We describe a highly sensitive glucose probe based on carbon dots modified with MnO2. A strong reduction of the green fluorescence of the carbon dots (CDs) happened due to the surface energy transfer (SET) from CDs to the deposited MnO2. In the presence of H2O2 (formed via enzymatic oxidation of glucose), fluorescence is restored because the MnO2 nanosheets are reduced to form colorless Mn(II) ions. These findings were used to design a fluorometric glucose assay that has a detection limit as low as 44 nM (at an S/N ratio of 3).
Graphical Abstract A strong reduction of the green fluorescence of the carbon dots (CDs) occurs due to surface energy transfer (SET) from CDs to the deposited MnO2. In the presence of H2O2 (formed by enzymatic action of glucose oxidase) the MnO2 nanosheets are reduced to form colorless Mn(II) ions, and glucose can be quantified by the fluorescence restored.
Carbon dots (CDs) possess superior fluorescent properties in that they do not blink, are biocompatible, chemically inert, have small size and well tunable photoluminescence (PL), can be easily functionalized with biomolecules, and can be multi-photon excited to give up-converted PL. This review (with 141 refs.) summarizes recent progress in the field of imaging using carbon dots doped with heteroatoms (X-CDs). Following an introduction, we discuss top-down and bottom-up strategies for synthesis and methods for surface modification. We also compare the differences in synthesis for undoped CDs and X-CDs. Specifically, CDs doped with heteroelemets nitrogen, phosphorus, sulfur, selenium, boron and silicium are treated. We then discuss method for determination of the properties (particle size, ZP), how doping affects fluorescence (spectra, quantum yields, decay times), and how dopants affect upconversion (UC, anti-Stokes luminescence). We finally review the progress made in fluorescent imaging of cells tissue, and other biomatter. This review also gives new hints on how to use synthetic methods for tuning the structure of X-CDs, how doping affects properties, and how to achieve new bioimaging applications.
Graphical abstract Carbon dots doped with heteroatoms (X-CDs) are a kind of fluorescent nanomaterials that display bright fluorescence, high quantum yield, photostability, biocompatibility and low toxicity. Hence, they possess large potential for both in-vitro and in-vivo bioimaging.
An electrochemical approach is introduced for synthesis of carbon dots (CDs) by exfoliating graphite rods at a voltage of 15 V in an electrolyte consisting of a mixture of water and two ionic liquids. It is found that the size of the CDs can be tuned by varying the fraction of water in the mixed electrolyte; CDs in sizes of 4.9, 4.1 and 3.1 nm are obtained if the electrolyte contains water in fractions of 24, 38 and 56 %, respectively. The CDs have a quantum yield of almost 10 % and display the typical excitation wavelength-dependent maxima of photoluminescence, strongest at excitation/emission wavelengths of 360/440 nm. Fourier transform infrared and X-ray photoelectron spectroscopy show the CDs to have oxygen functional groups on their surface which strongly improve solubility. The CDs were applied to image cells of the electricity-producing bacteria Shewanellaoneidensis MR-1.
Graphical Abstract An electrochemical approach is introduced to synthesize carbon dots by exfoliating graphite rods in mixed electrolyte of water and ionic liquids. The increasing size of carbon dots was realized by reducing the volume of water in the mixed electrolyte. The carbon dots were used to fluorescently image the electricity-producing bacterium Shewanellaoneidensis MR-1.
A simple method is described for the determination of copper(II) ions based on the cathodic electrochemiluminescence (ECL) of lucigenin which is quenched by Cu(II). The blue ECL is best induced at ?0.45 V (vs. Ag/AgCl) at a scan rate of 50 mV·s?1. Under optimum conditions, the calibration plot is linear in the 3.0 to 1000 nM Cu(II) concentration range. The limit of detection is 2.1 nM at a signal-to-noise ratio of 3. Compared to other analytical methods, the one presented here is simple, fast, selective and cost-effective. It has been successfully applied in the analysis of copper ions in spiked tap water samples with recoveries ranging from 93.0% (at 50 nM concentration) to 105.7% (at 150 nM).
Graphical abstract The inhibitory effect of Cu(II) on the cathodic electrochemiluminescence of lucigenin enables determination of Cu(II) with a 2.1 nM detection limit.
The authors describe a method for the preparation of orange-red emissive carbon dots (CDs) with excitation/emission peaks at 520/582 nm. The CDs were hydrothermally prepared by a one-pot strategy from trimesic acid and 4-aminoacetanilide. The fluorescence of the CDs is strongly quenched by hydrogen peroxide. The oxidation of glucose by glucose oxidase (GOx) produces H2O2 that quenches the fluorescence via static quenching. Based on this phenomenon, a fluorometric method was established for the determination of glucose. Under the optimum conditions, response is linear in the 0.5 to 100 μM glucose concentration range, with a 0.33 μM limit of detection. The method is selective for glucose over its analogues and was successfully applied to the determination of glucose in diluted human serum and in urine from diabetics and healthy individuals. Recoveries from spiked samples range from 98.7 to 102.5%.
