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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 21 — Oct. 17, 2005
  • pp: 8520–8525
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High-speed multispectral imaging of nanoplasmonic array

Gang L. Liu, Joseph C. Doll, and Luke P. Lee  »View Author Affiliations


Optics Express, Vol. 13, Issue 21, pp. 8520-8525 (2005)
http://dx.doi.org/10.1364/OPEX.13.008520


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Abstract

A multispectral microscopy imaging system is developed for the single-particle scattering spectroscopy of many individual plasmonic nanostructures simultaneously. The system dispenses with the need for the mechanical scanning of sample stage and thus enables high-speed plasmon resonance imaging of nanostructure arrays. The darkfield scattering intensity images of nanoplasmonic structures at individual wavelengths are acquired with a spectral resolution of 2 nm in the wavelength range from 500 nm to 800 nm, and a frame rate of 2 seconds/wavelength. The images are processed afterwards and the plasmon resonance wavelength of every nanostructure within the field of view can be obtained at once. The plasmon resonance wavelengths of more than 1000 Au colloidal nanoparticles and a nanofabricated Au nanowire array are measured within 5 minutes. The presented high-speed spectral imaging system promises the practical application of large-scale high-density nanoplasmonic sensor arrays for label-free biomolecular detections in the near future.

© 2005 Optical Society of America

1. Introduction

Here we propose and demonstrate a new multispectral imaging system to simultaneously monitor the individual scattering spectra and plasmon resonance wavelength of large numbers of nanostructures distributed within the field of view of a microscopy objective lens without mechanically scanning the sample. The multispectral imaging system currently supports frame rates as high as 2 seconds per frame (wavelength) that could potentially be increased by using a light source with a higher power or an image detector with greater sensitivity, by which the image signal to noise ratio can also be increased. As an exemplary application of our novel imaging system, more than 1000 plasmonic Au colloidal nanoparticles in various sizes are spectrally imaged in 5 minutes with a spectral resolution of 2 nm within a wavelength range from 500 to 800 nm. In another demonstration, a nanofabricated Au nanowire array is also spectrally imaged. The overall imaging time can be further reduced by using a smaller wavelength range or reducing the spectral resolution depending upon the requirements of a particular application.

2. Multispectral imaging system configuration

All images are stored as uncompressed, 16-bit grayscale data files and are analyzed by an image processing program. No noise reduction or smoothing algorithms were applied to the image data prior to analysis. The bright spot regions (typically 1~10 pixels) in each image are recognized by the analysis program as individual nanoplasmonic structures of interest. The mean intensity value of these small regions is extracted from the image at each wavelength as the raw scattering spectra data. The mean intensity value in a large, empty (black) region is also measured at each wavelength as the background spectrum, which is subsequently subtracted from the raw scattering spectra. The difference spectra are then scaled according to the previously-stored spectrum of the light output from the monochromator to yield the final scattering spectra. The process of the image analysis and the spectral data reconstruction is completely automated by the computer program.

Fig. 1. Configuration of the multispectral imaging system for the scattering spectra measurement of nanoplasmonic arrays.

3. Results and discussion

As a demonstration, we use randomly-dispersed Au colloidal nanoparticles on a glass slide as the imaging sample. The diameters of the Au nanoparticles vary from 20 nm to 80 nm, so their plasmon resonance wavelengths, and thus their scattering colors are different. Fig. 2a shows the true-color scattering image of the nanoparticles within ~1/10 of whole view field of the objective lens. The true-color image is taken in the same darkfield microscopy system but with a white-light illumination source and color camera. Figure 2(b) and 2(c) show the scattering intensity images of the same nanoparticles within the same field of view taken by our system at 550 nm and 630 nm, respectively. Figure 2(d) shows the scattering spectra of three representative nanoparticles marked in Fig. 2(a), (b) and (c). The plasmon resonance wavelengths (spectral peaks) of these three nanoparticles are respectively 560 nm, 580 nm and 630 nm, which agree well with their colors (green, yellow, and red) in Fig. 2(a), and their relative intensities in Fig. 2(b) and 2(c). The Au “particle” with red scattering color could be a cluster of a few Au nanoparticles, because the plasmon resonance wavelength of individual Au nanoparticle is shorter than 600 nm according to Mie scattering theoretical predictions. Although only the scattering spectra of three typical particles are shown here, the spectral information for all the other nanoparticles in the field of view are also stored at once and can be reconstructed in the same fashion.

