合成具濃度依賴性放光碳點及其應用於銅離子與銅葉綠素鈉的檢測

Abstract

雖然過去已發表的許多研究利用合成的碳點來檢測銅離子 (Cu2+)，且具良好的靈敏度，但這些方法在合成碳點時通常需要昂貴的儀器、高溫和額外提供能量。在檢測Cu2+離子的選擇性上也會受到Ni2+、Co2+、Hg2+等金屬離子的干擾。這些問題可能限制Cu2+離子實際樣品的檢測。而多數碳點在極性低的有機溶劑中分散性不佳，使有機相螢光碳點的特性較少被研究。本研究利用化學氧化法，以三油酸甘油酯為碳源通過濃硫酸的強氧化反應，在室溫下一鍋合成疏水性碳點 (TO-CDs)。TO-CDs具有良好的螢光量子產率 (23.2%)，其放光特性具濃度依賴性和激發依賴性。此外，在氫氧化鈉鹼溶液中，TO-CDs表面的酯基可藉由水解反應，使TO-CDs可轉換到水相。基於磺酸基團可貢獻於與Cu2+離子錯合的特性改善檢測Cu2+離子的選擇性。使用TO-CDs檢測Cu2+離子在S/N = 3下的偵測極限為0.21 M (13.3 ppb)，線性範圍為0.5–10 M，其定量極限與偵測極限皆低於美國環境保護署飲用水中Cu2+離子的標準 (1.27 ppm)。TO-CDs對於土壤中含量高的金屬具有好的容忍度，因此可用於土壤樣品中Cu2+離子的量測。其回收率介於97.8–99.0%之間，相對標準偏差小於2.04%。另外，TO-CDs也可用於銅葉綠素鈉的檢測，在S/N = 3下的偵測極限為0.61 M (以銅計：38.7 ppb)，線性範圍為1.0–10 M，其定量極限與偵測極限皆低於台灣衛生福利部食品藥物管理署定義不含酒精之調味飲料中銅葉綠素鈉的最高含量 (以銅計：64 ppm)。TO-CDs可通過簡單前處理檢測飲料中的銅葉綠素鈉，其回收率介於97.6–103%之間，相對標準偏差小於1.18%。以上結果說明TO-CDs檢測Cu2+離子與銅葉綠素鈉的可靠性相當高，並可能用於水相之外大量分析物的檢測，顯示出快速偵測環境銅離子樣品與檢測食品中銅葉綠素鈉的潛力。

In the previous studies, some carbon dots have been synthesized for the detection of copper ions (Cu2+ ions) with high sensitivity. However, the synthesis of carbon dots suffer some disadvantages such as requiring expensive equipment, high temperature, and/or need for additional energy. The detection of Cu2+ ions is easily interfered by Ni2+, Co2+, and Hg2+ ions. The detection of Cu2+ ions in real samples sometimes is limited by these problems. Because most carbon dots have poor dispersibility in nonpolar organic solvents, making the characteristics are rarely studied. In this study, a one-pot and simple chemical oxidation approach was applied for producing hydrophobic carbon dots (TO-CDs) at room temperature from triolein in concentrated sulfuric acid solution. TO-CDs have a fluorescence quantum yield as high as 23.2%, and exhibit concentration-dependent and excitation-dependent emission characteristics. Through the hydrolysis of ester groups on the TO-CDs in NaOH solution, they can be transferred into aqueous phase. Furthermore, the selectivity for the detection of Cu2+ ions is improved by sulfonyl groups which can contribute the coordination ability to Cu2+ ions. TO-CDs as a probe for the detection of Cu2+ ions through the analyte-induced fluorescence quenching with a linear range of 0.5–10 M and a limit of detection (LOD, signal-to-noise = 3) of 0.21 M (13.3 ppb) that is lower than the maximum allowable level (MAL) of copper in drinking water at 1.27 ppm set by the U.S. Environmental Protection Agency (EPA). TO-CDs possess high selectivity toward Cu2+ ions (tolerance at least five-fold relative to other metal ions). We obtained the percent recovery of Cu in the soil samples to be 97.8–99.0% by spikes, and the relative standard deviations (RSDs) are below 2.04%. Additionally, TO-CDs can also be used as a turn-off sensor for the detection of sodium copper chlorophyllin (SCC) with a linear response over the ranges from 1.0–10 M and a LOD of 0.61 M (38.7 ppb), which is lower than the MAL of SCC in non-alcoholic flavored drinks at 64 ppm (for copper) set by Taiwan Food and Drug Administration (TFDA). By applying a simple pretreatment, we obtained the %R of SCC in the drink samples to be 97.6–103% by matrix spikes, and the RSDs are below 1.18%. This simple, sensitive and selective approach, probably the access to a greater range of analytes by extending operation outside of the aqueous phase, appears to have practical potential for the rapid screening of Cu2+ ions in environmental samples and SCC in foods.