Effect of the Surface Chemical Composition and of Added Metal Cation Concentration on the Stability of Metal Nanoparticles Synthesized by Pulsed Laser Ablation in Water

Metal nanoparticles (NPs) made of gold, silver, and platinum have been synthesized by means of pulsed laser ablation in liquid aqueous solution. Independently from the metal nature, all NPs have an average diameter of 10 ± 5 nm. The ζ-potential values are: −62 ± 7 mV for gold, −44 ± 2 mV for silver and −58 ± 3 for platinum. XPS analysis demonstrates the absence of metal oxides in the case of gold and silver NPs. In the case of platinum NPs, 22% of the particle surface is ascribed to platinum oxidized species. This points to a marginal role of the metal oxides in building the negative charge that stabilizes these colloidal suspensions. The investigation of the colloidal stability of gold NPs in the presence of metal cations shows these NPs can be destabilized by trace amounts of selected metal ions. The case of Ag+ is paradigmatic since it is able to reduce the NP ζ-potential and to induce coagulation at concentrations as low as 3 μM, while in the case of K+ the critical coagulation concentration is around 8 mM. It is proposed that such a huge difference in destabilization power between monovalent cations can be accounted for by the difference in the reduction potential

Editorial, LIBS 2022

Held in Bari (Italy) from September 5 through 9, 2022, LIBS 2022 was the twelfth international LIBS conference, and the first that took place in hybrid in-person/online mode after the SARS-CoV-2 pandemic forced the 2020 edition in 100% online mode. The conference was organized by the LIBS group of Bari (Italy), with Alessandro De Giacomo (University of Bari), Vincenzo Palleschi (CNR – ICCOM- Pisa) and Roberta Fantoni (ENEA-Rome) acting as General Chairs, supported by Program Chairs Marcella Dell’Aglio (CNR – NANOTEC-Bari), Antonio Santagata (CNR – ISM -Tito Scalo), Stefano Legnaioli (CNR – ICCOM- Pisa), and Violeta Lazic (ENEA- Rome)

Nanoparticle Enhanced Laser Induced Breakdown Spectroscopy (NELIBS), a first review

In this paper, the promising variant of the Laser Induced Breakdown Spectroscopy (LIBS) technique, namely Nanoparticle - Enhanced LIBS (NELIBS) is described. The underlying mechanisms responsible for NELIBS are described. This is done by presenting both the properties of metallic particles interacting with high-energy laser radiation and the mechanisms of laser ablation enabled by the presence of nanoparticles. Clarifications are also made about the sample preparation for NELIBS in particular about how to reach the optimal surface concentration of nanoparticles. NELIBS applications on different kinds of samples are also described such as metals, transparent samples, fresh samples and liquids including biological fluids

Plasma Parameters During Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy (NELIBS) in the Presence of Nanoparticle-Protein Conjugates

Nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) is an optical emission technique based on the laser-induced plasma (LIP) on a sample after the deposition of plasmonic nanoparticles (NPs) on its surface. The employment of the NPs allows an enhancement of the signal with respect to the one obtained with the conventional laser-induced breakdown spectroscopy (LIBS) enabling an extremely high sensitivity and very low limits of detection compared with the LIBS performance. Recently, NELIBS was used for monitoring the NP protein corona formation. As a matter of fact, the NPs in the presence of proteins adsorbed on the surface change their surface properties, therefore the sensing of protein corona formation was possible because of the strong dependence of NELIBS effects on the NP organization on the substrate, which in turn is deeply affected by the surface properties of the NPs. A correlation was found between NELIBS enhancement and the structure of the NP-protein conjugate in terms of protein content absorbed on the NP surface. An interesting question that was not yet exploited regards the role of LIP during the NELIBS when the NPs are covered with proteins. Since the presence of organic matter can strongly quench the LIP emission, the study of the LIP properties during protein corona sensing by NELIBS is of interest for two main reasons: (i) to understand whether the plasma parameters can vary in the presence of proteins adsorbed on the NP surface and (ii) to investigate how and if the plasma parameters themselves can influence the NELIBS processes. With this aim, the study of plasma parameters, i.e., electron densities and temperatures, during the sensing of NP protein corona by NELIBS is presented and discussed. The NPs used during these experiments were ultrapure gold NPs (AuNPs) produced by pulsed laser ablation in liquid, which are stable without any stabilizer. The human serum albumin protein is used to form AuNP-protein conjugates further deposited on a titanium target in NELIBS measurements. Dynamic light scattering, surface plasmon resonance spectroscopy, and laser Doppler electrophoresis for zeta-potential determination were employed to monitor the protein coverage of NP surface in the conjugate solutions before the NELIBS measurements

