||Modification Nanomaterial Surface for Optical Nanoprobe of Detection of metal cations
||Department of Chemistry
Silver nanoparticles (Ag NPs)
Hexavalent chromium (Cr6+)
Carbon dots (CDs)
光學奈米探針是一種藉由奈米材料本身所具備的光學性質，會隨特定分析物濃度變化的光學偵測技術。奈米物質為其自身尺度大小介於1奈米到100奈米之間，此時，物質本身的物理化學性質會因尺度奈米化後，而和巨觀上有所不同，如：碳變成碳點時，就會具有螢光性質；或銀變成銀奈米時，會因局部表面電漿共振(localized surface plasma resonance, LSPR )而導致顏色變黃等等。貴重金屬(如:金和銀)所製備成的奈米粒子(noble metal nanoparticles, NMPs)，由於其LSPR所吸收的光介於紫外光¬-可見光範圍內，因此，常被用作為重金屬或小分子有機化合物的快速偵測。
一鍋化反應合成的三甲基十六烷基銨(CTA)修飾酒石酸根組裝的銀粒子(CTA-TA/Ag NPs)經紅外光光譜儀、動態光散色儀和穿透式電子顯微鏡等儀器鑑定後，確認其為奈米尺寸(水溶液中分布約為10~40奈米間(水合直徑))，且於酸性溶液中可偵測汞和六價鉻。而其作用原理為六價鉻在酸性溶液會進行氧化還原反應並侵蝕銀奈米粒子，導致銀奈米粒子崩解和LSPR吸收的改變；而當其與汞離子作用時，汞離子(Hg2+)會被還原成元素汞(Hg0)，進而沉積在銀奈米粒子表面，此種蝕刻銀奈米粒子並沉積在其表面的作用，不僅會使其產生較小的粒子(暫時被汞層保護，而不會再被蝕刻)，還會使得在銀奈米粒子所產生的表面電漿共振(SPR)吸收光，產生藍位移(blue shift)的現象。而在選擇性的分析上，CTA-TA/Ag NPs與其他13種常存在分析溶液中的金屬離子測試後，均不會發生明顯的光學變化，因此，可以有效用來辨別樣品中是否含有汞或六價鉻離子。而當將維他命C加入樣品後，再使用CTA-TA/Ag NPs來偵測，此時，僅會單一辨識汞。使用CTA-TA/Ag NPs作為光學奈米探針，其偵測六價鉻時的最低偵測極限為0.15μM，線性範圍為0.2 μM到17.5 μM，汞的最低偵測極限為0.08μM，線性範圍為0.25 μM到3.0 μM。
使用一鍋化步驟將乙二胺、半胱胺酸(Cys)、組胺酸(His)、賴胺酸(Lys)或精胺酸(Arg)等物質修飾於已先合成出的碳奈米量子點(碳點)表面，經紅外光光譜儀、動態光散色儀和穿透式電子顯微鏡等儀器鑑定其物理性質後，結果發現修飾不同官能基的碳點，不但電子能階狀態已被微調，且還能鉗合特定金屬離子於奈米碳點表面，進而產生螢光抑制或增強的效果。表面官能基不同的碳點，可用來偵測不同的金屬離子，而在溶液接近中性時，所有經過表面修飾的碳點，偵測特定金屬陽離子的濃度範圍，為介於10 ppb~100 ppb。最佳條件下，個別金屬離子的偵測極限分別為汞(II)：20.5 ppb、銅(II)：10.2 ppb、鋅(II)：8.8 ppb、鐵(III)：24.6 ppb,、鉻(III)：2.3 ppb。
The optical nanoprobes made up of nanomaterials with recognition units, have the optical signal intensity vary depended on the concentration of the analyte(s). Materials reducing the size or length between 1nm and 100 nm can exhibit a size-related property that is quite different from macroscopic scales, such as the localized surface plasmon resonance(LSPR) or the fluorescence. Noble metal nanoparticles(NMPs), such as gold(Au) and silver(Ag), possessing the SPR frequency can absorb the wavelength between 200nm and 800 nm (UV-Vis range), have been developed as a colorimetric probe for detection of heavy metal or small organic molecule.
