Opto-thermoelectric speckle tweezers

Optical Manipulation Heats up: Present and Future of Optothermal Manipulation

Optothermal manipulation is a versatile technique that combines optical and thermal forces to control synthetic micro-/nanoparticles and biological entities. This emerging technique overcomes the limitations of traditional optical tweezers, including high laser power, photon and thermal damage to fragile objects, and the requirement of refractive-index contrast between target objects and the surrounding solvents. In this perspective, we discuss how the rich opto-thermo-fluidic multiphysics leads to a variety of working mechanisms and modes of optothermal manipulation in both liquid and solid media, underpinning a broad range of applications in biology, nanotechnology, and robotics. Moreover, we highlight current experimental and modeling challenges in the pursuit of optothermal manipulation and propose future directions and solutions to the challenges.

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.

Bubble-pen lithography: Fundamentals and applications: Nanoscience: Special Issue Dedicated to Professor Paul S. Weiss

Developing on-chip functional devices requires reliable fabrication methods with high resolution for miniaturization, desired components for enhanced performance, and high throughput for fast prototyping and mass production. Recently, laser-based bubble-pen lithography (BPL) has been developed to enable sub-micron linewidths, in situ synthesis of custom materials, and on-demand patterning for various functional components and devices. BPL exploits Marangoni convection induced by a laser-controlled microbubble to attract, accumulate, and immobilize particles, ions, and molecules onto different substrates. Recent years have witnessed tremendous progress in theory, engineering, and application of BPL, which motivated us to write this review. First, an overview of experimental demonstrations and theoretical understandings of BPL is presented. Next, we discuss the advantages of BPL and its diverse applications in quantum dot displays, biological and chemical sensing, clinical diagnosis, nanoalloy synthesis, and microrobotics. We conclude this review with our perspective on the challenges and future directions of BPL.

Experimental Study of Transverse Trapping Forces of an Optothermal Trap Close to an Absorbing Reflective Film

The optothermal manipulation of micro-objects is significant for understanding and exploring the unknown in the microscale word, which has found many applications in colloidal science and life science. In this work, we study the transverse forces of an optothermal trap in front of a gold film, which is an absorbing reflective surface for the incident laser beam. It is demonstrated that optothermal forces can be divided into two parts: optical force of a standing-wave trap, and thermal force of a thermal trap. The optical force of the standing-wave trap can be obtained by measuring the optical trapping force close to a non-absorbing film with same reflectance. The thermal force can be obtained by subtracting the optical force of the standing-wave trap from the total trapping force of the optothermal trap close to the gold film. The results show that both optical and thermal trapping forces increase with laser power increasing. The optical trapping force is larger than the thermal trapping force, which is composed of convective drag force and thermophoretic force. Further experiment is run to study the composition of thermal force. The result shows that the convective flow is generated later than the thermophoretic flow. The results proposed here are useful for enabling users to optimize optothermal manipulation method for future applications.

Heat-Mediated Optical Manipulation

Progress in optical manipulation has stimulated remarkable advances in a wide range of fields, including materials science, robotics, medical engineering, and nanotechnology. This Review focuses on an emerging class of optical manipulation techniques, termed heat-mediated optical manipulation. In comparison to conventional optical tweezers that rely on a tightly focused laser beam to trap objects, heat-mediated optical manipulation techniques exploit tailorable optothermo-matter interactions and rich mass transport dynamics to enable versatile control of matter of various compositions, shapes, and sizes. In addition to conventional tweezing, more distinct manipulation modes, including optothermal pulling, nudging, rotating, swimming, oscillating, and walking, have been demonstrated to enhance the functionalities using simple and low-power optics. We start with an introduction to basic physics involved in heat-mediated optical manipulation, highlighting major working mechanisms underpinning a variety of manipulation techniques. Next, we categorize the heat-mediated optical manipulation techniques based on different working mechanisms and discuss working modes, capabilities, and applications for each technique. We conclude this Review with our outlook on current challenges and future opportunities in this rapidly evolving field of heat-mediated optical manipulation.

Plasmonic Nanotweezers and Nanosensors for Point-of-Care Applications

The capabilities of manipulating and analyzing biological cells, bacteria, viruses, DNAs, and proteins at high resolution are significant in understanding biology and enabling early disease diagnosis. We discuss progress in developments and applications of plasmonic nanotweezers and nanosensors where the plasmon-enhanced light-matter interactions at the nanoscale improve the optical manipulation and analysis of biological objects. Selected examples are presented to illustrate their design and working principles. In the context of plasmofluidics, which merges plasmonics and fluidics, the integration of plasmonic nanotweezers and nanosensors with microfluidic systems for point-of-care (POC) applications is envisioned. We provide our perspectives on the challenges and opportunities in further developing and applying the plasmofluidic POC devices.

Liquid Optothermoelectrics: Fundamentals and Applications

Liquid thermoelectricity describes the redistribution of ions in an electrolytic solution under the influence of temperature gradients, which leads to the formation of electric fields. The thermoelectric field is effective in driving the thermophoretic migration of charged colloidal particles for versatile manipulation. However, traditional macroscopic thermoelectric fields are not suitable for particle manipulations at high spatial resolution. Inspired by optical tweezers and relevant optical manipulation techniques, we employ laser interaction with light-absorbing nanostructures to achieve subtle heat management on the micro- and nanoscales. The resulting thermoelectric fields are exploited to develop new optical technologies, leading to a research field known as liquid optothermoelectrics. This Invited Feature Article highlights our recent works on advancing fundamentals, technologies, and applications of optothermoelectrics in colloidal solutions. The effects of light irradiation, substrates, electrolytes, and particles on the optothermoelectric manipulations of colloidal particles along with their theoretical limitations are discussed in detail. Our optothermoelectric technologies with the versatile capabilities of trapping, manipulating, and pulling colloidal particles at low optical power are finding applications in microswimmers and nanoscience. With its intricate interfacial processes and tremendous technological promise, optothermoelectrics in colloidal solutions will remain relevant for the foreseeable future.

Opto-Thermoelectric Tweezers: Principles and Applications

Opto-thermoelectric tweezers (OTET), which exploit the thermophoretic matter migration under a light-directed temperature field, present a new platform for manipulating colloidal particles with a wide range of materials, sizes, and shapes. Taking advantage of the entropically favorable photon-phonon conversion in light-absorbing materials and spatial separation of dissolved ions in electrolytes, OTET can manipulate the particles in a low-power and high-resolution fashion. In this mini-review, we summarize the concept, working principles, and applications of OTET. Recent developments of OTET in three-dimensional manipulation and parallel trapping of particles are discussed thoroughly. We further present their initial applications in particle filtration and biological studies. With their future development, OTET are expected to find a wide range of applications in life sciences, nanomedicine, colloidal sciences, photonics, and materials sciences.