Probe sonication-assisted rapid synthesis of highly fluorescent sulfur quantum dots.

A new type of heavy-metal free single-element nanomaterial, called sulfur quantum dots (SQDs), has gained significant attention due to its advantages over traditional semiconductor QDs for several biomedical and optoelectronic applications. A straightforward and rapid synthesis approach for preparing highly fluorescent SQDs is needed to utilize this nanomaterial for technological applications. Until now, only a few synthesis approaches have been reported; however, these approaches are associated with long reaction times and low quantum yields (QY). Herein, we propose a novel optimized strategy to synthesize SQDs using a mix of probe sonication and heating, which reduces the reaction time usually needed from 125 h to a mere 15 min. The investigation employs cavitation and vibration effects of high energy acoustic waves to break down the bulk sulfur into nano-sized particles in the presence of highly alkaline medium and oleic acid. In contrast to previous reports, the obtained SQDs exhibited excellent aqueous solubility, desirable photostability, and a relatively high photoluminescence QY up to 10.4% without the need of any post-treatment. Additionally, the as-synthesized SQDs show excitation-dependent emission and excellent stability in different pH (2-12) and temperature (20 °C-80 °C) environments. Hence, this strategy opens a new pathway for rapid synthesis of SQDs and may facilitate the use of these materials for biomedical and optoelectronic applications.

Modified Whale Optimization Algorithm based ANN: a novel predictive model for RO desalination plant.

In recent decades, nature-inspired optimization methods have played a critical role in helping industrial plant designers to find superior solutions for process parameters. According to the literature, such methods are simple, quick, and indispensable for saving time, money, and energy. In this regard, the Modified Whale Optimization Algorithm (MWOA) hybridized with Artificial Neural Networks (ANN) has been employed in the Reverse Osmosis (RO) desalination plant performance to estimate the permeate flux (0.118‒2.656 L/h m2). The plant's datasets have been collected from the literature and include four input parameters: feed flow rate (400‒600 L/h), evaporator inlet temperature (60‒80 °C), feed salt concentration (35‒140 g/L) and condenser inlet temperature (20‒30 °C). For this purpose, ten predictive models (MWOA-ANN Model-1 to Model-10) have been proposed, which are capable of predicting more accurate permeate flux (L/h m2) than the existing models (Response Surface Methodology (RSM), ANN and hybrid WOA-ANN models) with minimum errors. Simulation results suggest that the MWOA algorithm demonstrates a stronger optimization capability of finding the correct weights and biases so as to enable superior ANN based modeling without limitation of overfitting. Ten MWOA-ANN models (Model-1 to Model-10) have been proposed to investigate the plant's performance. Model-6 with a single hidden layer (H = 1), eleven hidden layer nodes (n = 11) and the thirteen search agents (SA = 13) produced most outstanding regression results (R2 = 99.1%) with minimal errors (MSE = 0.005). The residual errors for Model-6 are also found to be within limits (span of - 0.1 to 0.2). Finally, the findings show that the screened MWOA-ANN models are promising for identifying the best process parameters in order to assist industrial plant designers.

Construction of hydrophobic fire retardant coating on cotton fabric using a layer-by-layer spray coating method.

Multifunctional cotton fabric was prepared through a two-step layer-by-layer spray coating method, where the first layer of the coating comprising chitosan and ammonium phytate provided fire retardancy, and the second one with PDMS-ZnO composite imparted hydrophobicity to the fabric. A molecular dynamics (MD) simulation study was carried out to calculate interfacial adhesion of different components of the coating, based on which the sequencing of the coating layers was determined and used to prepare coated samples. The coated fabric demonstrated a significant improvement in fire retardancy through an increase in LOI from 18 % in control to 30 %, a reduction in char length from 30 cm to 7 cm, and a decrease in peak and total heat release rate values by 75 % and 33 %, respectively. The hydrophobicity of coated fabric was tested via water drop test where coated sample maintained a contact angle of 148° for up to 120 s, while the control sample showed 0°.

Highly sensitive and selective detection of dopamine with boron and sulfur co-doped graphene quantum dots.

