Fluorescent carbon dots for labeling of bacteria: mechanism and prospects-a review.

The search for bacteria-labeling agents that are more efficient and less toxic compared to existing staining dyes is ongoing. Fluorescent quantum dots and carbon dots (CDs) have been extensively researched for various bioimaging applications. Priority is given to CDs due to several advantages, including lower toxicity, versatility in tuning their properties, and better photostability compared to metal-based quantum dots. Although significant progress is still needed to replace existing dyes with CDs for bacteria labeling, they offer promising potential for further improvement in efficiency. Surface charges and functional groups have been reported as decisive factors for bacterial discrimination and live/dead assays; however, a complete guideline for preparing CDs with optimum properties for efficient staining and predicting their labeling performance is lacking. In this review, we discuss the application of fluorescent CDs for bacterial labeling and the underlying mechanisms and principles. We primarily focus on the application and mechanism of CDs for Gram differentiation, live imaging, live/dead bacteria differentiation, bacterial viability testing, biofilm imaging, and the challenges associated with application of CDs. Based on proposed mechanisms of bacterial labeling and ambiguous results reported, we provide our view and guidelines for the researchers in this field to overcome the challenges associated with bacteria labeling using fluorescent CDs.

High Amplification of the Antiviral Activity of Curcumin through Transformation into Carbon Quantum Dots.

It is demonstrated that carbon quantum dots derived from curcumin (Cur-CQDs) through one-step dry heating are effective antiviral agents against enterovirus 71 (EV71). The surface properties of Cur-CQDs, as well as their antiviral activity, are highly dependent on the heating temperature during synthesis. The one-step heating of curcumin at 180 °C preserves many of the moieties of polymeric curcumin on the surfaces of the as-synthesized Cur-CQDs, resulting in superior antiviral characteristics. It is proposed that curcumin undergoes a series of structural changes through dehydration, polymerization, and carbonization to form core-shell CQDs whose surfaces remain a pyrolytic curcumin-like polymer, boosting the antiviral activity. The results reveal that curcumin possesses insignificant inhibitory activity against EV71 infection in RD cells [half-maximal effective concentration (EC50 ) >200 µg mL-1 ] but exhibits high cytotoxicity toward RD cells (half-maximal cytotoxic concentration (CC50 ) <13 µg mL-1 ). The EC50 (0.2 µg mL-1 ) and CC50 (452.2 µg mL-1 ) of Cur-CQDs are >1000-fold lower and >34-fold higher, respectively, than those of curcumin, demonstrating their far superior antiviral capabilities and high biocompatibility. In vivo, intraperitoneal administration of Cur-CQDs significantly decreases mortality and provides protection against virus-induced hind-limb paralysis in new-born mice challenged with a lethal dose of EV71.

Detection of arsenic(III) through pulsed laser-induced desorption/ionization of gold nanoparticles on cellulose membranes.

We have developed an assay based on gold nanoparticle-modified mixed cellulose ester membrane (Au NPs-MCEM) coupled with laser-induced desorption/ionization mass spectrometry (LDI-MS)-for the detection of arsenic(III) ions (arsenite, AsO2(-)) in aqueous solution. When the Au NPs reacted with lead ions (Pb(2+)) in alkaline solution (5 mM glycine-NaOH, pH 12), Au-Pb complexes, PbO, and Pb(OH) were formed immediately on the Au NP surfaces. The Pb species reacted rapidly with subsequently added AsO2(-) to form PbOAs2O3, (PbO)2As2O3, and/or (PbO)3As2O3 shells (2-5 nm) on the Au NPs' surfaces. As a result, significant observable aggregation of the Au NPs occurred in the solution. This Pb(2+)/Au NP probe allowed the detection of AsO2(-) at concentrations as low as 0.6 µM with high selectivity (at least 100-fold over other anions and metal ions). To further improve the sensitivity, we prepared Au NPs-MCEM for the LDI-MS-based detection of AsO2(-) ions. The intensity of the signal for the [Pb](+) ions in the mass spectra increased when the Au NPs-MCEM reacted with AsO2(-); in contrast, the intensity of the signal for [Au](+) ions decreased. Accordingly, the [Pb](+)/[Au](+) peak ratio increased upon increasing the AsO2(-) concentration over the range from 10 nM to 10 µM. The limit of detection at a signal-to-noise ratio of 3 was 2.5 nM, far below the action level of As (133 nM, ca. 10 ppb) permitted by the US EPA for drinking water. Relative to other nanoparticle-based arsenic sensors, this approach is rapid, specific, and sensitive; in addition, it can be applied to the detection of AsO2(-) in natural water samples (in this case, streamwater, lake water, tap water, groundwater, and mineral water).

