OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 11 — May. 24, 2010
  • pp: 11335–11346
« Show journal navigation

Enhancing fluorescence of quantum dots by silica-coated gold nanorods under one- and two-photon excitation

Xin Li, Fu-Jen Kao, Chien-Chin Chuang, and Sailing He  »View Author Affiliations


Optics Express, Vol. 18, Issue 11, pp. 11335-11346 (2010)
http://dx.doi.org/10.1364/OE.18.011335


View Full Text Article

Acrobat PDF (2037 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Nano-composites of quantum dots (QDs) and gold nanorods (GNRs) or silica-coated GNRs (GNRs_SiO2) were synthesized. The attached GNRs modify the excitation intensity and spontaneous emission of QDs through the surface plasmonic effects. The fluorescence from QDs is enhanced and can be optimized by modifying the thickness of silica coated on GNRs, under both one- and two-photon excitations. The measurements of fluorescence intensity and lifetime demonstrate that the enhancement may be attributed to the matching of the localized surface plasmon resonance of GNR to the excitation wavelength. In addition to enhancing QD-fluorescence in QD-GNR@SiO2, GNRs also present as an effective contrast agent for bio-imaging, through light scattering and or two-photon emission, as well as for photo-thermal therapy. The composite’s multifunctional characteristics are highly valuable and to be exploited in bio-applications.

© 2010 OSA

1. Introduction

Fluorescence-based techniques have emerged as powerful methods in the field of biomedicine, and especially in bio-molecule detection and disease diagnosis [1

1. M. Bruchez Jr, M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, “Semiconductor nanocrystals as fluorescent biological labels,” Science 281(5385), 2013–2016 (1998). [CrossRef] [PubMed]

,2

2. W. C. W. Chan and S. Nie, “Quantum dot bioconjugates for ultrasensitive nonisotopic detection,” Science 281(5385), 2016–2018 (1998). [CrossRef] [PubMed]

]. Fluorescence enhancement not only is of great interest for improving bio-detective sensitivity but also constitutes an important subject in physics, chemistry, and materials science. Since the pioneering work of Purcell indicated that the lifetime of the excited state and the spontaneous emission can be modified by controlling the external nano-environment [3

3. E. M. Purcell, “Spontaneous emission probabilities at radio frequencies,” Phys. Rev. 69, 681 (1946).

], numerous studies have emerged to elucidate further the enhancement of emission when a fluorophore is combined with resonant cavities, photonic crystals and metallic structures [4

4. D. Kleppner, “Inhibited spontaneous emission,” Phys. Rev. Lett. 47(4), 233–236 (1981). [CrossRef]

,5

5. E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58(20), 2059–2062 (1987). [CrossRef] [PubMed]

]. Metallic structures, which possess particular surface plasmon properties, have been applied to enhance fluorescence from adjacent fluorophores [6

6. Z. Yang, W. H. Ni, X. S. Kou, S. Z. Zhang, Z. H. Sun, L. D. Sun, J. F. Wang, and C. H. Yan, “Incorporation of Gold Nanorods and Their Enhancement of Fluorescence in Mesostructured Silica Thin Films,” J. Phys. Chem. C 112, 18895–188903 (2008).

18

18. V. K. Komarala, Y. P. Rakovich, A. L. Bradley, S. J. Byrne, Y. K. Gun’ko, N. Gaponik, and A. Eychmüller, “Off-resonance surface plasmon enhanced spontaneous emission from CdTe quantum dots,” Appl. Phys. Lett. 89(25), 253118 (2006). [CrossRef]

]. The surface plasmon on metallic nanoparticles is modified in a manner that depends on the sizes and shapes of such particles, as predicted by Mie theory [19

19. H. C. Van de Hulst, “Light scattering by small particles,” Wiley-Interscience, New York (1957).

]. This unique characteristic offers a convenient means of generating insights on surface plasmon-induced fluorescence enhancement by modifying the surface plasmon properties by shaping nanoparticles.

In this work, gold nanorods (GNRs) are used as the enhancing metallic nanoparticles to study their effects on the emission of adjacent quantum dots (QDs). A GNR has two localized surface plasmon resonance (LSPR) extinction (longitudinal and transverse) bands. The longitudinal LSPR band can be tuned from visible to near-infrared by adjusting the rod’s aspect ratio (width to length) and is much stronger than the LSPR band of nanosphere structures [20

20. S. Link, M. B. Mohamed, and M. A. El-Sayed, “Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant,” J. Phys. Chem. B 103(16), 3073–3077 (1999). [CrossRef]

]. The strong LSPR band results in an enhanced electromagnetic field at the surface of the nanoparticle. This unique property makes GNRs excellent candidates for studying surface-enhanced Raman scattering [21

21. B. Nikoobakht and M. A. El-Sayed, “Surface-enhanced Raman scattering studies on aggregated gold nanorods,” J. Phys. Chem. A 107(18), 3372–3378 (2003). [CrossRef]

], optical antenna, and fluorescence enhancement [6

6. Z. Yang, W. H. Ni, X. S. Kou, S. Z. Zhang, Z. H. Sun, L. D. Sun, J. F. Wang, and C. H. Yan, “Incorporation of Gold Nanorods and Their Enhancement of Fluorescence in Mesostructured Silica Thin Films,” J. Phys. Chem. C 112, 18895–188903 (2008).

,7

7. R. Bardhan, N. K. Grady, J. R. Cole, A. Joshi, and N. J. Halas, “Fluorescence enhancement by Au nanostructures: nanoshells and nanorods,” ACS Nano 3(3), 744–752 (2009). [CrossRef] [PubMed]

]. GNRs also present great potential in bio-applications, because of their favorable properties for scattering and absorption [22

22. X. Li, J. Qian, and S. He, “Impact of the self-assembly of multilayer polyelectrolyte functionalized gold nanorods and its application to biosensing,” Nanotechnology 19(35), 355501 (2008). [CrossRef] [PubMed]

24

24. X. Huang, I. H. El-Sayed, W. Qian, and M. A. El-Sayed, “Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods,” J. Am. Chem. Soc. 128(6), 2115–2120 (2006). [CrossRef] [PubMed]

]. Pronounced two-photon absorption and luminescence from GNRs have also been observed. These properties are exploited very effectively in cellular imaging [25

25. N. J. Durr, T. Larson, D. K. Smith, B. A. Korgel, K. Sokolov, and A. Ben-Yakar, “Two-photon luminescence imaging of cancer cells using molecularly targeted gold nanorods,” Nano Lett. 7(4), 941–945 (2007). [CrossRef] [PubMed]

,26

26. X. Qu, J. Wang, Z. Zhang, N. Koop, R. Rahmanzadeh, and G. Hüttmann, “Imaging of cancer cells by multiphoton microscopy using gold nanoparticles and fluorescent dyes,” J. Biomed. Opt. 13(3), 031217 (2008). [CrossRef] [PubMed]

] and optical recording [27

27. P. Zijlstra, J. W. M. Chon, and M. Gu, “Five-dimensional optical recording mediated by surface plasmons in gold nanorods,” Nature 459(7245), 410–413 (2009). [CrossRef] [PubMed]

].

