Fluorescent Immunoassay for the Detection of Pathogenic Bacteria at the Single-Cell Level Using Carbon Dots-Encapsulated Breakable Organosilica Nanocapsule as Labels

Herein, carbon dots (CDs)-encapsulated breakable organosilica nanocapsules (BONs) were facilely prepared and used as advanced fluorescent labels for ultrasensitive detection of Staphylococcus aureus. The CDs were entrapped in organosilica shells by cohydrolyzation of tetraethyl orthosilicate and bis­[3-(triethoxysilyl)­propyl]­disulfide to form core–shell CDs@BONs, where hundreds of CDs were encapsulated in each nanocapsule. Immunofluorescent nanocapsules, i.e., anti-S. aureus antibody-conjugated CDs@BONs, were prepared to specifically recognize S. aureus. Before fluorescent detection, CDs were released from the BONs by simple NaBH₄ reduction. The fluorescent signals were amplified by 2 orders of magnitude because of hundreds of CDs encapsulated in each nanocapsule, compared with a conventional immunoassay using CDs as fluorescent labels. A linear range was obtained at the S. aureus concentration from 1 to 200 CFU mL^–1. CDs@BONs are also expected to expand to other systems and allow the detection of ultralow concentrations of targets

Copper-Based Metal–Organic Framework Nanoparticles with Peroxidase-Like Activity for Sensitive Colorimetric Detection of <i>Staphylococcus aureus</i>

Cu-MOF nanoparticles with an average diameter of 550 nm were synthesized from 2-aminoterephthalic acid and Cu­(NO₃)₂ by a mixed solvothermal method. The Cu-MOF nanoparticles can show peroxidase-like activity that can catalyze 3,3′,5,5′-tetramethylbenzidine to produce a yellow chromogenic reaction in the presence of H₂O₂. The presence of abundant amine groups on the surfaces of Cu-MOF nanoparticles enables facile modification of <i>Staphylococcus aureus</i> (<i>S. aureus</i>) aptamer on Cu-MOF nanoparticles. By combining Cu-MOF-catalyzed chromogenic reaction with aptamer recognition and magnetic separation, a simple, sensitive, and selective colorimetric method for the detection of <i>S. aureus</i> was developed

Bioimmobilization Matrices with Ultrahigh Efficiency Based on Combined Polymerizations of Chemical Oxidation and Metal Organic Coordination for Biosensing

Facile regulation and enhancing of the performance of bioimmobilization materials is a key factor for their applications for biosensing, biocatalysis, bioreactor, and so on. Here, we propose a method of combined polymerizations of chemical oxidation and metal organic coordination to develop enhanced bioimmobilization matrices for high performance biosensing. Being different from conventional methods that are based on sole polymerization, the new method elaborated chemical oxidation to one-pot obtain oligomers as ligands for metal–organic coordination polymerization. Two kinds of thiol that could be chemically oxidized by H₂O₂ and be coordinated with NaAuCl₄ were adopted as monomers. Glucose oxidase was adopted as the representative biomolecule. Chemical oxidation was proved to be efficient to lengthen monomers to produce oligomers (ligands) with different lengths by adjusting the concentrations of monomers and oxidant, as well as reaction time. This dynamic prelengthening process not only endows the coexisting biomolecules with active and protective oligomers shell to significantly enhance the immobilization efficiency but also regulates the structure of metal–organic coordination polymer. As crucial factors of immobilization, the entrapment ratio of enzyme and mass-transfer efficiency all achieved obvious increases compared with those based on sole chemical oxidation polymerization or metal–organic coordination polymerization; the entrapment ratio even reached an extreme value of 100%. Therefore, the biosensing performance was greatly promoted with sensitivities being among the best of those reported analogues. The biosensors also exhibited satisfactory selectivity, stability, and feasibility for blood serum samples. This method may provide a universal strategy for regulating and enhancing performance of ligand-constructed polymers and their composites for entrapment-based applications

