Optofluidic devices and applications

TL;DR: Optofluidic devices are most commonly fabricated using microfluidic technology into which photonic capability is embedded as discussed by the authors, which can be used for tunable optical devices, biophotonics, and more recently solar energy harvesting.

Abstract: Optofluidic devices are most commonly fabricated using microfluidic technology into which photonic capability is embedded. Lasers, microscopes, sensors, optical fibers, and lenses can be fabricated with this approach [1]. The application areas of optofluidics include tunable optical devices, biophotonics [2], and more recently solar energy harvesting [3].

Summary

1. Introduction

• Until now, to the best of their knowledge, the most common and reproducible methods of microscale manipulation have included mechanical and magnetic micro-manipulators [1,2] and various types of optical tweezers [3] including: holographic [4], plasmonic [5], antenna-based [6], and photonic crystal-based tweezers [7].
• The currents could be generated by heating with different wavelengths of light in the near IR spectrum shining on a variety of plasmonic structures and rough metal films [14,17–20].
• Also, they were done using light coupled through a microscope objective, which made the whole setup inflexible in terms of independent observation and manipulation.
• The authors substrate contains a continuous bi-metal layer , and this configuration has multiple advantages over traditional thermo-plasmonic structures.
• (c–h) Optical microscope images and corresponding three-dimensional models of the three regimes of opto-fluidic particle manipulation; (c,f) low power—no controllable particle movement; (d,g) medium power—trapping regime; (e,h) high power—levitation regime.

2. Optoelectrokinetics (OEK) Chips and Their Working Principles

• In their study, only a layer of a-Si:H was deposited, which was also classified into an a-Si:H based OEK chip.
• Specifically, if the value of the real part of the CM factor is higher than zero, a positive ODEP force will be generated and then the micro/nanoparticles will be attracted and moved to the illuminated area.
• Figure 2. Structure of P3HT/PCBM polymer-based OEK chip (reproduced from Ref. [47]).
• Another kind of OEK chip was devised based on TiOPc, an organic photosensitive material.

3.1. Separation and Assembly of Micro-Scaled Particles

• The OEK chip has been commonly used to perform manipulations such as separation, concentration and assembly on micro/nanoparticles, with the aid of an ODEP and/or ACEO mechanism.
• Manipulation and assembly of metallic microspheres into patterns were proposed [60].
• It has been further demonstrated that OEK can serve as a versatile and programmable microrobot to perform typical micromanipulations such as “load,” “transport,” and “deliver” [63].
• Figure 8G schematically presents the three-step process, which exhibited a higher moving velocity than when OEK was used alone.

3.2. Manipulation of Nano-Scaled Particles

• OEK has also been used to dynamically manipulate nano-scaled entities, including the separation of nanowires [64–67], the patterning of two-dimensional nanomaterials [68], and manipulation of nanoparticles [69–74].
• When the external voltage was higher than the “separation voltage,” i.e., the threshold one for moving the silicon nanowire, the silver nanowire could be separated from the silicon nanowire.
• First, a rapid and automatic assembly of 100 nm diameter gold nanoparticle (AuNP)-based microstructures was experimentally investigated [72].
• Using the triangle pattern as the virtual electrodes attracted most of the AuNPs into the locations of angular bisectors and formed a circle structure with three lines pointing toward the center of the triangle.
• Specifically, their resistance value could be controlled by the width and length of the microstructures: inversely increasing with the width and linearly increasing with the length .

4. Mask-Free Fabrication of Electrodes and Devices

• An optically-induced electrochemical reaction and deposition scheme was presented to enable dynamic, rapid and mask-free fabrication of microelectrodes [75–79].
• Then, the Au and Ag electrodes were rapidly fabricated onto the target MoS2 film.
• Then, the fabricated microstructures were transferred into an OEK chip for assembly, which was achieved by using microfluidic flow.
• Figure 16 illustrates the assembly of PEGDA-based microstructures with different sizes and shapes.
• Two alternating lines perpendicular to each other were designed to fabricate hydrogel microstructures, as shown in Figure 17a.

6. Conclusions and Prospects

• As discussed above, the OEK technique has been widely used by the microfluidic community to make a list of research achievements in terms of the manipulation and fabrication of micro/nanomaterials A lens-free holographic microscope was incorporated into the OEK chip to allow observing microparticles and cells in a large field of view [99].
• 16 Micromachines 2020, 11, 78 Finally, increased efforts are required to identify new possible applications of the OEK technique, which is the ultimate challenge and also the key to address the above two challenges.
• The authors declare no conflict of interest.

Figures

Table 1. Comparison of optofludic method with other DO detection techniques.

