Extended-Gate Graphene Aptamer Biosensor for Cortisol Detection
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Solution Overview
Problem
Existing FET-based biosensors face challenges in detecting cortisol in human biofluids due to the Debye screening effect, which limits the electrical potential, and the use of capturing probes like molecularly sensitive polymers and antibodies is difficult to synthesize and unstable, affecting sensitivity and selectivity.
Innovation Solution
A cortisol biosensor using a standard CMOS transistor with an externally extended gate covered by a platinum element and an atomically thin graphene layer decorated with 61-nucleotide aptamers, overcoming the Debye screening effect and enabling high sensitivity and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capturing probes like molecularly sensitive polymers and antibodies are used, then sensitivity and selectivity can be improved, but synthesis difficulty and stability problems arise
Solution Approach 1:
The patent extracts the recognition function from complex biological probes (antibodies, molecularly sensitive polymers) and implements it directly through the graphene surface's inherent properties. The graphene surface itself serves as the capturing interface, eliminating the need for separate capturing probe layers that are difficult to synthesize and stabilize.
Solution Approach 2:
The patent introduces aptamers as intermediary molecules that bridge the gap between cortisol detection and graphene surface interaction. These aptamers are synthesized in vitro with precise control, providing both the capturing functionality and stability without the synthesis difficulties of antibodies.
2Measurement precision
If capturing probes like molecularly sensitive polymers and antibodies are used, then sensitivity and selectivity can be improved, but stability problems arise
Solution Approach 1:
The patent adopts aptamers that can be synthesized in vitro with precise control over their properties. These aptamers are designed to be stable and reusable, replacing the unstable biological probes while maintaining detection performance.
3Device complexity
If standard nano-MOSFETs are used as transducers, then integration with read-out circuits is improved, but detection sensitivity is insufficient
Solution Approach 1:
The patent creates a composite sensing system that combines the electrical transduction capability of standard nano-MOSFETs with the high surface-area-to-volume ratio and quantum confinement effects of nanowires and nanoribbons. This composite structure maintains ease of integration while dramatically improving detection sensitivity through the enhanced surface interaction of the nanostructured materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The sensor achieves a wide concentration range, low limit of detection, extended linear range, high sensitivity, and negligible drift, suitable for both point-of-care and continuous measurements in wearable systems.
Implementation Method 1
a layer of graphene decorated with aptamers that is electrically connected to the gate of a semiconductor device. A change in the concentration of cortisol in the biofluid is mirrored in a change of the current of the semiconductor device.
Implementation Method 2
ISFETs are capable of converting any little variation of the electrical charge placed in the vicinity of the transistor gate, such as any species carrying charge (similarly to ions), and this variation becomes detectable by a variation of the FET drain current.
Data Source
AI summary
One embodiment of the present invention concerns a biosensor for sensing stress hormone cortisol concentration in a biofluid. The biosensor comprises: an electrical transistor transducer comprising a transistor gate electrode; a sensing electrode element comprising a metal element having a biofluid facing surface, and a graphene layer on the biofluid facing surface of the metal element, the sensing electrode element being connected to the transistor gate electrode by an electrical connector to form an extended gate configuration with the transistor gate electrode; and a reference electrode configured to be in contact with the biofluid, and configured to electrically bias the transistor gate electrode through the biofluid. The sensing electrode element is functionalised by at least a layer of aptamers placed indirectly or directly on the graphene layer, and configured to catch cortisol hormones in the biofluid to thereby change a surface potential of the sensing electrode element.