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Synthesizing MXenes from M

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 (CPDs

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.

In this work, we demonstrate a simple electrochemical approach to convert copper foil into a cost-effective and stable cobalt-doped hollow-structured CuBr@CuO electrocatalyst with high surface poro...

Uniform and stable interdigitated electrodes are essential for planar micro-supercapacitor applications. Two-dimensional (2D) materials, such as transition-metal MXenes have become attractive nanomaterials for micro-supercapacitor applications due to their layered structure and high electrical conductivity. However, the low stability of MXenes in aqueous media limits their long-term storage and application. Here, we demonstrate in-situ synthesis and capping of Ti3C2Tx MXenes with sodium ascorbate (SA) to obtain SA-MXene dispersion with high resistance against oxidation even after 80 days of storage at ambient temperature and exposed to air. The in-situ synthesis process increases the interlayer spacing of SA-MXene sheets, and increases their energy storage efficiency, without compromising their electrical conductivity. A printable SA-MXene ink was prepared with Triton X-100 and propylene glycol as modifiers to print interdigitated micro-supercapacitor electrodes with an inkjet printer. Our solid-state micro-supercapacitor made without current collector exhibits areal and volumetric capacitance of 108.1 mF cm−2 and 720.7 F cm−3, respectively. This work highlights the potential application of ligand-capped stable MXenes as a water-based ink in printing devices for the fabrication of micro-electronics and supercapacitors.

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 cm

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 [Ag

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.

Naznozymes have become an important alternative to natural enzymes for many sensing applications, due to their relatively high stability, easy synthesis, and cost-effectiveness. Nanozyme-based assays, especially paper-based assays are portable, and therefore, are convenient for use in field operations, especially in remote parts of the world. Decreasing water levels, depletion of water resources, and large scale mining create the need for rapid detection of heavy metal ions in various water samples. In comparison with traditional methods of heavy metal ion detection, nanozyme-based systems enable rapid and cheap screening on the spot with a very simple instrument such as a UV–Vis absorption spectrophotometer. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties. They often encounter selectivity issues, unlike natural enzyme-based assays. Therefore, different types of target recognition and inhibition/enhancement mechanisms have been reported to achieve high selectivity. In this short review, we mainly focus our discussion on various interaction of the heavy metal ions with the nanozyme, and their responses towards the catalytic activity in the sensing of target metal ions.

Nanomaterials possessing enzyme-like activity have been extensively studied owing to their high stability and tunable catalytic properties. In this work, a simple method has been developed for the synthesis of porous manganese oxide/manganese ferrite (MnOx/MnFe2O4) nanopopcorns (MFNPs) in neutral media. The MFNPs exhibit dual enzymatic activities towards selective oxidation of ketoses followed by H2O2-induced decline of its catalytic activity. MFNPs, with MnFe2O4 as the core material and an outer layer rich in MnOx, were synthesized from ammonium iron(III) citrate and potassium permanganate at 70 °C for 12 h followed by annealing at 300 °C for 6 h. The nanozyme, MFNPs, exhibited oxidase-like activity, which was proved by the oxidation of amplex red (AR) in the presence of dissolved oxygen in the solution, to form fluorescent resorufin. The activity of MFNPs is highly suppressed by H2O2 as a result of its induced dissolution of MnOx. In addition, MFNPs having catalytic activity towards the selective oxidation of ketoses (e.g., fructose) followed by the formation of H2O2. The as-formed H2O2 diminished the catalytic activity of MFNPs for the AR oxidation to form fluorescent resorufin. Upon increasing fructose concentration, the fluorescence of resorufin decreases. Since the MFNPs do not show catalytic activity towards aldose sugars, such as glucose, sucrose, and mannose, the AR/MFNPs probe has high selectivity and sensitivity for detection of fructose with a limit of detection of 32 μM. Our study shows its great potential for quantitation of fructose in honey samples.

