The diffraction limit does not permit us to reveal information from dimensions smaller than roughly one-half of the wavelength. Hence, it was traditionally impossible to optically interact selectively with nanoscale features. However, with the increasing trend towards nanoscience and nanotechnology, nano-optics science emerged. A central goal of nano-optics is to extend optical techniques to length scales beyond the diffraction limit. In recent years, several new approaches have been developed to overcome this limitation. Tip-enhanced near-field microscopy techniques, such as TERS and PiFM, are among the innovations built around an AFM system. In this work, first, an algorithm for batch processing of the measured AFM data is introduced and utilized to analyze the height distribution of the inactivated SARS-CoV-2 samples. In the next chapter, plasmonic probes, as the crucial components of any near-field optical microscopy techniques, are modeled and investigated. Here, complex and realistic particle shapes are used to analyze particle-based probes’ near- and far-field behavior. It has been shown that only the frontmost particle is decisive for the near-field signal. On the other hand, the rest of nanoparticles enhance the scattering intensity. Apart from the optical responses, the mechanical properties of tips are also modeled because higher harmonics of the tip’s oscillations are the foundation of new patents such as torsional force microscopy and photo-induced force microscopy (PiFM). In the last chapter, the PiFM is introduced and employed in various applications, i.e., plasmonic probe’s quality, field mapping, and optical response of the plasmonic NPs.