Abstract

Specially-treated glass substrates coated with a thin film of water soluble mercaptopropionic acid (MPA) capped CdTe nanocrystals (NCs) were prepared and found to undergo photoluminescence changes by as much as 40% when micro-droplets of organic molecules were placed in the nanometer-range proximity of the NCs. This imaging technique involving close proximity between a nano-crystal and an organic molecule is found to provide a 2 × –3 × enhanced contrast ratio over the conventional method of fluorescence imaging. Photoluminescence of NCs is recoverable upon removal of the organic molecules, therefore validating these NCs as potential all-optical organic molecular nanosensors. Upon optimization and with proper instrumentation, these nano-crystals could eventually serve as point-detectors for purposes of super-resolution optical microscopy. No solvents are required for the proposed sensing mechanism since all solutions were dried under argon flow. Fluorophores and fluorescent proteins were investigated, including fluorescein, Rhodamine 6G, and green fluorescent protein (GFP). Furthermore, NC photoluminescence changes were systematically quantified as a function of the solution pH and of the organic molecule concentration. Long duration (> 40 minutes) continuous excitation studies were conducted in order to evaluate the reliability of the proposed sensing scheme.

© 2014 Optical Society of America

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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]

2013 (1)

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

2012 (1)

N. Guillot and M. L. de la Chapelle, “Lithographied nanostructures as nanosensors,” J. Nanophotonics6(1), 064506 (2012).
[CrossRef]

2010 (1)

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

2009 (1)

J. Wang, “Biomolecule-functionalized nanowires: from nanosensors to nanocarriers,” ChemPhysChem10(11), 1748–1755 (2009).
[CrossRef] [PubMed]

2008 (1)

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

2007 (1)

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

2005 (3)

J. M. Dixon, M. Taniguchi, and J. S. Lindsey, “PhotochemCAD 2: a refined program with accompanying spectral databases for photochemical calculations,” Photochem. Photobiol.81(1), 212–213 (2005).
[CrossRef] [PubMed]

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

K. Aslan, J. R. Lakowicz, and C. D. Geddes, “Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering,” Anal. Chem.77(7), 2007–2014 (2005).
[CrossRef] [PubMed]

2004 (3)

K. Aslan, C. C. Luhrs, and V. H. Pérez-Luna, “Controlled and Reversible Aggregation of Biotinylated Gold Nanoparticles with Streptavidin,” J. Phys. Chem. B108(40), 15631–15639 (2004).
[CrossRef]

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

2003 (2)

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

2002 (1)

A. J. Haes and R. P. Van Duyne, “A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles,” J. Am. Chem. Soc.124(35), 10596–10604 (2002).
[CrossRef] [PubMed]

2001 (2)

F. Koberling, A. Mews, and T. Basché, “Oxygen-Induced Blinking of Single CdSe Nanocrystals,” Adv. Mater.13(9), 672–676 (2001).
[CrossRef]

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

1998 (2)

W. C. Chan and S. Nie, “Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection,” Science281(5385), 2016–2018 (1998).
[CrossRef] [PubMed]

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

1997 (1)

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

1995 (1)

R. Sjöback, J. Nygren, and M. Kubista, “Absorption and fluorescence properties of fluorescein,” Spectrochim. Acta, Part A51(6), L7–L21 (1995).
[CrossRef]

1974 (1)

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Aslan, K.

K. Aslan, J. R. Lakowicz, and C. D. Geddes, “Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering,” Anal. Chem.77(7), 2007–2014 (2005).
[CrossRef] [PubMed]

K. Aslan, C. C. Luhrs, and V. H. Pérez-Luna, “Controlled and Reversible Aggregation of Biotinylated Gold Nanoparticles with Streptavidin,” J. Phys. Chem. B108(40), 15631–15639 (2004).
[CrossRef]

Basché, T.

F. Koberling, A. Mews, and T. Basché, “Oxygen-Induced Blinking of Single CdSe Nanocrystals,” Adv. Mater.13(9), 672–676 (2001).
[CrossRef]

Bawendi, M. G.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Bol, A. A.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Chalmers, N. I.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Chan, W. C.

W. C. Chan and S. Nie, “Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection,” Science281(5385), 2016–2018 (1998).
[CrossRef] [PubMed]

Clapp, A. R.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Corkan, L. A.

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

de la Chapelle, M. L.

N. Guillot and M. L. de la Chapelle, “Lithographied nanostructures as nanosensors,” J. Nanophotonics6(1), 064506 (2012).
[CrossRef]

de Mello Donegá, C.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Dixon, J. M.

