ABSTRACT
We have rationally designed two-dimensional Au and Ag hole arrays for high performing surface plasmon resonance (SPR) sensing. The figure-of-merit (FOM), which is defined as sensitivity/linewidth, is found to be highly geometry-dependent. For sensitivity, we find it is equal to the period of array when exciting low order surface plasmon modes at low incident angle. Therefore, increasing period improves sensitivity. On the other hand, narrow linewidth can be obtained from small hole size so that the radiative decay loss is minimized. By using a pair of orthogonally oriented polarizer and analyzer, the signal-to-noise ratio (SNR) can be greatly enhanced due to the elimination of the nonresonant reflection background. As a proof of our strategy, we have obtained FOM larger than 100/RIU and SNR higher than 110 from Au arrays. Our results show the importance of understanding the basic properties of surface plasmon polaritons in order to systematically optimize the performance of the plasmonic system for a given application.
Subject(s)
Computer-Aided Design , Metals/chemistry , Models, Theoretical , Refractometry/instrumentation , Surface Plasmon Resonance/instrumentation , Transducers , Computer Simulation , Equipment Design , Equipment Failure Analysis , Light , Scattering, RadiationABSTRACT
Gold nanorods (Au-NRs) have attracted enormous interest due to their size and unique optical properties. Many studies have demonstrated their use in biomedical systems. However, their potential toxicity is not fully understood. This study evaluated the effects of the Au-NRs (15 nM × 64 nM) coated with CTAB (cetyltrimethylammonium bromide) or PEG (polyethylene glycol) in human erythrocytes on the induction of haemolysis and erythroptosis. In our study, erythroptosis (also known as eryptosis) was determined systematically through the measurement of feature events of apoptosis by flow cytometry. We found that the CTAB- and PEG-coated Au-NRs up to 0.5 nM did not cause severe haemolysis. However, the CTAB-Au-NRs were more toxic than the PEG-Au-NRs. The toxicity of the CTAB-Au-NRs was largely due to the CTAB residues from desorption or incomplete purification. Mechanistically, cytosolic Ca(2+) ions seem to be the key mediator in the eryptosis/erythroptosis mediated by the CTAB or CTAB-Au-NRs while caspase-3 and reactive oxygen species did not contribute much to the process.
Subject(s)
Apoptosis/drug effects , Cetrimonium Compounds/toxicity , Erythrocytes/drug effects , Gold/chemistry , Nanotubes/toxicity , Polyethylene Glycols/toxicity , Caspase 3/metabolism , Cetrimonium , Erythrocytes/enzymology , Hemolysis/drug effects , Humans , In Vitro Techniques , Oxidative Stress/drug effectsABSTRACT
We study surface plasmon polariton lifetimes in two-dimensional arrays of blind holes on gold surfaces. The lifetimes are determined from the line widths of the resonant dips appearing in the specular reflection spectra. We find a strong dependence of lifetimes on the resonant wavelength and the hole geometry. Through both experiments and numerical simulations, we analyze the validity of the Rayleigh approximation and also explore the range of wavelengths and geometric parameters where it fails. Finally, we show that, within the range of geometries and wavelengths considered in our experiments, the behavior of surface plasmon polariton lifetimes can be understood as resulting from the interplay between the intrinsic metal absorption and the scattering of surface waves by single isolated holes.
