# Recent Advances in Research from Nanoparticle to Nano-Assembly: A Review
## 3 Stimuli Dependent Techniques
### Chemical Stimuli-Based Self-Assembly of Nanomaterials
#### 3.1.2 Acid-Base-Induced Self-Assembly  
Stabilization of colloidal NPs purely relies on the surfactant molecules where they covalently or coordinately bonded to the NPs surface atoms. The terminal groups of ligands dictate the possible interaction depending on their charges. Electrostatic repulsions between the highly negatively charged surfaces or highly positive surfaces of NPs are responsible for the stability of NPs in an aqueous medium. Thus, modifying the solution pH, the protonation/deprotonation of pH-responsive terminal groups of ligands initiate the aggregation of NPs. Recently, [PERSON] and co-workers developed a caterpillar-shaped controlled SA of triblock glycopomers with the assistance of a pH-responsive poly(4-vinyl pyridine) (P4 VP) core [65]. In the first step, a hydrophobic PBuA-P4 VP core triblock terpolymer system with hydrophilic glycopolymer block spherical core/shell micelles were formed in water. While changing the pH, P4 VP triggered the hierarchical SA of terpolymer via the aggregation of micelles instead of collapsing the P4 VP block through ionization and deprotonation processes. TEM images of the respective changes with respect to pH are shown in Figure 3A. Generally, this approach is regulated by supplying the promoter or deactivator in the form of an acid or base with respect to the pH-responsive ligand. In  
Figure 2: (**A**) Solvent-assisted self-assembly of Cu NCs with improved quantum yield due to their aggregation with the addition of anti-solvent glycerol to the Cu NCs in DMSO solution, (**i**) overall schematic followed in this approach, (**ii**) TEM image of self-assembled Cu NCs, (**iii**) and the change in their fluorescent spectra of NCs before and after self-assembly. These images were cited and reproduced from the reference [57]. (**B**) Organization of Au nanorods having distinct ligands on the long and short ends and their self-assembly of (**i**) side-by-side and (**ii**) end-to-end patterns when exposed to stimuli in the form of anti-solvent. These images were cited and reproduced from the reference [61]. (**C**) Self-assembly of block co-polymer-stabilized Au NPs in the form of vesicular structures via emulsification in chloroform and dodecyl sulphate solution. These images were cited and reproduced from the reference [63]. (**D**) Promoter- or modifier-assisted self-assembly in oil-water interface, (**i**) TEM image of the metal liquid-like layer NPs assembly, (**ii**) and optical spectra for the obtained self-assembly. These images were cited and reproduced from the reference [64].  
another example [66], [PERSON] and co-workers studied the assembly and disassembly of citrate-capped Au NPs in the presence of 3-aminopropyltriethoxysilane (APTES) with the addition of NaOH and HCl as a promoter and deactivator. In the presence of APTES, Au NPs self-assembled with a visible color change from wine red to purple as shown in the Figure 3B (down right (ii)) digital image. Self-assembled Au NPs undergo disassembly in the presence of supplement base (NaOH), likely due to the deprotonation of amino acids in (3-Aminopropyl)triethoxysilane (APTES) causes visible color change from purple to red. In contrast, acid treatment protonated the amino acids and retained the SA of these Au NPs. The respective TEM images are shown in Figure 3B (down (i-iv).