Abstract
Purpose :
Splash injuries whereby the eye is exposed to acids or bases present as acute ocular emergencies. In managing these cases, tear film pH is measured at various sites in the ocular adnexa using multiple pH test strips on presentation and during the course of lavage until pH is normalized. Colorimetric pH test strips are open to errors of subjective interpretation and provide no quantitative record over time. The purpose of this study was to determine if a disposable pH sensor could be used to detect pH changes as they occur in an artificial tear film model.
Methods :
pH-sensitive electrolyte-gated graphene field-effect transistors (EG-GFET’s) were fabricated by patterning graphene microplatelets onto gapped gold-on-polyimide electrodes using a nanomaterials inkjet printer. Contact points were isolated from the active sensor region using inkjet-printed ultraviolet-cured dielectric. A flow-cell was used to exchange test solutions and record current flow through the EG-GFET. Laboratory reference pH test solutions, of pH= 2.0, 6.0 and 8.0 were used to calibrate the sensor. Contrived tears with lipids (Ursa BioScience) were pH-buffered using HCL (1M) or NAOH (1M) to produce tear solutions of pH= 3.9, 6.0, 7.45, 8.50 and 9.5. A laboratory-reference pH meter was used to verify the pH of each solution. For every solution tested, Dirac curves that demonstrate pH-dependent changes in current flow through the EG-GFET were measured using two source meters. Changes in the minimum gate-source transconductance point (Dirac point) were plotted as a function of pH.
Results :
Graphene EG-GFET devices were highly sensitive to pH changes in our tear film model. Dirac Voltage was linearly related to tear film pH, changing approximately 17.2 millivolts per pH unit over the range of solutions tested, from pH 2.0 to pH 9.5 (r2=0.977).
Conclusions :
We have fabricated disposable graphene sensors able to detect changes in tear film pH at the bedside within seconds of a teardrop application. EG-GFETs demonstrated a linear relationship between the change in the Dirac voltages and pH of the solutions tested. These devices can be used to accurately measure tear film pH and may be helpful in the emergency management of ocular adnexal exposure to acids or bases.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.