Graphene FET Sensor Surface Charge Tuning for Sensitive Detection

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Solution Overview

Problem

Existing FET-type sensors, particularly graphene FET biosensors, face challenges in maintaining high sensitivity due to the negative surface charge of graphene, which interferes with the detection of negatively charged target molecules, and existing methods to adjust surface charge can damage the graphene structure or result in decreased sensitivity depending on solution type.

Innovation Solution

A sensor with a field effect transistor-type element and positively charged molecules with a cationic functional group that are arranged on the surface of the sensor element, which are capable of detecting a substance to be detected in a solution with high sensitivity, using a detection method that includes capturing the substance with probe molecules and measuring electrical changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If positively charged molecules are arranged on the sensor element surface to relieve negative surface charge, then sensor sensitivity is improved, but the graphene structure may be damaged

Engineering Contradiction:

Improvesensor sensitivityVSAvoidgraphene structure integrity

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The patent uses an intermediary substance (such as poly-L-lysine or other positively charged polymers) that can be adsorbed onto the graphene surface without covalent bonding. This intermediary layer relieves the negative surface charge while preserving the underlying graphene structure, avoiding the damage that would occur with direct chemical modification.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the surface charge parameter of the graphene by introducing positively charged molecules, thereby adjusting the zeta potential from negative to near-zero or positive values. This parameter change improves sensitivity without requiring structural modification of the graphene itself.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If covalent bonds are used to arrange positively charged molecules on the sensor surface, then surface charge is adjusted, but the high functionality of graphene is damaged

Engineering Contradiction:

Improvesurface charge adjustmentVSAvoidgraphene functionality

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent employs non-covalent interactions (electrostatic adsorption, hydrogen bonding, or van der Waals forces) as intermediaries to attach positively charged molecules to the graphene surface. This approach adjusts surface charge while preserving the sp2 hybridization and electronic properties of graphene that are essential for its high functionality.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces covalent bonding (chemical system) with non-covalent adsorption (physical system) to achieve surface charge adjustment. This substitution maintains the mechanical and electronic integrity of graphene while still achieving the desired charge modification.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If poly-L-lysine is used to modify the sensor surface, then negative surface charge is relieved, but sensitivity decreases depending on solution type

Engineering Contradiction:

Improvesurface charge reliefVSAvoidsensitivity consistency across solutions

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent systematically adjusts multiple parameters including the type of positively charged molecule, its concentration, molecular weight, and charge density to optimize surface charge relief while maintaining sensitivity consistency. By changing these parameters, the patent achieves reliable performance across different solution types without the drawbacks of poly-L-lysine.

Inventive Principle:

Principle #35Parameter changes

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 high sensitivity in detecting substances by using positively charged molecules with no pH dependence and non-covalent bonds to preserve the material's electronic properties, thereby preserving the material's electronic properties.

Implementation Method 1

positively charged molecules having a cationic functional group the charge state of which has no pH dependence are arranged on at least a portion of a surface of the sensor element

Methodology Applied

Scientific EffectElectrostatic interaction: Electrostatics

Implementation Method 2

the charge of a graphene molecule is easily converted to a current signal

Methodology Applied

Scientific EffectField effect transistor charge conversion:

Implementation Method 3

probe molecules and positively charged molecules arranged on at least a portion of a surface of the sensor element

Methodology Applied

Scientific EffectMolecular recognition and binding:

Data Source

PatentUS20250389684A1Sensor and detection method

Publication Date: 2025.12.25 MURATA MFG CO LTD

AI summary

A sensor for detecting a substance to be detected in a solution includes a field effect transistor-type sensor element and probe molecules and positively charged molecules arranged on at least a portion of the surface of the sensor element. The positively charged molecules have a cationic functional group the charge state of which has no pH dependence.