Fig. 2. (a) True-color scattering image of thousands of dispersed Au nanoparticles. For the clarity of the image, a field of 100 μm × 100 μm is cropped from the whole view field of ~ 300 μm × 300 μm. The lower picture is the zoom-in image from the marked area (square) of the upper image. (b) and (c) show the scattering intensity image of the same Au nanoparticles as in (a) with 550 nm and 630 nm monochromatic illumination, respectively. (d) Scattering spectra of three representative particles marked as 1, 2 and 3 respectively in the images.

The ultimate goal of our system is the high-speed spectral imaging of large nanoplasmonic arrays, e. g. 100 × 100 elements, so we imaged a much smaller scale array as a proof-of-concept. The array is comprised of 11 Au nanowires fabricated on a transparent substrate via electron beam lithography. The lengths of all the Au nanowires are 70 μm, while their diameters vary from 20 nm to 150 nm. Figure 3(a) shows the scanning electron micrograph of the array. Due to the dependence of plasmon resonance wavelength upon nanowire diameter, the nanowires appear different colors under white light illumination and are shown in Fig. 3(b) when immersed in oil. The narrower nanowires such as 20 nm, 30 nm and so forth primarily scatter green light while the scattering color of wider nanowires are red shifted. Figure 3(c) and 3(d) show the scattering intensity images of the Au nanowires array within the same view field as in Fig. 3(e) at illumination wavelengths of 570 nm and 650 nm, respectively. The relative scattering intensities of each nanowire in these images agree well with their plasmon resonance wavelengths.

Fig. 3. The scanning electron micrograph (a), true-color scattering image (b), and scattering intensity images with 570 nm (c) and 650 nm (d) monochromatic illumination of an Au nanowire array. All scale bars stand for 1μm. (e) Scattering spectra of three representative Au nanowires.

It should be noted that the scattering intensities of narrower nanowires are much smaller compared to those of the wider nanowires because the Rayleigh or Mie scattering intensity is proportional to the sixth power of the scattering length, i.e. the nanowire diameter. Therefore the monochromatic scattering intensities of narrower nanowires such as 20, 30 or 40 nm nanowire are very small relative to the dynamic range of the detector, which compromises the signal to noise ratio in the spectral detection of those nanowires. This problem can be solved by applying a light source with a higher output power or longer image acquisition time. Fig. 3d shows the scattering spectra of three representative nanowires with widths of 50 nm, 90 nm and 150 nm, respectively. Because the distance between each nanowires is only 1 μm which is barely resolved by the 40X microscope objective lens, multiple resonance peaks on the spectra of those nanowires can be observed due to the scatter signal interference from adjacent nanowires.

4. Conclusion

Acknowledgments

The authors appreciate the help from Mr. Randy Rieger for providing the light source. This work is supported by Defense Science Office of Defense Advanced Research Project Agency (DARPA), USA. These two authors equally contributed to this work.

Reference and Links

1 .

R. Karlsson , “ SPR for molecular interaction analysis: a review of emerging application areas ,” J. Mol. Recognition 17 , 151 – 161 ( 2004 ). [CrossRef]

2 .

J. S. Shumaker-Parry , R. Aebersold , and C. T. Campbell , “ Parallel, quantitative measurement of protein binding to a 120-element double-stranded DNA array in real time using surface plasmon resonance microscopy ,” Anal. Chem. 76 , 2071 – 2082 ( 2004 ) [CrossRef] [PubMed]

3 .

M. Piliarik , H. Vaisocherova , and J. Homola , “ A new surface plasmon resonance sensor for high-throughput screening applications ,” Biosens. Bioelectron. 20 , 2104 – 2110 ( 2005 ) [CrossRef] [PubMed]

4 .

D. R. Rhodes , J. Yu , K. Shanker , N. Deshpande , R. Varambally , D. Ghosh , T. Barrette , A. Pandey , and A. M. Chinnaiyan , “ Large-scale meta-analysis of cancer microarray data identifies common transcriptional profiles of neoplastic transformation and progression ,” P. Natl. Acad. Sci. USA 101 , 9309 – 9314 ( 2004 ) [CrossRef]

5 .

A.D. McFarland and R.P. Van Duyne , “ Single silver nanoparticles as real-time optical sensors with zeptomole sensitivity ,” Nano Lett. 3 , 1057 – 1062 ( 2003 ) [CrossRef]

6 .

G. Raschke , S. Kowarik , T. Franzl , C. Sonnichsen , T. A. Klar , J. Feldmann , A. Nichtl , and K. Kurzinger , “ Biomolecular recognition based on single gold nanoparticle light scattering ,” Nano Lett 3 , 935 – 938 ( 2003 ). [CrossRef]

7 .