We have prepared graphene quantum dot-europium(III) complex composites by noncovalently connecting chelating ligands dibenzoylmethane (DBM) and 1,10-phenanthroline (Phen) with graphene quantum dots (GQDs) first, followed by coordination to Eu(III). The resulting composites are well water-soluble and display red fluorescence of high color purity. The composites were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Aqueous solutions of the composites under 365 nm excitation display fluorescence with a peak at 613 nm and a quantum yield as high as 15.5 %. The good water solubility and stable photoluminescence make the composites very different from other Eu(III)-based coordination complexes. The composites are cell viable and can be used to label both the cell membrane and the cytoplasm of MCF-7 cells. They are also shown to act as bioprobes for in-vivo localization of tumorous tissue. In our perception, such composites are expected to possess wide scope because of the many functionalizations that are possible with GQDs.
This article reports on the synthesis of water dispersible carbon quantum dots (CDs) by a one-step hydrothermal method using polyamidoamine (PAMAM) and (3-aminopropyl)triethoxysilane (APTES) as a platform and passivant. The resulting CDs are highly uniform and finely dispersed. The synergistic effect between PAMAM and APTES on the surface of the CDs results in a fluorescence that is much brighter than that of CDs modified with either APTES or PAMAM only. The fluorescence of the co-modified CDs is quenched by Hg(II) ions at fairly low concentrations. Under the optimum conditions, the intensity of quenched fluorescence drops with Hg(II) concentration in the range from 0.2 nM to 10 μM, and the detection limit is 87 fM. The effect of potentially interfering cations on the fluorescence revealed a high selectivity for Hg2+. The fluorescent probe was applied to the determination of Hg(II) in (spiked) waters and milk and gave recoveries between 95.6 and 107 %, with relative standard deviation between 4.4 and 6.0 %.
Graphical abstract Strongly fluorescent carbon quantum dots (CDs) modified with polyamidoamine (PAMAM) and 3-aminopropyltriethoxysilane (APTES) were synthesized by one-step hydrothermal strategy. The resulting co-modified CD s were used as fluorescent probe for sensitive and selective detection of Hg2+.
The authors introduce a method for spatially arranged DNA immobilization on 10-nm gold nanoparticles (GNP) deposited on a silicon substrate carrying nanogapped interdigitated electrodes. The GNPs are covalently bound to the surface via silane chemistry, and the single steps of fabrication are monitored by FTIR spectroscopy and atomic force microscopy. This GNP deposition technique is shown to reduce the size of the nanogaps to 130 nm. FTIR also was used to monitor the immobilization of DNA on the surface of the interdigitated electrodes. This method allows DNA to be immobilized in a uniform and homogenous way. The utility of the method is demonstrated by immobilizing probe DNA on the surface and detecting target DNA specific for the human papilloma virus via fluorescence with a detection limit as low as 1 pM. In our perception, this method for GNP-mediated DNA immobilization enables high-performance sensing of a wide range of target (analyte) DNA.
Graphical abstract Schematic presentation of gold nanoparticle-mediated and spatially resolved deposition of DNA on nano-gapped interdigitated electrodes. The method was applied to the chemiluminescent determination of the human papillomavirus
The authors describe a fluorometric glucose assay that is based on the use of MnO2 nanosheets and copper nanoclusters (CuNCs) acting as nanoprobes. The CuNCs were synthesized by using bovine serum albumin as a template by chemical reduction of copper(II) sulfate. On addition of MnO2 nanosheets to a colloidal solution of CuNCs, the fluorescence of CuNCs (measured at excitation/emission wavelengths of 335/410 nm) is quenched. However, in the presence of enzymatically generated H2O2, the MnO2 nanosheets are reduced to form Mn(II) ions. As a result, fluorescence intensity recovers. The glucose assay is based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2 and glucuronic acid. The calibration plot is linear in the 1 μM to 200 μM glucose concentration range, and the detection limit is 100 nM. The method was successfully applied to the determination of glucose in spiked human serum samples.
Graphical abstract A sensitive fluorescent bioassay is reported for the detection of glucose based on the hydrogen peroxide-induced decomposition of a quencher system composed of MnO2 nanosheets and copper nanoclusters (CuNCs).