J. M. Dixon, M. Taniguchi, and J. S. Lindsey, “PhotochemCAD 2: a refined program with accompanying spectral databases for photochemical calculations,” Photochem. Photobiol.81(1), 212–213 (2005).
[CrossRef] [PubMed]

Du, H.

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

Du-Thumm, L.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Elghanian, R.

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Fang, Z.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Fisher, B. R.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Frederix, P. L. T. M.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Fuh, R.-C. A.

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

Geddes, C. D.

K. Aslan, J. R. Lakowicz, and C. D. Geddes, “Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering,” Anal. Chem.77(7), 2007–2014 (2005).
[CrossRef] [PubMed]

Gerritsen, H. C.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Gryczynski, I.

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Gryczynski, Z.

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Gu, Z.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Guillot, N.

N. Guillot and M. L. de la Chapelle, “Lithographied nanostructures as nanosensors,” J. Nanophotonics6(1), 064506 (2012).
[CrossRef]

Guo, W.

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

Haes, A. J.

A. J. Haes and R. P. Van Duyne, “A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles,” J. Am. Chem. Soc.124(35), 10596–10604 (2002).
[CrossRef] [PubMed]

Hong, M.-Y.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Ishii, T.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Johnson, F. H.

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Kataoka, K.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Kim, H.-S.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Ko, H. C.

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

Koberling, F.

F. Koberling, A. Mews, and T. Basché, “Oxygen-Induced Blinking of Single CdSe Nanocrystals,” Adv. Mater.13(9), 672–676 (2001).
[CrossRef]

Kolenbrander, P. E.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Kubista, M.

R. Sjöback, J. Nygren, and M. Kubista, “Absorption and fluorescence properties of fluorescein,” Spectrochim. Acta, Part A51(6), L7–L21 (1995).
[CrossRef]

Lakowicz, J. R.

K. Aslan, J. R. Lakowicz, and C. D. Geddes, “Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering,” Anal. Chem.77(7), 2007–2014 (2005).
[CrossRef] [PubMed]

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Lau, P. C.

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

Lee, D.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Letsinger, R. L.

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Li, J.

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

Lin, S. H.

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

Lindsey, J. S.

J. M. Dixon, M. Taniguchi, and J. S. Lindsey, “PhotochemCAD 2: a refined program with accompanying spectral databases for photochemical calculations,” Photochem. Photobiol.81(1), 212–213 (2005).
[CrossRef] [PubMed]

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

Luhrs, C. C.

K. Aslan, C. C. Luhrs, and V. H. Pérez-Luna, “Controlled and Reversible Aggregation of Biotinylated Gold Nanoparticles with Streptavidin,” J. Phys. Chem. B108(40), 15631–15639 (2004).
[CrossRef]

Malicka, J.

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Mansuripur, M.

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

Mattoussi, H.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Mauro, J. M.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Medintz, I. L.

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

Meijerink, A.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Mews, A.

F. Koberling, A. Mews, and T. Basché, “Oxygen-Induced Blinking of Single CdSe Nanocrystals,” Adv. Mater.13(9), 672–676 (2001).
[CrossRef]

Mirkin, C. A.

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Morise, H.

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Mucic, R. C.

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Nagasaki, Y.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Nam, S.-H.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Nie, S.

W. C. Chan and S. Nie, “Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection,” Science281(5385), 2016–2018 (1998).
[CrossRef] [PubMed]

Norwood, R. A.

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

Nygren, J.

R. Sjöback, J. Nygren, and M. Kubista, “Absorption and fluorescence properties of fluorescein,” Spectrochim. Acta, Part A51(6), L7–L21 (1995).
[CrossRef]

Oh, E.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Otsuka, H.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Palmer, R. J.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Peng, X.

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

Pérez-Luna, V. H.

K. Aslan, C. C. Luhrs, and V. H. Pérez-Luna, “Controlled and Reversible Aggregation of Biotinylated Gold Nanoparticles with Streptavidin,” J. Phys. Chem. B108(40), 15631–15639 (2004).
[CrossRef]

Peyghambarian, N.

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

Qu, L.

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

Roll, D.

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Shi, W.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Shimomura, O.

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Sjöback, R.

R. Sjöback, J. Nygren, and M. Kubista, “Absorption and fluorescence properties of fluorescein,” Spectrochim. Acta, Part A51(6), L7–L21 (1995).
[CrossRef]

Storhoff, J. J.

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Sullivan, R.

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Sunaga, Y.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Tang, J.

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

Taniguchi, M.

