Multi-mode atomic force microscope as a versatile tool for bionanotechnology

The kernel of this dissertation is multi-mode atomic force microscopy (AFM) which is a useful and powerful tool for characterizing and analyzing samples of nano- or micro size. Various modes can satisfy specified requirements according to different samples, i.e., topography, surface electrostatic potential, magnetic domain visual observation, single molecular force analysis and a novel real-time monitoring cell viability system based on modification of AFM. No matter whether samples are in air or in liquid, topological image can be realized. Hence, the flexibility makes AFM a universal tool for exploring the biological nano-world. The subjects consist of different working modes towards biological applications. Firstly, topography is aimed at quantitative analysis of cellular morphology and surface changes, which are effected by uptake of nanoparticles. In the case of concentration-dependent experiments, the volume and number of filopodia is calculated by analyzing topological images of AFM. It is verified that cellular morphology plays an important role for quantitative indicating of harmful effects of NPs to cells. In addition, the roughness of the cellular surface which derives from disruption of cell membrane integrity, when the cells internalized magnetic NPs subjected to a rotating magnetic field, is evaluated for exploring magneto-cell-poration and magneto-cellanalysis. Secondly, single molecule force microscopy is aimed at quantitative analysis of elasticity of gold nanoparticles (Au NPs), which are coated with polyethylene glycol (PEG), whereby the diameter of the gold cores as well as the thickness of the shell of PEG was varied. A conical tip indent into single NP and then Sneddon’s equation is employed for calculating the elasticity, which serves as one of the basic physicochemical parameters having effect on structural and functional cell parameters. Thirdly, magnetic force microscopy is aimed at qualitative visual observation of magnetic domains of the sample, which is a multifunctional co-loading NP with anti-drug tetradine and superparamagnetic iron dioxide (Fe3O4) NPs. The magnetic domains of co-loading NPs, which is reflected in phase section, can present magnetic profile which is attributed to the Fe3O4 NPs. Thus such multifunctional co-loading NPs are further used for magnetic ablation to tumor cells, so that a dual enhanced anti-cancer NP can be successfully realized. Fourthly, electrostatic force microscopy (EFM) is aimed at qualitative visual observation of electrostatic potential on surface of the sample, which is a mutant purple membrane (PM) modified by functional NPs. A bias voltage between a conductive tip and the modified PM is applied in an oscillating mode. The tip is lifted such that it can induce a long term electrostatic force without effect of molecular repulsive force. Thus electric gradient dependent on surface of the PM makes phase shift in a given frequency and then the EFM signal is extracted. Therefore, the electric property of such a novel biomembrane is characterized. Fifthly, a generally applicable quantitative real-time cell viability monitoring system which uses cell adhesion property is successfully setup based on the oscillation system of AFM. The amplitude of an oscillating cantilever at a given frequency is highly dependent on the mass of the cantilever, in this situation, the mass of attached cells on the cantilever. In our method, the dynamic toxic process can be observed and recorded, and can be analyzed even at an early stage of intoxication. Therefore, this will be a greatly promising method for real-time exploring and quantitatively analyzing of cellular toxicity