Yuqing Lin

Hexagonal Cobalt Oxyhydroxide–Carbon Dots Hybridized Surface: High Sensitive Fluorescence Turn-on Probe for Monitoring of Ascorbic Acid in Rat Brain Following Brain Ischemia

In this study, we report a novel and efficient fluorescence probe synthesized by Tris(hydroxymethyl)aminomethane-derived carbon dots (CDs)-modified hexagonal cobalt oxyhydroxide(CoOOH) nanoflakes (Tris-derived CDs-CoOOH) for monitoring of cerebral ascorbic acid (AA) in brain microdialysate. The as-prepared Tris-derived CDs with the fluorescence quantum yield of 7.3% are prepared by a one-step pyrolysis strategy of the sole precursor and used as the signal output. After being hybridized with CoOOH nanoflakes to form Tris-derived CDs-CoOOH, the luminescence of the Tris-derived CDs can be efficiently quenched by CoOOH via fluorescence resonance energy transfer (FRET). Due to the specific redox reaction between the enediol group of AA and hexagonal CoOOH nanoflakes, AA can reduce the hexagonal CoOOH nanoflakes in the Tris-derived CDs-CoOOH and lead to collapse of the hybrized structure, then the release of Tris-derived CDs, and thus finally the fluorescence recovery. Moreover, cobalt ions (II), generated by CoOOH nanoflakes oxidizing AA, almost have no obvious interference on the fluorescence probe, i.e., Tris-derived CDs, which could be ascribed to the surface of Tris-derived CDs containing a few strong chelation groups such as amino/carboxyl/thiol groups, instead of plenty of -OH groups with weak chelation with Co(2+). On the basis of this feature, the Tris-derived CDs-CoOOH fluorescent probe demonstrates a linear range from 100 nM to 20 μM with the detection limit of ∼50 nM, i.e., with an improved sensitivity toward AA detection. Compared with other turn-on fluorescent methods using convenient fluorophore-nitroxide fluorescent probes for detection of AA, the method demonstrated here possesses a facial synthesis route, lower limit of detection, and wider linear range, which validates sensing of AA in the cerebral systems during the calm/ischemia process. This study provides a fluorescence assay for the simple yet facial detection of AA in the cerebral systems and assists in the understanding of the biological processes in the physiological and pathological study.

Aptasensor for electrochemical sensing of angiogenin based on electrode modified by cationic polyelectrolyte-functionalized graphene/gold nanoparticles composites

Herein, a label-free and highly sensitive electrochemical aptasensor for the detection of angiogenin was proposed based on a conformational change of aptamer and amplification by poly(diallyldimethyl ammonium chloride) (PDDA)-functionalized graphene/gold nanoparticles (AuNPs) composites-modified electrode. PDDA-functionalized graphene (P-GR) nanosheets as the building block in the self-assembly of GR nanosheets/AuNPs heterostructure enhanced the electrochemical detection performance. The electrochemical aptasensor has an extraordinarily sensitive response to angiogenin in a linear range from 0.1pM to 5nM with a detection limit of 0.064pM. The developed sensor provides a promising strategy for the cancer diagnosis in medical application in the future.

Co 3 O 4 nanoparticles anchored on nitrogen-doped reduced graphene oxide as a multifunctional catalyst for H 2 O 2 reduction, oxygen reduction and evolution reaction

This study describes a facile and effective route to synthesize hybrid material consisting of Co3O4 nanoparticles anchored on nitrogen-doped reduced graphene oxide (Co3O4/N-rGO) as a high-performance tri-functional catalyst for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and H2O2 sensing. Electrocatalytic activity of Co3O4/N-rGO to hydrogen peroxide reduction was tested by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry. Under a reduction potential at −0.6 V to H2O2, this constructing H2O2 sensor exhibits a linear response ranging from 0.2 to 17.5 mM with a detection limit to be 0.1 mM. Although Co3O4/rGO or nitrogen-doped reduced graphene oxide (N-rGO) alone has little catalytic activity, the Co3O4/N-rGO exhibits high ORR activity. The Co3O4/N-rGO hybrid demonstrates satisfied catalytic activity with ORR peak potential to be −0.26 V (vs. Ag/AgCl) and the number of electron transfer number is 3.4, but superior stability to Pt/C in alkaline solutions. The same hybrid is also highly active for OER with the onset potential, current density and Tafel slope to be better than Pt/C. The unusual catalytic activity of Co3O4/N-rGO for hydrogen peroxide reduction, ORR and OER may be ascribed to synergetic chemical coupling effects between Co3O4, nitrogen and graphene.

