| 摘要: | 近年來奈米科技已被廣泛應用於各領域中，造就了許多固有工業更進一步的創新，因此被視為二十一世紀最重要的新興科技之一。然而奈米材料大規模的生產與使用，終將使其進入環境的機率增高，成為新一代的污染物。有鑑於實驗室先前的計畫觀察到經硝酸氧化的多壁奈米碳管雖有效的增加了碳管於水中的分散性，但此時碳管對於懸浮狀態的細菌所造成的毒性效果卻反而減弱，其成因推論是由於碳管與細菌彼此間的表面靜電斥力所帶來的效應，然而確切的原因為何尚待證實。爰此，為了進一步判斷顆粒的表面電性是否為影響奈米碳管抑菌效果的顯著因子，本研究同樣以多壁奈米碳管(multi-walled carbon nanotubes, MWCNTs)及大腸桿菌(E. coli)作為模式顆粒與模式生物。首先透過官能化的方式，使碳管分別具帶負電位較高的MWCNT-COOH (-27.70 mV)與表面電位較低之MWCNT-ETA (-3.00 mV)。FTIR與TGA的分析結果可判定兩類碳管表面特定官能基的存在。毒性試驗的結果顯示，由於碳管與菌體兩顆粒間的靜電作用影響，確實可使得表面電位較低之MWCNT-ETA與E. coli直接接觸的機率增高，進而造成毒性上升的趨勢；其次，MWCNT-COOH由於其自身分散性高，在受到(機械)外力的擾動下，依舊可因此而提高與E. coli 的接觸機率，並進而造成顯著的毒性表現。整體而言，顆粒的分散性與表面電位皆會左右碳管與微生物的接觸機率，而造成不同的毒性效果。此外，本研究的結果也顯示藉由探討奈米碳管與細菌細胞彼此間的交互作用，可進一步推論奈米材料的潛在環境風險。;In recent years, nanotechnology has been widely applied in various fields, leading to further innovations in the corresponding sector. As such, nanotechnology is considered one of the most important emerging technologies in the 21st century. However, the large-scale production and a wide range use of engineered nanomaterials will eventually increase the chance of these novel materials entering the environment and become a new generation of pollutants. In our previous study, it was observed that while nitric acid reflux of carbon nanotubes (CNTs) effectively increased the dispersion of CNTs in water, toxicity of suspended CNTs on planktonic bacteria was significantly reduced. This might be due to surface electrostatic repulsion between CNTs and bacterial cells. However, the exact cause behind this observation remains to confirm. Therefore, to determine whether the surface charge is a critical factor controlling the antibacterial effect of CNTs, multi-walled carbon nanotubes (MWCNTs) and E. coli were used as model CNTs and microorganism respectively in this study. Surface functionalization of MWCNTs resulted in carboxyl- (i.e., MWCNT-COOH) and amino-containing MWCNTs (i.e., MWCNT-ETA) that had surface potentials of -27.70 mV and -3.00 mV, respectively. FTIR and TGA analyses confirmed the success in CNT surface modification. Results of toxicity assays showed that formation of carboxamido- and amino-functional groups indeed significantly favored the contact of MWCNTs with E. coli cells and thus caused stronger bactericidal effect. Interestingly, when MWCNT-COOH was subject to disturbance of mechanical shacking, the chance of MWCNT-COOH in contact with E. coli increased, which in turn led to increased toxicity. Together, our results indicated that in addition to surface charge, dispersivity of MWCNTs may play an equally important role in determining the antibacterial activity of suspended MWCNTs to planktonic E. coli cells. |