Due to the increasing global population, growing contamination of water and air, and wide spread of infectious diseases, antibiotics are extensively used as a major antibacterial drug. However, many microbes have developed resistance to antibiotics through mutation over time. As an alternative to antibiotics, antimicrobial nanomaterials have attracted great attention due to their advantageous properties and unique mechanisms of action toward microbes. They inhibit bacterial growth and destroy cells through complex mechanisms, making it difficult for bacteria to develop drug resistance, though some health concerns related to biocompatibility remain for practical applications. Among various antibacterial nanomaterials, carbon-based materials, especially graphene oxide (GO) and carbon dots (C-Dots), are promising candidates due to the ease of production and functionalization, high dispersibility in aqueous media, and promising biocompatibility. The antibacterial properties of these nanomaterials can be easily adjusted by surface modification. They are promising materials for future applications against multidrug-resistant bacteria based on their strong capacity in disruption of microbial membranes. Though many studies have reported excellent antibacterial activity of carbon nanomaterials, their impact on the environment and living organisms is of concern due to the accumulatory and cytotoxic effects. In this review, we discuss antimicrobial applications of the functional carbon nanomaterials (GO and C-Dots), their antibacterial mechanisms, factors affecting antibacterial activity, and concerns regarding cytotoxicity.

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.

Increasing water consumption and diminishing fresh water resources have created the need for new water treatment technologies to supply safe water for domestic and industrial needs. The development of polymeric nanofiltration (NF) membrane technology led to water treatment at lower operating pressures than that of reverse osmosis. NF membranes reject particles and multivalent ions, however, monovalent ions pass through them along with water molecules. Factors such as selectivity and permeability, and fouling also limit their application. Incorporating suitable nanomaterials with polymer membranes has solved major problems, such as biofouling, scaling, low flux rate, selectivity, and degradation. Recent studies reveal that nanoporous single layer graphene and stacked graphene oxide (GO) membranes with desired spacing between layers are capable of rejecting monovalent ions, and are promising materials for future nanofiltration-based desalination. GO has antifouling properties that are highly advantageous for improving membrane properties. The basic understanding of the mechanism of graphene-based nanofiltration have been reported mainly based on computational studies. Hence, a great deal of experimental research is essential to develop efficient graphene membrane-based desalination methods for practical use. In this review, we highlight various properties of graphene and its derivatives that are essential for improving salt rejection, flux, and antifouling.

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.

Treatment of age-related macular degeneration (AMD) is a challenge due to frequent intravitreal injection of drugs, low retention time, risk of infection, need for drugs with multiple therapeutic efficacies, such as anti-inflammatory, anti-oxidant, and anti-angiogenesis. Herein, we demonstrate the synthesis and application of metformin-loaded gold-poly(catechin) core-shell nanoparticles (MF/Au@pCH NPs) as a potential nanocomposite for the treatment of AMD, via sustained drug release to the lesion site. To achieve targeted drug delivery to macula of the AMD eye, we immobilized the complement component protein C3 to form C3-MF/Au@pCH NPs. With this targeted nanocomposite, we aim to utilize the anti-oxidative and anti-inflammatory properties of phenol-rich poly(catechin) and the anti-angiogenic activity of metformin for the synergistic recovery from macular degeneration. The pharmacological efficacy of a single intravitreal dose of C3-MF/Au@pCH NPs is superior to Au@pCH NPs and MF/Au@pCH NPs. In addition, C3-MF/Au@pCH NPs exhibited good in vitro and in vivo biocompatibility. Our study suggests the potential of this multifunctional modality for translation into a clinical intervention for AMD therapy, due to the sustained release of drugs and targeted drug delivery. The findings of this work reveals that Au@pCH NPs could be extended to the treatment of various other diseases with the loading of relative drugs.

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 ) 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.

