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

Eco-friendly N,P-CQDs from Phyllanthus emblica: A fluorescent Nanoprobe for ultra-sensitive detection of plasticizers in packaged dairy products

In this study, nitrogen- and phosphorus-co-doped carbon quantum dots (N,P-CQDs) were synthesized via a green hydrothermal method using Phyllanthus emblica for the sensitive detection of dibutyl phthalate (DBP) in plastic-packaged milk products. This research aimed to develop a sustainable, cost-effective sensing platform for monitoring food safety. The synthesized N,P-CQDs exhibited distinctive fluorescence properties with a quantum yield (QY) of 36.65 % and were characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy (UV-Vis). These N,P-CQDs showed stable fluorescence, good resistance to changes in pH, and the ability to adapt to changes in ionic strength. This made them ideal for detecting DBP in food materials. A fluorescence quenching assay revealed a broad linear response in the 1-25 μM range and achieved a low limit of detection (LOD) of 0.632 μM. Fluorescence lifetime analysis and FTIR studies confirmed a dynamic quenching mechanism driven by the inner filter effect (IFE) between DBP and N,P-CQDs. This fluorescence-based approach offers a more cost-effective, rapid, and environmentally friendly alternative than conventional DBP detection methods such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). Recovery experiments conducted in spiked food matrices (milk, cheese, and yogurt) demonstrated recovery rates ranging from 97.60 % to 101.67 %, further validating the method's reliability in complex food samples. This method provides a reliable, sustainable, and cost-effective strategy for DBP detection, ensuring food safety and environmental monitoring while addressing the limitations of conventional analytical techniques.

Fluorescence-based nanocomposite sensor for meclofenamic acid detection in dairy products

This study introduces a novel nanocomposite fluorescent probe (N-GQDs@Cit-HA@MIP) for the sensitive and selective detection of meclofenamic acid, a non-steroidal anti-inflammatory drug, in dairy products. The probe combines nitrogen-doped graphene quantum dots, citrate-functionalized hydroxyapatite, and a molecularly imprinted polymer, achieving a detection limit of 0.03 μg L-1 and recoveries of 93.2-99.9 % with RSDs below 3.1 %. The sensor offers superior sensitivity and reduced analysis time compared to chromatographic methods. Furthermore, its compatibility with smartphone-based detection systems highlights its potential for rapid on-site food safety monitoring.

Development of a smartphone integrated 3D-printed point of care platform for sensitive detection of bilirubin

Strategic design and development of nanomaterials-based detection platforms specific to critical biomarkers like bilirubin holds immense promise for revolutionizing early disease detection. Bilirubin (BR) plays a pivotal role as a biomarker for liver function, making accurate and timely detection of BR crucial for diagnosing and monitoring of liver diseases. In this work, we synthesized blue light emitting graphene quantum dots (GQDs) via a single step pyrolysis method, which exhibited excellent photostability and biocompatibility. Under optimal conditions, the fluorescence of GQDs was significantly quenched with the successive addition of BR achieving an ultra-low detection limit (38.96 nM) over a concentration range of 0.18 μM-14.29 μM with high selectivity, and rapid response towards free BR. The sensing mechanism was identified as the inner filter effect after extensive investigations. Thereafter, the sensor system was directly applied to human serum and urine samples and was further compared with the conventional Jendrassik and Grof method, yielding satisfactory recoveries. To demonstrate the sensor system's potential for real world applications, we designed and fabricated a prototype point-of-care device (POC) through 3D printing, incorporating paper microfluidic devices and fluorescence image analysis-based android application through smartphone. The compact 3D-printed POC device achieved a detection limit of 114.66 nM for BR detection, proving to be a promising platform for affordable, efficient and rapid BR detection.

Ultrasensitive and selective nanomolar detection of quercetin in 12 complex food matrices via 3D hierarchical SiO₂@MoS₂/MXenes heterostructured sensor

Quercetin (Que) is a ubiquitous flavonoid and polyphenol antioxidant. Negatively charged MoS2 was self-assembled onto the surface of positively charged SiO2 nanospheres to form SiO2@MoS2 core-shell materials. Subsequently, the materials were embedded into the interlayer of MXenes to form an effectively conductive three-dimensional heterostructured composite. The MoS2 shell formed on SiO2 not only retained the intrinsic properties of SiO2 but also improved its conductivity and specific surface area. In addition, the addition of SiO2@MoS2 to the interlayer of MXenes effectively alleviated the interference within the potential window and promoted the accurate electrical signal detection of Que. The detection range of the SiO2@MoS2/MXenes electrochemical sensor was 20 nM ∼ 30 μM, and the detection limit was 2 nM. The sensor can be effectively applied to the detection of Que. in 12 kinds of fruits, vegetables and agricultural products, and the results were comparable to those of UV spectrophotometry with satisfactory recovery.

