Micro-Liquid Volume Measurements Exploiting Specialty Optical Fibers and Plasmonic Phenomena

In this work, two sensor configurations have been realized and tested to measure micro/nano-liquid volumes. Measurement of micro/nano volumes is of high interest for a variety of application domains, such as calibrating micropipettes for biochemical uses or examining volume variations to prevent liquid leakage. The proposed sensor chips are based on patches of polymeric light diffusing fibers (P-LDFs), opportunely modified in two different ways. More specifically, one configuration is based on a polishing process, whereas the other one foresees five micro-holes achieved along the patch. For both sensor configurations, the P-LDF patches have been employed between a white light source and a surface plasmon resonance (SPR) platform connected to a spectrometer. In such a way, once a micro/nano-liquid volume is deposited on the sensitive P-LDF patch, the mode profile of the light into the SPR platform based on multimode plastic optical fibers changes. Consequently, the resonance wavelength varies as a function of the micro/nano-liquid volume in contact with the sensitive area of the P-LDF patch. The volume sensor systems were tested by using water micro-volumes in the range from 1 to
$5~\mu \text{L}$
with a step size of
$1~\mu \text{L}$
. The experimental results have demonstrated that both the proposed sensor configurations present a volume resolution of about 80 nL. This value is about seven times more minor than the value obtained by a similar sensor configuration which includes the same P-LDF patch without modifications.