Many serious public health emergencies around the globe are caused by viral epidemics. Thus, developing a reliable method for viral screening is in high demand. Multiplex assays for simultaneous detection and fast screening of high-risk pathogens are especially needed. This study employs metal nanoparticles to generate specific mass spectral signals for different RNA viruses, which enables simultaneous detection of whole viruses by laser desorption/ionization mass spectrometry (LDI-MS). We developed a nanoparticle-based sandwich immunosorbent assay as a sensing platform for the detection of viruses and viral nonstructural protein by LDI-MS. Cellulose acetate membrane (CAM) serves as the substrate for the fabrication of the sandwich immunosorbent assay with the advantages of clean mass spectra and high enrichment of analytes. Antibody-modified metal nanoparticles (Ab-MNPs; M = Au or Ag) act as metallic biocodes for the LDI-MS detection. The signal amplification readout for the virus is through the pulsed laser-induced formation of metal cluster ions ([M n]+; n = 1-3) from the Ab-MNPs which specifically bind on the CAM. Our sensing system is effective for the detection of intact viruses [Enterovirus 71 (EV71) and Japanese encephalitis virus (JEV)], nonstructural protein 1 (NS1) of Zika virus (ZIKV), EV71-spiked human serum samples, and the simultaneous detection of EV71 and ZIKV. Our probe efficiently detects EV71 in real clinical serum samples with >95% agreement with RT-qPCR results. This high-throughput LDI-MS viral detection system is simple, reliable, and high-throughput. We believe this platform has the potential to be employed for the routine screening of patients with viral infections.

We have developed a rapid and straightforward topical treatment method for dry eye disease (DED) using poly(catechin) capped-gold nanoparticles (Au@Poly-CH NPs) carrying amfenac [AF; a nonsteroidal anti-inflammatory drug (NSAID)] through effective attenuation of ocular surface tissue damage in dry eyes. A dual-targeted strategy based on ocular therapeutics was adopted to simultaneously block the cyclooxygenase enzymes-induced inflammation and reactive oxygen species (ROS)-induced oxidative stress, the primary two causes of DED. The self-assembled core-shell Au@Poly-CH NPs synthesized via a simple reaction between tetrachloroaurate(iii) and catechin possess a poly(catechin) shell (∼20 nm) on the surface of each Au NP (∼60 nm). The anti-oxidant and anti-inflammatory properties of AF/Au@Poly-CH NPs were evaluated by DCFH-DA and prostaglandin E2/VEGF assays, respectively. Our results demonstrate that Au@Poly-CH NPs not only act as an anti-oxidant to suppress ROS-mediated processes, but also serve as a drug carrier of AF for a synergistic effect on anti-inflammation. In vivo biocompatibility studies show good tolerability of AF/Au@Poly-CH NPs for potential use in the treatment of ocular surface pathologies. The dual-targeted therapeutic effects of AF/Au@Poly-CH NPs lead to rapid recovery from DED in a rabbit model. Au@Poly-CH NPs loaded with NSAIDs is a promising multifunctional nanocomposite for treating various inflammation- and oxidative stress-related diseases.

This study reports a two-step method to synthesize spermidine-capped fluorescent carbon quantum dots (Spd-CQDs) and their potential application as an antibacterial agent. Fluorescent carbon quantum dots (CQDs) are synthesized by pyrolysis of ammonium citrate in the solid state and then modified with spermidine by a simple heating treatment without a coupling agent. Spermidine, a naturally occurring polyamine, binds with DNA, lipids, and proteins involved in many important processes within organisms such as DNA stability, and cell growth, proliferation, and death. The antimicrobial activity of the as-synthesized Spd-CQDs (size ≈4.6 nm) has been tested against non-multidrug-resistant E. coli, S. aureus, B. subtilis, and P. aeruginosa bacteria and also multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The minimal inhibitory concentration value of Spd-CQDs is much lower (>25 000-fold) than that of spermidine, indicating their promising antibacterial characteristics. The mechanism of antibacterial activity is investigated, and the results indicate that Spd-CQDs cause significant damage to the bacterial membrane. In vitro cytotoxicity and hemolysis analyses reveal the high biocompatibility of Spd-CQDs. To demonstrate its practical application, in vitro MRSA-infected wound healing studies in rats have been conducted, which show faster healing, better epithelialization, and formation of collagen fibers when Spd-CQDs are used as a dressing material.

