Host-Guest Doping Modulated Afterglow Emission of Fluoroquinolones for Their Separation-Free Detection and Discrimination.

Detection and discrimination of fluoroquinolones (FQs) are crucial for food safety but remain a formidable challenge due to their minor differences in molecular structures and the serious interferences from food matrices. Herein, we propose an afterglow assay for the detection and discrimination of FQs through modulating their room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) properties by a host-guest doping strategy. FQs were doped into the boric acid host, forming boronic anhydride structures and hydrogen bonds, which prompted the RTP and TADF performance of FQs by stabilizing their excited states, preventing triplet exciton quenching, and reducing the energy gap between singlet and triplet states. The FQs can be quantitatively detected through monitoring the afterglow intensity of host-guest systems, as low as 0.25 µg/mL. The differences in the afterglow intensity and emission lifetime allowed accurate discrimination of 11 types of FQs through pattern recognition methods. Aided by the delayed signal detection model of afterglow emission, the background signal and the interferences from food matrices were effectively eliminated, which endow the detection and discrimination of mixed FQs in commercial meat samples, without multiple-step separation processes.

Cobalt oxyhydroxide nanosheet-modulated ratiometric fluorescence platform for the selective detection of malachite green in fish.

A ratiometric fluorescence platform was developed based on the cobalt oxyhydroxide (CoOOH) nanosheet-modulated fluorescence response of blue emissive copper nanoclusters (Cu NCs) and yellow emissive o-phenylenediamine (OPD). CoOOH nanosheets showed dual function of strong absorption and oxidation ability, which can effectively quench the blue fluorescence of Cu NCs, with an excitation and emission peak maximum at 390 and 450 nm, respectively , and transfer the OPD into yellow fluorescence products, with an excitation and emission peak maximum at 390 and 560 nm, respectively. Upon introducing butyrylcholinesterase (BChE) and its substrates, CoOOH nanosheets were decomposed into Co2+, and malachite green (MG) showed strong inhibition ability to this  process. This resulted in the obvious difference on the ratio of blue and yellow fluorescence recorded on the system in the presence and absence of MG, which was utilized for the quantitative detection of MG, with a limit of detection of 0.140 µM and a coefficient of variation of 3.5%. The fluorescence ratiometric assay showed excellent detection performances in practical sample analysis.

Detection and discrimination of glutathione among biological thiols based on oxalyl dihydrazide decorated sulfur nanodots.

The quantitative detection and discrimination of glutathione (GSH) were achieved based on oxalyl dihydrazide (ODH) decorated sulfur nanodots. ODH resulted in the aggregation and fluorescence quenching of the sulfur nanodots, and GSH selectively triggered fluorescence recovery through forming stronger hydrogen bonds with ODH than other biological thiols.

Fabrication of highly luminescent and thermally stable composites of sulfur nanodots through surface modification and assembly.

Sulfur nanodots (S-dots) have emerged as a promising luminescent material to excel over traditional heavy metal-based quantum dots. However, their relatively low emission efficiency and poor thermal stability in the solid state have limited their wide applications in photoelectric devices. In this work, highly luminescent, with a photoluminescence quantum yield higher than 50%, and thermally stable composites of S-dots were produced through modulating their surface states and aggregation behaviors by introducing pyromellitic dianhydride (PMDA) and benzoyleneurea (BEU), respectively. PMDA eliminated the relatively short-lived surface states and defects on the surface of S-dots and BEU regulated the aggregation states and facilitated the energy transfer from BEU to S-dots. The as-obtained composites also showed significantly improved thermal stability compared to S-dots, aided by the hydrophobic chemical groups and dense matrix of PMDA and BEU, which extended their applications in fabricating light-emitting diodes. Our presented results provide a new approach to produce highly luminescent S-dots, which widen their applications in the fields of bioimaging, sensing, photoelectric devices, and environmental science.

Sensitive detection of butyrylcholinesterase activity based on a stimuli-responsive fluorescence reaction.

A fluorogenic reaction between the chelate of Mn(II)-citric acid and terephthalic acid (PTA) was discovered, which was carried out through heating the aqueous mixture of Mn2+, citric acid and PTA. Detailed investigations indicated the reaction products were 2-hydroxyterephthalic acid (PTA-OH), which was attributed to the reaction between PTA and OH, formed by the triggering of Mn(II)-citric acid in the presence of dissolved O2. PTA-OH showed a strong blue fluorescence, peaked at 420 nm, and the fluorescence intensity presented a sensitive response to pH of the reaction system. Based on these mechanisms, the fluorogenic reaction was used for the detection of butyrylcholinesterase activity, achieving a detection limit of 0.15 U/L. The detection strategy was successfully applied in human serum samples, and it was also extended for the detection of organophosphorus pesticides and radical scavengers. Such a facile fluorogenic reaction and its stimuli-responsive properties offered an effective tool for designing detection pathways in the fields of clinical diagnosis, environmental monitoring and bioimaging.