On the stability of gold nanoparticles synthesized by laser ablation in liquids

“Naked” gold nanoparticles (AuNPs), synthesized in the absence of any capping agents, prepared by pulsed laser ablation in liquid (PLAL) are stabilized by negative charges. Common explanations for this phenomenon involve the presence of gold oxides and/or the anion adsorption. We have found that AuNP ablated in solutions of acids with very different oxidation power, viz. HCl, H2SO4, HNO3 share the same size and ζ-potential. Although, gold oxides have pKas ≈ 4, the ζ-potential of AuNPs ablated in solutions with pH ⩽ 4 is always negative. These evidences suggest that the gold oxidation and anion adsorptions have only a minor role on building the negative surface potential and we hypothesize, for the first time, that excess electrons formed within the plasma phase could charge the metallic particles. In our model, a crucial point is that the colloidal size of the NP maintains the energy of the electrons small enough to preclude chemical reactions but with a surface potential yet large enough to stabilize the AuNPs with respect to aggregation. A confirmation of the hypothesis of “electron-stabilized nanoparticles” is that either the addition of macroscopic metallic objects either the contact with a “grounded” copper wire induce the loss of charge and AuNPs aggregation

Study of the Effect of Water Pressure on Plasma and Cavitation Bubble Induced by Pulsed Laser Ablation in Liquid of Silver and Missed Variations of Observable Nanoparticle Features

In this work the effects of the pressure between 1–150 Bar on pulsed laser ablation in liquids (PLAL) during the production of silver nanoparticles (AgNPs) in water was investigated. The produced NPs are the results of two different well-known stages which are the plasma and the bubble evolution occurring until the generated material is released into the solution. The main aim of this work is to show which roles is played by the variation of water pressure on the laser induced plasma and the cavitation bubble dynamics during the NPs formation. Their implication on the comprehension of the as-produced NPs formation mechanisms is treated. The typical timescales of the different stages occurring in water at different pressures have been studied by optical emission spectroscopy (OES), imaging and shadowgraph experiments. Finally surface plasmon resonance (SPR) spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and scanning electron microscopy (SEM) for characterization of the material released in solution, have been used

Fundamental study and analytical applications of nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) of metals, semiconductors and insulators

Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy (NELIBS) is a recently proposed method to efficiently increase the LIBS emission signal of metals up to 2 orders of magnitude, by depositing metal nanoparticles (NPs) on the sample surface (De Giacomo A, Gaudiuso R, Koral C, Dell’Aglio M, De Pascale O Anal Chem 85). This considerable emission enhancement has been ascribed to two effects: (1) an improvement in the ablation effect, and (2) a more efficient production of seed electrons by field emission, in turn due to the enhancement of the laser electromagnetic field induced by the NPs themselves (De Giacomo A, Gaudiuso R, Koral C, Dell’Aglio M, De Pascale O Acta Part B, 98)

Pulsed laser ablation of wire-shaped target in a thin water jet: Effects of plasma features and bubble dynamics on the PLAL process

In this paper, emission spectroscopy and fast imaging surveys during pulsed laser ablation in liquid (PLAL) for nanoparticles (NPs) production have been used, in order to provide further details about the process involved and the potentialities offered by a wire-shaped sample ablated in a flowing water jet. This kind of set-up has been explored because the laser ablation efficiency in water increases when a thin water layer and a wire-shaped target are used. In order to understand the physical processes causing the increasing ablation efficiency, both the laser-induced plasma and bubble dynamics generated in a flowing liquid jet have been analysed. The plasma parameters and the bubble behaviour in such a system have been compared with those observed in conventional PLAL experiments, where either a bulk or a wire-shaped target is immersed in bulk water. From the data presented here it is evidenced that the plasma and shockwave induced during the breakdown process can play a direct role in the ablation efficiency variation observed. With regard to the cavitation bubbles evolving near a free surface (the interface between water and air) it should be noted that these have to be treated with caution as a consequence of the strong influence played in these circumstances by the boundary of the water jet during its expansion dynamics. The effects due to the size of the liquid layer, the presence of the water/air interface, the liquid characteristics, the target shape, the plasma evolution and the bubble dynamics together with their outcomes on the NPs' production, are presented and discussed