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

Abstract

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 ζ-potential determination were employed to monitor the protein coverage of NP surface in the conjugate solutions before the NELIBS measurements.

Nanoparticle-enhanced laser-induced breakdown spectroscopy for serum element analysis using an Ag NP-coated filter paper substrate

“…Further, the EF of K I 769.90 nm showed a maximum of 2.94 at 2.5 μL. The EF factors obtained in this work are similar to the recent results reported by Dell'Aglio et al , 39 who showed that the net NELIBS enhancement factor of titanium (Ti) targets containing a mixture of human serum albumin (HSA) and Au NPs was also about 3. This shows the advantage and application potential of NELIBS in element detection using minor sample volumes.…”

“…12,40,51,52 Meanwhile, the results also indicate that the plasma parameters are not strongly affected by the interaction between the Ag NPs and proteins, such as the protein corona, which has also been demonstrated in a study on protein corona and Au NPs. 39 Moreover, according to the simulation of the Cu I emission line by Soumyashree and Kumar, 53 when the electron density is in the order of 1 ×10 17 cm −3 and the electron temperature is within the range of 1-1.4 × 10 4 K, the EF would decrease with an increase in electron temperature, which also explains the downward trend of EF with decreasing Ag NPs concentration (with slightly increased T e ) in Fig. 8.…”

“…Moreover, the interaction of Ag NPs with many proteins in the serum may contribute to the EF changes with Ag NPs concentration because these interactions affect the coupling of the laser electromagnetic field and the plasma system. 39 The NPs in the serum are rapidly coated by proteins, forming a protein corona. 45 Therefore, the proteins act as a spacer and hinder the interaction between the electrolyte elements and Ag NPs; this can also explain the different EF trends for different elements.…”

“…12,40,51,52 Meanwhile, the results also indicate that the plasma parameters are not strongly affected by the interaction between the Ag NPs and proteins, such as the protein corona, which has also been demonstrated in a study on protein corona and Au NPs. 39…”