Red-emission carbon dots as fluorescent “on–off–on” probe for highly sensitive and selective detection of Cu2+ and glutathione

Polyethyleneimine capped silver nanoclusters based turn-off-on fluorescence sensor for the determination of glutathione

A polyethyleneimine capped silver nanoclusters (PEI-AgNCs) based turn-off-on fluorescence sensor has been developed to determine glutathione (GSH) effectively. The fluorescence intensity of silver nanoclusters (AgNCs) has been quenched by Cu(II) and recovered by adding GSH. The quenching of fluorescence intensity of PEI-AgNCs by Cu(II) and recovery of the emission intensity of PEI-AgNCs after the addition of GSH is supposed to be ground state adduct formation. Due to the greater affinity of Cu(II) towards GSH compared to that to PEI-AgNCs, the defragmentation of PEI-AgNCs-Cu(II) adduct occurs after the addition of GSH to the solution, resulting in the recovery of emission intensity of PEI-AgNCs. Characterisation studies of the probe have been done using FT-IR spectroscopy, XPS analysis, XRD analysis, UV-visible and Fluorescence spectrophotometry, EDX spectroscopy and TEM analysis. Different experimental parameters were optimised. Under optimised analytical conditions, the sensor showed a wide linear range for the quantification of GSH from 1.00 × 10-4 M to 3.00 × 10-6 M with a detection limit (LOD) of 8.00 × 10-7 M. Selectivity and interference studies were done in the presence of different structurally similar and coexisting species of GSH in blood. The practical utility of the proposed sensor has been validated in artificial blood serum.

Portable ratiometric fluorescence detection of Cu2+and thiram

Food contaminants pose a danger to human health, but rapid, sensitive and reliable food safety detection methods can offer a solution to this problem. In this study, an optical fiber ratiometric fluorescence sensing system based on carbon dots (CDs) and o-phenylenediamine (OPD) was constructed. The ratiometric fluorescence response of Cu2+and thiram was carried out by the fluorescence resonance energy transfer (FRET) between CDs and 2,3-diaminophenazine (ox-OPD, oxidized state o-phenylenediamine). The oxidation of OPD by Cu2+resulted in the formation of ox-OPD, which quenched the fluorescence of CDs and exhibited a new emission peak at 573 nm. The formation of a [dithiocarbamate-Cu2+] (DTC-Cu2+) complex by reacting thiram with Cu2+, inhibits the OPD oxidation reaction triggered by Cu2+, thus turning off the fluorescence signal of OPD-Cu2+. The as-established detection system presented excellent sensitivity and selectivity for the detection of Cu2+and thiram in the ranges of 1 ∼ 100μM and 5 ∼ 50μM, respectively. The lowest detection limits were 0.392μM for Cu2+and 0.522μM for thiram. Furthermore, actual sample analysis indicated that the sensor had the potential for Cu2+and thiram assays in real sample analysis.

Nitrogen and Sulfur co-doped Carbon dots as an "on-off-on" Fluorescent Sensor for the Detection of Hg2+ and Ampicillin

Herein, a fluorescent "on-off-on" nanosensor based on N,S-CDs was developed for highly precise and sensitive recognition of Hg2+ and ampicillin (AMP). Nitrogen and sulfur co-doped carbon dots with blue fluorescence were synthesized by one-pot hydrothermal method using ammonium citrate and DL-methionine as precursors. N,S-CDs exhibited a surface abundant in -OH, -COOH, and -NH2 groups, aiding in creating non-fluorescent ground state complexes when combined with Hg2+, leading to the suppression of N,S-CDs' fluorescence. Subsequent to additional AMP application, the mixed system's fluorescence was restored. Based on this N,S-CDs sensing system, the thresholds for detection for AMP and Hg2+ were discovered to be 0.121 µM and 0.493 µM, respectively. Furthermore, this methodology proved effective in identifying AMP in real samples of tap and lake water, yielding satisfactory results. Consequently, in the area of bioanalysis in intricate environmental sample work, the sensing system showed tremendous promise.

