A turn-on fluorescent sulfide probe prepared from carbon dots and MnO2 nanosheets

Size-matching compositing nanoprobe of AIE-type gold nanocluster supramolecular nanogels wrapped by hypergravity-tailored MnO2 nanosheets for cellular glutathione detection

Compositing has been the main approach for material creation via wisely combining material components with different properties. MnO2 nanosheets (MNSs) with thin 2 D morphology are usually applied to composite molecules or nanomaterials for biosensing and bioimaging applications. However, such composition is actually structurally unmatched, albeit performance matching. Here, a series of benefits merely on the basis of structural match have been unearthed via tailoring MNSs with four sizes by synthesis under controllable hypergravity field. The classical fluorophore-quencher couple was utilized as the subject model, where the soft supramolecular nanogels based on aggregation-induced emission (AIE)-active gold nanoclusters were wrapped by MNSs of strong absorption. By comparative study of one-on-one wrapping and one-to-many encapsulation with geometrical selection of different MNSs, we found that the one-on-one wrapping model protected weakly-bonded nanogels from combination-induced distortion and strengthened nanogel networks via endowing exoskeleton. Besides, wrapping pattern and size-match significantly enhanced the quenching efficiency of MNSs towards the emissive nanogels. More importantly, the well-wrapped nanocomposites had considerable enhanced biological compatibility with much lower cytotoxicity and higher transfection capacity than the untailored MNSs composite and could serve as cellular glutathione detection.

Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared Ag2S quantum dots and MnO2 nanosheets complex

Near infrared (NIR) emission Ag2S quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence Ag2S QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO2) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO2 nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of Ag2S QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of Ag2S QDs was restored when sulfide anion (S2-) was added, due to the reduction of MnO2 to Mn2+.The linear ranges for fluorescence and colorimetric analysis of S2- were 2-250 μM and 0.3-50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S2- in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.

Rapid and sensitive determination of Piroxicam by N-doped carbon dots prepared by plant soot

Piroxicam (PX) as a nonsteroidal anti-inflammatory drug (NSAID) can be effectively used for anti-inflammatory and analgesia. However, overdoses may induce side effects such as gastrointestinal ulcers and headaches. Therefore, the assay of piroxicam has considerable significance. In this work, nitrogen-doped carbon dots (N-CDs) was synthesized for PX detection. The fluorescence sensor was fabricated by hydrothermal method with plant soot and ethylenediamine. The strategy exhibited a detection range of 6-200 μg/mL and 250-700 μg/mL with the limited detection of 2 μg/mL. The mechanism of the PX assay base on the fluorescence sensor was the process of electron transfer between the PX and N-CDs. The assay subsequently demonstrated could be successfully used in actual sample. The results indicated that the N-CDs could be a superior candidate nanomaterial for piroxicam monitoring in the healthcare product industry.

Nitrogen-doped carbon dots with high selectivity for hydrosulfide sensing and their living cells imaging

Hydrosulfuric acid is an aqueous solution of hydrogen sulfide (H₂S). At physiological pH, approximately 80% of the total amount of H₂S exists in the form of monoanionic HS^-. Because HS^- is both widely distributed and highly toxic to humans, it is necessary to design an efficient method to detect HS^- with high sensitivity and selectivity. So, the nitrogen-doped carbon dots (NCDs) with green fluorescence are synthesized using a one-step hydrothermal method. The as-prepared NCDs show it can be effectively used as an indicator for monitoring HS^-. And the NCD fluorescence intensity exhibits a linear relationship with HS^- concentration. In addition, NCDs as a probe can be applied for fluorescence imaging in living cells to detect the presence of trace exogenous HS^-.

Branched poly(ethylenimine) carbon dots-MnO2 nanosheets based fluorescent sensory system for sensing of malachite green in fish samples

Malachite green (MG) is an organic dye compound that is frequently used as a fungicide and antiseptic in aquaculture. However, human or animal exposure to MG causes carcinogenic, teratogenic and mutagenic effects. Herein, a novel fluorescent assay was designed for the detection of MG using manganese dioxide nanosheets (MnO₂ NS) as an energy acceptor to quench the fluorescence of branched poly(ethylenimine) carbon dots (BPEI-CDs) via Förster resonance energy transfer. When butyrylcholinesterase is introduced to form thiocholine in the presence of S-butyrylthiocholine iodide, MnO₂ NS can be recovered by thiocholine to Mn²⁺, resulting in restoration of the fluorescence of BPEI-CDs. Exploiting these changes in fluorescence intensity in the above system, a fluorescence probe was successfully developed for the quantitative detection of MG. Besides, this assay was applied to fish samples, verifying the high potential for practical application of the proposed sensor for the monitoring of MG in aquatic products.