In bio-imaging applications, the large surface area of GNR-composites facilitates surface functionalization for organic or other conjugations. In addition to strengthening fluorescence from GNRs_SiO2-combined QDs, GNRs and GNRs_SiO2 also strongly scatter red light [38

38. Q. Q. Zhan, J. Qian, X. Li, and S. He, “A study of mesoporous silica-encapsulated gold nanorods as enhanced light scattering probes for cancer cell imaging,” Nanotechnology 21(5), 055704 (2010). [CrossRef]

,41

41. R. Hu, K. T. Yong, I. Roy, H. Ding, S. He, and P. N. Prasad, “Metallic Nanostructures as Localized Plasmon Resonance Enhanced Scattering Probes for Multiplex Dark-Field Targeted Imaging of Cancer Cells,” J. Phys. Chem. C 113(7), 2676–2684 (2009). [CrossRef]

], unlike cells in dark-field imaging, which scatter white-blue light. Additionally, under two-photon excitation, GNRs emit bright fluorescence with a very short lifetime, which differs from longer lifetime of QD-emission. The strong absorption of GNRs may be applied to heat the composites in cells for photo-thermal therapy in a 3D, highly spatially localized manner. Multifunctional properties make QD-GNR_SiO2 composites effective materials for bio-applications under a broad range of applications settings: one-, two-photon and dark-field imaging, as well as the effect of photo-thermal therapy.

2. Experimental section

2.1 Materials

Cetyltrimethylammonium bromide (CTAB), chloroauric acid (HAuCl4·3H2O), sodium borohydride (NaBH4), silver nitrate (AgNO3), ascorbic acid, anhydrous ethanol and ammonia aqueous were purchased from Sinopharm Chemical Reagent Co., Ltd.. Tetraethylorthosilicate (TEOS) and Dulbecco’s Modified Eagle’s medium (DMEM) were obtained from Sigma-Aldrich. Carboxyl capped CdSe QDs (emission peak 605 nm) were purchased from Invitrogen, Inc. The antibody anti-CEA8 (anti-CEAcam8/CD67) was purchased from Beijing Biosynthesis Biotechnology Co., Ltd.. Deionized (DI) water was used in all experimental steps.

2.2 Synthesis of GNR and GNR_SiO2

To synthesize GNRs with different LSPR peaks, gold nanoparticle seeds were firstly prepared by adding 0.6 ml 0.01 M ice-cold sodium borohydride to a 10 ml stirred solution of 0.1 M CTAB and 0.25 mM chloroauric acid. 80 mM 0.185 mL, 0.18 mL and 0.15 mL ascorbic acid were added into three bottles of 20 mL 0.04 mM, 0.128 mM and 0.14 mM aqueous silver nitrate, and mixed with 0.1 M CTAB and 0.5 mM chloroauric acid, to reduce Au3+ to Au+ and form three growth solutions. After the color of the solutions had turned from orange to colorless, 0.024 mL of gold seed solution was injected into each of the three growth solutions to grow the GNRs with LSPR peaks at 600 nm, 650 nm and 730 nm. To remove excess CTAB in the GNR-solution, centrifugation was carried out at 9,000 rpm for 15 min after the GNRs had grown for 12h. The concentrations of GNRs in the solution are estimated and simulated with reference to their sizes and absorbance optical densities [42

42. B. Nikoobakht, J. Wang, and M. A. El-Sayed, “Surface-enhanced Raman scattering of molecules adsorbed on gold nanorods: off-surface plasmon resonance condition,” Chem. Phys. Lett. 366(1-2), 17–23 (2002). [CrossRef]

]. 1 mL and 1.5 mL of 10 mM TEOS ethanol solutions were added to 8 mL of 10 nM aqueous GNRs at a pH of 9.0 (adjusted by adding aqueous ammonia) to synthesize 8 nm- and 13 nm-thick silica coatings on the GNRs. The reaction lasted for six hours at room temperature. Excess TEOS was removed by centrifuging at 6,500 rpm for 15 min.

2.3 Conjugation of QDs and antibodies with GNR and GNR_SiO2

2.4 Incubating cells with nanoparticles

Cervical cancer HeLa cells were cultured with DMEM supplemented with 10% fetal bovine serum in a humidified incubator at 37°Cunder 5% CO2. After two days of cell differentiation and proliferation, 50 μL sample-solutions with a particular QD-concentration (20 nM) were introduced into the cells. The endocytic process was performed for two hours. After the nanoparticles had been incubated, the cells on cover slips were rinsed several times using PBS buffer (pH 7.4) and then fixed with DMEM again to be directly observed under a microscope.

2.5 Optical experiments

All samples that were used in the optical experiments were prepared by dispersing 10 μL drops of different sample-solutions and the same concentration of QDs (20 nM) onto clean glass object slides with standard cover-slips. The FLIM system comprises a titanium-sapphire laser (Mira 900, Coherent), a diode laser (LDH-P-C-470, Picoquant), an avalanche photodiode (APD) detector, a scanning confocal microscope (FV-300, Olympus), a spectrometer, and a PC-based time correlated single-photon counting (TCSPC) system (shown in Fig. 1
Fig. 1 Schematic diagram of the FLIM system
). In the single-photon experiments, a diode laser with a wavelength of 470 nm was turned on with an excitation power of 5-500 μW and 480 nm long-pass filters were placed before the detector and the spectrometer. In the two-photon experiments, an fs laser with a wavelength of 750 nm was turned on with a pulse frequency of 76 MHz and a pulse duration of 120 fs. The power used for the two-photon excitation was 10 mW in the experiments without cells, 4 mW in the cell imaging experiments and 6 mW in cell photo-thermal therapy. 680 nm short-pass filters were placed before the detector and the spectrometer; a 600 nm bandpass filter with a bandwidth of 40 nm was introduced before the short-pass filter to eliminate auto-fluorescence in the cell experiments. A 60 × /1.42 oil objective was used in the experiments without cells, whereas both the 20 × /0.4 and the 60 × /1.42 oil objectives were used in the cell experiments.The spectrum and lifetime of fluorescence were measured using the spectrometer and an APD detector, respectively, for each scanning pixel. Lifetime was analyzed using software (SymphoTime, PicoQuant Inc.) based on the measurements of photon count rate and the arrival times made using the APD detector and TCSPC system. The time-resolved fluorescence decay curves were fitted single exponential decay curves and used to calculate the lifetime in single-sample experiments. Double exponential decay curve were fitted to the results of QD-GNR-composites experiments. All measurements were made several times to yield average data. The dark field images were obtained using a phase contrast condenser with a numerical aperture between 0.9 and 1.2 by collecting the strongly scattered light.

2.6 Characterization

A Shimadzu 2550 UV-vis scanning spectrophotometer was used to measure the extinction spectra of GNRs and GNR_SiO2 within 450 nm-800 nm wavelength region. A JEOL JEM-1200EX transmission electron microscope was used to record TEM imaging for the structures of the nanoparticles.

