A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet-light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up-conversion (UC)PL of these CDs is also observed. Moreover, flexible full-color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light-emitting diodes, full-color displays, and multiplexed (UC)PL bioimaging.

Truly fluorescent excitation-dependent carbon dots are prepared, and the relationship between their chemical composition and fluorescent emission is discussed. Furthermore, potential applications of the as-prepared carbon dots to multicolor bio-labeling and multidimodal sensing are demonstrated.

The achievement of high-efficient pure red emissive carbon dots (CDs) is still a great challenge as well as one of the most critical issues that hinders widespread applications of CDs. Herein, a facile approach for the preparation of high-efficient red emissive CDs (R-CDs) is reported, and they exhibit numerous unique features including pure red emission (λmax ≈ 640 nm), respectable quantum yield (22.9%), low cytotoxicity, two-photon excited fluorescence (TPEF), and high photothermal conversion efficiency (43.9% under irradiation of 671 nm laser). Moreover, the chemical composition and photophysical properties of the R-CDs are detailed characterized and analyzed, and from which their photoluminescence mechanism is proposed. Interestingly, the R-CDs are found to particularly light up RNA-rich nucleolus both in one-photon and two-photon modes as well as show excellent counterstain compatibilities with other classical subcellular dyes. The localization of the R-CDs in nucleolus is supported by ribonuclease digestion testing, and the stronger emission is further verified to be due to an accumulation process. In addition, the R-CDs are confirmed to be facilely conjugated with fluorescein isothiocyanate (FITC) and then bring it into living cells, which reveals their potentials to perform as carriers for delivery of drugs that cannot (or hardly) enter into living cells directly. Finally, the R-CDs are shown to be excellent in photothermal cancer therapy in vitro due to their high photothermal conversion efficiency. This study represents not only a facile method for the preparation of high-efficient R-CDs, but also opens many possibilities for applications, such as in biomedicine (multifunctional theranostic agents) and emitting/display devices, thanks to their unique and superior properties.

The cyanobacteria and red algae are two important groups of photosynthetic organisms that share a light-harvesting antenna known as the phycobilisome (PBS) [1][2][3][4] . PBSs are among the largest protein complexes in the living world and consist of phycobiliproteins (PBPs), including phycocyanin, phycoerythrin and allophycocyanin (APC), and linker proteins . Two subunits of PBPs, the α -and β -subunits, form an α β heterodimer that is conventionally called an (α β ) monomer. The monomer is then assembled into an (α β ) 3 trimer, the basic unit of PBS hierarchical assembly. The trimers of various PBPs are organized into a highly ordered supramolecular complex with the help of the linker proteins 1,5,6 . Four morphological types of PBS 1 are known: hemidiscoidal 7 , hemiellipsoidal 8 , block-type 9 and bundle-type 10. The hemidiscoidal PBS contains a central core surrounded by peripheral rods 1,11,12 . The chromophores in hemidiscoidal PBS are arranged in such a way that a photon absorbed by a chromophore in the peripheral rods is rapidly funnelled to chromophores in the core 13 and eventually to the terminal emitters (the core-membrane linker protein (L CM ) [14][15][16] or allophycocyanin D (ApcD) 17,18 ). The terminal emitters then transfer the energy to photosynthetic reaction centres 16,[19][20][21][22][23] . Currently, the mechanism of PBS assembly is poorly understood and the energy transfer routes within PBSs are not well defined. Although 3D structures of some individual PBPs have been reported (reviewed in refs 2, 3), the structures of most linker proteins are unknown and the complete structure of a PBS has not been published, to our knowledge. Here we report the cryo-electron microscopy (cryo-EM) structure of a PBS from the red alga Griffithsia pacifica at a resolution of 3.5 Å, which reveals details of the PBS architecture. Overall structureThe PBS from G. pacifica was purified and its intactness confirmed by its protein composition and spectroscopic features (Extended Data Fig. 1a-f). We reconstructed a 3D structure of the intact PBS by single particle cryo-EM with an overall resolution of 3.5 Å (Extended Data Table 1). Applying individual local masks improved the resolutions of local maps to 3.4-4.3 Å (Extended Data Fig. 2g). The PBS is one of the largest supramolecular complexes that has been reported, with a calculated molecular mass of approximately 16.8 megadaltons. The overall appearance is block-type 9 with twofold symmetry oriented perpendicularly to the thylakoid membranes (Fig. 1a-c and Extended Data Figs 1g-l, 3a-d). This PBS is larger than the hemiellipsoidal PBS isolated from Porphyridium cruentum8 and has dimensions of approximately 680 Å length, 390 Å height, and 450 Å thickness (Fig. 1a-c).The PBS contains a triangular core with the top cylinder B (formed by two APC trimers) sitting above two basal cylinders A and A′ (each formed by three APC trimers) surrounded by peripheral rods arranged in a staggered fashion (Fig. 1a-c and Extended Data Fig. 3c-e). In addition to the core and ...

