Quantum Dots as Immunoassay Probes. Roger M. Leblanc

Transcription

1 Quantum Dots as Immunoassay Probes Roger M. Leblanc

2 Definition Properties Introduction quantum dots A material that confines electrons in 3D 1-10 nm length scale (for most semiconductors) ize dependent emission arrow emission band: fwhm 35 nm igh quantum yields: 85 % Broad excitation spectra Chemical/photo stability Cde QDs (2.2, 2.6, 3.2, 4.3, and 5.5 nm) Abs., a.u. 400 λ, nm 700 PL Int., a.u λ, nm Cde QDs d = nm λ ex = 365 nm

3 Cd-Peptide QDs Cu 2+ Detection Peptide 3 C C 3 C 2 C C C 2 C C C C C 2 C C C C C 2 C 2 Cu 2+ binding motif C C 3 Linker Gly-is-Leu-Leu-Cys C 3 Fmoc solid phase synthesis, MW = For synthesis of QDs 2 soluble, white powder, Yield = 79 %, Purity = 96 % Gattás-Asfura, K. M. et al. Chem. Commun. 2003,

4 Cd-Peptide QDs Cu 2+ Detection Cd 2+ [ 1x10-3 M ] Peptide p , [a] 2- Gly-is-Leu-Leu-Cys-Cd 24 Å Aggregates visible in solution Abs., a.u. 60 nm 521 nm 379 nm TEM λ, nm Gattás-Asfura, K. M. et al. Chem. Commun. 2003, PL Int., cps, a.u.

5 Cd-Peptide QDs Cu 2+ Detection electivity Intensity, cps 6.0x x x λ, nm Differentiation = AgCl, insoluble & undetected K +, Mg 2+, Ca 2+, Co 2+, Blank i 2+, Fe 3+, Zn 2+, Cd 2+ + Cu 2+ or Ag + Gattás-Asfura, K. M. et al. Chem. Commun. 2003,

6 Cd-Peptide QDs Cu 2+ Detection 200% electivity, comparison Cd--C 2 -C Cd--C 2-2 Cd-Cys 200% 200% 150% 150% 150% 100% 100% 100% 50% 50% 50% 0% 0% Ref. K Cu Mg Ca Co i Fe Zn Cd Ag 200% 0% 200% 200% 150% 150% 150% 100% 100% 100% 50% 50% 50% 0% 0% 0% Ref. K Cu Mg Ca Co i Fe Zn Cd Ag Ref. K Cu Mg Ca Co i Fe Zn Cd Ag Ref. K Cu Mg Ca Co i Fe Zn Cd Ag Ref. K Cu Mg Ca Co i Fe Zn Cd Ag Ref. K Cu Mg Ca Co i Fe Zn Cd Ag Cd-CGG Cd-CLLGG Cd-CLLG X = Metallic ions Y = Relative PL intensity

7 Cd-Peptide QDs Cu 2+ Detection Detected Levels Max. PL quenching at a Cu 2+ /QD molar ratio of 17:1 (ε QD = 2 x 10 4 M -1 cm -1 ) PL Intensity, x10 4 cps R 2 = 0.99 exponential fit (nm detection capability) [Metal Ions], x10-6 M Gattás-Asfura, K. M. et al. Chem. Commun. 2003,

8 Conclusions Cd-Cys-Leu-Leu-is-Gly QDs detected Cu 2+ and Ag + with high selectivity and sensitivity Leu-Leu and is-gly residues played a critical role towards metallic ion selectivity Peptides facilitated fabrication of selective optical sensor by way of amino acid sequence design Gattás-Asfura, K. M. et al. Chem. Commun. 2003,

9 Cde QDs Composite Film Paraoxon Detection Layer-by-Layer technique (electrostatic interaction) Quartz slide Composite film Chitosan Cde--C 2 -C QDs rganophosphorus hydrolase (P) Constantine, C. A.; Gattas-Asfura, K. M.; Mello,. V.; Crespo, G.; Rastogi, V.; Cheng, T.-C.; DeFrank, J. J.; Leblanc, R. M. Langmuir; 2003; 19(23);

10 Cde QDs Composite Film Paraoxon Detection Film growth Absorbance a.u. Abs., a.u Absorbance umber of bilayers PL, Int., a.u. Intensity, cps Last layer (P) λ, nm 700 λ, nm λ, nm 1-7 = # QDs layers QD avg. size: 34 Å Constantine, C. A.; Gattas-Asfura, K. M.; Mello,. V.; Crespo, G.; Rastogi, V.; Cheng, T.-C.; DeFrank, J. J.; Leblanc, R. M. Langmuir; 2003; 19(23);

