Optical Microfluidic System Research Articles

Flow mechanism of Gaussian light-induced vortex motion inside a nanofluid droplet

PurposeThe purpose of this study is to use a weak light source with spatial distribution to realize light-driven fluid by adding high-absorbing nanoparticles to the droplets, thereby replacing a highly focused strong linear light source acting on pure droplets.Design/methodology/approachFirst, Fe3O4 nanoparticles with high light response characteristics were added to the droplets to prepare nanofluid droplets, and through the Gaussian light-driven flow experiment, the Marangoni effect inside a nanofluid droplet was studied, which can produce the surface tension gradient on the air/liquid interface and induce the vortex motion inside a droplet. Then, the numerical simulation method of multiphysics field coupling was used to study the effects of droplet height and Gaussian light distribution on the flow characteristics inside a droplet.FindingsNanoparticles can significantly enhance the light absorption, so that the Gaussian light is enough to drive the flow, and the formation of vortex can be regulated by light distribution. The multiphysics field coupling model can accurately describe this problem.Originality/valueThis study is helpful to understand the flow behavior and heat transfer phenomenon in optical microfluidic systems, and provides a feasible way to construct the rapid flow inside a tiny droplet by light.

Experiments and analytical solutions of light driven flow in nanofluid droplets

Adding nanoparticles with high light response characteristics to a light-transmitting fluid medium can form a light-driven nanofluid and achieve efficient use of light energy. This paper conducts the experimental observation and theoretical analysis of the light driven nanofluid flow behavior, which is the theoretical basis for achieving the precise control of optical drive nanofluid. To realize the efficient conversion of light energy into kinetic energy, here, the motion of Fe<sub>3</sub>O<sub>4</sub> particles with a diameter of 300 nm in droplets induced by the Marangoni effect is studied under different light sources by using the particle image velocimetry (PIV). The experimental results show that when the number density of particles is higher than the critical value, the vertical vortices with symmetrical structure can be induced. At the bottom of the droplet, the particles move from the periphery to the center of droplet, and at the top of the droplet, the particles move from the center to the periphery of droplet. In addition, the frequency of light source and the number density of particles are the dominant factors in this process. Subsequently, for the light driven nanofluid experiment in this paper, the analytical solution of the flow field distribution is achieved by using the Stokes equation and the surface tension gradient boundary condition. The analytical solution of the flow field distribution obtained here is consistent with the experimental results, confirming the validity of the quantitative theory. Finally, the correlation between various driving modes, including surface tension at the top surface, surface pressure at the bottom surface or concentrated light radiation force in bulk phase, is discussed. This research provides theoretical support for the precise regulation of flow behavior and efficient conversion of light energy in the optical microfluidic system.

Utilization of nanoparticles in microfluidic systems for optical detection

An increasing interest has been shown in microfluidic systems due to their properties including low consumption of reagents, short analysis time and easy integration. However, despite of these advantages over conventional methods, some limitations in sensitivity and selectivity still exist in microfluidic systems. Recently advancements in nanotechnology offer some new approaches for the detection of target analytes with high sensitivity and selectivity. As a result, it is an appropriate method to enhance the detection sensitivity through a combination between microfluidic system and nanotechnology. Optical detection is a dominant technique in microfluidics because of its noninvasive nature and easy coupling. Numerous studies that integrate optical microfluidic system with nanotechnology have been reported in recent years. Therefore, optical microfluidic systems in combination with nanomaterials (NMs) are reviewed in our work. We illustrate the functions of different NMs in optical microfluidic systems and the efforts of different researchers to improve the performance of devices. After the introduction of different nanoparticle-based optical detection methods, challenges and future directions in the development of nanoparticle-based optical detection schemes in microfluidics have also been discussed.

Two-phase microfluidic flow modeling in an electrowetting display microwell.

Digital microfluidics provides precise control of a single microdroplet, producing more opportunities for bio-molecule studies, chemical reaction and optofluidics applications. By manipulating the surface of droplets, light can be focused, scattered, or reflected toward different positions. We build a model of electro-responsive optical microfluidic system, operated based on the electrowetting mechanism, which can split or push droplets moving within a microwell. The initial close state and operated open state in a single microwell displays the color of a dye oil droplet and the substrate, respectively, represented as the dark and bright pixel in the display board. Our results indicate that the microdroplets interface could be successfully deformed and moved towards different directions within a short period of time.

