Electrochemical synthesis of nitrogen-doped carbon quantum dots decorated copper oxide for the sensitive and selective detection of non-steroidal anti-inflammatory drug in berries

Advances in ionic liquids as fluorescent sensors

Ionic liquids (ILs) are a class of liquid salts with characteristics such as a low melting point, an ionic nature, non-volatility, and tunable properties. Because of their adaptability, they have a significant influence in the field of fluorescence. This paper reviews the primary literature on the use of ILs in fluorescence sensing technologies. The kind of target material is utilized to classify the fluorescence sensors made with the use of ILs. They include using ILs as probes for metals, nitro explosives, small organic compounds, anions, and gases. The efficacy of an IL-based fluorescence sensor depends on the precise design to guarantee specificity, sensitivity, and a consistent reaction to the desired analyte. The precise method can differ depending on the chemical properties of the IL, the choice of fluorophore, and the interactions with the analyte. Overall, the viability of the aforementioned materials for chemical analysis is evaluated, and prospective possibilities for further development are identified.

Fluorescent folic acid-chitosan/carbon dot for pH-responsive drug delivery and bioimaging

Nowadays, one of the most important reasons of death in the world is cancer. With the development of nanotechnology, advanced methods for treatment of cancer have introduced. In this work, the fluorescent carbon dots (CDs) were prepared from chitosan as the second abundant polysaccharide present in the nature. The surface of CDs was modified with chitosan (CDs/CS) and then the amino groups of chitosan were conjugated with activated folic acid (CDs/CS-FA) for controlled delivery of doxorubicin (DOX) as anticancer drug against HeLa cancer cells. The DOX loading efficiency of fluorescent CDs/CS-FA was high and nearly 60 %. Due to pH sensitive swelling/deswelling of CS, the percentage of cumulative DOX release could reach 90 % at cancer tissue (pH of 5.0) and 52 % at normal tissue (pH of 7.4) within 30 h. The cytotoxicity study revealed that the synthesized CDs were highly compatible on HeLa cells with cell viability 97-88 %. Cellular imaging shows that the entry of CDs/CS-FA to HeLa cells causes a green fluorescence, while the CDs/CS without FA have a negligible fluorescence. These results are due to the important role of FA in cell internalization. Thus, the CDs/CS-FA nanocarrier is suitable candidate for controlled pH sensitive drug delivery and cellular imaging.

Nanotechnology-assisted treatment of pharmaceuticals contaminated water

The presence of pharmaceutical compounds in wastewater due to an increase in industrialization and urbanization is a serious health concern. The demand for diverse types of pharmaceutical compounds is expected to grow as there is continuous improvement in the global human health standards. Discharge of domestic pharmaceutical personal care products and hospital waste has aggravated the burden on wastewater management. Further, the pharmaceutical water is toxic not only to the aquatic organism but also to terrestrial animals coming in contact directly or indirectly. The pharmaceutical wastes can be removed by adsorption and/or degradation approach. Nanoparticles (NPs), such as 2D layers materials, metal-organic frameworks (MOFs), and carbonaceous nanomaterials are proven to be more efficient for adsorption and/or degradation of pharmaceutical waste. In addition, inclusion of NPs to form various composites leads to improvement in the waste treatment efficacy to a greater extent. Overall, carbonaceous nanocomposites have advantage in the form of being produced from renewable resources and the nanocomposite material is biodegradable either completely or to a great extent. A comprehensive literature survey on the recent advancement of pharmaceutical wastewater is the focus of the present article.

Synthetic strategies, properties and sensing application of multicolor carbon dots: recent advances and future challenges

Recently, carbon dots (CDs) as newly developed carbon-based nanomaterials due to advantages such as excellent photostability and easy surface functionalization have generated wide application prospects in fields such as biological imaging and chemical sensing. The multicolor emission carbon dots (M-CDs) were acquired through the selection of different carbon source precursors, change of synthesis conditions and synthesis environment. Therefore, the aim of this review is to summarize the latest research progress in polychromatic CDs from the perspectives of synthesis strategies, luminescent mechanisms, luminescent properties and applications. This review focuses on how to prepare MCDs by changing raw materials and synthesis conditions such as reaction temperature, synthesis time, synthesis pH, and synthesis solvent. This review also presents the optical properties of MCDs, concentration effects, solvent effects, pH effects, elemental doping, and surface passivation on them, as well as their creative applications in the field of sensing applications. It is anticipated that this review will serve as a guide for the development of multifunctional M-CDs and inspire future research on controllable design and preparation of M-CDs.