Monitoring of glutathione using ratiometric fluorescent sensor based on MnO2 nanosheets simultaneously tuning the fluorescence of Rhodamine 6G and thiamine hydrochloride

L-glutathione (GSH) which has reducibility and integrated detoxification plays an important role in maintaining normal immune system function. Its abnormal levels are relevant to some clinical diseases. In this work, a facile ratiometric fluorescence sensor for GSH was designed based on MnO₂ nanosheets, Thiamine hydrochloride (VB₁) and Rhodamine 6G (R6G). VB₁ could be oxidized into fluorescent ox-VB₁ due to the strong oxidizing property of MnO₂, and MnO₂ nanosheets simultaneously could quench the fluorescence of R6G based on the inner filter effect (IFE). MnO₂ could react with GSH to form Mn²⁺, which caused its losing oxidizing property and quenching capacity. According to this principle, the concentration of ox-VB₁ diminished, resulting in its fluorescence intensity decreasing at 455 nm and the fluorescence of R6G recovering at 560 nm. Under optimal conditions, the VB₁-MnO₂-R6G detection system showed a wide linear range towards GSH in the range of 1.0-300.0 µmolL^-1 with a low detection limit reaching 0.52 µmolL^-1. Furthermore, the method was also applied in the determination of GSH in human serum.

Ratiometric fluorescence and smartphone dual-mode detection of glutathione using carbon dots coupled with Ag+-triggered oxidation of o-phenylenediamine

Developing ratiometric fluorescence and smartphone dual-mode bioanalysis methods is important but challenging. A ratiometric fluorescence method for determining glutathione (GSH) using carbon dots (CDs) and Ag⁺-triggered o-phenylenediamine (OPD) oxidation is described here. Ag⁺oxidizes OPD to give 2,3-diaminophenazine (oxOPD), which effectively quenches CD fluorescence at 436 nm through the inner filter effect and causes a new emission peak at 561 nm. GSH chelates with Ag⁺and prevents the Ag⁺oxidizing OPD and therefore effectively preserves CD emission at 436 nm (blue) and allows only weak oxOPD fluorescence at 561 nm (orange) to occur. The oxOPD to CD fluorescence intensity ratio decreased linearly as the GSH concentration increased in the range 0-150 nM, and the detection limit was 15 nM. The ratiometric fluorescence probe lit with an ultraviolet lamp clearly changed color from orange to blue as the GSH concentration increased. An image was acquired using a smartphone camera and converted into digital values. The blue and red channel ratio was calculated and used to quantify GSH. The method therefore allows dual-mode detection of GSH.

Sensitive detection of picric acid in an aqueous solution using fluorescent nonconjugated polymer dots as fluorescent probes

Nonconjugated polymer dots (NPDs) were successfully used as fluorescent probes to selectively and sensitively detect picric acid (PA). The NPDs were prepared from polyethylenimine and 1,4-phthalaldehyde under mild conditions and had excitation and emission maxima of 351 and 474 nm, respectively. Fluorescence of the NPDs was efficiently quenched by PA through the inner filter effect because of the overlapping PA absorption band and NPD excitation spectrum. The NPDs allowed PA to be determined with a high degree of sensitivity. The linear range was 0-140μM and the detection limit was 0.5μM. The work involved developing a novel method for synthesizing NPDs and a promising platform for determining PA in environmental media.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.

"Turn-on" fluorometric probe for α-glucosidase activity using red fluorescent carbon dots and 3,3',5,5'-tetramethylbenzidine

A turn-on method for determining α-glucosidase activity is described using a chemical redox strategy in which the fluorescence of red fluorescent carbon dots (CDs) is modulated. The red fluorescent CDs were prepared using a solvothermal method with p-phenylenediamine and sodium citrate. The excitation and emission maxima of the CDs were 490 and 618 nm, respectively. Ce⁴⁺ ions catalyze the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) to give a blue oxidized TMB product (oxTMB). Absorption by oxTMB overlaps with the red light emitted by the CDs because of the fluorescence inner filter effect; therefore the presence of oxTMB decreases the intensity of fluorescence emission by the CDs. However, hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl by the enzyme α-glucosidase causes formation of ascorbic acid . Ascorbic acid reduces oxTMB to TMB, so that the inner filter effect disappeared and the fluorescence recovered. The strategy allows α-glucosidase activity to be successfully determined down to 0.02 U mL^-1 and gives a dynamic linear range of 0-5.5 U mL^-1. The strategy is very selective for α-glucosidase activity in the presence of potentially interfering substances. The method has been successfully applied to the determination of α-glucosidase activity in spiked human serum samples and gave satisfactory results. Graphical Abstract Schematic of the method used to prepare the carbon dots and the mechanisms involved in determining α-glucosidase activity.

