# Recent Advances in Research from Nanoparticle to Nano-Assembly: A Review
## 3 Stimuli Dependent Techniques
### Physical Stimuli-Based Self-Assembly of Nanomaterials
#### 3.2.3 Electric Field-Induced Self-Assembly  
Electrical field-induced SA refers to the organization of NPs into ordered structures under the influence of an applied electric field. This SA technique on electric field-induced SA was less explored when compared with others because of their complexity of field design, scalability, and material constraints. The NPs should possess better dielectric properties to respond to the electric field. Here, the particles are trapped at the liquid-liquid interface under the influence of the electric field due to the capillary and electrostatic interactions [86]. Generally, uncharged particles agglomerate at the liquid interface to minimize its surface tension, but charged particles repel each other at the interface due to electrostatic interactions. Therefore, two immiscible liquid systems solve this problem where the liquid-liquid interface acts as an ion permeable under an applied electric field [87]. Dielectrophoresis, electrophoresis, and electrostatic interactions are the three main pathways to obtain the ordered self-assembled particles. In the context of dielectrophoresis, a non-uniform electric field was used to control or manipulate the SA of particles into ordered structures. Depending on the variation in polarizability of particles and the surrounding medium, particles experience the positive or negative dielectrophoresis [107]. In detail, when a dielectric particle is placed under a non-uniform electric field, a dipole experiences unbalanced forces, causing particles to move either closer to or further away from the high electric field intensity. The SA of NPs in dielectrophoresis can be manipulated particularly by altering the electric field intensity, field distribution over NPs, size and shape of the particle, and polarizability of the medium [108]. The dielectrophoresis technique is not only useful for the non-contact manipulation and control of SA nanostructures, it can also be useful in the control and transport of micro-particles [109]. Non-contact separation makes dielectrophoresis advantageous in various fields such as microfluidics and biomedicine. In dielectrophoresis, the force extends for longer distances to trap the particle. However, due to a large area distribution of the electric field, the particle moves freely in the trap. Hence, the requirement of precise trapping for small-sized particles makes the dielectrophoresis technique less suitable for applications where accuracy is crucial. Therefore, developing and integrating a system which has both long-range forces to trap longer-distance particles and high-resolution systems that confine or hold the particle movement would be extremely valuable. In 2017, [PERSON] and co-workers demonstrated a method to trap NPs efficiently in small areas using a hybrid method. C-shaped engraving was used to create a small area to trap the particle and nanopillars were used to create dielectrophoresis forces, and it was confirmed that the probability trapping is better when compared to the conventional method. Apart from this, optoelectronic tweezers are one of the other proven versatile integrated tools in the manipulation and control of massive micro/nano SA structures that can be used in multiple applications [110; 111]. These optoelectronic tweezers were developed to overcome challenges that limit conventional optical tweezers and dielectrophoresis. Optoelectronic tweezers utilize illuminated light to induce the electric field on photoconductive surfaces. Light-induced changes on the localized conductance exerts gradient electric field forces on particles in the medium [112]. Optoelectronic tweezers require low optical power when compared to conventional optical tweezers as light does not directly exert the gradient force for SA of NPs. A wide range of nanostructures can be created on the photo-conducting surfaces by altering the optical excitation profile.