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Topographically Engineered Large Scale Nanostructures for Plasmonic Biosensing.

Xiao B, Pradhan SK, Santiago KC, Rutherford GN, Pradhan AK - Sci Rep (2016)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering and Center for Materials Research, Norfolk State University, Norfolk, VA 23504, USA.

ABSTRACT
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 ~15 nm 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.

No MeSH data available.


Related in: MedlinePlus

Transmission spectra through a nanostructured metal thin film and sharp resonance peak shift for biomolecular sensing.(a) Experimental optical transmission spectra of silver thin-film nanogratings under TM-polarized illumination for a grating period of 600 nm. 50 nm Ag nanostructured thin film (red) and the 50 nm Ag flat thin film (black). (b) Transmission spectra for a nanostructured gold thin film in DI water and NaCl solutions of various concentrations. The periodicity of the grating was 600 nm. (c) The magnitude of the total Hy component field and single SPP-mode waves in air and medium. (d) The spatial frequency spectra of the total field and single SPP waves in air and medium.
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f3: Transmission spectra through a nanostructured metal thin film and sharp resonance peak shift for biomolecular sensing.(a) Experimental optical transmission spectra of silver thin-film nanogratings under TM-polarized illumination for a grating period of 600 nm. 50 nm Ag nanostructured thin film (red) and the 50 nm Ag flat thin film (black). (b) Transmission spectra for a nanostructured gold thin film in DI water and NaCl solutions of various concentrations. The periodicity of the grating was 600 nm. (c) The magnitude of the total Hy component field and single SPP-mode waves in air and medium. (d) The spatial frequency spectra of the total field and single SPP waves in air and medium.

Mentions: This fabrication technique is a rapid way to reproduce large amounts of nanostructured chip devices. In addition, the large-scale nanostructures on the single chip allow us to perform optical characterization using conventional spectrophotometer systems. Unusually high transmission peaks with a distinct asymmetric Fano resonance line shape were identified from the transmission spectrum. As shown in Fig. 3a, nanostructures with the period of 600 nm were investigated, and the resonance wavelength was λ ≈ p (where p is the period). The transmission efficiencies observed at the resonance maxima are up to nearly one order of magnitude higher over those of the thin film with the same fraction and thickness. Strong coherent responses were revealed as the sharp resonance peaks, the FWHM of which is ~15 nm, which is limited by our EBL stitching accuracy. (The nanostructures developed from a single write field of EBL without stitching can achieve FWHMs below 10 nm.) The transmission spectra exhibited enhanced or extraordinary optical transmission (EOT) similar to that observed for subwavelength nanohole arrays719202122. Furthermore, the sharp resonance is a manifest of the coherent coupling the plasmonic oscillations, which are sensitive to the refractive index. Therefore, this plasmonic nanostructured thin film is a promising platform for SPR sensor devices. Most importantly, because the plasmonic momentum matching is modulated by the nanostructures, the signal input and detection are set up in a one-axis configuration in which a detection system would eliminate the requirement for sophisticated instrumentation. White light or natural light could be used as the incident source, and a conventional spectrophotometer is capable of performing the detection. (The transmission experiments and biosensing tests in Figs 3a,b and 4a are performed by a regular spectrophotometer, Perkin-Elmer Lambda 800, without any modification.) The refractive-index sensitivity is the basis of plasmonic detection. Figure 3b demonstrates this concept to determine the spectral shift using NaCl solutions of various concentrations (5%, 10%, 15% and 20%) in deionized water, corresponding to refractive indices of 1.3418, 1.3505, 1.3594, and 1.3684, respectively23. The measurements were performed under TM-polarized light at normal incidence. A general sensitivity figure, S = Δλ/Δn (nm RIU−1) was used to quantify the performance of the plasmonic nanostructure. For the nanogratings with a 600 nm pitch size, the nanostructures achieved a high sensitivity at ~600 nm RIU−1. Because we use the normal transmission for the sensing experiments, this spectral sensitivity number reaches the upper limit of the single-mode SPR spectral sensitivity. Sensitivity over this limit is beyond the scope of this letter. However, such sensitivities can be achieved by introducing incident or detection angles24. A general figure of merit, FOM = S (nm RIU−1)/Γ (nm), can also be used to quantify the performance of the plasmonic nanostructure in units of wavelength, where S is the sensitivity to refractive index and Γ is the resonance linewidth or FWHM. The sharp resonance peaks significantly improve the sensing performance. The measured FOMs are ~40 for the large scale nanostructures (6 mm × 10 mm). These FOMs are limited by our EBL stitching accuracy. The FOMs of the small scale nanostructures (80 μm × 80 μm in a single write field of EBL without stitching) can reach 80–130 reproducibly using the same fabrication method.


