Research

Research Overview

Our laboratory focuses on the development of new instrumental and methodologies to advance analytical chemistry, predominantly in the area of mass spectrometry. The development of a new measurement capability, or the marked improvement of an existing technique, can profoundly affect other areas of scientific exploration and generate new scientific discoveries.

Current Research areas:

- Distance-of-Flight Mass Spectrometry
- MALDI-DOFMS and ESI-DOFMS
- Soft-Landing Mass Spectrometry
- Solid-State Detector Arrays for Mass Spectrometry
- New Excitation Sources for Atomic Spectroscopy
- New Approaches for Bottom-up Proteomics
- LIBS and LAMIS
- Microwave-Assisted LIBS and LAMIS
- New Ionization Sources for Molecular Mass Spectrometry and Ambient Ionization Mass Spectrometry

Distance-of-Flight Mass Spectrometry (DOFMS)

The DOFMS employs a velocity-based m/z-separation approach that is the complement of traditional time-of-flight mass spectrometry (TOFMS). At a specific instant after acceleration, all m/z will achieve a sharp spatial focus and can then be directed onto the surface of a position-sensitive ion detector where their m/z is determined based upon location. Alternatively, a conventional TOFMS detector can be used for ion detection, in which case a constant-momentum acceleration (CMA) TOFMS experiment is conducted. DOFMS holds a number of benefits that derive from the ability to spatially separate ions of different m/z, simultaneously, and without complicated instrumentation. Our laboratory is currently involved in investigating new applications of DOFMS and in further developing the technique.

MALDI-DOFMS & ESI-DOFMS

Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) are capable of creating ions from larger biological constructs, like intact viruses or biomolecular protein complexes, current MS technologies are often unable to provide critical chemical information. In large part, the current limitation of MS can be traced to the mass analyzer technologies employed and the detectors used to quantify the ions. The use of DOFMS for ultra-large molecule MS overcomes many of the limitations that hinder current MS approaches. The DOFMS has no upper m/z-range of analysis, larger molecules can be analyzed simply by allowing a longer flight time period. This is in contrast to other MS approaches which do have a fundamental limit to the greatest m/z that can be accessed (e.g. ion trap technologies).

Soft-Landing Mass Spectrometry

The soft-landing MS strategy has shown that ions can be collected after MS analysis for subsequent use. Our laboratory is adapting DOFMS for soft-landing applications, specially in conjunction with MALDI. The ion optics required to realize the soft-landing MALDI-DOFMS are currently under development, and will be adapted to DOFMS analysis using other ionization sources and in other applications.

Solid-State Detector for Mass Spectrometry

Our group is developing a new type of solid-state focal plane array detector that is based on direct charge detection of ions using an array format. By directly detecting the charge of each ion upon neutralization, ion detection is achieved without mass bias, (i.e. electrons and biomolecules are detected with the same efficiency). Further, by using a multi-channel array approach, many different m/z can be detected at the simultaneously. The advanced semiconductor technology used in its fabrication makes it very sensitive and fast, allowing detection limits below 10 fundamental charges.

Our laboratory continues the evolution of this technology by exploring its use with various ionization sources to detect positive or negative ions in a wide range of applications.

New Excitation Sources for Atomic Spectroscopy

The solution-cathode glow discharge (SCGD) is an atmospheric-pressure glow discharge operated in the ambient atmosphere. The SCGD is particularly intriguing because this high-temperature, highly-ionized plasma is sustained directly on top of a liquid surface. A continuous flow of liquid cascades from the tip of a quartz capillary into a catch-basin. The SCGD (cf. Figure) is sustained under moderate power (800V/80mA) between the liquid surface (cathode) and a positively-biased metallic counter-electrode (anode). The liquid surface is the cathode of the glow discharge, allowing direct liquid sampling via ‘sputtering’ material into the SCGD plasma for atomic emission spectroscopy. This humble 100-watt discharge often provides performance competitive with conventional ICP-OES instrumentation.

In-Line Flow-Through Microwave-Assisted Proteomics

Our group is developing a new type of methodology for focused microwave-assisted proteomics by implementing microwave microstrip resonators. By focusing the microwave field into a finite volume localized heat generation based on the inherent dielectric loss of the materials can be achieved more efficiently. When coupled in-line with a flowing solution source and mass spectrometer, the new system (specially designed for ESI) allows the digestion and complete characterization and elucidation of a wide range of proteins peptides greatly reducing sample digestion times over conventional protocols.

Our laboratory continues the evolution of the current capabilities of the system for applications in bottom-up proteomics and rapidly-modulated digestion of biopolymers in mass spectrometry.

DMMA-Gated LIBS and LAMIS

Laser-induced breakdown spectroscopy (LIBS) and laser ablation molecular isotopic spectrometry (LAMIS) are techniques in which a high-power laser is focused onto the surface of a sample, ablating a small amount of sample material and generating a laser-induced plasma (LIP). The LIP is used to detect emission for elemental and isotopic analysis for LIBS and LAMIS, respectively. It is well-established that there is a temporal dependence on species detected. The most common method of temporal filtering, or temporal gating, is detection via intensified charge coupled device (ICCD) which is costly and fragile. Our group has demonstrated the use of a digital micromirror array (DMMA) as a device capable of gating on the LIBS/LAMIS timescale (100s of ns) as well as the added feature of spatial sampling of the plasma.

Microwave-Assisted LIBS and LAMIS

Injection of microwave into a LIBS plasma has been known to enhance LIBS spectra. Ongoing work in our lab look at employing microstrip resonators for the first time. This should result in higher electric fields and, thus, further enhancement. Preliminary results show significant emission enhancement.

New Ionization Sources for Molecular Mass Spectrometry and Ambient Ionization Mass Spectrometry

A novel strategy for MS analysis known as ambient mass spectrometry has been developed. Here, the emphasis is on sampling molecules directly from their native chemical environment and ionizing them within the ambient environment. In this way, sample processing steps can be greatly reduced, providing very rapid screening of samples.

Recent studies have investigated the influence of an intense microwave field on the electrospray ionization (ESI) process, a technique we have named Microwave-Assisted Electrospray Ionization (µAESI). By employing a novel waveguide structure, microwave energy can be focused into a very small and controlled volume By placing the ESI emitter within this volume, the effect of microwave radiation and dielectric heating on the ESI process are studied by using optical imaging and mass spectrometry. We are currently investigating how these changes influence the mass spectra collected using this new ionization source, as well as other means of employing microwave heating in similar strategies.

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