In this work, we report, the synthesis of Boron and Sulfur co-doped graphene quantum dots (BS-GQDs) and its applicability as a label-free fluorescence sensing probe for the highly sensitive and selective detection of dopamine (DA). Upon addition of DA, the fluorescence intensity of BS-GQDs were effectively quenched over a wide concentration range of DA (0-340 µM) with an ultra-low detection limit of 3.6 µM. The quenching mechanism involved photoinduced electron transfer process from BS-GQDs to dopamine-quinone, produced by the oxidization of DA under alkaline conditions. The proposed sensing mechanism was probed using a detailed study of UV-Vis absorbance, steady state and time resolved fluorescence spectroscopy. The high selectivity of the fluorescent sensor towards DA is established. Our study opens up the possibility of designing a low-cost biosensor which will be suitable for detecting DA in real samples.

Synergistic Enhancement of the Photoelectrochemical Performance of TiO2 Nanorod Arrays through Embedded Plasmon and Surface Carbon Nitride Co-sensitization.

We report a unique photoanode architecture involving TiO2, g-C3N4, and AuNPs wherein a synergistic enhancement of the photoelectrochemical (PEC) performance was obtained with photocurrent densities as high as 3 mA cm-2 under AM1.5G 1 sun illumination. The PEC performance was highly stable and reproducible, and a photoresponse was obtained down to a photon energy of 2.4 eV, close to the interband damping threshold of Au. The photocurrent enhancement was maximized when the Au plasmon band strongly overlapped the g-C3N4 emission band. Our photoanode architecture, which involved AuNPs buried under TiO2 and a plasmon-induced resonance energy transfer-like interaction between g-C3N4 quantum dots (CNQDs) and AuNPs, solved four major problems associated with plasmonic photoelectrocatalysis─it reduced recombination by limiting eliminating direct electrolyte access to AuNPs, it facilitated electron extraction through single-crystal TiO2 nanorod percolation pathways, it facilitated hole extraction through a defective TiO2 seed layer or canopy, and it expanded the range of visible light harvesting by pumping the Au surface plasmons from CNQDs through exciton-to-plasmon resonant energy transfer.

Ti3C2-MXene decorated with nanostructured silver as a dual-energy acceptor for the fluorometric neuron specific enolase detection.

Nanohybrids of two-dimensional (2D) layered materials have shown fascinating prospects towards the fabrication of highly efficient fluorescent immunosensor. In this context, a nanohybrid of ultrathin Ti3C2-MXene nanosheets and silver nanoparticles (Ag@Ti3C2-MXene) has been reported as a dual-energy acceptor for ultrahigh fluorescence quenching of protein-functionalized graphene quantum dots (anti-NSE/amino-GQDs). The Ti3C2-MXene nanosheets are decorated with silver nanoparticles (AgNPs) to obsolete the agglomeration and restacking through a one-pot direct reduction method wherein the 2D Ti3C2-MXene nanosheets acted both as a reducing agent and support matrix for AgNPs. The as-prepared nanohybrid is characterized by various techniques to analyze the optical, structural, compositional, and morphological parameters. The quenching efficiency and energy transfer capability between the anti-NSE/amino-GQDs (donor) and Ag@Ti3C2-MXene (acceptor) have been explored through steady state and time-resolved spectroscopic studies. Interestingly, the Ag@Ti3C2-MXene nanohybrid exhibits better quenching and energy transfer efficiencies in contrast to bare Ti3C2-MXene, AgNPs and previously reported AuNPs. Based on optimized donor-acceptor pair, a fluorescent turn-on biosensing system is constructed that revealed improved biosensing characteristics compared to Ti3C2-MXene, graphene and AuNPs for the detection of neuron-specific enolase (NSE), including higher sensitivity (∼771 mL ng-1), broader linear detection range (0.0001-1500 ng mL-1), better LOD (0.05 pg mL-1), and faster response time (12 min). Besides, remarkable biosensing capability has been observed in serum samples, with fluorescence recovery of ∼98%.

Tunable ionic conductivity and photoluminescence in quasi-2D CH3NH3PbBr3 thin films incorporating sulphur doped graphene quantum dots.

