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Review
. 2014 Sep 12:5:1523-41.
doi: 10.3762/bjnano.5.165. eCollection 2014.

Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays

Christoph Rehbock  1 , Jurij Jakobi  1 , Lisa Gamrad  1 , Selina van der Meer  1 , Daniela Tiedemann  2 , Ulrike Taylor  2 , Wilfried Kues  2 , Detlef Rath  2 , Stephan Barcikowski  1
Affiliations
Review

Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays

Christoph Rehbock et al. Beilstein J Nanotechnol. .

Abstract

Due to the abundance of nanomaterials in medical devices and everyday products, toxicological effects related to nanoparticles released from these materials, e.g., by mechanical wear, are a growing matter of concern. Unfortunately, appropriate nanoparticles required for systematic toxicological evaluation of these materials are still lacking. Here, the ubiquitous presence of surface ligands, remaining from chemical synthesis are a major drawback as these organic residues may cause cross-contaminations in toxicological studies. Nanoparticles synthesized by pulsed laser ablation in liquid are a promising alternative as this synthesis route provides totally ligand-free nanoparticles. The first part of this article reviews recent methods that allow the size control of laser-fabricated nanoparticles, focusing on laser post irradiation, delayed bioconjugation and in situ size quenching by low salinity electrolytes. Subsequent or parallel applications of these methods enable precise tuning of the particle diameters in a regime from 4-400 nm without utilization of any artificial surface ligands. The second paragraph of this article highlights the recent progress concerning the synthesis of composition controlled alloy nanoparticles by laser ablation in liquids. Here, binary and ternary alloy nanoparticles with totally homogeneous elemental distribution could be fabricated and the composition of these particles closely resembled bulk implant material. Finally, the model AuAg was used to systematically evaluate composition related toxicological effects of alloy nanoparticles. Here Ag(+) ion release is identified as the most probable mechanism of toxicity when recent toxicological studies with gametes, mammalian cells and bacteria are considered.

Keywords: albumin; gold-silver; implant alloy; laser ablation; nickel-titanium; size control; wear debris.