3. Results and discussion

Figure 2(a)
Fig. 2 (a) UV-visible absorbance spectra of GNRs with LSPR peaks at 600, 650 and 730 nm are shown as solid curves. UV-visible absorbance spectra of GNRs that were coated with 13 nm-thick silica with LSPR peaks at 615 nm, 665 nm, and 750 nm are shown as dashed curves. The emission spectrum of QDs with the peak at 605 nm is shown as a dotted curve. (b)-(d) TEM images of 650 nm-GNRs, 650 nm-GNRs coated with 8 nm silica and 13 nm silica. (e)-(g) TEM images of QDs conjugated with 650 nm-GNRs, 650 nm-GNRs coated with 8 nm silica and 13 nm silica.
shows the three LSPR spectral bands of synthesized GNRs as solid curves, with peaks at 600 nm, 650 nm and 730 nm. The thickness of silica coating on GNRs was controlled using various concentrations of TEOS [38

38. Q. Q. Zhan, J. Qian, X. Li, and S. He, “A study of mesoporous silica-encapsulated gold nanorods as enhanced light scattering probes for cancer cell imaging,” Nanotechnology 21(5), 055704 (2010). [CrossRef]

,43

43. C. Wang, Z. Ma, T. Wang, and Z. Su, “Synthesis, assembly, and biofunctionalization of silica-coated gold nanorods for colorimetric biosensing,” Adv. Funct. Mater. 16(13), 1673–1678 (2006). [CrossRef]

]. Two coatings, with thicknesses of 8 nm and 13 nm, were synthesized on the surface of GNRs [TEM images in Figs. 2(c), 2(d)]. Coating with silica red-shifted the LSPR peak of GNRs_SiO2 from that of the uncoated GNR, by increasing the local refractive index on GNRs. The dashed curves in Fig. 2(a) show a red-shift in the LSPR spectra of about 15-20 nm, corresponding to a coating thickness of 13 nm, for the three GNRs of different aspect ratios [38

38. Q. Q. Zhan, J. Qian, X. Li, and S. He, “A study of mesoporous silica-encapsulated gold nanorods as enhanced light scattering probes for cancer cell imaging,” Nanotechnology 21(5), 055704 (2010). [CrossRef]

]. Carboxyl-functionalized CdSe QDs with an emission peak at 605 nm [dotted curve in Fig. 2(a)] were conjugated on the surface of the GNRs and GNRs_SiO2 in coatings of two thicknesses (8 and 13 nm) via the electrostatic interaction. Considering the thickness of carboxyl on QD and CTAB on GNR, the separation between QD and GNR was estimated approximately 3 nm [32

32. X. Li, J. Qian, L. Jiang, and S. He, “Fluorescence quenching of quantum dots by gold nanorods and its application to DNA detection,” Appl. Phys. Lett. 94(6), 063111 (2009). [CrossRef]

]. From the TEM images in Figs. 2(f) and 2(g), the separations between QD and GNRs of various silica-coating-thicknesses are approximately 10 nm and 15 nm, respectively.

Although the excitation wavelength (470 nm) does not match the LSPR peak of 650-GNR, lower enhancement of excitation intensity is still found because GNR also has a weak SP extinction at the off-resonance wavelength- 470 nm as shown in Fig. 2(a). Increasing the coating thickness does not affect the fluorescence lifetime but does reduce the excitation enhancement. Herein, the maximum enhancement is achieved when the separation is around 15 nm or a little less. At this distance, the radiative and nonradiative decay rates are minimally changed from their original values. The excitation enhancement caused by the optical antenna- GNRs dominates the enhancement of fluorescence of adjacent QDs.

Two-photon excitation at a wavelength of 750 nm was adopted to examine further the mechanism of excitation enhancement. Prominent emission from GNRs with a spectral range of about 400 nm to 600 nm was also observed under two-photon excitation, which complicated the study of QD-enhancement. Such emission has a very short lifetime, which cannot be easily differentiated from the system impulse response function (IRF, less than 0.2 ns) [Fig. 4(A)
Fig. 4 (A) Normalized fluorescence decay curves of QDs, 650 nm-GNRs, QDs-650 nm-GNRs and QDs-665 nm-GNR_SiO2 under two-photon excitation at 750 nm; inset shows magnified fitting decay curves. (B) Emission spectra of QD-650 nm-GNRs, 650 nm-GNRs to which are added QD-emission spectra, QD-665 nm-GNR_SiO2, and QD-750 nm-GNR_SiO2 (from a to d) under two-photon excitation at 750 nm.
]. The QD-emission from QD-GNR composites can hardly be seen [Fig. 4(B)]. This means the fluorescence of QDs is also quenched under two-photon excitation. The FRET-like quenching effect, which is induced by the modification of the decay rate, occurs in the emission process and is independent of the type of excitation. Additionally, the emission from GNRs is a completely different process, which can only be excited by multi-photon absorption and therefore may not be influenced by the energy transfer from QDs to GNRs. The possible FRET from GNRs to QDs is also taken into account. However, no appreciable change (either in intensity or lifetime) was observed in the GNR-emission from QD-GNR composites by comparison with GNRs alone (data not shown). The fast decay rate of GNR-emission differs markedly from the slow FRET decay rate [47

47. A. R. Clapp, I. L. Medintz, B. R. Fisher, G. P. Anderson, and H. Mattoussi, “Can luminescent quantum dots be efficient energy acceptors with organic dye donors?” J. Am. Chem. Soc. 127(4), 1242–1250 (2005). [CrossRef] [PubMed]

]. Apparently, the FRET (from GNRs to QDs is negligible. The modification of emission of QDs by GNRs and the self-emission of GNRs can be regarded as two unrelated processes in this experiment. The decay curve of QD-GNR emission comprises two distinct parts -fast decay associated with GNR-emission and slow decay (the tail in the decay curve) associated with QD-emission [Fig. 4(A)]. The fitted curve for QDs (fitting curve in the tail part) in QD-GNR composites [inset in Fig. 4(A)] reveals faster decay and a shorter lifetime than the emission decay curve of QDs without GNRs shows. The results are consistent with the measurements under one-photon excitation, in which the increase in nonradiative decay rate shortens the fluorescence lifetime. For QD-GNR_SiO2 composites, the fitting curve for QDs (the tail part) is similar to that for the QDs without GNRs [inset in Fig. 4(A)]. Hence the changes in lifetime of QD-emission from QD-GNR_SiO2 are too small to influence the emission intensity. Fluorescence enhancements are made in all three QD-GNRs_SiO2 composites. 615 nm-GNR_SiO2 and 665 nm-GNR_SiO2 conjugated QDs exhibit the same fluorescence enhancement (data not shown). From Fig. 4(B), the 750 nm- GNR_SiO2 greatly increases QD-emission, such that the intensity of the highest emission peak at 605 nm is several times of the intensity of emission from QDs with unconjugated GNRs. This remarkable increase in excitation is attributed to the matching resonance of the excitation wavelength with the LSPR peak at 750 nm. A higher GNR-emission intensity is also observed when the GNR-LSPR is matched with the excitation peak [48

48. O. P. Varnavski, M. B. Mohamed, M. A. El-Sayed, and T. Goodson, “Relative enhancement of ultrafast emission in gold nanorods,” J. Phys. Chem. B 107(14), 3101–3104 (2003). [CrossRef]

].