A composite consisting of chitosan containing azidomethylferrocene covalently immobilized on sheets of reduced graphene oxide was drop-casted on a polyester support to form a screen-printed working electrode that is shown to enable the determination of nitrite by cyclic voltammetry and chronoamperometry. Both reduction and oxidation of nitrite can be accomplished due to the high electron-transfer rate of this electrode. Under optimal experimental conditions (i.e. an applied potential of 0.7 V vs. Ag/AgCl in pH 7.0 solution), the calibration plot is linear in the 2.5 to 1450 μM concentration range, with an ~0.35 μM limit of detection (at a signal-to-noise ratio of 3). The sensor was successfully applied to the determination of nitrite in spiked mineral water samples, with recoveries ranging between 95 and 101 %.
Graphical abstract We describe the design of ferrocene-functionalized reduced graphene oxide electrode and its electrocatalytic properties towards the determination of nitrite. Compared to a reduced graphene oxide electrode, the sensor exhibits enhanced electrocatalytic activity towards both oxidation and reduction of nitrite.
The authors describe a fluorescent probe for sulfide that is based on carboxy-functionalized semiconducting polymer dots (P-dots). The dots were prepared from carboxy-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′-3-thiadiazole)] (referred to as COOH-PFBT) via co-precipitation. The P-dots aggregate on addition of Cu(II) ions and their green fluorescence (with excitation/emission peaks at 455/540 nm) is then quenched. Fluorescence is restored on addition of sulfide to the aggregates due to the formation of CuS. This quenching-recovery (“off-on”) mechanism forms the basis for a new sulfide detection scheme. Fluorescence increases linearly in the 1.25 to 75.0 μM sulfide concentration range, with a 0.45 μM detection limit. Good selectivity over other anions is demonstrated. The method shows recoveries ranging between 98.6% and 105.7% when applied to the determination of sulfide in spiked real water samples.
Graphical abstract Schematic of a fluorescent off-on sensor for (hydrogen) sulfide based on the use of semiconducting polymer dots (PFBT-COOH) whose fluorescene is quenched by Cu(II) ion but restored on addition of (hydrogen) sulfide.
A strategy was developed for the voltammetric determination of the antibiotic drug levofloxacin (LV) based on a glassy carbon electrode modified with a composite consisting of poly(o-aminophenol) and graphene quantum dots (PoAP/GQD) that was fabricated by electropolymerization. The PoAP/GQD composite provides a large surface area and sensing interface and strongly promotes the oxidation current of LV. Under optimal conditions, the modified GCE displays an oxidation peak current (best measured at a working voltage of 1.05 V vs. SCE) that is linearly related to the levofloxacin concentration in the range from 0.05 to 100 μM, and the detection limit is 10 nM (at an S/N of 3). The method was applied to the determination of levofloxacin in spiked milk samples where is gave recoveries between 96.0 and 101.0 %.
Graphical Abstract We describe a one-step electrochemical polymerization method to synthesize a layer of conductive film of poly(o-aminophenol) and graphene quantum dots (PoAP/GQD) onto a glassy carbon electrode (GCE) surface. The composite film exhibited high electro catalytic activity for the quantitative determination of levofloxacin by stripping voltammetry.
We report on a novel kind of mitochondria-targeted theranostic nanoparticles (NPs). The NPs are doped with the oxygen-sensitive probe Pt(II)-porphyrins (PtTFPP) which exerts a dual role in acting as a diagnostic tool that can sense oxygen via quenching of luminescence, but also acts as an agent in photodynamic therapy (PDT) of cancer. In addition, it allows therapeutic efficacy to be assessed in-situ. Upon appropriate high-energy photoirradiation, the NPs generate singlet oxygen by energy transfer from triplet PtTFPP to ground state oxygen, and cell death is induced via PDT. Under low-energy light irradiation, in contrast, the NPs can be utilized to detect oxygen consumption rate via time-resolved luminescence measurements in order to study the efficacy of PDT. This is the first report where a single nanoagent is used to stimulate PDT and also to assess the efficacy of PDT. In our perception, the method provides a promising platform for testing anti-cancer drugs.
Graphical abstract We report on a kind of mitochondria-targeted theranostic nanoparticles (NPs) doped with Pt(II)-porphyrins for oxygen sensing via quenching of luminescence, efficient photodynamic therapy (PDT) of cancer and quantitative assessment of therapeutic response in-situ.
