Fluorescent carbon and graphene oxide nanoparticles synthesized by the laser ablation in liquid
Applied Physics A
Fluorescent carbon and graphene oxide nanoparticles synthesized by the laser ablation in liquid
A. Małolepszy 0 1 2
S. Błonski 0 1 2
J. Chrzanowska‑Giżyńska 0 1 2
M. Wojasiński 0 1 2
T. Płocinski 0 1 2
L. Stobinski 0 1 2
Z. Szymanski 0 1 2
0 Faculty of Materials Science and Engineering, Warsaw University of Technology , Wołoska 141, 02-507 Warsaw , Poland
1 Institute of Fundamental Technological Research, Polish Academy of Sciences , Pawinskiego 5B, 02-106 Warsaw , Poland
2 Faculty of Chemical and Process Engineering, Warsaw University of Technology , Warynskiego 1, 00-645 Warsaw , Poland
3 Z. Szymanski
The results of synthesis of the fluorescent carbon dots (CDots) from graphite target and reduced graphene oxide (rGO) nanoparticles performed by the nanosecond laser ablation in polyethylene glycol 200 (PEG200) are shown. Two-step laser irradiation (first graphite target, next achieved suspension) revealed a very effective production of CDots. However, the ablation in PEG appeared to be effective with 1064 nm laser pulse in contrast to the ablation with 355 nm laser pulse. In the case of rGO nanoparticles similar laser irradiation procedure was less efficient. In both cases, received nanoparticles exhibited strong, broadband photoluminescence with a maximum dependent on the excitation wavelength. The size distribution for obtained CDots was evaluated using the DLS technique and HRTEM images. The results from both methods show quite good agreement in nanoparticle size estimation although the DLS method slightly overestimates nanoparticle's diameter.
1 Introduction
Pulsed laser ablation in liquid (PLAL) is a widely
recognized method of synthesizing contamination-free
nanostructures especially nanoparticles [
1, 2
] among them fluorescent
carbon nanoparticles (FCNPs) [3], carbon polyynes [
4
], etc.
Most of the attention is given to fluorescent nanoparticles,
especially with diameters of 2–8 nm called carbon dots,
which are widely used for purposes of fluorescent imaging,
mainly of cells and tissues [
5, 6
]. Their most remarkable
property is the excitation-dependent fluorescence emission.
The laser synthesis of fluorescent carbon nanoparticles was
performed in several liquids such as deionized water [7],
isopropyl alcohol (IPA), acetone [
8
], polyethylene glycol
(PEG) [
5
], ethylenediamine (EDA) and ionic liquids [
9
]. In
the case of water, the fluorescent carbon dots are obtained
only after further functionalization, either with the use of
UV radiation [
7
] or by attaching simple organic species to
the acid-treated carbon particles [
5
].
A comprehensive review of laser synthesis of
nanoparticles in liquids has previously been presented [
2
].
Nanoparticles (NPs) approved in preclinical studies for
both imaging and therapy often include polyethylene
glycol. Attachment of PEG (PEGylation) improves the
bioavailability, safety and prolongs circulation time in the blood of
therapeutic agents [
10
]. Since NPs permeate through the
leaky tumor vasculature to a higher degree than through the
healthy tissue and remain in the area, they can be used for
signaling or therapy [
11
] and, therefore, PEG is
increasingly used to improve the properties of nanoparticles used
as therapeutic or diagnostic agents in biomedicine.
In addition, nanoparticles suspended in other liquids had
the tendency to agglomeration. Nanoparticles aggregate
when the attraction between particles is stronger than the
attraction with solvent particles. PEG decreases the surface
energy of NPs and minimizes van der Waals attraction [
10
].
In addition, PEG is a very effective passivation agent and
surface functionalization (passivation) of carbon
nanoparticles is necessary to make them fluorescent. Although the
origin of fluorescence from carbon nanoparticles is still
not completely clear the fluorescence properties of carbon
dots are associated with the particles’ surface, specifically
“surface defects” responsible for light absorbance. The
photoluminescence originates from the surface functional
groups attached to carbon nanodots and functionalization
with hydrocarbon chains such as in PEG is very effective [
5
].
However, the experiments with laser synthesis in PEG
are rather scarce [
3, 5, 12, 13
] and most of them were made
in graphite powder [
3, 12, 13
]. For carbon dots produced
by laser ablation of a carbon target in the presence of water
vapor photoluminescence was achieved only after dots’
surface passivation [5]. In this paper, the results of the synthesis
of the fluorescent carbon dots (CDots) from solid carbon
target and reduced graphene oxide (rGO) nanoparticles
performed by the laser ablation in PEG200 are presented.
2 Synthesis
Graphite target irradiation was performed in a quartz beaker
with diameter 40 mm using an Nd:YAG laser (Quantel, 981
E). The laser operated at a wavelength of 1064 and 355 nm
with a 10 ns pulse duration and repetition rate of 10 Hz. The
thickness of (...truncated)