Ion migration in hybrid halide perovskites is ubiquitous in all conditions. However, the ionic conductivity can be manipulated by changing the material composition, operating temperature, light illumination, and applied bias as well as the nature of the interfaces of the devices. There have been various reports on electron ion coupling in hybrid perovskite semiconductors which gives rise to anomalous charge transport behavior in these devices under an applied bias. In this investigation, we have synthesized a mixture of 2D/3D perovskites by incorporating sulphur-doped graphene quantum dots (SGQDs) and demonstrated that the optical and electrical properties of the hybrid system can be tuned by controlling the ion conductivity through the active layer. It has been observed that the recombination resistance in undoped CH3NH3PbBr3 perovskites follows an anomalous behavior while the doped CH3NH3PbBr3 perovskite shows a monotonic increase with increasing applied bias due to reduced ionic conductivity. SGQDs at the grain boundaries of 2D/3D perovskites prohibit ion migration through the active layer, and therefore the electronic-ionic coupling is reduced. This results in increased recombination resistance with increasing applied bias.

Microdesigned Nanocellulose-Based Flexible Antibacterial Aerogel Architectures Impregnated with Bioactive Cinnamomum cassia.

This work is strategically premeditated to study the potential of a herbal medicinal product as a natural bioactive ingredient to generate nanocellulose-based antibacterial architectures. In situ fibrillation of purified cellulose was done in cinnamon extract (ciE) to obtain microfibrillated cellulose (MFC). To this MFC suspension, carboxylated cellulose nanocrystals (cCNCs) were homogeneously mixed and the viscous gel thus obtained was freeze-dried to obtain lightweight and flexible composite aerogel architectures impregnated with ciE, namely, ciMFC/cCNCs. At an optimal concentration of 0.3 wt % cCNCs (i.e., for ciMFC/cCNCs_0.3), an improvement of around 106% in compressive strength and 175% increment in modulus were achieved as compared to pristine MFC architecture. The efficient loading and interaction of ciE components, specifically cinnamaldehyde, with MFC and cCNCs resulted in developing competent antibacterial surfaces with dense and uniform microstructures. Excellent and long-term antimicrobial activity of the optimized architectures (ciMFC/cCNCs_0.3) was confirmed through various antibacterial assays like the zone inhibition method, bacterial growth observation at OD600, minimum inhibitory concentration (MIC, here 1 mg/mL), minimum bactericidal concentration (MBC, here 3-5 mg/mL), and Live/Dead BacLight viability tests. The changes in the bacterial morphology with a disrupted membrane were further confirmed through various imaging techniques like confocal laser scanning microscopy, FESEM, AFM, and 3D digital microscopy. The dry composite architecture showed the persuasive capability of suppressing the growth of airborne bacteria, which in combination with antibacterial efficiency in the wet state is considered as an imperative aspect for a material to act as the novel biomaterial. Furthermore, these architectures demonstrated excellent antibacterial performance under real "in use" contamination prone conditions. Hence, this work provides avenues for the application of crude natural extracts in developing novel forms of advanced functional biomaterials that can be used for assorted biological/healthcare applications such as wound care and antimicrobial filtering units.

Targeted bioimaging and sensing of folate receptor-positive cancer cells using folic acid-conjugated sulfur-doped graphene quantum dots.

For the first time is reported a facile in situ synthesis of folic acid-conjugated sulfur-doped graphene quantum dots (FA-SGQDs) through simple pyrolysis of citric acid (CA), 3-mercaptopropionic acid (MPA), and FA. The as-prepared FA-SGQDs were extensively characterized to confirm the synthesis and incidence of FA molecule on the surface of SGQDs through advanced characterization techniques. Upon excitation at 370-nm wavelength, FA-SGQDs exhibited blue fluorescence with an emission band at 455 nm. While exhibiting relatively high quantum yield (~ 78%), favorable biocompatibility, excellent photostability, and desirable optical properties, the FA-SGQDs showed suitability as a fluorescent nanoprobe to distinguish the folate receptor (FR)-positive and FR-negative cancer cells. The experimental studies revealed that FA-SGQDs aptly entered into FR-positive cancer cells via a non-immunogenic FR-mediated endocytosis process. Additionally, the FA-SGQDs exhibited excellent free radical scavenging activity. Hence, these FA-SGQDs hold high promise to serve as efficient fluorescent nanoprobes for the pre-diagnosis of cancer through targeted bioimaging and other pertinent biological studies. Graphical abstract.