S.J. Oldenburg , C.C. Genick , K.A. Clark , and D.A. Schultz , “ Base pair mismatch recognition using plasmon resonant particle labels ,” Anal. Biochem. 309 , 109 – 116 ( 2002 ). [CrossRef] [PubMed]

8 .

C. Sonnichsen , B. M. Reinhard , J. Liphardt , and A. P. Alivisatos , “ A molecular ruler based on plasmon coupling of single gold and silver nanoparticles ,” Nat. Biotechnol. 23 , 741 – 745 ( 2005 ) [CrossRef] [PubMed]

9 .

C. Sonnichsen , T. Franzl , T. Wilk , G. von Plessen , and J. Feldmann , “ Drastic reduction of plasmon damping in gold nanorods ,” Phys. Rev. Lett. 88 , 077402 ( 2002 ) [CrossRef] [PubMed]

10 .

T. Itoh , K. Hashimoto , and Y. Ozaki , “ Polarization dependences of surface plasmon bands and surface-enhanced Raman bands of single Ag nanoparticles ,” Appl. Phys. Lett. 83 , 2274 – 2276 ( 2003 ) [CrossRef]

OCIS Codes
(110.0180) Imaging systems : Microscopy
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(290.5820) Scattering : Scattering measurements

ToC Category:
Research Papers

History
Original Manuscript: August 19, 2005
Revised Manuscript: October 1, 2005
Published: October 17, 2005

Citation
Gang Liu, Joseph Doll, and Luke Lee, "High-speed multispectral imaging of nanoplasmonic array," Opt. Express 13, 8520-8525 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-21-8520


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References

  1. R. Karlsson, �??SPR for molecular interaction analysis: a review of merging application areas,�?? J. Mol. Recognition 17, 151-161 (2004). [CrossRef]
  2. J. S. Shumaker-Parry, R. Aebersold, and C. T. Campbell, �??Parallel, quantitative measurement of protein binding to a 120-element double-stranded DNA array in real time using surface plasmon resonance microscopy,�?? Anal. Chem. 76, 2071-2082 (2004) [CrossRef] [PubMed]
  3. M. Piliarik, H. Vaisocherova, and J. Homola, �??A new surface plasmon resonance sensor for high-throughput screening applications,�?? Biosens. Bioelectron. 20, 2104-2110 (2005) [CrossRef] [PubMed]
  4. D. R. Rhodes, J. Yu, K. Shanker, N. Deshpande, R. Varambally, D. Ghosh, T. Barrette, A. Pandey, and A. M. Chinnaiyan, �??Large-scale meta-analysis of cancer microarray data identifies common transcriptional profiles of neoplastic transformation and progression,�?? P. Natl. Acad. Sci. USA 101, 9309-9314 (2004) [CrossRef]
  5. A.D. McFarland, and R.P. Van Duyne, �??Single silver nanoparticles as real-time optical sensors with zeptomole sensitivity,�?? Nano Lett. 3, 1057-1062 (2003) [CrossRef]
  6. G. Raschke, S. Kowarik, T. Franzl, C. Sonnichsen, T. A. Klar, J. Feldmann, A. Nichtl, and K. Kurzinger, �??Biomolecular recognition based on single gold nanoparticle light scattering,�?? Nano Lett 3, 935-938 (2003). [CrossRef]
  7. S.J. Oldenburg, C.C.Genick, K.A. Clark, and D.A. Schultz, �??Base pair mismatch recognition using plasmon resonant particle labels,�?? Anal. Biochem. 309, 109-116 (2002). [CrossRef] [PubMed]
  8. C. Sonnichsen, T. Franzl, T. Wilk, G. von Plessen, and J. Feldmann, �??Drastic reduction of plasmon damping in gold nanorods,�?? Phys. Rev. Lett. 88, 077402 (2002) [CrossRef] [PubMed]
  9. T. Itoh, K. Hashimoto, and Y. Ozaki, �??Polarization dependences of surface plasmon bands and surface-enhanced Raman bands of single Ag nanoparticles,�?? Appl. Phys. Lett. 83, 2274-2276 (2003) [CrossRef]
  10. C. Sonnichsen, B. M. Reinhard, J. Liphardt and A. P. Alivisatos, �??A molecular ruler based on plasmon coupling of single gold and silver nanoparticles,�?? Nat. Biotechnol. 23, 741-745 (2005)

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