Modulating Emission of Boric Acid into Highly Efficient and Color-Tunable Afterglow via Dehydration-Induced Through-Space Conjugation.

Inorganic boric acid (BA) is generally not considered an efficient afterglow material, and several groups have reported its extremely weak room-temperature phosphorescence (RTP) in the blue spectral region. It is discovered that heat treatment of BA results in increased afterglow intensity (27-fold increase) and prolonged emission lifetime (from 0.83 to 1.59 s), attributed to enhanced through-space conjugation (TSC) of BA. The afterglow intensity of BA can be increased further (≈415 folds) by introducing p-hydroxybenzoic acid (PHA), which contains a conjugated molecular motif, to further promote the TSC of the BA system. This combination results in the production of afterglow materials with a photoluminescence quantum yield of 83.8% and an emission lifetime of 2.01 s. In addition, a tunable multicolor afterglow in the 420-490 nm range is achieved owing to the enhancement of the RTP and thermally activated delayed fluorescence of PHA, where BA exerts a confinement effect on the guest molecules. Thus, this study demonstrates promising afterglow materials produced from extremely abundant and simple precursor materials for various applications.

Green-Emissive Copper Nanocluster with Aggregation-Enhanced Emission for Selective Detection of Al3.

Selective detection of Al3+ is of great significance both for the benefit of human health and environmental safety considerations. In this work, a sensitive and selective fluorescence assay for Al3+ was proposed based on the green-emissive Cu nanoclusters (Cu NCs). Different from the commonly reported works, the green emissive Cu NCs showed dual emission bands at 450 and 510 nm, attributed to the reaction product between polyvinyl pyrrolidone and ascorbic acid and the Cu core, respectively. Al3+ could induce the aggregation of Cu NCs by forming covalent bonds, which results in the enhancement of photoluminescence intensity. This enhancement phenomenon is rather selective to Al3+ , which endows the detection in real samples. These results provide new insights for the fluorescence mechanisms of metal NCs, which also provided a functional luminescent material for various applications, such as chemical sensing, bioimaging and photoelectric devices.

Solid-State Luminescent Materials with Multiple Emission Colors and Near-Unity Quantum Yield.

Developing solid luminescent materials with a unity quantum yield and tunable emission color is promising, although it is still a difficult task. A straightforward heat-treatment method has been developed to load 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) into the matrix of boric acid (BA) to produce powders with a near-unity quantum yield and tunable emission color from yellow to green. Our results suggest that the emission of the powders originates from PTCDA, and the tunability of the emission color is caused by the hydrolysis of PTCDA in the alkaline environment. The near-unity quantum yield is attributed to the BA matrix, which confines PTCDA. In addition, the powder also shows excellent thermal stability that allows its application in light-emitting diodes. The above results are important for the development of solid-state luminescent materials for various applications, and also provide a clue for studying the emission properties of luminescent materials.

Efficient blue TADF-type organic afterglow material via boric acid-assisted confinement.

A heat treatment method is developed to produce blue afterglow materials, achieving a photoluminescence quantum yield of 65% and an emission lifetime of 0.18 s (afterglow: >2 s). The afterglow is attributed to TADF of norfloxacin, activated by the confinement effect of boric acid.

Long-Lived Afterglow from Elemental Sulfur Powder: Synergistic Effects of Impurity and Structure.

Elemental sulfur is not traditionally considered as an afterglow material, even though it can be endowed with fluorescence properties through processing it into nanodots. Herein, we discovered that elemental sulfur powder could emit room temperature phosphorescence (RTP) with a lifetime of 3.7 ms. A long-lived (>12 s) afterglow emission at 77 K could also be observed by the naked eye. Detailed investigations suggested that such a special phenomenon was attributed to impurity-related traps coupled with conduction and valence bands. After the sulfur is processed into nanodots, the rigid environment formed by the cross-linking of the surface ligands could stabilize the excited charges from quenching. This results in the promotion of RTP intensity and lifetime to achieve an emission lifetime of 200 ms. These results confirm the unique RTP of elemental sulfur powder, and also suggest the potential of sulfur-based materials as versatile components for the development of RTP materials.

Fluorescence ratiometric assay for discriminating GSH and Cys based on the composites of UiO-66-NH2 and Cu nanoclusters.

