CMOS Capacitive Sensor Layout for Dry-Sample DNA Detection
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Solution Overview
Problem
Existing capacitive sensors for detecting nanoscale analytes like DNA and RNA are large, expensive, and not suitable for 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 protection layer, uses a sigma-delta switched-capacitor modulator for high-resolution detection without a reference electrode, and employs differential sensing and magnetic bead techniques to measure capacitance changes before and after sample drying.
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 this is acceptable as the sensor can be disposed of or electrodes replaced, enabling high-volume low-cost manufacturing on standard CMOS technologies
Solution Approach 2:
The patent extracts and removes the reference electrode from the sensor system entirely. By using a capacitive sensing architecture where one electrode is suspended and serves as both sensing and reference, the complex three-electrode system with noble metal reference electrodes is eliminated, reducing cost and complexity
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 many interdigitated fingers (typically 10-100 fingers per electrode), each with small area, but collectively providing large effective sensing area. This segmentation allows the electrodes to be miniaturized while maintaining sufficient total capacitance for measurement, enabling portable device integration
Solution Approach 2:
The patent transitions from planar electrodes to three-dimensional interdigitated finger structures, increasing the effective surface area by utilizing vertical spacing between fingers. This dimensional approach allows sufficient capacitance to be achieved in a compact footprint suitable for portable devices
3Stability of the object's composition
If reference electrode is added to control DC voltage, then voltage stability is improved, but device complexity increases and interference with analyte occurs
Solution Approach 1:
The patent merges the reference electrode function into one of the capacitive sensing electrodes. By using a suspended electrode configuration where one electrode serves dual purposes (sensing and reference), the separate reference electrode is eliminated, reducing device complexity while maintaining voltage stability through capacitive coupling
Solution Approach 2:
The patent introduces a dielectric layer as an intermediary between the suspended electrode and the substrate, which acts as the reference. This intermediary structure provides stable DC voltage control without requiring a physical reference electrode in contact with the analyte, preventing interference with DNA and other samples
4Ease of operation
If electrodes are made accessible for measurement, then measurement capability is improved, but susceptibility to corrosion and oxidation increases
Solution Approach 1:
The patent creates an inert environment by suspending one electrode above the substrate with a dielectric layer, isolating it from direct contact with corrosive liquids and oxygen. This protective configuration reduces corrosion and oxidation while maintaining measurement capability through capacitive coupling across the dielectric barrier
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 to nanoscale analytes, is cost-effective, compact, and robust, enabling rapid and accurate detection of DNA, RNA, and other biological molecules without interference, and allows for on-site quantification of fluids and particles.
Implementation Method 1
measuring capacitance of the sample
Implementation Method 2
Adsorption of Blood Proteins on Metals Using Capacitance Techniques
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.