SrTiO_3纳米晶多面体可控生长及其生物学行为研究
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摘要
纳米材料对细胞生长或组织形成等过程会产生各种特殊生物学效应,且其效应常取决于材料表面蛋白质吸附及其吸附状态。由于材料表面原子种类和排列结构是影响吸附最关键因素,因此,开展具有确定原子排列结构表面的单颗纳米晶与蛋白质相互作用以及与细胞响应性的研究,对理解纳米材料产生的生物效应具有重要的理论意义。本论文中以低密勒指数晶面的表面原子结构有显著差异的SrTiO3晶体为模型材料,以其非极性面{100}和极性面{110}为生长控制晶面,通过水热生长法,在晶面控制剂作用下,可控地制备了规则SrTiO3纳米晶多面体。研究{110}/{100}不同比例的规则纳米晶多面体与蛋白质之间的相互作用以及后续与细胞之间的相互作用行为。主要研究结果为：
以LiOH作为晶面生长控制剂,利用Li+离子易吸附在生长晶体的{001}面上,促进其面OH-基团脱水反应的产生,改变界面上液体层的组成与结构,减少吸附层对晶体生长的阻力和OH-离子进入晶格的几率,从而最终形成了100%由{100}面组成的SrTiO3纳米晶立方体,且尺寸在50-250nm范围内可调。
利用不同pKa值醇分子与材料表面作用强弱不同的特点,以此为晶面控制剂,通过选择合适pKa值的醇分子及其加入量,成功地制备了出由{100}和{110}晶面构成的SrTiO3规则纳米晶多面体,且其多面体的{110}/{100}比例在0至0.95范围内可调,多面体尺寸在30-250nm范围内可控。该纳米晶多面体几何特点为由6个{100}晶面和12个{110}晶面组成的十八面体。
醇分子晶面控制作用机理可理解为：1)随着醇分子pKa值的减小,醇羟基的氧原子与SrTiO3{110}晶面Ti原子的相互作用增强,降低了{110}晶面的表面能,使{110}.晶面在生长过程中暴露量增加。从而在一定范围内醇Pka值减小,出现相应纳米晶多面体{110}比例增加的变化规律；2)醇分子对溶液中新生成的SrTiO3晶核具有稳定作用,随着加入量的增加,其稳定效果越明显,从而在一定范围内醇量增加,出现相应纳米晶多面体尺寸减小的变化规律。通过BaTiO3规则纳米晶多面体水热生长,进一步验证了上述醇分子晶面生长控制剂在水热生长过程中发挥调控的机理。
选择尺寸为200nm左右的SrTiO3纳米晶立方体和十八面体作为模型纳米晶,研究不同蛋白质在其表面的吸附行为。SEM观察显示牛血清白蛋白质、猪血清球蛋白质和鱼精蛋白质均呈选择性地在{100}晶面上吸附,与{110}晶面没有作用。根据球差电子显微镜测得的SrTiO3纳米晶多面体的{100}和{110}晶面原子排列结构参数,由分子动力学(MD)理论模拟计算分析得知,其选择性归结于{100)晶面上的吸附水分子层无序且不稳定,而{110}晶面上的水分子层结构有序且非常稳定,有效地阻止蛋白质在其表面的吸附。对比(100)和(110)取向的SrTiO3体单晶片表面上吸附蛋白质行为的无明显差异性,显示出只有纳米尺度下SrTiO3表面才具有的特殊表面效应。
同样选择尺寸为200m左右的SrTiO3纳米晶立方体和十八面体作为模型纳米晶,研究了纳米晶多面体的{110}/{001}比例或其形貌对与细胞相互作用行为的影响。当SrTiO3纳米晶多面体与Hela细胞一起培养8小时后,会产生Hela细胞吞食纳米晶的现象。随着纳米晶多面体{100}晶面比例的增加,其被细胞吞食量也随之增加,由{100}晶面构成的立方体被细胞吞食量几乎是{110}/{100}为0.9的十八面体的60倍。同样通过对比(100)和(110)取向的SrTiO3单晶片表面上细胞相互作用行为的差异(无明显差别),可认为SrTiO3纳米晶多面体的{100}和{110}晶面上吸附蛋白质行为差异是引起Hela细胞吞食行为差别的主要原因。
通过本文研究,探明了在水热生长{110}/{001}不同比例的规则SrTiO3纳米晶多面体中醇分子晶面生长控制剂的作用机理,发现了SrTiO3纳米晶多面体中{110}和{100}晶面原子排列不同引起的蛋白质吸附巨大差异性,其差异性还会对Hela细胞吞食纳米晶多面体行为产生重要的影响。
本文研究结果显示,单颗纳米晶表面原子结构的设计和组合是调控纳米晶生物学效应的有效手段和途径。
The biological effects of nanomaterials have gradually attracted widespread attention and they are often dependent on protein adsorption behavior. Furthermore, the surface atomic structure of nanomaterial is considered to play a critical role on protein adsorption behavior. Therefore, selecting an ideal model material system and using its special surface atomic structure to control its interaction behaviors with protein and cell have been considered to be important to in-depth understand their mechanisms, evaluate the biological security of nanomaterials and broaden its biological application. We select simple cubic perovskite oxide SrTiO3nanocrystals as model, since its surface atomic structure of low Miller indexes are significantly different. SrTiO3polyhedral nanocrystals with the nonpolar facet{100} and polar facet{110} are controlled by using surfactant under hydrothermal method. Moreover, we study the influence of{110}/{100} ratio on its interaction behavior with proteins and cell subsequently. The main results are:
LiOH is used as the mineralization agent instead of KOH. Because Li+ions can adsorb on the surface of the crystal surface and promote the dehydration reaction of OH" on the surface, thereby reducing the resistance of crystal growth and the probability of OH-ions into the lattice, resulting in a perfect cube morphology (100%of{100} facet) of SrTiO3nanocrystals products. And the average particle sizes are from about50nm to250nm with narrow size distribution.
