Phage probes couple to DNA relaxation dynamics to reveal universal behavior across scales and regimes.

Microrheology has become an indispensable tool for measuring the dynamics of macromolecular systems. Yet, its ability to characterize polymer dynamics across spatiotemporal scales, which vary among polymers and concentration regimes, is limited by the selection of probe morphologies and sizes. Here, we introduce semiflexible M13 phage as a powerful microrheological probe able to circumvent these constraints to robustly capture the dynamics of polymeric solutions across decades of concentrations, sizes, and ionic conditions. We show that phage mobility directly couples to the relaxation dynamics of DNA solutions spanning from semidilute to entangled regimes with ionic strengths varying by four orders of magnitude. Phage mobility metrics across a broad range of timescales collapse onto universal master curves that are unexpectedly insensitive to ionic strength and exhibit robust crossovers from semidilute to entangled regime scaling, not captured by current theoretical models. Our results open the door to the use of phage probes to elucidate the complex dynamics of systems exhibiting a spectrum of thermal and active relaxation processes.