Novel sensor opens opportunities for pre-packaged microfluidic platform

Credit: Okinawa Institute of Science and Technology Graduate University (OIST)

Medical diagnostics have been transformed in recent years with the introduction of micro-fluidic platforms which allow doctors to test for various diseases from a single drop of a patient’s blood or urine sample. This test can be done at the point-of-care without the need for expensive instruments. However, doctors need to insert specific biomolecules in the micro-fluidic platform before testing the sample, and it is imperative that these biomolecules bind well with the inside of the device so that these are not flushed out by the incoming sample.

This is a time-consuming process, and it would be beneficial if specific biomolecules are pre-packaged and sealed within the micro-fluidic platforms. This sealing process of biomolecules requires exposure of the device to high energy ionized gas, and whether or not biomolecules can survive the sealing process was previously unknown.

However, researchers from the Micro/Bio/Nanofluidics Unit of Okinawa Institute of Science and Technology Graduate University (OIST) have developed a novel sensor which is able to detect biomolecules more accurately.

Using this sensor, the researchers demonstrated that biomolecules could be sealed successfully within micro-fluidic devices, and published their findings in the Nanoscale. The research is expected to significantly impact healthcare diagnostics and create new avenues for the production of pre-packaged micro-fluidic platform blood / urine testing devices.

Conventionally, metal oxide semiconductor (MOS) sensors, comprising of a silicon semiconductor layer, a glass insulator layer and a gold metal layer, are employed for detecting the binding of biomolecules to a surface. The sensors are incorporated in an electric circuit with the biomolecule placed in an electrolyte-filled plastic atop the sensor. The presence of biomolecules is then detected by applying a voltage and measuring the current, which is used to calculate the charge from the capacitance reading given off. Biomolecules with different charges result in different capacitance readings, enabling researchers to quantify the presence of biomolecules.

OIST’s novel sensor also employs the same technique to measures charge as conventional sensors, but also measures the mass of the biomolecules. Instead of a solid gold metal layer, the nano-metal-insulator semiconductor (nMIS) sensor uses a layer of small gold metal islands. The surface electrons of these nanostructures start oscillating at a specific frequency when light is shined on them, and this frequency changes in proportion to the mass of the biomolecule when biomolecules are added to the nano-islands.

Based on this change, researchers are able to measure biomolecules’ mass and confirm whether it survives exposure to ionized gas when being encapsulated in the micro-fluidic platform.

Using a single measurement of either charge or mass alone may be misleading as it might appear that a biomolecule has bounded to a surface when in fact they have not. However, by measuring the two fundamental properties of surface chemical reactions (mass and charge) on the same device, researchers can gain more confidence that biomolecules have indeed successfully been encapsulated, and can switch from one mode to the other to verify their results.

“We made a simple sensor that can answer very complex surface chemistry questions,” says Dr. Nikhil Bhalla who worked on the creation of the nMIS sensor. Dr. Bhalla added that scientists have to validate a single reaction using multiple techniques to confirm the authenticity of their observations.

“If you’ve got a sensor that enables the detection of two parameters on a single platform, then it is really beneficial for the sensing community,” says Dr. Bhalla.

Shivani Sathish, a PhD student, adds that combining the two measurement techniques in one compact platform opens new opportunities to create future portable and reliable sensing technologies.

The novel nMIS sensor has applications in micro-fluidic platforms that can test for various diseases. “It would be like a pre-packaged pregnancy test,” says Professor Amy Shen, head of OIST’s Micro/Bio/Nanofluidics Unit. “If there is already something adsorbed then all you have to do is introduce whatever sample you are using, such as urine or blood.”

According to researchers, the nMIS sensors can also be used to combine several biomarkers in the same device to test different diseases at the same time. Integrating the dual-sensing technology with ready-to-use devices can have significant implications for the field of healthcare diagnostics owing to its advantages of portability and point-of-care testing.

More information can be found at: Okinawa Institute of Science and Technology Graduate University.

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