Single molecule biophysical techniques have proven to be powerful approaches to illuminate physical principles behind a wide range of biological phenomena. Direct measurement of physical properties of individual biomolecules can reveal detailed dynamics by the molecule in real time without suffering from population averaging. Here, we first report salt-dependent cisplatin-induced DNA kinking and the consequent change in DNA elasticity, which was studied via micromanipulation of a single DNA molecule with magnetic tweezers. Upon binding to DNA, cisplatin, a potent mutagenic anti-cancer drug, was revealed to induce a dramatic change in the DNA persistence length in a strongly salt-dependent manner. Second, we examined a DNA bubble dynamics by monitoring via spFRET the fluctuation in the inter-strand distance of the bubble, which was formed in AT-rich region when the DNA molecule was underwound by magnetic tweezers. We observed at least 3 distinct FRET levels from an AT-rich palindromic region, which appears to indicate the formation of DNA cruciform. These studies shed light on understanding the efficacy of drugs that induce conformational changes in DNA and the dynamics of DNA bubble/cruciform which plays significant roles in DNA metabolism.