Singlet oxygen luminescence detecting in presence of hybrid associates of colloidal Ag 2 S quantum dots with methylene blue molecules

In our work we demonstrate some spectroscopic investigation of colloidal Ag2S QDs associates with methylene blue. The photosensitizing of singlet oxygen by associates of colloidal Ag2S QDs with methylene blue was found. Colloidal Ag2S quantum dots (QDs) are promising material for fluorescent labeling of biological objects, including tissues affected by severe diseases. It is possible due to their intense IR luminescence. Luminescence in the region of 800-1200 nm corresponds to the therapeutic window of transparency of biological objects [1-3]. Hybrid association of Ag2S QDs with molecules of thiazine dyes opens additional possibilities to control the quantum yield of QDs luminescence [3], and also to photosensitize singlet oxygen (O2). This is interesting for photodynamic therapy, particularly in combination with high-contrast fluorescent marking [4,5]. Furthermore, conjugation of QDs with dye molecules can to provide higher stability of dye, for example, methylene blue (MB) in the form, which produces singlet oxygen [6]. There is a problem of unambiguous fluorescent detection of singlet oxygen in the region of 1270 nm due to Ag2S QDs luminescence with peak at 1200 nm for most of known methods of their synthesis. This problem is also deepened due to significant duration of luminescence decay of Ag2S QDs, which is overlapped with kinetics of luminescence of singlet oxygen. Therefore we solved the problem of changing the position of IR luminescence peak of Ag2S QDs. This peak has weak size dependence. Its position was changed by replacing of stabilizer. Colloidal Ag2S QDs were synthesized in aqueous gelatin solution and using thioglycolic acid (TGA). The possibility of singlet oxygen photosensitization in water-ethanol solutions of mixtures of colloidal semiconductor Ag2S QDs, conjugated with MB molecules was investigated for synthesized samples. We used colloidal semiconductor Ag2S QDs with average size of 2.2 – 3.0 nm and MB molecules with concentration, provided QDs:MB=1:3 and QDs:MB=1:8 ratio respectively. Detection of singlet oxygen production was realized using a technique, based on the measurement of O2 molecules phosphorescence at 1270 nm. Registration of O2 molecules phosphorescence was realized using a highly stable low-noise photodiode PDF-10C/M and * Corresponding author: ovchinnikov_o_v@rambler.ru DOI: 10.1051/ , 0 (2017) 713203038 EPJ Web of Conferences epjconf/201 SPECTROSCOPY.SU 2016 132 3038 © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). monochromator MDR-4. The excitation sources was laser diode LPC-836 (λmax = 660 nm, Pmax = 250 mW). a b Fig. 1. UV-Vis absorption (a) and luminescence (b) spectra of MB in deferent solvents and mixtures of colloidal Ag2S QDs with MB in gelatin and TGA. Insert is scheme of interaction between Ag2S QDs and MB in TGA. As result of investigations it was found: 1) Synthesized Ag2S QDs in gelatin have an average size of 2.2 nm (according TEM) and 3.0 nm in TGA. The size effect is observed in UV-Vis absorption spectra (fig. 1, a). Replacement of stabilizer from gelatin to TGA provides a shift of Ag2S QDs luminescence peak from 1230 nm to 920 nm for similar size of Ag2S QDs (fig. 1b). This result indicates interface nature of center of recombinational IR luminescence of Ag2S QDs. 2) A slight shift of peak of the order 4-5 nm is observed in UVVis absorption spectra of MB molecules during formation of mixtures with Ag2S QDs. This indicates a relatively weak interaction between MB molecules and Ag2S QDs, realized probably by dipole-dipole mechanism with involving of dimethylamino groups of MB and incomplete bonds of QDs and also stabilizer molecules (fig. 1). 3) The association leads to a redistribution of the luminescence intensity of QDs and MB molecules. In the case of mixtures of Ag2S QDs and MB in TGA and gelatin we occur quenching of QDs luminescence under excitation from the absorption band of MB. Observed regularities are manifestation of interaction between MB molecules and Ag2S QDs. This fact can be explained by ionization of Ag2S QDs due to transfer of photoexcited electron to MB+, owned acceptor properties in its triplet state. 4) Singlet oxygen photosensitization was found in ethanol solution of MB (fig 1b). The peak of singlet oxygen phosphorescence at 1270 nm was detected in photoluminescence spectra of mixtures of Ag2S QDs and MB in TGA [5]. It is not typical for photoluminescence spectrum of pure Ag2S QDs in TGA. To observed similar peak for mixtures Ag2S QDs and MB in gelatin is difficult due to intense luminescence of Ag2S QDs (1230 nm). The work is supported by Russian Foundation of Basic Research (project No16-3200503-mol_a).

