Microfluidic Cell for Liquid Cell TEM pH Measurement
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Solution Overview
Problem
Liquid phase transmission electron microscopy (LP-TEM) imaging of electron beam-sensitive biological and soft nanomaterials faces challenges in quantifying local electron beam-induced changes to sample chemistry, particularly in measuring pH changes caused by electron beam-induced production of radicals and protons during imaging.
Innovation Solution
The use of electrochemical impedance spectroscopy (EIS) to measure local electron beam-induced pH changes by detecting changes in solution resistance, leveraging the differing diffusion behaviors of protons and hydroxide ions, and employing a microfluidic cell system with strategically positioned electrodes to selectively measure proton concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional imaging methods are used in LP-TEM, then structural information can be obtained, but electron beam-induced pH changes and radical production cannot be quantified
Solution Approach 1:
The patent introduces electrochemical impedance spectroscopy (EIS) as an intermediary measurement technique that indirectly detects pH changes through solution resistance measurements. This mediator approach allows pH quantification without directly interfering with the electron beam imaging process, resolving the contradiction between measurement capability and system simplicity
Solution Approach 2:
The measurement system is designed to perform multiple functions: structural imaging via LP-TEM and chemical environment monitoring via EIS. By making the system multi-functional, it can simultaneously obtain both structural information and pH data, eliminating the need for separate measurement systems
2Measurement precision
If electron beam current is increased to improve imaging quality, then image resolution improves, but electron beam-induced chemistry alterations increase
Solution Approach 1:
The patent implements a feedback mechanism where EIS measurements continuously monitor pH changes in real-time during imaging. This feedback allows researchers to adjust imaging parameters dynamically, reducing electron beam current when pH changes are detected, thereby maintaining image quality while minimizing chemical alterations
Solution Approach 2:
The system performs periodic EIS measurements interspersed with imaging acquisitions. This periodic monitoring and adjustment cycle allows the system to maintain optimal imaging conditions while periodically checking for and correcting electron beam-induced chemical changes
3Measurement precision
If ion selective electrodes are used to measure pH, then specific ion detection is achieved, but device complexity and measurement invasiveness increase
Solution Approach 1:
The patent replaces complex mechanical ion-selective electrodes with an electrochemical impedance spectroscopy system that measures solution resistance. This substitution uses electrical field interactions rather than physical electrode-sample contact, simplifying the device while maintaining measurement capability
Solution Approach 2:
The system measures changes in solution resistance as a proxy for pH changes, rather than directly measuring proton concentration with complex electrodes. By changing the measurement parameter from direct ion detection to resistance measurement, the system achieves simpler device architecture while maintaining measurement precision
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
Enables direct and sensitive measurement of pH changes over a wide pH range, confirming correlations with reaction-diffusion simulations and demonstrating the effectiveness of EIS in probing proton concentrations without ion-selective electrodes, thus allowing for controlled imaging conditions to minimize electron beam-induced chemistry alterations.
Implementation Method 1
electrochemical impedance spectroscopy (EIS) to detect changes in solution resistance resulting from electron beam-induced changes to solution pH
Implementation Method 2
detect changes in solution resistance
Implementation Method 3
protons and hydroxide ions are able to diffuse throughout the LP-TEM microchannel while reactive radicals recombine before they are able to diffuse away
Implementation Method 4
electron beam-induced production of radicals, molecules (protons, hydroxide ions, hydrogen peroxide), and dissolved gas (hydrogen and oxygen gas)
Data Source
AI summary
A microfluidic cell system to measure proton concentration in a fluid sample. The microfluidic cell system includes: a first microchip and a second microchip dimensioned to permit electron beam scanning of a fluid sample; a first membrane attached to the first microchip; a second membrane attached to the second microchip, the first membrane and the second membrane being disposed adjacent to one another with a space for the fluid sample therebetween, and the first membrane and the second membrane including a region of the fluid sample in which an electron beam is scanned; a first electrode patterned onto the first membrane and positioned a first distance from the region; a second electrode patterned onto the first microchip and positioned a second distance from the region, the first distance being less than the second distance; and a potentiostat in communication with the first electrode and the second electrode.