Synthesis, characterization and investigation of synergistic antibacterial activity and cell viability of silver-sulfur doped graphene quantum dot (Ag@S-GQDs) nanocomposites.

The excessive use of traditional antibiotic and antibacterial agents has globally increased the growth of antibiotic-resistant bacteria that poses serious health risks. Therefore, the development of new generation antibacterial or antimicrobial agents for effective inhibition of bacterial growth is highly desired. In this study, we report a facile one-step synthesis approach for the preparation of a nanocomposite composed of silver nanoparticles (AgNPs) decorated with sulfur-doped graphene quantum dots (S-GQDs). The nanocomposite was comprehensively characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectra, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrated that the AgNPs were closely and uniformly surrounded by the S-GQDs, and consequently, this ensured the dispersion and stability of the so formed nanocomposite (Ag@S-GQDs). Further, the antibacterial activity of the Ag@S-GQDs nanocomposite was investigated and compared with bare S-GQDs and AgNPs against Gram-positive S. aureus (MTCC 737) and Gram-negative P. aeruginosa (MTCC 424) bacteria using macrodilution and agar well diffusion methods. Minimum inhibitory concentration (MIC) values of 70 and 35 µg mL-1 of the Ag@S-GQDs nanocomposite were found to be sufficient to hinder the growth of P. aeruginosa and S. aureus. A fractional inhibition concentration (FIC) index below 0.5 confirmed the existence of a synergistic effect between AgNPs and S-GQDs in the Ag@S-GQDs nanocomposite. In addition, the cytotoxicity of the Ag@S-GQDs nanocomposite, AgNPs and S-GQDs was also investigated using HEK 293 cell lines. Interestingly, the Ag@S-GQDs nanocomposite exhibited superior cell viability as compared to AgNPs and S-GQDs. These improved antibacterial and biocompatibility data demonstrate that the Ag@S-GQDs nanocomposite can serve as a promising antibacterial agent for industry to fabricate next-generation self-sterile textiles, antibacterial coatings and useful health care products supporting cell viability.

Sulfur doped graphene quantum dots as a potential sensitive fluorescent probe for the detection of quercetin.

In this work, a novel, selective and sensitive fluorescent probe (sulfur doped graphene quantum dots, SGQDs) was designed for real-time detection of quercetin in red wine samples. SGQDs were synthesized by pyrolyzing citric acid (CA) and 3-Mercaptopropionic acid (MPA) and characterized through advanced techniques. It was observed that fluorescence intensity of SGQDs could be substantially quenched by the addition of quercetin through inner filter effect (IFE) mechanism. Additionally, a visual color change (colorless to light yellow) was also noticed after addition of quercetin into a solution of SGQDs. The change in SGQDs fluorescence intensity with varying quercetin content revealed good linearity in the 0-50.0 µM range with regression coefficient of 0.9943 and a lowest detection limit of 0.006 µg/mL. To authenticate the real-time application of SGQDs as a potential fluorescent probe, red wine samples having different quercetin concentrations were used for quantitative analysis, after the optimization of several analytical parameters.

A highly sensitive and selective detection of picric acid using fluorescent sulfur-doped graphene quantum dots.

