Laser-based analytical techniques such as Raman spectroscopy, fluorescence spectroscopy or the state-of-the-art laser-induced breakdown spectroscopy (LIBS) are highly sophisticated techniques for analyzing minute amounts of matter with regard to its structure, elemental composition, and other chemical properties.LIBS has been shown to be capable of analyzing extremely small samples with high sensitivity—nanolitre volumes with levels of detection in water of one part per million. LIBS works by focusing short laser pulses on to the surface of a
sample to create a hot plasma with temperatures of 10 000–20 000 1C. The plasma emits radiation that allows the observation of the characteristic atomic emission lines of the elements. The downside is that LIBS is complicated by the need for multiple laser pulses to generate asufficiently hot plasma and the need for focusing and switching a powerful laser, requiring relatively large and expensive instruments.
Research coming out of Drexel University has shown that light emitted from a new form of cold plasma in liquid—field emission generated, highly nonequilibrium, and high energy density—permits optical emission spectroscopy (OES) analysis of the elemental composition of solutions within nanoseconds from femtolitre (10–15 L) volumes.
‘‘We were able to generate, for the first time, a nonthermal corona discharge in liquid around electrodes with ultrasharp tips and around nanowires,’’ says Yury Gogotsi. ‘‘We have demonstrated that plasmas created with 50 nm probe tips or carbon nanotubes (CNTs)—what we have termed nanoscale corona discharge probes (NCDPs)—dispersed in solution allow simultaneous chemical analysis of multiple dissolved elements within nanoseconds. Time-resolved OES of NCDPs demonstrates narrow spectral lines that prove very useful for simple yet sensitive multi-elemental analysis, thus opening new possibilities in chemical detection, environmental monitoring, medicine, and many other applications.’’
Gogotsi, a professor in the Department of Materials Science and Engineering, heads the A.J. Drexel Nanotechnology Institute at Drexel University, and has worked with colleagues Gary Friedman from Drexel’s Department of Electrical and Computer Engineering; Alexander Gutsol (currently with Chevron); and Alexander Fridman (director of the A.J. Drexel Plasma Institute).
Gogotsi says that the OES method proposed by the Drexel scientists can be applied for ultra-fast, time-resolved, multi-elemental analysis of liquid in microfluidic reactors, living biological systems, or environmental sensors andfor diagnostics of femtolitre volumes with 1 mm or better spatial resolution. ‘‘Using this method, we have detected one part-per-million concentrations of sodium, calcium, and other elements in aqueous solutions.’
In comparison to LIBS, the researchers found that the observed spectra are of better quality, have significantly smaller analytical volumes, and are accomplished using drastically simpler, smaller, and less expensive equipment and materials. Furthermore, OES can be performed remotely, using nanorods and nanotubes dispersed in fluid.
The team describes how in a typical experiment, a tungsten wire with a tip sharpened to less than 50nm radius was used to generate the corona discharge. Negative corona discharges at the tips have been demonstrated in all cases. The pulsed voltage source provides 2–30 kV pulses 10–500 ns in duration at approximately 30 Hz repetition rate, achieving negative corona for a 50 nm radius tip with as little as 3 kV.
‘‘Considering existing theories of discharge initiation in liquids and our current experiments, there are several factors that contribute to the reasons why the NCDP is different from the streamer coronas previously observed in liquid and specifically why the two initial stages of the negative corona are observed,’’Gogotsi explains. ‘‘Our study is the first that simultaneously combines short rise-time voltages, nanosecond-duration pulses, high temporal resolution emission spectra, and most importantly, nanoscale tips.’’
The Drexel team is hopeful that the OES nanoscale probes may open a new era in micro/nanoscale chemical, environmental, and biological sensing and detection techniques.
‘‘Just as the discovery of AFM changed the world of microscopy, the OES nanoscale probes may change the world of chemical analysis, replacing the large and expensive instruments that are used for elemental analysis or measurements of cation concentration in thousands of labs worldwide by simple,portable, and very inexpensive tools that also add analytical capabilities not
available today, e.g. fast simultaneous quantitative analysis of multiple cations in solution,’’ says Gogotsi.
With regard to the nonthermal plasma in liquid, nanoscale corona discharge OES is presented as only the first of many potential applications for this newly discovered tool; applications in nanopatterning and surface functionalization as well as tools for cellular surgery are readily conceivable. Gogotsi and his colleagues expect this research to affect a broad spectrum of fields ranging from pharmaceuticals and biomedicine to nanotechnology and fundamental plasma chemistry.
Featured scientist: Yury Gogotsi
Organization: A.J. Drexel Nanotechnology Institute, Philadelphia, PA
(USA)
Relevant publication: David Staack, Alexander Fridman, Alexander
Gutsol, Yury Gogotsi, Gary Friedman: Nanoscale corona discharge
in liquids, enabling nanosecond optical emission spectroscopy.
