Topological Fracton Quantum Phase Transitions by Tuning Exact Tensor Network States.

Gapped fracton phases of matter generalize the concept of topological order and broaden our fundamental understanding of entanglement in quantum many-body systems. However, their analytical or numerical description beyond exactly solvable models remains a formidable challenge. Here we employ an exact 3D quantum tensor-network approach that allows us to study a Z_{N} generalization of the prototypical X cube fracton model and its quantum phase transitions between distinct topological states via fully tractable wave function deformations. We map the (deformed) quantum states exactly to a combination of a classical lattice gauge theory and a plaquette clock model, and employ numerical techniques to calculate various entanglement order parameters. For the Z_{N} model we find a family of (weakly) first-order fracton confinement transitions that in the limit of N→∞ converge to a continuous phase transition beyond the Landau-Ginzburg-Wilson paradigm. We also discover a line of 3D conformal quantum critical points (with critical magnetic flux loop fluctuations) which, in the N→∞ limit, appears to coexist with a gapless deconfined fracton state.

SU(3)_{1} Chiral Spin Liquid on the Square Lattice: A View from Symmetric Projected Entangled Pair States.

Quantum spin liquids can be faithfully represented and efficiently characterized within the framework of projected entangled pair states (PEPS). Guided by extensive exact diagonalization and density matrix renormalization group calculations, we construct an optimized symmetric PEPS for a SU(3)_{1} chiral spin liquid on the square lattice. Characteristic features are revealed by the entanglement spectrum (ES) on an infinitely long cylinder. In all three Z_{3} sectors, the level counting of the linear dispersing modes is in full agreement with SU(3)_{1} Wess-Zumino-Witten conformal field theory prediction. Special features in the ES are shown to be in correspondence with bulk anyonic correlations, indicating a fine structure in the holographic bulk-edge correspondence. Possible universal properties of topological SU(N)_{k} chiral PEPS are discussed.

The aggregation enhanced photoluminescence of gold nanorods in aqueous solutions.

The photoluminescence (PL) properties of single gold nanorod (AuNR) under one-photon excitation (OPE) have been reported recently. In this work, the PL of AuNRs in aqueous solutions were studied with OPE of 514 or 633 nm to characterize the emissions of transverse and longitudinal surface Plasmon resonance (TSPR and LSPR) bands, because the AuNRs aqueous solution was frequently used in bio-medical applications. We found that under 514 nm OPE the TSPR emissions of four groups of AuNRs with different aspect ratios in aqueous solutions were all strong dominating the PL emission with the quantum yield (QY) of 10(-4), which is at least three orders of magnitude higher than that of single AuNR. We further found that the aggregate was the basic form of AuNRs in aqueous solution and living cells, measured by the elastic light scattering and transmission electron microscopy measurements. The Plasmon coupling particularly the TSPR coupling between the neighbored AuNRs in aggregates enhanced the PL and increased the QY, because the conjugation of the rod side to side was a main aggregate mode. Under 633 nm OPE, only LSPR emissions of AuNRs aqueous solutions occurred with the QY level of 10(-5) which is very similar to that of singe AuNR, because of the negligible LSPR coupling.

Carbon nanodots featuring efficient FRET for two-photon photodynamic cancer therapy with a low fs laser power density.

The 5,10,15,20-tetrakis(1-methyl 4-pyridinio) porphyrins (TMPyP), a photosensitizer used for photodynamic therapy of cancers (PDT), were linked to carbon dots (CDots) to form the conjugates of CDot-TMPyP by the electrostatic force. The 415 nm emission band of CDots was well overlapped with the absorption band of TMPyP, so that the Cdots in conjugates can work as donor to transfer the energy to TMPyP moiety by fluorescence resonance energy transfer (FRET) with an FRET efficiency of 45%, determined by the fluorescence lifetime change between the free CDots and conjugated CDots. The two-photon absorption cross section (TPACS) of TMPyP is as low as 110 GM and the TMPyP thus be not suitable for two-photon PDT. Whereas the CDots have high TPACS, and their TPACS are excitation wavelength dependent with the maximum value of 15000 GM at 700 nm. Therefore, the conjugates of CDot-TMPyP were explored for two-photon excitation (TPE) PDT. The two-photon image of CDot-TMPyP in Hela cells was clearly seen under the excitation of a 700 nm femto-second (fs) laser. The singlet oxygen production of CDot-TMPyP was also much higher than that of TMPyP alone under TPE of a 700 nm fs laser. The in vitro PDT killing was further achieved with CDot-TMPyP by TPE of the 700 nm fs laser. Particularly herein the low power density of fs laser from unfocused laser beam was successfully used to carry out the TPE PDT, because of the high TPACS of CDots. These results demonstrate that the CDot-TMPyP conjugates are promising for TPE PDT and needed to investigate further.