Topographically Engineered Large Scale Nanostructures for Plasmonic Biosensing.

Xiao B, Pradhan SK, Santiago KC, Rutherford GN, Pradhan AK - Sci Rep (2016)

Transmission spectra through a nanostructured metal thin film and sharp resonance peak shift for biomolecular sensing.(a) Experimental optical transmission spectra of silver thin-film nanogratings under TM-polarized illumination for a grating period of 600 nm. 50 nm Ag nanostructured thin film (red) and the 50 nm Ag flat thin film (black). (b) Transmission spectra for a nanostructured gold thin film in DI water and NaCl solutions of various concentrations. The periodicity of the grating was 600 nm. (c) The magnitude of the total Hy component field and single SPP-mode waves in air and medium. (d) The spatial frequency spectra of the total field and single SPP waves in air and medium.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4829874&req=5

f3: Transmission spectra through a nanostructured metal thin film and sharp resonance peak shift for biomolecular sensing.(a) Experimental optical transmission spectra of silver thin-film nanogratings under TM-polarized illumination for a grating period of 600 nm. 50 nm Ag nanostructured thin film (red) and the 50 nm Ag flat thin film (black). (b) Transmission spectra for a nanostructured gold thin film in DI water and NaCl solutions of various concentrations. The periodicity of the grating was 600 nm. (c) The magnitude of the total Hy component field and single SPP-mode waves in air and medium. (d) The spatial frequency spectra of the total field and single SPP waves in air and medium.
Mentions: This fabrication technique is a rapid way to reproduce large amounts of nanostructured chip devices. In addition, the large-scale nanostructures on the single chip allow us to perform optical characterization using conventional spectrophotometer systems. Unusually high transmission peaks with a distinct asymmetric Fano resonance line shape were identified from the transmission spectrum. As shown in Fig. 3a, nanostructures with the period of 600 nm were investigated, and the resonance wavelength was λ ≈ p (where p is the period). The transmission efficiencies observed at the resonance maxima are up to nearly one order of magnitude higher over those of the thin film with the same fraction and thickness. Strong coherent responses were revealed as the sharp resonance peaks, the FWHM of which is ~15 nm, which is limited by our EBL stitching accuracy. (The nanostructures developed from a single write field of EBL without stitching can achieve FWHMs below 10 nm.) The transmission spectra exhibited enhanced or extraordinary optical transmission (EOT) similar to that observed for subwavelength nanohole arrays719202122. Furthermore, the sharp resonance is a manifest of the coherent coupling the plasmonic oscillations, which are sensitive to the refractive index. Therefore, this plasmonic nanostructured thin film is a promising platform for SPR sensor devices. Most importantly, because the plasmonic momentum matching is modulated by the nanostructures, the signal input and detection are set up in a one-axis configuration in which a detection system would eliminate the requirement for sophisticated instrumentation. White light or natural light could be used as the incident source, and a conventional spectrophotometer is capable of performing the detection. (The transmission experiments and biosensing tests in Figs 3a,b and 4a are performed by a regular spectrophotometer, Perkin-Elmer Lambda 800, without any modification.) The refractive-index sensitivity is the basis of plasmonic detection. Figure 3b demonstrates this concept to determine the spectral shift using NaCl solutions of various concentrations (5%, 10%, 15% and 20%) in deionized water, corresponding to refractive indices of 1.3418, 1.3505, 1.3594, and 1.3684, respectively23. The measurements were performed under TM-polarized light at normal incidence. A general sensitivity figure, S = Δλ/Δn (nm RIU−1) was used to quantify the performance of the plasmonic nanostructure. For the nanogratings with a 600 nm pitch size, the nanostructures achieved a high sensitivity at ~600 nm RIU−1. Because we use the normal transmission for the sensing experiments, this spectral sensitivity number reaches the upper limit of the single-mode SPR spectral sensitivity. Sensitivity over this limit is beyond the scope of this letter. However, such sensitivities can be achieved by introducing incident or detection angles24. A general figure of merit, FOM = S (nm RIU−1)/Γ (nm), can also be used to quantify the performance of the plasmonic nanostructure in units of wavelength, where S is the sensitivity to refractive index and Γ is the resonance linewidth or FWHM. The sharp resonance peaks significantly improve the sensing performance. The measured FOMs are ~40 for the large scale nanostructures (6 mm × 10 mm). These FOMs are limited by our EBL stitching accuracy. The FOMs of the small scale nanostructures (80 μm × 80 μm in a single write field of EBL without stitching) can reach 80–130 reproducibly using the same fabrication method.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering and Center for Materials Research, Norfolk State University, Norfolk, VA 23504, USA.

ABSTRACT
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 ~15 nm 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.

No MeSH data available.


Related in: MedlinePlus