Fluorescent carbon dots (CDs) have attracted much attention in recent years because of their superior optical and chemical properties, thus demonstrating many potential applications. However, the previously reported CDs mostly show strong emission only in the blue-light region, and the long-wavelength (i.e., yellow- to red-light) emissions are usually very weak. Such a drawback restricts their further applications, particularly in the biology-relevant fields. Herein, a rare example of N-doped CDs that emit bright-yellow fluorescence (i.e., y-CDs) is reported using 1,2,4-triaminobenzene as carbon precursor. The as-prepared y-CDs exhibit not only respectable emission quantum yield and highly optical stabilities but superior biocompatibility and biolabeling potentials. In addition, the y-CDs are found to show an interesting "ON-OFF-ON" three-state emission with the stepwise addition of Ag(+) and cysteine (Cys), indicating potential applications as a bifunctional sensing platform. Thanks to the highly intense emission of y-CDs, the gradual quenching and restoration of their fluorescence with the addition of Ag(+) and further Cys could also be observed with the naked eye. More importantly, the ensemble of the y-CDs and Ag(+) demonstrates practicability for the highly selective and sensitive detection of Cys in human plasma samples with satisfactory results.

The efficiency of chemical intercommunication between enzymes in natural networks can be significantly enhanced by the organized catalytic cascades. Nevertheless, the exploration of two-or-more-enzymes-engineered nanoreactors for catalytic cascades remains a great challenge in cancer therapy because of the inherent drawbacks of natural enzymes. Here, encouraged by the catalytic activity of the individual nanozyme for benefiting the treatment of solid tumors, we propose an organized in situ catalytic cascades-enhanced synergistic therapeutic strategy driven by dual-nanozymes-engineered porphyrin metal–organic frameworks (PCN). Precisely, catalase-mimicking platinum nanoparticles (Pt NPs) were sandwiched by PCN, followed by embedding glucose oxidase-mimicking ultrasmall gold nanoparticles (Au NPs) within the outer shell, and further coordination with folic acid (P@Pt@P–Au–FA). The Pt NPs effectively enabled tumor hypoxia relief by catalyzing the intratumoral H2O2 to O2 for (1) enhancing the O2-dependent photodynamic therapy and (2) subsequently accelerating the depletion of β-d-glucose by Au NPs for synergistic starving-like therapy with the self-produced H2O2 as the substrate for Pt NPs. Consequently, a remarkably strengthened antitumor efficiency with prevention of tumor recurrence and metastasis was achieved. This work highlights a rationally designed tumor microenvironment-specific nanoreactor for opening improved research in nanozymes and provides a means to design a catalytic cascade model for practical applications.

A novel, high sensitive, and specific DNA assay based on gold nanoparticle (AuNP) colorimetric detection and hybridization chain reaction (HCR) amplification has been demonstrated in this article. Two hairpin auxiliary probes were designed with single-stranded DNA (ssDNA) sticky ends which stabilize AuNPs and effectively prevent them from salt-induced aggregation. The target DNA hybridized with the hairpin auxiliary probes and triggered the formation of extended double-stranded DNA (dsDNA) polymers through HCR. As a result, the formed dsDNA polymers provide less stabilization without ssDNA sticky ends, and AuNPs undergo aggregation when salt concentration is increased. Subsequently, a pale purple-to-blue color variation is observed in the colloid solution. The system is simple in design and convenient in operation. The novel strategy eliminates the need for enzymatic reactions, separation processes, chemical modifications, and sophisticated instrumentation. The detection and discrimination process can be seen with the naked eye. The detection limit of this method is lower than or at least comparable to previous AuNP-based methods. Importantly, the protocol offers high selectivity for the determination between perfectly matched target oligonucleotides and targets with single base-pair mismatches.

Fluorescent probes with both excitation and emission in the near-infrared (NIR) region are highly attractive in the field of bioimaging. Herein, NIR emissive carbon dots (CDs, λ = 683 nm) capable of excitation with a NIR femtosecond pulse laser (850 nm) are reported for the first time. The NIR CDs also hold a variety of superior features including excellent water dispersibility, narrow emission bands, and high quantum yields (QY = 16.8%). Further studies reveal that the emission of the NIR CDs derives predominantly from the surface molecular state mechanism. More interestingly, the NIR CDs are verified to have very low cytotoxicity and show capabilities for two-photon fluorescence bioimaging. Finally, the NIR CDs are shown to be easily modified with fluorescein isothiocyanate (FITC) and moved into living cells. These findings demonstrate that the as-prepared NIR CDs could not only be potentially employed for deep-tissue two-photon bioimaging, but also used as an effective carrier for delivery of drugs that can't (or hardly) enter into living cells directly.