J. M. Dixon, M. Taniguchi, and J. S. Lindsey, “PhotochemCAD 2: a refined program with accompanying spectral databases for photochemical calculations,” Photochem. Photobiol.81(1), 212–213 (2005).
[CrossRef] [PubMed]

Van den Heuvel, D. J.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Van Duyne, R. P.

A. J. Haes and R. P. Van Duyne, “A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles,” J. Am. Chem. Soc.124(35), 10596–10604 (2002).
[CrossRef] [PubMed]

van Lingen, J. N. J.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

van Sark, W. G. J. H. M.

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Wang, J.

J. Wang, “Biomolecule-functionalized nanowires: from nanosensors to nanocarriers,” ChemPhysChem10(11), 1748–1755 (2009).
[CrossRef] [PubMed]

Watanabe, Y.

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Winant, J.

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Yoon, H. C.

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

Yu, W. W.

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

Yuan, C. T.

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

Zhang, N.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Zhang, Y.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Zhong, X.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Zhu, W.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Zou, L.

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

Adv. Mater. (1)

F. Koberling, A. Mews, and T. Basché, “Oxygen-Induced Blinking of Single CdSe Nanocrystals,” Adv. Mater.13(9), 672–676 (2001).
[CrossRef]

Anal. Chem. (2)

K. Aslan, J. R. Lakowicz, and C. D. Geddes, “Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering,” Anal. Chem.77(7), 2007–2014 (2005).
[CrossRef] [PubMed]

D. Roll, J. Malicka, I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, “Metallic colloid wavelength-ratiometric scattering sensors,” Anal. Chem.75(14), 3440–3445 (2003).
[CrossRef] [PubMed]

Appl. Environ. Microbiol. (1)

N. I. Chalmers, R. J. Palmer, L. Du-Thumm, R. Sullivan, W. Shi, and P. E. Kolenbrander, “Use of quantum dot luminescent probes to achieve single-cell resolution of human oral bacteria in biofilms,” Appl. Environ. Microbiol.73(2), 630–636 (2007).
[CrossRef] [PubMed]

Appl. Phys. Lett. (1)

H. C. Ko, C. T. Yuan, S. H. Lin, and J. Tang, “Blinking suppression of single quantum dots in agarose gel,” Appl. Phys. Lett.96(1), 012104 (2010).
[CrossRef]

Biochemistry (1)

H. Morise, O. Shimomura, F. H. Johnson, and J. Winant, “Intermolecular energy transfer in the bioluminescent system of Aequorea,” Biochemistry13(12), 2656–2662 (1974).
[CrossRef] [PubMed]

Chem. Mater. (1)

W. W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,” Chem. Mater.15(14), 2854–2860 (2003).
[CrossRef]

ChemPhysChem (1)

J. Wang, “Biomolecule-functionalized nanowires: from nanosensors to nanocarriers,” ChemPhysChem10(11), 1748–1755 (2009).
[CrossRef] [PubMed]

J. Am. Chem. Soc. (3)

E. Oh, M.-Y. Hong, D. Lee, S.-H. Nam, H. C. Yoon, and H.-S. Kim, “Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles,” J. Am. Chem. Soc.127(10), 3270–3271 (2005).
[CrossRef] [PubMed]

A. J. Haes and R. P. Van Duyne, “A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles,” J. Am. Chem. Soc.124(35), 10596–10604 (2002).
[CrossRef] [PubMed]

A. R. Clapp, I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi, “Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors,” J. Am. Chem. Soc.126(1), 301–310 (2004).
[CrossRef] [PubMed]

J. Mater. Chem. (1)

L. Zou, Z. Gu, N. Zhang, Y. Zhang, Z. Fang, W. Zhu, and X. Zhong, “Ultrafast synthesis of highly luminescent green- to near infrared-emitting CdTe nanocrystals in aqueous phase,” J. Mater. Chem.18(24), 2807 (2008).
[CrossRef]

J. Nanophotonics (1)

N. Guillot and M. L. de la Chapelle, “Lithographied nanostructures as nanosensors,” J. Nanophotonics6(1), 064506 (2012).
[CrossRef]

J. Phys. Chem. B (2)

K. Aslan, C. C. Luhrs, and V. H. Pérez-Luna, “Controlled and Reversible Aggregation of Biotinylated Gold Nanoparticles with Streptavidin,” J. Phys. Chem. B108(40), 15631–15639 (2004).
[CrossRef]

