of the CNDs covers from blue to red region, with emission peaks centered at 410 nm, 520 nm and 670 nm, and the corresponding photoluminescence quantum yields of the CNDs are 11%, 12% and 28%, respectively.Furthermore, bacterial imaging by using the biomass-based CNDs as fluorescent imaging agent has been demonstrated.This work provides a convenient ultrasonic-assisted way for fabrication multicolor and eco-friendly biomass CNDs, demonstrating their application in bacterial imaging.

    Keywords:Carbon nanodots Biomass Fluorescence Ultrasonic methods Bacterial imaging

    Fluorescent nanomaterials are of great interest in the field of display technology, detection and biomedical diagnosis/treatment[1-6].An important milestone in the development of fluorescent nanomaterials was the discovery of fluorescent semiconductor quantum dots (QDs), which have many recognized advantages,such as high quantum yield (QY), good photostability, and controllable preparation processes.However, these highly fluorescent QDs have also suffered from negative attention, as most of them contain heavy metal ions, and the issue of toxicity is always a concern[7,8].Increased efforts have been made to develop less toxic, better biocompatible fluorescent nanomaterials as a potential alternative to semiconductor QDs, promoting their application especially in the field of biomedicine.

    Carbon nanodots (CNDs), as a new class of fluorescent materials, have attracted much attention for their fantastic fluorescent properties and high stability [9-11].The heavy metal-free of CNDs is the obvious advantage over conventional QDs, the major element of CNDs is elemental C, while the latter mostly have lead and cadmium [12,13].In the past few years, there has been considerable progress in synthesis and application of CNDs [14,15].Until now, the emission region of CNDs extends from a single blue color to the deep ultraviolet and near-infrared regions [9,16,17].Light-emitting diodes, optical encryption and bio-imaging based on emissive CNDs have been realized [18-22].The fact why CNDs have so much application potential is partially due to variety of reaction precursors, that is, different precursors can be used for preparation CNDs with distinct properties.Precursors of CNDs can be small molecule compounds or some carbon-based materials such as carbon nanotubes and graphene, in addition to which biomass is also a very important source of precursors [23].On the one hand,it is possible way to convert waste biomass into a useful material.On the other hand, biomass has unique advantages over man-made carbon sources, such as cheapness, abundance of raw materials,and better environmental friendliness [24,25].There are already many examples of CNDs prepared using biomass as precursor, and applications based on these CNDs have also been demonstrated[26-28].Without exception, all of them involved typical processes of high-temperature carbonization.This process may involve a long time and high temperature, which is difficult to achieve large-scale batch production.Ultrasonics-assisted synthesis method is one of effective methods for preparing nanomaterials, which has been reported CNDs for synthesis of nanomaterials [29-33].Ultrasound produces cavitation in solution, where the high temperature and pressure environment created by this process can provide energy required for formation of nanodots [34].However, only single color biomass based CNDs are obtained by the ultrasonic method, and there are few reports available regarding the preparation of multicolor CNDs from biomass through ultrasonic-assisted method at room temperature.

    In this work, biomass based fluorescent CNDs have been demonstrated through ultrasonic-assisted method at room temperature.The CNDs can emit blue, green and red emission by tuning biomass precursors.The photoluminescence (PL) QY of the asprepared CNDs with blue, green and red fluorescence is 11%, 12%and 28%, respectively.In addition, bacteria imaging by using the CNDs has been investigated, in which blue and green CNDs emissive can label all bacteria, while red emissive CNDs enable the identification of gram-positive and gram-negative bacteria due to competition between electrostatic repulsion and hydrophobic interaction.

    The multicolor biomass based CNDs are obtained from different precursors with the assistance of ultrasonic and bacteria imaging by using the CNDs as imaging agents has been demonstrated,as illustrated in Fig.1.In general, the three precursors were each weighed to 4 g.Among these, honeysuckle was added to a 500 mL DMSO solution and turmeric and perilla leaves were separately added to 500 mL of dichloromethane.Blue, green and red emissive CNDs were obtained after ultrasonic treatment for 10 min.The as-prepared CNDs are further purified by silica gel chromatography to remove any excess impurities.For convenience, the CNDs with blue, green and red fluorescence are named as b-CNDs, g-CNDs and r-CNDs, respectively.The morphologies of the CNDs were characterized by a transmission electron microscope (TEM).From Figs.2a-c, all of the CNDs have uniform size and exhibit spherelike shapes, with average diameters of 3.7 nm, 2.6 nm and 4.2 nm(bottom inset), respectively.The high-resolution TEM (HR-TEM) images (Top inset) indicate the high crystallinity of the CNDs, with a lattice spacing of 0.21 nm [9].These results indicate that biomass can form CNDs in a short time under ultrasonic action, without the need for additional heating procedures.