Preparation of carbon quantum dots from ionic liquid modified biomass for the detection of Fe3+ and Pd2+ in environmental water

A new type of green carbon quantum dots (ILB-CQDs) was prepared by hydrothermal method using ionic liquid as a modifier and grape skin as carbon source, and was obtained from hydrogen-bonded lattice structure ionic liquid preparation, which makes the CQDs in a ring-like stable structure with a stability period of more than 90 day. There is also the catalytic effect of the ionic liquid on cellulose, which makes the prepared CQDs show good advantages, such as uniform particle size, high quantum yield (26.7%), and very good fluorescence performance. This is a smart material for the selective detection of Fe³⁺ and Pd²⁺. It has a detection limit of 0.001 nM for Fe³⁺ and 0.23 µM for Pd²⁺ in pure water. It has a detection limit of 3.2 nmol/L for Fe³⁺ and 0.36 µmol/L for Pd²⁺ in actual water, both of which meet the requirements of WHO drinking water standards. And there is to achieve more than 90% of water restoration effect.

Sulfur and nitrogen co-doped carbon quantum dots as fluorescent probes for the determination of some pharmaceutically-important nitro compounds

In this study, highly fluorescent sulfur and nitrogen co-doped carbon quantum dots (SN-CQDs) were synthesized by a simple one-pot hydrothermal method using thiosemicarbazide and citric acid as starting materials. Various spectroscopic and microscopic techniques were applied to characterize the prepared SN-CQDs. The synthesized SN-CQDs' maximum fluorescence emission was obtained at 430 nm after excitation at 360 nm. Rifampicin (RFP), tinidazole (TNZ), ornidazole (ONZ), and metronidazole (MNZ) all quantitatively and selectively quenched the SN-CQDs' native fluorescence, which was the base-for their-spectrofluorimetric estimation without the need for any tedious pre-treatment steps or high-cost instrumentation. SN-CQDs demonstrated a "turn-off" fluorescence response to RFP, TNZ, ONZ, and MNZ over the ranges of 1.0-30.0, 10.0-200.0, 6.0-200.0, and 5.0-100.0 μM with detection limits of 0.31, 1.76, 0.57, and 0.75 μM and quantitation limits of 0.93, 5.32, 1.74, and 2.28 μM respectively. The suggested method was successfully used to determine the investigated drugs in their commercial dosage forms. The method was further extended to their determination in spiked human plasma samples, with satisfactory mean % recoveries (99.44-100.29) and low % RSD values (< 4.52). The mechanism of fluorescence quenching was studied and discussed. The suggested method was validated in accordance with ICH recommendations.

Photoluminescence Performance and Photocatalytic Activity of Modified Carbon Quantum Dots Derived from Pluronic F127

The photocatalytic degradation of organic dyes in waste water using carbon quantum dots (CQDs) remains a hot topic due to the importance of environmental protection. However, identifying suitable carbon resources and successful surface modification are still challenging. Herein, the hydrothermal method and surface modification of ammonia and thionyl chloride were applied to synthesize CQDs with different surface groups using PEO₁₀₆PPO₇₀PEO₁₀₆ (Pluronic F127) as a carbon source. The average particle size of the as-prepared CQDs was in the range of 2.3-3.5 nm. The unmodified CQDs had the highest relative photoluminescence intensity, while all as-prepared CQDs exhibited abnormal photoluminescence located outside the scope of the visible spectrum. Interestingly, CQDs modified with ammonia achieved a degradation rate of 99.13% (15 d) for 50 mg/L indigo carmine solution, while CQDs modified with thionyl chloride reached a degradation rate of 97.59% (15 d) for light green SF yellowish solution. Therefore, in this work, two typical organic dyes can be effectively photocatalytically degraded by as-prepared CQDs, with suitable surface modification.

Sunlight-driven antibacterial activity of a novel zinc oxide quantum dot and its optimization using Box-Behnken design-A medicament for communicable disease protective wearables

The current study focuses on microwave-assisted zinc oxide quantum dots synthesis (ZnO-QDs) from zinc oxide bionanocomposite (ZnO-BC) preparation. The novelty lies in the preparation of ZnO-QDs, since the natural elements present in ZnO-BC itself acted as a surface penetration enhancer without using any chemical agent. Under ultraviolet (UV) light ZnO-QDs emitted a blue glow, confirming the fluorescence property. Using Box-Behnken design, the experimental factors of ZnO-QDs were optimized, yielding a positive response of 350 nm absorbance and these results also matched with the UV-visible spectroscopy characterization studies of ZnO-QDs. Using Escherichia coli, the antibacterial activity of ZnO-BC in comparison to ZnO-QDs was determined using the well diffusion method and an inhibition zone ranging from 11 to 23 mm and in the broth assay the OD values were reduced by almost seven and 10 times for ZnO-BC and ZnO-QDs, respectively, when compared to the control (untreated). The antibacterial activity demonstrated that our newly prepared BC and its QDs have superior activity when compared to the standard antibiotics such as ampicillin. This type of nanomaterial can be used as a new bioactive natural material with light-assisted activity for antibacterial coatings in the manufacture of personal protective equipment.

