Chains of superparamagnetic particles linked by DNA are used as probes to investigate the viscoelasticity of bacteriophage Pf1 networks in the range of concentrations 0–2.5 mg/ml. The loss and storage moduli are obtained by video tracking of the chain in an AC magnetic field applied perpendicularly to the steady field and by determining the amplitude and phase lag of the filament oscillations. The obtained results show the power law dependencies of the storage and loss moduli on the frequency.

1. Introduction. Microrheology has attracted a great interest nowadays as a promising tool for investigating the viscoelastic properties of different networks of biogenic origin [1]. Different schemes for deformation of the minute quantities of networks have been proposed and they include: the motion of a ferromagnetic bead under the action of a nonhomogeneous field [2–4], twisting of phagocytized ferromagnetic particles attached to the cytoskeleton [5, 6], the motion of neutral particles induced by an oscillating laser trap [7], passive methods such as observation of Brownian fluctuations of beads [8] and methods based on the investigation of the oscillation of an ensemble of magnetic needles in an AC magnetic field registred by light scattering [9]. Viscoelastic properties of the cytoskeleton of HeLa cells by video tracking the oscillation of the chains of magnetic endosomes formed by the endocytosis pathway are investigated in [10, 11]. Here, by using DNA linked superparamagnetic beads as probes [12], the viscoelastic properties of networks of Pf1 bacteriophage are investigated. An advantage of this method in contrast to [9] is the fixed size of the probes during measurements and precise registration of the orientation of the chain of linked superparamagnetic particles.