    Fig.1.Schematic illustration of preparation of multicolor biomass based CNDs and bacteria imaging using the CNDs as imaging agent.

    To investigate surface functional groups onto these CNDs,Fourier transform infrared (FTIR) spectra were recorded, as shown in Figs.S1-S3 (Supporting information).The absorption bands at around 3432 cm-1can be assigned to the stretching vibrations of-OH.The peaks at 2920 cm-1and 2850 cm-1are attributed to symmetric stretching of -CH3and -CH2, which indicates that the selected CNDs contain a series of hydrocarbon groups [35].The peak at 1640 cm-1corresponds to C=C bending vibrations [30],the signal can be observed in the spectra of the CNDs.In addition,C=O signals were observed in the spectra of the g- and r-CNDs,indicating some carboxyl groups on the surface CND.

    X-ray photoelectron spectroscopy (XPS) was used to further investigate the surfaces of the CNDs.Figs.2d-f show the XPS spectra of the three CNDs.Only C 1s (285 eV) and O 1s (531 eV) signals can be observed from that of b- and g-CNDs, indicating b- and g-CNDs do not contain element N.This is most likely from the fact that the active ingredients of biomass precursors (honeysuckle and turmeric) are mostly carbohydrates, which the major elements are C and O elements.C, O and N elements are present in the r-CNDs from full XPS spectrum of r-CNDs.The origin of element N may be derived from chlorophyll of precursor perilla, which was doped into the r-CNDs during the ultrasonic process.The high-resolution XPS C 1s spectra are shown in Figs.2g-i.The C 1s envelope of the b- and g-CNDs can be deconvoluted into three Gaussian peaks corresponding to sp2C (C-C/C=C), sp3C (C-O), and C=O at 288.2 eV,respectively [36].The C 1s spectrum of the r-CNDs can be divided into sp2/sp3carbons (C-C/C=C, 284.5 eV), C-N/C-O at 285.7 eV,and C=O at 288.2 eV.Moreover,13C NMR spectra were recorded,as shown in Figs.S4 and S5 (Supporting information).Unfortunately, the NMR spectrum of the b-CNDs was not collected even though we tried for many times.For g-CNDs and r-CNDs, signals in the range of 20-50 ppm correspond to sp3carbon atoms.In addition, resonance signals in the 120-145 ppm range are attributed to sp2carbon atoms, indicating the formation of sp2structural domains.Moreover, signals greater than 200 ppm was also observed in the13C NMR spectrum of the g-CNDs, corresponding to the carbonyl group [16].The above results indicate the sp2and sp3carbon atoms within the CNDs synthesized by ultrasonic assisted method.

    Fig.2.TEM images of (a) b-CNDs, (b) g-CNDs, and (c) r-CNDs, and the insets are size distribution of the corresponding CNDs.XPS patterns of (d) b-CNDs, (e) g-CNDs and(f) r-CNDs.High-resolution XPS spectra of the C 1s for (g) b-CNDs, (h) g-CNDs, and (i) r-CNDs.

    The optical properties of the three CNDs are investigated, as presented in Fig.3.The excitation-emission contour plots of the three CNDs show that the emission centers of three CNDs are virtually unshifted over a wide excitation range, indicating that the excitation-independent PL feature of the as-prepared CNDs in this work.As shown in Fig.3a, the as-prepared b-CNDs solutions show the characteristic fluorescence property with emission peaks centered at 410 nm.The UV-vis absorption spectra of all three kinds of CNDs have a strong absorption band before 300 nm, which originates from theπ-π*transition of C=C [18].The UV-vis spectra of the b-CNDs show a strong absorption peak at 330 nm (Fig.3b),which is due to the n-π*transition of C=O.However, significant aggregation in water can lead to fluorescence quenching of the CNDs, limiting their application in bioimaging.Surface modification is an effective means of avoiding aggregation between CNDs[37].In order to achieve water-soluble CNDs, the obtained CNDs were modified by amphiphilic polymers, and the modified CNDs show bright emission in aqueous solution.The corresponding spectra of the CNDs after modification are shown in Fig.3c, and the images of the CNDs in different solution were taken (Fig.3d).Fig.3e is excitation-independent PL feature of the as-prepared g-CNDs with emission peaks centered at 520 nm.In the case of the g-CNDs, there is a strong absorption band at 430 nm (Fig.3f), which is very close to the excitation center, suggesting that the fluorescence of the g-CNDs derives from the n-π*transition under excitation of 430 nm.The modified g-CNDs are also effective in avoiding aggregation quenching, and the corresponding PL spectra and images in water, ethanol and DMSO are shown in Figs.3g and h.For the r-CNDs, emission peaks of r-CNDs centered at 670 nm (Fig.3i), and the corresponding absorption spectra cover from UV to red region, as shown in Fig.3j.Specifically, two absorption peaks centered at 420 nm and 670 nm can be observed, which is due to the enlarged conjugate region [9].Similar to the above results, the r-CNDs maintained well PL properties in water and other solutions after modification (Figs.3k and l), which facilitates their bioimaging applications.In addition, photostability of the three CNDs were measured (Fig.S6 in Supporting information), and the fluorescence intensity of the CNDs can keep consistent under continuous UV irradiation for 6 h, indicating their good photostability.