Zinc nitride quantum dots as an efficient probe for simultaneous fluorescence detection of Cu2+ and Mn2+ ions in water samples

The exceptional ascending heights of graphene (carbon) and boron nitride nanostructures have invited scientists to explore metal nitride nanomaterials. Herein, Zn3N2 quantum dots (QDs) were prepared via a simple hydrothermal route from the reaction between zinc nitrate hexahydrate and ammonia solution that possess efficient strength towards sensing applications of metal ions (Cu2+ and Mn2+). The as-prepared Zn3N2 QDs show bright fluorescence, displaying an emission peak at 408 nm upon excitation at 320 nm, with a quantum yield (QY) of 29.56%. It was noticed that the fluorescence intensity of Zn3N2 QDs linearly decreases with the independent addition of Cu2+ and Mn2+ ions, displaying good linearity in the ranges 2.5-50 µM and 0.05-5 µM with detection limits of 21.77 nM and of 63.82 nM for Cu2+ and Mn2+ ions, respectively. The probe was successfully tested for quantifying Cu2+ and Mn2+ in real samples including river, canal, and tap water, providing good recoveries with a relative standard deviation  < 2%. Furthermore, the masking proposition can successfully eliminate the interference if the two metal ions exist together. It was found that thiourea is efficiently able to mask Cu2+ and selectively quenches Mn2+, and L-cysteine is able to halt the quenching potential of Mn2+ and is selectively able to sense Cu2+. The Zn3N2 QDs provide a simple way for the simultaneous detection of both Cu2+ and Mn2+ ions in environmental samples at low sample preparations requirements.

Green synthesis of carbon dots from fish scales for selective turn off-on detection of glutathione

Carbon dots as fluorescent probes were fabricated using readily available grass carp fish scales as the carbon source via one-step synthesis based on a pyrolytic reaction. The as-prepared grass carp fish scale carbon dots (GF-CDs) exhibited good biocompatibility and excellent optical properties with a high fluorescence quantum yield of 23.8%. Glutathione (GSH) is an essential small tri-peptide molecule present in every body cell and plays a crucial role in vivo and performs a wide range of biological functions. Ag+ can effectively quench the fluorescence of GF-CDs because of the electron transfer between GF-CDs and Ag+; however, the addition of GSH can significantly increase GF-CD-Ag+ fluorescence. Because of their combination with Ag+ and GSH, GF-CDs show selective fluorescence recovery. GF-CDs can serve as fluorescent probes for GSH detection. This detection method covered a wide linear range (1.6-36.0 μg mL-1) with the lowest detection limit of 0.77 μg mL-1 and manifested great advantages such as a short analysis time, good stability, repeatability, and ease of operation.

Xylan derived fluorescence carbon dots composite with cotton cellulose paper as 'turn-off' fluorescence platform for sensitive and selective detection Cu2+ in real samples

The pollution of heavy metals such as Cu2+ is still serious and the discharge of sewage of Cu2+ will cause damage to soil environment and human health. Herein, a biomass-based solid-state fluorescence detection platform (CPU-CDs) was developed as fluorescent sensor for detection Cu2+ via fluorescence and colorimetric dual-model methods in real time. CPU-CDs was composed of xylan-derived CDs (U-CDs) and cotton cellulose paper, which exhibiting good reusability, non-toxicity, excellent fluorescence characteristics and high biocompatibility. Further, CPU-CDs displayed high effectiveness and sensitivity for Cu2+ with the detection limit as low as 0.14 μM, which was well below U.S. EPA safety levels (20 μM). Practical application indicated that CPU-CDs could achieve precision response of Cu2+ change in real environment water samples with good recovery range of 90 %-119 %. This strategy demonstrated a promising biomass solid-state fluorescence sensor for Cu2+ detection for water treatment research, which is of great significance in dealing with water pollution caused by heavy metal ions.

