INTRODUCTION: Nanoparticles exhibit significantly different physical and chemical properties compared to their bulk counterparts, due to the large surface area-to-volume ratio. In recent years, there has been a growing interest in using these nano-systems in various applications, such as biosensing, drug delivery, imaging, catalysis, and environmental and energy-based applications. Reverse micelle deposition (RMD) is a polymer templating method that uses di-block copolymers to produce highly uniform, well-dispersed nanoparticles with controlled size and spacing [1]. In RMD, an amphiphilic di-block copolymer, such as poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP), in a non-polar solvent, self-assembles into reverse micelle nanoreactors. Precursor salts can be added to the solution, diffusing into the polar core. When using RMD, the size of the nanoparticles is dependent on the amount of precursor salt added to the reverse micelle solution, referred to as the ‘loading ratio’ (LR), and defined as the ratio of the salt added with the number of P2VP units. One challenge when using RMD as a self-assembly technique is measuring the amount of added material that actually infiltrates into the micelles in relation to the loading ratio. METHODS: PeakForce Quantitative Nano-Mechanical mapping (QNM) is a high-resolution atomic force microscopy (AFM) technique that interprets data generated by PeakForce Tapping to extract quantitative material properties including the elastic modulus. By comparing the elastic modulus of micelles with varying loading ratios or stirring times, it is possible to gain insight into the internal structure of loaded reverse micelles [2]. Quartz Crystal Microbalance (QCM) is another highly sensitive analytical technique that is able to measure changes in mass on a crystal sensing surface. Shifts in the resonant frequency of the crystal can be detected and converted to the mass of the deposited material through the Sauerbrey equation, as they are directly proportional to each other. RESULTS: Gold nanoparticles (AuNPs) of various loading ratios were fabricated using PS-b-P2VP nanoreactors. The micelle topography and Young’s modulus map were obtained by drawing a line profile across each micelle, for samples. The line profile clearly illustrates the substantial difference in the stiffness of the silicon substrate and the polymeric micelles. Across the micelle, the stiffness seems to reach a minimum near the corona and a maximum in the core. After loading the precursor Au salt, the relative modulus of the micelle core (unloaded vs loaded) experienced an exponential trend and a plateau around LR 0.6, showing the upper limit of salt loading permissible by the polymer (Figure 1a). To evaluate the mass of material in the micelle solution in QCM, 2uL of AuNP solution was dispensed onto the Au sensor surface, which was assembled into the open QCM module. The AuNP solution was then allowed to evaporate by opening the module lid until dry and all signals stabilized. Figure 1d shows that a higher loading ratio of AuNP solution deposited onto the sensor surface resulted in a more significant frequency shift, indicating a larger mass of AuNPs. A similar exponential trend was obtained compared to micelle size and relative modulus, where the amount of infiltrated Au precursor reached a maximum at around LR 0.6. CONCLUSION: Understanding this upper limit is important when fabricating nanoparticles using RMD, as the use of excess salt does not help increase particle size but negatively affects the ordering of the nanoparticles. The infiltration of precursor salts can be quantified as a function of the loading ratio and stirring time through these two techniques, which allows better control of micelle stability and nanoparticle formation on the surface. The uniformity and high surface area will allow specific chemical conjugation and modifications for tailored functional properties and diverse applications ranging from biosensing to energy to photonics. [1] A. Turak, "Reverse micelles as a universal route to solution processed nanoparticles for optical, optoelectronic and photonic applications: A story of salt complexation, micellar stability, and nanoparticle spatial distribution," Vid. Proc. Adv. Mater, vol. 2, p. 2103166, 2021. [2] G. Hanta, "Nanomechanical Dependence of Micelles on Salt Loading Ratios: A Story of Salt Complexation, Micellar Stability, and Nanoparticle Spatial Distribution," 2019. Figure 1