Two orders of magnitude fluorescence enhancement of aluminum phthalocyanines by gold nanocubes: a remarkable improvement for cancer cell imaging and detection.

The metal-enhanced fluorescence (MEF) by metal nanoparticles is a useful technique for fluorescence detections in biological systems. The MEF effects with gold nanorods (AuNRs) and nanocubes (AuNCs) for fluorescence enhancements of sulfonated aluminum phthalocyanine (AlPcS), a commonly used and clinical approved photosensitizer for photodynamic therapy of cancers, were studied in this work. For the AuNRs which have the low aspect ratios with the corresponding longitudinal surface plasma resonance (LSPR) band in the region of 600-750 nm, the fluorescence quenching of conjugated AlPcS was found. Whereas for the AuNRs that have the LSPR bands of 800-900 nm, the MEF of AlPcS was obtained with the enhancing factor of 2-6 times, respectively. Using AuNCs, a great enhancement of AlPcS fluorescence was achieved with an enhancing factor of 150 times. Using two cancer cell lines as in vitro models, an outstanding fluorescence enhancement of AlPcS-AuNCs conjugates in cells, relative to AlPcS alone, was obtained under one-photon excitation (OPE) of 405 nm. Moreover, the bright fluorescence image of AlPcS-AuNCs in cells was also achieved under the two-photon excitation (TPE) of an 800 nm femtosecond laser. The high-quality cell imaging with either OPE or TPE demonstrated the potential of AlPcS-AuNCs in cancer cell detections.

Study of polycation-capped Mn:ZnSe quantum dots as a novel fluorescent probe for living cells.

Transition metal manganese ion (Mn(2+)) doped zinc selenide quantum dots (Mn:ZnSe D-Dots) have been considered as a new material for fluorescent probes in biological labeling. However, this application is limited by the low membrane permeability of D-Dots. In this work, Mn:ZnSe D-Dots were capped with the polycation Sofast to label living cells. For the first time, the efficiency of cellular uptake in living cells is significantly enhanced. Various molar ratios of Sofast to D-Dots were explored and compared to obtain the optimal reaction conditions between Sofast and D-Dots for preparing Sofast/D-Dots nano-compound. A comparison on the fluorescence labeling ability of living cells were made between Sofast/D-Dots and pure D-Dots. Results from laser scanning confocal microscope show that Sofast/D-Dots complexes enter the cells more efficiently than pure D-Dots, even with a lower concentration and shorter incubation time. The cytotoxicities of D-Dots and Sofast/D-Dots were also studied. It was found that Sofast/D-Dots have a much lower cytotoxicity than cadmium-containing quantum dots (i.e. CdTe and CdTe/ZnS). Our results suggest that the non-heavy-metal-containing Sofast/D-Dots complexes have a great potential in the application of biological labeling, especially of long-time bioimaging in living cells.

Conjugates of folic acids with zinc aminophthalocyanine for cancer cell targeting and photodynamic therapy by one-photon and two-photon excitations.

