The velocity of a liquid flowing through the core of a hollow core photonic crystal fiber (driven by
capillary forces) is used for the determination of a liquid’s viscosity, using volumes of less than 10 nl.
The simple optical technique used is based on the change in propagation characteristics of the fiber
as it fills with the liquid of interest via capillary action, monitored by a laser source. Furthermore,
the liquid filled hollow core photonic crystal fiber is then used as a vessel to collect Raman scattering
from the sample to determine the molecular fingerprint of the liquid under study. This approach has
a wide variety of indicative uses in cases where nano-liter samples are necessary. We use 10–12 cm
lengths of hollow core photonic crystal fibers to determine the viscosity and Raman spectra of small
volumes of two types of monosaccharides diluted in a phosphate buffer solution to demonstrate the
principle. The observed Raman signal is strongest when only the core of the hollow core photonic
crystal fiber is filled, and gradually decays as the rest of the fiber fills with the sample.