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R. Das et al.
intensity. R. Hai et al. demonstrated a two times enhancement in the LIBS intensity
of aluminum-lithium alloy and multi-element doped graphite due to magnetic confinement [31]. The enhancement in intensity is attributed to the increase in plasma
density and temperature due to the presence of the external magnetic field. Z. Hao
et al. used a ring magnet to improve the detection sensitivity of vanadium (V) and
manganese (Mn) elements in steel [30]. The enhancement in intensity is attributed to
the simultaneous spatial and magnetic confinement of the plasma plume due to the
ring-magnetic confinement, which significantly increases the electron density and
temperature of the plasma. However, these methods are only suitable for laboratory
purposes and potentially inconvenient for field or in-situ applications.
1.4 Nanoparticle Enhanced LIBS
In comparison to the other physical methods mentioned above, NELIBS is a relatively
new method that utilizes nanoparticles (NP) for enhancing the LIBS signal strength
[19]. In recent years, this method is found to be a more promising and flexible
analytical tool for elemental mapping since it does not require any modification of the
experimental setup rather, a small amount of NPs are dispersed on the sample surface.
The sample treatment in NELIBS is minimal, inexpensive, and more importantly,
nanoparticle emission lines’ contribution does not much affect the analyte emission
lines. The manipulation of the sample surface in NELIBS is relatively easy and
straight forward. Usually, a few micro drops of a colloidal solution containing NPs
are deposited on a small area on the surface where the laser is focused. Hence the
area of the manipulated surface is negligible, and it does not alter the chemical
composition. It rather changes the surface properties, preferably enhances the lightmatter interaction followed by improving the strength of the signal. The deposited
nanoparticles can be easily removed entirely during the experiments. Hence, it can
be directly employed for the commercial LIBS setups.
Nanoparticles have been widely used in vibrational spectroscopy techniques such
as Raman spectroscopy and Laser-induced Fluorescence (LIF) spectroscopy in order
to enhance the extremely weak signals and to improve the detection limits and sensitivity [32, 33]. Unlike the LIBS technique, these techniques are non-destructive
and employ low power lasers to avoid photothermal damage and structural modifications. Hence, the role and properties of nanoparticles in such conditions have
been investigated thoroughly for quite some time now. After decades of debate, it is
now almost accepted that the SERS enhancement is mainly due to the electromagnetic amplification that is generated by the excitation of localized surface plasmons
resonance (LSPR) [32].
However, in 2009, Ohta et al. provided the first insight of using metallic nanoparticles to enhance the LIBS intensity on plant leaves [34]. They have used metallic
colloidal nanoparticles of silver and gold on the leaf surface in order to monitor the
nutrients in plant leaves. By applying the NPs, the authors have succeeded in ablating
the raw leaf and producing the transient micro-plasma even at very low energy (<1
R. Das et al.
intensity. R. Hai et al. demonstrated a two times enhancement in the LIBS intensity
of aluminum-lithium alloy and multi-element doped graphite due to magnetic confinement [31]. The enhancement in intensity is attributed to the increase in plasma
density and temperature due to the presence of the external magnetic field. Z. Hao
et al. used a ring magnet to improve the detection sensitivity of vanadium (V) and
manganese (Mn) elements in steel [30]. The enhancement in intensity is attributed to
the simultaneous spatial and magnetic confinement of the plasma plume due to the
ring-magnetic confinement, which significantly increases the electron density and
temperature of the plasma. However, these methods are only suitable for laboratory
purposes and potentially inconvenient for field or in-situ applications.
1.4 Nanoparticle Enhanced LIBS
In comparison to the other physical methods mentioned above, NELIBS is a relatively
new method that utilizes nanoparticles (NP) for enhancing the LIBS signal strength
[19]. In recent years, this method is found to be a more promising and flexible
analytical tool for elemental mapping since it does not require any modification of the
experimental setup rather, a small amount of NPs are dispersed on the sample surface.
The sample treatment in NELIBS is minimal, inexpensive, and more importantly,
nanoparticle emission lines’ contribution does not much affect the analyte emission
lines. The manipulation of the sample surface in NELIBS is relatively easy and
straight forward. Usually, a few micro drops of a colloidal solution containing NPs
are deposited on a small area on the surface where the laser is focused. Hence the
area of the manipulated surface is negligible, and it does not alter the chemical
composition. It rather changes the surface properties, preferably enhances the lightmatter interaction followed by improving the strength of the signal. The deposited
nanoparticles can be easily removed entirely during the experiments. Hence, it can
be directly employed for the commercial LIBS setups.
Nanoparticles have been widely used in vibrational spectroscopy techniques such
as Raman spectroscopy and Laser-induced Fluorescence (LIF) spectroscopy in order
to enhance the extremely weak signals and to improve the detection limits and sensitivity [32, 33]. Unlike the LIBS technique, these techniques are non-destructive
and employ low power lasers to avoid photothermal damage and structural modifications. Hence, the role and properties of nanoparticles in such conditions have
been investigated thoroughly for quite some time now. After decades of debate, it is
now almost accepted that the SERS enhancement is mainly due to the electromagnetic amplification that is generated by the excitation of localized surface plasmons
resonance (LSPR) [32].
However, in 2009, Ohta et al. provided the first insight of using metallic nanoparticles to enhance the LIBS intensity on plant leaves [34]. They have used metallic
colloidal nanoparticles of silver and gold on the leaf surface in order to monitor the
nutrients in plant leaves. By applying the NPs, the authors have succeeded in ablating
the raw leaf and producing the transient micro-plasma even at very low energy (<1