Universal Determination of Gold Concentration in Colloids with UV–vis Spectroscopy

Abstract

Extinction at 400 nm is a convenient, cheap, and fast method for in situ determination of Au concentration in colloids with good accuracy even in the presence of Au(+3) ions and other interference factors. However, these possibilities have been validated only with common citrate gold nanospheres and, in part, with gold nanorods. Here, we demonstrate the universality of the UV−vis extinction method with six experimental and theoretical models: (1) CTAC-stabilized gold nanospheres; (2) small and large nanosphere clusters; (3) gold nanorods with plasmon resonances (PRs) ranging from 670 to 980 nm; (4) 2D nanotriangles and (5) 2D nanoplates with PRs from 600 to 775 nm; and (6) gold nanostars with PRs from 680 to 820 nm. In total, we fabricated 34 samples with different nanoparticle sizes, shapes, morphologies, and Au concentrations. From COMSOL, T-matrix, and generalized multiparticle Mie simulations, we derived a universal relation between the extinction cross section and the particle or cluster volume V: C ext (nm 2 ) = 0.51 × V (nm 3 ), 10 2 ≤ V (nm 3 ) ≤ 10 5 , which gives a universal relation between the gold concentration and extinction [Au 0 ] (mM) = 0.44 × A 400 . The same relation is derived from atomic absorption spectroscopy and inductively coupled plasma mass spectroscopy experimental determination of [Au 0 ] concentration correlated with A 400 . While the universality of the derived equation is demonstrated by an unprecedented set of gold nanoparticle sizes, shapes, morphologies, and particle clusters, its accuracy can be limited by 20−30%. This uncertainty results from the light scattering contribution that violates the proportionality between the extinction cross section and the particle or cluster volume. However, for a particular colloidal system, the application of the derived relation can be useful in monitoring reduction or aggregation processes.

Efficient quenching sheds light on early stages of gold nanoparticle formation

“…The extinction at 400 nm E400 is directly proportional to the concentration of Au NPs and therefore allows to track the overall conversion of the Au salt to Au NPs quantitatively. 54,55 According to Fig. S5 in the ESI,† E400 almost reaches its final value at a quenching time of 2 s, which is in line with the transition from rapid to slow Au NP growth.…”

Anisotropic Gold Nanomaterial Synthesis Using Peptide Facet Specificity and Timed Intervention

“…Increased optical absorption at higher wavelengths which then decreases in intensity has been linked to the particle clusters and A,B) correspond to changes in optical extinction at λ = 400 and 1000 nm, respectively, for samples prepared with Z2 being added after different times or without Z2. Optical extinction at 400 nm is associated with the overall Au(0) concentration, 40,47 and optical extinction at 1000 nm is consistent with the presence of plate-like particles. 3,8,42 formation of nuclei near the surface of existing particles, i.e., secondary nucleation.…”

“…(A,B) correspond to changes in optical extinction at λ = 400 and 1000 nm, respectively, for samples prepared with Z2 being added after different times or without Z2. Optical extinction at 400 nm is associated with the overall Au(0) concentration, , and optical extinction at 1000 nm is consistent with the presence of plate-like particles. ,, …”

Stable Photopolymerizable Resins Modified with Functionalized Silica-Coated Gold Nanostructures for the Fabrication of Optically Clear 3D Objects with Remote Photothermal Activation

“…After this time, a heat treatment was performed consisting of stirring the reaction mixture in a water bath at 60 °C for 1 h. The resulting Au@SiO 2 NPs suspension was split into two fractions. To one of them, the necessary amount of ethanol was added to obtain a stock solution of Au@SiO 2 NPs with an Au 0 concentration of 1.04 mM (based on the absorbance value at 400 nm of its extinction spectrum). , The second fraction was used for surface functionalization with methacrylate groups (MA) as described below.…”

“…To one of them, the necessary amount of ethanol was added to obtain a stock solution of Au@SiO 2 NPs with an Au 0 concentration of 1.04 mM (based on the absorbance value at 400 nm of its extinction spectrum). 33,34 The second fraction was used for surface functionalization with methacrylate groups (MA) as described below.…”