11 Cde QDs Composite Film Paraoxon Detection Response of film upon exposure to paraoxon 0.12 P P 2 P, 2 + Absorbance, a.u. Abs., a.u Paraoxon, M λ, nm λ, nm 1-7 (bottom-top) = 0, 0.5, 1, 2, 5, 10, and 15 min. Constantine, C. A.; Gattas-Asfura, K. M.; Mello,. V.; Crespo, G.; Rastogi, V.; Cheng, T.-C.; DeFrank, J. J.; Leblanc, R. M. Langmuir; 2003; 19(23);

12 Cde QDs Composite Film Paraoxon Detection Response of film upon exposure to paraoxon P P 2 P, PL, Intensity, Int., cps a.u min. a c d e f b g h M Blank M λ, λ, nm 640

13 Cde QDs Composite Film Paraoxon Detection Epifluorescence images of film 895µm 793 µm Before exposure to paraoxon After exposure to paraoxon

14 Conclusions QDs were successfully incorporated into composite films via the layer-by-layer technique and electrostatic interaction. The QDs/P ultra thin film selectively detected paraoxon at the nm levels.

15 Detection of paraoxon using QDs/P bioconjugate urface modification P P Zn Cde P P C 2 C Zn Cde P P P ydrophobic ydrophilic Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

16 Detection of paraoxon using QDs/P bioconjugate Bioconjugation Zn Cde P p = 7.3 P P P Zn Cde P P P ( = Active ite of P ) Isoelectric point of P : 7.6 Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

17 Detection of paraoxon using QDs/P bioconjugate econdary structure analysis of bioconjugates Molar Ellipticity Per Residue (deg*cm 2 *dmol -1 ) 3x10 4 P only P/QDs bioconjugate P/QDs bioconjugate in paraoxon 2x10 4 1x x10 4-2x10 4-3x Wavelength (nm) CD spectra of pure P and P/QDs bioconjugates with and without paraoxon. P concentration is M in all cases. The P/QDs molar ratio of bioconjugates is 10. Paraoxon concentration is 10-6 M Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

18 Detection of paraoxon using QDs/P bioconjugate econdary structure analysis of bioconjugates α R α-helix Percentage of econdary tructure (%) α D β R β-strands β D Turns (T) Unordered (U) P P/QDs bioconjugates P/QDs bioconjugates with paraoxon (10-6 M) econdary structure data of P, P/QDs bioconjugates and P/QDs bioconjugates in 10-6 M of paraoxon. The subscripts R and D represent ordered and disordered, respectively. Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

19 Detection of paraoxon using QDs/P bioconjugate Fluorescence responses of bioassay ormalized PL Intensity QD:P=10:1 (a) 0 M 4.2 x 10-8 M 1.5 x 10-7 M 1.1 x 10-6 M 2.6 x 10-6 M 4.2 x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M ormalized PL Intensity M P:QDs = 100:1 4.2 x 10-8 M 1.5 x 10-7 M x 10-6 M (b) 2.6 x 10-6 M x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M ormalized PL Intensity Wavelength (nm) 1.2 QDs only 0 M 4.2 x 10-8 M 1.5 x 10-7 M x 10-6 M (c) 2.6 x 10-6 M x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M Wavelength (nm) Photoluminescence spectra of (a) 10:1 and (b) 100:1 molar ratio P/QDs bioconjugates; (c) pure QDs in different concentrations of paraoxon. All samples were excited at 350 nm Wavelength (nm) Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

20 Detection of paraoxon using QDs/P bioconjugate Fluorescence responses of bioassay ormalized PL Intensity QD:P=10:1 (a) 0 M 4.2 x 10-8 M 1.5 x 10-7 M 1.1 x 10-6 M 2.6 x 10-6 M 4.2 x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M ormalized PL Intensity M P:QDs = 100:1 4.2 x 10-8 M 1.5 x 10-7 M x 10-6 M (b) 2.6 x 10-6 M x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M ormalized PL Intensity Wavelength (nm) 1.2 QDs only 0 M 4.2 x 10-8 M 1.5 x 10-7 M x 10-6 M (c) 2.6 x 10-6 M x 10-6 M 2.6 x 10-5 M 4.2 x 10-5 M Wavelength (nm) Wavelength (nm) Facts: 1. The quenching of the PL is dependent to the concentration of paraoxon 2. The quenching of the PL has a maximum value in certain range of concentrations 3. The decrease of the PL intensity does not show a linear relationship to the [paraoxon] Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

21 Detection of paraoxon using QDs/P bioconjugate Proposed mechanism of quenching 2 P P 2 econdary structure change P P QDs QDs PL Quenching P + 2