    Fig.3.(a) Excitation-emission contour plots of the b-CNDs.(b) UV-vis absorption spectra of the b-CNDs.The insets are the images of CNDs under sunlight and 365 nm excitation.(c) The PL spectra of modified b-CNDs are dispersed in water, ethanol and DMSO, and (d) the corresponding images under sunlight and 365 nm excitation.(e)Excitation-emission contour plots of the g-CNDs.(f) UV-vis absorption spectra of the g-CNDs.(g) PL spectra of g-CNDs dispersed in different solvents.(h) Image of g-CNDs dispersed in different solvents.(i) Excitation-emission contour plots of the r-CNDs.(j) UV-vis absorption spectra of the r-CNDs.(k) PL spectra of r-CNDs dispersed in different solvents.(l) Image of r-CNDs dispersed in different solvents.

    In view of excellent optical property, their bacterial imaging ability was assessed.In addition, CNDs prepared using biomass as precursors have better biocompatibility compared with synthetic chemicals, which has been confirmed in our previous work [38].In previous work, CNDs have been demonstrated in imaging and labeling cells of mammalian systems [9,14].The labeling and imaging of mammalian cell strongly suggest the feasibility of extending CNDs to label bacteria.Four bacteria were selected as representative models, including two kinds of gram-positive bacteria (Staphylococcus aureus, Enterococcus faecium) and two kinds of gram-negative bacteria (Escherichia coli, Salmonella).The bacterial toxicity of the three CNDs in dark conditions was tested forStaphylococcus aureusandEscherichia coli(Fig.S7 in Supporting information), and the results showed that none of the three CNDs were dark toxicity to bacteria.The three multicolor CNDs were incubated with the mentioned bacteria for half an hour, and a confocal laser scanning microscope was used for imaging observation.In Fig.4, strong signals can be detected from the b-CNDs stained bacteria in blue region under excitation of 405 nm, and the fluorescence signals can cover all parts of the bacteria.The similar results also obtained from g-CNDs, indicating good capabilities of the CNDs as bio-imaging agents.While there is a clear difference in the group of bacteria incubated with r-CNDs.Bright red signals can be easy detected in gram-positive bacteria, whereas for gramnegative bacteria that have been incubated, barely red signals can be detected under the same excitation conditions.Red fluorescence signal was detected on the surface of the gram-negative bacteria by using HyD detector and increasing excitation intensity (Fig.S8 in Supporting information).This indicates that r-CNDs are still present on the surface of the gram-negative bacteria, but in small numbers compared to the other gram-positive bacteria.This difference in imaging between bacteria may be attributed to the fact that the r-CNDs are more favorable for adhering to gram-positive bacteria and away from gram-negative bacteria.

    Fig.4.The confocal laser scanning microscope images of live S.aureus, E.faecium(gram-positive bacteria) and E.coli, Salmonella (gram-negative bacteria) treated by CNDs with a concentration of 200 μg/mL for 30 min.Scale bar: 25 μm.

