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Abstract
To amplify the difference in localized surface plasmon resonance (LSPR) spectra of gold nano-islands due to intermolecular binding events, gold nanoparticles were used. LSPR-based optical biosensors consisting of gold nano-islands were readily made on glass substrates using evaporation and heat treatment. Streptavidin (STA) and biotinylated bovine serum albumin (Bio-BSA) were chosen as the model receptor and the model analyte, respectively, to demonstrate the effectiveness of this detection method. Using this model system, we were able to enhance the sensitivity in monitoring the binding of Bio-BSA to gold nano-island surfaces functionalized with STA through the addition of gold nanoparticle-STA conjugates. In addition, SU-8 well chips with gold nano-island surfaces were fabricated through a conventional UV patterning method and were then utilized for image detection using the attenuated total reflection mode. These results suggest that the gold nano-island well chip may have the potential to be used for multiple and simultaneous detection of various bio-substances.
Highlights
Impingement of external photons or electrons with specific energies induces collective oscillations of charge densities in metal 3-D nano-structures, which are defined as localized surface plasmon resonance (LSPR)
As already reported in previous studies [7,9,10], heat treatment after the formation of gold NI leads to a blue shift of the LSPR band of gold NI to the visible range and the absorption peak appears near 550 nm, similar to the absorption spectra of gold nanoparticles immobilized on transparent substrates
We have shown in a previous report [7] that the absorbance intensity of gold NI film measured by the attenuated total reflection (ATR) mode is considerably larger than that measured by the normal transmission mode; we expect that even minute differences in the absorption intensity of each sample could be significantly amplified, such that they would be detectable when measured in the ATR mode with a prism
Summary
Impingement of external photons or electrons with specific energies induces collective oscillations of charge densities in metal 3-D nano-structures, which are defined as localized surface plasmon resonance (LSPR). We have developed a novel approach for the detection of biomolecules, in which LSPR optical detection with gold NI was implemented to analyze binding of proteins to surfaces functionalized with the corresponding high affinity ligands This method was used to rapidly detect recombinant GST-tagged hIL6 expressed in Escherichia coli by attenuated total reflection (ATR) image measurements [7]. When large molecules, such as proteins, are used as the receptors, the sensitivity in detecting binding events with LSPR is expected to be noticeably lower This is expected since the penetration depth of the LSP field in metal 3-D nanostructures is at most a few tens of nanometers. We have developed another approach, in which gold NPs were employed to enhance the sensitivity in monitoring the binding of analytes to large receptors such as proteins with LSPR using gold NI chips. The gold NI chip was extended to a type of microwell array and we demonstrated that the well-array chip could be readily utilized as a simple assay tool, with the help of ATR imaging, for detection of various biological species
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