The intensity and lifetime measurements of the fluorescence from QDs that are combined with GNRs and GNRs_SiO2 with different LSPR peaks demonstrated that excitation enhancement dominates the increase in emission, and the passive quenching modifies the decay rate when separation between QDs and GNRs is small. The enhancement factor is maximal when the separation is around 15 nm, at which the change in the lifetime of QD-emission is very small. These findings demonstrate that reducing modifications in the decay rate is critical to maximizing the enhancement. This fact may be attributable to the fact that the absorption dominates in GNR-LSPR extinction (just with a smaller scattering cross section) [49

49. P. K. Jain, K. S. Lee, I. H. El-Sayed, and M. A. El-Sayed, “Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine,” J. Phys. Chem. B 110(14), 7238–7248 (2006). [CrossRef] [PubMed]

], increasing the nonradiative decay rate, such that it dominates the overall change in the decay rate, even when the change is reduced by increasing the separation. GNRs therefore do not help to promote the emission of adjacent fluorophores by modifying their decay rates, as determined comparison with other metallic nanostructures such as nanoshells [7

7. R. Bardhan, N. K. Grady, J. R. Cole, A. Joshi, and N. J. Halas, “Fluorescence enhancement by Au nanostructures: nanoshells and nanorods,” ACS Nano 3(3), 744–752 (2009). [CrossRef] [PubMed]

]. However, the magnified local electromagnetic field close to the GNRs causes the increase in excitation intensity to dominate the fluorescence enhancement when the excitation wavelength is matched with the LSPR spectrum. Accordingly, in the QD-GNR_SiO2 composites, the fluorescence of QDs is strongly enhanced by the excitation enhancement. These QD-GNR_SiO2 composites with enhanced QD-emission are applied for bio-imaging.

As Scheme 1
Scheme 1 GNR, silica coated on GNR using TEOS, and both GNR and GNR_SiO2 conjugated with QDs and anti-CEAcam8.
shows, GNRs and GNRs_SiO2 are conjugated with both QDs and anti-CEA8 via electrostatic interaction. HeLa cells with over-expressed CEA8 can take up these composites efficiently. Figure 5
Fig. 5 Images made by transmitted light (left), one-photon (middle) and two-photon FLIM images (right) of HeLa cells treated with (a)-(c) QDs and anti-CEA8, (d)-(f) QD-750 nm-GNR composites functionalized with anti-CEA8, (g)-(i) QD-GNR_SiO2 composites functionalized with anti-CEA8. Color bar shows different colors, used in the images to represent varying fluorescence lifetime.
displays FLIM images of HeLa cells that have been treated with these composites. A control experiment using QDs mixed with anti-CEA8 is performed, as shown in Figs. 5(a), 5(b) and 5(c). The carboxyl group on the QDs prevents the negatively charged anti-CEA8 from being conjugated with the QDs. QDs cannot label the HeLa cells without efficient uptake, and so no fluorescence is observed upon one- or two-photon excitation when only QDs are mixed with the antibody. The advantages of surface functionalization make GNRs and GNRs_SiO2 convenient vehicles for bio-applications, including cell uptake, for delivering small molecules [50

50. C. C. Chen, Y. P. Lin, C. W. Wang, H. C. Tzeng, C. H. Wu, Y. C. Chen, C. P. Chen, L. C. Chen, and Y. C. Wu, “DNA-gold nanorod conjugates for remote control of localized gene expression by near infrared irradiation,” J. Am. Chem. Soc. 128(11), 3709–3715 (2006). [CrossRef] [PubMed]

] and particles. Conjugated with GNRs and GNRs_SiO2, QD-composites are efficiently functionalized with anti-CEA8 and can be easily taken up by cancer cells. For QD-GNR composites, GNRs quench the fluorescence of QDs. Therefore, Figs. 5(e) and 5(f) present only weak fluorescence with a long lifetime (red signal in the figure). Figure 5(f) displays two-photon emission of the GNRs, which is indicated on the cells. Figure 5(h) displays enhanced fluorescence of QDs in QD-GNR_SiO2 composites under one-photon excitation; Fig. 5(i) displays enhanced fluorescence under two-photon excitation. Two-photon emission of GNRs_SiO2, with a green color and short lifetime, is also observed in Fig. 5(i) at the same positions as the QD-emission. This finding demonstrates that the QD-GNR_SiO2 emits both GNR-emission and QD-emission under two-photon excitation. GNR_SiO2 drives the QDs onto cells and enhances QD-emission under both one- and two-photon excitation; it can also scatter light as revealed by dark-field imaging and exploitable in photo-thermal therapy in bio- applications.

Figure 6(a)
Fig. 6 Dark-field images (left) and one-photon fluorescence images (right) of HeLa cells treated with (a),(b) QD-GNR_SiO2 composites and (c),(d) QD-GNR composites that had been functionalized with anti-CEA8.
shows the dark-field image of HeLa cells that were treated with QD-GNR_SiO2. Red spots of light scattered by GNRs_SiO2 in the cells (which themselves scatter white-blue light) are seen. Figure 6(b) shows the fluorescence image in the same field as Fig. 6(a) shows. QD-emission is enhanced where the scattering signals of GNRs_SiO2 are observed. This spatial matching indicates that both red light scattering and fluorescence arise from QD-GNR_SiO2 in the cells. A control experiment using QD-GNR composites is carried out. Dark-field imaging of the QD-GNR in the cells is the same performance as that of QD-GNR_SiO2 [Fig. 6(c)], because the scattering properties of GNRs and GNRs_SiO2 are very similar. However, for QD-GNR, QD-emission is not enhanced but quenched, so the fluorescence image in Fig. 6(d) shows hardly any emission. Photo-thermal therapy is another bio-application of QD-GNR_SiO2. GNRs generate a very large amount of localized heat to kill tumor cells as they absorb strongly when they are excited at the wavelength of the LSPR peak. The results of thermal treatment with rods will be shown elsewhere. Besides its usefulness in diagnosing cancer using various imaging methods, QD-GNR_SiO2 has promising clinical treatment applications.

4. Conclusions

In conclusion, this work demonstrates the enhancement of fluorescence from QDs by adjacent GNRs. The strong absorption of GNRs is such that the modification of decay rate by GNRs to dominate the quenching of QD-emission. Excitation intensity is increased near the GNRs by the optical antenna effect because of the presence of a magnified local electromagnetic field. QD-emission is maximally enhanced when the QD-GNR separation is around 15 nm, balancing the reduction in the quenching effect with the excitation enhancement, and when the excitation wavelength is matched with the GNR-LSPR (maximizing the excitation enhancement). The QD-GNR_SiO2 composites exhibit enhanced QD-emission under both one- and two-photon excitation. This composite promotes surface functionalization and is useful in the diagnosis of cancer cells by a wide range of imaging methods. Photo-thermal therapy is another important bio-application of this multifunctional hybrid composite.