Immobilization of Enzymes by Electrochemical and Chemical Oxidative Polymerization of L‑DOPA to Fabricate Amperometric Biosensors and Biofuel Cells

Electrochemical/chemical oxidative synthesis and biosensing/biofuel cell applications of poly­(L-DOPA) (PD) are studied versus polydopamine (PDA) as a recent hotspot biomaterial. The enzyme electrode developed by coelectrodeposition of PD and glucose oxidase (GOx), uricase, or tyrosinase shows biosensing performance superior to that of the corresponding PDA-based enzyme electrode. The chemical oxidative polymerization of L-DOPA (PD_C) by NaAuCl₄ in GOx-containing neutral aqueous solution is used to immobilize GOx and gold nanoparticles (AuNPs). The thus-prepared chitosan (CS)/GOx-PD_C-AuNPs/Au_plate/Au electrode working in the first-generation biosensing mode responds linearly to glucose concentration with a sensitivity of 152 μA mM^–1 cm^–2, which is larger than those of the CS/GOx-PDA_C-AuNPs/Au_plate/Au electrode, the CS/GOx-poly­(3-anilineboronic acid) (PABA)-AuNPs/Au_plate/Au electrode, and the most reported GOx-based enzyme electrodes. This PD_C-based enzyme electrode also works well in the second-generation biosensing mode and as an excellent bioanode in biofuel cell construction, probably because PD as an amino acid polymer has the higher biocompatibility and the more favorable affinity to the enzyme than PDA. The PD material of great convenience in synthesis, outstanding biocompatibility for preparing high-performance bionanocomposites, and strong capability of multifunctional coatings on many surfaces may find wide applications in diversified fields including biotechnology and surface-coating

Enhanced Cathodic Preconcentration of As(0) at Au and Pt Electrodes for Anodic Stripping Voltammetry Analysis of As(III) and As(V)

We report that the cathodic preconcentration of electron-insulating As(0) on Au and Pt electrodes can be enhanced by chemical reduction of As­(III) and As­(V) by electrogenerated H₂, as studied by cyclic voltammetry. This finding is used for sensitive anodic stripping voltammetry (ASV) analysis of As­(III) and/or As­(V) at the Au electrode. About three As(0) monolayers were cathodically preconcentrated on the Pt electrode at −0.3 V (vs SCE) in 0.5 M aqueous H₂SO₄, as a result of both the chemical reduction of the solution-state As­(III) near the electrode surface by the electrogenerated H₂ and the direct electroreduction of As­(III) on the highly catalytic surface Pt sites. Only one As(0) monolayer was electrodeposited at −0.2 V (vs SCE) on the Au electrode in 0.5 M aqueous H₂SO₄, but about two As(0) monolayers were deposited on the Au electrode at a more negative potential at which the mild evolution of H₂ occurred. The electrogenerated H₂ could also chemically reduce As­(V), though the direct electroreduction of As­(V) was sluggish on the Au electrode. Linear sweep ASV (LSASV) oxidation of the preconcentrated As(0) to As­(III) and then to As­(V) at a fast scan rate gave two sharper and higher anodic peaks on the Au electrode than on the Pt electrode. On the basis of these observations, sensitive dual-signal LSASV analysis of As­(III) and/or As­(V) was achieved on the Au electrode, with limits of detection of 1.0 nM for As­(III) and 5.4 nM for As­(V) under optimized experimental conditions. Our method was successfully applied for analysis of As­(III) and/or As­(V) in real water samples. The insights into cathodic As(0) deposition provided here may help the better understanding of electrochemical deposition of many other electron-insulating thin films, especially those obeying the electrode material-dependent inner-sphere mechanism, for electrochemical and surface-coating applications

Polyamidoamine Dendrimer and Oleic Acid-Functionalized Graphene as Biocompatible and Efficient Gene Delivery Vectors