Fabrication of a novel electrochemical biosensor based on a molecular imprinted polymer-aptamer hybrid receptor for lysozyme determination

In this work, a novel, sensitive, and rapid electrochemical biosensor was employed to detect lysozyme (Lys) using a double receptor of molecular imprinted polymer (MIP)-aptamer. First, a glassy carbon electrode (GCE) was modified with a nanocomposite consisting of multi-wall carbon nanotubes (MWCNTs), nitrogen-doped carbon quantum dots (N-CQDs), and chitosan. Subsequently, aptamer (Apt)-Lys complex was immobilized on MWCNTs-N-CQDs-chitosan/GCE via binding between carboxyl groups present in the nanocomposite and the terminal amine groups of the aptamer. Following that, methylene blue monomer was electrochemically polymerized around the Apt-Lys complex on the MWCNTs-N-CQDs-chitosan/GCE surface. Finally, after the template removal, the remaining cavities along with the aptamers created a new hybrid receptor of MIP-aptamer. The MWCNTs-N-CQDs-chitosan nanocomposite could provide large amounts of carboxyl groups for binding to amino-functionalized aptamers, considerable electrical conductivity, and a high surface-to-volume ratio. These beneficial features facilitated the Apt-Lys complex immobilization and gave improved electrochemical signal. The obtained MIP-aptamer hybrid receptor allowed lysozyme determination even at concentrations as low as 4.26 fM within the functional range of 1 fM to 100 nM.

Nitrogen and sulfur-doped carbon quantum dots as fluorescent nanoprobes for spectrofluorimetric determination of olanzapine and diazepam in biological fluids and dosage forms: application to content uniformity testing

A validated, sensitive, and simple spectrofluorimetric method was developed for the analysis of two important CNS-acting drugs, olanzapine and diazepam, in their commercial tablets without the need for any pretreatment steps. The developed method relied on the quantitative quenching effect of each of olanzapine and diazepam on the native fluorescence of nitrogen and sulfur-doped carbon quantum dots (NS@CQDs). NS@CQDs were prepared from thiosemicarbazide and citric acid by a facile one-pot hydrothermal technique. The synthesized NS@CQDs were characterized by different spectroscopic and microscopic techniques. NS@CQDs produced a maximum emission peak at 430 nm using 360 nm as an excitation wavelength. Calibration curves showed a good linear regression over the range of 5.0–200.0 and 1.0–100.0 μM with detection limits of 0.68 and 0.29 μM for olanzapine and diazepam, respectively. The adopted method was used for the determination of the investigated drugs in their tablets with high % recoveries (98.84–101.70%) and low % RSD values (< 2%). As diazepam is one of the most commonly abused benzodiazepines, the developed method was successfully applied for its determination in spiked human plasma with high % recoveries and low % RSD values, providing further insights for monitoring its potential abuse. The quenching mechanism was also studied and confirmed to be through dynamic and static quenching for olanzapine and diazepam, respectively. Due to the high selectivity and sensitivity, content uniformity testing of low-dose tablets was successfully performed by applying the United States Pharmacopoeia guidelines. The method's validation was performed in compliance with ICHQ2 (R1) recommendations.

Electrochemical sensing system for the analysis of emerging contaminants in aquatic environment: A review

This survey distinguishes understudied spaces of arising impurity research in wastewaters and the habitat, and suggests bearing for future checking. Thinking about the impeding effect of toxins on human wellbeing and biological system, their discovery in various media including water is fundamental. This review sums up and assesses the latest advances in the electrochemical detecting of emerging contaminants (ECs). This survey is expected to add to the advancement in electrochemical applications towards the ECs. Different electrochemical insightful procedures like Amperometry, Voltammetry has been examined in this overview. The improvement of cutting edge nanomaterial-based electrochemical sensors and biosensors for the discovery of drug compounds has accumulated monstrous consideration because of their benefits, like high affectability and selectivity, continuous observing, and convenience has been reviewed in this survey. This survey likewise features the diverse electrochemical treatment procedures accessible for the removal of ECs.