To improve the photodynamic detection and therapy of cancers (PDT), folic acid (FA) was conjugated with zinc tetraaminophthalocyanine (ZnaPc) to form ZnaPc-FA. The uptake efficiency of ZnaPc-FA to a FR-positive (folate receptor overexpressed) KB cell line (human nasopharyngeal epidermal carcinoma) was much higher than that of ZnaPc demonstrating an enhanced binding ability of ZnaPc-FA to KB cells. When KB cells were pretreated with free FA followed by incubation of ZnaPc-FA, the high uptake rate of ZnaPc-FA disappeared which demonstrated the special binding function of the FA terminal of ZnaPc-FA on KB cells. The confocal fluorescence images further showed that the affinity of ZnaPc-FA to FR-negative A549 cells (human lung epithelial carcinoma cancer cells) was very low, confirming that ZnaPc-FA can only target FR-positive cancers. The two-photon absorption cross-section of ZnaPc-FA was also higher than that of sulfonated aluminum phthalocyanine (AlPcS), an approved PS for clinical applications. With a 780 nm femto-second (fs) laser, the fluorescence image of ZnaPc-FA in KB cells under two-photon excitation (TPE) can be clearly seen, and the two-photon induced singlet oxygen in ZnaPc-FA solution was found to be proportional to the irradiation dose of the fs laser. The PDT damaging effect of ZnaPc-FA on KB cells was much effective relative to AlPcS under common one-photon excitation, and the killing efficacy of ZnaPc-FA under TPE was 10-fold higher than that of AlPcS. These results suggest that ZnaPc-FA is a promising candidate for PDT improvements and particularly for TPE PDT.

One-step synthesis of water-dispersible silicon nanoparticles and their use in fluorescence lifetime imaging of living cells.

We report a novel method for synthesizing water-dispersible silicon nanoparticles (Si NPs) with a simple one-step procedure using mild reagents (3-aminopropyl) trimethoxysilane (APTES) and ascorbate sodium (AS). This is the first report of "green" synthesis of Si NPs on a large scale and at low cost. The method involves a quick reaction in a commonly used round bottom flask at room temperature and pressure without additional treatment and any special equipment. The as-prepared Si NPs have an average diameter of 2 nm and an emission band at 530 nm with a full width at half maximum height (FWHM) of 70 nm and a quantum yield (QY) of 0.21. Moreover, the fluorescence lifetime of these Si NPs is much longer than that of native fluorophores in living cells. Therefore, these Si NPs allow effective imaging of living cells with a fluorescence lifetime imaging microscope (FLIM). Using the time gating model in FLIM, an excellent image was obtained in which the auto-fluorescence interference of cellular fluorophores was suppressed demonstrating that the Si NPs are promising probes for cell imaging particularly using the FLIM technique.

The use of femto-second lasers to trigger powerful explosions of gold nanorods to destroy cancer cells.

Gold nanorods (AuNRs) with an aspect ratio of 3-4 exhibit large cross sections for single and multi photon light absorption processes in the near infrared region due to surface plasmon resonances. 800 nm laser pulses with the 150 fsec pulse duration (fs laser) can trigger explosions of AuNRs. The fs laser pulses at 20 W/mm(2) equivalent continuous wave (cw) power density blasted AuNRs in QGY human carcinoma cells as confirmed using transmission electron microscopy, while a cw laser at the same power density and dose did not. Cell survival studies further demonstrated that the cw laser at a dose of 15 J/mm(2) resulted in the death of 15% of AuNRs-loaded cells, probably due to a photothermal effect, while the fs laser at only 1.5 J/mm(2) killed more than 90% of AuNRs-loaded cells, indicating that the fs laser-triggered explosions of intracellular AuNRs are powerful enough to instantaneously kill tumour cells.

The conjugates of gold nanorods and chlorin e6 for enhancing the fluorescence detection and photodynamic therapy of cancers.

Gold nanorods (AuNRs) were conjugated with chlorin e6 (Ce6), a commonly used photosensitizer, to form AuNRs-Ce6 by electrostatic binding. Due to the strong surface plasmon resonance coupling, the fluorescence of conjugated Ce6 was enhanced 3-fold and the production of singlet oxygen was increased 1.4-fold. AuNRs-Ce6 were taken up by the HeLa and KB cell lines more easily than free Ce6, enhancing the intracellular delivery of Ce6. The increased cellular amount of Ce6 leads to a 3-fold more efficient photodynamic killing of these two cell lines. This demonstrates the potential of this approach to improve photodynamic detection and therapy of cancers.