Development of 3D-printed conducting microneedle-based electrochemical point-of-care device for transdermal sensing of chlorpromazine

Despite the various benefits of chlorpromazine, its misuse and overdose may lead to severe side effects, therefore, creating a user-friendly point-of-care device for monitoring the levels of chlorpromazine drug to manage the potential side effects and ensure the effective and safe use of the medication is highly desired. In this report, we have demonstrated a simple and scalable manufacturing process for the development of a 3D-printed conducting microneedle array-based electrochemical point-of-care device for the minimally invasive sensing of chlorpromazine. We used an inkjet printer to print the carbon and silver ink onto a customized 3D-printed ultrasharp microneedle array for the preparation of counter, working, and reference electrodes. After physical characterization and electrochemical parameter optimization, the developed microneedle array-based three-electrode system was explored for the detection of chlorpromazine. The analytical results showed high sensitivity and selectivity toward chlorpromazine with a good linearity range from 5-120 μM and a low detection limit (0.09 μM). The proof-of-concept study results obtained from the skin-mimicking model indicated that the developed conductive microneedle array-based sensor can easily monitor the micromolar levels of chlorpromazine in artificial interstitial fluid; this type of system can be further explored for the development of other minimally invasive electrochemical biosensors.

A label-free electrochemical biosensor based on graphene quantum dots-nanoporous gold nanocomposite for highly sensitive detection of glioma cell

BACKGROUND

Glioma accounts for 80 % of all malignant primary brain tumors with a high mortality rate. Histopathological examination is the current diagnostic methods for glioma, but its invasive surgical interventions can cause cerebral edema or impair neural functioning. Liquid biopsy proves to be an efficient method for glioma detection. However, the blood-brain barrier restricts the number of circulating tumor cells (CTCs) in the bloodstream, posing a challenge for sensitive detection of glioma CTCs. This study aims to use the unique characteristics of nanocomposites and the specificity of Angiopep2 (Ang-2) to develop a method that can sensitively identify glioma CTCs.

RESULTS

Herein, a novel label-free impedimetric biosensor was successfully constructed for glioma CTCs detection by using graphene quantum dots (GQDs)-nanoporous gold (NPG) nanocomposites as the immobilized platform and the Ang-2 protein as biorecognition element. The GQDs was homogeneously assembled onto NPG, resulting in the creation of a novel GQDs-NPG nanocomposite with unique structure and function properties. Due to the high electron transfer efficiency of the GQDs-NPG nanocomposite, the developed biosensor exhibited a wild detection range from 1 to 1 × 106 cell mL-1, with a minimal detection limit of 1 cell mL-1. Additionally, the glioma cell biosensor demonstrated a strong anti-interference ability against multiple cell lines, and the stability of the biosensor remained at 96 % after 21 days of storage. Besides, the quantities of glioma cells detected in human serum samples by the glioma cell biosensor demonstrated outstanding consistency with the standard values added to the samples.

SIGNIFICANCE

The study provided a novel GQDs-NPG nanocomposite and an electrochemical biosensor based on GQDs-NPG was firstly developed for glioma CTCs detection. The glioma cell biosensor showed high sensitivity, low detection limit, strong anti-interference ability, and good stability in complex biological matrix. The reliable detection of glioma cell was successfully realized in human serum, providing an excellent option for liquid biopsy of glioma CTCs identification and early diagnosis of glioma diseases.

Analytical control of imatinib in bioanalytical samples using graphene quantum dots sensing

An analytical method for the determination of imatinib (IMA, the primary treatment for chronic myeloid leukemia), based on the fluorescence properties of graphene quantum dots (GQDs), is reported in this work. The method is addressed to the analytical control of IMA in biological and pharmaceutical samples, due to the present interest in the control of the doses of this anticancer drug, as well as the therapeutic monitoring. The whole method involves the use of a solid-phase extraction (SPE) procedure, followed by an evaporation step, for the treatment of biological samples. For that, tC18 sorbent cartridges were used. After the sample treatment, the solution containing the analyte was mixed with an aqueous solution of GQDs at pH 7.2, and the fluorescent quenching of GQDs was measured. IMA was determined in the 10-250 µg L-1 range, with a limit of detection of 21 µg L-1 and a precision of 1.5% as relative standard deviation, measured in terms of reproducibility. The recovery for biological samples was in the 84-113% range.

A ratiometric fluorescent probe based on UiO-66-TCPP for selective and visual detection of quercetin in food

Quercetin (QCT) is a flavonoid with significant health benefits, necessitating sensitive detection methods for food safety and quality control. This study presents a novel UiO-66-TCPP ratiometric fluorescent probe for the quantitative and visual detection of QCT. Under optimal conditions, the fluorescence intensity of UiO-66-TCPP decreased linearly with increasing QCT concentration, with a detection limit of 26 nM. The probe demonstrated high specificity, showing no significant interference from various substances and QCT analogues. Practical applicability was confirmed by testing artificially contaminated juice samples, achieving recovery rates between 98.0% and 104.8%. Furthermore, a paper-based sensor was developed by incorporating UiO-66-TCPP onto Whatman#1 chromatography paper. This sensor exhibited stable fluorescence and a reliable, sensitive visual response to QCT concentrations, detectable via a smartphone-based color recognizer application. The UiO-66-TCPP ratiometric fluorescent probe provides a sensitive, specific, and practical method for detecting QCT in food matrices, offering significant potential for both laboratory and on-site applications.

