Polymer chain dynamics (e.g., conformation and movement) in complex fluids is important in both biomedical and industry applications. Conventional polymer chains are either too small to be directly observed or too difficult to be strained by fluorescence dyes. In this study, we investigate the vortex formation and single molecular dynamics in a contraction microflow with dilute and concentrated DNA solutions. Vortex formation in 4:1 contraction microflow at different Weissenberg number can be visualized by fluorescent particle in spin-disk confocal microscopy. By labeling DNA molecules with fluorescence dye, we can directly observe their dynamics in dilute and concentrated solutions. Simulations using mesoscopic CONNFFESSIT method and coarse-grained Brownian dynamics simulation method are also carried out to simulate the vortex evolution in the viscoelastic flow and single DNA dynamics in dilute solution.