Acknowledgments

The authors would like to thank the Swedish Foundation for Strategic Research (SSF), the National Science Council of the Republic of China, Taiwan (NSC 97-3112-B-010-006, NSC 96-2112-M-010-001, and NSC98-2112-M-010-001-MY3), as well as the Ministry of Education of the Republic of China, Taiwan under the “Aim for Top University“ project, and Dr. Vladimir Ghukasyan for assisting in preparation of the cell culture. Ted Knoy is appreciated for his editorial assistance.

References and links

1.

M. Bruchez Jr, M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, “Semiconductor nanocrystals as fluorescent biological labels,” Science 281(5385), 2013–2016 (1998). [CrossRef] [PubMed]

2.

W. C. W. Chan and S. Nie, “Quantum dot bioconjugates for ultrasensitive nonisotopic detection,” Science 281(5385), 2016–2018 (1998). [CrossRef] [PubMed]

3.

E. M. Purcell, “Spontaneous emission probabilities at radio frequencies,” Phys. Rev. 69, 681 (1946).

4.

D. Kleppner, “Inhibited spontaneous emission,” Phys. Rev. Lett. 47(4), 233–236 (1981). [CrossRef]

5.

E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58(20), 2059–2062 (1987). [CrossRef] [PubMed]

6.

Z. Yang, W. H. Ni, X. S. Kou, S. Z. Zhang, Z. H. Sun, L. D. Sun, J. F. Wang, and C. H. Yan, “Incorporation of Gold Nanorods and Their Enhancement of Fluorescence in Mesostructured Silica Thin Films,” J. Phys. Chem. C 112, 18895–188903 (2008).

7.

R. Bardhan, N. K. Grady, J. R. Cole, A. Joshi, and N. J. Halas, “Fluorescence enhancement by Au nanostructures: nanoshells and nanorods,” ACS Nano 3(3), 744–752 (2009). [CrossRef] [PubMed]

8.

Y. P. Hsieh, C. T. Liang, Y. F. Chen, C. W. Lai, and P. T. Chou, “Mechanism of giant enhancement of light emission from Au/CdSe nanocomposites,” Nanotechnology 18(41), 415707 (2007). [CrossRef]

9.

Y. S. Chi, H. R. Byon, B. S. Lee, B. Kong, H. C. Choi, and I. S. Choi, “Polymeric Rulers: Distance-Dependent Emission Behaviors of Fluorophores on Flat Gold Surfaces and Bioassay Platforms Using Plasmonic Fluorescence Enhancement,” Adv. Funct. Mater. 18(21), 3395–3402 (2008). [CrossRef]

10.

O. Kulakovich, N. Strekal, A. Yaroshevich, S. Maskevich, S. Gaponenko, I. Nabiev, U. Woggon, and M. Artemyev, “Enhanced luminescence of CdSe quantum dots on gold colloids,” Nano Lett. 2(12), 1449–1452 (2002). [CrossRef]

11.

P. Anger, P. Bharadwaj, and L. Novotny, “Enhancement and quenching of single-molecule fluorescence,” Phys. Rev. Lett. 96(11), 113002 (2006). [CrossRef] [PubMed]

12.

P. Bharadwaj and L. Novotny, “Spectral dependence of single molecule fluorescence enhancement,” Opt. Express 15(21), 14266–14274 (2007). [CrossRef] [PubMed]

13.

J. Zhang and J. R. Lakowicz, “Metal-enhanced fluorescence of an organic fluorophore using gold particles,” Opt. Express 15(5), 2598–2606 (2007). [CrossRef] [PubMed]

14.

J. C. Ostrowski, A. Mikhailovsky, D. A. Bussian, M. A. Summers, S. K. Buratto, and G. C. Bazan, “Enhancement of phosphorescence by surface-plasmon resonances in colloidal metal nanoparticles: The role of aggregates,” Adv. Funct. Mater. 16(9), 1221–1227 (2006). [CrossRef]

15.

F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, “Plasmonic enhancement of molecular fluorescence,” Nano Lett. 7(2), 496–501 (2007). [CrossRef] [PubMed]

16.

S. Kühn, U. Håkanson, L. Rogobete, and V. Sandoghdar, “Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna,” Phys. Rev. Lett. 97(1), 017402 (2006). [CrossRef] [PubMed]

17.

M. Thomas, J. J. Greffet, R. Carminati, and J. R. Arias-Gonzalez, “Single-molecule spontaneous emission close to absorbing nanostructures,” Appl. Phys. Lett. 85(17), 3863 (2004). [CrossRef]

18.

V. K. Komarala, Y. P. Rakovich, A. L. Bradley, S. J. Byrne, Y. K. Gun’ko, N. Gaponik, and A. Eychmüller, “Off-resonance surface plasmon enhanced spontaneous emission from CdTe quantum dots,” Appl. Phys. Lett. 89(25), 253118 (2006). [CrossRef]

19.

H. C. Van de Hulst, “Light scattering by small particles,” Wiley-Interscience, New York (1957).

20.

S. Link, M. B. Mohamed, and M. A. El-Sayed, “Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant,” J. Phys. Chem. B 103(16), 3073–3077 (1999). [CrossRef]

21.

B. Nikoobakht and M. A. El-Sayed, “Surface-enhanced Raman scattering studies on aggregated gold nanorods,” J. Phys. Chem. A 107(18), 3372–3378 (2003). [CrossRef]

22.

X. Li, J. Qian, and S. He, “Impact of the self-assembly of multilayer polyelectrolyte functionalized gold nanorods and its application to biosensing,” Nanotechnology 19(35), 355501 (2008). [CrossRef] [PubMed]

23.

R. S. Norman, J. W. Stone, A. Gole, C. J. Murphy, and T. L. Sabo-Attwood, “Targeted photothermal lysis of the pathogenic bacteria, Pseudomonas aeruginosa, with gold nanorods,” Nano Lett. 8(1), 302–306 (2008). [CrossRef]

24.

X. Huang, I. H. El-Sayed, W. Qian, and M. A. El-Sayed, “Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods,” J. Am. Chem. Soc. 128(6), 2115–2120 (2006). [CrossRef] [PubMed]

25.

N. J. Durr, T. Larson, D. K. Smith, B. A. Korgel, K. Sokolov, and A. Ben-Yakar, “Two-photon luminescence imaging of cancer cells using molecularly targeted gold nanorods,” Nano Lett. 7(4), 941–945 (2007). [CrossRef] [PubMed]

26.

X. Qu, J. Wang, Z. Zhang, N. Koop, R. Rahmanzadeh, and G. Hüttmann, “Imaging of cancer cells by multiphoton microscopy using gold nanoparticles and fluorescent dyes,” J. Biomed. Opt. 13(3), 031217 (2008). [CrossRef] [PubMed]

27.

