Micro-PADI sources for applications in 2-D chemical imaging

用于二维化学成像应用的 Micro-PADI 源

• 批准号: EP/I028722/1
• 负责人: James Bradley
• 金额: $ 43.34万
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FI028722%2F1
• 关键词: Micro; PADI; sources; applications; chemical

In the last few years with the availability of high-resolution, small-scale (and portable) mass spectrometers, there has been a flurry of exciting developments in ambient ionisation mass spectrometry. In this technique the chemical composition of the surface of ordinary samples in their native environment can be analysed directly with minimal sample preparation. It has been applied successfully to the analysis many different materials, for instance in pharmaceuticals and forensics.One of the principle desorption-ionisation techniques is desorption electrospray ionization (DESI) first introduced by the group of Cooks in 2004, which has been applied to a plethora of samples in ambient conditions. However, some of the most exciting developments in ambient ionization employ a variety of atmospheric-pressure plasmas as the medium for desorption and ionisation. The plasma-based technique at the heart of this project is plasma-assisted desorption ionization (PADI) which is showing significant promise for the analysis of many materials including biological samples, allowing species of mass < 500 Da to be routinely detected. Conventional PADI is based on the RF (13.56 MHz) plasma needle configuration producing a cold non-equilibrium plasma (gas temperatures around 300K). It is simple in construction, runs at low voltages and produces a relatively localised plasma plume at the needle tip of about 1 mm in width and up to several mm's in length allowing it to remotely activate the surface through direct contact of the plasma. The current PADI configuration may have potential advantages over electro-spraying techniques (DESI), since its design allows for the introduction of surface etching or chemical ionisation reagents in the He feedstock. It is also easier to use than DESI, lower in cost, and with less precise requirements for plasma-sample angles and produces little damage to the sample (except at the highest powers). Most importantly, it produces cleaner spectra with generally higher signal intensities than DESI (5-10 times typically).Despite the success of the plasma-based ambient desorption-ionization techniques none of these techniques provide the sufficient spatial control necessary to distinguish chemical features with less than a few hundred microns resolution. This clearly limits current plasma techniques for 2-D surface chemical imaging applications, for instance in scanning-probe microscopy. To date, DESI is the most successful technique for imaging (spatially resolved chemical information) since it has small reagent beams with spatial resolutions reported to be down to 40 microns. However, for large area, 2D imaging applications the relatively large volume of costly and potentially hazardous solvent required by DESI (1-10 micro-L/min) makes the 2-D approach impractical. We believe the solution to producing small-scale plasma technology, suitable for high-resolution surface imaging, is to further develop micro-plasma sources originally designed for other applications. These are micro-hollow cathode discharges, open-ended micro-channel discharges and needle geometry discharges. Through careful design they will produce small volume plasmas necessary to achieve a spatial resolution of the desorption footprint down to 10 microns. The most promising configurations will be developed further and integrated into existing mass spectroscopic systems. One key feature of this research will be the use of repetitive nanosecond duration, high-voltage pulsing, for each of chosen source designs to allow operation in ambient air, both static and flowing conditions. The project has 5 main research tasks. These are, plasma source design and fabrication, source operation and testing, plasma characterisation and diagnosis, study of desorption and ionisation and the development of 2-D imaging through scanning probe microscopy.

在过去的几年里，随着高分辨率，小规模（和便携式）质谱仪的可用性，在敞开式电离质谱中有一系列令人兴奋的发展。在这项技术中，普通样品在其自然环境中的表面化学成分可以直接分析，样品制备量最少。解吸电喷雾离子化（DESI）是一种主要的解吸电离技术，由Cooks团队于2004年首次引入，已在环境条件下应用于大量样品的分析。然而，一些最令人兴奋的发展，在环境电离采用各种大气压等离子体作为介质的解吸和电离。该项目的核心技术是等离子体辅助解吸电离（PADI），该技术在分析包括生物样品在内的许多材料方面显示出巨大的前景，可以常规检测质量< 500 Da的物质。传统的PADI是基于RF（13.56 MHz）等离子体针配置产生冷非平衡等离子体（气体温度约300 K）。它结构简单，在低电压下运行，并在针尖处产生相对局部化的等离子体羽流，宽度约为1 mm，长度可达几mm，从而允许其通过直接接触等离子体远程激活表面。目前的PADI配置可能具有潜在的优势，超过电喷雾技术（DESI），因为它的设计允许在He原料中引入表面蚀刻或化学电离试剂。它也比DESI更容易使用，成本更低，对等离子体样本角度的精确要求更低，并且对样本产生的损坏很小（最高功率除外）。最重要的是，它产生更干净的光谱，通常比DESI更高的信号强度（通常为5-10倍）。尽管基于等离子体的环境解吸电离技术取得了成功，但这些技术都没有提供足够的空间控制来区分具有小于几百微米分辨率的化学特征。这显然限制了目前的等离子体技术的2-D表面化学成像应用，例如在扫描探针显微镜。迄今为止，DESI是最成功的成像技术（空间分辨化学信息），因为它具有小的试剂束，据报道空间分辨率低至40微米。然而，对于大面积的2D成像应用，DESI所需的相对大体积的昂贵且潜在危险的溶剂（1-10微升/分钟）使得2D方法不切实际。我们相信，生产适用于高分辨率表面成像的小规模等离子体技术的解决方案是进一步开发最初为其他应用设计的微等离子体源。这些是微空心阴极放电，开放式微通道放电和针形放电。通过精心设计，它们将产生小体积等离子体，以实现低至10微米的解吸足迹的空间分辨率。最有前途的配置将进一步开发和集成到现有的质谱系统。这项研究的一个关键特征将是使用重复的纳秒持续时间，高压脉冲，为每个选定的源设计，以允许在环境空气中操作，静态和流动条件。该项目有5个主要研究任务。这些是，等离子体源的设计和制造，源操作和测试，等离子体表征和诊断，解吸和电离的研究和2-D成像的发展，通过扫描探针显微镜。

项目成果

Surface Analysis using a new PADI source for Mass Spectrometry in ambient air

使用新的 PADI 源进行环境空气中的质谱分析

• 期刊: Rev Sci. Instrum.
• 作者: Andrew Bowfield (Author)

Surface analysis using a new plasma assisted desorption/ionisation source for mass spectrometry in ambient air.

• DOI: 10.1063/1.4729120
• 发表时间: 2012-06
• 期刊: The Review of scientific instruments
• 作者: A. Bowfield;David A. Barrett;M. Alexander;C. Ortori;F. Rutten;T. Salter;I. Gilmore;J. Bradley

Mass spectrometric diagnosis of an atmospheric pressure helium microplasma jet

• DOI: 10.1088/0022-3727/46/46/464018
• 发表时间: 2013-10
• 期刊: Journal of Physics D: Applied Physics
• 作者: K. McKay;Jun-Seok Oh;James L. Walsh;James W. Bradley

Studying Townsend and glow modes in an atmospheric-pressure DBD using mass spectrometry

• DOI: 10.1088/1361-6595/aa9cb0
• 发表时间: 2017-12
• 期刊: Plasma Sources Science and Technology
• 影响因子: 3.8
• 作者: K. McKay;D. Donaghy;Feng He;J. Bradley

Characterisation of a micro-plasma for ambient mass spectrometry imaging.

• DOI: 10.1039/c4an01110d
• 发表时间: 2014-09
• 期刊: The Analyst
• 作者: A. Bowfield;J. Bunch;T. Salter;R. Steven;I. Gilmore;David A. Barrett;M. Alexander;K. McKay;J. Bradley