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Optofluidic Microrheometer: study of viscosity behavior in transient networks
1 , 2 , 2 , 3 , 3 , 1 , * 2
1  Dept. of Medical Biotechnology and Translational Medicine, Universita degli Studi di Milano, via Fratelli Cervi 93, I-20090 Segrate, MI, Italy.
2  ​Dept. of Electrical, Computer, and Biomedical Engineering; Università di Pavia Via Ferrata, 5 A I-27100 Pavia ITALY
3  Istituto di Fotonica e Nanotecnologie (IFN-CNR) & Dipartimento di Fisica, Politecnico di Milano,Piazza Leonardo da Vinci 32, 20133 Milano, Italy


It is well known that analyzing the dynamic behavior of reversible gels is a tough job, as it requires a detailed control of geometry, bond lifetimes, etc… .  In this context, we use an optofluidic microrehometer to investigate the properties of a system composed by DNA nanostars.

The device, allowing to test samples with volume smaller than 1 uL, consists in a square section microchannel realized in a glass substrate and having a couple of facing waveguides, realized by fs-laser inscription technique, on the two sides of the channel. Using the optical-shooting technique (T. Yang, et al. Scientific Reports 6, 23946 2016; T. Yang et al. Micromachines 8, 65, 2017.), we investigated the system viscosity as a function of the temperature and of the applied optical force, observing the transition from Newtonian to shear-thinning behavior while lowering the temperature below the gelation threshold.

Stress-strain curves analysis allowed assessing the system activation energy, which is in good agreement with that obtained by dynamic light scattering measurements.

Keywords: optical forces; hydrogel; DNA; rheometry