Micromachined, planar-geometry, atmospheric-pressure, battery-operated microplasma devices (MPDs) on chips for analysis of microsamples of liquids, solids, or gases by optical-emission spectrometry

Abstract

Because of their desirable characteristics, for example small size, lightness, low power and gas consumption, and potential for portability, miniaturized plasma sources are receiving significant attention in the scientific literature. To take advantage of these characteristics we micromachined and fabricated new, planar-geometry, self-igniting, atmospheric-pressure microplasma devices (MPDs) on chips. These microplasmas required such low power for their operation they could be operated from a re-chargeable battery (of the type used in cordless power-tools). Despite their advantages, most miniaturized plasma sources reported in the literature have not performed well with liquid samples; analysis of powders or solids that can be converted to a powder (and processed and used as slurries) is even more difficult. To address these shortcomings we coupled an electrothermal, mini-in-torch vaporization (mini-ITV) "dry" sample-introduction system to the low-power planar microplasma devices we developed. In this preliminary investigation, absolute detection limits obtained from microsamples of single-element liquid standards and optical emission spectrometry with photomultiplier-tube detection and a spectral bandpass similar to that of portable, commercially available fiber-optic spectrometers were in the low-pg to ng range, for example 2 pg (for K) to 25 ng (for Pb). Mini-ITV also enabled (as far as we are aware, for the first time) measurement of analyte emission from microsamples of powdered solids (as slurries). In addition to the 3% H2 in Ar mixtures, the ac-operated microplasmas were sustained by use of a variety of electrode materials and different plasma-support gases (e.g. Ar, He and 3% H2 in He) thus indicating fabrication versatility and operational flexibility. Such flexibility has the potential to enable microplasmas to be tailored to analytical problems, and this is demonstrated by using a He MPD and chlorine emission measurements (837.594 nm) from gaseous microsamples as an example.

Rapid Prototyping of Hybrid, Plastic-Quartz 3D-Chips for Battery-Operated Microplasmas

“…For instance, there are several research groups world-wide working on microplasmas for chemical analysis applications. Thus far, microplasmas have been described in books (Becker et al, 2004;Hutchison, 2005;Lieberman, 2005;Fridman, 2008;Hippler at al., 2008;Fridman, 2011;Inan & Gokowski, 2011), in review articles (Karanassios, 2004;Broekaert & Siemens, 2004;Broekaert & Jakubowski, 2007;Gianchandani et al, 2009) and in papers describing their analytical applications (Karanassios et al, 2007;Weagant & Karanassios, 2009;Weagant et al, 2010;Weagant et al, 2011;Vautz et al, 2008;Olenici-Craciunescu, 2009;Hoskinson et al, 2011;Marcus et al, 2011), their characteristics and their other uses (Janasek et al, 2006;Frimat et al, 2009;Olenici-Craciunescu, 2011;Xu & Hopwood, 2007;Zhu et al, 2008;Chen & Eden, 2008;Wright & Chianchandani, 2009;McKay et al, 2010;Liu et al, 2010). From the cited literature it can be concluded that although microplasma research has been (mostly) application driven, "microplasmas represent a new realm in plasma physics that still is not fully understood" (Iza, 2008).…”

“…The sputter electrodes also served as contact pads. The chip and the plate were aligned and were bonded (Karanassios et al, 2007) to provide hermetic seal. To reduce the costs of prototyping a new microplasma device any time one of the electrodes was damaged and to enable deeper etches crystalline silicon wafers were replaced by amorphous glass wafers (or substrates).…”

“…2. The chips were bonded to provide a hermetic seal (Karanassios et al, 2007). A high voltage dc (HVdc) was applied between the sputtered electrodes to initiate and sustain the microplasma.…”

“…These were so named by analogy to nano-electrospray and to nano flow injection. As before, the chips were bonded to provide a hermetic seal (Karanassios et al, 2007). To reduce or eliminate electrode stress from the high voltage dc (HVdc) applied to the electrodes, the HVdc power supply was replaced by a high voltage ac (HVac) power supply.…”

“…The plate was added because quartz is optically transparent to ultra-violet (UV), as required for measurements in this spectral region. These microplasma devices on hybrid chips (with area roughly that of a small postage stamp) were used for development and characterization of microplasmas primarily for elemental analysis applications (Karanassios, 2004;Karanassios et al, 2007;Weagant & Karanassios, 2009, Weagant et al, 2011Karanassios, 2011). Elemental analysis is as a sub-set of the discipline called chemical analysis or analytical chemistry.…”