P. Zijlstra, J. W. M. Chon, and M. Gu, “Five-dimensional optical recording mediated by surface plasmons in gold nanorods,” Nature 459(7245), 410–413 (2009). [CrossRef] [PubMed]

28.

Y. Chen, K. Munechika, and D. S. Ginger, “Dependence of fluorescence intensity on the spectral overlap between fluorophores and plasmon resonant single silver nanoparticles,” Nano Lett. 7(3), 690–696 (2007). [CrossRef] [PubMed]

29.

Y. Chen, K. Munechika, I. Jen-La Plante, A. M. Munro, S. E. Skrabalak, Y. Xia, and D. S. Ginger, “Excitation enhancement of CdSe quantum dots by single metal nanoparticles,” Appl. Phys. Lett. 93(5), 053106 (2008). [CrossRef]

30.

E. Dulkeith, A. C. Morteani, T. Niedereichholz, T. A. Klar, J. Feldmann, S. A. Levi, F. C. J. M. van Veggel, D. N. Reinhoudt, M. Möller, and D. I. Gittins, “Fluorescence quenching of dye molecules near gold nanoparticles: radiative and nonradiative effects,” Phys. Rev. Lett. 89(20), 203002 (2002). [CrossRef] [PubMed]

31.

T. Soller, M. Ringler, M. Wunderlich, T. A. Klar, J. Feldmann, H. P. Josel, Y. Markert, A. Nichtl, and K. Kürzinger, “Radiative and nonradiative rates of phosphors attached to gold nanoparticles,” Nano Lett. 7(7), 1941–1946 (2007). [CrossRef]

32.

X. Li, J. Qian, L. Jiang, and S. He, “Fluorescence quenching of quantum dots by gold nanorods and its application to DNA detection,” Appl. Phys. Lett. 94(6), 063111 (2009). [CrossRef]

33.

C. S. Yun, A. Javier, T. Jennings, M. Fisher, S. Hira, S. Peterson, B. Hopkins, N. O. Reich, and G. F. Strouse, “Nanometal surface energy transfer in optical rulers, breaking the FRET barrier,” J. Am. Chem. Soc. 127(9), 3115–3119 (2005). [CrossRef] [PubMed]

34.

J. Lee, A. O. Govorov, J. Dulka, and N. A. Kotov, “Bioconjugates of CdTe nanowires and Au nanoparticles: Plasmon-excition interactions, luminescence enhancement, and collective effects,” Nano Lett. 4(12), 2323–2330 (2004). [CrossRef]

35.

A. O. Govorov, J. Lee, and N. A. Kotov, “Theory of plasmon-enhanced Forster energy transfer in optically excited semiconductor and metal nanoparitcles,” Phys. Rev. B 76(12), 125308 (2007). [CrossRef]

36.

G. L. Liu, Y. T. Long, Y. Choi, T. Kang, and L. P. Lee, “Quantized plasmon quenching dips nanospectroscopy via plasmon resonance energy transfer,” Nat. Methods 4(12), 1015–1017 (2007). [CrossRef] [PubMed]

37.

P. Viste, J. Plain, R. Jaffiol, A. Vial, P. M. Adam, and P. Royer, “Enhancement and quenching regimes in metal-semiconductor hybrid optical nanosources,” ACS Nano 4(2), 759–764 (2010). [CrossRef] [PubMed]

38.

Q. Q. Zhan, J. Qian, X. Li, and S. He, “A study of mesoporous silica-encapsulated gold nanorods as enhanced light scattering probes for cancer cell imaging,” Nanotechnology 21(5), 055704 (2010). [CrossRef]

39.

V. Ghukasyan, Y. Y. Hsu, S. H. Kung, and F. J. Kao, “Application of fluorescence resonance energy transfer resolved by fluorescence lifetime imaging microscopy for the detection of enterovirus 71 infection in cells,” J. Biomed. Opt. 12(2), 024016 (2007). [CrossRef] [PubMed]

40.

V. Ghukasyan and F. J. Kao, “Monitoring Cellular Metabolism with Fluorescence Lifetime of Reduced Nicotinamide Adenine Dinucleotide,” J. Phys. Chem. C 113(27), 11532–11540 (2009). [CrossRef]

41.

R. Hu, K. T. Yong, I. Roy, H. Ding, S. He, and P. N. Prasad, “Metallic Nanostructures as Localized Plasmon Resonance Enhanced Scattering Probes for Multiplex Dark-Field Targeted Imaging of Cancer Cells,” J. Phys. Chem. C 113(7), 2676–2684 (2009). [CrossRef]

42.

B. Nikoobakht, J. Wang, and M. A. El-Sayed, “Surface-enhanced Raman scattering of molecules adsorbed on gold nanorods: off-surface plasmon resonance condition,” Chem. Phys. Lett. 366(1-2), 17–23 (2002). [CrossRef]

43.

C. Wang, Z. Ma, T. Wang, and Z. Su, “Synthesis, assembly, and biofunctionalization of silica-coated gold nanorods for colorimetric biosensing,” Adv. Funct. Mater. 16(13), 1673–1678 (2006). [CrossRef]

44.

J. Wenger, D. Gérard, J. Dintinger, O. Mahboub, N. Bonod, E. Popov, T. W. Ebbesen, and H. Rigneault, “Emission and excitation contributions to enhanced single molecule fluorescence by gold nanometric apertures,” Opt. Express 16(5), 3008–3020 (2008). [CrossRef] [PubMed]

45.

T. H. Taminiau, F. D. Stefani, and N. F. van Hulst, “Single emitters coupled to plasmonic nano-antennas: angular emission and collection efficiency,” N. J. Phys. 10(10), 105005 (2008). [CrossRef]

46.

S. He, Y. Cui, Y. Ye, P. Zhang, and Y. Jin, “Optical nano-antennas and metamaterials,” Mater. Today 12(12), 16–24 (2009). [CrossRef]

47.

A. R. Clapp, I. L. Medintz, B. R. Fisher, G. P. Anderson, and H. Mattoussi, “Can luminescent quantum dots be efficient energy acceptors with organic dye donors?” J. Am. Chem. Soc. 127(4), 1242–1250 (2005). [CrossRef] [PubMed]

48.

O. P. Varnavski, M. B. Mohamed, M. A. El-Sayed, and T. Goodson, “Relative enhancement of ultrafast emission in gold nanorods,” J. Phys. Chem. B 107(14), 3101–3104 (2003). [CrossRef]

49.

P. K. Jain, K. S. Lee, I. H. El-Sayed, and M. A. El-Sayed, “Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine,” J. Phys. Chem. B 110(14), 7238–7248 (2006). [CrossRef] [PubMed]

50.