W. G. J. H. M. van Sark, P. L. T. M. Frederix, D. J. Van den Heuvel, H. C. Gerritsen, A. A. Bol, J. N. J. van Lingen, C. de Mello Donegá, and A. Meijerink, “Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy,” J. Phys. Chem. B105(35), 8281–8284 (2001).
[CrossRef]

Langmuir (1)

Y. Nagasaki, T. Ishii, Y. Sunaga, Y. Watanabe, H. Otsuka, and K. Kataoka, “Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot,” Langmuir20(15), 6396–6400 (2004).
[CrossRef] [PubMed]

Nanotechnology (1)

P. C. Lau, R. A. Norwood, M. Mansuripur, and N. Peyghambarian, “An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals,” Nanotechnology24(1), 015501 (2013).
[CrossRef] [PubMed]

Photochem. Photobiol. (2)

J. M. Dixon, M. Taniguchi, and J. S. Lindsey, “PhotochemCAD 2: a refined program with accompanying spectral databases for photochemical calculations,” Photochem. Photobiol.81(1), 212–213 (2005).
[CrossRef] [PubMed]

H. Du, R.-C. A. Fuh, J. Li, L. A. Corkan, and J. S. Lindsey, “PhotochemCAD: A Computer-Aided Design and Research Tool in Photochemistry,” Photochem. Photobiol.68(2), 141–142 (1998).

Science (2)

W. C. Chan and S. Nie, “Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection,” Science281(5385), 2016–2018 (1998).
[CrossRef] [PubMed]

R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger, and C. A. Mirkin, “Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles,” Science277(5329), 1078–1081 (1997).
[CrossRef] [PubMed]

Spectrochim. Acta, Part A (1)

R. Sjöback, J. Nygren, and M. Kubista, “Absorption and fluorescence properties of fluorescein,” Spectrochim. Acta, Part A51(6), L7–L21 (1995).
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

System setup for measuring the PL of CdTe NCs as well as that of dye molecules under argon gas flow. The illumination is through the bottom of the glass substrate, The PL signal was collected in the reflected path toward the EMCCD, also from the bottom side of the substrate.

Fig. 2
Fig. 2

Photoluminescence of NCs as collected by an EMCCD camera (described in procedure) with a fixed exposure time of 500 ms. The emission filter was set at λ = 605 ± 15 nm, coinciding with the peak emission of the NCs. (a) PL profile of water soluble MPA capped CdTe NCs before rinsing. (b) PL profile of NCs after 1st round of ethanol rinsing. (c) PL profile of NCs after 2nd round of ethanol rinsing. (d) Averaged PL count per pixel (after background subtraction) for each case (a)-(c). Upon rinsing with ethanol, no significant PL decay or removal of NCs was detected. Similar results were obtained for NCs rinsed with water.

Fig. 3
Fig. 3

Absorption (blue) and emission (red) spectra of (a) Fluorescein, (b) R6G, (c) NC 615, and (d) NC 655. The green and orange bands indicate the emission filters used for conventional imaging and NC-cp imaging, respectively.

Fig. 4
Fig. 4

PL images of Fluorescein microdroplets added on top of an NC thin film, which was partially scratched using a sharp knife.(a) image acquired using a 525 ± 15 nm filter. There is no PL intensity difference between areas where NCs are present and scratched areas where NCs are absent. (b) Image acquired using a 605 ± 15 nm filter where bright areas are due to the PL from NCs, the dark straight lines are scratch marks created with the knife in order to remove the NCs, and the circular spots are regions where PL is suppressed due to NC-fluorescein close proximity interactions.

Fig. 5
Fig. 5

(a)-(d) Photoluminescence observations of NCs (peak emission at 615 nm) immobilized on a glass substrate. Each picture is obtained through the specified bandpass filter using a wide field Zeiss fluorescence microscope. The immobilized NCs are covered with micro-droplets of fluorescein (0.0625mg/mL, peak emission at 525 nm) injected through a tapered glass needle. Injecting the solution (at a volume of <1 microL) creates a random array of droplets of different sizes. Shown in these pictures are two distinct droplets: one that has a diameter of 100 μm, and a smaller one near the center having a 5 μm diameter. It is evident from (c) that the NCs’ PL is quenched wherever fluorescein molecules cover the NCs. (e) and (f) The PL of the NCs recovers after washing the sample’s surface with ethanol; a residual trace of fluorescein at the droplet boundary remains visible in (f). These observations were carried out under continuous argon flow at 5 lpm to ensure a stable PL behavior of the NCs. The excitation irradiance was 2.3 W/cm2 at 405 nm.

