CMOS Capacitive Sensor for Dry-Wet Nanoscale Analyte Detection
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Solution Overview
Problem
Existing capacitive sensors for detecting nanoscale analytes like DNA and RNA are large, expensive, and not amenable to miniaturization, portability, or high-volume low-cost manufacturing, and often interfere with the analytes due to the use of noble metals and reference electrodes.
Innovation Solution
A capacitive sensor with CMOS architecture and inter-digitated electrodes, covered by a nitride layer, eliminates reference electrodes and uses a sigma-delta switched-capacitor modulator for high-resolution detection of femtoFarad and attoFarad changes, allowing for 'wet' and 'dry' measurements to enhance sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noble metal electrodes (gold, platinum, mercury) are used to reduce corrosion and oxidation, then electrode stability is improved, but manufacturing cost increases and miniaturization becomes difficult
Solution Approach 1:
The patent replaces expensive noble metal electrodes with inexpensive aluminum electrodes that are sacrificial and can be replaced. The aluminum electrodes corrode over time but provide sufficient service life for the application, eliminating the need for costly precious metals while maintaining functional reliability through periodic replacement.
Solution Approach 2:
The patent substitutes the electrochemical electrode system with a capacitive sensing system using aluminum electrodes. This replacement eliminates corrosion and oxidation issues inherent in traditional electrochemical electrodes, as the capacitive measurement does not involve electrochemical reactions that degrade the electrode material.
2Measurement precision
If large electrode area (0.05 cm2) is used to obtain sufficient capacitance for measurement, then measurement sensitivity is improved, but device size increases and portability becomes difficult
Solution Approach 1:
The patent divides the electrode into multiple interdigitated fingers arranged in a compact pattern. This segmentation increases the effective capacitance measurement area within a small footprint by creating multiple parallel capacitive paths between alternating fingers, thereby achieving sufficient sensitivity without requiring large overall electrode area.
Solution Approach 2:
The patent transitions from planar electrode arrangements to three-dimensional interdigitated structures with vertical stacking capability. By utilizing the vertical dimension and creating overlapping electrode layers, the effective capacitance area is dramatically increased within a minimal planar footprint, enabling portable device integration.
3Measurement precision
If reference electrodes are included in the sensor system to control DC voltage, then measurement accuracy is improved, but device complexity increases and interference with analyte may occur
Solution Approach 1:
The patent removes the reference electrode from the sensor system by transitioning to an AC capacitive measurement technique. This extraction eliminates the complexity and potential analyte interference associated with reference electrodes, as the AC measurement method does not require a stable DC reference potential and avoids electrochemical reactions at the reference electrode interface.
Solution Approach 2:
The patent replaces the DC voltage control system with reference electrodes with an AC capacitive sensing system. This substitution eliminates the need for DC voltage stabilization and reference electrode maintenance, simplifying the overall device architecture while maintaining measurement precision through frequency-domain signal analysis.
4Power
If electrodes are made large and exposed to achieve sufficient capacitance signal, then signal strength is improved, but susceptibility to corrosion and oxidation increases
Solution Approach 1:
The patent accepts that aluminum electrodes will corrode over time but designs them as disposable or replaceable components. This approach allows using large exposed aluminum electrode areas to maximize signal strength without concern for long-term stability, as the electrodes can be economically replaced rather than protected from corrosion.
Solution Approach 2:
The patent substitutes electrochemical electrodes susceptible to corrosion with capacitive aluminum electrodes where the measurement process itself does not cause degradation. The AC capacitive sensing method avoids electrochemical reactions that lead to corrosion and oxidation, allowing large electrode areas to be used safely without the same degradation mechanisms.
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 provides compact, portable, and cost-effective detection of nanoscale analytes with high sensitivity, eliminating interference and corrosion issues, and enabling rapid, on-site quantification of biological analytes without the need for expensive materials.
Implementation Method 1
measuring capacitance of the sample
Implementation Method 2
Adsorption of Blood Proteins on Metals Using Capacitance Techniques
Implementation Method 3
the electrodes (3, 4) are covered by a protection layer (5)... In one embodiment, the electrodes are covered by nitride
Implementation Method 4
said capacitors form the front-end (11) of a second-order sigma-delta switched-capacitor modulator A-to-D converter (12) providing a one-bit digital output bit stream representing the charge balancing between sensing and reference capacitors
Data Source
AI summary
An analyte in a liquid sample is detected using a capacitive sensor having electrodes and a sensor surface, and a signal processor. The sample is dried to reduce its liquid content, and capacitive measurements are made after the drying and preferably also before the drying. The sample may include particles, and the analyte is part of or attached to the particles, and the particles provide a major part of the capacitance change compared to absence of particles. In another example the particles are degenerative and form an integral mass upon application of heat, enhancing the extent of capacitance change.