We sucessfully synthesize of size and shape controlled SrTiO3nanocrystals by using a series of alcohols with different PKa values as the surfactant molecules. The morphology of obtained nanocrystals are cubic bounded by six{100} facets and truncated rhombic dodecahedra bounded by six{100} facets and12{110} facets, and the ratio of{110}/{100} are varied between0and0.95. And the average particle sizes are from about30nm to250nm with narrow size distribution.
The growth mechanism is considered to be a dissolution-recrystallization growth mechanism.In this system, the stability of new-formed SrTiO3nucleus can be enhanced by the TiO2·nH2O gel surrounding them, which will produce smaller particle size, therefore the particle size decreases with the increasing of alcohol concentration. And we here assume that the relative interaction strength (adsorption energy) between {110} facet and alcohol molecules would be enhanced with the reduced pKa value of alcohol molecular added, thus expose more surface area of{110} facets of nanocrystal surface. By using1,2-propanediol as the surfactant, we have also synthesized BaTiO3nanocrystals with systematic morphology evolution from cubic to edge-truncated cubic and rhombic dodecahedral. These results indicate that alcohols could be a general surfactants in the shape-controlled synthesis of pervoskite titanates with systematic morphology evolution.
We also study the adsorption behavior of proteins on model truncated rhombic dodecahedra SrTiO3nanocrystals, which are bounded by six{100} facets and12{110} facets, and the average particle sizes are200nm. SEM results show that all the proteins achieve high packing density on the{100} facets of truncated rhombic dodecahedra, while{110} facets adsorb nothing. We further carry out atomistic molecular dynamic (MD) simulations to explore the structures of the interfacial water molecules onto the{100} and{110} facets of SrTiO3, to gain insight into the facet-selective adsorption of proteins onto the facets of SrTiO3nanocrystals. The results indicate that the immobile surface hydration layer might play a role of barrier to effectively prevent protein adsorption on specific{110} facet. Moreover, we compare the results of the protein adsorption behavior on SrTiO3single crystal substrates to show the special effects of nanoscale.
The effects of proportion of different facets exposed of SrTiO3nanocrystals on their interaction behavior with cell are also study. We study cell uptake behavior of Hela of SrTiO3nanocrystals after8h incubation. The results indicate that the amount of cell uptake of SrTiO3nanocrystals increase upon on the increasing ratio of{100} facets. And the amount of cell uptake of cubic nanocrystal is almost60s more than that nanocrystal with{110}/{100} of0.9. We further study cell interaction behavior on the same facet exposed substrate. The results suggest that the protein interaction behavior might be the main cause of the differences in cell uptake behavior.
