Development and performance of a microsensor for the ocular health evaluation.

Abstract

Purpose : Ocular surface diseases are a major health public problem, constituting a primary causes of ophthalmological consultation at the global scale. The first alternative to treat dry eye syndrome is by means of artificial tears (AT) existing many types available in the market, thus producing confusion in the adequate selection.
One alternative to evaluate physical properties of viscoelastic solutions is the Quartz Crystal Microbalance (QCM).
In this work, the characterization of different commercial AT brands were developed by using a QCM device to sense frequency and dissipation changes to help in the selection of a personalized artificial tear for a correct treatment.

Methods : A 10 MHz AT-cut QCM crystals with Au electrodes were used in the experiment (Fig. 1). The change in the resonance frequency (fr) is directly proportional to the deposited mass, according to the Sauerbrey equation:

Δfr = -C_rΔm/A

where Δfr is the fr shift, Δm is the mass change on the QCM interface , and A is the size of the quartz surface.The dissipation index is defined by the following equation:

D = 1/Q = E_Dissipated/2πE_Stored

where Q is the quality factor, E_Dissipated is the energy dissipated during one oscillatory cycle and E_Stored is the energy stored in the system. For the data acquisition, the Digilent Analog Discovery 2TM was used. The solutions used were ultra pure water and 8 different commercial AT.

Results : The frequency shift and dissipation results using different commercial AT are shown in Fig. 2. The mean values of the frequency shift and dissipation for each AT show to be different.

Conclusions : The developed biosensor is able to discriminate different types of commercial AT and also with a low dispersion. Samples 4 and 7 show lower fr due to a higher viscosity of the artificial tear since both are gels.

It is observed that, with the exception of certain excipients, the ophthalmic solutions that behave similarly do not share any main compound. The low dispersion presented determines the reliability of the samples showing good repeatability. Future developments will allow us to evolve to a commercial device for clinical use, to evaluate tear fluid under conditions of normality and ocular surface pathologies.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Fig. 1. QCM system.

 

Fig. 2. AT:1- Refresh Tears, 2- Optive, 3-PH Lágrimas, 4- Latlas gel, 5- Latlas tears, 6- Systane Balance, 7- Systane Gel, 8- Systane Ultra, and 9- Ultrapure water. a) Frequency. b) Dissipation.