Functional gold nanoparticles coupled with microporous membranes: a flow controlled assay for colorimetric visualization of proteins.

We report a rapid and simple assay for colorimetric visualization of thrombin at nanomolar levels using functional gold nanoparticles (FAuNPs) coupled with microporous membranes. We used a 29-mer thiolated-thrombin-binding-aptamer (TBA29) to prepare TBA29 functionalized AuNPs (TBA29-AuNPs) for the selective detection of human thrombin. The sensing mechanism is based on the principle of TBA29-AuNPs flowing down through the nitrocellulose membrane (NCM) pores at different flow rates after binding to thrombin. Compared with free TBA29-AuNPs, when thrombin-TBA29-AuNPs were dropped on the NCM, the particles flowed down more easily through the NCM pores along with the buffer solution due to the increase in the gravity of particles. Therefore, color intensities of TBA29-AuNPs on the NCM depended on the concentration of thrombin; the color intensity was lighter when the concentration of thrombin was higher. Thrombin can be detected at the nanomolar level with the naked eye using this colorimetric probe. A protein G modified AuNP based probe (PG-AuNPs/NCM) was employed to detect human immunoglobulin G (hIgG) in plasma samples to demonstrate the practicality of our sensing system. Also, fibrinogen modified Au NPs were analyzed to demonstrate that this concept of detection could be extended to other proteins or systems, by functionalizing with suitable molecules.

Nitrite ion-induced fluorescence quenching of luminescent BSA-Au(25) nanoclusters: mechanism and application.

Fluorescence quenching is an interesting phenomenon which is highly useful in developing fluorescence based sensors. A thorough understanding of the fluorescence quenching mechanism is essential to develop efficient sensors. In this work, we investigate different aspects governing the nitrite ion-induced fluorescence quenching of luminescent bovine serum albumin stabilized gold nanoclusters (BSA-Au NCs) and their application for detection of nitrite in urine. The probable events leading to photoluminescence (PL) quenching by nitrite ions were discussed on the basis of the results obtained from ultraviolet-visible (UV-Vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence measurements, circular dichroism (CD) spectroscopy, zeta potential and dynamic light scattering (DLS) studies. These studies suggested that PL quenching mainly occurred through the oxidation of Au(0) atoms to Au(i) atoms in the core of BSA-Au NCs mediated by nitrite ions. The interference caused by certain species such as Hg(2+), Cu(2+), CN(-), S(2-), glutathione, cysteine, etc. during the nitrite determination by fluorescence quenching was eliminated by using masking agents and optimising the conditions. Based on these findings we proposed a BSA-Au NC-modified membrane based sensor which would be more convenient for the real life applications such as nitrite detection in urine samples. The BSA-Au NC-modified nitrocellulose membrane (NCM) enabled the detection of nitrite at a level as low as 100 nM in aqueous solutions. This Au NC-based paper probe was validated to exhibit good performance for nitrite analysis in environmental water and urine samples, which makes it useful in practical applications.

Carbonization of quercetin into nanogels: a leap in anticoagulant development.