Functionalized graphene has good potential in biomedical applications. To address a better and multiplex design of graphene-based gene vectors, the graphene-oleate-polyamidoamine (PAMAM) dendrimer hybrids were synthesized by the oleic acid adsorption and covalent linkage of PAMAM dendrimers. The micromorphology, electrical charge property, and amount of free amine groups of the graphene-oleate-PAMAM hybrids were characterized, and the peripheral functional groups were identified. The PAMAM dendrimers could be tethered onto graphene surface in high density. The graphene-oleate-PAMAM hybrids exhibit relatively good dispersity and stability in aqueous solutions. To evaluate the potential application of the hybrids in gene delivery vectors, cytotoxicity to HeLa and MG-63 cells and gene (plasmid DNA of enhanced green fluorescent protein) transfection capacity of the hybrids were investigated in detail. The graphene-oleate-PAMAM hybrids show mammalian cell type- and dose-dependent in vitro cytotoxicity. Under the optimal condition, the hybrids possess good biocompatibility and gene transfection capacity. The surface modification of graphene with oleic acid and PAMAM improves the gene transfection efficiency 13 times in contrast to the ultrasonicated graphene. Moreover, the hybrids show better transfection efficiency than the graphene oxide-PAMAM without the oleic acid modification

Redistribution of Activator Tuning of Photoluminescence by Isovalent and Aliovalent Cation Substitutions in Whitlockite Phosphors

Many strategies, including double substitution, addition of charge compensation, cation-size-mismatch and neighboring-cation substitution, have contributed to tuning photoluminescence of phosphors for white light-emitting diodes. These strategies generally involve modification of a certain special site where the activator occupies; tuning strategy based on multiple cation sites is very rare and desirable. Here we report that isovalent (Sr²⁺) and aliovalent (Gd³⁺) substitutions for Ca²⁺ tune the photoluminescence from one band to multiple bands in whitlockite β-Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ and β-Ca_{3–3<i>y</i>/7}Gd_2<i>y</i>/7(PO₄)₂:Eu²⁺ phosphors. The saltatory variation of the emission spectra is caused by the removal of Eu²⁺ from the site M(4) to other sites. Moreover, we found the mechanisms of dopant redistribution tuning the luminescence are different. The incorporation of Gd³⁺ makes the site M(4) empty according to the scheme 3Ca²⁺ = 2Gd³⁺ + □, while Sr²⁺ substitution causes the cation sites to be enlarged due to cation size mismatch. Additionally, the influence of the cation substitutions on the photoluminescence thermal stability of phosphors is researched. The strategies, emptying and enlarging sites, developed herein are expected to provide a general route for tuning luminescence of phosphors with multiple sites in the future

Three-Dimensional Graphene Networks as a New Substrate for Immobilization of Laccase and Dopamine and Its Application in Glucose/O₂ Biofuel Cell

We report here three-dimensional graphene networks (3D-GNs) as a novel substrate for the immobilization of laccase (Lac) and dopamine (DA) and its application in glucose/O₂ biofuel cell. 3D-GNs were synthesized with an Ni²⁺-exchange/KOH activation combination method using a 732-type sulfonic acid ion-exchange resin as the carbon precursor. The 3D-GNs exhibited an interconnected network structure and a high specific surface area. DA was noncovalently functionalized on the surface of 3D-GNs with 3,4,9,10-perylene tetracarboxylic acid (PTCA) as a bridge and used as a novel immobilized mediating system for Lac-based bioelectrocatalytic reduction of oxygen. The 3D-GNs-PTCA-DA nanocomposite modified glassy carbon electrode (GCE) showed stable and well-defined redox current peaks for the catechol/<i>o</i>-quinone redox couple. Due to the mediated electron transfer by the 3D-GNs-PTCA-DA nanocomposite, the Nafion/Lac/3D-GNs-PTCA-DA/GCE exhibited high catalytic activity for oxygen reduction. The 3D-GNs are proven to be a better substrate for Lac and its mediator immobilization than 2D graphene nanosheets (2D-GNs) due to the interconnected network structure and high specific surface area of 3D-GNs. A glucose/O₂ fuel cell using Nafion/Lac/3D-GNs-PTCA-DA/GCE as the cathode and Nafion/glucose oxidase/ferrocence/3D-GNs/GCE as the anode can output a maximum power density of 112 μW cm^–2 and a short-circuit current density of 0.96 mA cm^–2. This work may be helpful for exploiting the popular 3D-GNs as an efficient electrode material for many other biotechnology applications