A rationally designed fluorescent probe for sulfur dioxide and its derivatives: applications in food analysis and bioimaging

Exogenous sulfur dioxide (SO2) and its derivatives (SO32-/HSO3-) have been extensively utilized in food preservation and endogenous SO2 is recognized as a significant gaseous signaling molecule that can mediate various physiological processes. Overproduction and/or extensive intake of these species can trigger allergic reactions and even tissue damage. Therefore, it is highly desirable to monitor SO2 and its derivatives effectively and quantitatively both in vitro and in vivo. Herein, a new mitochondria-targeted fluorescent probe (PIB) had been constructed, which could ratiometrically recognize SO2 and its derivatives with excellent sensitivity (DL = 15.9 nM) and a fast response time (200 s). The obtained high selectivity and good adaptability of this SO2-specific probe in a wide pH range (6.5-10.0) allowed for quantitatively tracking of SO2 and its derivatives in real food samples (granulated sugar, crystal sugar, and white wine). In addition, PIB could locate at mitochondrion and was capable of imaging exogenous/endogenous SO2 in the cells and zebrafish. In particular, our findings represented one of the rare examples that have demonstrated endogenous SO2 is closely related with the apoptosis of cells. Importantly, probe PIB was successfully employed for in situ metabolic localization in mouse organs, implying the potential applications of our probe in further exploration on SO2-releated pathological and physiological processes.

Emission enhanced fluorometric biosensor by functionalized carbon polymer dots for glutathione detection in human real samples and molecular logic gate operation

Glutathione (GSH), an active peptide, plays pivotal roles in many physiological processes and detection of GSH inside of human body is of great importance for the playing of its biological effects. Here silver-phosphorus co-doped carbonized polymer dots (Ag@PCPDs) were prepared via solvothermal treatment of citric acid and phytic acid in the presence of Ag+ for GSH determination. The physicochemical and optical performance of the Ag@PCPDs were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR), X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), fluorescence spectroscopy and ultraviolet-visible (UV-Vis) spectroscopy analyses. The prepared Ag@PCPDs have outstanding water solubility with high monodispersity (7.81 ± 0.31 nm) and exhibited excellent optical properties with excitation-dependent emission, high photostability, pH, and ionic strength tolerance. An optimized excitation at 358 nm, the Ag@PCPDs showed strong photoluminescent (PL) emission at 456 nm with a PL quantum yield (QYs) of 15.6%. Furthermore, the Ag@PCPDs were used as a PL sensing platform for detection GSH in a linear range of 0-200 μM with a low limit of detection at 0.68 μM. In addition, the proposed system can construct molecular logic gates with GSH and Fe3+ ions as the chemical inputs and PL emissions as the output. And the Ag@PCPDs were successfully used for GSH determination in real samples resulting in high sensitivity and satisfactory recoveries (92.81--107.45%). More importantly, the Ag@PCPDs showed low cytotoxicity at 500 μg/mL and superior cell imaging capability in HeLa cells, which offer a new path for detection and categorization of GSH in biomedical applications.

Highly sensitive detection of microRNA-21 by nitrogen-doped carbon dots-based ratio fluorescent probe via nuclease-assisted rolling circle amplification strategy

