Rapid detection of silver ions based on luminescent carbon nanodots for multicolor patterning, smartphone sensors, and bioimaging applications

Effect of 4-mercaptophenylboronic acid functionalized MoS2 quantum dots on amyloid aggregation of bovine serum albumin

In recent years, seeking and screening of compounds that can inhibit and/or depolymerize protein aggregation has been a hot issue in the field of pharmaceutical research. As a new material, quantum dots have been widely concerned by medical researchers. In present study, a novel 4-mercaptophenylboronic acid functionalized MoS2 quantum dots (4-MPBA-MoS2 QDs) was successfully synthesized through a one-pot hydrothermal approach by using molybdate dehydrate and 4-mercaptophenylboronic acid as Mo and S source, respectively. Transmission electron microscopy observation showed that the morphology and microstructure of the 4-MPBA-MoS2 QDs displayed uniform spherical shape with a diameter of approximately 1.5 ∼ 3.0 nm. The UV and fluorescence spectra experiments indicated that the prepared QDs had good water solubility and two weak absorption peaks were appeared at 280 nm and 310 nm. When the excitation wavelength was set to 310 nm, the 4-MPBA-MoS2 QDs had the strongest fluorescence intensity, and the maximum emission wavelength appeared at 405 nm. In vitro experiments showed that the 4-MPBA-MoS2 QDs could significantly reduce the aggregation of bovine serum albumin (BSA). Especially when the mass ratio of BSA to 4-MPBA-MoS2 QDs was 1:5, the inhibition rate could reach 76.4%. Cell experiment showed that the presence of 4-MPBA-MoS2 QDs could obviously decrease the cytotoxicity induced by BSA amyloid fibrils. Moreover, the depolymerization of BSA amyloid fibrils by 4-MPBA-MoS2 QDs and its excellent cell permeability were also observed. Molecular docking studies have shown that 4-MPBA-MoS2 QDs may stabilize the BSA structure through van der Waals forces, hydrophobic force, electrostatic interactions and hydrogen bonds formed between the outer layer of 4-MPBA and BSA to prevent fibrosis aggregation. The results of this study suggested that 4-MPBA-MoS2 QDs showed low cytotoxicity, good biocompatibility and solubility, and had a great potential in the design of new drugs for the treatment of amyloid-related diseases.

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.

Multicolor emission-based nitrogen, sulfur and boron co-doped photoluminescent carbon dots for sequential sensing of Fe3+ and cysteine: RGB color sensor and live cell imaging

Herein, a simple hydrothermal synthesis is used to prepare multiple heteroatom-doped photoluminescent carbon dots (CDs) from thiourea (N and S source) and boric acid (B source) as precursors. The optical and physicochemical properties of the as-synthesized NSB-CDs were studied using UV-Vis, photoluminescence, TEM, FT-IR, XRD, Raman, and XPS analyses. The NSB-CDs exhibited excellent stability, high photostability, pH, and ionic strength tolerance; they retained their excellent stability independent of excitation. The NSB-CDs featured small sizes of approximately 3.2 ± 0.4 nm (range: 2.0-5.0 nm) as evidenced using TEM measurements. The NSB-CDs were used as a photoluminescent sensing platform to detect Fe3+ as well as cysteine (Cys) molecules. The competitive binding of Cys to Fe3+ resulted in NSB-CDs that retained their photoluminescence. For the rapid identification and quantification of Fe3+ and Cys, NSB-CDs were developed as a "switch-on" dual-function sensing platform. The linear detection range of Fe3+ was 0-20 μM (limit of detection [LOD]: 54.4 nM) and that of Cys was 0-50 μM (LOD: 4.9 nM). We also introduced a smartphone RGB analysis method for detecting low-concentration solutions based on digital images. The NSB-CDs showed no toxicity at 100 μg/mL. Photoluminescent probes for multicolor live-cell imaging can be used with NSB-CDs at this concentration, suggesting that NSB-CDs may be promising photoluminescent probes.