Tartrate-capped silver nanoparticles modified by cetyl trimethyl ammonium (CTA-TA/Ag NPs) were synthesized via one pot synthesis and confirmed by transmission electron microscopy, IR spectrometry, and Dynamic Light Scatter. CTA-TA/Ag NPs can redox with mercury ion (Hg2+) and hexavalent chromium (Cr6+) at around pH 2. While Cr6+ devastated Ag NPs via the redox reaction, the Ag NPs will vanish and result in diminishing of the LSPR absorption. When Ag NPs were oxidized by Hg2+, it is not only etched but also formation of Hg0-Ag nanoalloy on the Ag NPs surface. This kind of reaction will reduce the particle size and cause the blue shift of the LSPR absorbance. Comparing the LSPR change of CTA-TA/Ag NPs mixed with other 13 common ions, the selectivity is excellent for Hg2+ and Cr6+. While the sample solution mixed with vitamin C, the probe is specifically to detect Hg2+. The detection limit of Hg2+ and Cr6+ ions are 0.08 μM and 0.15 μM, respectively. The linearity is ranging from 0.25 μM to 3 μM for Hg2+ and from 0.2 μM to 17.5 μM for Cr6+.
On the other hand, carbon nanodots (CDs) modified with ethylene diamine and the amino acids (AAs) Cys, His, Lys or Arg were synthesized by one pot procedure, and their structures were confirmed by high resolution transmission electron microscopy, Raman spectrometry, and X-ray photoelectron spectrometry. It is found that derivatization the N-doped carbon dots with various AAs systemically modulates their electronic properties, and this results in a tunable selectivity in detection of metal cations via fluorescence quenching. The assays can be performed in aqueous solutions at near-neutral pH values. The drop of fluorescence is directly proportional to the concentration of metal cations in the 1 to 100 ppb range, and the limits of detection are 20.5 ppb, 10.2 ppb, 8.8 ppb, 24.6 ppb, 2.3 ppb, respectively, for Hg(II), Cu(II), Zn(II), Fe(III), and Cr(III).
Both Ag NPs and CDs based probes can be applied to detection of heavy metals in the water sample. CTA-TA/Ag NPs can effectively distinguish Cr6+ from Cr3+. Moreover, the Ag NPs can singlely detect Hg2+ when vitamin C was pre-mixed. It turns to a powerful tool for judging the product wether containing the hazard element, Cr6+ and Hg2+, or not. In the other word, the AA-modified CDs with the different fluorescence response can be converted to logic gates and applied to photoelectronic nanoprobes by using microprocessors. This assay has a large potential in terms of high-throughput screening for trace amounts of metal ions.
List of tables IX
List of figures X
Chapter 1 Introduction 1
1.1 Metal Nanoparticles based Colorimetric Nanoprobe 1
1.1.1 Optical Absorption Properties of NMPs 1
1.1.2 Strategies of Colorimetric Nanoprobes 3
1.1.3 Synthesis of colorimetric nanoprobes 6
1.2 Carbon dots 8
1.2.1 Carbon dots as Fluorescence nanoprobe 8
1.2.2 Synthesis of Functionalized Carbon dots 10
1.3 The introduction of heavy metal: 11
1.4 Overview of this thesis 12
Chapter 2 Experiments 13
2.1. Reagents 13
2.2 Apparatus 14
2.3 Preparation of CTA modified Tartrate-capping Ag NPs(TA/AgNPs) 14
2.4 Preparation of all CDs 15
2.5 Verification of the nanomaterials of CTA-TA/Ag NPs and all CDs 16
2.6 Preparartion of the water samples 16
Chapter 3 Characterization and the Results 17
3.1 Characterization of CTA-TA/Ag NPs 17
3.1.1 FT-IR spectra 17
3.1.2 Tranmission Electron Microscopy and Dynamic Light of Scatter 18
3.1.3 UV-VIS spectroscopy 18
3.2 Characterization of all CDs 19
3.2.1 XRD and HRTEM 19
3.2.2 FT-IR spectrum 21
3.2.3 Raman spectroscopy 22
3.2.4 XPS 23
3.2.5 Absorption and fluorescence 24
Chapter 4 Discussion and Application- the detection of heavy metals 27
4.1 Mechanism of CTA-TA/Ag NPs as the optical nanoprobe 27
4.1.1 The reaction time 28
4.1.2 The effect of pH 29
4.1.2 Selectivity and Sensitivity of the Ag NPs 29
4.1.3 Linearity and Limit of Detection 31
4.1.4 Sample Analysis 32
4.2 The C-dots as the fluorenscene nanoprobe 33
4.2.1 The effect of pH 33
4.2.2 The Selectivity and Sensitivity of all CDs 34
4.2.3 Linearity and Limit of Detection 35
4.2.4 CDs nanoprobe applied to Sample analysis 36
4.3 CONCLUSION 37
Chapter 5 Future Aspect 39
A1 Characteristics of CDs 47
A1-1 DLS of CDs 47
A1-2 XPS curved fitting data 48
A2 Comparing the sizes of CTA-TA/Ag NPs without or with Hg2+ or Cr6+ 52
A3 Calibration curve of all CD with its sensitive ions 53
A4 Inferences of CDs 54
A5 Ionic strength effect of CDs 54
A6 CDs comparison data from other references 55
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