Arvind Chandrasekaran

Integrated microfluidic biophotonic chip for laser induced fluorescence detection

Integrated Lab-on-a-Chip or Micro-Total Analysis Systems offer several advantages for the detection of active chemical and biological species. In this work, an integrated microfluidic biophotonic chip is proposed for carrying out laser induced fluorescence detection. A Spectrometer-on-Chip device, specifically designed for multiple fluorescence detections at different emission wavelengths is integrated with the opto-microfluidic chip fabricated on Silicon-Polymer hybrid platform. The input fiber from the laser source, and output fiber coupled with a Spectrometer-on-Chip were integrated with the microfluidic channel so as to make a robust setup. Fluorescence detection was carried out using Alexafluor 647 tagged antibody particles. The experimental results show that the proposed biophotonic microfluidic device is highly suitable for high throughput detection of chemical and biological specimens.

Hybrid Integrated Silicon Microfluidic Platform for Fluorescence Based Biodetection

The desideratum to develop a fully integrated Lab-on-a-chip device capable of rapid specimen detection for high throughput in-situ biomedical diagnoses and Point-of-Care testing applications has called for the integration of some of the novel technologies such as the microfluidics, microphotonics, immunoproteomics and Micro Electro Mechanical Systems (MEMS). In the present work, a silicon based microfluidic device has been developed for carrying out fluorescence based immunoassay. By hybrid attachment of the microfluidic device with a Spectrometer-on-chip, the feasibility of synthesizing an integrated Lab-on-a-chip type device for fluorescence based biosensing has been demonstrated. Biodetection using the microfluidic device has been carried out using antigen sheep IgG and Alexafluor-647 tagged antibody particles and the experimental results prove that silicon is a compatible material for the present application given the various advantages it offers such as cost-effectiveness, ease of bulk microfabrication, superior surface affinity to biomolecules, ease of disposability of the device etc., and is thus suitable for fabricating Lab-on-a-chip type devices.

Geometrical tuning of microdiffuser/nozzle for valveless micropumps

Valveless micropumps require the integration of microdiffusers/nozzles for flow rectification in microfluidic systems. The flow directing capability of a micropump is determined by the efficiency of the diffuser. With the reduction in size of the micropump, conventional microdiffuser geometrical parameters are not suitable for obtaining high flow efficiencies due to several fluidic effects such as channel friction, wall shear stress, vena contracta, etc, and therefore it is important to modify the diffuser geometry according to the requirements of the pressure coefficients in order to obtain improved flow rates. This paper presents a simple and microfabrication friendly geometrical tuning method which offers the user a broad range of dependent tunable geometric parameters to improve the performance of the microdiffuser for valveless micropumps. Herein, for a given flow condition, the flow behaviour and the variation of pressure coefficients of the microdiffuser/nozzle with geometric tuning have been studied for different diffuser angles using finite element modelling (FEM). The results show that the proposed method is highly suitable for tuning the geometry of microdiffusers for a wide range of operating conditions of valveless micropumps. The performances of the best diffuser geometries for different diffuser angles have been experimentally verified, and the test results are used for the validation of the results of the FEM. The comparison between the FEM and experimental results shows a close agreement.

Experimental investigation of evanescence-based infrared biodetection technique for micro-total-analysis systems

The advent of microoptoelectromechanical systems (MOEMS) and its integration with other technologies such as microfluidics, microthermal, immunoproteomics, etc. has led to the concept of an integrated micro-total-analysis systems (microTAS) or Lab-on-a-Chip for chemical and biological applications. Recently, research and development of microTAS have attained a significant growth rate over several biodetection sciences, in situ medical diagnoses, and point-of-care testing applications. However, it is essential to develop suitable biophysical label-free detection methods for the success, reliability, and ease of use of the microTAS. We proposed an infrared (IR)-based evanescence wave detection system on the silicon-on-insulator platform for biodetection with microTAS. The system operates on the principle of bio-optical interaction that occurs due to the evanescence of light from the waveguide device. The feasibility of biodetection has been experimentally investigated by the detection of horse radish peroxidase upon its reaction with hydrogen peroxide.

Experimental investigation of cavitation behavior in valveless micropumps

Recently, there have been several reports on the observation of cavitation in microfluidics and in micropumps. Though cavitation is a common occurrence in micropumping, this is one of the least understood of all micropumping phenomena, and very limited progress has been made to study the behavior of cavitation in micropumps. Hence, a dedicated study on cavitation in micropumps and its effects on the performance of the micropump would be very useful. This work presents an experimental study on the behavior of cavitation in valveless micropump. The mechanism of cavitation occurrence in valveless micropumps has been explained by applying macroscale pumping principles to suit micropumping. The different stages of micropump cavitation have been defined through suitably conducted experiments and the results have been presented.