Tunable Fluorescent Silica-Coated Carbon Dots: A Synergistic Effect for Enhancing the Fluorescence Sensing of Extracellular Cu2+ in Rat Brain

Carbon quantum dots (CDs) combined with self-assembly strategy have created an innovative way to fabricate novel hybrids for biological analysis. This study demonstrates a new fluorescence platform with enhanced selectivity for copper ion sensing in the striatum of the rat brain following the cerebral calm/sepsis process. Here, the fabrication of silica-coated CDs probes is based on the efficient hybridization of APTES which act as a precursor of organosilane self-assembly, with CDs to form silica-coated CDs probes. The fluorescent properties including intensity, fluorescence quantum yield, excitation-independent region, and red/blue shift of the emission wavelength of the probe are tunable through reliable regulation of the ratio of CDs and APTES, realizing selectivity and sensitivity-oriented Cu(2+) sensing. The as-prepared probes (i.e., 3.33% APTES-0.9 mg mL(-1) CDs probe) show a synergistic amplification effect of CDs and APTES on enhancing the fluorescence signal of Cu(2+) detection through fluorescent self-quenching. The underlying mechanism can be ascribed to the stronger interaction including chelation and electrostatic attraction between Cu(2+) and N and O atoms-containing as well as negatively charged silica-coated CDs than other interference. Interestingly, colorimetric assay and Tyndall effect can be observed and applied to directly distinguish the concentration of Cu(2+) by the naked eye. The proposed fluorescent platform here has been successfully applied to monitor the alteration of striatum Cu(2+) in rat brain during the cerebral calm/sepsis process. The versatile properties of the probe provide a new and effective fluorescent platform for the sensing method in vivo sampled from the rat brain.

Electrochemical immunosensor for detection of epidermal growth factor reaching lower detection limit: toward oxidized glutathione as a more efficient blocking reagent for the antibody functionalized silver nanoparticles and antigen interaction.

Blocking reagent is of vital importance for an immunosensor because it ensures the antifouling of the sensing interface and thus selective determination of the target. This Letter investigates a small inactive peptide, oxidized glutathione (GSSG), to replace the commonly used bovine serum albumin (BSA) as blocking reagent for immunosensor fabrication to lower the detection limit of electrochemical immunosensors. The EGF (epidermal growth factor) detection as an example is used here to compare the blocking effects from GSSG and BSA, respectively. The relatively big size of BSA sterically hinders EGF and antibody functionalized silver nanoparticles (Ab-AgNPs) binding. By comparison, GSSG cannot hinder EGF and Ab-AgNPs binding since it is much smaller than EGF, verified by scanning electron microscopy (SEM) results. The established GSSG blocking-based immunosensor for EGF reaches a very low detection limit of 0.01 pM, exhibits wide linearity range between 0.1 pM and 0.1 μM and is more sensitive than the BSA blocking strategy. The proposed GSSG-blocking strategy in the immunoassay paves an attractive platform for other biomolecules to reach a lower detection limit.

Iron incorporation affecting the structure and boosting catalytic activity of β-Co(OH)2: exploring the reaction mechanism of ultrathin two-dimensional carbon-free Fe3O4-decorated β-Co(OH)2 nanosheets as efficient oxygen evolution electrocatalysts

It is significantly important to develop highly active catalysts for the oxygen evolution reaction (OER) for designing various renewable energy storage and conversion devices. Herein, we report a series of ultrathin two-dimensional (2D) carbon-free Fe3O4-decorated β-Co(OH)2 nanosheets (Fe3O4/Co(OH)2 NSs) as OER electrocatalysts with different Co/Fe mole ratios from 1 to 31. It is found that the different amounts of iron incorporation into Co(OH)2 NSs affects the structure of Fe3O4/Co(OH)2 NSs, while the optimized incorporation boosts the electrocatalytic activity of Co(OH)2 NSs for OER, i.e. the Fe3O4/Co(OH)2 NSs with a Co/Fe molar ratio of 15 demonstrate superior catalytic properties with respect to the lowest overpotential and smallest Tafel slope in alkaline media. First principles calculations used for exploring mechanisms show that Fe3+ from Fe3O4/Co(OH)2 NSs adsorbs water molecules more energetically favorably on the surface and would offer far more improvement of the catalytic activity compared with Fe2+. Combined with structure analysis and calculation results, the better catalytic activity is attributed to the ultrathin structure, high active site exposure, lower adsorption energy towards water molecules and the increased positive charge of adsorbed water molecules. This research paves a way to develop highly active and durable substitutes for noble metal OER electrocatalysts.

Facile synthesis of nickel hydroxide–graphene nanocomposites for insulin detection with enhanced electro-oxidation properties

This study describes a facile and effective one-pot route to synthesize structurally uniform and electrochemically active nickel hydroxide–graphene nanocomposites (Ni(OH)2–GN) and investigates the electrocatalytic activity toward the oxidation of insulin. Graphene here was used to tether Ni2+ precursor onto surfaces and eventually grow Ni(OH)2 nanoparticles to form hybrid materials. The synthetic Ni(OH)2–GN nanocomposite has a uniform surface distribution, which was characterized with scanning electron microscopy (SEM). Moreover, the composition of synthetic Ni(OH)2–GN nanocomposite was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR spectra). The Ni(OH)2–GN were electrochemically treated in 0.1 M NaOH solution through cyclic voltammograms, and then gradually transited into nickel oxyhydroxide–graphene nanocomposites (NiOOH–GN), which demonstrated high catalytic activity and improved stability to insulin oxidation. The steady-state current response increases linearly with insulin concentration from 800 nM to 6400 nM with a fast response time of less than 2 s and a detection limit of 200 nM. The excellent performance of insulin sensor, including long term stability, can be ascribed to the synergistic effects of the large surface area (resulting in high loading ability), dispersing ability and conductivity of graphene and the large surface-to-volume ratio and electrocatalytic activity of Ni(OH)2 nanoparticles.