The development of an analytical probe to monitor highly mutagenic picric acid (PA) carries enormous significance for the environment and for health. A novel, simple and rapid fluorescence analytical assay using sulfur-doped graphene quantum dots (SGQDs) was designed for the highly sensitive and selective detection of PA. SGQDs were synthesized via simple pyrolysis of 3-mercaptopropionic acid and citric acid and characterized using advanced analytical techniques. Fluorescence intensity (FI) of SGQDs was markedly quenched by addition of PA, attributed to the inner filter effect and dominating static quenching mechanism between the two, in addition to a significant colour change. The calibration curve of the proposed assay exhibited a favourable linearity between quenched FI and PA concentration over the 0.1-100 µΜ range with a lowest detection limit of 0.093 µΜ and a correlation coefficient of 0.9967. The analytical assay was investigated for detection of trace amounts of PA in pond and rain water samples and showed great potential for practical applications with both acceptable recovery (98.0-100.8%) and relative standard deviation (1.24-4.67%). Analytical performance of the assay in terms of its detection limit, linearity range, and recovery exhibited reasonable superiority over previously reported methods, thereby holding enormous promise as a simple, sensitive, and selective method for detection of PA.

Biofunctionalized Graphene Quantum Dots Based Fluorescent Biosensor toward Efficient Detection of Small Cell Lung Cancer.

Quantitative detection of cancer biomarkers with higher accuracy and sensitivity provides an effective platform for screening, monitoring, early diagnosis, and disease surveillance. The present work demonstrates the fabrication and application of fluorescent turn-on biosensor for ultrasensitive detection of small cell lung cancer biomarker utilizing biofunctionalized graphene quantum dots as the energy donor and gold nanoparticles (AuNPs) as the energy acceptor. One-pot and the bottom-up hydrothermal route have been employed for the synthesis of in situ amine-functionalized and nitrogen-doped graphene quantum dots (amine-N-GQDs) and further characterized experimentally by different analytical techniques. The molecular simulation studies were performed using the Material Studio software for optimizing the possible chemical structure of synthesized amine-N-GQDs, a comprehensive analysis of experimental results to validate the presence of potential N-doping and amine functionalization sites. Then monoclonal neuron-specific enolase antibodies (anti-NSE) were covalently immobilized to amine-N-GQDs to provide the biofunctionalized GQDs (anti-NSE/amine-N-GQDs). A label-free and efficient fluorescent biosensor based on nanosurface energy transfer (NSET) between anti-NSE/amine-N-GQDs and AuNPs has been developed for neuron-specific enolase (NSE) detection. The fluorescence response studies of anti-NSE/amine-N-GQDs@AuNPs nanoprobe conducted as a function of NSE antigen exhibited fast response time (16 min), broader linear detection range (0.1 pg mL-1 to 1000 ng mL-1), and remarkably low detection limit (0.09 pg mL-1). Additionally, the fluorescent biosensor exhibited excellent performance in real samples, with an average recovery value of 94.69%.

Effect of sulfur doping on fluorescence and quantum yield of graphene quantum dots: an experimental and theoretical investigation.

Graphene quantum dots (GQDs) are one of the most promising luminescent carbon derived nanomaterials decorated with multiple useful functional groups and remarkable optoelectronic properties. Heteroatom doping of hexagonal carbon sheet of GQDs is an effective strategy to tailor their properties to meet desired application. In this work, sulfur doped GQDs (S-GQDs) were synthesized by simply pyrolyzing citric acid (CA) as a source of carbon and 3-Mercaptopropionic acid as a source of sulfur dopant. The optimal reaction conditions (ratio of the carbon to dopant source, temperature and time of reaction) were obtained while investigating their effect on the quantum yield and fluorescence properties of GQDs and, are hereby, reported for the first time. The as-synthesized S-GQDs were extensively characterized by different analytical techniques such as transmission electron microscopy (TEM), UV-vis Spectroscopy (UV), Fourier transform infrared spectroscopy, photoluminescence (PL) and x-ray Photoelectron Spectroscopy. S-GQDs were found uniform in size (∼4 nm) and spherical in shape with strong blue fluorescence. Further, for in-depth analysis of experimental results and underlying phenomena, theoretical studies based on density functional theory were performed for chemical structure optimization, possible sites of doping and density of states calculation. The synthesized S-GQDs exhibited excellent solubility in water, a stronger fluorescence and desirably higher quantum yield (57.44%) as compared to that of previously reported undoped GQDs. These successfully demonstrated unique and improved properties of S-GQDs present them as a potential candidate for biomedical, optical, electrical and chemical applications.