Laser Ablation Cell with Constant Cross-Section for ICPMS Imaging
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Solution Overview
Problem
Current laser ablation cells for inductively coupled plasma mass spectrometry (ICPMS) lack the spatial resolution necessary for imaging single cells within tissue samples, primarily due to long aerosol washout times which lead to signal overlap and limited imaging capabilities.
Innovation Solution
A laser ablation cell design with a 'tube cell' configuration that minimizes cross-sectional area variations, maintaining laminar flow and positioning the sample close to the flow channel to reduce aerosol dispersion, achieving washout times below 30 ms and allowing for improved spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external laser ablation cells are used for imaging applications, then scanning of the laser spot becomes easier and larger samples can be analyzed, but aerosol washout times increase to seconds making high spatial resolution imaging difficult
Solution Approach 1:
The ablation cell is segmented into distinct functional zones: a laser interaction region with minimal gas flow for controlled ablation, and a rapid washout region with high gas flow velocity to quickly clear aerosol. This segmentation allows the cell to provide both easy laser scanning capability and rapid aerosol removal, resolving the contradiction between operational ease and washout time.
2Reliability
If longer aerosol washout time is used, then more complete sample analysis is achieved, but signal overlap between neighboring sample spots increases reducing spatial resolution
Solution Approach 1:
The system uses periodic laser pulsing combined with periodic gas flow modulation. During each laser pulse, gas flow is reduced to allow complete ablation and aerosol formation. Between pulses, gas flow increases to rapidly washout the aerosol before the next pulse occurs. This periodic action ensures complete sample analysis during the ablation phase while maintaining spatial resolution through rapid clearance during the washout phase.
3Loss of time
If faster washout time is achieved through in-torch ablation, then single shot signal duration is reduced to milliseconds, but scanning of the laser spot becomes very difficult and is limited to very small samples
Solution Approach 1:
An intermediary gas flow system is introduced between the laser ablation region and the mass spectrometer inlet. This intermediary system provides rapid aerosol transport and washout without requiring the laser to be positioned directly in the high-velocity gas stream, thus maintaining both fast signal duration and easy laser scanning capability over larger sample areas.
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 design significantly reduces aerosol washout time, enabling higher spatial resolution and minimizing signal overlap, making it suitable for single-cell imaging in tissue samples and other biological materials.
Implementation Method 1
A laser beam is directed through the flow channel onto a sample positioned below the flow channel so as to ablate material from the sample and create an aerosol
Implementation Method 2
A carrier gas is induced to flow through a flow channel at a flow rate sufficient to transport an aerosol plume created by laser ablation of a sample through the flow channel to an outlet of the flow channel
Implementation Method 3
A lateral opening is provided in a first wall portion of the flow channel... The flow channel has substantially constant cross-sectional area... maintaining laminar flow and positioning the sample close to the flow channel to reduce aerosol dispersion
Data Source
AI summary
A laser ablation cell (1) comprises a flow channel (11) having an essentially constant cross-sectional area so as to ensure a strictly laminar flow in the flow channel. A sample chamber (21) is provided adjacent to a lateral opening (14) of the flow channel. A laser beam (41) enters the sample chamber (21) through a lateral window (16) and impinges on a surface (24) of a sample (23) to ablate material from the sample. The sample may be positioned in such a distance from the flow channel that the laser-generated aerosol mass distribution has its center within the flow channel. This leads to short aerosol washout times. The laser ablation cell is particularly well suited for aerosol generation in inductively coupled plasma mass spectrometry (ICPMS), including imaging applications.