結合光子晶體與奈米探測材開發環境光學感測元件

Abstract

環境感測器主要為提供有效、即時之環境資訊，以作環境品質確保、突發污染事件範圍確定及追蹤與污染控制成效判定等等運用，須具備於複雜環境基質中快速分析出目標物質之能力。光學感測器以光做為感測訊號轉譯機制，具有可量測訊號種類多、反應快與非接觸等等特點，常見於各類環境感測應用。然光學感測器一般有使用藥劑與光學元件成本偏高等缺點，限制了其環境感測應用範圍。 光子晶體為不同折射率材料以週期性規則排列之結構，具有可反射特定波長光之光能隙。利用此一特性，可將光學感測訊號直接轉譯或放大，有助於拓展光學感測器之環境應用範圍與提高其感測效能。本研究將光子晶體光能隙特性與奈米感測材料結合，開發可簡易且快速感測水中雙酚A與Cu2+離子之奈米光學元件。分別利用具反蛋白石結構之分子拓印矽基材料，吸附雙酚A後造成光子晶體光能隙變化進行雙酚A感知，與利用一維光子晶體--膽固醇液晶膜之布拉格反射鏡機制，使量子點螢光訊號放大並提高其Cu2+離子感知能力。 雙酚A為製造塑膠製品常使用之原料，國際間普遍認為其具環境荷爾蒙物質特性，需密切關注其於環境之流佈狀況。本研究以分子拓印聚合物(molecularly imprinted polymers, MIPs)技術，製備出對雙酚A具有良好選擇性吸附能力之矽基分子拓印材料，並以聚苯乙烯微米球自組裝之模板，將其製成具光子晶體特性之反蛋白石結構，藉由材料吸附雙酚A後，整體折射率改變並造成反射光波長偏移特性，進行水中雙酚A濃度感測。本研究所製得雙酚A矽基分子拓印材料之拓印因子(α)為10.5，與4-叔丁基苯酚比較之選擇性係數(β)為3.94，以此拓印材料製得的反蛋白石感測元件可於10分鐘內響應分析物濃度，並對水中BPA濃度1 - 100 mg/L範圍具訊號線性關係(r2=0.974)。 銅因良好電與熱導體特性，為工業製造常使用之原物料，然銅亦屬對生態系統與人類健康有不良影響之重金屬，需嚴格監測其於水體中存在狀況。本研究以巰基包覆CdS/ZnS量子點為Cu2+離子感測探針，藉由低成本、材料穩定之一維光子晶體—膽固醇液晶膜，放大量子點螢光感測訊號強度與提高其應用性。研究顯示，以L-半胱氨酸、2-巰基琥珀酸與巰基乙酸等包覆劑所製備水溶性CdS/ZnS量子點，具備感測含高濃度Ca2+，Mg2+，Na+，K+和NH4+等陽離子之TFT-LCD工業廢水中微量Cu2+離子能力，可做為工業廢水Cu2+離子排放是否超出0.15 mg/L排放標準之早期預警工具。另結合具光子晶體光能隙特性之膽固醇液晶膜與鏡子基板，可放大CdS/ZnS量子點感測Cu2+離子之螢光訊號達7.5-10.3倍，於自來水樣品外添加0.5-1.0 mg/L濃度Cu2+離子之回收率可達88-114 %。顯示膽固醇液晶膜搭配鏡子基板為一低成本、高穩定度之螢光訊號放大方法，有助於擴大量子點螢光感測法之應用範圍。

Environmental sensors are developed for demands of efficient analysis of pollutants in order to well control environmental quality, identify scope of contamination areas, and evaluate treatment performance. In the regard, they have to be capable of identifying targets rapidly and selectively in complex matrix. Optical sensors, due to the advantages of multi-signals, rapid response, and non-contact detection, are popular in various environmental monitoring and sensing applications. However, the chemicals and optical components used for optical sensors are expensive, thus constraining the growth in the market. Photonic crystals (PCs) are periodically structured dielectric media with specific photonic bandgaps. The light with the energy underlying the bandgap cannot propagate through the structure. This unique optical property can be applied in sensing systems in terms of translating stimuli events into optical signals or amplifying optical signals of sensing probes. In this study, we combined photonic crystals with nano-probes to develop two photonic-crystal-based sensing systems for detection of bisphenol A (BPA) and Cu2+ ions, in which photonic crystals were used as a signal transducer and an amplifier, respectively. BPA, being considered as one of environmental hormones, is commonly used for manufacturing plastic products. In this study, a silicon-based molecularly imprinted polymers (MIPs) with good selectivity for BPA was fabricated, and it was also constructed as an inverse opal film (IOF) by using a polystyrene microsphere opal as the template. The reflection wavelength of inverse opal film will be shifted after BPA adsorption due the overall refractive index of MIPs changed. Compared with the analog compound of 4-tert-Butyl phenol (4-BP), the imprinting factor (α) and selectivity coefficient (β) of the BPA silicon-based MIPs prepared in this study were 10.5 and 3.94, respectively. The MIP-IOF sensor responded BPA molecules within 10 minutes and had a signal linearity (r2 = 0.974) in the concentration range of 1 - 100 mg / L. Copper is widely used as a conductive material in the manufacturing industries. Because of the serious impact of Cu2+ ions on the ecosystem and human health, the discharge of Cu species should be monitored in the effluent of wastewater treatment plants. In this study, thiol-capped CdS/ZnS quantum dots (QDs) were used as fluorescence probes for Cu2+ ions determination. Three types of ligands, including L-cysteine (LC), mercaptosuccinic acid (MSA), and thioglycolic acid (TGA), were used as capping agents for stabilizing and functionalizing the QDs. They have well performance, high recovery (81.7-114.5 %), high precision (relative standard deviation=0.36-4.56 %), for detection of Cu2+ ions in the field samples, even though it contained Ca2+, Mg2+, Na+, K+ and NH4+ ions, which were 300-16,600 times higher in concentrations than the target. A cholesteric liquid crystal (CLC), which is one-dimensional PCs, and an aluminium mirror were further introduced into the system to enhance the fluorescence of TGA-capped CdS/ZnS QDs for Cu2+ ions determination. The intensities of enhanced-fluorescence were 7.5-10.3 times higher than the original values. The results clearly show that the low cost optical systems are sensitive and reliable for environmental sensing.