Fig. 6
Fig. 6

Magnitude of contrast ratio comparison between NC-cp imaging and conventional fluorescence imaging. Two analytes are investigated: Fluorescein (a) and R6G (b). Concentrations of NC thin films are kept at approximately 75 ± 15 NCs/μm2. The blue dotted line indicates the minimum detection threshold of the EMCCD (c) Actual image acquisition for fluorescein as collected by EMCCD with 615 nm and 525 nm emission filters at different concentrations. (d) Actual image acquisition for R6G as collected by EMCCD with 655 nm and 565 nm emission filters at different concentrations. Absorption cross sections for both CdTe NCs and fluorescein molecules are acquired for concentration measurements. The NC’s absorption cross section is found based on the observations by Yu et al [14]; that of the fluorescein and R6G molecules are based on the results of Dixon and Du et al [15,16]. These are found to be around 1.27 × 10−15 cm2 for NCs, 3.9 × 10−17 cm2 for fluorescein, and 6.22 × 10−18cm2 for R6G with fixed excitation at λ = 405 nm.

Fig. 7
Fig. 7

(a) Magnitude of the contrast ratio as a function of irradiance of the mercury arc lamp (the illumination source) at λ = 405 nm excitation. Fluorescein micro-droplets were placed over the NC layer, as shown in frames (b)-(e), which are the actual pictures captured by the EMCCD at different irradiance levels. Deliberate scratch marks made on the NC layer are visible as straight dark lines in these pictures; this is to assess accurately the background counts as irradiance increases. The emission filter is set at 615 ± 15 nm, and the exposure time of the EMCCD is fixed at 500 ms.

Fig. 8
Fig. 8

(a) Fluorescein droplets viewed through the 525 ± 15 nm filter (b) Two additional droplets were found at peak emission filter of R6G (565 ± 15 nm), indicating the location of R6G droplets as depicted by the red circles. (c) Magnitude of the contrast ratio for the R6G droplets at 655 ± 15 nm filter is two times lower than that for the fluorescein droplets. This proves that NC 655 has higher sensitivity towards fluorescein at fixed concentration of 1000 molecules/μm2.

Fig. 9
Fig. 9

(a) Contrast ratio versus the pH level of the fluorescein solution. NC-cp imaging in red, conventional imaging in black. (b) EMCCD-captured photographs showing the results of changing the pH from 5.5 to 12. The top row is obtained with the emission filter at 615 ± 15 nm, while the bottom row corresponds to the 525 ± 15 nm filter. The concentration of fluorescein at the NC layer is kept at 1000 molecules/μm2, which provides maximum contrast, according to Fig. 6.

Fig. 10
Fig. 10

Plot of the contrast ratio versus time for NC regions of a sample covered with fluorescein molecules. The inset at right shows an actual EMCCD picture of the sample, where the fluorescein micro-droplet clearly suppresses the NC PL getting through 615 ± 15nm emission filter. The scratch marks were deliberately made to measure the real time background intensity. The inset at left shows the PL signals of the NCs with and without coverage by fluorescein. Excitation irradiance was set at 2 W/cm2 and the exposure time for each frame was 2s. The sample was exposed to continuous argon flow at 5 lpm.

Fig. 11
Fig. 11

Enhanced contrast ratio for the NC-cp imaging in (b) compared to the GFP microdroplets acquired via the conventional fluorescence method (a). The wild type GFP with peak emission at 515 nm has insignificant spectral leakage [22] at 615 nm pass-band. (c) The structure of GFP is a cage-like structure with a width of 1 nm and length of about 4 nm. It is approximately 5-10 times larger than the R6G and Fluorescein molecules.

Fig. 12
Fig. 12

Schematic view of an array of NCs with different emission wavelengths, affixed to a glass substrate and covering a typical area of 200 × 200 nm2, with 50 nm spacing. An organic molecule coming into contact with (or in close proximity to) an NC will affect the NC’s photoluminescence at the specific location, hence changing the spectral profile of the array. By monitoring the spectral changes and correlating them with the known coordinates of the various NCs, one can obtain sub-wavelength-resolution information about the movements of the organic molecule.

Tables (1)

Tables Icon

Table 1 Measured contrast ratio for all the samples reported in this paper. Measurements were made with sample concentrations that give the highest contrast ratio. The NC thin film concentration was kept at about 150 ± 30 NCs per square micron. Excitation wavelength and intensity were fixed at 405 nm and 2.3 W/cm2, respectively. Depending on the type of NC thin film, observations were made either at 615 nm or at 655 nm, as indicated.

Equations (1)

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Contrast Ratio= P L red box 615/525 PL blue box 615/525 1.

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