Abstract.In our work we demonstrate some spectroscopic investigation of colloidal Ag2S QDs associates with methylene blue.The photosensitizing of singlet oxygen by associates of colloidal Ag2S QDs with methylene blue was found.
Colloidal Ag2S quantum dots (QDs) are promising material for fluorescent labeling of biological objects, including tissues affected by severe diseases.It is possible due to their intense IR luminescence.Luminescence in the region of 800-1200 nm corresponds to the therapeutic window of transparency of biological objects [1][2][3].Hybrid association of Ag2S QDs with molecules of thiazine dyes opens additional possibilities to control the quantum yield of QDs luminescence [3], and also to photosensitize singlet oxygen ( 1 O2).This is interesting for photodynamic therapy, particularly in combination with high-contrast fluorescent marking [4,5].Furthermore, conjugation of QDs with dye molecules can to provide higher stability of dye, for example, methylene blue (MB) in the form, which produces singlet oxygen [6].
There is a problem of unambiguous fluorescent detection of singlet oxygen in the region of 1270 nm due to Ag2S QDs luminescence with peak at 1200 nm for most of known methods of their synthesis.This problem is also deepened due to significant duration of luminescence decay of Ag2S QDs, which is overlapped with kinetics of luminescence of singlet oxygen.Therefore we solved the problem of changing the position of IR luminescence peak of Ag2S QDs.This peak has weak size dependence.Its position was changed by replacing of stabilizer.Colloidal Ag2S QDs were synthesized in aqueous gelatin solution and using thioglycolic acid (TGA).
The possibility of singlet oxygen photosensitization in water-ethanol solutions of mixtures of colloidal semiconductor Ag2S QDs, conjugated with MB molecules was investigated for synthesized samples.We used colloidal semiconductor Ag2S QDs with average size of 2.2 -3.0 nm and MB molecules with concentration, provided QDs:MB=1:3 and QDs:MB=1:8 ratio respectively.
Detection of singlet oxygen production was realized using a technique, based on the measurement of 1 O2 molecules phosphorescence at 1270 nm.Registration of 1 O2 molecules phosphorescence was realized using a highly stable low-noise photodiode PDF-10C/M and As result of investigations it was found: 1) Synthesized Ag2S QDs in gelatin have an average size of 2.2 nm (according TEM) and 3.0 nm in TGA.The size effect is observed in UV-Vis absorption spectra (fig. 1, a).Replacement of stabilizer from gelatin to TGA provides a shift of Ag2S QDs luminescence peak from 1230 nm to 920 nm for similar size of Ag2S QDs (fig. 1b).This result indicates interface nature of center of recombinational IR luminescence of Ag2S QDs. 2) A slight shift of peak of the order 4-5 nm is observed in UV-Vis absorption spectra of MB molecules during formation of mixtures with Ag2S QDs.This indicates a relatively weak interaction between MB molecules and Ag2S QDs, realized probably by dipole-dipole mechanism with involving of dimethylamino groups of MB and incomplete bonds of QDs and also stabilizer molecules (fig.1).3) The association leads to a redistribution of the luminescence intensity of QDs and MB molecules.In the case of mixtures of Ag2S QDs and MB in TGA and gelatin we occur quenching of QDs luminescence under excitation from the absorption band of MB.Observed regularities are manifestation of interaction between MB molecules and Ag2S QDs.This fact can be explained by ionization of Ag2S QDs due to transfer of photoexcited electron to MB + , owned acceptor properties in its triplet state.4) Singlet oxygen photosensitization was found in ethanol solution of MB (fig 1b).The peak of singlet oxygen phosphorescence at 1270 nm was detected in photoluminescence spectra of mixtures of Ag2S QDs and MB in TGA [5].It is not typical for photoluminescence spectrum of pure Ag2S QDs in TGA.To observed similar peak for mixtures Ag2S QDs and MB in gelatin is difficult due to intense luminescence of Ag2S QDs (1230 nm).
The work is supported by Russian Foundation of Basic Research (project №16-32-00503-mol_a).

monochromator MDR- 4 .Fig. 1 .
Fig. 1.UV-Vis absorption (a) and luminescence (b) spectra of MB in deferent solvents and mixtures of colloidal Ag2S QDs with MB in gelatin and TGA.Insert is scheme of interaction between Ag2S QDs and MB in TGA.