Highly sensitive and selective detection of microRNA-21 (miRNA-21) in biological samples is critical for the disease diagnosis and cancer treatment. In this study, a nitrogen-doped carbon dots (N-CDs)-based ratio fluorescence sensing strategy was constructed for miRNA-21 detection with high sensitivity and excellent specificity. Bright-blue N-CDs (λ_ex/λ_em = 378 nm/460 nm) were synthesized by facile one-step microwave-assisted pyrolysis method by using uric acid as the single precursor, and the absolute fluorescence quantum yield and fluorescence lifetime of N-CDs were 35.8% and 5.54 ns separately. The padlock probe hybridized with miRNA-21 firstly and then was cyclized by T4 RNA ligase 2 to form a circular template. At the present of dNTPs and phi29 DNA polymerase, the oligonucleotide sequence in miRNA-21 was prolonged to hybridize with the surplus oligonucleotide sequences in circular template, generating long and reduplicated oligonucleotide sequences containing abundant guanine nucleotides. Separate G-quadruplex sequences were generated after the addition of Nt.BbvCI nicking endonuclease, and then hemin bound with G-quadruplex sequence to construct the G-quadruplex DNAzyme. Such G-quadruplex DNAzyme catalyzed the redox reaction of o-phenylenediamine (OPD) with H₂O₂, finally producing the yellowish-brown 2,3-diaminophenazine (DAP) (λ_em = 562 nm). Due to the inner filter effect between N-CDs and DAP, the ratio fluorescence signal of DAP with N-CDs was utilized for sensitive detection of miRNA-21 with detection limit of 0.87 pM. Such approach has practical feasibility and excellent specificity for miRNA-21 analysis during highly homological miRNA family in HeLa cell lysates and human serum samples.

Histamine Recognition by Carbon Dots from Plastic Waste and Development of Cellular Imaging: Experimental and Theoretical Studies

The present work highlights the sustainable approach for the transformation of plastic waste into fluorescent carbon dots (CDs) through carbonization and then they were functionalized with L-cysteine and o-phenylenediamine. CDs which were characterized by different analytical techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to recognize Cu2+, Fe2+, and Hg2+ ions. The results show that the fluorescence emission was considerably quenched, and it is consistent with the interference and Jobs plots. The detection limit was found to be 0.35µM for Cu(II), 1.38 µM for Hg(II), and 0.51µM Fe(III). The interaction of CDs with metal ions enhances the fluorescence intensity detecting histamine successfully. It shows that plastic waste-based CDs can be applied clinically to detect toxic metals and biomolecules. Moreover, the system was employed to develop the cellular images using Saccharomyces cerevisiae cells with the support of a confocal microscope. Furthermore, theoretical studies were performed for the naphthalene layer (AR) as a model for C-dots, then optimized its structure and analyzed by using the molecular orbital. The obtained TD-DFT spectra coincided with experimental spectra for CDs/M2+/histamine systems.

A highly selective and sensitive ICT-based Cu2+ fluorescent probe and its application in bioimaging

Cu²⁺ is an essential trace element for the organism, but its excess can also cause irreversible damage to the organism. As such, a "Turn-Off" fluorescent probe DPAP for the specific detection of Cu²⁺ was successfully constructed. DPAP exhibits large Stokes shift (120 nm), fast reaction speed (1 min), low detection limit (15.2 nM), low toxicity, and good cell permeability. Cu²⁺ quenches the fluorescence of DPAP by blocking its intramolecular charge transfer process to achieve the detection of Cu²⁺ and has been confirmed by HRMS, ¹H NMR and DFT calculations. Excitingly, the five-cycle detection of Cu²⁺ and the successful recovery of trace Cu²⁺ in environmental water samples fully demonstrate the potential of DPAP for practical applications. In particular, DPAP can observe the distribution and translocation patterns of exogenous Cu²⁺ in HeLa cells and zebrafish in real-time. This research concept has offered important theoretical support for the study of the environmental behavior of heavy metal ions.

Bioengineered dual fluorescent carbon nano dots from Indian long pepper leaves for multifaceted environmental and health utilities

