HEALTH


Gregory Herman’s team at Oregon State University (OSU), US, is


using flexible, transparent sensors to monitor glucose levels in the tears of Type 1 diabetes patients. Ultimately, the researchers want to expand the sensors to detect a range of tear biomarkers to identify ocular disorders such as dry eye disease, diabetic retinopathy and glaucoma, cancers and multiple sclerosis. The technology was developed initially for consumer electronics.


While working in industry, Herman and a couple of colleagues developed a semiconductor based on indium gallium zinc oxide (IGZO) that produced higher resolution displays on televisions, smartphones and tablets while saving power and improving touchscreen sensitivity. He later began investigating biomedical applications after moving to OSU in 2009. ‘These biosensors probably won’t put blood labs out of business,’


says Herman. ‘But I think that we can do a lot of diagnostics using information that can be extracted from tear drops in the eye.’ Herman’s team created a biosensor containing a transparent sheet


of IGZO field-effect transistors (FETs) and glucose oxidase, an enzyme that breaks down glucose.1, 2


The enzyme oxidises any glucose present,


resulting in a pH change, which triggers a response in the electrical current flowing through the IGZO transistor. ‘We use field effect sensing which measures changes in the electric field near a surface, which in turn changes the conductivity of the semiconductor material,’ Herman says.


However, glucose concentrations in the eye are much lower than in


blood or interstitial fluid under the skin so lens biosensors have to be much more sensitive. To address this problem, the team uses colloidal nanosphere lithography to minimise the size of the semiconductor


08 | 2017 19


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