Angew. Chem., Int. Ed., 47, 8020–8024.
Source
Nano-Society
www.rsc.org/nanoscience
sample to create a hot plasma with temperatures of 10 000–20 000 1C. The plasma emits radiation that allows the observation of the characteristic atomic emission lines of the elements. The downside is that LIBS is complicated by the need for multiple laser pulses to generate asufficiently hot plasma and the need for focusing and switching a powerful laser, requiring relatively large and expensive instruments.
Research coming out of Drexel University has shown that light emitted from a new form of cold plasma in liquid—field emission generated, highly nonequilibrium, and high energy density—permits optical emission spectroscopy (OES) analysis of the elemental composition of solutions within nanoseconds from femtolitre (10–15 L) volumes.
‘‘We were able to generate, for the first time, a nonthermal corona discharge in liquid around electrodes with ultrasharp tips and around nanowires,’’ says Yury Gogotsi. ‘‘We have demonstrated that plasmas created with 50 nm probe tips or carbon nanotubes (CNTs)—what we have termed nanoscale corona discharge probes (NCDPs)—dispersed in solution allow simultaneous chemical analysis of multiple dissolved elements within nanoseconds. Time-resolved OES of NCDPs demonstrates narrow spectral lines that prove very useful for simple yet sensitive multi-elemental analysis, thus opening new possibilities in chemical detection, environmental monitoring, medicine, and many other applications.’’
Gogotsi, a professor in the Department of Materials Science and Engineering, heads the A.J. Drexel Nanotechnology Institute at Drexel University, and has worked with colleagues Gary Friedman from Drexel’s Department of Electrical and Computer Engineering; Alexander Gutsol (currently with Chevron); and Alexander Fridman (director of the A.J. Drexel Plasma Institute).
Gogotsi says that the OES method proposed by the Drexel scientists can be applied for ultra-fast, time-resolved, multi-elemental analysis of liquid in microfluidic reactors, living biological systems, or environmental sensors andfor diagnostics of femtolitre volumes with 1 mm or better spatial resolution. ‘‘Using this method, we have detected one part-per-million concentrations of sodium, calcium, and other elements in aqueous solutions.’
In comparison to LIBS, the researchers found that the observed spectra are of better quality, have significantly smaller analytical volumes, and are accomplished using drastically simpler, smaller, and less expensive equipment and materials. Furthermore, OES can be performed remotely, using nanorods and nanotubes dispersed in fluid.
The team describes how in a typical experiment, a tungsten wire with a tip sharpened to less than 50nm radius was used to generate the corona discharge. Negative corona discharges at the tips have been demonstrated in all cases. The pulsed voltage source provides 2–30 kV pulses 10–500 ns in duration at approximately 30 Hz repetition rate, achieving negative corona for a 50 nm radius tip with as little as 3 kV.
‘‘Considering existing theories of discharge initiation in liquids and our current experiments, there are several factors that contribute to the reasons why the NCDP is different from the streamer coronas previously observed in liquid and specifically why the two initial stages of the negative corona are observed,’’Gogotsi explains. ‘‘Our study is the first that simultaneously combines short rise-time voltages, nanosecond-duration pulses, high temporal resolution emission spectra, and most importantly, nanoscale tips.’’
The Drexel team is hopeful that the OES nanoscale probes may open a new era in micro/nanoscale chemical, environmental, and biological sensing and detection techniques.
‘‘Just as the discovery of AFM changed the world of microscopy, the OES nanoscale probes may change the world of chemical analysis, replacing the large and expensive instruments that are used for elemental analysis or measurements of cation concentration in thousands of labs worldwide by simple,portable, and very inexpensive tools that also add analytical capabilities not
available today, e.g. fast simultaneous quantitative analysis of multiple cations in solution,’’ says Gogotsi.
With regard to the nonthermal plasma in liquid, nanoscale corona discharge OES is presented as only the first of many potential applications for this newly discovered tool; applications in nanopatterning and surface functionalization as well as tools for cellular surgery are readily conceivable. Gogotsi and his colleagues expect this research to affect a broad spectrum of fields ranging from pharmaceuticals and biomedicine to nanotechnology and fundamental plasma chemistry.
Featured scientist: Yury Gogotsi
Organization: A.J. Drexel Nanotechnology Institute, Philadelphia, PA
(USA)
Relevant publication: David Staack, Alexander Fridman, Alexander
Gutsol, Yury Gogotsi, Gary Friedman: Nanoscale corona discharge
in liquids, enabling nanosecond optical emission spectroscopy.
Angew. Chem., Int. Ed., 47, 8020–8024.
Source
Nano-Society
www.rsc.org/nanoscience
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