【作者】 许娟；

【导师】 江志裕；

【作者基本信息】 复旦大学 ， 物理化学， 2007， 博士

【摘要】 纳米TiO₂是一种n型半导体，具有很强的光催化效率。其发生光催化氧化作用的原理是：在紫外光（λ＜390nm）照射下，TiO₂受到光激发形成光生空穴-电子对。在空间电场的作用下，空穴可以与电子发生分离，并分别与水和溶解氧作用生成OH·、H₂O₂和HO₂·等活性氧类。这些活性氧类与有机物、细菌、病毒和细胞等发生光催化氧化作用，从而分解有机物和杀灭生物体。纳米TiO₂因具有独特的光催化氧化能力以及无毒、化学性质稳定、成本低等优点而被广泛应用于涂料、生物医学、环境工程等很多方面。癌症是当今世界威胁人类健康的大敌，癌症发病率的不断提高要求研究人员不断地寻找新颖且有效的治疗方法，纳米TiO₂光催化杀伤癌细胞是一种新的探索中的治疗癌症的方法。已有的研究成果证明，纳米TiO₂有望成为能有效治疗癌症且对人体毒副反应小的光敏药物，所以探索纳米TiO₂对癌细胞的光催化杀伤作用具有理论意义和实用价值。但是目前纳米TiO₂用于光催化杀伤癌细胞的研究还较少，还有一些问题需要做进一步的研究和探索。其不足之处表现为：（1）纳米TiO₂表面光生电子—空穴对的复合几率较高，其光催化杀伤癌细胞的效率还较低，需要较大浓度的纳米TiO₂，但是过高浓度的光敏剂不适宜用于人体治疗；（2）正常细胞在紫外光照下也可以被纳米TiO₂杀死，所以需要通过提高纳米TiO₂对肿瘤细胞的“靶向性”吸附能力来增强其对肿瘤细胞的杀伤效果，减少其对正常细胞的副作用。为了克服上述缺点，本论文采用化学修饰的方法来提高纳米TiO₂光催化杀伤癌细胞的效率和选择性。同时还研究了纳米TiO₂及其复合物在生物电化学领域中的其它用途，主要研究内容有：1．采用沉积-沉淀法（DP）和硼氢化钠还原法合成了Au纳米粒子修饰的P25TiO₂（Au／P25）和Au纳米粒子修饰的锐钛矿型TiO₂（Au／锐钛矿TiO₂），首次深入探讨了Au纳米粒子修饰后纳米TiO₂对癌细胞的杀伤作用。实验结果表明：沉积-沉淀法和化学还原法均可实现Au纳米粒子在TiO₂样品表面的均匀沉积；黑暗中TiO₂纳米粒子和Au／TiO₂纳米复合物对LoVo细胞几乎没有毒性；在紫外光激发下，纳米TiO₂（P25或锐钛矿型）可以通过光催化氧化作用对LoVo细胞产生杀伤作用，而且锐钛矿型TiO₂对LoVo细胞的杀伤效果明显比P25 TiO₂更好；Au沉积能有效提高纳米TiO₂的光催化效率。当加入50μg／mL的P25 TiO₂或锐钛矿TiO₂时，紫外光（光强1.8 mW／cm²）照射100min后，分别有40％和60％的LoVo细胞被杀死。当加入50μg／mL的2 wt％Au／P25 TiO₂和2 wt％Au／锐钛矿TiO₂时，紫外光（1.8 mW／cm²）照射100min后，杀伤LoVo细胞分别达到100％和93％。而且Au沉积对光催化效率的提高效果受到沉积量的控制，Au的最佳沉积量为2％；从机理上分析，Au／TiO₂对癌细胞光催化杀伤的作用主要来源于紫外光激发下Au／TiO₂表面生成的活性物种羟基自由基（·OH）。2．首次将癌胚抗原单抗与纳米TiO₂粒子进行结合，提出利用癌胚抗原单抗与肿瘤细胞的特异性结合将纳米TiO₂粒子导向癌细胞表面，再利用电穿孔的方法促使它们进入癌细胞中，然后用紫外光照射，使TiO₂纳米粒子在癌细胞内部产生光催化氧化作用杀死癌细胞。紫外-可见吸收光谱和荧光光谱证明了抗体在纳米TiO₂表面的吸附，共聚焦荧光显微镜图像表明了抗体．纳米TiO₂复合物与LoVo癌细胞的选择性结合。而细胞毒性实验结果显示：无光照下纳米TiO₂悬浮液对LoVo癌细胞和正常TE353．sk细胞均无明显的细胞毒性；在紫外光（强度为4mW／cm²）照射60分钟后，仅用纳米TiO₂时对LoVo细胞的杀死率为47％，而用抗体-纳米TiO₂复合物时癌细胞的死亡率上升为61％；当抗体-纳米TiO₂复合物结合了电穿孔技术后，具有最高的癌细胞杀伤效率和选择性，紫外灯（强度1.8 mW／cm²）光照90 min后，LoVo癌细胞全部被杀死，而正常TE353．sk细胞仍然有61％的存活率。综上所述，本论文利用抗原和抗体之间的特异性反应和电穿孔技术实现了纳米TiO₂粒子与癌细胞的选择性结合，提高了纳米TiO₂粒子对癌细胞的光催化杀伤效应。3．以三嵌段高分子非离子表面活性剂(EO₂₀PO₇₀EO₂₀，P123)为结构导向剂，采用模板组装法合成了孔径分布均一、比表面积高的有序介孔二氧化钛材料，并以大肠杆菌（E．coli）为实验对象，首次研究了该有序纳米介孔TiO₂对大肠杆菌的光催化杀菌效应。实验结果表明：合成的介孔TiO₂具有较大的孔径（约6.5nm），且孔径分布较窄、比表面积（BET）为208m²／g，约为无表面活性剂时合成的TiO₂（50m²／g）的四倍；制备的有序介孔纳米TiO₂材料具有良好的光催化杀菌效应，光照60分钟后，大肠杆菌的存活率仅为10％，光照120min后，大肠杆菌的存活率几乎为零；随着有序介孔纳米TiO₂量的增加，对大肠杆菌的杀死效率也提高；在一定的菌液浓度条件下，存在一个发挥杀菌效率最佳的TiO₂量，本实验中TiO₂的最佳浓度为1mg／ml。4．采用沉积．沉淀法合成了Au负载量为8 wt％的Au纳米粒子修饰的纳米TiO₂复合物（AuNP-TiO₂），并将其应用于固定辣根过氧化物酶（HRP），考察利用Au纳米粒子修饰的纳米TiO₂复合物加速HRP与玻碳电极之间的直接电子传递行为，探索研制非媒介体型的过氧化氢传感器。实验结果表明：当纳米TiO₂用Au纳米粒子修饰后，电极的反应电阻大大下降，TiO₂／GC电极的反应电阻为1548 O，而AuNP-TiO₂／GC电极的反应电阻为1134 O；Au在纳米TiO₂上的修饰提高了HRP的电化学响应，HRP／AuNP-TiO₂／GC电极的氧化还原峰电流大于HRP／TiO₂／GC电极的峰电流；HRP／AuNP-TiO₂／GC电极中的HRP对过氧化氢具有较强的催化作用，对H₂O₂具有快速地电流响应，能在小于2秒的时间内达到95％的稳态电流；HRP／AuNP-TiO₂／GC电极具有较小的表观米氏常数K_M^app（234μM），说明固定在AuNP-TiO₂膜中的HRP显示了较高的酶催化活性和对过氧化氢的高亲和力；HRP／AuNP-TiO₂／GC电极的重现性较好，对浓度为200μM过氧化氢连续测试6次，其相对标准偏差（R．S．D．）为4.3％。5．初步尝试以高压汞灯作为紫外线的光源，以纳米TiO₂溶胶作为载体，采用简便的紫外光还原法制备了纳米Au／TiO₂复合半导体粒子。用紫外—可见光谱，SEM和XRD进行了表征，证实了纳米Au粒子的形成，并采用提拉法将此复合溶胶固定在ITO基底上制备成薄膜，测量纳米Au／TiO₂复合膜电极的光电流，考察纳米Au／TiO₂复合膜的光电化学性质。实验结果表明：光电流起于345 nm，并在360 nm波长时光电流达到峰值，然后光电流值开始减小，当波长达到395 nm时，光电流会变得较弱；纳米Au／TiO₂电极的光电流值明显大于没有修饰纳米Au的TiO₂电极，当光的波长为360nm时，纳米TiO₂膜电极的光电流值为23nA／cm²，而纳米Au／TiO₂复合膜电极的光电流为37 nA／cm²。总体来说，纳米Au的修饰能显著提高TiO₂电极光电响应，从而提高TiO₂电极的光电转换效率。更多还原