C. C. Chen, Y. P. Lin, C. W. Wang, H. C. Tzeng, C. H. Wu, Y. C. Chen, C. P. Chen, L. C. Chen, and Y. C. Wu, “DNA-gold nanorod conjugates for remote control of localized gene expression by near infrared irradiation,” J. Am. Chem. Soc. 128(11), 3709–3715 (2006). [CrossRef] [PubMed]

OCIS Codes
(170.3880) Medical optics and biotechnology : Medical and biological imaging
(170.6280) Medical optics and biotechnology : Spectroscopy, fluorescence and luminescence
(240.6680) Optics at surfaces : Surface plasmons
(260.2510) Physical optics : Fluorescence
(160.4236) Materials : Nanomaterials

ToC Category:
Materials

History
Original Manuscript: April 8, 2010
Revised Manuscript: May 9, 2010
Manuscript Accepted: May 9, 2010
Published: May 13, 2010

Virtual Issues
Vol. 5, Iss. 10 Virtual Journal for Biomedical Optics

Citation
Xin Li, Fu-Jen Kao, Chien-Chin Chuang, and Sailing He, "Enhancing fluorescence of quantum dots by silica-coated gold nanorods under one- and two-photon excitation," Opt. Express 18, 11335-11346 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-11-11335


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. M. Bruchez, M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, “Semiconductor nanocrystals as fluorescent biological labels,” Science 281(5385), 2013–2016 (1998). [CrossRef] [PubMed]
  2. W. C. W. Chan and S. Nie, “Quantum dot bioconjugates for ultrasensitive nonisotopic detection,” Science 281(5385), 2016–2018 (1998). [CrossRef] [PubMed]
  3. E. M. Purcell, “Spontaneous emission probabilities at radio frequencies,” Phys. Rev. 69, 681 (1946).
  4. D. Kleppner, “Inhibited spontaneous emission,” Phys. Rev. Lett. 47(4), 233–236 (1981). [CrossRef]
  5. E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58(20), 2059–2062 (1987). [CrossRef] [PubMed]
  6. Z. Yang, W. H. Ni, X. S. Kou, S. Z. Zhang, Z. H. Sun, L. D. Sun, J. F. Wang, and C. H. Yan, “Incorporation of Gold Nanorods and Their Enhancement of Fluorescence in Mesostructured Silica Thin Films,” J. Phys. Chem. C 112, 18895–188903 (2008).
  7. R. Bardhan, N. K. Grady, J. R. Cole, A. Joshi, and N. J. Halas, “Fluorescence enhancement by Au nanostructures: nanoshells and nanorods,” ACS Nano 3(3), 744–752 (2009). [CrossRef] [PubMed]
  8. Y. P. Hsieh, C. T. Liang, Y. F. Chen, C. W. Lai, and P. T. Chou, “Mechanism of giant enhancement of light emission from Au/CdSe nanocomposites,” Nanotechnology 18(41), 415707 (2007). [CrossRef]
  9. Y. S. Chi, H. R. Byon, B. S. Lee, B. Kong, H. C. Choi, and I. S. Choi, “Polymeric Rulers: Distance-Dependent Emission Behaviors of Fluorophores on Flat Gold Surfaces and Bioassay Platforms Using Plasmonic Fluorescence Enhancement,” Adv. Funct. Mater. 18(21), 3395–3402 (2008). [CrossRef]
  10. O. Kulakovich, N. Strekal, A. Yaroshevich, S. Maskevich, S. Gaponenko, I. Nabiev, U. Woggon, and M. Artemyev, “Enhanced luminescence of CdSe quantum dots on gold colloids,” Nano Lett. 2(12), 1449–1452 (2002). [CrossRef]
  11. P. Anger, P. Bharadwaj, and L. Novotny, “Enhancement and quenching of single-molecule fluorescence,” Phys. Rev. Lett. 96(11), 113002 (2006). [CrossRef] [PubMed]
  12. P. Bharadwaj and L. Novotny, “Spectral dependence of single molecule fluorescence enhancement,” Opt. Express 15(21), 14266–14274 (2007). [CrossRef] [PubMed]
  13. J. Zhang and J. R. Lakowicz, “Metal-enhanced fluorescence of an organic fluorophore using gold particles,” Opt. Express 15(5), 2598–2606 (2007). [CrossRef] [PubMed]
  14. J. C. Ostrowski, A. Mikhailovsky, D. A. Bussian, M. A. Summers, S. K. Buratto, and G. C. Bazan, “Enhancement of phosphorescence by surface-plasmon resonances in colloidal metal nanoparticles: The role of aggregates,” Adv. Funct. Mater. 16(9), 1221–1227 (2006). [CrossRef]
  15. F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, “Plasmonic enhancement of molecular fluorescence,” Nano Lett. 7(2), 496–501 (2007). [CrossRef] [PubMed]
  16. S. Kühn, U. Håkanson, L. Rogobete, and V. Sandoghdar, “Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna,” Phys. Rev. Lett. 97(1), 017402 (2006). [CrossRef] [PubMed]
  17. M. Thomas, J. J. Greffet, R. Carminati, and J. R. Arias-Gonzalez, “Single-molecule spontaneous emission close to absorbing nanostructures,” Appl. Phys. Lett. 85(17), 3863 (2004). [CrossRef]
  18. V. K. Komarala, Y. P. Rakovich, A. L. Bradley, S. J. Byrne, Y. K. Gun’ko, N. Gaponik, and A. Eychmüller, “Off-resonance surface plasmon enhanced spontaneous emission from CdTe quantum dots,” Appl. Phys. Lett. 89(25), 253118 (2006). [CrossRef]
  19. H. C. Van de Hulst, Light scattering by small particles, (Wiley-Interscience, New York, 1957).
  20. S. Link, M. B. Mohamed, and M. A. El-Sayed, “Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant,” J. Phys. Chem. B 103(16), 3073–3077 (1999). [CrossRef]
  21. B. Nikoobakht and M. A. El-Sayed, “Surface-enhanced Raman scattering studies on aggregated gold nanorods,” J. Phys. Chem. A 107(18), 3372–3378 (2003). [CrossRef]
  22. X. Li, J. Qian, and S. He, “Impact of the self-assembly of multilayer polyelectrolyte functionalized gold nanorods and its application to biosensing,” Nanotechnology 19(35), 355501 (2008). [CrossRef] [PubMed]
  23. R. S. Norman, J. W. Stone, A. Gole, C. J. Murphy, and T. L. Sabo-Attwood, “Targeted photothermal lysis of the pathogenic bacteria, Pseudomonas aeruginosa, with gold nanorods,” Nano Lett. 8(1), 302–306 (2008). [CrossRef]
  24. X. Huang, I. H. El-Sayed, W. Qian, and M. A. El-Sayed, “Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods,” J. Am. Chem. Soc. 128(6), 2115–2120 (2006). [CrossRef] [PubMed]
  25. N. J. Durr, T. Larson, D. K. Smith, B. A. Korgel, K. Sokolov, and A. Ben-Yakar, “Two-photon luminescence imaging of cancer cells using molecularly targeted gold nanorods,” Nano Lett. 7(4), 941–945 (2007). [CrossRef] [PubMed]