We have developed a simple solid-state synthesis procedure to functionalize fluorescent carbon quantum dots (CQDs), using ammonium citrate as a carbon source and appropriate molecules as recognition ligands. Mannose and folic acid were used to modify CQDs to selectively label Escherichia coli ( E. coli ) and tumor cells, respectively. First, fluorescent-core CQDs (approximate size: 3 nm) were synthesized through carbonization of ammonium citrate via dry heating. In the second step, CQDs were heated with mannose and folic acid to prepare mannose-functionalized CQDs (Man–CQDs) and folic acid-functionalized CQDs (FA–CQDs), respectively, through a dehydration reaction in the solid state. Solid-state synthesis of the self-functional CQDs is achievable without a coupling agent. We optimized the labeling efficiencies of self-functional Man–CQD and FA–CQD to cells by controlling the ratio of mannose or folic acid to CQDs, as well as the reaction temperature during synthesis. The solid-state synthesized Man–CQDs and FA–CQDs exhibited excitation-dependent fluorescence with excitation and emission maxima of 365 and 450 nm, respectively, and a fluorescence quantum yield of approximately 9%. Man–CQDs can be used for selective labeling of E. coli and detection at concentrations as low as 100 colony forming units mL −1 in real samples ( e.g. , drinking water, apple juice, urine). Furthermore FA–CQDs are highly selective for labeling of folate receptor-overexpressing tumor cells. The synthesis of self-functional CQDs is simple, cost effective, and easily scaled up, and can be extended to the synthesis of various functional carbon nanomaterials, such as graphene oxide nanosheets, carbon nanotubes, fullerene nanoparticles and carbon nanodiamonds, with different ligands for other biolabeling applications and targeted therapies.

In this work, we demonstrate that carbon dots (CDs) can be used as a dispersing agent for graphene as well as a reducing agent for KMnO4 for the synthesis of manganese oxide (MnOx)–graphene hybrid nanocomposites for supercapacitor applications. CDs obtained from the pyrolysis of ammonium citrate under dry heating possess excellent solubility in water due to their oxygen- and nitrogen-containing functional groups. In addition, the sp2-carbon-rich CDs exhibited strong interaction with graphene through π–π stacking for self-immobilizing on graphene in the preparation of water-soluble CD/graphene nanocomposites (CDGs). Interestingly, MnOx could be grown in situ on CDGs after reaction with KMnO4 in aqueous solution under a mild reaction temperature (75 °C). Under the mild reaction conditions, CDs undergo sacrificial oxidation for the formation of MnOx nanoparticles on graphene, whereas the graphene’s graphitic carbons are protected. The as-formed nanostructured MnOx on CDGs (MnOx–CDGs) was employed to fabricat...

We have synthesized aptamer-functionalized copper nanoparticles (Apt–Cu NPs) using simple ascorbate-mediated reduction of Cu(II) ions in Apt-T n templates comprising an aptamer (Apt) sequence with a poly(dT) motif at both the 3′- and 5′-termini. The as-prepared Apt–Cu NPs underwent rapid oxidation to Apt-T n –CuO/Cu 2 O NPs. The CuO/Cu 2 O NPs tended to have rod-like shapes when the Apt-T n templates had long poly(dT) units ( n > 30). Interestingly, the as-formed Apt-T n –CuO/Cu 2 O NPs exhibited intrinsic peroxidase-like activity for the H 2 O 2 -mediated oxidation of Amplex Red (AR) to fluorescent resorufin. The catalytic activity of thrombin binding aptamer-templated CuO/Cu 2 O NPs (TBA-T n –CuO/Cu 2 O NPs) was significantly suppressed after the specific binding of thrombin to the aptamer units on the particles’ surfaces. The H 2 O 2 /AR–TBA-T n –CuO/Cu 2 O NP probe provided a limit of detection (LOD) of thrombin in serum samples of 0.5 nM. Using Mucin1 binding aptamer-templated CuO/Cu 2 O NPs (Apt MUC1 -T 30 –CuO/Cu 2 O NPs), we applied this sensing platform to the detection of Mucin1-overexpressing tumor cells (LOD: ca. 100 cells). This study suggests that the Apt−T n can be used as a universal template for preparation of enzyme-like CuO/Cu 2 O NPs for detection of proteins and labeling of tumor cells when using appropriate aptamers.