22 Detection of paraoxon using QDs/P bioconjugate Effect of P:QDs molar ratio on the sensitivity of the bioassay Quenching Percentage (%) Paraoxon, 4.2 x 10-6 M Paraoxon, 4.2 x 10-5 M P:QDs (molar ratio) Concentration effect of P to the sensitivity of bioassay Ji, X. J.; Zheng, J.; Xu, J.; Rastogi, V. K.; Cheng, T. C.; DeFrank, J. J.; Leblanc R. M. J. Phys. Chem. B 2005, 109,

23 Conclusions The P and Cde(Zn) QDs can form stable bioconjugate through electrostatic interaction CD spectrum indicate a secondary structure change of P in presence of paraoxon The intensity of photoluminescence of P/QDs bioconjugate was quenched in presence of paraoxon The secondary structure change of P was responsible for the observed PL quenching Increasing the molar ratio of P over QDs will not increase the sensitivity of P/QDs biosensor

24 Imaging the formation of β-sheet using QDs/peptide conjugates 2 (A) C 3 (A') C 3 C 3 C 3 2 (B) (B') 2 (C) C 3 (C') C 3 tructures of the synthetic peptides with cysteine linker and covalently bonded Dansyl group: (A) 2 -Cys-Ile-Ile-Gly-Leu-Met-, (B) 2 -Cys-Ile-Ile-Pro-Leu- Met-, (C) 2 -Cys-Leu-Ile-Met-Ile-Gly-, (A ) Dansyl-Ile-Ile-Gly-Leu-Met-, (B ) Dansyl-Ile-Ile-Pro-Leu-Met-, and (C ) Dansyl-Cys-Leu-Ile-Met-Ile-Gly-

25 Imaging the formation of β-sheet using QDs/peptide conjugates chematic illustration of the surface coating of synthetic peptide on TP-coated Cde/Zn

26 Imaging the formation of β-sheet using QDs/peptide conjugates teric configuration analysis by Circular Dichroism spectroscopy Molar Ellipticity per Residue (deg*cm 2 *dmol -1 ) 1x Cys-Ile-Ile-Gly-Leu-Met- (Peptide A) 2 -Cys-Ile-Ile-Pro-Leu-Met- (Peptide B) 0-1x10 5-2x10 5-3x Cys-Leu-Ile-Met-Ile-Gly- (Peptide C) Wavelength( nm) (a) Molar Ellipticity per Residue (deg*cm 2 *dmol -1 ) 1.0x10 4 Aβ(1-42) 5.0x10 3 Aβ(1-40) x x Wavelength (nm) (b) Circular Dichroism spectra of (a) three model peptides and (b) full length peptides. Ji X., D,aistat, C. Li, J. rbulescu and R.M. Leblanc, Colloids and urfaces B: Biointerfaces 2006, in press.

27 Imaging the formation of β-sheet using QDs/peptide conjugates econdary structural data of Aβ (1-40), and Aβ (1-42) peptides. The subscripts R and D represent ordered and disordered, respectively. Percentage of econdary tructure α-helix β-strands Turns (T) Unorder ed (U) α R α D β R β D Aβ (1-40) Aβ (1-42) Ji X., D,aistat, C. Li, J. rbulescu and R.M. Leblanc, Colloids and urfaces B: Biointerfaces 2006, in press.

28 Imaging the formation of β-sheet using QDs/peptide conjugates Epifluorescence micrographs of model peptides and controlled peptides QDs-CIIGLM- QDs-CIIPLM- QDs-CLIMIG- Dansyl-CIIGLM- Dansyl-CIIPLM- Dansyl-CLIMIG- Ji X., D,aistat, C. Li, J. rbulescu and R.M. Leblanc, Colloids and urfaces B: Biointerfaces 2006, in press.

29 Imaging the formation of β-sheet using QDs/peptide conjugates Epifluorescence micrographs of full length peptides Aβ (1-40) / QDs mixture Aβ (1-42) / QDs mixture Aβ (1-40) / Dansyl acid mixture Aβ (1-42) / Dansyl acid mixture Ji X., D,aistat, C. Li, J. rbulescu and R.M. Leblanc, Colloids and urfaces B: Biointerfaces 2006, in press.

30 Conclusions The model Aβ peptides with cystein linker and Dansyl group were designed and synthesized A phase transfer approach was applied to conjugate the peptides onto the surface of the QDs The steric configuration study by CD spectroscopy revealed that the main secondary structural component of the aggregation is β-strands Epifluorescence microscopic research showed that QDs luminescent label approach showed a much higher intensity and better contrast for imaging than organic dye

31 PhD Graduate tudents: Jiayin Zheng (March 2006) Kerim M. Gattás-Asfura (December 2005) Xiaojun Ji (December 2005) David aistat (December 2005) Changqing Li (June 2005) Robert Triulzi Jianmin Xu Liang Zhao r. Research Associate: Jhony rbulescu

32 Funding ational cience Foundation U.. Army Research ffice