【Abstract】 Titanium dioxide （TiO₂） is n-type semiconductor and has unique photocatalytic properties. Its principle is as follows: （1） When TiO₂ photocatalysts were illuminated under UV light with wavelengths of less than 385 nm, electrons in the valence band of the TiO₂ semiconductor nanoparticles are excited to jump to the conduction band, and create photo-induced electron-hole pairs at the surface of the TiO₂; （2） Under the action of electric field in space charge layer, the photoinduced electrons and holes separated; （3） The photogenerated holes can react with adsorbed hydroxyl ions （OH^-） or water （H₂O） to produce the highly reactive oxygen species （ROS） such as the radicals OH and HO₂; （4） The photoinduced electrons can react with oxygen vacancies to form superoxide ions （O₂^-）. These ROS will react with organic substance, bacteria, virus, cancer cells, which results in the decomposition and damage of organism structure through a series of oxidation reaction. TiO₂ nanoparticle has important applications in catalysis, environmental protection, medicine and health, electronic industry because of its unique characteristics such as safety, little noxious and side effect, minor wound, excellent chemical stability, and low price.Cancer has become severe harm to people’s health in our country. The rising incidence of cancer in the world demands an increase in effort towards the development of novel and effective therapy for killing cancer cells. TiO₂ photocatalytic oxidation killing cancer cells is an exploring therapy for cancer. As one kind of photosensitize, TiO₂ nanoparticle is an attractive minimal-invasive treatment reagent for cancers because of the localized phototoxic effect upon irradiation and has been successfully used to treat gastric cancer, colon carcinoma, and so on. It is important and worthwhile to explore further the photocatalytic killing effect of TiO₂．However, up till now, such researches on TiO₂ photocatalytic killing cancer cells have still been few. Furthermore, TiO₂ nanoparticles have some drawbacks in clinical use: （1） The high degree of recombination between photogenerated electrons and holes is a major limiting factor controlling the photocatalytic efficiency; （2） TiO₂ has insufficient selectivity and low efficiency resulted from lack of cell-specific accumulation of TiO₂ on cancer cells. In order to improve the selectivity and photocatalytic efficiency of TiO₂ on cancer cells, we took chemical modification methods. In addition, we studied other application of TiO₂ and Au/TiO₂ in bioelectrochemical area. The main results and conclusions are summarized as follows:1．