AFM images were acquired in tapping mode by Multimode Nanoscope III system (Bruker, Santa Barbara, CA) and MFP-3D AFM (Asylum Research, CA) using TESPA and MSNL (Bruker, CA) probes in air and in buffer medium respectively. The nominal spring constant for TESPA and MSNL probes were ~42 N/m and ~0.1 N/m, respectively. AFM topographic images were analyzed using Femtoscan Online software (Advanced Technologies Center, Moscow, Russia). The volume of the aggregates was obtained from the ‘Enum feature’ and ‘grain analysis’ tool in the software. The data obtained have been plotted in Origin software (OriginPro 2016) to generate the histograms and then they were fitted with Gaussian distribution to measure the mean value and errors38.