高選擇性/靈敏度奈米核殼結構生物感測器設計研究

Abstract

生物感測器利用生物辨識元件獨特之高度選擇性(selectivity)、靈敏性(sensitivity)與轉換元件(transducer)之快速訊號處理及顯示之即時輸出(real-time output)所組成。在奈米科技蓬勃發展之下，利用奈米科技可以大幅增加感測材料表面積，有助於提升感測靈敏性，但因奈米材料本身特性—容易聚集(agglomeration)，因而造成表面積減少影響感測靈敏性；因此，本研究設計以奈米載體的core-shell結構分散金屬奈米粒子，來達到提升感測靈敏性。除此之外，為了有效提升對特定物質的感測選擇性，設計利用不同電荷特性，操控pH值來達到在待測物(analyte)略帶正電的情形下，達到良好的感測選擇性。以下為本研究結果的摘要說明— 首先，我們以modified Stöber method製備奈米銀粒子佈植在二氧化矽奈米粒子（核殼型二氧化矽@奈米銀粒子）--奈米銀粒子控制在平均大小1、3和5nm，分別佈植在二氧化矽奈米載體的表面，製備SiO2 @奈米銀球。利用奈米核殼球具有的表面電漿共振特性，以三聚氰胺為待測物的偵測上，靈敏性可以達到ppb等級。同時在理論模型模擬，與實驗結果顯現高度的一致性，證明利用核殼型二氧化矽@奈米銀粒子作為生物感測器是相當具有發展潛力及應用的。 在成功開發偵測小分子三聚氰胺的核殼型二氧化矽@奈米銀粒子液態型生物感測器，我們更進一步的發展固態型薄膜感測器，發現了固態型比液態型的感測零敏性提高了2~4倍。同時，以古典Mie theory and effective medium theory (EMT)為基礎，提出了一個新的理論模型，將可以比現存模型計算更接近於固態型的結果，此一結果，除了可以應用於透明固態光學奈米感測器，也有助於探索此一固態感測器在其他感測應用的理論預測。 奈米金屬粒子已廣泛應用於檢測各種有機物質。尤其，奈米金粒子因具有優異的表面電漿共振特性，被廣應用於表面電漿共振感測器。但是，針對特定待測物的奈米金感測器，必須結合特定的“配體”(ligand)分子，才能對特定待測物具有感測選擇性。然而，此類型的 “配體”分子，例如蛋白質，肽，核酸等物質，價格相當昂貴，而且容易受到環境影響產生變化，若以此一方式，將配體結合在金的表面上，成本將會居高不下，且可能因環境影響感測可靠性。因此，我們設計開發了一個新的方法，透過使用一些“裸”奈米金棒，佈植在幾丁聚醣形成核殼結構的膠體型感測器。利用調整溶液的pH值，檢測蛋白質，例如，人血清白蛋白，溶菌酶，證明可以有效的提升此一膠態奈米探針的零敏性及選擇性。這種新的檢測方法利用操控奈米探針的pH值條件，可以作為醫療檢測，診斷和生物工程等應用。

Sensing technologies based on metallic nanoparticles, known as Ag, Au, etc. have raised enormous interest for their extraordinary sensing resolution and sensitivity to analytes of chemical or biological importance under optical detection have received wide attentions in recent decade. Currently, discrete nanoparticle in a free-standing form, either being organically or biologically modified the nanoparticle surface, on a given substrate surface region, has been employed for photosensing purpose. However, metallic nanoparticles suffering from physical and chemical instability such as oxidation, interparticle coupling, agglomeration, etc. during the processing stages may render undesirable outcomes, which further results in poor performance than theoretical expectation. Here, we propose a facile and elegant concept to prepare an Ag-decorated silica nanoparticles (hereinafter termed core-shell SiO2@Ag nanosphere) based on the modified Stöber method. The Ag nanoparticles with an average size controlled at about 1, 3 and 5 nm, respectively, deposited over the surface of the silica nanocarrier were well separated, making the resulting SiO2@Ag nanospheres. The nanospheres showed physically- and optically-stable surface plasmon resonance spectra and also demonstrated a relatively high Ag-sized dependent sensitivity to ppb level for the detection of analyte molecule, i.e., melamine. Theoretical model fitting has been well managed to correlate the optical behavior of the nanosensors, and the outcomes strongly indicated a promising potential of the Ag-decorated SiO2 core-shell nanospheres for sensory applications. A liquid-type sensor based on Ag-functionalized SiO2 nanoparticles was successfully developed and a promising sensing capability to small organic molecule, i.e., melamine, was technically characterized. Here we further discovered a significant improvement by 2-4 folds in detection sensitivity of the SiO2@Ag satellite nanoparticles with respect to organic melamine, as a model molecule, while consolidating into a solid-type thin-film entity. A new theoretical model, based on classical Mie theory and effective medium theory (EMT), was successfully proposed which provided superior calculation outcomes to those existing models for the LSPR spectra of the solid-state assemblies. We envisioned that such a SiO2@Ag thin film offers not only a potential candidate as transparent solid-state optical nanosensors for the detection of organic molecules, but the resulting new plasmonic resonance model helps a better understanding on using such a solid-state nanosensor for a number of sensory applications. Metallic nanoparticles have been utilized as an analytical tool to detecting a wide variety of organic analytes. Among them, gold nanoparticles demonstrating outstanding surface plasmonic resonance property have been well recognized and received widely attention for plasmon-based sensing applications. However, in literature, gold-based nanosensor has to be integrated with specific “ligand” molecule in order to gain molecular recognition ability. However, “ligand” molecules, included proteins, peptides, nucleic acids, etc. are expensive and vulnerable to environmental change, in the meantime, anchoring procedure of the “ligand” molecules to gold surface may be cost-ineffective and endangered to the ligand’s activity, making a final analytic probe less reliable and risk in production capability. Here, we develop a new approach by designing a colloid-type sensor using a few “bare” Au nanorods deposited on the surface of a colloidal chitosan carrier. By tuning the solution pH, the resulting colloidal nanoprobe is capable of detecting proteins, i.e., human serum albumin and lysozyme, with high specificity and sensitivity. This new approach allows a new type of the molecular probes to be well manipulated to monitor important biomolecules for medical detection, diagnosis, and bioengineering applications.