    In order to understand the adhesion ability of three kinds of CNDs to different types of bacteria, the zeta potential of bacteria and CNDs in water were tested, as shown in Fig.S9 (Supporting information).Bacteria have a strong negative charge, while the band g-CNDs have a low charge.Therefore, there is no obvious repulsion between the b-, g-CNDs and all bacteria.Thus, b- and g-CNDs can adhere to the surface of the bacteria without resistance.For r-CNDs, the surface has strong negative charge, and electrostatic repulsion will hinder the contact between CNDs and bacteria.However, it is noted from the above results that the red fluorescence signal is readily detected in the gram-positive group, so it is likely that another force counteracts the electrostatic repulsion between the r-CNDs and the gram-positive bacteria.The hydrophobic chains on the surface of the r-CNDs endow them with affinity ability with gram-positive bacteria by hydrophobic action [20,39].It has also been confirmed in previous reports that weak hydrophobic ability of materials is beneficial to the affinity with grampositive bacteria, which is dominated by the difference in membrane structure between gram-positive and gram-negative bacteria[40].Subsequently, hydrophobic properties of r-CNDs was tested by a shake flask method [41], the hydrophobic coefficient of r-CNDs is less than 3, indicating r-CNDs is typical weak hydrophobic nanomaterials.Therefore, hydrophobic interaction between grampositive and r-CNDs plays a key role for staining gram-positive bacteria.In addition to animal cells, fungi are also an important part of eukaryotic cells.In order to investigate whether the CNDs can be used for fungal cell imaging,Fusarium graminearumandSaccharomyceswere selected as representative models.Both fungal cells were incubated with the multicolor CNDs for half an hour, and a laser confocal microscope was used for imaging observation.In Fig.S10 (Supporting information), strong signals can be detected from the b-CNDs stained fungal cells in blue region under excitation of 405 nm, and the fluorescence signals can cover all parts of the fungal.The similar results also obtained from g-CNDs and r-CNDs stained cells in green and red region, indicating good capabilities of the CNDs as fungal cell agents.

    In conclusion, biomass based CNDs with blue, green and red fluorescence have been demonstrated by ultrasonic-assisted method.The entire synthesis process does not involve any synthetic high-purity chemical reagents, high temperature and pressure, leading to a significant decrease in the cost of synthesis.Optical characterizations indicate that the as-prepared CNDs have good photostability and optical properties.Additionally, bacterial imaging by using the as-prepared CNDs demonstrates the potential as imaging agents for staining bacteria.

    Declaration of competing interest

    The authors declare no conflict of interest.

    Acknowledgments

    This work was supported by the National Natural Science Foundation of China (Nos.11904326, 62075198), China Postdoctoral Science Foundation (Nos.2019TQ0287, 2019M662510).

    Supplementary materials

    Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2021.08.084.