Gold-capped TiO₂ （AU/TiO₂） nanocomposites with different Au ratio （1-4 wt%） were successfully prepared by gold deposition on the surface of TiO₂ nanoparticles （P25 or anatase TiO₂） using deposition-precipitation （DP） and chemical reduction methods. The synthesized Au/TiO₂ nanocomposites were characterized by X-ray reflection diffraction （XRD）, transmission electron microscopy （TEM）, inductively coupled plasma atom emission spectroscopy （ICP-AES） and UV-vis spectroscopy. The photocatalytic killing effect of TiO₂ nanoparticles and Au/TiO₂ nanocomposites on cancer cells was investigated quantitatively and compared using human colon carcinoma LoVo cells as a model. The experimental results show that in comparison with photoexcited pure TiO₂ nanoparticles, the modification of gold nanoparticles on the surface of the TiO₂ nanoparticles （P25 or anatase TiO₂） can greatly improve the photocatalytic killing effect on LoVo cancer cells. In the case of using culture medium containing 2 wt% Au/P25 TiO₂ nanocomposites, the LoVo cancer cells were totally photokilled within 100 min under the irradiation of UV light （λ=365nm, 1．8 mW/cm²） , while only 40% cancer cells were photokilled in the case using P25 TiO₂ nanoparticles. Furthermore, the noble metal amount on the TiO₂ surface influence the efficiency of the photocatalytic process and the maximum photocatalytic killing effect was obtained with about 2 wt% Au on TiO₂ sample.2．We firstly conjugated TiO₂ nanoparticles with a specific antibody against the carcinoembryonic antigen （CEA） of human LoVo cancer cells, which is useful for target accumulation of TiO₂ nanoparticles on LoVo cancer cells. Furthermore, we utilized electroporation to improve the delivery of antibody-TiO₂ bioconjugates into the cancer cells. The combination of electroporation and synthesized antibody-TiO₂ bioconjugates can improve the photokilling selectivity and efficiency of photoexcited TiO₂ on cancer cells. The experimental results demonstrate that highly cell-specific antibody-TiO₂ bioconjugates were achieved and delivered into human LoVo cancer cells using electroporation technique. Under UV light （365 nm） irradiation, 100% of the cancer cells were photokilled within 90 min, while in control, only 39% of the normal cells were killed. This combination method shows high cell-specificity and efficiency in photokilling cancer cells, indicating the potential of this bioconjugates as photosensitizes for photodynamic therapy. Furthermore, this method may be used to photokill various kinds of caner cells by using similar procedure, just need to change the corresponding antibodies.3．