In this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100-1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical Abstract Identification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates.

Laser desorption/ionization (LDI) coupled with mass spectrometry (MS) has evolved as an important tool for the analysis of a wide range of analytes, from small molecules to biomacromolecules. The LDI-MS technique requires a suitable matrix or substrate to absorb laser energy for the desorption and ionization of analytes. LDI-MS performed with an organic matrix easily suffers from many matrix effects, such as the formation of many adduct ions, high noise in the low-molecular-weight region, and poor reproducibility. Nanomaterials can reduce the interference of matrix molecules, and improve the reproducibility, sensitivity and even selectivity of LDI-MS. Among the nanomaterial substrates, gold nanoparticles (Au NPs) are an excellent nano-substrate for LDI-MS due to their high photoabsorption, photothermal conversion, and heat-transfer efficiency. Moreover, substantial amount of surface ligand ions and Au cluster ions are formed during the LDI process. By monitoring the ligand ions and Au cluster ions, it is possible to amplify the mass spectral signals and analyze macromolecules with minimum errors. This review highlights some of the applications of functionalized Au NPs coupled with LDI-MS for signal amplification in biosensing and bioimaging applications.

In this work, we synthesized metal (Au, Ag or Cu)–based nanoclusters (NCs) with different photoluminescence (PL) properties and investigated their application for the specific detection of heavy metal ions in water samples. Bovine serum albumin (BSA) and thiosalicylic acid (TSA) acted as protecting ligands for the synthesis of metallic NCs (MNCs). The as–prepared TSA/BSA–Au NCs, TSA/BSA–Ag NCs and TSA/BSA–Cu NCs exhibit PL emission at 700, 624, and 430 nm, with average lifetimes of 1540, 30.9, and 11.7 ns, respectively, when excited at 350 nm. MNCs has a metal core and metal–thiolate shell, where shell species are Au38–SR24, Ag9–SR7 and Cu3–14–SRm in the TSA/BSA–Au NCs, TSA/BSA–Ag NCs, and TSA/BSA–Cu NCs, respectively. PL quenching of MNCs induced through metallophilic interaction, metal–thiol complexation and/or inner filter effect, which enables the quantitation of Hg2+, As3+, and Cr6+ ions, with linear ranges of 1–350, 1–20, and 50–400 nM, and with limits of detection of 0.25, 0.34 and 3.54 nM, respectively. The TSA/BSA–Au NCs, TSA/BSA–Ag NCs, and TSA/BSA–Cu NCs probe systems exhibit the advantages of simplicity, rapidity, selectivity, sensitivity, and practicality for the quantitation of metal ions in water samples.

We demonstrate the synthesis of antibacterial carbon quantum dots (CQDs) through a one-step pyrolysis of biogenic polyamine (PA) and dopamine (DA) mixture. SPM/DA-CQDs synthesized from DA combined with spermine (SPM) exhibit effective antibacterial activity and high adhesion properties on glass and surfaces of polymeric contact lens material. The antimicrobial activity of SPM/DA-CQDs is primarily due to their ability to disrupt the bacterial membrane, and they possess wide spectrum antimicrobial activity against Gram-negative bacteria (Escherichia coli, Salmonella enterica serovar Enteritidis, and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and its multidrug-resistant strain, methicillin-resistant S. aureus). The minimal inhibitory concentration (MIC) of SPM/DA-CQDs against the tested bacteria was >17-fold and >7-fold lower than those of CQDs prepared solely from spermine and dopamine, respectively. The great biocompatibility of our SPM/DA-CQDs is revealed from the in vitro cytotoxicity and hemolysis assays and in vivo evaluation of morphological and physiological changes of rabbit corneas. We further prepared SPM/DA-CQDs-coated coverslips and contact lenses, which display excellent stability and antibiofilm properties. Moreover, in vivo tests show that SPM/DA-CQDs suppress bacterial keratitis (BK) formation in a corneal-injured rabbit model. Our results indicate that SPM/DA-CQDs have great potential as a coating material for inhibition of biofilm formation on contact lenses, and broadly to protect medical devices from contamination.