New spectrophotometric and smartphone-based colorimetric methods for determination of atenolol in pharmaceutical formulations

Novel spectrophotometric and smartphone-based colorimetric methods were developed and validated for the estimation of atenolol (ATE) in pharmaceutical formulations. The measurement procedure is based on the de-diazotization reaction, in which ATE is able to inhibit the diazotized sulfanilic acid from reacting with 8-hydroxy quinoline (8-HQ) in a basic medium. As a result, the formation of red-orange color azo-dye is hindered, and the color intensity is decreased proportionally to concentration of ATE. In spectrophotometric method the azo-dye color fate was monitored at 495 nm. While in smartphone-based colorimetric (SBC) method the captured image in the design processed by RGB App and transferred to the absorbance. The reactant concentrations were optimized using a central composite design (CCD) and response surface method. The methods exhibit good linearity in the 8.0 to 60.0 µg mL-1 range with no significant effect of interferences. The spectrophotometric method yields a linear equation with a slope of 0.0187 (R2 = 0.9993), a limit of detection (LOD) of 1.28 µg mL-1, and a limit of quantification (LOQ) of 4.28 µg mL-1. On the other hand, the smartphone-based colorimetric (SBC) method demonstrates a linear equation with a slope of 0.0127 (R2 = 0.9965), an LOD of 2.13 µg mL-1, and an LOQ of 7.09 µg mL-1. Analyzing ATE in pharmaceutical tablets was utilized to validate the applicability of the developed methods, and the results were statistically compared with those obtained by the HPLC method using the t-test and F-test.

Carbon dots and composite materials with excellent performances in cancer-targeted bioimaging and killing: a review

Carbon dots (CDs) are nanomaterials with excellent properties, including good biocompatibility, small size, ideal photoluminescence and surface modification, and are becoming one of the most attractive nanomaterials for the imaging, detection and treatment of tumors. Based on these advantages, CDs can be combined other materials to obtain composite particles with improved, even new, performance, mainly in photothermal and photodynamic therapies. This paper reviews the research progress of CDs and their composites in targeted tumor imaging, detection, diagnosis, drug delivery and tumor killing. It also discusses and proposes the challenges and perspectives of their future applications in these fields. This review provides ideas for future applications of novel CD-based materials in the diagnosis and treatment of cancer.

Two-dimensional bismuth oxyselenide quantum dots as nanosensors for selective metal ion detection over a wide dynamic range: sensing mechanism and selectivity

Bismuth oxyselenide (Bi2O2Se) nanosheets, a new 2D non-van der Waals nanomaterial having unique semiconducting properties, could be favorable for various sensing applications. In the present report, a top-down chemical approach was adopted to synthesize ultrathin Bi2O2Se quantum dots (QDs) in an appropriate solution. The as-prepared 2D Bi2O2Se QDs with an average size of ∼3 nm, exhibiting strong visible fluorescence, were utilized for heavy-metal ion detection with high selectivity. The QDs show a high optical band gap and a reasonably high fluorescence quantum yield (∼4%) in the green region without any functionalization. A series of heavy metal ions were detected using these QDs. The as-prepared QDs exhibit selective detection of Fe3+ over a wide dynamic range with a high quenching ratio and a low detection limit (<0.5 μM). The mechanism of visible fluorescence and Fe3+ ion-induced quenching was investigated in detail based on a model involving adsorption and charge transfer. Density functional theory (DFT) first principles calculations show that fluorescence quenching occurred selectively due to the efficient trapping of electrons in the bandgap states created by the Fe atoms. This work presents a sustainable and scalable method to synthesize 2D Bi2O2Se QDs for heavy metal ion sensing over a wide dynamic range and these 2D QDs could find potential uses in gas sensors, biosensors and optoelectronics.

Facile synthesis of phosphorus and nitrogen co-doped carbon dots with excellent fluorescence emission towards cellular imaging

Fluorescent carbon nanomaterials have attracted increasing attention owing to their unique photoluminescence properties, good biocompatibility and low toxicity in bioimaging as well as biosensing. Heteroatom doping is usually used to improve photoluminescence properties by tuning the functional groups and the particle size domain effect, thus leading to redshifted emission. Here, we report a straightforward strategy for the fabrication of a mixture of fluorescent phosphorus and nitrogen carbon nanodots (P,N-CDs) followed by separating two kinds of fluorescent fractions based on their different negative charges. Such a one-pot hydrothermal method using formamide, urea and hydroxyethylidene diphosphonic acid as the precursor yields fluorescent P,N-CDs. Specifically, blue-emitting CDs (bCDs) and green-emitting CDs (gCDs) were separated by using column chromatography. The quantum yields of bCDs and gCDs were 20.33% and 1.92%, respectively. And the fluorescence lifetimes of bCDs and gCDs were 6.194 ns and 2.09 ns, respectively. What is more, the resultant P,N-CDs exhibited low toxicity and excellent biocompatibility. Confocal fluorescence microscopy images were obtained successfully, suggesting that P,N-CDs have excellent cell membrane permeability and cellular imaging. This work provides a promising fluorescent carbon nanomaterial with tunable emission as a probe for versatile applications in bioimaging, sensing and drug delivery.

