# A Review on Optoelectrokinetics-Based Manipulation and Fabrication of Micro/Nanomaterials
## 1 Introduction  
Accurate manipulation and fabrication of micro/nanomaterials in liquid is fundamental for a range of applications such as micro/nanoelectronics [1, 2], biosensors [3, 4], biomedicine [5, 6], biosensing [7, 8] and energy harvesting [9, 10]. Various attempts have been made to make that happen. For example, silver nanoparticles were integrated into the luminol system to enable more efficient electrochemiluminescence and thereby allow for ultrasensitive detection of cardiac troponin [11]. Combining graphene and traditional integrated circuits, a high-mobility, high-resolution, and broadband image digital sensor was developed to capture ultraviolet, visible, and infrared light [12]. Gold nanoparticles were assembled into micro/nanowires to fabricate a flexible pressure sensor that offers a detection limit up to 25 Pa [13]. This sensor is also sensitive to pulses in different regions of the human body, offering an approach to facilitating the development of wearable devices. To address real-world needs for manipulation and fabrication of micro/nanomaterials, a number of micro-/nano-scaled methods have been presented. Typical examples include microfluidic [14, 15],acoustic [16; 17], electrokinetics [18; 19], magnetic [20; 21], optical [22; 23], thermal [24; 25], and atomic force microscope [26; 27] approaches. An emerging topic on the manipulation and fabrication of micro/nanoparticles is about how to develop a novel mechanism that can complement what a single technique can offer. The long-term aim is to create valuable techniques that can help extend the applicability of micro/nanomaterials. Combining acoustic and magnetic fields, an approach that can aggregate nanoparticles in the presence of a magnetic field and move them towards the wall of a microchannel under the action of an external acoustic wave was proposed [28]. This approach bears significant potential for application in target drug delivery and biomedical surgery. There is also a technique called the acoustofluidic tweezers, which integrates acoustic waves into a microfluidic system and offers a label-free and high-throughput way to isolate 110-nm particles from a mixture of micro/nanoparticles with a purity as high as 99% [29]. By incorporating white light source from light-emitting diode into a microfluidic system, the absorbance of micro/nanoparticles at different diameters as well as the bit error rate can be determined, which allows easy and rapid measurement of micro/nanoparticle concentration [30]. In addition, a hybrid isomotive dielectrophoresis (DEP)-microfluidic technique was proposed for label-free separation of same-/differently-sized micro/nanoparticles based on their crossover-frequency features [31]. This technique also enables reliable and repeatable separation and dynamically adjusting the purity and yield of separated beads. A new hybrid and novel manipulation technique called optically-induced dielectrophoresis (ODEP) or optoelectronics (OEK) was proposed for programmable, contact-free, flexible, automatic, dynamic, and rapid manipulation of micro/nano-entities [32]. OEK has attracted much attention in micro/nanomanipulation fields since it was invented in 2005. This technique combines the merits of optical, electrokinetics, and microfluidic schemes, offering a more versatile approach to micro-/nano-scaled manipulation and fabrication over other competing lab-on-a-chip techniques. Optically-projected images are custom-designed on a computer using graphic animation software. These images are then transmitted by a commercial projector and focused onto the surface of the OEK chip, thereby triggering the photosensitive material and changing the distribution of the external AC bias potential. Most of the AC bias potential will shift to the liquid layer, which generates a non-uniform electric field around the illuminated area. Meanwhile, various electrokinetics forces are produced.