The authors describe an electrochemical sensor for the neonicotinoid insecticide imidacloprid (IMI) based on Pt-In catalytic nanocomposite film and Bromophenol blue amplification. The Pt-In nanocomposite film was deposited on the surface of a modified glassy carbon electrode. The composite molecularly imprinted polymer (MIP) was prepared by electro-polymerization using bromophenol blue doped o-aminophenol as functional monomer and 4-tert-butylcalix[6]arene-IMI supramolecular inclusion complex as template molecule. The experimental results showed that the current intensity of IMI was clearly amplified in the potential range from ?0.3 to ?1.8 V, because of the double amplification, based on the Pt-In film and Bromophenol blue catalysis. Moreover, the double recognition ability of the sensor, which relied on the MIP and the vacuum structure of 4-tert-butylcalix[6]arene, effectively increased the specific recognition performance. The feasibility of its practical applications has been demonstrated by the analysis of vegetable samples.
Graphical abstract A supramolecular imprinted electrochemical sensor for imidacloprid determination was prepared based on Pt-In nanocomposite film and bromophenol blue amplification. Because of the advantages of the specific recognition sites in MIPs and supramolecular chemistry, the sensor showed good selectivity for imidacloprid.
The authors report on a simple strategy for sensitive determination of the activity of terminal deoxynucleotidyl transferase (TdT) using copper nanoclusters (CuNCs) as fluorescent probes. TdT-polymerized long chain AT-rich DNA serves as a template for the synthesis of the CuNCs, and TdT activity is detected fluorometrically at excitation/emission wavelengths of 340/570 nm. The protocol relies on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs. The calibration plot is linear in the 0.7 to 14 U L?1 activity range, with a 60 mU L?1 detection limit (at a signal-to-noise ratio of 3). The protocol was applied to determine TdT activity in acute lymphatic leukemia cells. This approach is selective, simple, convenient and cost-efficient because a complex DNA sequence is not required. In our perception, the method provides a viable new platform for monitoring the activity and inhibition of TdT.
Graphical abstract Based on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs with strong fluorescence, a turn-on fluorescence assay for TdT activity is presented.
This review (with (318) refs) describes progress made in the design and synthesis of morphologically different metal oxide nanoparticles made from iron, manganese, titanium, copper, zinc, zirconium, cobalt, nickel, tungsten, silver, and vanadium. It also covers respective composites and their function and application in the field of electrochemical and photoelectrochemical sensing of chemical and biochemical species. The proper incorporation of chemical functionalities into these nanomaterials warrants effective detection of target molecules including DNA hybridization and sensing of DNA or the formation of antigen/antibody complexes. Significant data are summarized in tables. The review concludes with a discussion or current challenge and future perspectives.
This review (with 85 refs.) summarizes the recent literature on the adsorption of common aromatic pollutants by using modified metal-organic frameworks (MOFs). Four kinds of aromatic pollutants are discussed, namely benzene homologues, polycyclic aromatic hydrocarbons (PAHs), organic dyes and their intermediates, and pharmaceuticals and personal care products (PPCPs). MOFs are shown to be excellent adsorbents that can be employed to both the elimination of pollutants and to their extraction and quantitation. Adsorption mechanisms and interactions between aromatic pollutants and MOFs are discussed. Finally, the actual challenges of existence and the perspective routes towards future improvements in the field are addressed.
Graphical abstract Recent advance on adsorption of common aromatic pollutants including benzene series, polycyclic aromatic hydrocarbons, organic dyes and their intermediates, pharmaceuticals and personal care products by metal-organic frameworks.
A composite material obtained by ultrasonication of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) was loaded with manganese dioxide (MnO2), poly(diallyldimethylammonium chloride) and gold nanoparticles (AuNPs), and the resulting multilayer hybrid films were deposited on a glassy carbon electrode (GCE). The microstructure, composition and electrochemical behavior of the composite and the modified GCE were characterized by transmission electron microscopy, Raman spectra, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode induces efficient electrocatalytic oxidation of dopamine at a rather low working voltage of 0.22 V (vs. SCE) at neutral pH values. The response is linear in the 0.5 μM to 2.5 mM concentration range, the sensitivity is 233.4 μA·mM￣1·cm￣2, and the detection limit is 0.17 μM at an SNR of 3. The sensor is well reproducible and stable. It displays high selectivity over ascorbic acid, uric acid and glucose even if these are present in comparable concentrations.
Graphical abstract Gold nanoparticles were self-assembled onto the surface of the MnO2 decorated graphene oxide-carbon nanotubes composites with poly(diallyldimethylammonium chloride) (PDDA) as a coupling agent. Further, a sensitive electrochemical sensor of dopamine was developed via immobilizing this nanocomposite on a glassy carbon electrode (GCE).
An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell of molecularly imprinted polymer (Ag@MIP). The MIP is prepared by using bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10?9 mol·L?1.
Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.
Graphical Abstract Nano-LEGO: Assembling two types of separately prepared nanoparticles into a hetero-dimer is the first step towards complex nano-architectures. This study shows a solid support approach to combine a gold and a magnetite nanocrystal.