Comparison of the killing effects between nitrogen-doped and pure TiO2 on HeLa cells with visible light irradiation.

The killing effect of nitrogen-doped titanium dioxide (N-TiO2) nanoparticles on human cervical carcinoma (HeLa) cells by visible light photodynamic therapy (PDT) was higher than that of TiO2 nanoparticles. To study the mechanism of the killing effect, the reactive oxygen species produced by the visible-light-activated N-TiO2 and pure-TiO2 were evaluated and compared. The changes of the cellular parameters, such as the mitochondrial membrane potential (MMP), intracellular Ca2+, and nitrogen monoxide (NO) concentrations after PDT were measured and compared for N-TiO2- and TiO2-treated HeLa cells. The N-TiO2 resulted in more loss of MMP and higher increase of Ca2+ and NO in HeLa cells than pure TiO2. The cell morphology changes with time were also examined by a confocal microscope. The cells incubated with N-TiO2 exhibited serious distortion and membrane breakage at 60 min after the PDT.

Femto-second laser beam with a low power density achieved a two-photon photodynamic cancer therapy with quantum dots.

Focusing the femto-second (fs) laser beam on the target was the usual way to carry out a two-photon excitation (TPE) in previous photodynamic therapy (PDT) studies. However, focusing the laser deep inside the tissues of the tumor is unrealistic due to tissue scattering, so that this focusing manner seems unfit for practical TPE PDT applications. In this work, we prepared a conjugate of quantum dots (QDs) and sulfonated aluminum phthalocyanine (AlPcS) for TPE PDT, because QDs have a very high two-photon absorption cross section (TPACS) and thus QDs can be excited by an unfocused 800 nm fs laser beam with a low power density and then transfer the energy to a conjugated AlPcS via fluorescence resonance energy transfer (FRET). The FRET efficiency of the QD-AlPcS conjugate in water was as high as 90%, and the FRET process of the cellular QD-AlPcS was also observed in both KB and HeLa cells under TPE of a 800 nm fs laser. The singlet oxygen (1O2) products were produced by the QD-AlPcS under the TPE of the unfocused 800 nm fs laser via FRET mediated PDT. Moreover, the QD-AlPcS can effectively destroy these cancer cells under the irradiation of the 800 nm unfocused fs laser beam with a power density of 92 mW mm-2, and particularly the killing efficiency of the TPE is comparable to that of the commonly used one-photon excitation (OPE) at visible wavelengths. These results highlight the potential of QD-AlPcS for TPE PDT with a near infrared wavelength.

Quantum dot-aluminum phthalocyanine conjugates perform photodynamic reactions to kill cancer cells via fluorescence resonance energy transfer.

Sulfonated aluminum phthalocyanines (AlPcSs), commonly used photosensitizers for photodynamic therapy of cancers (PDT), were conjugated with amine-dihydrolipoic acid-coated quantum dots (QDs) by electrostatic binding, achieving 70 AlPcSs per QD. The AlPcS-QD conjugates can utilize the intense light absorptions of conjugated QDs to indirectly excite AlPcSs producing singlet oxygen via fluorescence resonance energy transfer (FRET), demonstrating a new excitation model for PDT. The AlPcS-QD conjugates easily penetrated into human nasopharyngeal carcinoma cells and carried out the FRET in cells, with efficiency around 80%. Under the irradiation of a 532-nm laser, which is at the absorption region of QDs but not fit for the absorption of AlPcSs, the cellular AlPcS-QD conjugates can destroy most cancer cells via FRET-mediated PDT, showing the potential of this new strategy for PDT.

Conjugation of sulfonated aluminum phthalocyanine to doxorubicin can improve the efficacy of photodynamic cancer therapy.

