Ashis Kumar Sen

The mechanical properties of cells have been considered as biomarkers to indicate the presence of various diseases and changes in cell states. In literature, various conventional techniques have been established for studying cell mechanics such as atomic force microscopy (AFM), optical tweezers (OT), micropipette aspiration (MA), and cell stretching. Traditional techniques are time consuming and produce low throughput which is inadequate for time-sensitive analysis as well as has lesser clinical relevance. Toward this, microfluidic techniques provide attractive and suitable platform for cell phenotyping because of comparatively higher throughput, requirement of small sample volume, integration capability, biocompatibility, fast response, and dimensional match with biological cells. In the last few years, various microfluidic techniques have been developed for studying the mechanics of single cells. In this chapter, we present some of the recently developed microfluidic techniques and explain their benefit over the traditional techniques.

This chapter enumerates the methods, protocol, and safety procedures of various fabrication techniques for polymer-based microfluidic devices. The polymer materials can be a solid or a liquid, and the fabrication protocol needs to be executed accordingly. Various techniques demonstrating the fabrication of microfluidic devices using solid and liquid polymers are described. Procedure for each fabrication process is delineated with detailed images. Further, dos and don’ts for all the fabrication techniques are explained in the notes of each section. This chapter will benefit those interested in the microfluidic device fabrication using polymers and guide them to avoid mistakes so as to obtain an elegant device. The techniques are listed as follows: 1.Replica molding2.Microcontact printing3.Micro-transfer molding4.Solvent-assisted molding5.Hot embossing6.Injection molding7.CNC micromachining8.Laser photo ablation9.X-ray lithography10.UV patterning11.Plasma etching12.Ion beam etching13.Capillary molding14.Micro-stereolithography.

Circulating tumor cells (CTC) are released from the primary tumors into the bloodstream. These CTCs hold a crucial role in cancer metastasis; hence, they could be used for early diagnosis of cancer, evaluation of cancer development, and even helpful in drug development. In recent years, many novel microfluidic-based techniques for CTCs detection and isolation are explored. However, still, they cannot fulfill the current clinical requirement because of numerous current technological limitations. The heterogeneous nature of CTCs makes it further complicated. This chapter provides current advancements in CTC detection and isolation in a microfluidics platform. Different techniques are evaluated based on various parameters, such as purity, throughput, and cell viability. We discussed the concepts, limitations, advantages, drawbacks, and challenges, and at the end, we also discussed future application prospect.

Disease detection, single-cell analysis, biochemical reactions, etc. are of profound interest in several biomedical and bioengineering applications. These important processes require several profound aspects, e.g., lower consumption of reagent, rapid reactions, rapid detection, high throughput, etc. needs to be satiated. Droplet microfluidics has addressed all the desired aspects needed to achieve these applications by providing a compatible environment for biosensing and bioengineering reactions, smaller footprint, rapid detection, quick reaction, etc. These advantageous features have made droplet microfluidics a potent high throughput platform for biomedical research and applications. In addition to this, droplet microfluidics facilitates encapsulation of cells, reagents, drugs, particle synthesis, which makes droplet microfluidics a promising tool for biosensing and bioengineering applications. In this chapter, we will discuss both open surface and in-channel droplet microfluidics and their role in several biomedical applications.