Minimally invasive detection of buprenorphine using a carbon-coated 3D-printed microneedle array

A machine learning-assisted 3D-printed conducting microneedle-based electrochemical sensing platform was developed for wireless, efficient, economical, and selective determination of buprenorphine. The developed microneedle array-based sensing platform used 3D printing and air spray coating technologies for rapid and scalable manufacturing of a conducting microneedle surface. Upon optimization and understanding of the electrode stability, redox behavior, and electrochemical characteristics of as-prepared conducting microneedle array, the developed electrochemical platform was investigated for monitoring different levels of buprenorphine in the artificial intestinal fluid and found to be highly sensitive and selective towards buprenorphine for a wide detection range from 2 to 140 μM, with a low limit of detection of 0.129 μM. Furthermore, to make the sensing platform user accessible, the experimentally recorded sensing data was used to train a machine learning model and develop a web application for the numerical demonstration of buprenorphine levels at the point of site. Finally, the proof-of-concept study demonstrated that by advancing our prevailing 3D printing and additive manufacturing techniques, a low-cost, user-accessible, and compelling wearable electrochemical sensor could be manufactured for minimally invasive determination of buprenorphine in interstitial fluid.

Ti3C2 MXene quantum dots as an efficient fluorescent probe for bioflavonoid quercetin quantification in food samples

BACKGROUND

Quercetin (QC) is known as a typical antioxidant as a bioflavonoid, and its quick, sensitive, and specific detection is crucial for assessing food products. In this study, for the purpose of luminescence-based sensing of QC, bright bluish-green emissive quantum dots of N-doped MXene-based titanium carbide (Ti3C2) were fabricated. Recently, MXene quantum dots (MX-QDs), the rapidly emerging zero-dimensional nanomaterials made from two-dimensional transition metal carbides, have attracted much interest due to their unique physical and chemical features. These include the extremely large surface-to-volume ratio, biocompatibility, luminescence tunability, and hybridization capability while retaining properties of their two-dimensional counterpart including good conductivity and charge transferability.

RESULTS

The fabricated Ti3C2 MX-QDs had a quantum yield of 8.13 % at the emission wavelength of λem = 465 nm and displayed excellent photostability with great colloidal stability. It was found that introducing QC to near Ti3C2 MX-QDs reduced their fluorescence signals due to quenching effects. These quenching effects that occurred in a very broad linear range of QC (25-600 nM) enabled QC to be sensed quantitatively with the limit of detection of QC (1.35 nM), being the lowest ever reported to date. The quenching phenomena that caused such excellent sensitivity could be accounted for by combined effects of static quenching/radiation-free complex formation and inner filter effects (IFE) of Ti3C2 MX-QDs with QC.

SIGNIFICANCE

In addition, the quenching-based detection demonstrated excellent specificity against structurally relevant interferants. Therefore, the presented sensing strategies with Ti3C2 MX-QDs-based fluorescence quenching can be one of the strongest candidates as a reliable and cost-effective solution to highly sensitive quantification of QC in food samples.

Facile synthesis of N-doped graphene quantum dots as a fluorescent sensor for Cr(vi) and folic acid detection

The development of stable fluorescent sensors for toxic pollutants and drugs is meaningful to the environment and public health. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were facially synthesized by a one-step hydrothermal method using soluble starch and l-arginine as carbon and nitrogen sources in pure water at 190 °C for 4 h. The as-synthesized N-GQDs were well characterized and displayed blue fluorescence emission at 445 nm with excellent pH stability, salt tolerance, thermostability, photobleaching resistance and reproducibility. Moreover, N-GQDs could serve as an "on-off" sensor for selective detection of Cr(vi) and folic acid with low detection limit (0.80 and 2.1 μM), good linear correlation over wide linear range (0-50 μM and 0-200 μM) as well as short response time (<10 s). The practical applications of N-GQDs for Cr(vi) and folic acid detection in actual samples were further investigated and showed acceptable recoveries (92-105%) with relative standard deviations less than 5%. These results indicated that this N-GQDs-based sensor could be a potential alternative for Cr(vi) and folic acid detection in the fields of environmental monitoring and drug analysis.