Sulfonated aluminum phthalocyanine (AlPcS), a widely used photosensitizer for photodynamic therapy of cancer, was conjugated to doxorubicin (Dox), a chemotherapy drug, through electrostatic binding. The fluorescence resonance energy transfer from Dox to AlPcS showed the formation of AlPcS-Dox conjugates, as the fluorescence intensity of conjugated Dox was decreased and that of the AlPcS moiety was enhanced. This AlPcS-Dox conjugation was further confirmed by electrophoresis. The AlPcS-Dox conjugates enhanced the cellular uptake of AlPcS three times more than unconjugated AlPcS in both human hepatocellular carcinoma cell line 7701 and rat basophilic leukemia cell line. Moreover, the photodynamic killing effect of the conjugates was markedly increased as compared with that of AlPcS alone or the cytotoxicity of Dox alone, showing an enhanced effect of the AlPcS-Dox conjugates. These results indicate that the conjugation of a photosensitizer with a chemotherapy drug may improve photodynamic cancer therapy.

Gallium phthalocyanine photosensitizers: carboxylation enhances the cellular uptake and improves the photodynamic therapy of cancers.

The octacarboxyl gallium (GaPcC) and metal-free (H2PcC) phthalocyanines were prepared using the carboxyl as the peripheral substituent. The carboxylation improves the intracellular delivery of these two PcCs into KB and QGY cancer cells as compared to that of sulfonated aluminum phthalocyanines (AlPcS), a popularly used photosensitizer (PS). Moreover, GaPcC maintains high photoproduction of singlet oxygen. With a short incubation time of 3 hours, GaPcC accumulates sufficiently in both KB and QGY cells and improves photodynamic therapy (PDT) by effectively killing these cancer cells. AlPcS and H2PcC show much lower PDT effects under the same conditions, because AlPcS have a slow cellular uptake rate resulting in a low cellular amount and the ability of H2PcC to produce 1O2 is low. Carboxylation is a promising way to prepare water-soluble metal phthalocyanines (MPcCs) and facilitates the cellular uptake of MPcCs for PDT improvement.

Study on the visible-light-induced photokilling effect of nitrogen-doped TiO2 nanoparticles on cancer cells.

Nitrogen-doped TiO2 (N-TiO2) nanoparticles were prepared by calcining the anatase TiO2 nanoparticles under ammonia atmosphere. The N-TiO2 showed higher absorbance in the visible region than the pure TiO2. The cytotoxicity and visible-light-induced phototoxicity of the pure- and N-TiO2 were examined for three types of cancer cell lines. No significant cytotoxicity was detected. However, the visible-light-induced photokilling effects on cells were observed. The survival fraction of the cells decreased with the increased incubation concentration of the nanoparticles. The cancer cells incubated with N-TiO2 were killed more effectively than that with the pure TiO2. The reactive oxygen species was found to play an important role on the photokilling effect for cells. Furthermore, the intracellular distributions of N-TiO2 nanoparticles were examined by laser scanning confocal microscopy. The co-localization of N-TiO2 nanoparticles with nuclei or Golgi complexes was observed. The aberrant nuclear morphologies such as micronuclei were detected after the N-TiO2-treated cells were irradiated by the visible light.

Enhancement of intracellular delivery of anti-cancer drugs by the Tat peptide.

The arginine-rich cationic Tat peptides have been reported to enhance the intracellular delivery of macromolecules, including DNA, RNA, and proteins. In this work an arginine cationic peptide derived from the HIV-1 Tat protein was conjugated with noncovalent bonds to sulfonated aluminum phthalocyanine (AlPcS, a photosensitizer for the light-activated photodynamic cancer therapy), doxorubicin (DOX, a chemotherapeutic agent), or quantum dots (QDs, often used as carriers for the delivery of anticancer drugs). The fluorescence of intracellular conjugates of AlPcS-Tat, DOX-Tat, and QDs-Tat was studied by means of confocal laser scanning microscopy in the human nasopharyngeal carcinoma KB cells and cervical carcinoma Hela cells in vitro. The Tat peptide with noncovalent links can enhance at least a twofold of intracellular delivery of AlPcS, DOX, and QDs via an endocytotic pathway in the two tumor cell lines. This finding may suggest that the Tat peptide-mediated intracellular delivery of anticancer drugs may have the potential for improving efficacy of cancer therapy.