An Overview of Synthetic Methods and Applications of Photoluminescent Properties of Carbon Quantum Dots

Carbon quantum dots (CQDs) are promising carbonaceous nanomaterials fortuitously discovered in 2004. CQDs are the rising stars in the nanotechnology ensemble because of their unique properties and widespread applications in sensing, imaging, medicine, catalysis, and optoelectronics. CQDs are notable for their excellent solubility and effective luminescence, and as a result, they are also known as carbon nanolights. Many strategies are used for the efficient and economical preparation of CQDs; however, CQDs prepared from waste or green sustainable methods have greater requirements due to their safety and ease of synthesis. Sustainable chemical strategies for CQDs have been developed, emphasizing green synthetic methodologies based on "top-down" and "bottom-up" approaches. This review summarizes many such studies relevant to the development of sustainable methods for photoluminescent CQDs. Furthermore, we have emphasized recent advances in CQDs' photoluminescent applications in chemical and biological fields. Finally, a brief overview of synthetic processes utilizing the green source and their associated applications are tabulated, providing a clear understanding of the new optoelectronic materials.

Simple One-step Solid-state Synthesis of Highly Crystalline N Doped Carbon Dots As Selective Turn Off-sensor for Picric Acid and Metanil Yellow

A simple one-step solid-state pyrolysis method has been employed to synthesize highly crystalline nitrogen-doped carbon dots using adipic acid and urea as carbon and nitrogen sources. The prepared carbon dots displayed UV emission ( λ_ex = 290 nm and λ_em = 370 nm) and blue fluorescence emission ( λ_ex = 360 nm and λ_em = 420 nm). These crystalline nitrogen-doped carbon dots exhibited a quantum yield of 6% with tryptophan as standard at 370 nm emission and 14% with quine sulfate as standard at 420 nm emission. The synthesized carbon dots were spherical, having a mean particle diameter of 2.56 ± 0.57 nm. The prepared carbon dots have large functional groups on their surface, which renders excellent water solubility to them. Carbon dots was used as selective and sensitive turn off sensor for detection of picric acid Metanil yellow with the linear response for picric acid ranging from 2 μM to 22 μM and 2-45 μM with a detection limit of 0.06 μM and 0.45 μM and for Metanil yellow ranging from 1 μM to 30 μM with a detection limit of 0.32 μM. The mechanism for detecting metanil yellow is proposed to be the inner filter effect. At the same time, it is both the inner filter effect and FRET for picric acid. The actual sample application of carbon dots as a nanosensor was tested to detect metanil yellow as an adulterant in turmeric powder.

One-pot hydrothermal synthesis of high quantum yield orange-emitting carbon quantum dots for sensitive detection of perfluorinated compounds

A carbon quantum dot with orange high quantum yield is used to detect PFOS/PFOA in cells.

Highly selective fluorescence sensor sensing benzo[a]pyrene in water utilizing carbon dots derived from 4-carboxyphenylboronic acid

4-Carboxyphenylboronic acid was used as the single precursor to facilely prepare fluorescent carbon quantum dots by one-step solvothermal method. The as-obtained carbon dots (CDs) exhibited highly selective and sensitive for benzo[a]pyrene (BaP), and may be a splendid sensor for sensing BaP. The principle was that the as-prepared CDs could form a complex with BaP through hydrophobic interaction which causes the decrease of fluorescence intensity of CDs by static quenching principle. The constructed fluorescent sensor exhibited excellent linearity ranged from 0.002 to 0.06 μg mL^-1 and provided a low limit of detection of 0.16 ng mL^-1. The experimental results showed that this fluorescent sensor resulted in simplicity, rapidness, low cost, short analytical time, and high sensitivity and stability. Validation with real water samples endowed the sensor high reliability and feasibility for BaP determination in practical application in various samples.

Fluorescent Carbon Quantum Dots-Synthesis,Functionalization and Sensing Application in FoodAnalysis

Carbon quantum dots (CQDs) with stable physicochemical properties are one of theemerging carbon nanomaterials that have been studied in recent years. In addition to the excellentoptical properties such as photoluminescence, photobleaching resistance and light stability, thismaterial also has favorable advantages of good biocompatibility and easy functionalization, whichmake it an ideal raw material for constructing sensing equipment. In addition, CQDs can combinedwith other kinds of materials to form the nanostructured composites with unique properties, whichprovides new insights and ideas for the research of many fields. In the field of food analysis,emerging CQDs have been deeply studied in food composition analysis, detection and monitoringtrace harmful substances and made remarkable research progress. This article introduces andcompares the various methods for CQDs preparation and reviews its related sensing applicationsas a new material in food components analysis and food safety inspection in recent years. It isexpected to provide a significant guidance for the further study of CQDs in the field of foodanalysis and detection. CQDs; synthesis; fluorescent sensing; food analysis.

