Jayan Ozhikandathil

Gold nanoisland structures integrated in a lab-on-a-chip for plasmonic detection of bovine growth hormone

Three-dimensional gold nanostructures fabricated through a novel convective assembly method are treated thermally to obtain a nanoisland morphology. The new structure is proved to be adequate for the detection of bovine growth hormone, by using an immunoassay method based on the localized surface plasmon resonance band of gold. The nanoisland structures are integrated into a microfluidic device and the spectral measurements are carried out by introducing the device directly in the light beam of a ultraviolet-visible spectrophotometer. The principal motivation for this work is the need for a simple and rapid method of detection of hormone levels in milk and milk products.

Silica-on-silicon waveguide integrated polydimethylsiloxane lab-on-a-chip for quantum dot fluorescence bio-detection.

Integration of microfluidics and optical components is an essential requirement for the realization of optical detection in lab-on-a-chip (LOC). In this work, a novel hybrid integration of silica-on-silicon (SOS) waveguide and polydymethylsiloxane (PDMS) microfluidics for realizing optical detection based biochip is demonstrated. SOS is a commonly used platform for integrated photonic circuits due to its lower absorption coefficient of silica and the availability of advanced microfabrication technologies for fabricating complicated optical components. However, the fabrication of complex microfluidics circuits on SOS is an expensive process. On the other hand, any complex 3D and high-aspect-ratio microstructures for the microfluidic applications can be easily patterned on PDMS using soft lithography. By exploring the advantages of these two materials, the proposed hybrid integration method greatly simplifies the fabrication of optical LOC. Two simple technologies--namely, diamond machining and soft lithography--were employed for the integration of an optical microfluidic system. Use of PDMS for the fabrication of any complex 3D microfluidics structures, together with the integration of low loss silica-on-silicon photonic waveguides with a straight microfluidic channel, opens up new possibilities to produce low-cost biochips. The performance of SOS-PDMS-integrated hybrid biochip is demonstrated with the detection of laser induced fluorescence of quantum dots. As quantum dots have immense application potential for biodetection, they are used for the demonstration of biodetection.

Simulation and Implementation of a Morphology-Tuned Gold Nano-Islands Integrated Plasmonic Sensor

This work presents simulation, analysis and implementation of morphology tuning of gold nano-island structures deposited by a novel convective assembly technique. The gold nano-islands were simulated using 3D Finite-Difference Time-Domain (FDTD) techniques to investigate the effect of morphological changes and adsorption of protein layers on the localized surface plasmon resonance (LSPR) properties. Gold nano-island structures were deposited on glass substrates by a novel and low-cost convective assembly process. The structure formed by an uncontrolled deposition method resulted in a nano-cluster morphology, which was annealed at various temperatures to tune the optical absorbance properties by transforming the nano-clusters to a nano-island morphology by modifying the structural shape and interparticle separation distances. The dependence of the size and the interparticle separation distance of the nano-islands on the LSPR properties were analyzed in the simulation. The effect of adsorption of protein layer on the nano-island structures was simulated and a relation between the thickness and the refractive index of the protein layer on the LSPR peak was presented. Further, the sensitivity of the gold nano-island integrated sensor against refractive index was computed and compared with the experimental results.

Detection of Fluorophore-Tagged Recombinant Bovine Somatotropin (rbST) by Using a Silica-on-Silicon (SOS)-PDMS Lab-on-a-Chip

The presence of potentially harmful substances in milk is a concern for consumers. The discovery of recombinant DNA technology allowed the production of large quantities of recombinant bovine somatotropin (rbST), which is allowed to be used to increase milk and meat production in many countries. The use of rbST is controversial because of its potential effects on animal and human health. Use of the existing large instruments for the detection of rbST suffers disadvantages such as the need of large quantities of reagents, increased time of assays and most importantly, the high cost of equipment, etc. In this paper, a novel optical lab-on-a-chip (LOC) is proposed for the detection of a fluorophore-tagged rbST. The advantages of a silica-on-silicon platform for the optical waveguide and polydimethylsiloxane for microfluidics are exploited for the fabrication of a low-cost LOC. The tagging of rbST with two different types of fluorophores, such as FITC and Alexa-647, is carried out and used for detection in the proposed LOC.

Nano-islands integrated evanescence-based lab-on-a-chip on silica-on-silicon and polydimethylsiloxane hybrid platform for detection of recombinant growth hormone

Integration of nano-materials in optical microfluidic devices facilitates the realization of miniaturized analytical systems with enhanced sensing abilities for biological and chemical substances. In this work, a novel method of integration of gold nano-islands in a silica-on-silicon-polydimethylsiloxane microfluidic device is reported. The device works based on the nano-enhanced evanescence technique achieved by interacting the evanescent tail of propagating wave with the gold nano-islands integrated on the core of the waveguide resulting in the modification of the propagating UV-visible spectrum. The biosensing ability of the device is investigated by finite-difference time-domain simulation with a simplified model of the device. The performance of the proposed device is demonstrated for the detection of recombinant growth hormone based on antibody-antigen interaction.

Plasmonic Gold Decorated MWCNT Nanocomposite for Localized Plasmon Resonance Sensing

The synergism of excellent properties of carbon nanotubes and gold nanoparticles is used in this work for bio-sensing of recombinant bovine growth hormones (rbST) by making Multi Wall Carbon Nanotubes (MWCNT) locally optically responsive by augmenting it optical properties through Localized Surface Plasmon Resonance (LSPR). To this purpose, locally gold nano particles decorated gold–MWCNT composite was synthesized from a suspension of MWCNT bundles and hydrogen chloroauric acid in an aqueous solution, activated ultrasonically and, then, drop-casted on a glass substrate. The slow drying of the drop produces a “coffee ring” pattern that is found to contain gold–MWCNT nanocomposites, accumulated mostly along the perimeter of the ring. The reaction is studied also at low-temperature, in the vacuum chamber of the Scanning Electron Microscope and is accounted for by the local melting processes that facilitate the contact between the bundle of tubes and the gold ions. Biosensing applications of the gold–MWCNT nanocomposite using their LSPR properties are demonstrated for the plasmonic detection of traces of bovine growth hormone. The sensitivity of the hybrid platform which is found to be 1 ng/ml is much better than that measuring with gold nanoparticles alone which is only 25 ng/ml.

Detection of recombinant growth hormone by evanescent cascaded waveguide coupler on silica‐on‐silicon

An evanescent wave based biosensor is developed on the silica-on-silicon (SOS) with a cascaded waveguide coupler for the detection of recombinant growth hormone. So far, U -bends and tapered waveguides are demonstrated for increasing the penetration depth and enhancing sensitivity of the evanescent wave sensor. In this work, a monolithically integrated sensor platform containing a cascaded waveguide coupler with optical power splitters and combiners designed with S -bends and tapper waveguides is demonstrated for an enhanced detection of recombinant growth hormone. In the cascaded waveguide coupler, a large surface area to bind the antibody with increased penetration depth of evanescent wave to excite the tagged-rbST is obtained by splitting the waveguide into multiple paths using Y splitters designed with s -bends and subsequently combining them back to a single waveguide through tapered waveguide and combiners. Hence a highly sensitive fluoroimmunoassay sensor is realized. Using the 2D FDTD (Finite-difference time-domain method) simulation of waveguide with a point source in Rsoft FullWAVE, the fluorescence coupling efficiency of straight and bend section of waveguide is analyzed. The sensor is demonstrated for the detection of fluorescently-tagged recombinant growth hormone with the detection limit as low as 25 ng/ml.

Gold nanostructure-integrated silica-on-silicon waveguide for the detection of antibiotics in milk and milk products

Antibiotics are extensively used in veterinary medicine for the treatment of infectious diseases. The use of antibiotics for the treatment of animals used for food production raised the concern of the public and a rapid screening method became necessary. A novel approach of detection of antibiotics in milk is reported in this work by using an immunoassay format and the Localized Surface Plasmon Resonance property of gold. An antibiotic from the penicillin family that is, ampicillin is used for testing. Gold nanostructures deposited on a glass substrate by a novel convective assembly method were heat-treated to form a nanoisland morphology. The Au nanostructures were functionalized and the corresponding antibody was absorbed from a solution. Solutions with known concentrations of antigen (antibiotics) were subsequently added and the spectral changes were monitored step by step. The Au LSPR band corresponding to the nano-island structure was found to be suitable for the detection of the antibody antigen interaction. The detection of the ampicillin was successfully demonstrated with the gold nano-islands deposited on glass substrate. This process was subsequently adapted for the integration of gold nanostructures on the silica-on-silicon waveguide for the purpose of detecting antibiotics.

Silica-on-silicon (SOS)-PDMS platform integrated lab-on-a-chip (LOC) for quantum dot applications

Integration of microfluidics with the integrated optical waveguides enables the realization of devices capable of performing the biodetection and analysis on small scale using fluorescence biolabels such as Quantum Dot (QD). Polydimethylsiloxane (PDMS) has been an excellent choice to build the optical bio-microfluidic systems because of its biocompatibility, optical properties and low cost fabrication process. In this work, we report a method to integrate the microfluidics channels and waveguides fabricated on Silica-on-silicon (SOS) and PDMS platform for the realization of a Lab-on-a-chip (LOC). Performance of the device tested by measuring fluorescence from the laser excited Quantum Dot (QD655) solution reveals that the developed device is suitable for performing the QD based biodetection and analysis efficiently.

A brief review on microfluidic platforms for hormones detection

Lab-on-chip technology is attracting great interest due to its potential as miniaturized devices that can automate and integrate many sample-handling steps, minimize consumption of reagent and samples, have short processing time and enable multiplexed analysis. Microfluidic devices have demonstrated their potential for a broad range of applications in life sciences, including point-of-care diagnostics and personalized medicine, based on the routine diagnosis of levels of hormones, cancer markers, and various metabolic products in blood, serum, etc. Microfluidics offers an adaptable platform that can facilitate cell culture as well as monitor their activity and control the cellular environment. Signaling molecules released from cells such as neurotransmitters and hormones are important in assessing the health of cells and the effect of drugs on their functions. In this review, we provide an insight into the state-of-art applications of microfluidics for monitoring of hormones released by cells. In our works, we have demonstrated efficient detection methods for bovine growth hormones using nano and microphotonics integrated microfluidics devices. The bovine growth hormone can be used as a growth promoter in dairy farming to enhance the milk and meat production. In the recent years, a few attempts have been reported on developing very sensitive, fast and low-cost methods of detection of bovine growth hormone using micro devices. This paper reviews the current state-of-art of detection and analysis of hormone using integrated optical micro and nanofluidics systems. In addition, the paper also focuses on various lab-on-a-chip technologies reported recently, and their benefits for screening growth hormones in milk.