Nanoscale Characterization of Gold Colloid Monolayers:  A Comparison of Four Techniques

Abstract

Atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and near-field scanning optical microscopy (NSOM) have been used to characterize the nanostructure of Au colloid-based surfaces. Because these substrates are composed of particles whose dimensions are known prior to assembly, they are well-suited for a critical comparison of the capabilities and limitations of each nanoscale imaging technique. The three criteria for this comparison, which are relevant to the field of nanoparticle assemblies in general, are (i) accuracy in establishing particle size, particle coverage, and interparticle spacing; (ii) accuracy in delineating surface topography; and (iii) ease of sample preparation, data acquisition, and image analysis. For colloidal Au arrays, TEM gives the most reliable size and spacing information but exhibits the greatest constraints with regard to sample preparation; in contrast, AFM is widely applicable but yields data that are the least straightforward to interpret. For accurate information regarding nanometer-scale architecture of particle-based surfaces, a combination of at least one scanning probe method (AFM, NSOM) and one accelerated-electron method (TEM, FE-SEM) is required.

Gold Nanoparticle Monolayer Formation on a Chemically Modified Glass Surface

“…The Au nanoparticles synthesized using citrate-reduction method are negatively charged: they are adsorptive to a positively charged aminemodified surface. [16][17][18] Keating et al analyzed an adsorption isotherm of 12-nm-diameter Au nanoparticles on an APTMSderivatized glass surface, as examined using UV/vis spectrophotometry. 18 Although values a were smaller because of the larger nanoparticles and the fact that K was larger than that in their study, we found that the respective signs of g¢ were opposite for 12-nm and 30-nm nanoparticles.…”

“…5,[11][12][13] On the other hand, several research groups have revealed that Au nanoparticles synthesized using a citrate-reduction method are strongly adsorbed onto a glass surface coated with bifunctional-organosilanes. [14][15][16][17][18] Their approach was later applied for fabricating an Au-nanoparticle-monolayer-based LSPR optical sensor for use in biomolecule interaction measurements. Several groups have reported the potential use of such nanoparticles for molecular interaction analyses of Au nanoparticle monolayers on a glass substrate surface.…”

“…One report described that the aggregation of nanoparticles spoils the utility of a LSPR sensor for biosensing; a 39 nm Au nanoparticle exhibited the highest sensing ability. 19 Typically, nanoparticles smaller than 20 nm were used in prior studies for monolayer or multilayer formation of Au nanoparticles; [15][16][17][18][23][24][25][26] physicochemical properties different according to the nanoparticle size. 27 Selfassembling characteristics of nanoparticles larger than 20 nm on surfaces and interfaces are not fully understood.…”

Atomic Force Microscopy and Magnetic Force Microscopy Study of Model Colloids

“…[2]), a value of 150 nm is obtained for particle lateral diameter (corresponding to the radius r c in Eq. [2]). A mean value of 17…”

“…Previous studies using AFM on colloidal particles imaged mainly gold particles for comparison with other imaging techniques (2) or for applications as tip characterizers and calibrating samples as well as for characterization of coadsorbed biomolecules (3). Recently, images of silica and polystereneencapsulated silica particles were presented (4) to confirm the synthesis outcome.…”