Modification of electrodes with N-and S-doped carbon dots. Evaluation of the electrochemical response

Nitrogen and sulphur-doped Carbons Dots (N-CDs and S-CDs) were synthesized by a hydrothermal method and incorporated as surface electrode modifiers to evaluate their properties for electrochemical sensing. The first task was to characterize the synthesized materials, for which different spectroscopies, scanning microscopes, mass spectrometry and elementary analysis were performed. Next, a glassy carbon electrode (GCE) was surface-modified with the doped CDs and applied to check the electrochemical signal of different organic compounds corresponding to different families. Water solubility of the doped carbon dots forced us to incorporate them in a graphite-polystyrene ink to complete the modification of electrodes. This modification needed a first activation to obtain a properly conductive surface. The organic compounds examined were salicylic acid, cysteine and ascorbic acid. The modified GCEs exhibited an enhanced sensitivity, probably caused by the increase of active surface, but in addition, signals of salicylic acid were shifted ca. 200 mV to lower potentials, what is a proof of the increase of the heterogeneous electron transfer rate, and a demonstration of an enhanced catalytic response.

2D MnO2 nanosheets generated signal transduction with 0D carbon quantum dots: synthesis strategy, dual-mode behavior and glucose detection

A natural resource such as peony flower has been employed for the first time as a new carbon precursor to prepare green-emitting carbon nanodots (CDs). The emission peak is situated at 523 nm and the excitation wavelength can be extended to the visible light range (452 nm). Due to the formation of CD-MnO₂ nanocomposites, the emission intensity of CDs is sharply reduced as a consequence of Förster resonance energy transfer (FRET). Moreover, glucose can be recognized due to the enzymatic conversion of glucose by glucose oxidase to generate H₂O₂. The MnO₂ nanosheets are reduced to form Mn(ii) ions, and the fluorescence of CDs can be recovered. The fluorescence intensity has been improved linearly based on the increasing concentration of glucose (0.5-250 μM) with a detection limit as low as 0.18 μM. This strategy gives a new selection of eco-friendly precursors in carbon nanomaterials and such a consecutive recognition process provides valuable insights for bio-analysis.

Blue- and green-emitting hydrophobic carbon dots: preparation, optical transition, and carbon dot-loading

In the past decade, hydrophobic fluorescent carbon dots (OCDs) have received little attention, and its potential application and light transition mechanism is seldom explored. Here we report a novel one-step approach for synthesizing blue- and green-emitting hydrophobic fluorescent carbon dots (OCD_b and OCD_g) by calcinating with the uses of citric acid and hexadecylamine as initial reactants. The optimal conditions for preparing OCD_b and OCD_g were obtained by using the Taguchi L25 (3⁵) orthogonal array. The highest quantum yield and product yield of OCDs reached 80.2% and 57.1%, respectively, larger than those from most of all the known reports. The fluorescent stability of OCD_b and OCD_g was excellent under UV irradiation (30 W) for days. The luminescent color of OCDs showed a great dependence on reaction conditions. It is easier to get OCD_g via a reaction kept at a high temperature for a long time. The optical transition mechanism was studied for the two kinds of color OCDs, and therefore proposed in combination with their optical properties and surface groups. The reason for light transition is probably related to an appropriate critical ratio and surface density of the C=O and N-H bond in the surface structure of the product. For the OCD_g, the concentration matching ratio of N-H and C=O bonds in the surface structure of the green-emitting product is approximately between d/2 and 3d/2, where d is a fixed constant. Lower than or higher than this critical ratio range, the product emits blue light. Based on their high fluorescence quantum efficiency and the advantages mentioned above, these OCDs were then respectively used for preparing hydrophobic fluorescent carbon dot-loading liposomes and acrylate films, both exhibiting a perfect performance with no fluorescence quenching.

Carbon-based quantum particles: an electroanalytical and biomedical perspective

Carbon-based quantum particles, especially spherical carbon quantum dots (CQDs) and nanosheets like graphene quantum dots (GQDs), are an emerging class of quantum dots with unique properties owing to their quantum confinement effect.