In this study, shape controlled SrTiO3polyhedral nanocrystals with different ratio of {110}/{100} are achieved by using alcohol molecules as surfactant under hydrothermal method. And we found that the differences in surface atomic structure of SrTiO3{110} and{100} facets determine the protein adsorption and cell interaction behavior subsequently.
It is concluded that the design and combination of surface atomic structure of single nanocrystal is an effective means to control its biological effects.
以LiOH作为晶面生长控制剂,利用Li+离子易吸附在生长晶体的{001}面上,促进其面OH-基团脱水反应的产生,改变界面上液体层的组成与结构,减少吸附层对晶体生长的阻力和OH-离子进入晶格的几率,从而最终形成了100%由{100}面组成的SrTiO3纳米晶立方体,且尺寸在50-250nm范围内可调。
利用不同pKa值醇分子与材料表面作用强弱不同的特点,以此为晶面控制剂,通过选择合适pKa值的醇分子及其加入量,成功地制备了出由{100}和{110}晶面构成的SrTiO3规则纳米晶多面体,且其多面体的{110}/{100}比例在0至0.95范围内可调,多面体尺寸在30-250nm范围内可控。该纳米晶多面体几何特点为由6个{100}晶面和12个{110}晶面组成的十八面体。
醇分子晶面控制作用机理可理解为：1)随着醇分子pKa值的减小,醇羟基的氧原子与SrTiO3{110}晶面Ti原子的相互作用增强,降低了{110}晶面的表面能,使{110}.晶面在生长过程中暴露量增加。从而在一定范围内醇Pka值减小,出现相应纳米晶多面体{110}比例增加的变化规律；2)醇分子对溶液中新生成的SrTiO3晶核具有稳定作用,随着加入量的增加,其稳定效果越明显,从而在一定范围内醇量增加,出现相应纳米晶多面体尺寸减小的变化规律。通过BaTiO3规则纳米晶多面体水热生长,进一步验证了上述醇分子晶面生长控制剂在水热生长过程中发挥调控的机理。
选择尺寸为200nm左右的SrTiO3纳米晶立方体和十八面体作为模型纳米晶,研究不同蛋白质在其表面的吸附行为。SEM观察显示牛血清白蛋白质、猪血清球蛋白质和鱼精蛋白质均呈选择性地在{100}晶面上吸附,与{110}晶面没有作用。根据球差电子显微镜测得的SrTiO3纳米晶多面体的{100}和{110}晶面原子排列结构参数,由分子动力学(MD)理论模拟计算分析得知,其选择性归结于{100)晶面上的吸附水分子层无序且不稳定,而{110}晶面上的水分子层结构有序且非常稳定,有效地阻止蛋白质在其表面的吸附。对比(100)和(110)取向的SrTiO3体单晶片表面上吸附蛋白质行为的无明显差异性,显示出只有纳米尺度下SrTiO3表面才具有的特殊表面效应。
同样选择尺寸为200m左右的SrTiO3纳米晶立方体和十八面体作为模型纳米晶,研究了纳米晶多面体的{110}/{001}比例或其形貌对与细胞相互作用行为的影响。当SrTiO3纳米晶多面体与Hela细胞一起培养8小时后,会产生Hela细胞吞食纳米晶的现象。随着纳米晶多面体{100}晶面比例的增加,其被细胞吞食量也随之增加,由{100}晶面构成的立方体被细胞吞食量几乎是{110}/{100}为0.9的十八面体的60倍。同样通过对比(100)和(110)取向的SrTiO3单晶片表面上细胞相互作用行为的差异(无明显差别),可认为SrTiO3纳米晶多面体的{100}和{110}晶面上吸附蛋白质行为差异是引起Hela细胞吞食行为差别的主要原因。
通过本文研究,探明了在水热生长{110}/{001}不同比例的规则SrTiO3纳米晶多面体中醇分子晶面生长控制剂的作用机理,发现了SrTiO3纳米晶多面体中{110}和{100}晶面原子排列不同引起的蛋白质吸附巨大差异性,其差异性还会对Hela细胞吞食纳米晶多面体行为产生重要的影响。
本文研究结果显示,单颗纳米晶表面原子结构的设计和组合是调控纳米晶生物学效应的有效手段和途径。
The biological effects of nanomaterials have gradually attracted widespread attention and they are often dependent on protein adsorption behavior. Furthermore, the surface atomic structure of nanomaterial is considered to play a critical role on protein adsorption behavior. Therefore, selecting an ideal model material system and using its special surface atomic structure to control its interaction behaviors with protein and cell have been considered to be important to in-depth understand their mechanisms, evaluate the biological security of nanomaterials and broaden its biological application. We select simple cubic perovskite oxide SrTiO3nanocrystals as model, since its surface atomic structure of low Miller indexes are significantly different. SrTiO3polyhedral nanocrystals with the nonpolar facet{100} and polar facet{110} are controlled by using surfactant under hydrothermal method. Moreover, we study the influence of{110}/{100} ratio on its interaction behavior with proteins and cell subsequently. The main results are:
LiOH is used as the mineralization agent instead of KOH. Because Li+ions can adsorb on the surface of the crystal surface and promote the dehydration reaction of OH" on the surface, thereby reducing the resistance of crystal growth and the probability of OH-ions into the lattice, resulting in a perfect cube morphology (100%of{100} facet) of SrTiO3nanocrystals products. And the average particle sizes are from about50nm to250nm with narrow size distribution.
