Synthesis, Stability and Antimicrobial Properties of Silver Nanoparticle/Clay Hybrids

本研究利用片狀矽酸鹽黏土(NSP)來使奈米銀粒子(AgNP)穩定地在其表面上被合成出來，而合成的奈米銀粒子在熱、紫外光照射、超聲波震盪等處理下皆具有相當高的穩定性，且在空氣下亦不會氧化變質。另外，在原位還原硝酸銀的過程中，我們亦可藉由調控不同含量的NSP和硝酸銀來控制奈米銀粒子大小，其在不同的Ag/NSP重量比下的尺寸可以由3.6奈米直至16.8奈米。接著我們開始對這些奈米銀粒子的材料進行一系列穩定性研究，藉由觀察其在紫外光−可見光光譜上吸收峰的變化來判定穩定與否，並與利用高分子或天然黏土來穩定的奈米銀粒子材料相比較。由結果說明，NSP的存在有很大程度的貢獻使奈米銀粒子具有相當高的穩定性，其主要是因為NSP的高表面積和離子電荷兩性質，使銀粒子和NSP之間具有密集的相互作用力。因此，銀粒子的聚集或結合成大顆粒或和空氣氧化變質成氧化銀在此是完全沒有發生的。相比之下，在相同條件的穩定性測試中，常見的使用有機分散劑分散的奈米銀粒子卻被發現是較不穩定的且不斷惡化。因此，這種具有高縱寬比和離子電荷表面之獨特性質的黏土種類在穩定銀上是必要的。 我們進一步研究AgNP/NSP奈米複合物的殺菌效果，針對大腸桿菌與金黃色葡萄球菌進行了抗菌實驗。我們發現NSP的存在可以增強抗菌的效果，由於NSP表面帶有電荷可能有助於此AgNP/NSP材料貼附在細菌表面，進而達到抗菌效果的提升。另外，由於NSP緊密的附著可防止固定在其表面上的AgNP進入細胞體內，可以避免進一步的DNA損害發生，這結果說明了AgNP和NSP之間可能存在著強的相互作用力。另外，這也是此奈米複合物的一個優勢，當其履行其抗菌功能時，有害的AgNP在正常細胞中累積的這種窘境是不會發生的，因此不會對健康造成危害。The hybrids of silver nanoparticles (AgNP) on clay silicate platelets (NSP) were synthesized and analyzed to have precise controls in particle size and high stability against thermal, ultraviolet, ultrasonic and air oxidative deterioration. Various hybrids of the composition (weight ratio of Ag/silicate) in corresponding to the Ag particle size of 3.6 to 16.8 nm in diameter were tailored by changing the starting material ratio of NSP and silver nitrate under reduction conditions. The stability of the AgNP was investigated by examining the absorption peak shifts of UV–visible spectra and compared with the AgNP stabilized by the polymers and the pristine clays. The presence of NSP could largely contribute the high stability of the AgNP due to the intensive interaction between Ag nanoparticles and NSP of high surface area and ionic charges. The Ag particle coalescence, aggregation to larger particles and air oxidation to Ag2O were totally subsided by NSP. By comparison, the conventional AgNP materials with the common organic stabilizers were generally unstable and deteriorating under the same tests of heat, UV and air. The unique characteristics of the clay species with high−aspect−ratio and ion charged surface are essential for stabilizing the Ag0 particles. We further investigate the bactericidal efficacy of the AgNP/NSP nanohybrids. The antimicrobial tests were performed on Escherichia coli and Staphylococcus aureus. The antibacterial effect was enhanced by the presence of NSP which facilitates the nanohybrids adhesion onto the bacterial surface and consequently achieves the high efficacy. It was found that the close attachment could prevent the AgNP entering into the cell body and avoid the possible damage on DNA. It is an advantage for the hybrid to fulfill its antimicrobial function without the adversity of accumulation in normal cell and harmfulness to the health