Picolitre viscometry using optically rotated particles

TL;DR

This paper presents a microviscometer based on optical tweezers capable of measuring fluid viscosity in tiny samples with high accuracy, including within cells and tear fluid, over a wide viscosity range.

Contribution

The study introduces a novel microviscometer that requires only microlitre samples, characterizes its performance, and demonstrates its application in biological fluids and cellular environments.

Findings

Accurately measures viscosities over two orders of magnitude.

Can insert probe particles into cells to measure intramembranous viscosity.

Successfully measures tear fluid viscosity, showing potential for biomedical applications.

Abstract

Important aspects in the field of microrheology are the studies of the viscosity of fluids within structures with micron dimensions and fluid samples where only microlitre volumes are available. We have quantitatively investigated the performance and accuracy of a microviscometer based on rotating optical tweezers, that requires as little as one microlitre of sample. We have characterised our microviscometer, including effects due to heating, and demonstrated its ability to perform measurements over a large dynamic range of viscosities (at least two orders of magnitude). We have also inserted a probe particle through the membrane of a cell and measured the viscosity of the intramembranous contents. Viscosity measurements of tears have also been made with our microviscometer, which demonstrate its potential use to study un-stimulated eye fluid.