In this article, we present the synthesis of Piper longum leaves-derived ethanolic carbon dots (PLECDs) using the most simplistic environmentally friendly solvothermal carbonization method. The PLECDs fluoresced pink color with maximum emission at 670 nm at 397 nm excitation. Additionally, the dried PLECDs dissolved in water showed green fluorescence with higher emission at 452 nm at 370 nm excitation. The UV spectra showed peaks in the UV region (271.25 nm and 320.79 nm) and a noticeable tail in the visible region, signifying the efficient synthesis of nano-sized carbon particles and the Mie scattering effect. Various functional groups (-OH, -N-H, -C-H, -C = C, -C-N, and -C-O) were identified using Fourier transform infrared spectroscopy (FTIR). Its nanocrystalline property was revealed by the sharp peaks in the X-ray diffraction (XRD). High-resolution transmission electron microscopy (HRTEM) photomicrograph displayed a roughly spherical structure with a mean size of 2.835 nm. The energy dispersive X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS) revealed the elemental abundance of C, O, and N. The high-performance thin-layer chromatography (HPTLC) fingerprint of PLECDs showed an altered pattern than its precursor (Piper longum leaves ethanolic extract or PLLEE). The PLECDs sensed Cu²⁺ selectively with a limit of detection (LOD) and limit of quantification (LOQ) of 0.063 μM and 0.193 μM, respectively. It showed excellent cytotoxicity toward MDA-MB-231 (human breast cancer), SiHa (human cervical carcinoma), and B16F10 (murine melanoma) cell lines with excellent in vitro bioimaging outcomes. It also has free radical scavenging activity. The PLECDs also showed outstanding bacterial biocompatibility, pH-dependent fluorescence stability, photostability, physicochemical stability, and thermal stability.

Detection of mercury(II) and glutathione using a carbon dots-based "off-on" fluorescent sensor and the construction of a logic gate

In this paper, we proposed an efficient method for mercury(II) and glutathione detection using a fluorescent nanoprobe as a sensor. Carbon dots were synthesized from polyethyleneimine and ammonium citrate via a one-step hydrothermal method. The fluorescence of carbon dots was quenched since electron transfer occurred due to the interaction between mercury(II) and functional groups on the surface of carbon dots. Adding glutathione to the carbon dots-mercury(II) system, the fluorescence was recovered due to the stronger binding ability of glutathione to mercury(II). Based on the above-mentioned principle, this "off-on" fluorescent sensor can easily achieve the detection of mercury(II) and glutathione, which provided limits of detection of 22.45 nM and 61.89 nM, respectively. In this paper, the proposed method has been applied to detect mercury(II) and glutathione in real lake water and serum, respectively, and a logic gate for sensing glutathione was presented. The developed "off-on" fluorescent sensor with high sensitivity and selectivity has shown great potential for mercury(II) and glutathione detection in environmental and biosensing fields.

Investigation on conformational variation and enzymatic activity of trypsin affected by Ti3C2 QDs via spectroscopic technique and molecular modeling

In this paper, Ti₃C₂ quantum dots (Ti₃C₂ QDs) were synthesized by simply treating Ti₃C₂ MXene powder with acid and base via hydrothermal method. Ti₃C₂ QDs exhibited superior fluorescence property and were used for the fluorescent imaging of living HeLa cells successfully. In order to evaluate the influence of Ti₃C₂ QDs on protease with specific biological functions, binding interaction of Ti₃C₂ QDs with trypsin was studied comprehensively and deeply through spectroscopic strategies and molecular modeling technique. The intrinsic fluorescence of trypsin was spontaneously quenched by Ti₃C₂ QDs through static quenching mode under van der Waals interaction force, and Ti₃C₂ QDs bound with the inactive residue domain of trypsin firmly with stoichiometric ratio of 1:1. Ti₃C₂ QDs induced the microenvironmental variation of the amino acid residues in trypsin, reducing the thermal stability of trypsin significantly. Gel electrophoresis experiments and microscopic imaging experiments demonstrated that Ti₃C₂ QDs inhibited the enzymatic activity of trypsin on the digestion of human serum albumin and HeLa cells obviously. These results revealed not only the deep interaction mechanism between Ti₃C₂ QDs and protease but also the influence of Ti₃C₂ QDs on the enzymatic activity of trypsin, paving the way for the safe biological application of Ti₃C₂ QDs in the diagnosis and the therapy of protease-related diseases.