Review on Hyaluronic Acid Functionalized Sulfur and Nitrogen Co-Doped Graphene Quantum Dots Nano Conjugates for Targeting of Specific Type of Cancer

Many people lose their lives to cancer each year. The prevalence of illnesses, metabolic disorders, high-risk infections, and other conditions has been greatly slowed down by expanding scientific research. Chemotherapy and radiation are still the initial lines of treatment for cancer patients, along with surgical removal of tumors. Modifications have been made in chemotherapy since medicines frequently have substantial systemic toxicity and poor pharmacokinetics and still do not reach the tumor site at effective concentrations. Chemotherapy may now be administered more safely and effectively thanks to nanotechnology. Nanotechnology-based graphene quantum dots (GQDs) are very applicable in breast cancer detection, as a drug delivery system, and in the treatment of breast cancer because of their physical and chemical properties, lower toxicity, small size, fluorescence, and effective drug delivery. This paper analyzes the GQDs as cutting-edge platforms for biotechnology and nanomedicine also its application in drug delivery in cancer. It shows that GQDs can be effectively conjugated with hyaluronic acid (HA) to achieve efficient and target-specific delivery.

Selective dual sensing strategy for free and vitamin D3 micelles in food samples based on S,N-GQDs photoinduced electron transfer

A reliable nanotechnological sensing strategy, based on an S,N-co-doped graphene quantum dot (GQD) platform, has been developed to distinctly detect two key variants of vitamin D3, specifically the free (VD3) and the nanoencapsulated form (VD3Ms). For this purpose, food-grade vitamin D3 micelles were self-assembled using a low-energy procedure (droplet size: 49.6 nm, polydispersity index: 0.34, ζ-potential: -33 mV, encapsulation efficiency: 90 %) with an innovative surfactant mixture (Tween 60 and quillaja saponin). Herein, four fluorescent nanoprobes were also synthesized and thoroughly characterized: S,N-co-doped GQDs, α-cyclodextrin-GQDs, β-cyclodextrin-GQDs, and γ-cyclodextrin-GQDs. The goal was to achieve a selective dual sensing strategy for free VD3 and VD3Ms by exploiting their distinctive quenching behaviors. Thus, the four nanosensors allowed the individual sensing of both targets to be performed (except α-CD-GQD for VD3Ms), but S,N-GQDs were finally selected due to selectivity and sensitivity (quantum yield, QY= 0.76) criteria. This choice led to a photoinduced electron transfer (PET) mechanism associated with static quenching, where differentiation was evidenced through a displayed 13-nm hypsochromic (blue) shift when interacting with VD3Ms. The reliability of this dual approach was demonstrated through an extensive evaluation of analytical performance characteristics. The feasibility and accuracy were proven in commercial food preparations and nutritional supplements containing declared nanoencapsulated and raw VD3, whose results were validated by a paired Student's t-test comparison with a UV-Vis method. To the best of our knowledge, this represents the first non-destructive analytical approach addressing the groundbreaking foodomic trend to distinctly detect different bioactive forms of vitamin D3, while also preserving their native nanostructures as a chemical challenge, thus providing reliable information about their final stability and bioavailability.

Additive manufacturing of microneedles for sensing and drug delivery

INTRODUCTION

Microneedles (MNs) are miniaturized, painless, and minimally invasive platforms that have attracted significant attention over recent decades across multiple fields, such as drug delivery, disease monitoring, disease diagnosis, and cosmetics. Several manufacturing methods have been employed to create MNs; however, these approaches come with drawbacks related to complicated, costly, and time-consuming fabrication processes. In this context, employing additive manufacturing (AM) technology for MN fabrication allows for the quick production of intricate MN prototypes with exceptional precision, providing the flexibility to customize MNs according to the desired shape and dimensions. Furthermore, AM demonstrates significant promise in the fabrication of sophisticated transdermal drug delivery systems and medical devices through the integration of MNs with various technologies.

AREAS COVERED

This review offers an extensive overview of various AM technologies with great potential for the fabrication of MNs. Different types of MNs and the materials utilized in their fabrication are also discussed. Recent applications of 3D-printed MNs in the fields of transdermal drug delivery and biosensing are highlighted.

EXPERT OPINION

This review also mentions the critical obstacles, including drug loading, biocompatibility, and regulatory requirements, which must be resolved to enable the mass-scale adoption of AM methods for MN production, and future trends.

Recent Progress of Fluorescent Carbon Dots and Graphene Quantum Dots for Biosensors: Synthesis of Solution Methods and their Medical Applications

In the fields of health and biology, fluorescent nanomaterials have emerged as highly potential and very useful candidates for use in biosensor applications. These typical highly powerful nanomaterials are carbon dots (CDs) and graphene quantum dots (GQDs) among many other metallic nanomaterials. In the context of medical biosensors, this review article investigates the techniques of synthesis, and many uses of these nanomaterials, the obstacles that they face, and the potential for their future. We cover the significance of fluorescent nanomaterials, their use in the medical field, as well as the several techniques of synthesis for CDs and GQDs, including ultrasonication, hydrothermal, electrochemical method, surface modification, and solvothermal. In addition, we also discuss their biomedical applications, which include biomolecule detection, disease diagnosis and examine the obstacles and prospective possibilities for development of ultra-bright, ultra-sensitive, and selective biosensors for use in in-vivo research.Fluorescent carbon dots and graphene quantum dots is synthesized by using several types of raw material and methods. These Carbon dots and graphene quantum dots are used in the medical field includes detection of biomaterials, detection of cancer, virus and mutation in DNA.