Graphene oxide (GO) has unique structural properties, can effectively adsorb single-strand DNA through π-π stacking, hydrogen bonding and hydrophobic interactions, and is useful in many biotechnology applications. In this study, we developed a thrombin-binding-aptamers (15- and 29-mer) conjugated graphene oxide (TBA15/TBA29-GO) composite for the efficient inhibition of thrombin activity towards the formation of fibrin from fibrinogen. The TBA15/TBA29-GO composite was simply obtained by the self-assembly of TBA15/TBA29 hybrids on GO. The high density and appropriate orientation of TBA15/TBA29 on the GO surface enabled TBA15/TBA29-GO to acquire an ultrastrong binding affinity for thrombin (dissociation constant = 2.9 × 10-12 M). Compared to bivalent TBA15h20A20/TBA29h20A20 hybrids, the TBA15/TBA29-GO composite exhibited a superior anticoagulant potency (ca. 10-fold) against thrombin-mediated coagulation as a result of steric blocking effects and a higher binding affinity for thrombin. In addition, the prolonged thrombin clotting time, prothrombin time (PT), and activated partial thromboplastin time (aPTT) of TBA15/TBA29-GO were at least 2 times longer than those of commercially available drugs (heparin, argatroban, hirudin, and warfarin). The in vitro cytotoxicity and hemolysis analyses revealed the high biocompatibility of TBA15/TBA29-GO. The rat-tail bleeding assay of the hemostasis time and ex vivo PT and aPTT further revealed that TBA15/TBA29-GO is superior (>2-fold) to heparin, which is commonly used in the treatment and prevention of thrombotic diseases. Our multivalent, oligonucleotide-modified GO nanocomposites are easy to prepare, cost-effective, and highly biocompatible and they show great potential as effective anticoagulants for the treatment of thrombotic disorders.

Nanoparticle-assisted laser desorption/ionization mass spectrometry (LDI-MS) is a powerful tool for the analysis of a wide range of molecules. Many of the drawbacks in the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) can be avoided with the application of nanomaterials as matrices as well as substrates for the LDI-MS to achieve a low background noise in low m/z region and high reproducibility. Surface-assisted LDI (SALDI)-MS, especially the nanoparticle-based LDI-MS, has emerged as a promising technique for the analysis of trace amounts of substances in various biological samples due to their high surface area for analyte enrichment, efficient desorption/ionization, and homogeneous crystallization of sample. Therefore, it is highly useful in clinical, forensic, medical, food and drug analyses, disease diagnosis, and various other fields. In this review, we briefly discuss the application of various nanomaterials, which include metal-based, carbon-based, silicon-based nanomaterials and nanocomposites, as matrices and substrates for LDI-MS based drug and metabolite analyses and possible detection strategies. Also, we discuss the idea of using “mass tag” for signal amplification for drug and metabolite detection using nanoparticle assisted LDI-MS. Keywords: Drugs, Laser desorption and ionization, Mass spectrometry, Matrix, Metabolites, Nanoparticles

In this study, we used a simple one-step dry heating method to synthesize mannose-modified fluorescent carbon quantum dots (Man-CQDs) from solid ammonium citrate and mannose, and successfully applied for labeling Escherichia coli. The highly soluble Man-CQDs had an average particle diameter of 3.1±1.2 nm and exhibited a quantum yield of 9.8% at excitation and emission wavelengths of 365 and 450 nm, respectively. The fluorescent Man-CQDs could selectively bind to the FimH lectin unit in the flagella of the wild-type 1 E. coli K12 strain. We optimized the labeling efficiency of the Man-CQDs by controlling the ratio of ammonium citrate to mannose during their synthesis. The specific binding of the mannose units to E. coli allowed quantitative detection of the bacteria at levels down to 450 colony forming units mL(-1) in lab samples, and facilitate the application of the Man-CQDs for bacterial analyses of real samples (tap water, apple juice, human urine). The synthesis of our Man-CQDs, their labeling, and their use in the detection of bacteria were all simple, inexpensive and efficient processes.

