磁性模組原子力顯微鏡掃描技術對磁性微粒影像分析之探討

Abstract

本論文主要利用磁性模組原子力顯微鏡（簡稱MFM）對不具磁性的蛋白質如去核鐵蛋白、白金微粒與去氧核醣核酸（簡稱DNA）、弱磁性的鐵蛋白，以及具磁性的磁鐵微粒（Fe3O4）進行影像分析。實驗進行時，我們也利用導電模組原子力顯微鏡（簡稱CFM）對這些奈米微粒進行導電度影像進行分析，以了解這些物質的本性差異。實驗結果顯示：奈米物質與MFM探針間的交互作用力會使探針的phase shift（Δψ）產生偏移，因此可藉以探討物質是否具有磁性。此外，我們也發現外加電場會造成Δψ偏移，其偏移程度與偏壓平方成正比。有鑒於此，我們可藉以分析弱磁性物質。再者，我們也發現在一定電場下，磁鐵微粒與鐵蛋白對探針的影響最明顯，但當鐵蛋白的鐵核被去除後，其影響便明顯下降，與其他弱磁性物質相似。據此，我們推論鐵蛋白中的鐵核對鐵蛋白成像與否應具有影響性。

There is an increasing amount of evidence showing links between protein mutations and biological function disorders. In view of the fact that mutations may cause surface conformation changes to proteins, we attempt to characterize mutated proteins with magnetic mode atomic force microscopic techniques (MFM) by using apoferritin to mimic mutated ferritin. Preliminary results based on ferritin and apoferritin show that MFM is a sensitive tool, responding to ferritin and apoferritin protein distinctly in terms of phase shift. Although both show similar corona-shaped images, we consider that the images are contributed more from the fringing effects than the magnetic iron core. Despite this, applying external electric field to both proteins can substantially enhance their MFM images, in which ferritin shows a stronger dependence on the applied biases than its demetalated counterpart. We also characterize ferritin and apoferritin with the conductive mode AFM (CFM). Based on the surface conductivity obtained from CFM and the phase shifts in MFM, we find that ferritin and apoferritin can be differentiated. For verification, we also compare the data with those from DNA and platinum miniatures. According to these results, we consider MFM and CFM are potential alternatives for the analysis of mutated proteins besides other existing surface techniques.