This thesis presents optical trapping of various single nanoparticles, and the method for integrating the optical trap system into a microfluidic channel to examine the trapping stiffness and to study binding at the single molecule level.Optical trapping is the capability to immobilize, move, and manipulate small objects in a gentle way. Conventional trapping methods are able to trap dielectric particles with size greater than 100 nm. Optical trapping using nanostructures has overcome this limitation so that it has been of interest to trap nanoparticles for bio-analytical studies. In particular, aperture optical trapping allows for trapping at low powers, and easy detection of the trapping events by noting abrupt jumps in the transmission intensity of the trapping beam through the aperture. Improved trapping efficiency has been achieved by changing the aperture shape from a circle; for example, to a rectangle, double nanohole (DNH), or coaxial aperture. The DNH has the advantage of a well-defined trapping region between the two cusps where the nanoholes overlap, which typically allows only single particle trapping due to steric hindrance. Trapping of 21 nm encapsulated quantum dot has been achieved which shows optical trapping can be used in technologies that seek to place a quantum dot at a specific location in a plasmonic or nanophotonic structure.The DNH has been used to trap and unfold a single protein. The high signal-to-noise ratio of 33 in monitoring single protein trapping and unfolding shows a tremendous potential for using the double nanohole as a sensor for protein binding events at a single molecule level. The DNH integrated in a microfluidic chip with flow to show that stable trapping can be achieved under reasonable flow rates of a few ?L/min. With such stable trapping under flow, it is possible to envision co-trapping of proteins to study their interactions. Co-trapping is achieved for the case where we flow in a protein (bovine serum albumin--BSA) and co-trap its antibody (anti-BSA).

Optical trapping and manipulation by laser beams offers the unique possibility to handle single micrometer-sized particles such as living cells without any mechanical contact, damage or contamination. A second hot topic in biology is microfluidics, where the examination of biological samples in channel structures with widths below 100 µm reduces the used sample volume significantly. While the combination of both techniques results in attractive lab-on-a-chip structures for particle sorting and analysis, the commonly bulky trapping setup is contradictory to the miniaturized concept. Here, the use of vertical-cavity surface-emitting lasers (VCSELs) as light sources in optical trapping systems allows a strong reduction of the setup complexity owing to the small dimensions, low cost and high beam quality of these devices. This thesis gives a detailed study on optical manipulation systems based on vertically emitting laser diodes. A standard optical tweezers setup as well as a novel, miniaturized system, the so-called integrated optical trap are investigated. The latter aims for particle separation and sorting in microfluidics resulting in low-cost, portable modules. A classical optical tweezers system based on a high numerical aperture objective in combination with a VCSEL light source is investigated. Standard multi-mode as well as single-mode surface relief VCSELs are used as laser source. With both kinds of VCSELs, optical trapping of polystyrene particles of sizes ranging from 4 to 15µm is demonstrated with some milliwatts of optical power at the sample stage. A maximum trapping force of 4.4 pN for 15 µm particles is achieved with the multi-mode laser, proving the suitability of multi-mode lasers for optical manipulation despite their inferior beam profile. By using two-dimensional VCSEL arrays instead of solitary lasers, the system is extended to a multiple optical tweezers setup in a straightforward manner. To avoid any additional optics, densely packed VCSEL arrangements with a device spacing of less than 25 µm are used, where a novel fabrication process allows the seamless integration of the inverted surface relief technique for enhanced beam quality. By electrical switching between individual devices of the array, non-mechanical particle translation with velocities of up to 12 µm/s is achieved. With a tilted linear VCSEL array, an optical lattice is generated in the optical tweezers setup, and continuous deflection of particles is realized. By substituting the sample stage in the optical tweezers setup with a microfluidic chip fabricated from polydimethylsiloxane (PDMS), particle redirection at a channel junction is realized using a solitary VCSEL source as well as a tilted linear VCSEL array. For the latter, the particles are deflected when passing the optical lattice, thus, the position of the lasers is fixed and no moving parts are necessary, which further reduces the setup complexity. To achieve a drastic miniaturization of the trapping setup, namely the integrated optical trap, the laser source is placed directly underneath the sample chamber. A weakly focused laser beam is generated in the particle solution by integrating an additional microlens on the VCSEL output facet. To determine appropriate lens geometries, the beam propagation inside the integrated trap structure is calculated and the thermal reflow process for lens fabrication is studied in detail concerning lens diameter, reflow temperature and substrate material. By combining the microlens with the inverted relief technique, the quality of the focused beam is strongly improved with respect to divergence, transverse beam profile and beam diameter, where a minimum of 7 µm is measured at the focal point. With first solitary integrated optical traps, deflection, levitation and transverse trapping of 10 µm polystyrene particles is demonstrated for optical powers of 5mW. In a next step, integrated optical trap arrays are realized based on closely spaced twodimensional arrangements of lensed relief VCSELs. To transfer the continuous deflection scheme demonstrated in the classical tweezers setup to the integrated trap, linear arrays of parallel working VCSELs are investigated. To support the design of the multiple integrated trap structure, a simulation of the optical deflection process is performed. Here, a dependence on the geometric and material properties of the particles is predicted, so applications in microfluidic particle sorting are intended. Compact and portable modules are obtained by integrating the laser chip with the microfluidic chip using flip-chip bonding. Although the finished modules show strong heating of the VCSEL chip resulting in a significant reduction of the device performance, simultaneous trapping as well as continuous particle deflection was successfully demonstrated with a total optical power of just 5mW. The results presented in this work demonstrate the potential of VCSELs as laser sources for optical trapping and microparticle manipulation. In conventional optical tweezers setups, the use of VCSELs reduces the setup complexity significantly, while first prototypes of ultra-compact integrated optical traps based on VCSELs confirm the feasibility of portable and inexpensive microfluidic sorting systems.