The discriminative detection of glutathione (GSH) from cysteine (Cys) remains a challenge because of their similarity in structure and chemical properties. This study reported a strategy for selective and sensitive detection of GSH based on the GSH-promoted blue fluorescence of UiO-66-NH2 and aggregation-enhanced emission (AEE) feature of orange emissive Cu nanoclusters (NCs). A relatively weak blue fluorescence of UiO-66-NH2 was converted to strong after reacting with GSH due to the rotation-restricted emission enhancement mechanism. In addition, the GSH-activated UiO-66-NH2 was further used as a template and reducing reagent for synthesizing orange-red AEE active Cu NCs composites (UiO-66-NH2@Cu NCs). A ratiometric fluorescence response was observed after forming UiO-66-NH2@Cu NCs, helping discriminate GSH over Cys. In addition, UiO-66-NH2@Cu NCs were further utilized for the detection of GSH in clinical samples. The present findings provide an efficient strategy to discriminate GSH over Cys and open a new door for utilizing and functionalizing metal-organic frameworks (MOFs) for various applications.

Fabrication of Highly Luminescent and Thermally Stable Phosphors through In-Situ Formation of BaSO4 on Sulfur Nanodots.

Producing high performance phosphors using abundant and non-toxic precursors yet straightforward methods are promising but still a challenging task. Herein, highly luminescent and thermally stable phosphors were fabricated through an in situ precipitation synthesis strategy. Sulfur nanodots (S-dots) act as the precursors for precipitation reactions and also provide the luminescent centers. Structural and optical characterization investigations suggest that S-dots are incorporated in the matrix of BaSO4 , and BaSO4 provides passivation effect for the surface ligands or traps of S-dots. This results in the promotion of photoluminescence quantum yield from 23 % to 58 %, and the BaSO4 matrix also leads to the obvious promotion of thermal stability. These merits endow the construction of phosphor-based light-emitting diodes by utilizing the S-dots@BaSO4 hybrid phosphors as a color conversion layer. These research results are significant for developing sulfur-based luminescent materials, and also provide a solid and universal theory to produce high quality phosphors.

Highly Selective Detection of Paraoxon in Food Based on the Platform of Cu Nanocluster/MnO2 Nanosheets.

Selective and sensitive identification of paraoxon residue in agricultural products is greatly significant for food safety but remains a challenging task. Herein, a detection platform was developed by integrating Cu nanoclusters (Cu NCs) with MnO2 nanosheets, where the fluorescence of Cu NCs was effectively quenched. Upon introducing butyrylcholinesterase and butyrylcholine into the system, their hydrolysate, thiocholine, leads to the decomposition of the platform through a reaction between the MnO2 nanosheets and thiol groups on thiocholine. The electron-rich groups on thiocholine can further promote the fluorescence intensity of Cu NCs through host-guest interactions. Adding paraoxon results in the failure of fluorescence recovery and further promotion, which could be utilized for the quantitative detection of paraoxon, and a limit of detection as low as 0.22 ng/mL can be achieved. The detection platform shows strong tolerance to common interference species, which endows its applications for the detection of paraoxon in vegetables and fruit. These presented results not only open a new door for the functionalization of metal nanoclusters but also offer an inspiring strategy for analytic techniques in nanomedicine and environmental science.

A ratiometric fluorescent sensor for tetracyclines detection in meat based on pH-dependence of targets with lanthanum-doped carbon dots as probes.

Although some ratiometric fluorescent sensors have been reported to detect tetracyclines, most of ratiometric fluorescent sensors were established based on europium ion with a narrow linear range. In this work, a ratiometric fluorescent sensor for tetracyclines detection was established based on the dual-emission lanthanum-doped carbon dots (La-CDs) as probes combining with the characteristic pH-response of tetracyclines. The fluorescence intensity of tetracyclines will be enhanced in high pH, and the emission peak of tetracyclines overlapped with the peak of probes. The superposition effect of tetracyclines and probes at 515 nm greatly improved the sensitivity of the ratiometric fluorescent sensor and widened the detection range, and linear ranges for oxytetracycline (OTC) and tetracycline (TC) were respectively 0.00-805.20 µM and 0.00-1039.50 µM. Moreover, the preparation procedure of the La-CDs was simple and time saving and the coupling agent was not required. A comparison of La-CDs with undoped carbon dots (un-CDs) showed that the optical performance and sensing performance of La-CDs were improved. In addition, a portable paper sensor with La-CDs as probes was preliminarily explored in this work, and the sensor has been applied to detect OTC and TC in pork and fish with satisfactory results.

Glutathione modulated fluorescence quenching of sulfur quantum dots by Cu2O nanoparticles for sensitive assay.

Sulfur quantum dots (S-dots) show great potential for applications in various field, due to their favorable biocompatibility, high stability, and antibacterial properties. However, the use of S-dots in chemical sensing is limited by the lack of functional groups on the surface. In this work, a fluorescence glutathione (GSH) assay is developed based on the GSH modulated quenching effect of Cu2O nanoparticles (NP) on S-dots. The fluorescence of S-dots is effectively quenched after forming complex with Cu2O NP through a static quenching effect (SQE). Introducing of GSH can trigger the decomposition of Cu2O NP into GSH-Cu(I) complex, which leads to the weaken of SQE and the partial recover of the fluorescence. The intensity of recovered fluorescence shows a positive correlation with the concentration of GSH in the concentration range of 20 to 500 µM. The fluorescence GSH assay shows excellent selectivity and robustness towards various interferences and high concentration salt, which endow the successful detection of GSH in human blood sample. The presented results provide a new door for the design of fluorescence assays, which also provides a platform for the applications in nanomedicine and environmental science.

