含冠醚與羧酸之奈米金於目測辨識肌酸酐之研究：相鄰官能基對酯化及水解之協力催化反應

Abstract

金奈米粒子(gold nanoparticles，GNPs)有很強的表面電漿共振吸收(surface plasmon resonance，SPR)，其吸收峰位置會隨粒子間距改變而產生位移的現象，故藉由金奈米粒子間的分散─聚集狀態所產生的紅色─藍色之顏色變化可應用於目測辨識之比色法偵測。 本論文要介紹的是利用官能基間的協力效應(cooperative effect)所產生之催化酯化及催化水解反應的方法，並以此方法偵測人體肌肉收縮代謝之最終產物─肌酸酐(creatinine)。肌酸酐會藉由腎絲球的排泄而排入尿液中，且在正常人的尿液中之濃度恆定，因此藉由檢測尿液中的肌酸酐濃度可粗篩出由腎絲球病變所引起的腎臟疾病。我們利用兩階段的官能基置換方式依序在金奈米粒子表面修飾thioctic acid (TA)及([15]crown-5)CH2O(CH2)4SH (簡寫成15c5-C4-SH)兩種官能基，稱之為15c5-C4-S/TA-GNP。利用酯化反應使15c5-C4-S/TA-GNP在溶液中呈現穩定分散的紅色，而添加肌酸酐(creatinine)後，酯化之15c5-C4-S/TA-GNP因進行水解反應而產生聚集的藍色，藉由金奈米粒子由分散到聚集所產生的顏色變化以偵測肌酸酐。15c5-C4-S/TA-GNPs的酯化反應是在pH 2~5的甲醇溶液(含有10%水)中進行，此時金奈米粒子會因為TA官能基上的羧酸基酯化成甲酯基，而15c5官能基則是藉由抓住溶液中的鈉離子來提供正電斥力，故金奈米粒子能藉由兩官能基間的協力效應而穩定分散於溶液中，溶液呈現紅色；相對地，在酯化反應的控制實驗中，金奈米粒子會因為TA上的羧酸基間產生的氫鍵吸引而聚集，溶液呈現藍色。最後將含有肌酸酐的樣品加入含已酯化之金奈米粒子的溶液中，此時15c5與肌酸酐上之質子化的胺基作用，使得鄰近於15c5之TA上的甲酯基能接受質子化的胺基所釋出之質子而進行酸催化的水解反應，令TA上的甲酯基因水解而回復成羧酸基，因此金奈米粒子間會因氫鍵的生成而聚集，溶液呈現藍色，故此法可簡易地直接以肉眼觀察到的顏色變化來做快速的腎臟疾病篩檢。

Gold nanoparticles (GNPs) exhibit intense red color due to the surface plasmon absorbance whose peak position is sensitive to the interparticle distance. By taking advantage of the color transition of red to blue associated with the dispersive to aggregated states of GNPs, many colorimetric sensing strategies have been developed. Presented here is a novel approach that cooperatively catalytic esterification and hydrolysis are involved. We examine the model system using creatinine, which is a metabolite of muscle contraction and is cleared from the body by kidney via glomerular filtration. The concentrations of the serum or urinary creatinine are almost constant for healthy people such that the creatinine levels are used as an indicator to evaluate kidney function. GNPs are first bifunctionalilzed by ([15]crown-5)CH2O(CH2)4SH (denoted 15c5-C4-SH) and thioctic acid (TA). Secondly, esterification takes place and stabilizes GNPs when the bifunctionalized 15c5-C4-S/TA-GNPs are dissolved in a pH 2~5 methanol (containing ~10% water). In control experiments without esterification, hydrogen bonding at the carboxylic-moiety drives aggregation and destabilizes GNPs. For the sensing examination, creatinine is introduced in to esterified GNPs and a cooperatively catalytic hydrolysis leads to the aggregation of GNPs via the developed interparticle hydrogen bonding. Ultimately, rapid evaluation of kidney function by the naked-eye is successful through colorimetric sensing of creatinine with the use of the bifunctionalized-gold nanoparticle assay.