Singlet Oxygen Generation from Water-soluble Quantum Dot-Organic Dye Nanocomposites

Lixin Shi, Ana Gamboa, Billy Hernandez, Araceli B. Dasalla, and Matthias Selke*Department of Chemistry and Biochemistry, California State University, Los Angeles, Los Angeles, CA 90032

Results and discussion In a typical assay, the Uv-vis spectra of QD-TSPP nanocomposites are slightly blue shifted

compared with that of free TSPP (Figure 1a), this could be caused by surface plasma change as

TSPP deposited on the surface of the QDs, H-aggregates was achieved.8 An aqueous solution

of TSPP with an absorption of 0.10 at 355 nm corresponds to a concentration of 410-2 mM.

After TSPP was deposited on the QDs surface, the absorption of nanocomposites at 355 nm

was improved significantly to 0.476 corresponding to s a TSPP concentration 2.610-2 mM.

Emission intensity of CdTe-TSPP nanocomposites decreased when TSPP deposited on the CdTe

surface. The most likely cause is the quenching of photoexcited QDs through charge transfer

to the electron-accepting TSPP, which is bound to QDs (Figure 1b).

CdTe-TSPP nanocomposites effectively generate 1O2 with a quantum yield of 30±9% as shown

in Figure 3a. No 1O2 was observed when the CdTe nanocrystal was measured in absence of

TSPP (Figure 3b).

Scheme 1. Fabrication and 1O2 generation of CdTe-TSPP nanocomposites

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Introduction Colloidal semiconductor nanocrystals (Quantum Dots, QDs) can provide three-

dimensional (3D) architectures and have attracted widespread interest, since their

nano-size physical properties are quite different from those of the bulk materials

depending upon their size, shape, and packing density.1 Meanwhile, QDs are very

attractive as biology labels, because of their small size, emission tunability, superior

photostability and longer photoluminescence decay times. QDs can be used mark

moleculer of into living cells. 2

Photodynamic therapy (PDT) is an emerging modality for the treatment of a certain

types of cancer.3 Recent papers have reported high quantum yields of singlet oxygen

(1O2) being generated by combining nanoparticles with photosensitizers.4, 5

Nanoparticles can be ideal carriers of photosensitizer molecules for PDT. The

combination of nanomaterials alone with photosensitizers has emerged as a new

interdisciplinary research field.6 However, to the best of our knowledge, no studies on

the water-soluble QDs-organic dye nanocomposites for generating singlet oxygen are

published to date. Water-soluble species are critical for artificial biocompatibility

materials which are widely used as drug delivery carriers, live cell imaging and in vivo

imaging.7

We report herein the first preparation of water-soluble QDs, CdTe, fabricated together

with an organic dye, Meso-Tetra (4-sulfonatophenyl) Porphine Dihydrochloride (TSPP), a

photosensitizer, using electrostatic interactions as a versatile means to bind

photosensitizers to water-soluble CdTe nanocrystals.

Future research•To investigate the relationship of QD size and quantum yield.

•To investigate the relationship of space between QD and organic dye on quantum

yield.

QD

++ +

+

++++

+

+

- ---

QD

light3O2 1O2

QDPS

Meso-Tetra (4-sulfonatophenyl) Porphine Dihudrochloride ( TSPP )

2.202.202.402.402.602.602.802.803.003.003.203.203.403.403.603.603.803.804.004.00 2.202.202.402.402.602.602.802.803.003.003.203.203.403.403.603.603.803.804.004.00

2.202.202.402.402.602.602.802.803.003.003.203.203.403.403.603.603.803.804.004.00 2.202.202.402.402.602.602.802.803.003.003.203.203.403.403.603.603.803.804.004.00

CdTe-TSPP nanocomposties after 30 min. irradiation

Figure 2. High resolution TEM image of CdTe nanocrystals(10-3 mM), left, and CdTe-TSPP nanocomposites ( 10-3 mM CdTe with 10-3 mM TSPP), right. Scale bar 5 nm.

Photooxidation experiments were carried out to determine the stability of the nanocomposites

and possible oxidation of the nanocomposites by 1O2 using 1H NMR. Methionione was added into

prepared samples of CdTe and CdTe-TSPP, respectively. At high concentration no decomposition

or oxidation was detected by 1H NMR spectroscopy, which further confirms that no singlet oxygen

is produced by CdTe nanocrystals.

Figure 3. a) Relative intensity of 1O2 production vs. absorbance of CdTe-TSPP nanocomposites, TSPP, and Rose Bengal at 355 nm. b). 1O2 luminescence decay of CdTe and CdTe-TSPP in presence/absence of Sodium Azide at 355 nm in D2O. C). Photooxidation of CdTe-TSPP nanocomposites at different irradiation times.

Figure 1. a) Uv-vis spectra for the fabrication of CdTe with TSPP in 0.1 M pH 7.0 PBS. b) Fluorescence spectra of CdTe, TSPP and CdTe-TSPP nanocomposites, respectively.

CdTe-TSPP nanocomposites in D2O

CdTe nanoparticles in D2O

CdTe nanoparticles after 30 min irradiation

b)

c)

a) b)

Acknowledgment:

The authors thank the NSF PREM and NIH MBRS programs for financial support, and Carol M. Garland of CalTech for TEM measurements.

a)