Point-of-care testing of butyrylcholinesterase activity through modulating the photothermal effect of cuprous oxide nanoparticles.

Butyrylcholinesterase (BChE) is an important indicator for clinical diagnosis of liver dysfunction, organophosphate toxicity, and poststroke dementia. Point-of-care testing (POCT) of BChE activity is still a challenge, which is a critical requirement for the modern clinical diagnose. A portable photothermal BChE assay is proposed through modulating the photothermal effects of Cu2O nanoparticles. BChE can catalyze the decomposition of butyrylcholine, producing thiocholine, which further reduce and coordinate with CuO on surface of Cu2O nanoparticle. This leads to higher efficiency of formation of Cu9S8 nanoparticles, through the reaction between Cu2O nanoparticle and NaHS, together with the promotion of photothermal conversion efficiency from 3.1 to 59.0%, under the excitation of 1064 nm laser radiation. An excellent linear relationship between the temperature change and the logarithm of BChE concentration is obtained in the range 1.0 to 7.5 U/mL, with a limit of detection of 0.076 U/mL. In addition, the portable photothermal assay shows strong detection robustness, which endows the accurate detection of BChE in human serum, together with the screening and quantification of organophosphorus pesticides. Such a simple, sensitive, and robust assay shows great potential for the applications to clinical BChE detection and brings a new horizon for the development of temperature based POCT.

Identification and genome analysis of Comamonas testosteroni strain JLU460ET, a novel steroid-degrading bacterium.

In this work, C. testosteroni JLU460ET isolated from animal waste was confirmed to have great degradation capability for 17ß-estradiol and testosterone. This bacterium could degrade nearly 90% of 17ß-estradiol (5 mg L-1) in 4 days and transform it into estrone for further degradation. One hundred percent testosterone (144 mg L-1) could be completely degraded after 9 h of incubation. This is the first report of C. testosteroni strains with the ability to degrade both estrogens and testosterone. The whole genome sequence of C. testosteroni JLU460ET was obtained and annotated, containing one chromosome (5,497,097 bp) with 61.37% GC content. A total of 4805 protein-coding genes and 134 RNA genes (including 29 rRNA genes, 102 tRNA genes and three ncRNA genes) were identified. Furthermore, the complete genome sequence of C. testosteroni JLU460ET was compared with four other C. testosteroni strains. Altogether, these five C. testosteroni strains contain 3508 core genes and 7616 pan genes. A steroid degradation pathway including 11 steroid degradation genes exists in core genes of five C. testosteroni strains. Twenty-two steroid degradation genes were found in the C. testosteroni JLU460ET genome, which has the most reported steroid degradation genes among the five C. testosteroni genomes. Further functional genomic analysis identified a gene cluster responsible for testosterone degradation in C. testosteroni JLU460ET, as well as a gene encoding 17ß-HSD, the key enzyme for transforming 17ß-estradiol into estrone. This work could enrich the genome sources of steroid-degrading strains and promote the study of steroid-degradation mechanism in bacteria.

Ratiometric sensing of butyrylcholinesterase activity based on the MnO2 nanosheet-modulated fluorescence of sulfur quantum dots and o-phenylenediamine.

Butyrylcholinesterase (BChE) can modulate the expression level of cholinesterase, which emerges as an important clinical diagnose index. However, the currently reported assays for BChE are suffering from the problem of interferences. A ratiometric fluorescence assay was developed based on the MnO2 nanosheet (NS)-modulated fluorescence of sulfur quantum dots (S-dots) and o-phenylenediamine (OPD). MnO2 NS can not only quench the fluorescence of blue emissive S-dots, but also enhance the yellow emissive OPD by catalyzing its oxidation reactions. Upon introducing BChE and substrate into the system, their hydrolysate can reduce MnO2 into Mn2+, leading to the fluorescence recovery of S-dots and failure of OPD oxidation. BChE activity can be quantitatively detected by recording the change of fluorescence signals in the blue and yellow regions. A linear relationship is observed between the ratio of F435/F560 and the concentration of BChE in the range 30 to 500 U/L, and a limit of detection of 17.8 U/L has been calculated. The ratiometric fluorescence assay shows an excellent selectivity to acetylcholinesterase and tolerance to various other species. The method developed  provides good detection performances in human serum medium and for screening of  inhibitors.

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.