Gugu Rutherford

Topographically Engineered Large Scale Nanostructures for Plasmonic Biosensing.

We demonstrate that a nanostructured metal thin film can achieve enhanced transmission efficiency and sharp resonances and use a large-scale and high-throughput nanofabrication technique for the plasmonic structures. The fabrication technique combines the features of nanoimprint and soft lithography to topographically construct metal thin films with nanoscale patterns. Metal nanogratings developed using this method show significantly enhanced optical transmission (up to a one-order-of-magnitude enhancement) and sharp resonances with full width at half maximum (FWHM) of ~15nm in the zero-order transmission using an incoherent white light source. These nanostructures are sensitive to the surrounding environment, and the resonance can shift as the refractive index changes. We derive an analytical method using a spatial Fourier transformation to understand the enhancement phenomenon and the sensing mechanism. The use of real-time monitoring of protein-protein interactions in microfluidic cells integrated with these nanostructures is demonstrated to be effective for biosensing. The perpendicular transmission configuration and large-scale structures provide a feasible platform without sophisticated optical instrumentation to realize label-free surface plasmon resonance (SPR) sensing.

Enhanced optical transmission and Fano resonance through a nanostructured metal thin film

Artificial and engineered nanostructures expand the degrees of freedom with which one can manipulate the intricate interplay of light and matter. Certain nanostructural arrangements in the excited state enable the efficient electromagnetic coupling of propagating light with localized fields. Here, we demonstrate that light transmitted through a nanostructured metal thin film without any apertures can be significantly enhanced. Distinct asymmetric Fano resonances are observed in the zero-order transmission spectra using an incoherent light source. The transmission efficiency surpasses that of a metal thin film with the same area and thickness at the resonance maxima. The transmission minima and the sharp resonance maxima bear a strong resemblance to the extraordinary optical transmission observed in sub-wavelength nanohole array structures The resonance wavelength closely matches the nanostructural periodicity. The sensitivity of the resonances to the surrounding medium and the transmission efficiency demonstrate the potential for use in energy harvesting, imaging, optical processing and sensing applications.

Quantum-dot-conjugated graphene oxide as an optical tool for biosensor.

We have demonstrated a novel platform of quantum dots (QDs) core-shell conjugated graphene oxide (GO) biosensor for effective protein detection. The advantage in making core shell nanostructure allows preserving stable QDs, by improving quantum yield, and lowering the toxicity of the core. Both QDs and GO are efficient nanoparticle systems that can potentially be used for drug delivery, diagnosis, and biosensors scaffolds. However, our study indicates that the conjugation between these two nanoparticle systems makes their properties even more effective. The change in fluorescent intensity through fluorescence resonance energy transfer from quantum dots to GO produced a novel method for detection of the target and allows for the optimization of the recognition limit of Bovine serum albumin (BSA) due to efficient fluorescence resonance energy transfer as observed through time resolved relaxation spectroscopy. It is observed that the quenching of photoluminescence peak of QDs due to GO shell produced an applicable strategy and could be conveniently extended for detection of other biomolecules. We obtained significantly enhanced spectral signal through successful conjugation of GO with CdSe/CdS core shell, which can potentially be used for the detection of biomolecules with high sensitivity and selectivity. Our study underlines the efficiency of QD conjugated GO core shell in spectral detection of proteins even at very low concentration (0.25 mmol).