Journal: Investigative Ophthalmology & Visual Science, 2020

Authors: Martin Zalazar; Gabriel Muñoz; Rodrigo M Torres


Purpose : Ocular surface (OS) diseases, principally dry eye syndromes, are a major health public problem, constituting a primary cause of ophthalmological consultation worldwide. Usually, their diagnosis and treatment response are made based on subjective clinical observations.

High Fundamental Frequency Quartz Crystal Microbalance (HFFQCM) transducers are known due to it high sensitivity and are suitable for in liquid applications. The aim of this work was to evaluate the application of a HFFQCM-based microsensor for the characterization of artificial tears (AT) and human tears (HT).

Methods : HFFQCM (AWSensors) were based on 50 MHz crystals, being assembled in a PPS support. Electrodes (chromium/gold) had a sensitive area of 0.785 mm2. A 3D printed housing was made for the sensor chip to be placed (Fig. 1).

Crystal parameters were measured, namely resonance frequency (f0) and dissipation index (D). f0 is directly proportional to the deposited mass, and D is defined as a relation between the dissipated and stored energy in the system. A Vector Network Analyzer (DG8SAQ VNWA 3) was used to obtain f0 and D.

Eight different commercial AT were used, and HT were extracted from six healthy volunteers ranged 20-40 years old. Each collected sample were used to carry out 5 different measurements (4 ��l each).

Results : f0 and D parameters for each commercial AT and HT are shown in Fig. 2.

Conclusions : The developed microsensor is able to discriminate different types of commercial AT and also with a low dispersion. AT-8 shows lower f0 due to a higher viscosity since it is gel. The low dispersion presented determines the reliability of the samples showing good repeatability. Despite they have the same main compound, AT-3 presents higher D than AT-4 due to a bigger concentration . On the other hand, AT-6 and AT-7 behave similarly even not sharing any main compound.