Figure 11. (a) Fabricated microelectrodes with respect to deposition time; scale bar: 10 μm. (b) Surface roughness of microelectrode by atomic force microscope (AFM) and SEM. (c) Thickness and (d) surface roughness of microelectrodes with respect to deposition time and solution concentration (reproduced from Ref. [75]).

Figure 10. Signal intensity traces in counts per 0.1 ms were collected for (a) unfocused operation over 150 s and (b) focused operation over 300 s. (c–f) Histogram distributions for signal intensity and fluid velocity show more consistent signal with three-dimensional hydrodynamic focusing (3DHDF).

Figure 11. (a) Fabricated microelectrodes with respect to deposition time; scale bar: 10 μm. (b) Surface roughness of microelectrode by atomic force microscope (AFM) and SEM. (c) Thickness and (d) surface roughness of microelectrodes with respect to deposition time and solution concentration (reproduced from Ref. [75]).

Figure 11. (a) Fabricated microelectrodes with respect to deposition time; scale bar: 10 μm. (b) Surface roughness of microelectrode by atomic force microscope (AFM) and SEM. (c) Thickness and (d) surface roughness of microelectrodes with respect to deposition time and solution concentration (reproduced from Ref. [75]).

Figure 12. Synthesis of various silver nanostructures by optically-projected patterns in OEK chip. (a) Silver crystal nanoparticles. (b) Stacked silver hexagonal nanoplates. (c) Crystallized silver octahedra and hexagonal silver nanoplates. (d) An array of silver nanoparticles-based micropillars (reproduced from Ref. [77]).

Figure 13. SEM images of MoS2 thin-film transistors fabricated with Au (a) and Ag (d) electrodes; (b,e) are the enlarged view of the rectangle areas in (a,d), respectively; (c,f) are the AFM characterization results of the heights of MoS2 thin-film transistors (reproduced from Ref. [78]).

Figure 14. SEM images of poly (ethylene glycol) (PEG)-diacrylate (PEGDA)-basedmicro/nanostructures fabricated using optically-projected spot patterns with different exposure times. The heights in (a–f) measured by AFM were 233 nm, 455 nm, 687 nm, 950 nm, 1.34 μm, and 1.62 μm, respectively (reproduced from Ref. [80]).

Figure 15. (a) PEGDA-based hydrogel tube with a length of ~20 μm, an outer diameter of ~10 μm, and an inner diameter of ~5 μm. (b) PEGDA-based hydrogel tube with a length of ~35 μm, an outer diameter of ~25 μm, and an inner diameter of ~20 μm (reproduced from Ref. [82]).

Table 1. Comparison of optofludic method with other DO detection techniques.

Figure 16. (A–G) Captured microscope image showing the dynamic process of assembling microstructures with different sizes and shapes; (H–L) the experimental process of assembling two different microstructures (reproduced from Ref. [83]).

Figure 17. (a) Projected patterns alternating at a time interval (Δt0); (b–d) are the optical microscope, SEM and AFM observation results, respectively; (e,f) are the optical microscope and SEM images of folded PEGDA hydrogel grids, respectively (reproduced from Ref. [84]).

Figure 10. Signal intensity traces in counts per 0.1 ms were collected for (a) unfocused operation over 150 s and (b) focused operation over 300 s. (c–f) Histogram distributions for signal intensity and fluid velocity show more consistent signal with three-dimensional hydrodynamic focusing (3DHDF).

Figure 10. Signal intensity traces in counts per 0.1 ms were collected for (a) unfocused operation over 150 s and (b) focused operation over 300 s. (c–f) Histogram distributions for signal intensity and fluid velocity show more consistent signal with three-dimensional hydrodynamic focusing (3DHDF).

Full text

Optofluidic
Devices and
Applications
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Francisco Yubero and Fernando Lahoz
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Optofluidic Devices and Applications • Francisco Yubero and Fernando Lahoz

Optofluidic Devices and Applications

Optofluidic Devices and Applications
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Francisco Yubero
Fernando Lahoz
MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade • Manchester • Tokyo • Cluj • Tianjin

Editors
Francisco Yubero
Instituto de Ciencia de Materiales de Sevilla (CSIC–Univ. Sevilla)
Spain
Fernando Lahoz
Universidad de La Laguna, Santa Cruz de Tenerife
Spain
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Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Optofluidic devices and applications optofluidic devices and applications" ?

In this paper, the authors summarize a variety of differently structured OEK chips, followed by a discussion on how they are fabricated and the ways in which they work. The authors also review how three differently sized polystyrene beads can be separated simultaneously, how a variety of nanoparticles can be assembled, and how micro/nanomaterials can be fabricated into functional devices. The authors provide a summary of the current challenges facing the OEK technique and its future prospects at the end of this paper.