Quercetin, a flavonoid abundantly found in onions, fruits, and vegetables, is recognized for its pharmacological potential, especially for its anticoagulant properties that work by inhibiting thrombin and coagulation factor Xa. However, its clinical application is limited due to poor water solubility and bioavailability. To address these limitations, we engineered carbonized nanogels derived from quercetin (CNGsQur) using controlled pyrolysis and polymerization techniques. This led to substantial improvements in its anticoagulation efficacy, water solubility, and biocompatibility. We generated a range of CNGsQur by subjecting quercetin to varying pyrolytic temperatures and then assessed their anticoagulation capacities both in vitro and in vivo. Coagulation metrics, including thrombin clotting time (TCT), activated partial thromboplastin time (aPTT), and prothrombin time (PT), along with a rat tail bleeding assay, were utilized to gauge the efficacy. CNGsQur showed a pronounced extension of coagulation time compared to uncarbonized quercetin. Specifically, CNGsQur synthesized at 270 °C (CNGsQur270) exhibited the most significant enhancement in TCT, with a binding affinity to thrombin exceeding 400 times that of quercetin. Moreover, variants synthesized at 310 °C (CNGsQur310) and 290 °C (CNGsQur290) showed the most substantial delays in PT and aPTT, respectively. Our findings indicate that the degree of carbonization significantly influences the transformation of quercetin into various CNGsQur forms, each affecting distinct coagulation pathways. Additionally, both intravenous and oral administrations of CNGsQur were found to extend rat tail bleeding times by up to fivefold. Our studies also demonstrate that CNGsQur270 effectively delays and even prevents FeCl3-induced vascular occlusion in a dose-dependent manner in mice. Thus, controlled pyrolysis offers an innovative approach for generating quercetin-derived CNGs with enhanced anticoagulation properties and water solubility, revealing the potential for synthesizing self-functional carbonized nanomaterials from other flavonoids for diverse biomedical applications.

In Situ Hybridization of Polymeric Curcumin to Arginine-Derived Carbon Quantum Dots for Synergistic Treatment of Bacterial Infections.

Effective infectious keratitis treatment must eliminate the pathogen, reduce the inflammatory response, and prevent persistent damage to the cornea. Infectious keratitis is generally treated with broad-spectrum antibiotics; however, they have the risk of causing corneal epithelial cell damage and drug resistance. In this study, we prepared a nanocomposite (Arg-CQDs/pCur) from arginine (Arg)-derived carbon quantum dots (Arg-CQDs) and polymeric curcumin (pCur). Partial carbonization of arginine hydrochloride in the solid state by mild pyrolysis resulted in the formation of CQDs, which exhibited enhanced antibacterial activity. pCur was formed by the polymerization of curcumin, and further crosslinking reduced its cytotoxicity and improved antioxidative, anti-inflammatory, and pro-proliferative activities. The pCur in situ conjugated with Arg-CQDs to form the Arg-CQDs/pCur nanocomposite, which showed a minimum inhibitory concentration of ca. 10 µg mL-1, which was >100-fold and >15-fold lower than that of the precursor arginine and curcumin, respectively, against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The Arg-CQDs/pCur nanocomposite with combined antibacterial, antioxidative, anti-inflammatory, pro-proliferative properties, and long-term retention on cornea enabled synergistic treatment of bacterial keratitis. In a rat model, it can effectively treat P. aeruginosa-induced bacterial keratitis at a concentration 4000-fold lower than the commercially used drug, Sulmezole eye drops. Arg-CQDs/pCur nanocomposites have great potential for application in antibacterial and anti-inflammatory nanoformulations for clinical use to treat infectious diseases.

Dual-emissive carbonized polymer dots for the ratiometric fluorescence imaging of singlet oxygen in living cells.

Singlet oxygen (1O2) is a type of reactive oxygen species (ROS), playing a vital role in the physiological and pathophysiological processes. Specific probes for monitoring intracellular 1O2 still remain challenging. In this study, we develop a ratiometric fluorescent probe for the real-time intracellular detection of 1O2 using o-phenylenediamine-derived carbonized polymer dots (o-PD CPDs). The o-PD CPDs possessing dual-excitation-emission properties (blue and yellow fluorescence) were successfully synthesized in a two-phase system (water/acetonitrile) using an ionic liquid tetrabutylammonium hexafluorophosphate as a supporting electrolyte through the electrolysis of o-PD. The o-PD CPDs can act as a photosensitizer to produce 1O2 upon white LED irradiation, in turn, the generated 1O2 selectively quenches the yellow emission of the o-PD CPDs. This quenching behavior is ascribed to the specific cycloaddition reaction between 1O2 and alkene groups in the polymer scaffolds on o-PD CPDs. The interior carbon core can be a reliable internal standard since its blue fluorescence intensity remains unchanged in the presence of 1O2. The ratiometric response of o-PD CPDs is selective toward 1O2 against other ROS species. The developed o-PD CPDs have been successfully applied to monitor the 1O2 level in the intracellular environment. Furthermore, in the inflammatory neutrophil cell model, o-PD CPDs can also detect the 1O2 and other ROS species such as hypochlorous acid after phorbol 12-myristate 13-acetate (PMA)-induced inflammation. Through the dual-channel fluorescence imaging, the ratiometric response of o-PD CPDs shows great potential for detecting endogenous and stimulating 1O2in vivo.