    国产亚洲精品久久久久久毛片| 老女人水多毛片| 久久99精品国语久久久| 男女那种视频在线观看| 国产片特级美女逼逼视频| 国产伦精品一区二区三区视频9| 亚洲av电影不卡..在线观看| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 成人亚洲欧美一区二区av| 亚洲av不卡在线观看| 精品欧美国产一区二区三| 久久6这里有精品| 欧美精品国产亚洲| 少妇人妻一区二区三区视频| 成年女人看的毛片在线观看| 精品久久久久久成人av| 欧洲精品卡2卡3卡4卡5卡区| 国产中年淑女户外野战色| 99久久精品国产国产毛片| 高清毛片免费观看视频网站| 成年免费大片在线观看| 欧美成人一区二区免费高清观看| 熟女人妻精品中文字幕| 亚洲不卡免费看| 黄色欧美视频在线观看| 欧美性猛交╳xxx乱大交人| 亚洲av一区综合| 深夜a级毛片| 色哟哟哟哟哟哟| 在线a可以看的网站| 日本黄色片子视频| 国产真实乱freesex| 免费搜索国产男女视频| 久久综合国产亚洲精品| 一区福利在线观看| www.av在线官网国产| 免费无遮挡裸体视频| 国产精品嫩草影院av在线观看| 亚洲av一区综合| 亚洲无线在线观看| 亚洲av成人av| 国产男人的电影天堂91| 18禁黄网站禁片免费观看直播| 欧美日韩一区二区视频在线观看视频在线 | 老司机影院成人| 最近的中文字幕免费完整| 又爽又黄a免费视频| 亚洲在线观看片| 久久精品国产亚洲av天美| 国产精品人妻久久久久久| 久久久久久久久久成人| 亚洲第一区二区三区不卡| 欧美又色又爽又黄视频| 日日撸夜夜添| 久久久久久久午夜电影| 欧美日本亚洲视频在线播放| 亚洲精品国产成人久久av| 青青草视频在线视频观看| 99在线视频只有这里精品首页| 欧美3d第一页| 久久精品久久久久久久性| 可以在线观看毛片的网站| 尾随美女入室| 欧美日本亚洲视频在线播放| 日日撸夜夜添| 精品久久久久久久久av| 免费搜索国产男女视频| 国模一区二区三区四区视频| 尤物成人国产欧美一区二区三区| 看片在线看免费视频| 九九在线视频观看精品| 日韩欧美精品v在线| 天堂√8在线中文| 一级毛片电影观看 | 国产av不卡久久| 免费看美女性在线毛片视频| 免费搜索国产男女视频| 亚洲不卡免费看| 国产精品电影一区二区三区| 久久精品人妻少妇| 菩萨蛮人人尽说江南好唐韦庄 | 精品久久久久久久久av| 毛片一级片免费看久久久久| 亚洲欧美精品综合久久99| 男女那种视频在线观看| 国内精品美女久久久久久| 日本与韩国留学比较| 亚洲激情五月婷婷啪啪| 午夜视频国产福利| 老司机福利观看| 亚洲不卡免费看| 亚洲在久久综合| 人体艺术视频欧美日本| 插逼视频在线观看| 国产 一区精品| 婷婷色综合大香蕉| 免费搜索国产男女视频| 热99re8久久精品国产| 天堂网av新在线| 搞女人的毛片| 免费观看a级毛片全部| 26uuu在线亚洲综合色| 日本成人三级电影网站| 女的被弄到高潮叫床怎么办| 成年版毛片免费区| 此物有八面人人有两片| 99在线人妻在线中文字幕| 日韩成人av中文字幕在线观看| 一个人观看的视频www高清免费观看| 热99re8久久精品国产| 别揉我奶头 嗯啊视频| 欧美日韩国产亚洲二区| 午夜免费男女啪啪视频观看| 麻豆av噜噜一区二区三区| av视频在线观看入口| 嫩草影院入口| 亚洲五月天丁香| 亚洲七黄色美女视频| av免费在线看不卡| 一边亲一边摸免费视频| 一边亲一边摸免费视频| 国产成人91sexporn| 久久久成人免费电影| 国产蜜桃级精品一区二区三区| 久久久久久久久久黄片| 国产精品一区www在线观看| 亚洲av电影不卡..在线观看| 99久国产av精品| 赤兔流量卡办理| 变态另类成人亚洲欧美熟女| 亚洲成人中文字幕在线播放| 中文字幕熟女人妻在线| 免费看日本二区| 国产 一区 欧美 日韩| 九草在线视频观看| 国产午夜精品久久久久久一区二区三区| 国产不卡一卡二| 亚洲av第一区精品v没综合| 久久人人爽人人爽人人片va| 日韩成人av中文字幕在线观看| 久久精品国产99精品国产亚洲性色| 又黄又爽又刺激的免费视频.