  26. X. Qu, J. Wang, Z. Zhang, N. Koop, R. Rahmanzadeh, and G. Hüttmann, “Imaging of cancer cells by multiphoton microscopy using gold nanoparticles and fluorescent dyes,” J. Biomed. Opt. 13(3), 031217 (2008). [CrossRef] [PubMed]
  27. P. Zijlstra, J. W. M. Chon, and M. Gu, “Five-dimensional optical recording mediated by surface plasmons in gold nanorods,” Nature 459(7245), 410–413 (2009). [CrossRef] [PubMed]
  28. Y. Chen, K. Munechika, and D. S. Ginger, “Dependence of fluorescence intensity on the spectral overlap between fluorophores and plasmon resonant single silver nanoparticles,” Nano Lett. 7(3), 690–696 (2007). [CrossRef] [PubMed]
  29. Y. Chen, K. Munechika, I. Jen-La Plante, A. M. Munro, S. E. Skrabalak, Y. Xia, and D. S. Ginger, “Excitation enhancement of CdSe quantum dots by single metal nanoparticles,” Appl. Phys. Lett. 93(5), 053106 (2008). [CrossRef]
  30. E. Dulkeith, A. C. Morteani, T. Niedereichholz, T. A. Klar, J. Feldmann, S. A. Levi, F. C. J. M. van Veggel, D. N. Reinhoudt, M. Möller, and D. I. Gittins, “Fluorescence quenching of dye molecules near gold nanoparticles: radiative and nonradiative effects,” Phys. Rev. Lett. 89(20), 203002 (2002). [CrossRef] [PubMed]
  31. T. Soller, M. Ringler, M. Wunderlich, T. A. Klar, J. Feldmann, H. P. Josel, Y. Markert, A. Nichtl, and K. Kürzinger, “Radiative and nonradiative rates of phosphors attached to gold nanoparticles,” Nano Lett. 7(7), 1941–1946 (2007). [CrossRef]
  32. X. Li, J. Qian, L. Jiang, and S. He, “Fluorescence quenching of quantum dots by gold nanorods and its application to DNA detection,” Appl. Phys. Lett. 94(6), 063111 (2009). [CrossRef]
  33. C. S. Yun, A. Javier, T. Jennings, M. Fisher, S. Hira, S. Peterson, B. Hopkins, N. O. Reich, and G. F. Strouse, “Nanometal surface energy transfer in optical rulers, breaking the FRET barrier,” J. Am. Chem. Soc. 127(9), 3115–3119 (2005). [CrossRef] [PubMed]
  34. J. Lee, A. O. Govorov, J. Dulka, and N. A. Kotov, “Bioconjugates of CdTe nanowires and Au nanoparticles: Plasmon-excition interactions, luminescence enhancement, and collective effects,” Nano Lett. 4(12), 2323–2330 (2004). [CrossRef]
  35. A. O. Govorov, J. Lee, and N. A. Kotov, “Theory of plasmon-enhanced Forster energy transfer in optically excited semiconductor and metal nanoparitcles,” Phys. Rev. B 76(12), 125308 (2007). [CrossRef]
  36. G. L. Liu, Y. T. Long, Y. Choi, T. Kang, and L. P. Lee, “Quantized plasmon quenching dips nanospectroscopy via plasmon resonance energy transfer,” Nat. Methods 4(12), 1015–1017 (2007). [CrossRef] [PubMed]
  37. P. Viste, J. Plain, R. Jaffiol, A. Vial, P. M. Adam, and P. Royer, “Enhancement and quenching regimes in metal-semiconductor hybrid optical nanosources,” ACS Nano 4(2), 759–764 (2010). [CrossRef] [PubMed]
  38. Q. Q. Zhan, J. Qian, X. Li, and S. He, “A study of mesoporous silica-encapsulated gold nanorods as enhanced light scattering probes for cancer cell imaging,” Nanotechnology 21(5), 055704 (2010). [CrossRef]
  39. V. Ghukasyan, Y. Y. Hsu, S. H. Kung, and F. J. Kao, “Application of fluorescence resonance energy transfer resolved by fluorescence lifetime imaging microscopy for the detection of enterovirus 71 infection in cells,” J. Biomed. Opt. 12(2), 024016 (2007). [CrossRef] [PubMed]
  40. V. Ghukasyan and F. J. Kao, “Monitoring Cellular Metabolism with Fluorescence Lifetime of Reduced Nicotinamide Adenine Dinucleotide,” J. Phys. Chem. C 113(27), 11532–11540 (2009). [CrossRef]
  41. R. Hu, K. T. Yong, I. Roy, H. Ding, S. He, and P. N. Prasad, “Metallic Nanostructures as Localized Plasmon Resonance Enhanced Scattering Probes for Multiplex Dark-Field Targeted Imaging of Cancer Cells,” J. Phys. Chem. C 113(7), 2676–2684 (2009). [CrossRef]
  42. B. Nikoobakht, J. Wang, and M. A. El-Sayed, “Surface-enhanced Raman scattering of molecules adsorbed on gold nanorods: off-surface plasmon resonance condition,” Chem. Phys. Lett. 366(1-2), 17–23 (2002). [CrossRef]
  43. C. Wang, Z. Ma, T. Wang, and Z. Su, “Synthesis, assembly, and biofunctionalization of silica-coated gold nanorods for colorimetric biosensing,” Adv. Funct. Mater. 16(13), 1673–1678 (2006). [CrossRef]
  44. J. Wenger, D. Gérard, J. Dintinger, O. Mahboub, N. Bonod, E. Popov, T. W. Ebbesen, and H. Rigneault, “Emission and excitation contributions to enhanced single molecule fluorescence by gold nanometric apertures,” Opt. Express 16(5), 3008–3020 (2008). [CrossRef] [PubMed]
  45. T. H. Taminiau, F. D. Stefani, and N. F. van Hulst, “Single emitters coupled to plasmonic nano-antennas: angular emission and collection efficiency,” N. J. Phys. 10(10), 105005 (2008). [CrossRef]
  46. S. He, Y. Cui, Y. Ye, P. Zhang, and Y. Jin, “Optical nano-antennas and metamaterials,” Mater. Today 12(12), 16–24 (2009). [CrossRef]
  47. A. R. Clapp, I. L. Medintz, B. R. Fisher, G. P. Anderson, and H. Mattoussi, “Can luminescent quantum dots be efficient energy acceptors with organic dye donors?” J. Am. Chem. Soc. 127(4), 1242–1250 (2005). [CrossRef] [PubMed]
  48. O. P. Varnavski, M. B. Mohamed, M. A. El-Sayed, and T. Goodson, “Relative enhancement of ultrafast emission in gold nanorods,” J. Phys. Chem. B 107(14), 3101–3104 (2003). [CrossRef]
  49. P. K. Jain, K. S. Lee, I. H. El-Sayed, and M. A. El-Sayed, “Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine,” J. Phys. Chem. B 110(14), 7238–7248 (2006). [CrossRef] [PubMed]
  50. C. C. Chen, Y. P. Lin, C. W. Wang, H. C. Tzeng, C. H. Wu, Y. C. Chen, C. P. Chen, L. C. Chen, and Y. C. Wu, “DNA-gold nanorod conjugates for remote control of localized gene expression by near infrared irradiation,” J. Am. Chem. Soc. 128(11), 3709–3715 (2006). [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited