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.

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.

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.

This paper reports a novel method to detect ammonia by using the ninhydrin -PDMS composite. The polymer composite film is prepared by integrating ninhydrin into the PDMS polymer matrix. Further, an optical lab-on-a-chip device is developed by integrating the ninhydrin-polymer composite into a microfluidic device for the detection of ammonia. The chemisorption of ammonia onto the composite resulted in the change in its optical absorption property. The proposed device has an integrated light emitting diode and photoresistor in order to measure the change in absorption and hence the detection and quantification of ammonia are performed. The response time of the sensor was found to be linear for a wide range of ammonia concentrations and it is shortest for the thin (100 μm) composite film. The limit of detection of the proposed device is found to be as low as 2ppm. The proposed sensor platform is also demonstrated for the detection of amino acids.

A novel method of integration of a silver-polydimethylsiloxane (PDMS) nanocomposite in a microfluidic channel for the realization of a lab-on-a-chip is reported in this work. By using a silver nitrate aqueous precursor solution, silver nanostructures are formed on the surface of PDMS, by in-situ reduction. The silver aggregates formed by reduction have a wide absorbance band in the UV-Visible range. Separated silver nano-islands, having narrow absorbance bands are formed by using the post-reduction annealing process. The plasmonic property of the silver nanostructures is used for the detection of bovine growth hormone. Subsequently, the nanocomposite was integrated into a microfluidic channel and the detection experiments were carried out in a microfluidic environment as well. The experiments confirmed that the nanocomposite can be integrated into the microfluidic device in order to enhance the detection sensitivity.