Optical microfluidic system based on ionophore modified gold nanoparticles for the continuous monitoring of mercuric ion

An optical microfluidic system based on the use of modified gold nanoparticles for monitoring Hg(II) is presented. The system is based on the specific recognition of the heavy metal by a new synthesized ionophore based on a modified thiourea, which is attached to the gold nanoparticles. This interaction generates a change on the gold Surface Plasmon Resonance (SPR) band. The sensitivity and selectivity of the procedure is firstly studied in batch. The obtained results demonstrate the mercury selective response over the different tested ions that can be found in environmental water samples. Due to the remarkable unusual rapid signal change observed during the interaction of the metal and the modified gold nanoparticles, the reaction can be easily performed in a microfluidic system. Results obtained by using the microfluidic system revealed improved analytical features compared to batch experiments such as a lower detection limit (11ppb), higher sensitivity and faster analysis time, all this with an easy and automated procedure. Therefore, the approach has shown great potential for designing low cost instrumentation for automatic in-field discrete or continuous measurements of Hg(II).

A scheme for variable optofluidic attenuator: Design and simulation

A novel scheme for variable optofluidic attenuator is proposed, by using the multi-bend waveguide structure, and combining with microfluidic channel filled with fluid mixture. The optical performance of our proposed device is numerically investigated by the beam propagation method. The results show that not only large dynamic range and low optical loss for both TE and TM mode input can be achieved, but the dependence of wavelength and polarization is weak in our configuration. Moreover, the proposed optical attenuator has large fabrication tolerance. The proposed device provides an effective means of manipulating optical attenuation, which is useful for applications in the photonic integrated system and optical microfluidic system.

Silica-on-silicon waveguide integrated polydimethylsiloxane lab-on-a-chip for quantum dot fluorescence bio-detection

Integration of microfluidics and optical components is an essential requirement for the realization of optical detection in lab-on-a-chip (LOC). In this work, a novel hybrid integration of silica-on-silicon (SOS) waveguide and polydymethylsiloxane (PDMS) microfluidics for realizing optical detection based biochip is demonstrated. SOS is a commonly used platform for integrated photonic circuits due to its lower absorption coefficient of silica and the availability of advanced microfabrication technologies for fabricating complicated optical components. However, the fabrication of complex microfluidics circuits on SOS is an expensive process. On the other hand, any complex 3D and high-aspect-ratio microstructures for the microfluidic applications can be easily patterned on PDMS using soft lithography. By exploring the advantages of these two materials, the proposed hybrid integration method greatly simplifies the fabrication of optical LOC. Two simple technologies--namely, diamond machining and soft lithography--were employed for the integration of an optical microfluidic system. Use of PDMS for the fabrication of any complex 3D microfluidics structures, together with the integration of low loss silica-on-silicon photonic waveguides with a straight microfluidic channel, opens up new possibilities to produce low-cost biochips. The performance of SOS-PDMS-integrated hybrid biochip is demonstrated with the detection of laser induced fluorescence of quantum dots. As quantum dots have immense application potential for biodetection, they are used for the demonstration of biodetection.

Absorption detection of enzymatic reaction using optical microfluidics based intermittent flow microreactor system

The advantages of integrating microfluidics into photonics-based biosensing for fabricating microreactor type lab-on-a-chip devices carries a lot of advantages, such as smaller sample volume handling, controlled drug delivery and high throughput diagnosis, which is useful for in situ medical diagnosis and point-of-care (POC) testing. A hybrid integrated optical microfluidic system has been developed for the study of single molecules and enzymatic reactions. The method of optical absorption has been employed for biosensing and the feasibility of absorption-based detection on the microfluidic platform has been demonstrated using horseradish peroxidase and hydrogen peroxide, as an example. The results show that the device is useful for the analysis of both the individual chemical specimen and also the study of chemical and biological reaction between two reacting species. The hybrid integration of microfluidics and optical ensembles thus forms the basis for developing the microreactor type lab-on-a-chip device, which would have several important applications in the area of nanobiotechnology.