| 亚洲电影在线观看av| 日本色播在线视频| or卡值多少钱| 欧美色视频一区免费| 中文字幕免费在线视频6| 婷婷亚洲欧美| 91av网一区二区| 超碰av人人做人人爽久久| 最近手机中文字幕大全| 亚洲不卡免费看| 欧美日本视频| 22中文网久久字幕| 又粗又硬又长又爽又黄的视频 | 美女 人体艺术 gogo| 亚洲欧美精品综合久久99| 国产成人a区在线观看| 在线天堂最新版资源| 免费观看a级毛片全部| 欧美激情在线99| 能在线免费观看的黄片| 成人亚洲精品av一区二区| 美女被艹到高潮喷水动态| 国产高清三级在线| 成年版毛片免费区| 91午夜精品亚洲一区二区三区| 97在线视频观看| 18禁裸乳无遮挡免费网站照片| 午夜久久久久精精品| 熟妇人妻久久中文字幕3abv| 26uuu在线亚洲综合色| 我要看日韩黄色一级片| 成人性生交大片免费视频hd| 中文字幕免费在线视频6| 麻豆乱淫一区二区| 免费看日本二区| 人人妻人人看人人澡| 国产白丝娇喘喷水9色精品| 久久精品国产自在天天线| 一级二级三级毛片免费看| 亚洲欧美日韩高清专用| 久久久久久久久中文| 日本黄色视频三级网站网址| 蜜臀久久99精品久久宅男| 日韩欧美三级三区| 欧美xxxx黑人xx丫x性爽| 直男gayav资源| 国内精品一区二区在线观看| 国产精品av视频在线免费观看| 日韩强制内射视频| 国内精品宾馆在线| 欧美变态另类bdsm刘玥| 国产爱豆传媒在线观看| 国产成人福利小说| 嫩草影院入口| 夜夜爽天天搞| 性色avwww在线观看| av视频在线观看入口| 欧美色视频一区免费| 高清在线视频一区二区三区 | 欧洲精品卡2卡3卡4卡5卡区| 99热这里只有精品一区| 精品99又大又爽又粗少妇毛片| 色5月婷婷丁香| 欧美三级亚洲精品| 国产女主播在线喷水免费视频网站 | 麻豆乱淫一区二区| 久久久久国产网址| 久久这里只有精品中国| 给我免费播放毛片高清在线观看| 精品久久久久久久久久免费视频| 亚洲中文字幕一区二区三区有码在线看| 草草在线视频免费看| 日韩三级伦理在线观看| 国产精品嫩草影院av在线观看| 国产v大片淫在线免费观看| 一本久久中文字幕| 天天躁日日操中文字幕| 国产成人影院久久av| 欧美xxxx黑人xx丫x性爽| 国产日本99.免费观看| 日韩 亚洲 欧美在线| 亚洲国产精品成人久久小说 | 欧美高清成人免费视频www| 国产一级毛片七仙女欲春2| 午夜a级毛片| 国产伦精品一区二区三区视频9| 男女啪啪激烈高潮av片| 欧美成人精品欧美一级黄| 九九爱精品视频在线观看| 极品教师在线视频| 国产精品野战在线观看| 日韩国内少妇激情av| 欧美日韩一区二区视频在线观看视频在线 | 久久综合国产亚洲精品| 中国国产av一级| 精品免费久久久久久久清纯| 国产精品久久久久久av不卡| 久久久久九九精品影院| 极品教师在线视频| 联通29元200g的流量卡| 国产亚洲5aaaaa淫片| 18禁在线无遮挡免费观看视频| 欧美成人精品欧美一级黄| 亚洲第一区二区三区不卡| 久久久久久久久久成人| 婷婷色综合大香蕉| 熟女人妻精品中文字幕| 国产免费男女视频| 日韩中字成人| 国产一区二区三区在线臀色熟女| 久久草成人影院| 国产精品野战在线观看| 91麻豆精品激情在线观看国产| 亚洲av熟女| 真实男女啪啪啪动态图| 精品人妻偷拍中文字幕| 亚洲va在线va天堂va国产| 尤物成人国产欧美一区二区三区| 中文欧美无线码| 国产黄色小视频在线观看| 国产av一区在线观看免费| 女同久久另类99精品国产91| 久久久精品94久久精品| 久久99热6这里只有精品| h日本视频在线播放| 一区福利在线观看| 麻豆乱淫一区二区| 久久久久国产网址| 九九热线精品视视频播放| 麻豆精品久久久久久蜜桃| 国产老妇女一区| 爱豆传媒免费全集在线观看| 99riav亚洲国产免费| av在线老鸭窝| 国产亚洲精品久久久久久毛片| 中国国产av一级| 国产69精品久久久久777片| 久久精品91蜜桃| 久久久久久久久大av| 久久99热6这里只有精品| 白带黄色成豆腐渣| 淫秽高清视频在线观看| 成熟少妇高潮喷水视频| 只有这里有精品99| 一夜夜www| 99精品在免费线老司机午夜| av在线蜜桃| 日韩av在线大香蕉| 亚洲在线观看片| 欧美日韩精品成人综合77777| 免费人成视频x8x8入口观看| 亚洲欧美成人精品一区二区| 九九久久精品国产亚洲av麻豆| 青春草国产在线视频 | avwww免费| 在线观看午夜福利视频| 国产伦理片在线播放av一区 | 久久人人精品亚洲av| 欧美日韩在线观看h| 91久久精品电影网| 看非洲黑人一级黄片| 九九久久精品国产亚洲av麻豆| 六月丁香七月| 