In this paper, we report a simple one-step synthesis method for silver-gold bimetallic nanoparticles deposition on silver chloride nanosheets to form Ag-Au/AgCl nanohybrid with oxidase-like and peroxidase-like catalytic activity. We used these nanohybrid in the detection of spermine. First, 13 nm-sized Au NPs were synthesized by citrate reduction of HAuCl4 solution, and then, Ag+ ions were added to the solution without any purification. The added Ag+ reacted with the Cl− ions in the dispersion, thus immediately forming AgCl nanosheets through a precipitation reaction, and the aurophilic interactions with the Au NPs resulted in the formation and in situ self-deposition of Ag-Au NPs on the AgCl nanosheets at room temperature. We investigated the enzyme-mimicking activity of the Ag-Au/AgCl nanohybrid in detail via the O2- or H2O2-Amplex Red (AR) redox system. The Ag-Au/AgCl nanohybrid exhibited at least 150-fold higher catalytic activity than that of Ag-Au NPs or AgCl nanosheets, due to synergistic effect. Spermine inhibited the enzyme-mimic activity of the Ag-Au/AgCl nanohybrid, thereby allowing for the construction of a probe for detecting nanomolar concentrations of spermine in urine samples. This cost-effective sensing system was used to easily and rapidly detect the concentrations of spermine in complex urine samples.

A graphene oxide (GO) nanosheet-modified N+-nylon membrane (GOM) has been prepared and used as an extraction and spray-ionization substrate for robust mass spectrometric detection of malachite green (MG), a highly toxic disinfectant in liquid samples and fish meat. The GOM is prepared by self-deposition of GO thin film onto an N+-nylon membrane, which has been used for efficient extraction of MG in aquaculture water samples or homogenized fish meat samples. Having a dissociation constant of 2.17 × 10−9 M−1, the GOM allows extraction of approximately 98% of 100 nM MG. Coupling of the GOM-spray with an ion-trap mass spectrometer allows quantitation of MG in aquaculture freshwater and seawater samples down to nanomolar levels. Furthermore, the system possesses high selectivity and sensitivity for the quantitation of MG and its metabolite (leucomalachite green) in fish meat samples. With easy extraction and efficient spray ionization properties of GOM, this membrane spray-mass spectrometry technique is relatively simple and fast in comparison to the traditional LC-MS/MS methods for the quantitation of MG and its metabolite in aquaculture products.

In this paper, we report a simple one-step synthesis of well-dispersed amorphous cobalt hydroxide/oxide-modified graphene oxide (CoOxH-GO) possessing peroxidase-like catalytic activity, and its application for the detection of H2O2, glucose, and CN- ions. CoOxH is formed and deposited in situ on the GO surface through the reaction between GO (size ~ 240nm) and Co2+ in basic solution at room temperature. We investigated the enzyme-mimicking activity of the CoOxH-GO nanohybrid in detail via the H2O2-mediated oxidation of Amplex Red (AR) to form fluorescent resorufin. The peroxidase-like activity of CoOxH-GO is utilized herein for the quantitation of H2O2 in a wide concentration range, from 100nM to 100μM. When coupled with glucose oxidase (GOD), the AR/CoOxH-GO system can determine glucose level in blood samples. Interestingly, cyanide ions (CN-) significantly inhibit the catalytic activity of the CoOxH-GO nanohybrid, which allows for the construction of a probe for the detection of CN- in water samples and laboratory wastes. We fabricated a membrane-based CoOxH-GO probe for the visual detection of CN- by preparing a thin film of CoOxH-GO on a positively charged and porous nylon membrane (N+M). The CoOxH-GO/N+M operates on the principle that CN- inhibits the catalytic activity of CoOxH-GO towards the H2O2-mediated oxidation of AR to form reddish resorufin on the membrane. The intensity of the red color of the membrane decreases with increasing CN- concentration, which can be easily observed with the naked eye at the nanomolar level. This cost-effective sensing system allows for the rapid and simple determination of the concentrations of CN- in complicated wastewater samples.