Pulsed laser irradiation induces the generation of alloy cluster ions for the screening of protease activity.

Pulsed laser irradiation can cause the fragmentation of nanoparticles, which generates cluster ions. This allows nanoparticles to be adopted as mass tag/signal amplifiers in laser desorption/ionization mass spectrometry (LDI-MS) bioassays. Herein, we demonstrate the potential of using the signal from alloy cluster ions in bioassays through a fibrin clot model to determine the activity of thrombin. A mixed solution of silver and gold nanoparticles functionalized with fibrinogen (Fg‒Ag NPs/Fg‒Au NPs) treated with thrombin can form clots composed of aggregated fibrin-Au NPs/Ag NPs. These clots analyzed with LDI-MS are noted to form intense Ag-Au alloy cluster ions, especially [Ag2Au]+, which were used to detect thrombin concentration with a dynamic range of 2.5-50 pM in human plasma. This sensing platform was further employed for the screening of direct thrombin inhibitors. This work developed a novel bioassay utilizing metallic gas-phase reactions generated from pulsed laser irradiation of aggregated nanoparticles to monitor enzymatic activity and to screen inhibitors. We believe that LDS-MS can serve as a new platform for gas-phase reaction-based bioassays.

Carbon-based low-pressure filtration membrane for the dynamic disruption of bacteria from contaminated water.

Carbon-based materials, especially graphene oxide (GO) and carbon dots possessing antibacterial properties, are widely used for various applications. Recently, we reported the antibacterial and antioxidant properties of carbonized nanogels (CNGs) for the treatment of bacterial keratitis, and as a virostatic agent against infectious bronchitis virus. In this work, we demonstrate the use of CNGs/GO nanocomposite (GO@CNGs) membrane for the efficient removal of Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria from contaminated water. The GO@CNGs composite membrane with an optimized ratio of GO to CNGs could achieve more than 99% removal efficiency toward E. coli and S. aureus. Various strains of bacteria interact differently with the membrane, and hence the membrane shows different removal rate, which can be optimized by controlling the interaction time through regulating the water flux. The GO@CNGs membrane with an active area of 2.83 cm2 achieved > 99% bacterial removal efficiency at a water flux of 400 mL min-1 m-2. The dynamic disruption of bacteria by GO@CNGs plays a crucial role in eliminating the bacteria. Rather than filtering out the bacteria, GO@CNGs membrane allows them to pass through it, interact with the bacteria and rupture the bacterial cell membranes. Our GO@CNGs membrane shows great potential as a filter to remove bacteria from contaminated water samples, operating under tap water pressure without any extra power consumption.

Synthesis and in situ sulfidation of molybdenum carbide MXene using fluorine-free etchant for electrocatalytic hydrogen evolution reactions.

Synthesizing MXenes from Mn+1AXn (MAX) phases using hazardous hydrogen fluoride is a common and effective method. However, fluorine termination on the basal planes and edges of the resulting MXenes is undesirable for the electrocatalytic hydrogen evolution reaction (HER), while oxygen (O), hydroxyl (OH), and sulfur (S) termination favors this reaction. Herein, we unveil a simple fluorine-free exfoliation and two-step vulcanization method for synthesizing molybdenum sulfide-modified molybdenum carbide (MoS2/Mo2CTx MXene, T = OH, O, S) for the HER in alkaline medium. Microwave-assisted hydrothermal treatment of the MAX phase (Mo3AlC2) with sodium hydroxide-sodium sulfide as an etching solution and thioacetamide as a source of sulfide ions enabled the selective dissolution of the aluminum (Al) layer and sulfidation of the surface Mo atoms to form amorphous MoS2. Thus, the vulcanization of Mo2CTx MXene resulted in the formation of MoS2/Mo2CTx MXene. The MoS2 formed on the surface of Mo2CTx provided enhanced stability by preventing oxidation. MoS2/Mo2CTx exhibited enhanced electrocatalytic activity toward the HER, mainly due to the O, OH, and amorphous MoS2 functionalities. The MoS2 sites on the surface exhibited an overpotential of 110 ± 7 mV at a current density of 10 mA cm-2 as a result of enhanced charge transfer and mass transfer. Thus, the sulfidation method demonstrated herein is capable of producing amorphous MoS2 structures on Mo2CTx MXene, which could be applied for the surface modification of other molybdenum-based nanomaterials or electrocatalysts to improve stability and enhance electrocatalytic activity.