亚洲成a人片在线一区二区| 真实男女啪啪啪动态图| 白带黄色成豆腐渣| 亚洲欧美精品专区久久| 一级黄片播放器| 麻豆成人av视频| 亚洲18禁久久av| 桃色一区二区三区在线观看| 麻豆成人av视频| 国产一区二区亚洲精品在线观看| 夜夜夜夜夜久久久久| 人人妻人人澡人人爽人人夜夜 | 成人午夜精彩视频在线观看| 伦精品一区二区三区| 亚洲成人久久性| 少妇被粗大猛烈的视频| 亚洲av男天堂| 嫩草影院精品99| 亚洲国产精品国产精品| 人人妻人人澡欧美一区二区| 老司机影院成人| 在线国产一区二区在线| 国产av不卡久久| a级毛色黄片| 午夜福利在线观看免费完整高清在 | 99热6这里只有精品| 亚洲国产精品合色在线| 99九九线精品视频在线观看视频| 亚洲第一电影网av| 国产成人午夜福利电影在线观看| 99热只有精品国产| 亚洲成a人片在线一区二区| ponron亚洲| 欧美一区二区国产精品久久精品| 亚洲精品456在线播放app| 欧美三级亚洲精品| 青青草视频在线视频观看| 国产欧美日韩精品一区二区| 国产 一区精品| 美女 人体艺术 gogo| 老熟妇乱子伦视频在线观看| 观看美女的网站| 内地一区二区视频在线| 国产探花极品一区二区| 我要搜黄色片| 一本精品99久久精品77| 菩萨蛮人人尽说江南好唐韦庄 | 亚洲七黄色美女视频| 99久久人妻综合| 中文欧美无线码| 午夜老司机福利剧场| 欧美人与善性xxx| 亚洲一级一片aⅴ在线观看| 国产亚洲精品久久久com| av专区在线播放| 亚洲欧美精品专区久久| 久久人人爽人人片av| 亚洲欧美日韩东京热| 黄色视频,在线免费观看| 亚洲欧美精品综合久久99| 亚洲自拍偷在线| 亚洲精品久久国产高清桃花| 国产精品一区二区三区四区免费观看| 国产av不卡久久| 天堂网av新在线| 日本与韩国留学比较| 国产黄色视频一区二区在线观看 | 日韩高清综合在线| 日韩成人伦理影院| 国产精品精品国产色婷婷| 国产91av在线免费观看| 国产午夜精品久久久久久一区二区三区| 亚洲精品影视一区二区三区av| 欧美激情国产日韩精品一区| 国产av不卡久久| 男女那种视频在线观看| 美女大奶头视频| 男人狂女人下面高潮的视频| 亚洲成人av在线免费| 不卡视频在线观看欧美| 亚洲av免费在线观看| 亚洲不卡免费看| 国产免费一级a男人的天堂| 日韩欧美精品免费久久| 国产伦理片在线播放av一区 | 可以在线观看的亚洲视频| 成人特级黄色片久久久久久久| 久久精品综合一区二区三区| 欧美最黄视频在线播放免费| 99久久精品热视频| av黄色大香蕉| 亚洲自拍偷在线| 一级黄片播放器| 夫妻性生交免费视频一级片| 亚洲va在线va天堂va国产| 国产精品人妻久久久久久| 91久久精品国产一区二区三区| 蜜桃久久精品国产亚洲av| 蜜臀久久99精品久久宅男| av视频在线观看入口| 亚洲欧美成人精品一区二区| 综合色丁香网| 免费av观看视频| 我要搜黄色片| 国产成人午夜福利电影在线观看| 国产黄片视频在线免费观看| 在线播放国产精品三级| 美女大奶头视频| 一级av片app| 欧美+亚洲+日韩+国产| 国产美女午夜福利| 欧美三级亚洲精品| 人妻少妇偷人精品九色| 全区人妻精品视频| 亚洲成人久久爱视频| 网址你懂的国产日韩在线| 久久精品国产清高在天天线| 国产高清三级在线| 丰满的人妻完整版| 丝袜喷水一区| 91av网一区二区| 亚洲不卡免费看| 国产精品99久久久久久久久| 免费大片18禁| 国内精品一区二区在线观看| 亚洲av第一区精品v没综合| 亚洲色图av天堂| 九九热线精品视视频播放| 在线播放无遮挡| 国产伦精品一区二区三区视频9| 国产av一区在线观看免费| 亚洲一级一片aⅴ在线观看| 精品久久久久久成人av| 国产精品久久久久久精品电影| 99久国产av精品| 久久欧美精品欧美久久欧美| 能在线免费观看的黄片| av.