Preparation of nitrogen-doped carbon nanoblocks with high electrocatalytic activity for oxygen reduction reaction in alkaline solution

The oxygen reduction reaction (ORR) is traditionally performed using noble-metals catalysts, e.g. Pt. However, these metal-based catalysts have the drawbacks of high costs, low selectivity, poor stabilities, and detrimental environmental effects. Here, we describe metal-free nitrogen-doped carbon nanoblocks (NCNBs) with high nitrogen contents (4.11%), which have good electrocatalytic properties for ORRs. This material was fabricated using a scalable, one-step process involving the pyrolysis of tris(hydroxymethyl)aminomethane (Tris) at 800 ℃. Rotating ring disk electrode measurements show that the NCNBs give a high electrocatalytic performance and have good stability in ORRs. The onset potential of the catalyst for the ORR is -0.05 V (vs Ag/AgCl), the ORR reduction peak potential is -0.20 V (vs Ag/AgCl), and the electron transfer number is 3.4. The NCNBs showed pronounced electrocatalytic activity, improved long-term stability, and better tolerance of the methanol crossover effect compared with a commercial 20 wt% Pt/C catalyst. The composition and structure of, and nitrogen species in, the NCNBs were investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The pyrolysis of Tris at high temperature increases the number of active nitrogen sites, especially pyridinic nitrogen, which creates a net positive charge on adjacent carbon atoms, and the high positive charge promotes oxygen adsorption and reduction. The results show that NCNBs prepared by pyrolysis of Tris as nitrogen and carbon sources are a promising ORR catalyst for fuel cells.

Facile development of Au-ring microelectrode for in vivo analysis using non-toxic polydopamine as multifunctional material

In this study, we describe a facile and fast wet deposition technique to bottom-up fabricate Au-ring microelectrodes (Au-RMEs) using non-toxic polydopamine as multifunctional grafting material instead of commonly used (3-aminopropyl)-trimethoxysilane (APTMS). The Au-RMEs are fabricated by growing Au film uniformly inside of a pulled glass capillary. Au-RMEs with tip apex diameter ranging from 15 to 50 μm were fabricated involving four consequent steps, i.e. hydroxylating the inside wall of a pulled glass capillaries, grafting adhesive polydopamine (PDA) film to hydroxyl group surface, seeding gold nanoparticles (AuNPs) onto PDA surface and finally growing thickness-tunable gold layer on top of gold nanoparticles. After 3-mercaptopropionic acid (MPA) self-assembled monolayers (SAMs) modification, the Au-RMEs obtain improved specificity and sensitivity for monitoring of dopamine (DA) with respect to alleviating ascorbic acid (AA) interference. The current response is in wide linearity to DA concentration in the range of 0.2-100.0 μM with a correlation coefficient of 0.998 and the detection limit as low as 50.0 nM (S/N=3). In addition, the designed glass substrates of Au-RMEs were mechanically stronger and their tips can be further sharped by adjusting the pulling program. In order to demonstrate the utility of these fabricated microelectrodes in neurochemistry, Au-RMEs were used for electrochemical monitoring of DA release stimulated by K(+) in the striatum of rats. Thus, this study offers a novel and reliable strategy for preparing Au microelectrodes and maybe an attractive alternative to the traditional options for continuous and in vivo electrochemical monitoring of DA in various physiological processes.

Aptasensor for label-free square-wave voltammetry detection of potassium ions based on gold nanoparticle amplification

Herein, we present a very simple and label-free square-wave voltammetry (SWV) aptasensor to detect potassium ions (K+), in which a K+-specific aptamer was used as an ion recognition element, and a redox couple [Fe(CN)6]3−/4− as a redox probe. At the bare gold electrode, the redox couple [Fe(CN)6]3−/4− can very easily access the electrode surface to produce a very strong SWV signal. At the K+-specific aptamer/gold electrode surface, in the presence of K+, the single-stranded DNA with guanine (G)-rich sequences could fold into a secondary structure, G-quadruplex, which resulted in less availability for a redox reaction, and led to a smaller SWV current. To improve signal intensity, gold nanoparticles (AuNPs) were anchored to a gold electrode surface which had been previously modified with self-assembled monolayers of p-aminothiophenol. The SWV peak current decreased with K+ concentration, and the plot of the SWV peak current against the logarithm of K+ concentration is linear over the range from 10 pM to 0.1 μM and 0.5 μM to 1 mM, with a detection limit of 0.13 pM. The aptasensor also showed a very good selectivity for K+ without being affected by the coexistence of other ions.