Improving lab-on-chip at-home diagnostic tests with graphene

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The current PCR test, considered the gold standard for COVID-19 testing, must be sent to labs for further testing. But this test takes a long time to give results. Quick home alternatives, lateral flow tests, provide quick results but with less accuracy.

The sensor called an ion-sensitive field-effect transistor (ISFET) serves as the best alternative for PCR tests. When combined with electronics, it serves as tests for infectious diseases.

The test works by detecting the change in the pH of fluids. It can be combined with ‘lab-on-chip’ technology to process results on the same chip very quickly.

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The problem arises when liquids come into contact, causing the sensor surface to change. It thus causes “drift” – an uncontrollable, continuous, slow change of the output signal without changes in the acidity of the fluid.

Now, Imperial scientists have improved the ISFET sensor by adding a graphene sheet. Reduces drift by 50 percent. It also combats the chemical instability of the sensor at its origin – the sensor surface.

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Combined with further improvements, this approach could allow a new generation of modified surface sensors for lab-on-chip applications such as in-house disease testing.

Lead author of the corresponding paper, Dr Christophoros Panteli, from the Department of Electrical and Electronic Engineering at Imperial, said: “The need for fast and reliable laboratory systems is very high. Our innovation means that surface-modified ISFETs could be a new, and possibly even better, method for high-performance in vitro chemical sensing systems on a chip against infectious diseases.”

During manufacturing, the process used to produce the ISFET’s electronic wafer deposits on the pH-sensitive surface of the liquid being tested. This upper sensing layer is modified as it comes into contact with the liquid, causing the real-time chemical drift present on the sensor.

By modifying the surface, the scientists found an effective way to improve the performance of the sensor without additional circuitry.

Scientists note, A further improvement method could be developed to address all sensor defects. The next step will be to improve the quality of graphene transfer to the sensor surface. This will include talking with industry about deposition methods that keep costs low at large scales and developing these methods in the laboratory.”

Journal reference:
  1. Cristophorus Pantelli et al. Drift reduction of ISFET CMOS sensors using graphene sheets. DOI: 10.1109/JSEN.2021.3074748

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