Methods and systems for using dynamic light scattering, for investigating local rheological responses of complex fluids over a frequency range larger than that provided by standard instrumentation. A low-coherence radiation source is used with fiber optics to allow measurements of small volume spacing of up to approximately 1/10 of a picoliter. The methods and systems are based on dynamic light scattering, for investigating the local rheological response of a complex fluid over a frequency range larger than that provided by standard mechanical instrumentation. The low-coherence radiation used in a fiber optics configuration allows the measurements to be confined to a small volume around a tenth of a picoliter. The ability of the method to accurately measure both loss and storage moduli has been tested using both simple Newtonian liquids and viscoelastic, complex fluids. Monitoring liquid-gel transitions in polymer solutions has also been demonstrated. The unique capability of the technique to localize the measurement volume can be used for three-dimensional mapping of rheological properties in heterogeneous systems. Other embodiments can use open-air setups instead of optical fibers to transmit and receive the low coherence light.