Nitrogen and Chlorine Co-doped Carbon Dots as a Highly Selective and Sensitive Fluorescent Probe for Sensing of PH, Tetracycline Detection and Cell Imaging

Carbon dots have been widely focused on the field of sensing and detection due to their excellent optical property. Herein, novel orange fluorescent nitrogen and chlorine co-doped carbon dots (N,Cl-CDs) are obtained by one-pot hydrothermal method using o-phenylenediamine and neutral red. Based on the inner filter effect, the prepared N,Cl-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline. The proposed sensor was utilized to realize the determination of tetracycline in Rirver water samples/milk samples (λex = 390 nm, λem = 606 nm) with satisfactory recoveries and relative standard deviations. The linear range of are 0.05 to 45 μM and 45 to135 μM, and detection limit is 3.9 nM (3σ/m). Meanwhile, the luminescent intensity of N,Cl-CDs was reduced gradually when pH changed continuously from 12 to 2, showing a pH-responsive fluorescence property with two linear ranges of pH 3-7 and pH 7-10. In addition, due to the characteristics of low toxicity and excellent biocompatibility, the N, Cl-CDs were also used in the imaging of oocystis cells, which is hopeful to realize the detection of tetracycline in living cells.

Synthesis and Characterization of Carbon-Based Quantum Dots and Doped Derivatives for Improved Andrographolide's Hydrophilicity in Drug Delivery Platforms

Carbon-based quantum dots (CBQDs), sulfur-doped carbon-based quantum dots (S-CBQDs), and nitrogen-doped carbon-based quantum dots (N-CBQDs) have strong potential for drug delivery platforms. They were conjugated with andrographolide, a well-known hydrophobic drug, to study the concomitant changes in hydrophilicity. The interactions between these nanomaterials and the drug were studied by characterizing the optical and structural properties of the nanoparticles before and after coupling with the drug. It was found that the interaction of the drug with these nanomaterials produced noticeable changes in their optical and structural properties. Moreover, the partition coefficient for the nanocomposites was determined by NMR. The results indicate that conjugating the drug with the nanoparticles significantly enhanced its affinity for the aqueous phase, from 2.632 to 0.1117, thereby opening the possibility of using this approach for developing an effective drug delivery platform for this hydrophobic drug.

One-pot synthesis of nano Zr-based metal-organic frameworks for fluorescence determination of quercetin and Hg2

In this study, a nanoscale Zr-based metal-organic framework (nano-Zr-MOF) was prepared by one-pot method using meso-tetra(4-carboxyphenyl)porphyrin as organic ligand and Zr4+ as metal unit. The nanoscale structure endows it with excellent dispersion in water. The nano-Zr-MOF exhibited intense red fluorescence, which could be significantly quenched by the addition of quercetin, probably due to its electron-rich framework. The high selectivity for quercetin detection was verified with analogues and common ions as interfering agents. Moreover, the nano-Zr-MOF could be used as a highly selective and sensitive sensor for the detection of Hg2+. The detection limits for quercetin and Hg2+ were 0.026 μM and 0.039 μM, respectively. This fluorometric method was successfully applied to detect quercetin in red wine and food samples with satisfactory recoveries ranging from 83.7-112.3% and 81.8-115.9%, respectively. The recovery in detection of Hg2+ in lake water were ranging from 97.1-109.2%.

Facile Synthesis of S-doped Carbon Quantum Dots and Their Application in the Detection of Sudan I in Saffron

This study employed citric acid as a carbon source and thiourea as a sulphur source to conduct a straightforward one-step microwave synthesis of sulphur-doped carbon quantum dots (SCQDs). For the characterization of as-synthesized SCQDs, several methods such as fluorescence spectroscopy, X-Ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD), and zeta potential analyzer were utilized. XRD and XPS spectroscopy are used to examine the chemical composition and morphological aspects. These QDs have a limited size distribution spanning up to 5.89 nm, with a maximum distribution at 7 nm, according to zeta size analyser examinations. At an excitation wavelength of 340 nm, the highest fluorescence intensity (FL intensity) of SCQDs was attained. With a detection limit of 0.77 M, the synthesized SCQDs were employed as an efficient fluorescent probe for the detection of Sudan I in saffron samples.

