Optical tweezers for trapping in a microfluidic environment

Enrichment of Aggregation-Induced Emission Aggregates Using Acoustic Streaming Tweezers in Microfluidics for Trace Human Serum Albumin Detection

Aggregation-dependent brightness (ADB) indirectly limits the in vitro performance of a pure aggregation-induced emission (AIE) probe in many ways; thus, controlling the aggregation state of the AIE probe is helpful for detecting an object of interest. Many studies are focused on the molecule design of the AIE probes, while less efforts have been made for the control of the aggregation of the AIEs. Here, an acoustic streaming tweezer (AST) generated using a gigahertz bulk acoustic wave resonator was applied to manipulate the aggregation status of the AIE probe and further enhance their performance for human serum albumin (HSA) detection. As the trapping size of the AST matches the working size of the AIE probe, the streaming can enrich and accumulate AIE nanoparticles, which then further trigger larger aggregates. Due to the ADB effect, the fluorescence intensity strongly increased, and thus, the detection limit of HSA was reduced to 0.5 μg/mL, which is low enough for kidney disease detection. Such an AST-assisted ADB strategy is potentially applicable to other AIE probes and can work as a portable choice for the biomedical detection.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Optofluidic Particle Manipulation: Optical Trapping in a Thin-Membrane Microchannel

We demonstrate an optofluidic device which utilizes the optical scattering and gradient forces for particle trapping in microchannels featuring 300 nm thick membranes. On-chip waveguides are used to direct light into microfluidic trapping channels. Radiation pressure is used to push particles into a protrusion cavity, isolating the particles from liquid flow. Two different designs are presented: the first exclusively uses the optical scattering force for particle manipulation, and the second uses both scattering and gradient forces. Trapping performance is modeled for both cases. The first design, referred to as the orthogonal force design, is shown to have a 80% capture efficiency under typical operating conditions. The second design, referred to as the gradient force design, is shown to have 98% efficiency under the same conditions.

Capillary-Mediated Single-Cell Dispenser

Single-cell manipulation, sorting, and dispensing into multiwell plates is useful for single-cell multiomics studies. Here, we develop a single-cell dispenser inspired by electrohydrodynamic jet printing that achieves accurate droplet generation and single-cell sorting and dispensing using fused silica capillary tubing as both the optical detection window and nozzle for droplet dispensing. Parameters that affect droplet dispensing performance-capillary inner and outer diameter, flow rate, applied voltage, and solution properties-were optimized systematically with COMSOL simulations and experimentation. Small (5-10 nL) droplets were obtained by using 100-μm inner diameter and 160-μm outer diameter capillary tubing and allowed efficient encapsulation and dispensing of single cells. We demonstrate an application of this easy-to-assemble single-cell dispenser by sorting and dispensing cells into multiwell plates for single-cell PCR analysis.

Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective

Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.