壓阻式微懸臂梁生化感測系統溫度效應之量測、消除與應用

Abstract

在廣大市場及快速發展的生物技術下，生物晶片的發展，正以低成本、具有高靈敏性、可攜帶式、速度快、少量濃度即可達成檢測的優勢，並逐漸取代傳統相形笨重和高成本且速度緩慢之檢驗設備。而微奈米機電系統技術(Micro/Nano Electromechanical System Technology)是一跨領域整合技術，可將生物檢測晶片的尺寸製作於微米與奈米間，已成為科學與生醫跨領域的重要技術。 本論文研究以壓阻式微懸臂梁作為力學感測之生醫晶片，偵測生物分子專一性鍵結所引起之表面應力，可作為生物標記蛋白質之疾病偵測，因此，其應用潛力相當高。由於壓阻式微懸臂梁之量測對溫度相當靈敏，因此在實務應用上一直受到限制。本文首度提出一創新的方法，可以成功地將微懸臂梁對熱效應靈敏的影響消除，顯著降低溫度引起的雜訊並進而提升微懸臂梁的偵測訊雜比與靈敏度，可使微懸臂梁的量測去除龐大的恆溫槽，使得整體量測系統可微型化與可攜式，甚至未來可植入式。 常見雙根微懸臂梁系統，利用惠斯通電橋電路上的特性將電訊號讀出並放大，由於這兩根感測與參考微懸臂梁的表面材質不同，其訊號會隨著化學酸鹼濃度的不同而干擾真實訊號，本研究選擇以單微懸臂梁之方式進行量測，且為了避免壓阻自熱效應(self-heating)，影響訊號的準確性，均使用0.3伏特的操作電壓。本實驗所使用之單根壓阻微懸臂梁，每1℃的變化約會造成 ＝ 的變化量 (轉換為電壓表示約25.73μV/0C)，而偵測生物蛋白質分子也僅產生約8μV)，因此，溫度對微懸臂梁的影響非常顯著。藉由實驗結果發現，此訊號的變化，主要來自於壓阻熱效應 (Temperature Coefficient of Resistance )， (轉換為電壓表示約24μV/0C)。再者，單根微懸臂梁本身結構為多層材料組合而成的複合梁，每一種材料的熱膨脹系數不同，所引發梁彎曲的雙膜效應(Bimorph effect) = (約4.45μV/0C )，因此，本論文透過單根微懸臂梁結構作為量測的方式，首次可以區分微懸臂梁本身的壓阻熱效應的電訊號比雙膜效應約大10倍。再者，雙膜效應與溫度影響的壓阻係數為各別獨立的雜訊，目前仍無法由文獻中最廣為使用之全對稱性惠司通電橋來解決，因此，本文首度提出一創新的方法，透過溫度補償機制，才有辦法將量測的應用面更上提升。 本研究在微懸臂梁感測晶片上，額外置入一固定壓阻作為溫度感測，利用固定壓阻(Resistor on chip)與微懸臂梁壓阻(Cantilever resistor )的溫度量測(Calibration)，將阻值與溫度間的關係使用二次函數表示成 、 ，a∼f均為量測之參數，與材料有關，利用溫度T的量測，就能在 與 間作轉換與減除，藉以達到溫度補償之效果。並在大溫差環境下，證明本方法具有優越的溫度補償能力。 最後，在不需任何恆溫裝置，使用具溫度監控與溫度補償功能之壓阻式微懸臂梁生物感測系統，利用人體內發炎指標C-反應蛋白抗原作為量測，並藉由量測結果計算出C-反應蛋白之抗原與抗體，在懸臂梁表面所造成的表面應力、專一性鍵結之結合常數，成功地驗證壓阻式微懸臂梁的感測能力與本系統架構的可行性。 總結，本文壓阻式微懸臂梁系統不僅具有生物、化學量測的能力，更同時具有溫度監測與溫度補償之雙重功能，相較於原本需使用恆溫裝置才有機會作準確量測的壓阻式微懸臂梁感測系統，又有了微小化與更多應用面的突破。

In this study, polycrystal silicon piezoresistive material is being designed and discussed for electro-mechanical transduction. Utilizing MEMS and semi-conductor ion doping technologies, this work demonstrates design, fabrication and integration of a piezoresistive microcantilever embedded in a microfluidic channel chip system with a Wheatstone Bridge to transfer mechanical bending into electrical voltage for output. Also, the microprobe and spectrum analyzer were introduced for the detection of Gauge factor and noise measurement in the piezoresistive microcantilever biosensor. In a conventional configuration of double-beamed microcantilever systems, the distinctive surfaces of sensing and reference free-standing cantilever beams yield independent signal outcome due to the effect of pH values in solution. In this study, the single free-standing microcantilever is chosen for detection in biochemical environments. However, the single free-standing microcantilever was significantly affected by a temperature change of about 25.73 μV/0C, which failed to be practical in application. Those are attributed to the temperature coefficient of resistance (TCR) and bimorph effect of multiple layers of distinctive materials, in which TCR has approximate 10 times in noise signal far larger than that of bimorph effect. The independence of TCR and bimorph effect still remains unsolved by the most commonly used Wheatstone bridge electrical circuit configuration of the current state of art. Therefore, a novel self thermal deduction by a temperature feedback approach is firstly developed for the piezoresistive microcantilever to eliminate temperature-induced noise and to achieve high performance. Utilizing the fixed polysilicon resistance on chip as temperature sensor to obtain temperature T allows calculation and obtains relation between fixed and cantilever resistances for temperature feedback. Accurate temperature feedback has been proved available under large-scale temperature difference. Furthermore, the detection of C-reactive protein antigen was achieved without bulky temperature control devices. The surface stress induced by C-reactive protein antibody-antigen binding was measured with the elimination of microcantilever thermal-sensitive effect by the feedback apporoach. This approach has proven the feasibility of piezoresistive microcantilever and this system.