Synthesis and Application of Carbon Quantum Dots Derived from Carbon Black in Bioimaging

Carbon quantum dots (CQDs) are a new type of fluorescent QDs that consists mainly of carbon atoms. In this research, CQDs were synthesized through harsh oxidizing conditions applied on carbon black and subsequent N-doping using hexamethylenetetramine (Hexamine) and polyethyleneimine (PEI). The synthesized CQDs were characterized using FTIR, AFM, UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, and fluorescence imaging respectively. The AFM images showed that the dots are in the range of 2-8 nm. N-doping of the CQDs increased the PL intensity. The PL enhancement for the CQDs that were N-doped with PEI was higher compared to those N-doped with hexamine. The shift in PL by changing the excitation wavelength has been attributed to the nano-size of the CQDs, functional groups, defect traps, and quantum confinement effect. The in vitro fluorescence imaging revealed that N-doped CQDs can internalize into the cells and be used for fluorescent cell imaging.

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0-29.7 μM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner.

From Pristine to Heteroatom-Doped Graphene Quantum Dots: An Essential Review and Prospects for Future Research

Graphene quantum dots (GQDs) are carbon-based zero-dimensional materials that have received considerable scientific interest due to their exceptional optical, electrical, and optoelectrical properties. Their unique electronic band structures, influenced by quantum confinement and edge effects, differentiate the physical and optical characteristics of GQDs from other carbon nanostructures. Additionally, GQDs can be synthesized using various top-down and bottom-up approaches, distinguishing them from other carbon nanomaterials. This review discusses recent advancements in GQD research, focusing on their synthesis and functionalization for potential applications. Particularly, various methods for synthesizing functionalized GQDs using different doping routes are comprehensively reviewed. Based on previous reports, current challenges and future directions for GQDs research are discussed in detail herein.

Computational approaches to delivery of anticancer drugs with multidimensional nanomaterials

Functionalized nanotubes (NTs), nanosheets, nanorods, and porous organometallic scaffolds are potential in vivo carriers for cancer therapeutics. Precise delivery through these agents depends on factors like hydrophobicity, payload capacity, bulk/surface adsorption, orientation of molecules inside the host matrix, bonding, and nonbonding interactions. Herein, we summarize advances in simulation techniques, which are extremely valuable in initial geometry optimization and evaluation of the loading and unloading behavior of encapsulated drug molecules. Computational methods broadly involve the use of quantum and classical mechanics for studying the behavior of molecular properties. Combining theoretical processes with experimental techniques, such as X-ray crystallography, NMR spectroscopy, and bioassays, can provide a more comprehensive understanding of the structure and function of biological molecules. This integrated approach has led to numerous breakthroughs in drug discovery, enzyme design, and the study of complex biological processes. This short review provides an overview of results and challenges described from erstwhile investigations on the molecular interaction of anticancer drugs with nanocarriers of different aspect ratios.

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.

Lights and Dots toward Therapy-Carbon-Based Quantum Dots as New Agents for Photodynamic Therapy

The large number of deaths induced by carcinoma and infections indicates that the need for new, better, targeted therapy is higher than ever. Apart from classical treatments and medication, photodynamic therapy (PDT) is one of the possible approaches to cure these clinical conditions. This strategy offers several advantages, such as lower toxicity, selective treatment, faster recovery time, avoidance of systemic toxic effects, and others. Unfortunately, there is a small number of agents that are approved for usage in clinical PDT. Novel, efficient, biocompatible PDT agents are, thus, highly desired. One of the most promising candidates is represented by the broad family of carbon-based quantum dots, such as graphene quantum dots (GQDs), carbon quantum dots (CQDs), carbon nanodots (CNDs), and carbonized polymer dots (CPDs). In this review paper, these new smart nanomaterials are discussed as potential PDT agents, detailing their toxicity in the dark, and when they are exposed to light, as well as their effects on carcinoma and bacterial cells. The photoinduced effects of carbon-based quantum dots on bacteria and viruses are particularly interesting, since dots usually generate several highly toxic reactive oxygen species under blue light. These species are acting as bombs on pathogen cells, causing various devastating and toxic effects on those targets.

Metal-Organic Framework with Near-Infrared Luminescence for "Switch-on" Determination of Kaempferol and Quercetin by the Antenna Effect

The establishment of a reliable and sensitive method for the detection of flavonoids, such as kaempferol (Kae) and quercetin (Que), is important and challenging in food chemistry and pharmacology because numerous structural analogues may interfere with the detection. Until now, designing an efficient switch-on fluorescence sensing strategy for Kae and Que was still in the unachievable stage. In this work, a switch-on near-infrared (NIR) luminescence sensing assay for Kae and Que was fabricated based on a metal-organic framework (MOF) called IQBA-Yb for the first time. The fluorescence enhancing mechanism was that analytes served as additional "antenna" of Yb³⁺, leading to the efficient switch-on NIR emission under excitation at 467 nm. Meanwhile, the combination results of experiment and theoretical calculation revealed that there existed hydrogen bonds between Kae, Que, and the MOF skeleton, further promoting the energy transfer between the analyte and Yb³⁺ and facilitating fluorescence enhancement response. The developed probe possessed excellent sensing capability for Kae and Que, accompanied by a wide linear range (0.04-70, 0.06-90 μM), low detection limit (0.01, 0.06 μM), and short response time (20 min, 6 min), which was used to determine the Kae and Que contents in Green Lake and eatable Que samples with satisfactory results.