Integrated optical detection in a microfluidic platform recently got an immense attention, on such integrated platforms light and fluids are engineered synergistically to implement highly sensitive and portable lab-on-chip biochemical sensors. Integrated optofluidic platforms were successfully demonstrated in last few years for various applications such as controlling liquid motion using light, sunlight-based fuel-production, and flow cytometry. Various microflow analyzers were developed for different applications including counting and studying biological cells, bacteria, molecular biology, and cellular DNA. Microflow cytometer is an instrument, which interrogates a small volume of fluid to detect and sort biological cells/samples present in a sample fluid. Presently, the flow cytometry is the state of the art for biological sample analysis due to its capability for detailed analysis. However, conventional flow cytometers are very expensive and thus are available only in centralized research facilities and major health care centers. Similarly, due to its complexity, regular maintenance and skilled expertise are required to operate the machine, analyze data, and make reports. In the last few years, several research works have been carried out to design cost-effective and portable microflow cytometer by employing the advancements in the field of microfluidic and microfabrication technology. However, the complicated techniques required for three-dimensional focusing of biological cells flowing inside the microchannel and controlling inter distance between them in the optical window are the primary hindrances in the development of a microflow cytometer. Another challenge in the development of microflow cytometer is the isolation of target cells downstream after detection. In literature, various techniques have been reported to achieve the sorting of target cells. Therefore, development of microflow cytometers is mainly concentrated on focusing of samples in a microchannel, miniaturization of optical and supporting flow systems, integration of electronics on the same chip, and development of optimal sorting technique. Hence, by incorporating above mentioned developments, microflow cytometer can be used successfully to focus, detect, and sort the particles with a high throughput which can lead to a proper analysis of biological samples.

On-demand droplet generation from a continuously flowing stream of aqueous phase has profound applications in dropletbased microfluidics for rare event encapsulation studies. Here, we present acoustic relocation-based droplet generation from co-flowing immiscible fluids in an on-demand manner using bulk acoustic wave (BAW). After on-demand droplet generation, droplets are isolated using the same acoustic force resulted from BAW. Two different acoustic relocation regimes are observed, namely, stream to droplet relocation and stream to stream relocation regime. Our experimental observation reveals that to generate droplets from co-flowing fluids, the following conditions must be satisfied. First, the co-flowing immiscible stream should be maintained in acoustic relocation conditions (Cac > 1); Second, the capillary instability should be triggered during the relocation process, which happens at capillary numbers of the co-flowing fluids should be less than 0.2 (CaL and CaH < 0.2). Finally, using BAW microfluidic chip, droplets containing microparticle were produced ondemand from co-flowing streams wherein the microparticles are added in one of the phases.

Sensory systems are available today at all length scales and formulate an important mandate in sustainability of environment and health. They use a wide spectrum of transduction mechanisms and signal conversion approaches with different levels of accuracy and rapidity. Sensors as deployed in various ranges of applications span from relatively simple temperature measurement bimetallic thermocouple structures to the detection of specific entities using advanced physical principles. The best example of sensors emanates from nature itself. Almost all living beings are blessed with sensory systems to sense and act to various environmental stimuli. There is a lot of inferential learning from such systems which can be translated to modern day sensor research. Within the environmental, chemical, and medical domains sensing can be carried out across a variety of length scales like the macroscale, microscale, or nanoscale. In a very organized manner a sensory system can be simplified into an analyte of interest (external to the sensor), a detection element (which is fixated to the sensory surface), a single transduction mechanism (to record measurable signal coming out from the change of analyte concentration), an analyzer and a decision tool. Further, the sensory systems can be using mechanical, microelectronic, micromechanical or electromechanical, optical, electrochemical, colorimetric, and other means to perform rapid sensing in the physical, chemical, and biological types of analytes. This book describes the basic mechanisms, fabrication techniques, and recent advancements in developments related to environmental, chemical, and medical sensors.

Early detection of infectious diseases by employing point-of-care (POC) technologies, which are highly sensitive and specific, user-friendly, and robust, would find great significance specifically in developing nations. Rapid and real-time detection of such diseases helps in proper treatment and useful in preventing transmission. With the advent of nanotechnology, a wide range of biological assays is developed by coupling nanosensors with microfluidics devices that are advantageous over traditional methods. One particular type of such integration of bio-nanosensors with microfluidics is the localized surface plasmon resonance (LSPR) biosensors (broadly nanoplasmonic) toolbox developed for biological applications such as drug discovery, rapid and clinical diagnosis, and further studies of biological cells or biomolecules. Further, nanoplasmonic sensors provide great versatility such as multiplexing, portable, and implantable, making them unique candidates for use as POC diagnostics devices. This chapter presents some of the recently developed on-chip biomarker detection devices by coupling LSPR biosensors with microfluidics platform for rapid diagnostics of infectious diseases.