Carbon nanogels exert multipronged attack on resistant bacteria and strongly constrain resistance evolution.

Developing antimicrobial agents that can eradicate drug-resistant (DR) bacteria and provide sustained protection from DR bacteria is a major challenge. Herein, we report a mild pyrolysis approach to prepare carbon nanogels (CNGs) through polymerization and the partial carbonization of l-lysine hydrochloride at 270 °C as a potential broad-spectrum antimicrobial agent that can inhibit biopolymer-producing bacteria and clinical drug-resistant isolates and tackle drug resistance issues. We thoroughly studied the structures of the CNGs, their antibacterial mechanism, and biocompatibility. CNGs possess superior bacteriostatic effects against drug-resistant bacteria compared to some commonly explored antibacterial nanomaterials (silver, copper oxide, and zinc oxide nanoparticles, and graphene oxide) through multiple antimicrobial mechanisms, including reactive oxygen species generation, membrane potential dissipation, and membrane function disruption, due to the positive charge and flexible colloidal structures resulting strong interaction with bacterial membrane. The minimum inhibitory concentration (MIC) values of the CNGs (0.6 µg mL-1 against E. coli and S. aureus) remained almost the same against the bacteria after 20 passages; however, the MIC values increased significantly after treatment with silver nanoparticles, antibiotics, the bacteriostatic chlorhexidine, and especially gentamicin (approximately 140-fold). Additionally, the CNGs showed a negligible MIC value difference against the obtained resistant bacteria after acclimation to the abovementioned antimicrobial agents. The findings of this study unveil the development of antimicrobial CNGs as a sustainable solution to combat multidrug-resistant bacteria.

Aminoglycoside-mimicking carbonized polymer dots for bacteremia treatment.

Bacteremia and associated bacterial sepsis are potentially fatal and occur when the host response to microbial invasion is impaired or compromised. This motivated us to develop carbonized polymer dots (CPDsMan/AA) from a mixture of mannose (Man) and positively charged amino acids [AAs; lysine, arginine (Arg), or histidine] through a one-step mild pyrolysis procedure, which effectively inhibited drug-resistant bacterial strains isolated from septic patients. The as-prepared CPDsMan/AA showed broad-spectrum antibacterial activity, including multidrug-resistant bacteria, even in human plasma. The minimal inhibitory concentration of CPDsMan/Arg is ca. 1.0 µg mL-1, which is comparable to or lower than those of other tested antibiotics (e.g., ampicillin, gentamicin, and vancomycin). In addition to directly disrupting bacterial membranes, the CPDsMan/Arg feature a structure similar to aminoglycoside antibiotics that could bind to 16S rRNA, thereby blocking bacterial protein synthesis. In vitro cytotoxic and hemolytic assays demonstrated the high biocompatibility of the CPDsMan/AA. In addition, in vivo studies on methicillin-resistant Staphylococcus aureus-infected mice treated with the CPDsMan/Arg showed a significant decrease in mortality-even better than that of antibiotics. Overall, the synthesis of the CPDsMan/AA is cost-efficient, straightforward, and effective for treating bacteremia. The polymeric features of the CPDsMan/Arg, including cationic charges and specific groups, can be recognized as a safe and broad-spectrum biocide to lessen our reliance on antibiotics to treat systemic bacterial infections in the future.

Evaluation of chemotherapeutic response in living cells using subcellular Organelle‒Selective amphipathic carbon dots.