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Figures

Figure 1
Figure 1
Influence of laser pulse length on particle size distribution. A) Representative normalized weight frequency of nanoparticle diameter of gold nanoparticles obtained from PLAL in deionized water using picosecond (black curve) and nanosecond (red curve) pulses. B) Gold nanoparticles obtained from femtosecond laser ablation showing a bimodal particle size distribution. (Reprinted with permission from [50]. Copyright 2003 AIP Publishing ICC).
Figure 2
Figure 2
Size control of laser-fabricated nanoparticles by pulsed laser fragmentation in liquid (PLFL) tuning particles in a diameter range from 4–30 nm. A) Concept of PLFL. B) Size control by laser fluence in a size range from 2–15 nm (note that particle radius instead of diameter is plotted here) (Reproduced with permission from [68]. Copyright 2007 The Royal Society of Chemistry). C) Size control of gold nanoparticles by pressure (Reprinted with permission from [69]. Copyright 2013 American Chemical Society). D) Size control of Si nanoparticles by mass concentration during fragmentation of microcolloids. Reproduced with permission from [70]. Copyright 2013 The Royal Society of Chemistry).
Figure 3
Figure 3
Size tuning of gold nanoparticles by pulsed laser melting in liquids (PLML) controlling particle diameters in a range of 100–400 nm. A) Heating-melting-evaporation mechanism for the formation of SMS. Higher laser fluence induces formation of larger particles until fragmentation occurs when a certain threshold energy is reached (Reproduced with permission from [72]. Copyright 2013 John Wiley and Sons). B) Correlation between laser fluence and particle diameter including theoretical calculations of phase transitions [72] as well as experimental data for citrate capped nanoparticles [74] (Reproduced with permission from [72]. Copyright 2013 John Wiley and Sons). C) Totally ligand-free Au-SMS generated by laser post irradiation of aggregated particles including representative SEM image (left) as well as particle number distribution calculated from SEM images fitted with a log-normal function (right) [80].
Figure 4
Figure 4
Size control by delayed conjugation in liquid flow allowing size control from 15–45 nm. A) Concept of delayed bioconjugation in liquid-flow. B) Size control by delayed conjugation by variation of flow-rate (black curve) and position of biomolecule injection (red curve) (data adapted from [92]).
Figure 5
Figure 5
A) Size quenching effect of gold nanoparticles in the presence of different NaCl concentrations measured by analytical disk centrifugation as well as 2 representative size distributions and images from TEM (adapted from [81]). B) Proposed growth mechanism of laser-fabricated gold nanoparticles in the presence of electrolytes: Ions accumulate or adsorb on the surface of freshly formed primary nanoparticles stabilizing them electrostatically. At higher salinities growth is quenched at an early stage leading to smaller nanoparticles. At lower salinities, however, no sufficient stabilization is reached and particles growth continues and larger, polydisperse nanoparticles are found. (Reproduced with permission from [81]. Copyright 2013 The Royal Society of Chemistry).
Figure 6
Figure 6
Size quenching of AuAg alloy nanoparticles is impaired by surface oxidation. A) Influence of in situ addition of NaCl on the formation of AuAg alloy nanoparticles at variable GMF. B) Cartoon illustrating elevated surface oxidation of silver nanoparticles followed by accumulation of surface hydroxides, which electrostatically blocks further anion adsorption and hence prevents size quenching.
Figure 7
Figure 7
Size control for biocompatible gold nanoparticles by 4 different methods: I) Pulsed laser melting in liquid (PLML); II) Delayed conjugation; III) Size quenching by salts; IV) Pulsed laser fragmentation in liquid (PLFL).
Figure 8
Figure 8
Stabilization of gold nanoparticles in the presence of serum albumin. A) Colloidal stability of gold nanoparticles at varying albumin concentrations and different salinities of sodium phosphate buffer (NaPP). The boxes indicate the minimum stabilizing concentrations (Reproduced with permission from [81]. Copyright 2013 The Royal Society of Chemistry). B) Long-term stability of gold nanoparticles in serum-rich Androhep-medium for 28 days. (Reproduced with permission from [81]. Copyright 2013 The Royal Society of Chemistry).
Figure 9
Figure 9
A) Stoichiometry of NiTi nanoparticles. Left: TEM images of NiTi nanoparticles generated by femtosecond laser ablation in acetone (transferred into polymeric matrix and cut by an ultramicrotome). Right: electron energy loss spectroscopy mapping of NiTi nanoparticle with 60 nm diameter. Green spots mark coordinates of nickel, titanium is marked red (Reproduced from Figure 4 in [115] with kind permission. Copyright 2010 Springer Science and Buisiness Media). B) TEM-EDX-line scan of a representative NiTi nanoparticle, laser-fabricated in water, indicating a segregated Ni-TiOx core–shell structure as illustrated in the cartoon.
Figure 10
Figure 10
Nanoparticle fabrication from medically applied ternary stainless steel bulk material (material reference number 1.4404) yields particles with totally homogeneous elemental distribution. A) TEM size distribution of ternary steel alloy nanoparticles. B) Representative EDX line scan of a single steel nanoparticle revealing a totally homogeneous elemental distribution.
Figure 11
Figure 11
Precise tuning of particle composition in AuAg alloy nanoparticles. Top: Representative colloids of variable composition. Bottom left: Representative UV–vis spectra. The occurence of a single peak indicates alloy formation. The position of the SPR-peak red shifts with increasing portion of Au (GMF). Bottom right: SPR-peak position linearly shifts with increasing GMF. (Reproduced with permission from [35]. Copyright 2014 The Royal Society of Chemistry).
Figure 12
Figure 12
Laser-fabricated AuAg alloy nanoparticles possess a completely homogeneous elemental distribution. A) Representative TEM image acquired at GMF = 0.5. B) Particle size distribution of AuAg alloy nanoparticles at GMF = 0.5. C) EDX line scan at GMF = 0.8 indicating totally homogenous elemental distribution on a single particle level.
Figure 13
Figure 13
Bio-response of AuAg alloy nanoparticles is non-linearly correlated with the particle composition. A) Influence of AuAg alloy nanoparticles on oocyte maturation indicating a significant decrease at GMF = 0.2. (Reproduced with permission from [35]. Copyright 2014 The Royal Society of Chemistry). B) Inhibitory and toxic concentrations of AuAg alloy nanoparticle on viability of human gingival fibroblasts for varying silver molar fraction (adapted from [148]).
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