Specific Chemiluminescence Imaging and Enhanced Photodynamic Therapy of Bacterial Infections by Hemin-Modified Carbon Dots.

Antibacterial photodynamic therapy (aPDT) is a promising antibiotics-alternative strategy for bacterial infectious diseases, which features broad-spectrum antibacterial activity with a low risk of inducing bacterial resistance. However, clinical applications of aPDT are still hindered by the hydrophobicity-caused inadequate photodynamic activity of conventional photosensitizers and the hypoxic microenvironment of bacterial infections. To address these problems, herein, a promising strategy is developed to achieve specific chemiluminescence (CL) imaging and enhanced PDT of bacterial infections using hemin-modified carbon dots (H-CDs). The H-CDs can be facilely prepared and exhibit favorable water solubility, augmented photodynamic activity, and unique peroxidase-mimicking capacity. Compared with the free CDs, the photodynamic efficacy of H-CDs is significantly augmented due to the increased electron-hole separation efficiency. Moreover, the peroxidase catalytic performance of H-CDs enables not only infection identification via bacterial infection microenvironment-responsive CL imaging but also oxygen self-supplied aPDT with hypoxia-relief-enhanced bacteria inactivation effects. Finally, the enhanced aPDT efficiencies of H-CDs are validated in both in vivo abscess and infected wound models. This work may provide an effective antibacterial platform for the selective imaging-guided treatment of bacterial infections.

Two-Step Oxidation Synthesis of Sulfur with a Red Aggregation-Induced Emission.

Sulfur is not normally considered a light-emitting material, even though there have been reports of a dim luminescence of this compound in the blue-to-green spectral region. Now, it is shown how to make red-emissive sulfur by a two-step oxidation approach using elemental sulfur and Na2 S as starting materials, with a high photoluminescence quantum yield of 7.2 %. Polysulfide is formed first and is partially transformed into Na2 S2 O3 in the first step, and then turns back to elemental S in the second step. The elevated temperature and relatively oxygen-deficient environment during the second step transforms Na2 S2 O3 into Na2 SO3 incorporated with oxygen vacancies, thus resulting in the formation of a solid-state powder consisting of elemental S embedded in Na2 SO3 . It shows aggregation-induced emission properties, attributed to the influence of oxygen vacancies on the emission dynamics of sulfur by providing additional lower energy states that facilitate the radiative relaxation of excitons.

A MXene of type Ti3C2Tx functionalized with copper nanoclusters for the fluorometric determination of glutathione.

Luminescent copper nanoclusters (Cu NCs) are chosen to functionalize Ti3C2Tx MXene flakes to form a new kind of nanohybrid. It was applied to the determination of glutathione (GSH) via photoluminescence (PL). The Cu NCs and MXene flakes are in close contact, and the blue PL of the Cu NCs (with excitation/emission peaks at 380/425 nm) is quenched. The addition of GSH triggers the separation of the nanohybrid. This results in the recovery of PL. GSH also promotes the PL of Cu NCs via host-guest interactions. Thus, target recognition, corresponding signal output and further magnification are accomplished in a single step. Under optimum conditions, the nanohybrid can detect GSH in the 5.0 to 100 µM concentration range and with a 3.0 µM detection limit. The assay is very specific and shows high selectivity towards metal ions, small biomolecules, amino acids, and thiol containing molecules. Graphical abstractLuminescent copper nanoclusters are used to functionalize Ti3C2Tx MXene flakes, forming a nanohybrid, which is applied to detect glutathione. Target recognition, signal output and magnification are accomplished in a single step, resulting in high selectivity.

Hydrogen Peroxide Assisted Synthesis of Highly Luminescent Sulfur Quantum Dots.

An H2 O2 -assisted top-down approach is used to synthesize brightly luminescent, color-tunable sulfur quantum dots (SQDs), with a photoluminescence quantum yield of up to 23 %. The formation of SQDs involves dissolution of bulk sulfur powder into small particles in an alkaline environment in the presence of polyethylene glycol, followed by H2 O2 -assisted etching of polysulfide species, which has the advantage of the passivation of surface states. This synthetic strategy allows us to simultaneously control the final size of SQDs, to tune their emission color, and to improve their emission quantum yield by eliminating surface traps. Down-conversion white light emitting diodes were also fabricated using blue emissive SQDs and orange emissive copper nanoclusters, with CIE color coordinates of (0.33, 0.32) and a high color rendering index of 91. The water-soluble, highly luminescent SQDs are promising luminescent materials that can be produced from abundant precursor materials.

Controllable Assembly of Cu2+ and Chlorin E6 for H2 S-Activatable Recognition of Bacterial Infection and Enhanced Antibacterial Therapy.

