Highly Controlled Synthesis and Super-Radiant Photoluminescence of Plasmonic Cube-in-Cube Nanoparticles
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Abstract:
The plasmonic properties of metal nanostructures have been heavily utilized for surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF), but the direct photoluminescence (PL) from plasmonic metal nanostructures, especially with plasmonic coupling, has not been widely used as much as SERS and MEF due to the lack of understanding of the PL mechanism, relatively weak signals, and the poor availability of the synthetic methods for the nanostructures with strong PL signals. The direct PL from metal nanostructures is beneficial if these issues can be addressed because it does not exhibit photoblinking or photobleaching, does not require dye-labeling, and can be employed as a highly reliable optical signal that directly depends on nanostructure morphology. Herein, we designed and synthesized plasmonic cube-in-cube (CiC) nanoparticles (NPs) with a controllable interior nanogap in a high yield from Au nanocubes (AuNCs). In synthesizing the CiC NPs, we developed a galvanic void formation (GVF) process, composed of replacement/reduction and void formation steps. We unraveled the super-radiant character of the plasmonic coupling-induced plasmon mode which can result in highly enhanced PL intensity and long-lasting PL, and the PL mechanisms of these structures were analyzed and matched with the plasmon hybridization model. Importantly, the PL intensity and quantum yield (QY) of CiC NPs are 31 times and 16 times higher than those of AuNCs, respectively, which have shown the highest PL intensity and QY reported for metallic nanostructures. Finally, we confirmed the long-term photostability of the PL signal, and the signal remained stable for at least 1 h under continuous illumination.Keywords:
Photobleaching
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Thionine
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Background: In recent years, 5‐aminolaevulinic acid (ALA) has become an increasingly popular photosensitizing drug for use in both photodynamic therapy (PDT) and photodetection (PD) of cancers. ALA metabolizes within tissue to form the photosensitizer protoporphyrin IX (PpIX). Like most photosensitizers, PpIX is fluorescent, and this fluorescence progressively decreases during PDT. This phenomenon is referred to as photobleaching. Aim: Our aim in carrying out this experiment was twofold: firstly, to compare the relative capacity of red and blue light to cause photobleaching; and secondly, to compare the capacity of a fixed light dose to cause photobleaching, when delivered at different intensities. Method: In this paper, we describe the implementation of a compact fluorescence spectrometer in monitoring the photobleaching of ALA‐induced PpIX in vivo on the skin of healthy volunteers. Results: We have been able to show that blue light causes more rapid photobleaching than red light, and that under illumination with red or blue light, delivery of a fixed light dose at a lower intensity results in more photobleaching. Conclusion: Comparison of the photobleaching rates suggests that a blue light intensity of 5 mW/cm 2 gives the same rate of photobleaching as the typical red light PDT intensity of 100 mW/cm 2 . Further investigation of the correlation between PpIX photobleaching and PDT effect would be beneficial in interpreting the clinical significance of our findings.
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A novel photobleaching model was proposed, in which a D-P photobleaching mechanism was developed. By combining with the conventional D-D and D-O photobleaching mechanisms, the dependence of photobleaching rate on the excitation power is well illustrated. The validity of this model was demonstrated with GFP photobleaching experiments in cases of one-photon excitation (1PE) and two-photon excitation (2PE) respectively. Previously inexplicable experimental results published in literature were also illustrated with this new model.
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Abstract The photobleaching of protoporphyrin IX (PP IX) and hematoporphyrin derivative (HpD) solutions was followed using three different methods: spectrophotometry, fluorometry and photodynamically induced cytotoxicity. The latter entails photoirradiation of HT29 human colon adenocarcinoma cells in the presence of preirradiated solutions of HpD and PP IX (λ 415 nm). The highest cytotoxicity was observed in the presence of unirradiated dye and decreased with the time of preirradiation. This decay in photocytotoxicity was further used to determine the porphyrin photobleaching kinetics in solution. For both sensitizers, quantum yields of photobleaching obtained by matching fluoresence were higher than that obtained from absorbance measurements (10 and 11 times for HpD and PP IX, respectively). This difference reflects preferential photobleaching of photolabile monomeric forms compared to aggregates. The highest quantum yield was obtained in the biological test (decay in cytotoxicity) which was 14 times higher for HpD and 30 times higher for PP IX than the quantum yield obtained from absorbance measurements. The absence of correlation between biological and fluorescence measurements has to be taken into account in the in vivo situation. Dark storage of preirradiated sensitizers (37°C, 24 h) completely restored photocytotoxity for PP IX but only partially for HpD, whereas fluorescence patterns were partially restored for both sensitizers.
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Hematoporphyrin
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With the development of the basic research of photodynamic therapy (PDT), photosensitizer photobleaching has become a highly focused area of research within PDT in recent years. In this paper, the photobleaching mechanism of quantum dots in the FBS solution and HL60 cell solutions with oxygen substrate were investigated by the method of theoretical derivation. The results demonstrated that the photobleaching in the single solution was corresponded with the first order kinetics while the photobleaching in the complex solution was corresponded with the second order kinetics. The curve and rate of CdSe photobleaching were obtained by determining the vis absorption spectrum of the CdSe and using of the Beer. Additionally, the photobleaching properties of quantum dot (CdSe) whose theoretical derivation can be confirmed by our experiment were gained.
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In the present study, the biological testing of the photodegradation of protoporphyrin IX (PP IX) is proposed. The method implies preirradiation of PP IX ((lambda) < 415 nm) in buffer solution (with or without serum) with the following adding to cells and irradiation of this mixture ((lambda) < 415 nm). The increase in survival with increase in preirradiation fluence was used for estimation of rate and quantum yield of PP IX photobleaching in solutions. The quantum yield estimated by the proposed method was compared with quantum yields of photodegradation of PP IX by decay in absorbance and decay in fluorescence. The highest quantum yield of photodegradation of PP IX was obtained by the test of cells photoinactivation, the lowest by the decay monitored by absorbance. The different values of quantum yield of photodegradation are discussed in the view of photobleaching of monomeric forms which are much more photolabile than aggregates and of photoproduct formation. Biological testing of photodegradation of monomeric species of PP IX seems to be the most specific.
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Fluorescence correlation spectroscopy (FCS) can be used to investigate the photobleaching properties of fluorophores in solution. The advantage with this method is that in addition to the photobleaching rate the formation and decay rates of the triplet state can be measured. In this way, it is possible to calculate the photodestruction quantum yield and relate the photostability of a fluorescent compound in a certain environment to the photodynamical behaviour of the singlet-triplet transitions. This is likely to contribute to a better understanding of the mechanisms of photobleaching given the central importance of dye triplet states in photobleaching processes. The approach was applied to the measurement and characterization of the photobleaching of Rh6G in aqueous solution and FITC in 1 mM sodium carbonate buffer (pH 9). The photobleaching yields measured are discussed in view of the simultaneous triplet properties at different excitation intensities, oxygen concentrations as well as in the presence or absence of quencher molecules. This study suggests that FCS is likely to provide a valuable tool for the elucidation of the mechanisms of photobleaching, which are far from understood in all their details.
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