One-pot hydrothermal synthesis of Si-doped carbon quantum dots with up-conversion fluorescence as fluorescent probes for dual-readout detection of berberine hydrochloride

Here, the high fluorescent silicon-doped carbon quantum dots (Si-CQDs) were prepared by a facile and one-pot hydrothermal assay using 3-aminopropyltrimethoxysilane as the carbon and silicon source. The prepared Si-CQDs exhibit favorable water-soluble, high-temperature resistance, acid resistance, alkali resistance, high ionic strength resistance, high photostability, film-forming ability and solid-state fluorescence. Compared to other Si-CQDs that have been reported, the prepared Si-CQDs show unique up-conversion fluorescence. Furthermore, it is found that berberine hydrochloride (BH) can effectively quench the down- and up-conversion fluorescence of the Si-CQDs, making it can be used as a highly sensitive and specific probe for BH dual-mode sensing. Meanwhile, the linear range of down-conversion fluorescence detection for BH is 0.5-30.0 µmol/L with a limit of detection (LOD) of 50 nmol/L, and the linear range of up-conversion fluorescence assay for BH is 0-25.0 µmol/L. The mechanism of down-conversion fluorescence quenching by BH was investigated through a series of studies. The results show the quenching mechanism is the inner filter effect (IFE). Moreover, this proposed strategy has been well used to analyze BH in urine samples with satisfactory results.

Graphene quantum dots: synthesis, properties, and applications to the development of optical and electrochemical sensors for chemical sensing

GQDs exhibits exceptional electrochemical activity owing to their active edge sites that make them very attractive for biosensing applications. However, their use in the design of new biosensing devices for application to the detection and quantification of toxins, pathogens, and clinical biomarkers has so far not investigated in detail. In this regard, herein we provide a detailed review on various methodologies employed for the synthesis of GQDs, including bottom-up and top-down approaches, with a special focus on their applications in biosensing via fluorescence, photoluminescence, chemiluminescence, electrochemiluminescence, fluorescence resonance energy transfer, and electrochemical techniques. We believe that this review will shed light on the critical issues and widen the applications of GQDs for the design of biosensors with improved analytical response for future applications. HIGHLIGHTS: • Properties of GQDs play a critical role in biosensing applications. • Synthesis of GQDs using top-down and bottom-up approaches is discussed comprehensively. • Overview of advancements in GQD-based sensors over the last decade. • Methods for the design of selective and sensitive GQD-based sensors. • Challenges and opportunities for future GQD-based sensors.

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.

Graphene quantum dots: A review on the effect of synthesis parameters and theranostic applications

The rising demand for early-stage diagnosis of diseases such as cancer, diabetes, neurodegenerative can be met with the development of materials offering high sensitivity and specificity. Graphene quantum dots (GQDs) have been investigated extensively for theranostic applications owing to their superior photostability and high aqueous dispersibility. These are attractive for a range of biomedical applications as their physicochemical and optoelectronic properties can be tuned precisely. However, many aspects of these properties remain to be explored. In the present review, we have discussed the effect of synthetic parameters upon their physicochemical characteristics relevant to bioimaging. We have highlighted the effect of particle properties upon sensing of biological molecules through 'turn-on' and 'turn-off' fluorescence and generation of electrochemical signals. After describing the effect of surface chemistry and solution pH on optical properties, an inclusive view on application of GQDs in drug delivery and radiation therapy has been given. Finally, a brief overview on their application in gene therapy has also been included.

One-step hydrothermal synthesis of fluorescent silicon nanoparticles for sensing sulfide ions and cell imaging

We have presented a hydrothermal approach for synthesizing fluorescent silicon nanoparticles (F-SiNPs) with yellow-green emission. The obtained F-SiNPs exhibited excellent stability and good biocompatibility. By virtue of the specific reaction between S^2- and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), colorimetric assay of S^2- was realized with a good linear range of 0-100 μM. The colorimetric detection system could be further combined with F-SiNPs to construct a probe for fluorescence turn-off sensing S^2- in aqueous solution due to inner filter effect. In the fluorescent detection system, a good linearity with S^2- concentration in the range of 0-50 μM was accomplished. And as low as 0.1 μM S^2- was successfully detected. Moreover, the F-SiNPs displayed low cytotoxicity and good biocompatibility, and was further utilized for cell imaging. These results demonstrated the promising applications of F-SiNPs in S^2- analysis and bioimaging.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.