In the present book, various applications of microfluidics and nanofluidics are introduced. Microfluidics and nanofluidics span a broad array of disciplines including mechanical, materials, and electrical engineering, surface science, chemistry, physics and biology. Also, this book deals with transport and interactions of colloidal particles and biomolecules in microchannels, which have great importance to many microfluidic applications, such as drug delivery in life science, microchannel heat exchangers in electronic cooling, and food processing industry. Furthermore, this book focuses on a detailed description of the thermal transport behavior, challenges and implications that involve the development and use of HTFs under the influence of atomistic-scale structures and industrial applications.

The concept of a miniaturised laboratory on a disposable chip is now a reality, and in everyday use in industry, medicine and defence. New devices are launched all the time, prompting the need for a straightforward guide to the design and manufacture of lab-on-a-chip (LOC) devices. This book presents a modular approach to the construction and integration of LOC components in detection science. The editors have brought together some of the leading experts from academia and industry to present an accessible guide to the technology available and its potential. Several chapters are devoted to applications, presenting both the sampling regime and detection methods needed. Further chapters describe the integration of LOC devices, not only with each other but also into existing technologies. With insights into LOC applications, from biosensing to molecular and chemical analysis, and presenting scaled-down versions of existing technology alongside unique approaches that exploit the physics of the micro and nano-scale, this book will appeal to newcomers to the field and practitioners requiring a convenient reference.

Optical traps have played a central role in the exploration of biological systems through the examination of molecular motors, biopolymers, and many other interactions at the nano and micro length scales. This thesis seeks to extend the applications of optical trapping instrumentation and the knowledge of biological systems by building new tools, expanding traditional measurements and developing new assays. First, an economical design of a high-end optical trap is presented as a teaching implement for an undergraduate lab. In addition to equipment specifications and construction directions, three experimental modules highlighting concepts in biology and physics are put forward including single molecule measurement of protein motor torque and the mechanical properties of DNA. A second optical trap design is developed to promote the integration of optical forces and semiconductor materials. This project provides a non-invasive method for control, construction, and measurement that leverages existing semiconductor fabrication techniques while retaining the nanometer position resolution and piconewton force sensitivity of an optical trap encouraging applications in MEMS, microfluidics, and single molecule studies. To better understand the properties of components of biological assembly, assays for single molecule measurement of adhesion force and kinetic off rate are established and carried out for short 12 amino acid sequences previously selected to adhere to glass surfaces and sapphire substrates. Finally, the mechanism of motility for the biological motor kinesin is investigated in depth using the optical trap in two assays. One researches motility in a heterodimeric kinesin with one motor head unable to hydrolyze ATP. The second establishes the force generation mechanism of kinesin through selective mutation of the N-terminal coverstrand segment of the enzyme.

This book presents a compilation of self-contained chapters covering a wide range of topics within the broad field of soft condensed matter. Each chapter starts with basic definitions to bring the reader up-to-date on the topic at hand, describing how to use fluid flows to generate soft materials of high value either for applications or for basic research. Coverage includes topics related to colloidal suspensions and soft materials and how they differ in behavior, along with a roadmap for researchers on how to use soft materials to study relevant physics questions related to geometrical frustration.