Antibacterial photodynamic therapy (APDT) has emerged as one of the intriguing strategies to combat bacterial resistance. However, the antibacterial efficacy of APDT is found to be severely impacted by the hydrogen sulfide (H2 S)-overproduced bacterial infection microenvironment. Herein, a multifunctional APDT platform is developed by assembling Cu2+ and chlorin e6 (Ce6), which exhibits unique H2 S-activatable fluorescence (FL) and antibacterial features. Noteworthily, the assembly conditions are crucial for achievement of Cu-Ce6 nanoassemblies (NAs) with the on-demand responsive properties. The quenched FL and photosensitization of Cu-Ce6 NAs can be selectively activated by the overexpressed H2 S in infected area, enabling specific recognition of bacterial infection and localized antibacterial therapy with minimized side effects. Significantly, amplified oxidative stress is achieved owning to the effective consumption of H2 S by Cu2+ in the NAs, leading to an enhanced APDT. The antibacterial mechanisms including broad-spectrum APDT activity of released Ce6, inherent sterilization effects of produced copper polysulfides and the accompanying disturbance of bacterial sulphide metabolism are further identified. This study may pave a new avenue for the rational design of intelligent APDT platform using minimalist biological building units and thus facilitating the clinical translation of nano-antibacterial agents.

Modulating Emission of Nonconventional Luminophores from Nonemissive to Fluorescence and Room-Temperature Phosphorescence via Dehydration-Induced Through-Space Conjugation.

Processing nonconventional luminophores into ultralong room-temperature phosphorescence (RTP) materials with bright emission is extremely difficult but highly desired because of their intrinsic advantages together with the relatively weak spin-orbit coupling and rapid nonradiative decay in comparison to traditional aromatic compounds. Here, a straightforward heat treatment method was developed to promote the intersystem crossing efficiency and to suppress nonradiative pathways. A "dehydration-induced through-space conjugation" mechanism was proposed for explaining the activating of fluorescence and RTP of nonconventional luminophores. RTP materials with a phosphorescence quantum yield of 23.8% and emission lifetime of 1.3 s are developed. In addition, the emission color and lifetimes can be modulated by tuning the structure of ligands, which allows their applications in multilevel information encryption. These results open the door for designing highly efficient ultralong RTP materials, which also provides a clue to clarify the detailed emission profiles of RTP materials.

Photoluminescence investigations of sulfur quantum dots synthesized by a bubbling-assisted strategy.

Sulfur quantum dots (S-dots) emerge as promising luminescent materials owing to their remarkable optical properties. However, the mechanisms of their formation and photoluminescence remain concealed. We reveal these mechanisms by the bubbling-assisted synthesis and spectroscopic study of S-dots formed from sulfur ions produced by the alkaline oxidation of bulk sulfur under the passivation of PEG. The emission colour of the S-dots depends on the size, explained by the quantum confinement effect. The dots' luminescent quantum efficiency is strongly affected by the surface sulfur species, which is optimized by the proper surface oxidation. The simple synthesis, excellent luminescence properties, and metal-free nature attract S-dots to optoelectronic and electroluminescence applications.

Ultrasonication-promoted synthesis of luminescent sulfur nano-dots for cellular imaging applications.

An ultrasonication-promoted strategy was proposed to synthesize luminescent S-dots, which reduced the synthesis time from the commonly used 5 days to several hours. The as-synthesized S-dots show a high photostability and low cytotoxicity, and are then successfully applied for cellular imaging.

Ligand-assisted reduction and reprecipitation synthesis of highly luminescent metal nanoclusters.

Solid-state luminescent materials play a key role in fabricating light-emitting diodes (LEDs). Herein, highly luminescent metal nanoclusters (NCs) are synthesized using a ligand-assisted reduction and reprecipitation process. Glutathione (GSH) dissolved in a good solvent (water) is injected into a poor solvent (ethanol in which Cu2+ is dissolved), where the fast reduction of Cu2+ by GSH and the supersaturation-induced aggregation triggered by the solubility change of GSH upon solvent mixing occur. Nanoparticles with diameters of around 50-80 nm embedded with small-sized Cu NCs (around 2 nm) can be obtained and processed into powders simply by drying the solvent. The powders show bright-orange emission with a photoluminescence quantum yield as high as 48%. Nearly monoexponential behavior was observed in the photoluminescence decay profiles of the Cu NCs, which can be attributed to the abundance of metal defect-related states formed with the assistance of coordination between Cu and ethanol. Moreover, white LEDs were fabricated using blue-emissive commercial phosphors and orange-emissive Cu NCs as color converters integrated with UV LED chips.

Stimuli-Responsive Luminescent Copper Nanoclusters in Alginate and Their Sensing Ability for Glucose.

Visually observable pH-responsive luminescent materials are developed by integrating the properties of aggregation-induced emission enhancement of Cu nanoclusters (NCs) and the Ca2+-triggered gelatin of alginate. Sodium alginate, CaCO3 nanoparticles, and Cu NCs are dispersed in aqueous solution, which is in a transparent fluid state, showing weak photoluminescence (PL). The introduced H+ can react with the CaCO3 nanoparticles to produce free Ca2+, which can cross-link the alginate chains into gel networks. Meanwhile, a dramatic increase in the PL intensity of Cu NCs and a blue shift in the PL peak appeared, assigned to the Ca2+-induced enhancement and gelatin-induced enhancement, respectively. Their potential application as a sensor for glucose is also demonstrated based on the principle that glucose oxidase can recognize glucose and produce H+, which further triggers the above-mentioned two-stage enhancement. A linear relationship between the PL intensity and the concentration of glucose in the range of 0.1-2.0 mM is obtained, with the limit of detection calculated as 3.2 × 10-5 M.