在线天堂| 在线观看午夜福利视频| 九九在线视频观看精品| 婷婷六月久久综合丁香| 久久草成人影院| 一区福利在线观看| 一级av片app| 成人国产麻豆网| 99热6这里只有精品| 亚洲欧美精品专区久久| 一本久久精品| h日本视频在线播放| 日韩高清综合在线| 一级黄色大片毛片| 精品人妻熟女av久视频| 亚洲人成网站在线播放欧美日韩| 国产黄色视频一区二区在线观看 | 久久精品国产自在天天线| 日韩 亚洲 欧美在线| 少妇人妻一区二区三区视频| 久久精品国产鲁丝片午夜精品| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 国产精品麻豆人妻色哟哟久久 | 久久久久久久久中文| 国产亚洲91精品色在线| 看黄色毛片网站| 欧美精品国产亚洲| 中文字幕av在线有码专区| 国产高清视频在线观看网站| 欧美变态另类bdsm刘玥| 国产精品久久久久久精品电影| 联通29元200g的流量卡| 激情 狠狠 欧美| 尾随美女入室| 18禁在线无遮挡免费观看视频| 国产精品一区二区三区四区免费观看| 精品久久久久久久末码| 亚洲精华国产精华液的使用体验 | 99视频精品全部免费 在线| 亚洲av第一区精品v没综合| 国产精品一区二区在线观看99 | 日本黄大片高清| 青春草亚洲视频在线观看| 成人欧美大片| 亚洲精品国产成人久久av| 99久久精品一区二区三区| 最近视频中文字幕2019在线8| 黄色欧美视频在线观看| 久久久精品欧美日韩精品| 久久这里有精品视频免费| 中文字幕熟女人妻在线| 亚洲三级黄色毛片| 欧美性感艳星| 日韩一区二区视频免费看| 日日干狠狠操夜夜爽| 国产欧美日韩精品一区二区| 国产精品三级大全| 一个人看视频在线观看www免费| 我要搜黄色片| 你懂的网址亚洲精品在线观看 | 成人二区视频| av在线观看视频网站免费| 国产精品永久免费网站| 国产精品av视频在线免费观看| 99热精品在线国产| 国产精品av视频在线免费观看| 日本一本二区三区精品| 深爱激情五月婷婷| 国产伦在线观看视频一区| 18禁裸乳无遮挡免费网站照片| 在线a可以看的网站| 久久久国产成人免费| av免费观看日本| 极品教师在线视频| 国产男人的电影天堂91| 九九爱精品视频在线观看| 精品久久国产蜜桃| 特级一级黄色大片| 久久6这里有精品| 国产亚洲精品av在线| 欧美性猛交╳xxx乱大交人| 尾随美女入室| 最近手机中文字幕大全| 国产成人一区二区在线| 日本一二三区视频观看| 人体艺术视频欧美日本| a级毛色黄片| 国内少妇人妻偷人精品xxx网站| 久99久视频精品免费| 成人三级黄色视频| 国产精品久久电影中文字幕| 亚洲国产欧美人成| 免费一级毛片在线播放高清视频| 国产高清有码在线观看视频| 97超碰精品成人国产| 能在线免费看毛片的网站| 亚洲性久久影院| 两个人视频免费观看高清| 国产成人精品久久久久久| 啦啦啦啦在线视频资源| 久久中文看片网| 日日摸夜夜添夜夜添av毛片| 日韩欧美精品免费久久| 国产三级在线视频| 99热这里只有是精品50| 亚洲七黄色美女视频| 国产高潮美女av| 九九爱精品视频在线观看| 亚洲无线在线观看| 国产老妇女一区| 久久精品久久久久久久性| 99久久中文字幕三级久久日本| 国产伦一二天堂av在线观看| 高清毛片免费观看视频网站| 欧美日韩在线观看h| 日韩视频在线欧美| 91久久精品国产一区二区成人| 中文字幕制服av| 国产成人精品婷婷| 日韩,欧美,国产一区二区三区 | 亚洲在线自拍视频| 一区二区三区四区激情视频 | 亚洲av电影不卡..在线观看| 久久久久久国产a免费观看| 成年版毛片免费区| 人妻系列 视频| 亚洲精品色激情综合| 亚洲国产日韩欧美精品在线观看| 性色avwww在线观看| 国产一区二区三区av在线 | 校园人妻丝袜中文字幕| 国产女主播在线喷水免费视频网站 | 色播亚洲综合网| 日韩国内少妇激情av| 精品人妻熟女av久视频| 亚洲综合色惰| 老师上课跳d突然被开到最大视频| 成人漫画全彩无遮挡| 人体艺术视频欧美日本| 国产人妻一区二区三区在| 亚洲欧洲国产日韩| 内地一区二区视频在线| 青春草亚洲视频在线观看| 国产午夜福利久久久久久| 可以在线观看的亚洲视频| 久久久久久伊人网av| 九九爱精品视频在线观看| 哪里可以看免费的av片| 国产精品.久久久| 亚洲欧美清纯卡通| 哪个播放器可以免费观看大片| 欧美最黄视频在线播放免费| 深爱激情五月婷婷| 国产高潮美女av| 国产老妇伦熟女老妇高清| av在线观看视频网站免费| 亚洲三级黄色毛片| 亚洲内射少妇av| 国产精品不卡视频一区二区| 99riav亚洲国产免费| 精品一区二区三区人妻视频| 中文字幕免费在线视频6| 乱人视频在线观看| 国产毛片a区久久久久| 久久久久性生活片| 久久精品影院6| 中文资源天堂在线| 精品欧美国产一区二区三| 成人国产麻豆网| 日韩视频在线欧美| 成人无遮挡网站| 久久99蜜桃精品久久| 蜜桃久久精品国产亚洲av|