Monitoring of structural changes in subcellular organelles is critical to evaluate the chemotherapeutic response of cells. However, commercial organelle selective fluorophores are easily photobleached, and thus are unsuitable for real-time and long-term observation. We have developed photostable carbon-dot liposomes (CDsomes)-based fluorophores for organellar and suborganellar imaging to circumvent these issues. The CDs synthesized through a mild pyrolysis/hydrolysis process exhibit amphipathic nature and underwent self-assembly to form liposome-like structures (CDsomes). The controlled hydrophilicity or hydrophobicity-guided preparation of CDsomes are used to selectively and rapidly (<1 min) stain nucleolus, cytoplasm, and membrane. In addition, the CDsomes offer universal high-contrast staining not only in fixed cells but also in living cells, allowing real-time observation and morphological identification in the specimen. The as-prepared CDsomes exhibit excitation-dependent fluorescence, and are much more stable under photoirradiation (e.g., ultraviolet light) than traditional subcellular dyes. Interestingly, the CDsomes can be transferred to daughter cells by diluting the particles, enabling multigenerational tracking of suborganelle for up to six generations, without interrupting the staining pattern. Therefore, we believe that the ultra-photostable CDsomes with high biocompatibility, and long-term suborganellar imaging capabilities, hold a great potential for screening and evaluating therapeutic performance of various chemotherapeutic drugs.

A review on metal nanozyme-based sensing of heavy metal ions: Challenges and future perspectives.

Large scale mining, manufacturing industries, exploitation of underground water, depletion of groundwater level, and uncontrolled discharge of industrial wastes have caused severe heavy metal ion pollution to the environment throughout the world. Therefore, the rapid detection of such toxic metal ions is inevitable. However, conventional methods require sophisticated instruments and skilled manpower and are difficult to operate in on-field conditions. Recently, metal nanozyme-based assays have been found to have the potential as an alternative to conventional methods due to their portability, simplicity, and high sensitivity to detect metal ion concentration to as low as parts per trillion (ppt). Metal nanozyme-based systems for heavy metal ions enable rapid and cheap screening on the spot with a very simple instrument such as a UV-vis absorption spectrophotometer and therefore, are convenient for use in field operations, especially in remote parts of the world. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties and specific interactions with particular metal ion species. Such method often encounters selectivity issues, unlike natural enzyme-based assays. Therefore, in this review, we mainly focus our discussion on different types of target recognition and inhibition/enhancement mechanisms, and their responses toward the catalytic activity in the sensing of target metal ions, design strategies, challenges, and future perspectives.

Controlling morphology evolution of titanium oxide-gold nanourchin for photocatalytic degradation of dyes and photoinactivation of bacteria in the infected wound.

We report a one-pot, room-temperature, morphology-controlled synthesis of titanium oxide (TiOx)-gold nanocomposites (TiOx-Au NCs) using HAuCl4 and TiCl3 as precursors, and catechin as reducing agent. TiOx-Au NCs have a range of morphologies from star-like to urchin-like shape depending on the concentration of TiCl3 in the reaction mixture. The urchin-shaped TiOx-Au NCs exhibited excellent photocatalytic activity toward dye degradation due to strong light absorption, plasmon-induced excitation, high conductivity of the gold, and reduced hole-electron pair recombination. TiOx-Au NCs have the advantage of a wide range of light absorption and surface plasmon absorption-mediated excitation due to their abundant gold spikes, which enabled the degradation of dyes over 97% in 60 min, using a xenon lamp as a light source. In addition, TiOx-Au NCs are highly efficient for the photoinactivation of Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans through the photodynamic generation of reactive oxygen species (ROS) and damage to the bacterial membrane. The catechin derivatives on the NCs effectively promoted curing MRSA infected wounds in rats through inducing collagen synthesis, migration of keratinocytes, and neovascularization.

Electrocatalytic CuBr@CuO nanoparticles based salivary glucose probes.

Highly electrocatalytic cuprous halide/copper oxide nanoparticles (CuX@CunO NPs; X = Cl, Br or I; n = 1 or 2) have been fabricated on copper foils for sensitive detection of glucose. Formation of CuX@CunO NPs involves two steps- in situ electrochemical deposition of CuX on the foil and then conversion of CuX to CunO. The deposited CuX converts to CunO, leading to the generation of abundant oxygen vacancies in the CuO lattice, enhancing the number of catalytically active sites, and improving the charge transfer efficiency. Among the as-prepared electrodes, CuBr@CuO NP ones provide the highest electrocatalytic activity toward the oxidation of glucose. The electrode provides electrocatalytic activity toward the oxidation of glucose at a low overpotential of 0.25 V (vs. SCE), which is lower than that (0.40 V) of unmodified copper electrodes. The generated anodic current is proportional to glucose concentration in an alkaline medium, with a good linear range from 5.0 µM to 3.51 mM (R2 = 0.995). Its reliability has been validated by detecting the glucose concentration in saliva samples at different time intervals after a meal. The results are in good correlation with the blood glucose level determined by using a commercial blood glucose meter. Our CuBr@CuO NP electrode possesses great potential for monitoring salivary glucose to achieve the purpose of noninvasive glucose monitoring for patients with diabetes in the future.