Liposome encapsulation of thiol-capped CdTe quantum dots for enhancing the intracellular delivery.

Although water soluble thiol-capped quantum dots (QDs) have been widely used as photoluminescence (PL) probes in various applications, the negative charges on thiol terminals limit the cell uptake hindering their applications in cell imaging. The commercial liposome complex (Sofast®) was used to encapsulate these QDs forming the liposome vesicles with the loading efficiency as high as about 95%. The cell uptakes of unencapsulated QDs and QD loaded liposome vesicles were comparatively studied by a laser scanning confocal microscope. We found that QD loaded liposome vesicles can effectively enhance the intracellular delivery of QDs in three cell lines (human osteosarcoma cell line (U2OS); human cervical carcinoma cell line (Hela); human embryonic kidney cell line (293 T)). The photobleaching of encapsulated QDs in cells was also reduced comparing with that of unencapsulated QDs, measured by the PL decay of cellular QDs with a continuous laser irradiation in the microscope. The flow cytometric measurements further showed that the enhancing ratios of encapsulated QDs on cell uptake are about 4-8 times in 293 T and Hela cells. These results suggest that the cationic liposome encapsulation is an effective modality to enhance the intracellular delivery of thiol-capped QDs.

Conjugates of folic acids with BSA-coated quantum dots for cancer cell targeting and imaging by single-photon and two-photon excitation.

Bovine serum albumin (BSA)-coated CdTe/ZnS quantum dots (BSA-QDs) were selected to conjugate with folic acid (FA), forming FA-BSA-QDs. This study aims to develop these small FA-BSA-QDs (less than 10 nm) for the diagnosis of cancers in which the FA receptor (FR) is overexpressed. The enhancement of cellular uptake in FR-positive human nasopharyngeal carcinoma cells (KB cells) for FA-BSA-QDs was found by means of confocal fluorescence microscopy under single-photon and two-photon excitation. The uptake enhancement for FA-BSA-QDs was further evaluated by flow-cytometric analysis in 10(4) KB cells, and was about 3 times higher than for BSA-QDs on average. The uptake enhancement was suppressed when KB cells had been pretreated with excess FA, reflecting that the enhancement was mediated by the association of FR at cell membranes with FA-BSA-QDs. When human embryonic kidney cells (293T) (FR-negative cells) and KB cells, respectively, were incubated with FA-BSA-QDs (1 µM) for 40 min, the FA-BSA-QD uptake by 293T cells was much weaker than that by KB cells, demonstrating that FA-BSA-QDs could undergo preferential binding on FR-positive cancer cells. These characteristics suggest that FA-BSA-QDs are potential candidates for cancer diagnosis.

Plasmonic gold nanorods can carry sulfonated aluminum phthalocyanine to improve photodynamic detection and therapy of cancers.

Hexadecyltrimethylammonium bromide-coated gold nanorods (AuNRs) with positive charges were effectively bound to negatively charged sulfonated aluminum phthalocyanine (AlPcS), a photosensitizer for photodynamic detection and therapy, due to the electrostatic force, with a loading content of 10(4) AlPcS molecules per rod. A 5-fold increase in the AlPcS fluorescence of the AlPcS-AuNRs complex was seen. The excitation fluorescence spectrum of the AlPcS-AuNRs with a typical 520 nm band fits well with the resonance band of AuNR surface plasmons, suggesting that such increased AlPcS fluorescence is produced from the strong surface plasmons of AuNRs. The intracellular distribution of AlPcS-AuNRs was studied in the QGY liver cancer cells by respectively imaging the AlPcS fluorescence and AuNRs reflectance with a confocal microscope. Furthermore, the AlPcS-AuNRs-loaded cells were photodynamically damaged after being exposed to red light in a light-dose-dependent manner. In contrast, no phototoxicity of the cells was seen after incubation with the same amount of free AlPcS, indicating that the AlPcS-AuNRs can enhance the AlPcS-mediated photodynamic effect. In addition, the loaded AlPcS can be photothermally released from AuNRs in the cells by the irradiation with an 800 nm femtosecond laser, demonstrating the potential for controlled drug release.