過去處理重金屬汙染的方法以物理或化學處理居多，這些方法雖能高效率的吸收重金屬離子，但在處理的過程中可能會同時使用有毒溶劑，對於環境產生雙重傷害，近來使用生物性方法來吸附重金屬離子且同時生成相對應的金屬奈米粒子的研究逐漸受到重視，但生物處理程序需要大量的能源輸入才能收集生物質量，因此本研究冀望建立利用介電泳技術辨認吸附金屬離子微藻的微流體系統，以此建立低能耗、高效率的採收方式。研究項目包括 (1)評估微藻移除溶液中金離子的效率，(2)評估微藻利用溶液中的金屬離子生成金奈米粒子的可能性，並利用FTIR，XRD和UV-Vis光譜儀來驗證奈米粒子的生成，(3)設計基於介電泳的微流體系統來辨別吸附金離子/含金奈米粒子的藻體和(4)建立理論模型來觀察微藻胞內介電係數的變化對介電泳的影響。
實驗結果顯示加入500 μM HAuCl4後，小球藻吸收金離子的效率高達70%，雖然小球藻在低濃度(500 μM)的HAuCl4中可以有效的移除金離子，且從FTIR可觀察出微藻內的胺基官能基的特徵波數吸收度增加，顯示微藻細胞內的蛋白質與金離子有交互作用，但XRD顯示這些金離子並未被合成奈米粒子。若將HAuCl4的濃度提高至1 mM~3 mM，移除效率可高達82~92%，並在UV-Vis的觀測到金奈米粒子特徵吸收峰(540 nm)，且吸收峰隨著HAuCl4濃度增加而波長增加。最後，本研究找出了可辨認HAuCl¬4處理的微藻細胞介電泳參數，在電導率分別為0.08 S/m、0.12 S/m和0.16 S/m的緩衝溶液中施加頻率至1 MHz及5 Vpp的電壓，可分離吸附金離子的微藻(正介電泳)以及未吸附金離子的微藻(負介電泳)，並成功建立理論模型擬合其介電泳速度，經由擬合的結果顯示微藻細胞膜的相對介電常數和電導率及細胞壁的電導率在吸附金離子後皆有明顯的變化。未吸附前微藻細胞膜的相對介電常數和電導率分別為1.05和4.92×10-6 S/m，吸附後的細胞膜的相對介電常數和電導率為79.48和2.48 S/m; 而微藻細胞壁的電導率由0.74 S/m下降至0.022 S/m。

Physical and chemical methods have been widely used to deal with heavy metal pollution in the waterbody. These methods are efficient in removing heavy metal ions from the environment; however, the process produces toxic waste that causes secondary pollution. Recently, biological methods have gradually gained attention because of the benign conditions and the capability of producing nanoparticles in the process. However, biological treatments need extensive energy input to harvest biomass. Therefore, this project aims to develop a microfluidic device based on the dielectrophoresis technique to collect the Au ion adsorbing microalgae cells to reduce the energy input. The tasks include (1) using microalgae to adsorb gold (Au) ions; (2) evaluating if microalgae can use Au ions to synthesize Au nanoparticles; and (3) designing and fabricating the microfluidic system based on dielectrophoresis to identify Au ion adsorbing microalgae cells and (4) establish a theoretical model to interpret the influence of the Au adsorbing on the dielectric properties of microalgae.
Results show that Chlorella vulgaris removed 70% of Au3+ when 500 μM of HAuCl4 was applied. C. vulgaris effectively removed Au3+ in low concentration of HAuCl4, and the absorbance of characteristic wavenumbers generated by amine functional groups in microalgae increased, indicating that intracellular proteins and Au3+ have interactions. However, XRD showed that Au nanoparticles were not synthesized. When the concentration of HAuCl4 increased from 1 mM to 3 mM, the removal efficiency ranged between 82~92%. UV-Vis spectrometry observed the characteristic absorption peak (540nm) of Au nanoparticles, and the absorption peak shifted as the concentration of HAuCl4 increased.
Finally, this study found the dielectrophoresis parameters capable of separating Au ion adsorbing microalgae cells from untreated ones. Applying a voltage of 1 MHz and 5 Vpp in a buffer solution with the conductivity of 0.08 S/m, 0.12 S/m or 0.16 S/m can separate the Au ion adsorbing microalgae(pDEP) and untreated microalgae(nDEP). A theoretical model was successfully established to fit the experiment dielectrophoresis velocity. The fitting results showed that the relative permittivity and conductivity of the microalgae cell membrane and the conductivity of the cell wall all changed significantly after adsorbing Au ions. The relative permittivity and conductivity of the cell membrane before Au ion adsorbing were 1.05 and 4.92×10-6 S/m, respectively, and the relative permittivity and conductivity of the cell membrane after Au ion adsorbing were 79.48 and 2.48 S/m. The conductivity of the cell wall decreased from 0.74 S/m to 0.022 S/m after the Au ion adsorption.

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