Thermally driven formation of polyphenolic carbonized nanogels with high anticoagulant activity from polysaccharides.

We have demonstrated that alginate with negligible anticoagulant activity can be converted into carbonized nanogels with potent anticoagulant activity through a solid-state heating process. The conversion of alginate into graphene-like nanosheet (GNS)-embedded polyphenolic-alginate nanogels (GNS/Alg-NGs) has been carried out through condensation and carbonization processes. The GNS/Alg-NGs exhibit much stronger anticoagulant activity (>520-fold) compared to untreated alginate, mainly because their polyphenolic structures have a high binding affinity [dissociation constant (Kd) = 2.1 × 10-10 M] toward thrombin. In addition, the thrombin clotting time delay caused by the GNS/Alg-NGs is 10-fold longer than that of natural polyphenolic compounds, such as quercetin, catechin, naringenin, caffeic acid, and ferulic acid. The thrombin- or kaolin-activated thromboelastography of whole-blood coagulation reveals that the GNS/Alg-NGs display a much stronger anticoagulant ability than that of untreated alginate and naturally sulfated polysaccharides (fucoidan). The GNS/Alg-NGs exhibit superior biocompatibility and anticoagulant activity, as observed with an in vivo rat model, revealing their potential as a blood thinner for the treatment of thrombotic disorders.

Carbon quantum dots for the detection of antibiotics and pesticides.

Carbon quantum dots (CQDs) are novel nanomaterials with interesting physical and chemical properties, which are intensely studied only in the last decade. Unique properties, such as its inherent fluorescent property, high resistance to photobleaching, high surface area, ease of synthesis, flexible choice of precursor, and surface tunability enable CQDs for promising application in biosensing. Therefore, it is highly useful in clinical, forensic, medical, food and drug analyses, disease diagnosis, and various other fields of biosensing. In addition, their fluorescence properties are tunable by the interaction with certain molecules via different mechanisms, which enables their application for sensing of those molecules, such as pesticides and antibiotics. The detection of antibiotics and pesticides is especially important as they are commonly used in both the medical and agricultural fields and can affect both humans and their environment. However, these molecules do not have a specific recognition element unlike for antibodies, proteins, enzymes, and other biomarkers. Thus, the fluorescence quenching mechanism alone cannot be applied as a sensing mechanism for the CQDs-based sensing of pesticides and antibiotics. In this review, we discuss the application of various CQDs, in the detection of antibiotics, pesticides (herbicide, fungicide, insecticide), and other medicinal drugs through various detection strategies and their current limitations.

Fluorescent Carbon Dots for Selective Labeling of Subcellular Organelles.

With the recent advancement in understanding and control of the structure and optical properties of fluorescent carbon dots (CDs), they have been shown to be valuable in biolabeling of bacteria, tumor cells, tissues, and organelles. Their extremely small size and tunable functional properties coupled with ultrastable fluorescence enable CDs to be used for easy and effective labeling of various organelles. In addition, CDs with advantages of easy preparation and functionalization with recognition elements and/or drugs have emerged as nanocarriers for organelle-targeted drug delivery. In this review, we mainly discuss the applications of fluorescent CDs for the labeling of organelles, including lysosome, nucleoli, nucleus, endoplasmic reticulum, and mitochondria. We highlight the importance of the surface properties (functional groups, hydrophobicity/hydrophilicity, charges, zwitterions) and the size of CDs for labeling. Several interesting examples are provided to highlight the potential and disadvantages of CDs for labeling organelles. Strategies for the preparation of CDs for specific labeling of organelles are suggested. With the edge in preparation of diverse CDs, their potential in labeling and drug delivery is highly expected.