Hybrid bulk micro-machining process suitable for roughness reduction in optical MEMS devices

A hybrid micro-machining technique suitable for reducing surface roughness in different optical micro-systems environment is presented. In general, the Micro-Opto-Electro-Mechanical Systems (MOEMS) consist of waveguide-based devices and non-waveguide-based micro-systems. The proposed technique is suitable for both kinds of applications. This paper also presents two types of micro-machining, namely, isotropic gas phase Xenon difluoride (XeF2) pulse etching and wet anisotropic etching with Tetra Methyl Ammonium Hydroxide (TMAH), along with the mechanism of hybrid micro-machining. The influence of surface roughness on scattering loss in the two kinds of optical micro-systems has been analysed and the results are presented. The improvement in surface roughness due to the proposed technique is demonstrated by experimental characterisation of the roughness parameters using a Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). The results indicate a clear improvement in surface roughness and the induced scattering loss due to the proposed hybrid micro-machining technique.

MOEMS based integrated microfluidic fiber-optic waveguides for biophotonic applications

Fiber-optic waveguides based Micro-Opto-Electro-Mechanical Systems (MOEMS) form a significant class of biosensors which have notable advantages like light weight, low cost and more importantly, the ability to be integrated with bio-systems. In this work, integrated microfluidic fiber-optic waveguide biosensor is presented. The phenomenon of evanescence is employed for sensing mechanism of the device. Herein, the fiber-optic waveguide is integrated with bulk micromachined fluidic channel across which different chemical and biological samples are passed through. The significant refractive index change due to the presence of biological samples that causes the evanescent field condition in the waveguides leads to optical intensity attenuation of the transmitted light. The study of the modulation in optical intensity is used to detect the properties of the species used in the evanescent region. The intensity modulation of light depends upon the geometry of the waveguide, the length of evanescent field, the optical properties of specimen used for producing evanescence and the changes in the properties by their reaction with other specimen. Therefore, this device is proposed for biosensing applications. The Finite Element Analysis (FEA) has been carried out for wave propagation under the evanescent condition for different parametric variations.

Integrated micro-total analysis system (μTAS) for biophotonic enzymatic detections

Lab-on-a-chip or Micro total analysis systems (μTAS) technologies offer a lot of potential applications for biosensing and biomedical detections. This paper presents the design, fabrication and characterization of a fully integrated siliconpolymer based biophotonic Micro-Total Analysis System for the real-time detection of enzymes and antigens. This device uses optical detection methods i.e, optical absorption, Laser induced fluorescence and evanescence measurement technique to detect the presence, concentration and the activity of biomolecules. The main components of the proposed system are microfluidic unit and micromechanical fluid actuation system, integrated with the optical detection systems. An Echelle grating based Spectrometer-on-Chip on Silica-on-Silicon (SOS) is integrated with the opto-microfluidic assembly for fluorescence detection. On-Chip fabrication and integration of valveless micropump has been carried out in order to facilitate the transportation of fluid within the system. The important advantages of the proposed μTAS are functional independence of each module of the system, simultaneous multi-analyte detection, rapid, precise and discriminating results, low background/high signal-to-noise ratio, lack of moving parts, robust, portability, and feasibility of bulk fabrication.

Integrated biophotonic μTAS for flow cytometry and particle detection

Recent advancements in the integration of photonic technologies with microfluidics for Micro-Total Analysis Systems (μTAS) have paved way for the realization of a lot of potential applications in the field of biosensing and biomedical detections. Some of the prominent features of these integrated μTAS are improved performance, high sensitivity and signal-to-noise ratio, reduced consumption of samples and reagents, and portability, among others. In this work, a hybrid integrated biophotonic μTAS on silicon-polymer platform is presented. Herein, the optical fibers are directly integrated with the Silicon microfluidic chip and an Echelle grating based Spectrometer-on-Chip on Silica-on-Silicon (SOS) is integrated with the opto-microfluidic assembly. Flow actuation within the system is enabled by a mechanical Piezodriven Valveless Micropump (PVM). Finite Element Analysis (FEA) has been carried out in order to study the behavior of the fluid flow within the microfluidic channels due to the piezo actuation, and the geometry of the bio-detection chamber within the microfluidic system has been optimized accordingly in order to obtain no-stagnation flow conditions. The opto-microfluidic performance and the piezo-actuated valveless micropump were characterized in separate experiments. The integrated μTAS was tested for flow cytometry and particle detection using laser induced fluorescence. The experimental results show that the system is suitable for high throughput biodetections.

Integrated Optical Microfluidic Lab-on-a-chip

Bio-security for health monitoring and diagnosis are the needs of the hour, for rapid detection of biological and chemical species. This calls for a necessity to develop a cost effective miniaturized and portable biosensor device for in-situ biomedical applications and Point-of-Care Testing (POCT). While portability of the biosensor is required for in-situ medical detections, miniaturization is essential for handling smaller sample volumes and high throughput. Thus, the above mentioned concerns cannot be addressed unless a fully integrated biosensor system is developed. In this work, an integrated opto microfluidic based Lab-on-a-chip device is proposed for carrying out fluorescence based biodetection. The input and output fibers were integrated with the microfluidic channel so as to make a robust setup. Fluorescence detection was carried out using Alexafluor 647 tagged antibody particles and the output was measured with a Spectrometer-on-Chip, integrated with the device. The experimental results prove that the proposed device is highly suitable for Lab-on-a-Chip applications.