We synthesized ordered mesoporous TiO₂ using block copolymer EO₂₀ PO₇₀ EO₂₀ （P123） as the template. The mesoporous material presents high surface area （BET surface area: 208m²/g） and high ordered structure. The photocatalytic bactericidal behaviors of this mesoporous TiO₂ are firstly studied. Experimental results show that E.coli can be efficiently killed by the mesoporous TiO₂ under UV irradiation and the cell viability is only 10% of initial cell amount after 60min illumination. After 120min irradiation, E.coli can be completely killed. The effect of different TiO₂ loading on the inactivation of E.coli is investigated, revealing that the optimum concentration of TiO₂ is 1 mg/mL. Compared with other TiO₂ materials, ordered mesoporous TiO₂ shows its high photocatalytic bactericidal capability. After 60min irradiation, the ordered mesoporous TiO₂ can photokill 90% of E.coli, but the bactericidal efficiency of commercial bulk TiO₂ and nano-TiO₂ is 25% and 70%, respectively. The possible bactericidal mechanism is also discussed.4．Gold nanoparticles-modified TiO₂ nanocomposite （AuNP-TiO₂） was used to immobilize horseradish peroxidase （HRP） on a glassy carbon electrode surface for the construction of an amperometric hydrogen peroxide （H₂O₂） biosensor. The properties of HRP immobilized in the AuNP-TiO₂ film were characterized by the electrochemical methods. The HRP immobilized in the AuNP-TiO₂/GC electrode retained its bioactivity and exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks at about-0．330 V versus saturated calomel electrode （SCE） in pH 7．0 buffers. Moreover, the HRP immobilized in AuNP-TiO₂/GC electrode exhibited a rapid electrocatalytical response （less than 2 s）, a linear calibration range from 2．0μM to 280μM and a sensitivity of 16μA mM^-1 for monitoring of H₂O₂．The apparent Michaelis-Menten constant (K_m^app) of the biosensor was calculated to be 234μM. The good direct electrochemical behavior of HRP and electrocatalytical response to H₂O₂ reduction was due to the enhancement of specific surface area and the reduction of electron transfer resistance by the uniform deposition of gold nanoparticle on TiO₂ surface.5．Au/TiO₂ nanocomposites have been prepared by using high-pressure mercury lamp as the light source to illuminate the HAuCl₄/nano-TiO₂ solution. SEM, XRD and UV-Vis absorption spectrum confirmed the existence of the Au nanoparticles in the composite material. The formation mechanism of Au nanoparticles is proposed. The nano-Au/TiO₂ composite film modified ITO presented higher photocurrent than the pure TiO₂ film modified ITO. The improvement of this photoelectrochemical performance can be explained as the inhibition in charge recombination of photo-induced electrons and holes, and the improvement in interfacial charge-transfer kinetics at nano-Au/TiO₂ composite film. The nano-Au/semiconductor composite films have potential applications in photocatalytic system and photoelectrochemical solar cells.更多还原