Synthesis of Ultrathin Nitrogen-Doped Graphitic Carbon Nanocages as Advanced Electrode Materials for Supercapacitor

Synthesis of nitrogen-doped carbons with large surface area, high conductivity, and suitable pore size distribution is highly desirable for high-performance supercapacitor applications. Here, we report a novel protocol for template synthesis of ultrathin nitrogen-doped graphitic carbon nanocages (CNCs) derived from polyaniline (PANI) and their excellent capacitive properties. The synthesis of CNCs involves one-pot hydrothermal synthesis of Mn₃O₄@PANI core–shell nanoparticles, carbonization to produce carbon coated MnO nanoparticles, and then removal of the MnO cores by acidic treatment. The CNCs prepared at an optimum carbonization temperature of 800 °C (CNCs-800) have regular frameworks, moderate graphitization, high specific surface area, good mesoporosity, and appropriate N doping. The CNCs-800 show high specific capacitance (248 F g^–1 at 1.0 A g^–1), excellent rate capability (88% and 76% capacitance retention at 10 and 100 A g^–1, respectively), and outstanding cycling stability (∼95% capacitance retention after 5000 cycles) in 6 M KOH aqueous solution. The CNCs-800 can also exhibit great pseudocapacitance in 0.5 M H₂SO₄ aqueous solution besides the large electrochemical double-layer capacitance. The excellent capacitance performance coupled with the facile synthesis of ultrathin nitrogen-doped graphitic CNCs indicates their great application potential in supercapacitors

Electrochemical Conversion of Fe₃O₄ Magnetic Nanoparticles to Electroactive Prussian Blue Analogues for Self-Sacrificial Label Biosensing of Avian Influenza Virus H5N1

A serious impetus always exists to exploit new methods to enrich the prospect of nanomaterials. Here, we report electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) to electroactive Prussian blue (PB) analogues accompanied by three interfacial effects and its exploitation for novel label self-sacrificial biosensing of avian influenza virus H5N1. The ECC method involves a high-potential step to create strong acidic condition by splitting H₂O to release Fe³⁺ from the MNPs, and then a low-potential step leading to the reduction of coexisting K₃Fe­(CN)₆ and Fe³⁺ to K₄Fe­(CN)₆ and Fe²⁺, respectively, which react to form PB analogues. Unlike conventional solid/liquid electrochemical interfaces that need a supply of reactants by transportation from bulk solution and require additional template to generate porosity, the proposed method introduces MNPs on the electrode surface and makes them natural nanotemplates and nanoconfined sources of reactants. Therefore, the method presents interesting surface templating, generation–confinement, and refreshing effects/modes, which benefit the produced PB with higher porosity and electrochemical activity, and 3 orders of magnitude lower requirement for reactant concentration compared with conventional methods. Based on the ECC methods, a sandwich immunosensor is designed for rapid detection of avian influenza virus H5N1 using MNPs as self-sacrificial labels to produce PB for signal amplification. Taking full advantages of the high abundance of Fe in MNPs and three surface effects, the ECC method endows the biosensing technology with high sensitivity and a limit of detection down to 0.0022 hemagglutination units, which is better than those of most reported analogues. The ECC method may lead to a new direction for application of nanomaterials and new electrochemistry modes