Recent progress on graphene quantum dots-based fluorescence sensors for food safety and quality assessment applications

The versatile photophysicalproperties, high surface-to-volume ratio, superior photostability, higher biocompatibility, and availability of active sites make graphene quantum dots (GQDs) an ideal candidate for applications in sensing, bioimaging, photocatalysis, energy storage, and flexible electronics. GQDs-based sensors involve luminescence sensors, electrochemical sensors, optical biosensors, electrochemical biosensors, and photoelectrochemical biosensors. Although plenty of sensing strategies have been developed using GQDs for biosensing and environmental applications, the use of GQDs-based fluorescence techniques remains unexplored or underutilized in the field of food science and technology. To the best of our knowledge, comprehensive review of the GQDs-based fluorescence sensing applications concerning food quality analysis has not yet been done. This review article focuses on the recent progress on the synthesis strategies, electronic properties, and fluorescence mechanisms of GQDs. The various GQDs-based fluorescence detection strategies involving Förster resonance energy transfer- or inner filter effect-driven fluorescence turn-on and turn-off response mechanisms toward trace-level detection of toxic metal ions, toxic adulterants, and banned chemical substances in foodstuffs are summarized. The challenges associated with the pretreatment steps of complex food matrices and prospects and challenges associated with the GQDs-based fluorescent probes are discussed. This review could serve as a precedent for further advancement in interdisciplinary research involving the development of versatile GQDs-based fluorescent probes toward food science and technology applications.

One-step synthesis of N, S-doped carbon dots with orange emission and their application in tetracycline antibiotics, quercetin sensing, and cell imaging

Water soluble N, S-doped carbon dots (N, S-CDs) with orange emission were synthesized from basic fuchsin and sulfosalicylic acid by the typical hydrothermal route. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline antibiotics (for example, chlortetracycline (CTC)) and quercetin. The proposed sensor was utilized to realize the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm) with satisfactory recoveries and relative standard deviations (RSD). The linear range and detection limit (LOD) of CTC is 1.24-165 μM and 32.36 nM, respectively. For quercetin, the linear ranges are 0.98-34 μM and 34-165 μΜ, and the LOD is 6.87 nM (3σ/m). By virtue of the good biocompatibility and long-wavelength emission, N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bio-imaging and sensing. In this paper, N, S-doped carbon dots (N, S-CDs) with orange emission (λem = 605 nm) were synthesized from basic fuchsin and sulfosalicylic acid. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for the sensing of tetracycline antibiotics (for example: chlortetracycline (CTC)) and quercetin. The sensor has been successfully applied to the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm). The linear range and detection limit (LOD) of CTC is 1.24-165 μM and 32.36 nM respectively. For quercetin, the linear ranges are 0.98-34 μM and 34-165 μΜ, and the LOD is 6.87 nM (3σ/m). In addition, due to the characteristics of good biocompatibility and long-wavelength emission, the N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bioimaging and sensing.

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.

Application of micro/nanomaterials in adsorption and sensing of active ingredients in traditional Chinese medicine

Traditional Chinese medicine (TCM) has been widely applied for the prevention and cure of various diseases for centuries. Ingredient with pharmacological activity is the key to the application of TCM. Hence, it is of significance to separate and detect active ingredients in TCM effectively. Micro/nanomaterial is the promising candidate for adsorption and sensing due to its unique physical and chemical properties. For years, many efforts have been made to develop functional micro/nanomaterials to realize the effective adsorption or sensing of bioactive compounds in TCM. In this review, we discussed recent progresses in the application of various functional micro/nanomaterials for adsorption or detection (electrochemical detection, fluorescent detection, and colorimetric detection) of active ingredients. Based on the kind of matrix materials, micro/nano-adsorbents or sensors can be classified into following categories: metal-based micro/nanomaterials, porous materials, carbon-based materials, graphene/graphite-liked micro/nanomaterials and hybrid micro/nanomaterials.

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.

Integration of fluorescent probes into metal–organic frameworks for improved performances

Recent years have witnessed a rapid development of fluorescent probes in both analytical sensing and optical imaging. Enormous efforts have been devoted to the regulation of fluorescent probes during their development, such as improving accuracy, sensitivity, selectivity, recyclability and overcoming the aggregation-caused quenching effect. Metal–organic frameworks (MOFs) as a new class of crystalline porous materials possess abundant host–guest chemistry, based on which they display a great application potential in regulating fluorescent probes. This review summarized the research works on the regulation of fluorescent probes using MOFs, with emphasis on the methods of integrating fluorescent probes into MOFs, the regulation effects of MOFs on fluorescent probes, the superiorities of MOFs in regulating fluorescent probes, and the outlook of this subject. It is desirably hoped that this review can provide a useful reference for the researchers interested in this field.

This review surveyed the research works for the regulation of fluorescent probes with metal–organic frameworks based on host–guest chemistry.