Nitrogen and sulfur co-doped photoluminescent carbon dots for highly selective and sensitive detection of Ag+ and Hg2+ ions in aqueous media: Applications in bioimaging and real sample analysis

In this study, we report the synthesis of photoluminescent (PL) nitrogen (N) and sulfur (S) co-doped carbon dots (NS-CDs) from nitazoxanide and 3-mercaptopropionic acid as a precursors via a one-pot hydrothermal methods. N and S co-doped materials allows more active sites in the CDs surface resulting in an enhancement of their PL properties. NS-CDs show bright blue PL, excellent optical properties, good water solubility, and a high quantum yield (QY) of 32.1%. The as-prepared NS-CDs were confirmed by UV-Visible, photoluminescence, FTIR, XRD and TEM analysis. An optimized excitation at 345 nm, the NS-CDs exhibited strong PL emission at 423 nm with an average size of 3.53 ± 0.25 nm. Under optimized conditions, the NS-CDs PL probe shows high selectivity with Ag⁺/Hg²⁺ ions detected, while other cations no significant changes the PL signal. The PL intensity of NS-CDs linearly quenching and enhancement with Ag⁺ and Hg²⁺ ions from 0 to 50 × 10^-6 M, with the detection limit of 2.15 × 10^-6 M and 6.77 × 10^-7 M (S/N = 3). More interestingly, as-synthesized NS-CDs shows a strong binding to Ag⁺/Hg²⁺ ions with the PL quenching and enhancement to precise and quantitative detection of Ag⁺/Hg²⁺ ions in living cells. The proposed system was effectively utilized for the sensing of Ag⁺/Hg²⁺ ions in real samples resulting in high sensitivity and good recoveries (98.4-109.7%).

Multiple heteroatom dopant carbon dots as a novel photoluminescent probe for the sensitive detection of Cu2+ and Fe3+ ions in living cells and environmental sample analysis

Heavy metal ion pollution harms human health and the environment and continues to worsen. Here, we report the synthesis of boron (B), phosphorous (P), nitrogen (N), and sulfur (S) co-doped carbon dots (BP/NS-CDs) by a one-step facile hydrothermal process. The optimum synthetic parameters are of 180 °C temperature, 12 h reaction time and 15% of PBA mass. The as-synthesized BP/NS-CDs exhibits excellent water solubility, strong green photoluminescence (PL) at 510 nm, and a high quantum yield of 22.4%. Moreover, BP/NS-CDs presented high monodispersity (7.2 ± 0.45 nm), excitation-dependent emission, PL stability over large pH, and high ionic strength. FTIR, XRD, and XPS are used to confirm the successful B and P doping of BP/NS-CDs. BP/NS-CD photoluminescent probes are selectively quenched by Cu²⁺ and Fe³⁺ ions but showed no response to the presence of other metal cations. The PL emission of BP/NS-CDs exhibited a good linear correlation with Cu²⁺ and Fe³⁺ concentrations with detection limits of 0.18 μM and 0.27 μM for Cu²⁺ and Fe³⁺, respectively. Furthermore, the HCT116 survival cells kept at 99.4 ± 1.3% and cell imaging capability, when the BP/NS-CDs concentration is up to 300 μg/mL by MTT assay. The proposed sensor is potential applications for the detection of Cu²⁺ and Fe³⁺ ions in environmental water samples.

Nitrogen, sulfur, and phosphorus Co-doped carbon dots-based ratiometric chemosensor for highly selective sequential detection of Al3+ and Fe3+ ions in logic gate, cell imaging, and real sample analysis

Heteroatom-doped photoluminescent (PL) carbon dots (CDs) have recently gained attention as optical sensors due to their excellent tunable properties. In this work, we propose a one-pot hydrothermal synthesis of PL nitrogen (N), sulfur (S), and phosphorus (P) co-doped carbon dots (NSP-CDs) using glutathione and phosphoric acid (H₃PO₄) as precursors. The synthesized NSP-CDs were characterized using different spectroscopic and microscopic techniques, including ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy, Fourier-transform infrared (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. The NSP-CDs exhibited excellent PL properties with green emission at 492 nm upon excitation at 417 nm, a high quantum yield of 26.7%, and dependent emission behavior. The as-prepared NSP-CDs were spherical with a well-monodispersed average particle size of 5.2 nm. Moreover, NSP-CDs demonstrate high PL stability toward a wider pH, high salt ionic strength, and various solvents. Furthermore, the NSP-CDs showed a three-state "off-on-off" PL response upon the sequential addition of Al³⁺ and Fe³⁺ ions, with a low limit of detection (LOD) of 10.8 nM for Al³⁺ and 50.7 nM for Fe³⁺. The NSP-CD sensor can construct an INHIBIT logic gate with Al³⁺ and Fe³⁺ ions as the chemical inputs and emissions as the output mode. Owing to an excellent tunable PL property and biocompatibility, the NSP-CDs were applied for sensing Al³⁺ and Fe³⁺ ions as well as live cell imaging. Furthermore, NSP-CDs were designed as PL sensors for detecting Al³⁺ and Fe³⁺ ions in real water show their potential application.

