Aqueous Dilution of Noble NPs Bulk Dispersions: Modeling Instability due to Dissolution by AF4 and Stablishing Considerations for Plasmonic Assays

Abstract

Among different nanomaterials, gold and silver nanoparticles (AuNPs and AgNPs) have become useful tools for a wide variety of applications in general, and particularly for plasmonic assays. Particle size and stability analysis are key elements for their practical applications since the NPs properties depend on these parameters. Hence, in the present work, asymmetrical flow field flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, has been evaluated for stability studies of citrate-capped AuNPs and AgNPs aqueous dispersions. First, experimental parameters, such as mobile phase or cross-flow rate were optimized. Sodium azide to pH 7 for AuNPs and pH 9.2 for AgNPs were selected as the optimum mobile phase. The analytical response of bulk dispersions of AuNPs (20, 40, 60 and 80 nm) and AgNPs (20, 40 and 60 nm) and their dilutions have been studied. Fractograms showed a decrease on the absorbance signal in diluted dispersions as a function of time and particle size for the diluted dispersions that can be explained by dissolution in diluted dispersion since hydrodynamic diameter was constant. The results indicated that the dependence of the signal with time was more intense for AgNPs than for AuNPs, which can be correlated with its lower stability. These findings should be considered when plasmonic assays are realized. Here, assays involving non-oxidant acidic acids as use cases, were tested for several batches of NPs and considerations about their stability and operability stablished.

Study of the Stability of Citrate Capped AgNPs in Several Environmental Water Matrices by Asymmetrical Flow Field Flow Fractionation

“…These changes depend on the kinetics of individual NPs subject to local variations and thereof, time is an important parameter. In order to prove this in [ 35 ], we measured citrate-capped Au and AgNPs diluted with ultrapure water (1/4) of different sizes at different times after their dilution (up to 72 h). Fractograms showed that there was a decrease in the absorbance signal with time due to dissolution of NPs, and that decrease depended on the type of NP and its size, being lower for Au and for 20 nm core size for both types of NPs.…”

“…Phenomena such as dissolution and/or passivation can be considered as a consequence of prolonged exposure to atmospheric conditions of the batch dispersion M1 [35,[38][39][40][41]. So that a part of AgNPs of the dispersion can be dissolved and released into the environment as Ag + , or it can be oxidized, generating an Ag 2 O surface film, which was indicated in other works by means of a bathochromic shift of the plasmonic band, as well as a broadening and a lower height (see Table 2 and Figure 2c).…”

“…In a previous paper [ 35 ], our group studied the dilution-induced variation with time (up to 72 h) of citrate capped AuNPs and AgNPs of several sizes with ultrapure water by AF4 coupled with UV-Vis and DLS detectors. Absorbance signal in diluted dispersions decreased as a function of time and particle size being dissolution the process due to hydrodynamic diameter was constant.…”

Characterization and Quantitation of Carbon Black Nanomaterials in Polymeric and Biological Aqueous Dispersants by Asymmetrical Flow Field Flow Fractionation

“…In this context, electrophoresis has been proposed for quantification studies on biological samples; however, size distribution is not defined. For this aim, asymmetrical flow field flow fractionation (AF4) has been demonstrated to be a powerful separation strategy in the characterization and/or determination of several (nano)­materials. , AF4 coupled to UV–vis and DLS detectors in series is a very useful technique for characterization of a wide range of particle dispersions allowing their separation and establishing their distribution and stability. , The AF4-UV–vis system was employed to analyze only the size of CB particles used in ink by dispersing CB powder in aqueous media containing polymeric dispersants . However, stability studies on different dispersant matrices have not been yet performed for CB.…”

“…34,35 AF4 coupled to UV−vis and DLS detectors in series is a very useful technique for characterization of a wide range of particle dispersions allowing their separation and establishing their distribution and stability. 36,37 The AF4-UV−vis system was employed to analyze only the size of CB particles used in ink by dispersing CB powder in aqueous media containing polymeric dispersants. 38 However, stability studies on different dispersant matrices have not been yet performed for CB.…”