Morphological Design for Plasmonic Colloidal Nanosensors with High selectivity and Nano-to-Femtomolar Detection Sensitivity
|關鍵字:||表面電漿共振;奈米感測器;人血清白蛋白;三聚氰胺;溶菌酶;surface plasmon resonance;nanosensor;human serum albumin;melamine;lysozyme|
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。
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.