利用色胺酸作為螢光溫度計定量金奈米粒子之光熱轉換效率

Quantifying the photothermal efficiency of gold nanoparticles using tryptophan as an in situ fluorescent thermometer

丘珉瑞(Chiu, Ming Jui)

指導教授 ： 朱立岡

國立清華大學/理學院/化學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00082

摘要

金奈米粒子具有表面電漿共振的光學性質，隨著不同的粒徑、形狀與環境介電常數，其共振吸收波長可由可見光波段位移到紅外光的波段，且在吸收光能後，得以熱的形式將能量釋出，即具有光熱轉換的特性。在過去十幾年中，金奈米粒子被視為奈米熱源的最佳材料，並廣泛應用於生物醫療領域，尤其在癌症熱治療。然而在金奈米粒子的光熱效應的定量研究，並未有一致的結論。本篇論文利用色胺酸的螢光強度變化與溫度所具有相依性，建立一套光致熱效螢光調變偵測系統。有別於以往利用熱電偶測量法的實驗技術，吾人以光譜技術觀察金奈米粒子其光致熱的過程，並以熱傳導模型分析加熱體積內的熱散失過程及定量各粒徑金奈米粒子的光熱轉換效率。
實驗中藉由調變532 nm連續光源雷射能量(45.8-67.6 mJ cm-2)激發六種不同粒徑(22-86 nm)的金奈米粒子，並以色胺酸螢光作為在原位的(in situ)分子溫度計，偵測金奈米粒子光熱效應造成的溫度變化。當環境溫度上升1 oC，色胺酸螢光強度衰減2.05 %，溫度偵測極限為0.2 oC。在激發樣品時，激發光束(0.83 mm)完全包覆偵測光束(0.81 mm)，確保擷取到的色胺酸螢光強度變化皆為金奈米粒子熱效應所影響。在溶液樣品在532 nm的消光度一致的前提下，隨著金奈米粒子的粒徑越大，其光熱效應造成環境的溫度變化逐漸變小。根據溫度梯度所建立的熱傳導模型能適當地描述整體熱散失的過程，並得到各粒徑金奈米粒子的絕對光熱轉換效率，而相對於22 nm的金奈米粒子之光熱轉換效率隨粒徑變化的趨勢也與米氏理論相符。
吾人所建立的光致熱效應螢光調變偵測系統有別於以往使用熱電偶測量法，色胺酸螢光強度變化能即時反映金奈米粒子光熱效應造成的環境溫度變化，使訊號得到更佳的訊雜比以及實驗再現性。此外，色胺酸的螢光強度與溫度的相依性，亦可應用上於生物的熱影像的研究。

關鍵字

金奈米粒子 ； 光熱效應 ； 色胺酸 ； 螢光

並列摘要

The photothermal efficiencies, denoting the efficiency of transducing incident light to heat, of gold nanoparticles of different diameters (Ø = 22–86 nm) were quantified upon exposure at 532 nm. The fluorescence of tryptophan at 300–450 nm upon 280 nm excitation serves as an in situ fluorescent thermometer to illustrate the evolution of the average temperature change in the heating volume of the nanoparticle solution. The fluorescence intensity decreases as the temperature increases, having a linear gradient of 2.05% fluorescence decrease per degree Celsius increment from 20 to 45 oC. The presence of gold nanoparticles at the nM level does not perturb the temperature-dependent fluorescence of tryptophan in terms of fluorescence contour and temperature response. The heating volume was defined by overlapping the collimated 532 nm laser (Ø = 0.83 mm) for exciting the nanoparticles and the 280 nm continuous-wave beam (Ø = 0.81 mm) for exciting tryptophan in a 2 mm × 2 mm square tube, and the fluorescence was collected perpendicularly to the collinear alignment. This method has satisfactory reproducibility and a sufficient temperature detectivity of 0.2 oC. The profiles of the average temperature evolution of the mixtures containing nanoparticles and tryptophan were derived from the evolution of fluorescence and analyzed using collective energy balancing. The relative photothermal efficiencies for different sizes of gold nanoparticles with respect to the 22 nm nanoparticle agree with those predicted using Mie theory. The employment of tryptophan as a fluorescent thermometer not only provides an in situ tool to monitor the photothermal effect of nanostructures but is also applicable to thermal imaging in biological applications.

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