Colorimetric and fluorescent dual-mode strategy for sensitive detection of sulfide: Target-induced horseradish peroxidase deactivation

Environmental pollution caused by sulfide compounds has become a major problem for public health. Hence, accurate detection of sulfide anions (S^2-) level is valuable and vital for environmental monitoring and protection. Here, we report a new colorimetric/fluorescent dual-mode sensor for the determination of S^2- based on the inhibition of enzyme activity and the unique optical properties of produced 2,3-diaminophenazine (DAP), thus making the analytical results more convincing. In this strategy, horseradish peroxidase (HRP) enzyme is used for catalyzing the H₂O₂-mediated oxidation of o-phenylenediamine (OPD) to produce DAP, and the color changed to bright yellow and produced orange yellow fluorescence. But the presence of S^2- could cause the deactivation of HRP, which decreased the amount of DAP and consequently resulted in a substantial SPR band fading and an evident fluorescence quenching simultaneously. The mechanism of S^2- sensor was examined by combining the UV-vis absorption spectra, fluorescence spectra and electrospray ionization mass spectrometry analysis. Under optimal conditions, the colorimetric and fluorescent linear responses of the proposed method exhibited a wide linear range from 2.5 nM-7.5 μM with ultralow detection limits of 1.2 nM and 0.9 nM, respectively. Some potential interferents (such as F^-, Cl^-, Br^-, I^-, SO₄^2-, SO₃^2-, SCN^-, H₂PO₄^-, HPO₄^2-, Ac^-, NO₃^-, CO₃^2-) in real samples showed no interference. Moreover, the proposed method offered advantages of simple, low-cost instruments and rapid assay without the utilization of nanomaterials and has been successfully applied to determine S^2- content in lake water samples with satisfying recoveries over 97.6%. More importantly, the present S^2- sensor not only afforded a new optical sensing pattern for bioanalysis and environment monitoring, but also extends the application field of HRP-catalyzed OPD-H₂O₂ system.

One minute synthesis of green fluorescent copper nanocluster: The preparation of smartphone aided paper-based kit for on-site monitoring of nanomolar level mercury and sulfide ions in environmental samples

We wish to report, a minute synthesis of green fluorescent copper nanocluster by simple sonication. 1-Thio-β-d-glucose was used as a capping ligand to synthesis copper nanocluster (TG-CuNCs). The TG-CuNCs exhibit the emission maximum at 430 nm. The synthesized TG-CuNCs was well characterized by UV-vis, fluorescent, XRD, HR-TEM and FT-IR techniques. After the addition of Hg²⁺ or S^2- into TG-CuNCs, the fluorescence was quenched. Based on the quenching of fluorescence, we have calculated the detection limit 1.7 nM and 1.02 nM for Hg²⁺ and S^2-, respectively. Finally, we have applied TG-CuNCs for the detection of Hg²⁺ and S^2- in tap, river, pond water. Importantly, the smartphone aided paper-based kit was developed for on-site monitoring of Hg²⁺ and S^2- ions. To the best of our knowledge, this is the first report for the one-minute synthesis of TG-CuNCs and the preparation of smartphone aided paper-based kit for on-site monitoring of Hg²⁺ and S^2- ions. Further, it is anticipated that this synthesis of TG-CuNCs and smartphone aided paper-based kit for Hg²⁺ and S^2- will be useful materials in the filled with the biosensor, material science and nanotechnology.

Direct and sensitive detection of sulfide ions based on one-step synthesis of ionic liquid functionalized fluorescent carbon nanoribbons

Despite widely reported fluorescence sensors for cations, direct detection of anions is nevertheless still rare. In this work, ionic liquid-functionalized fluorescent carbon nanoribbons (IL-CNRs) are one-step synthesized and serve as the fluorescent probes for direct and sensitive detection of sulfide ions (S²⁻). The IL-CNRs are synthesized based on electrochemical exfoliation of graphite rods in a water-IL biphasic system. The as-prepared IL-CNRs exhibit uniform structure, high crystallinity, strong blue fluorescence (absolute photoluminescence quantum yield of 11.4%), and unique selectivity towards S²⁻. Based on the fluorescence quenching of IL-CNRs by S²⁻, a fluorescence sensor is developed for direct, rapid and sensitive detection of S²⁻ in the range of 100 nM to 1 μM and 1–300 μM with a low detection limit (LOD, 85 nM). Moreover, detection of S²⁻ in a real sample (tap water) is also demonstrated.

Sensitive detection of sulfide ions is realized based on one-step synthesis of ionic liquid functionalized fluorescent carbon nanoribbons.