We sucessfully synthesize of size and shape controlled SrTiO3nanocrystals by using a series of alcohols with different PKa values as the surfactant molecules. The morphology of obtained nanocrystals are cubic bounded by six{100} facets and truncated rhombic dodecahedra bounded by six{100} facets and12{110} facets, and the ratio of{110}/{100} are varied between0and0.95. And the average particle sizes are from about30nm to250nm with narrow size distribution.
The growth mechanism is considered to be a dissolution-recrystallization growth mechanism.In this system, the stability of new-formed SrTiO3nucleus can be enhanced by the TiO2·nH2O gel surrounding them, which will produce smaller particle size, therefore the particle size decreases with the increasing of alcohol concentration. And we here assume that the relative interaction strength (adsorption energy) between {110} facet and alcohol molecules would be enhanced with the reduced pKa value of alcohol molecular added, thus expose more surface area of{110} facets of nanocrystal surface. By using1,2-propanediol as the surfactant, we have also synthesized BaTiO3nanocrystals with systematic morphology evolution from cubic to edge-truncated cubic and rhombic dodecahedral. These results indicate that alcohols could be a general surfactants in the shape-controlled synthesis of pervoskite titanates with systematic morphology evolution.
We also study the adsorption behavior of proteins on model truncated rhombic dodecahedra SrTiO3nanocrystals, which are bounded by six{100} facets and12{110} facets, and the average particle sizes are200nm. SEM results show that all the proteins achieve high packing density on the{100} facets of truncated rhombic dodecahedra, while{110} facets adsorb nothing. We further carry out atomistic molecular dynamic (MD) simulations to explore the structures of the interfacial water molecules onto the{100} and{110} facets of SrTiO3, to gain insight into the facet-selective adsorption of proteins onto the facets of SrTiO3nanocrystals. The results indicate that the immobile surface hydration layer might play a role of barrier to effectively prevent protein adsorption on specific{110} facet. Moreover, we compare the results of the protein adsorption behavior on SrTiO3single crystal substrates to show the special effects of nanoscale.
The effects of proportion of different facets exposed of SrTiO3nanocrystals on their interaction behavior with cell are also study. We study cell uptake behavior of Hela of SrTiO3nanocrystals after8h incubation. The results indicate that the amount of cell uptake of SrTiO3nanocrystals increase upon on the increasing ratio of{100} facets. And the amount of cell uptake of cubic nanocrystal is almost60s more than that nanocrystal with{110}/{100} of0.9. We further study cell interaction behavior on the same facet exposed substrate. The results suggest that the protein interaction behavior might be the main cause of the differences in cell uptake behavior.
In this study, shape controlled SrTiO3polyhedral nanocrystals with different ratio of {110}/{100} are achieved by using alcohol molecules as surfactant under hydrothermal method. And we found that the differences in surface atomic structure of SrTiO3{110} and{100} facets determine the protein adsorption and cell interaction behavior subsequently.
It is concluded that the design and combination of surface atomic structure of single nanocrystal is an effective means to control its biological effects.
引文
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105. Gagner, J.E. et al. Effect of gold nanoparticle structure on the conformation and function of adsorbed proteins. Biomaterials 33,8503-8516 (2012).
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