This paper reports the use of unmodified mixed cellulose ester membrane (MCEM) as a simple, novel and efficient substrate in matrix-free pulsed laser desorption/ionization mass spectrometry (LDI-MS) for the detection of lead ions (Pb 2+ ) in water (tap water and coastal seawater) and biological (urine) samples and drinking straws. The discovery of trace amounts of lead in the original MCEM prompted us to investigate the special interactions between the MCEM and the Pb 2+ ions. When using an MCEM, first to concentrate Pb 2+ ions and then as an efficient LDI substrate, our membrane-based LDI-MS approach exhibited high sensitivity [limit of detection (LOD): 0.05 nM] and selectivity (tolerance at least 1000-fold relative to other metal ions) for the detection of Pb 2+ ions in aqueous solutions. Based on the special ability of the MCEM, an easy method has been developed to detect Pb 2+ ions in drinking straws, by simply rubbing the straws with MCEM and then using LDI-MS. The ability of the MCEM to adsorb metal ions and its interesting surface functional properties should open up new opportunities for its application in LDI-MS for the detection of other contaminants in environmental samples.

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).

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.

We report an efficient method for the determination of iodide (I(-)) ions by using gold-iodide hybrid cluster ions on gold nanoparticles (Au NPs) modified mixed cellulose ester membrane (Au NPs-MCEM) by pulsed laser desorption/ionization mass spectrometry (LDI-MS). When I(-) ions were deposited and concentrated on the surfaces of Au NPs (32 nm) via strong Au(+)-I(-) interaction on the MECM, the Au NPs-MCEM was observed to function as an efficient surface-assisted LDI substrate with very low background noise. When pulsed laser radiation (355 nm) was applied, I(-) binding to Au NPs ions induced the enhancement of the desorption and ionization efficiency of gold-iodide hybrid cluster ions from the Au NPs surfaces. The reproducibility of the probe for both shot-to-shot and sample-to-sample (both less than 10%) ion production was also improved by the homogeneous nature of the substrate surface. Thus, it allows the accurate and precise quantification of I(-) ions in high-salinity real samples (i.e., edible salt samples and urine) at the nanomolar range. This novel LDI-MS approach provides a simple route for the high-speed analysis of I(-) ions with high sensitivity and selectivity in real biological samples.

Platinum nanoparticles found very wide application in electrocatalysis and sensor. However, Pt must be deposited in a stable matrix to increase stability and avoid fouling. In this work polydiphenylamine-Pt (PDPA-Pt) composite has been synthesized by electrochemical method on glassy carbon electrode. PDPA-Pt has been characterized by scanning electrochemical microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The SEM studies showed well dispersed Pt nanoparticles on PDPA surface. The electrocatalytic activity of PDPA-Pt film modified electrode toward the oxidation of NO2−was studied by cyclic voltammetry and amperometry. Cyclic voltammograms showed that NO2−undergoes irreversible oxidation at 0.85 V at PDPA-Pt modified electrode which is 0.33 V less than that of bare GCE. This shows the efficient electrocatalytic activity of the composite film. The electroanalytical application of the composite film was done by amperometric technique. The film shows a response time of less than 1 s and wide linear range of detection from 1 μM to 9.5 mM. PDPA-Pt is a promising material for electrochemical and biosensor applications. The good recoveries achieved in the various water samples for the determination of nitrite shows the practicality of the proposed sensor.

We report a highly sensitive amperometric sensor for the determination of carbamazepine (CBZ) at an electrochemically reduced graphene oxide (ERGO) and single walled carbon nanotube (SWCNT) composite film modified glassy carbon electrode (GCE). The π – π stacking interactions between ERGO and SWCNT add good stability to the composite film which was confirmed by UV–visible and FTIR spectroscopy. Compared with SWCNT modified electrode, ERGO–SWCNT composite film modified electrode exhibits a 3.2 fold enhancement in peak current for CBZ oxidation. The proposed sensor detects CBZ as low as 29 nM and has a sensitivity of 5.1076 μA μM −1 cm −2 in the linear range of 50 nM to 3 μM. The practicality of this sensor has been evaluated by the determination of CBZ from Tegratol tablets showing good sensitivity and linearity.