Reversible Modulation of Aptamer-Ligand Binding in RNA Light-Up Aptamers Containing G-Quadruplex Using Chemical Stimuli

Regulating a system in equilibrium transiently to out-of-equilibrium by using certain stimuli is the strategy used by natural biomolecules to function. Herein, we showed that the interaction of synthetic RNA aptamers, having a G-quadruplex core structure, with their corresponding ligands could be regulated from their equilibrium state to non-equilibrium state in a reversible manner using simple chemical stimuli (Ag⁺ and cysteine). The approach would be useful for designing aptamer regulators that work in a dynamic nucleic acid network, where a strict control on aptamer-ligand interaction is needed. In addition, to the best of our knowledge, this is the first report which shows that RNA G-quadruplexes can be disrupted by the addition of silver ions. This would be useful not only in designing RNA-based sensors or regulators but would also be useful for understanding the role of metal ions in RNA folding and catalysis.

SARS-CoV-2 main protease (3CLpro) interaction with acyclovir antiviral drug/methyl-β-cyclodextrin complex: Physiochemical characterization and molecular docking

During the current outbreak of the novel coronavirus disease 2019 (COVID-19), researchers have examined several antiviral drugs with the potential to inhibit the proliferation of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The antiviral drug acyclovir (AVR), which is used to treat COVID-19, in complex with methyl-β-cyclodextrin (Mβ-CD) was examined in the solution and solid phases. UV-visible and fluorescence spectroscopic analyses confirmed that the guest (AVR) was included inside the host (Mβ-CD) cavity. A solid inclusion complex of AVR was prepared by co-precipitation, physical mixing, kneading, and bath sonication methods at a 1:1 ratio of Mβ-CD:AVR. The prepared Mβ-CD:AVR inclusion complex was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) analysis. Phase solubility studies indicated the Mβ-CD:AVR inclusion complex exhibited a higher stability constant and linear enhancement in AVR solubility with increasing Mβ-CD concentrations. In silico analysis of the Mβ-CD/AVR inclusion complex confirmed that AVR drugs show potential as inhibitors of SARS-CoV-2 3C-like protease (3CL^pro) receptors. Results obtained using the PatchDock and FireDock servers indicated that the most favorable docking ligand was Mβ-CD:AVR, which interacted with SARS-CoV-2 (3CL^Pro) protease inhibitors with high geometric shape complementarity scores (2522 and 5872) and atomic contact energy (-313.77 and -214.70 kcal mol^-1). Our results suggest that the Mβ-CD/AVR inclusion complex inhibits the main protease of SARS-CoV-2, although further wet-lab experiments are needed to verify these findings.

Easy Synthesis and Characterization of Novel Carbon Dots Using the One-Pot Green Method for Cancer Therapy

In this study, hyaluronic acid (HA) and carboxymethyl chitosan (CMCS) were used for the synthesis of novel targeted nanocarrier carbon dots (CDC-H) with photo-luminescence using a one-step hydrothermal method. Doxorubicin (DOX), a common chemotherapeutic agent, was loaded with the CDC-H through electrostatic interactions to form DOX-CDC-H complexes as a targeted antitumor drug delivery system. The synthesized CDC-H show a particle size of approximately 6 nm and a high fluorescence quantum yield of 11.64%. The physical and chemical character properties of CDC-H and DOX-CDC-H complexes were investigated using various techniques. The results show that CDC-H have stable luminescent properties and exhibit excellent water solubility. The in vitro release study showed that DOX-CDC-H exhibited pH-dependent release for 24 h. Confocal laser scanning microscopy was applied to investigate the potential of CDC-H for cell imaging and the cellular uptake of DOX-CDC-H in different cells (NIH-3T3 and 4T1 cells), and the results confirmed the target cell imaging and cellular uptake of DOX-CDC-H by specifically binding the CD44 receptors on the surface of tumor cells. The r MTT results suggest that the DOX-CDC-H complex may induce apoptosis in 4T1 cells, reducing the cytotoxicity of free DOX-induced apoptosis. In vivo antitumor experiments of DOX-CDC-H exhibited enhanced tumor cancer therapy. CDC-H have potential applications in bioimaging and antitumor drug delivery.