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A paper-based colourimetric assay for the Point-of-Care Testing (PoCT) of bilirubin has been developed based on the formation of a green-coloured copper-bilirubin complex from a blue-coloured tetraamminecopper(II) sulphate complex. The reaction was studied and optimized by UV-Visible absorption spectroscopy and translated onto a paper strip. Hydrophobic circular well patterns on Whatman chromatography paper were created by wax printing. The tetraamminecopper(II) sulphate complex was drop cast and dried on the reagent zones in the wax-patterned paper. The images of reagent zones captured using a scanner were analyzed using ImageJ software. Bilirubin spiked blood serum was tested in the concentration range of 1.2 to 950 µM. The PAD exhibited sensitivities of 0.4197 a.u/μM and 0.1040 a.u/μM for concentration ranges of bilirubin 1.2 to 96 μM and 105 to 950 μM respectively and a low detection limit of 0.799 µM. The method is highly selective to bilirubin, even in the presence of other biomarkers in serum. A plasma separation membrane incorporated PAD was fabricated for the final testing and quantification of bilirubin from whole blood.

Lab-on-a-chip diagnostic devices can be used as quick tools to identify the onset of diseases at an early stage. An integrated LoC platform usually consists of a set of microfluidic elements, each of which has dedicated functions like fluid mixing, fluid manipulation, and flow control, sample preparation, detection, and a read-out that can perform the conventional laboratory procedures on a miniaturized chip. The lab-on-a-chip device can be developed on a paper or polymeric platform and is usually fabricated using pattern transfer techniques or additive and subtractive manufacturing processes. Thorough knowledge of the physics involved in microfluidic technology is essential for developing miniaturized components required for a stand-alone Point-of-Care LoC device. This chapter discusses different types of lab-on-a-chip devices, the essential principles governing the design of these systems, and different fabrication techniques. The chapter concludes with some of the prominent applications of lab-on-a-chip devices.

In this paper, we report the design and development of easy-to-fabricate, low cost electromagnetically actuated ON/OFF valves to control multiple fluids on a programmable microfluidics platform. The valves were fabricated using mild steel pieces glued onto a PDMS membrane and its deflection was effected by using an array of solenoids. The activation of solenoid array was controlled using a programmed microcontroller. Numerical studies were carried out to optimize design parameters such as the distance between the valve and the solenoid, membrane thickness and the diameter of the deflection zone. The deflection of the valves was also studied using a high-speed digital camera and the results were in good conformity with the simulation results. Deflections up to 1200 μm could be achieved with a response of 3 ms. The efficiency of the developed platform for controlling multiple fluids was verified by experimental studies using coloured solutions and biosensors.

Magnetic actuation is promising in realizing flow-control devices because of the simplicity in in fabrication and its fast response. A normally-closed active microvalve based on magnetic actuation has been designed, simulated and fabricated for controlled delivery of fluids. By incorporating magnetic particles onto a deflectable membrane, the magnetic activity can be tuned and the actuation can be controlled using an electromagnet. Studies were focused to optimize the design and thickness of the deflectable membrane and the incorporation of magnetic nanoparticles for efficient actuation. Magnetic actuation was carried out using a programmed microcontroller that controls the activity of individual electromagnets which in turn controls the deflection of the membrane. The geometries were designed using CADian and CleWin software and deflection of the membrane was analyzed using computational fluid dynamics (CFD) tool Comsol Multiphysics. The optimized design was fabricated using direct laser write lithography following standard procedures and the simulation results were verified experimentally.

We present an analysis of the effect of incorporating ridges in straight and meander shaped pressure-driven Y-type micromixers. Triangular and rectangular ridges were incorporated on the inner walls of straight and meandered microfluidic channels, and their effect on mixing was evaluated. The incorporation of ridges greatly enhances mixing in the flow path due to strong laminar perturbations. Also, the effect of the geometry of ridges and their arrangement pattern in the microchannel was studied extensively. Incorporation of ridges in the microchannels resulted in enhanced performance of the mixer in terms of reduction in mixing time and length. Meander channels with ridges provided greater than 90 % mixing in less than 2 mm, whereas straight channels with ridges required a mixing length of 10 mm. The optimum design was fabricated using direct-laser write photolithography followed by soft lithography. The performance of the micromixer was validated using coloured solutions and biosensors. The micromixer is compact, simple in fabrication and operation, and easy-to-integrate with other microfluidic components enabling them for real-time applications. Its scope for the development of microfluidic devices where mixing is crucial has been demonstrated using glucose biosensors.

To improve the efficiency of passive micromixers, microchannels of varying geometry have been widely studied. A highly efficient passive micromixer was developed by alternatively varying the cross-sectional diameter along the flow. Microfluidic channels of various geometries were designed and the fluid flow patterns were studied using COMSOL Multiphysics. The extent of mixing in the microchannels for the various designs were analyzed and the most efficient micromixer was further optimized for best mixing performance. The optimized design was fabricated using direct laser write lithography. The spin speed, exposure energy, baking temperature, baking and development time were observed to play an important role in fabrication. Experimental evaluation of the simulation results was carried out by injecting coloured solutions through the PDMS microchannels and by electrochemical studies. Display Omitted Numerical studies using Comsol Multiphysics to optimize the geometry of a passive micromixer.Meander channels with alternately varying diameter were effective in mixing at a shorter length.Fabrication of the optimized microfluidic design using direct laser write lithographyVerification of simulation results by flow visualization experiments

Uniform and rapid mixing between various streams in a microfluidic device is essential for the development of device involving reaction between multiple streams. In this work, microfluidic channels of various geometries were designed and their fluid flow patterns were analyzed to optimize complete mixing of different fluids. The designs were modified by incorporating different types of ridges (square, curved and triangular shaped) in the microfluidic channels. Numerical analysis of the designs was carried out using COMSOL Multiphysics 4.3a. The extent of mixing in each of the design was calculated and the optimized design was fabricated using photolithography followed by soft lithography. The performance of the developed micromixer was studied using colored solutions and it was found to be in good agreement with the simulated results.

Computational simulation for the fluid flow in a paper based microfluidic system was performed and was experimentally validated in this work. Comsol Multiphysics based simulation was performed and the module used was species transport in porous medium. Two separate simulation for the reagent distribution and the interaction of sample with the immobilized reagent in paper based microfluidics devices were carried out. This was performed by varying the parameters such as adsorption constant, diffusivity and average velocity of fluid in the porous medium for finding the concentration profile. Finer mesh were used for the simulation which gives more accurate results with less computational time. The reagent distribution was experimentally validated by dropping methylorange indicator over Whatman filter paper.