Xue-Ji Zhang

Ferrocyanide-Ferricyanide Redox Couple Induced Electrochemiluminescence Amplification of Carbon Dots for Ultrasensitive Sensing of Glutathione

Here we report a novel solid-state ECL sensor for ultrasensitive sensing of glutathione (GSH) based on ferrocyanide-ferricyanide redox couple (Fe(CN)6(3-/4-)) induced electrochemiluminescence (ECL) amplification of carbon dots (C-dots). The electropolymerization of C-dots and (11-pyrrolyl-1-yl-undecyl) triethylammonium tetrafluoroborate (A2) enabled immobilization of the hydrophilic C-dots on the surface of glassy carbon electrode (GCE) perfectly, while the excellent conductivity of polypyrrole was exploited to accelerate electron transfer between them. The Fe(CN)6(3-/4-) can expeditiously convert the C-dots and S2O8(2-) to C-dot(•-) and SO4(•-), respectively. High yields of the excited state C-dots (C-dots*) were obtained, and a ∼10-fold ECL amplification was realized. The C-dots* obtained through the recombination of electron-injected and hole-injected processes may be impeded due to the interference of GSH to K2S2O8. Therefore, the constructed sensor for GSH showed a detection limit down to 54.3 nM (S/N = 3) and a wide linear range from 0.1-1.0 μM with a correlation coefficient of 0.997.

Carbon Nitride Nanosheet-Supported Porphyrin: A New Biomimetic Catalyst for Highly Efficient Bioanalysis

A highly efficient biomimetic catalyst was fabricated based on ultrathin carbon nitride nanosheets (C3N4)-supported cobalt(II) proto-porphyrin IX (CoPPIX). The periodical pyridinic nitrogen units in C3N4 backbone could serve as electron donors for great affinity with Co(2+) in PPIX, which resembled the local electronic structure as vitamin B12 and heme cofactor of hemoglobin. UV-vis kinetics and electrochemistry revealed its competitive (electro)catalysis with conventional peroxidase, while X-ray photoelectron spectroscopy and theoretical calculations suggest that the rehybridization of Co 3d with N orbitals from the backside can result in significant changes in enthalpy and charge density, which greatly promoted the activity of CoPPIX. The prepared nanocatalyst was further conjugated with streptavidin via multiple amines on the edge plane of C3N4 for facile tagging. Using biotinylated molecular beacon as the capture probe, a sensitive electrochemiluminescence-based DNA assay was developed via the electroreduction of H2O2 as the coreactant after the hairpin unfolded by the target, exhibiting linearity from 1.0 fM to 0.1 nM and a detection limit of 0.37 fM. Our results demonstrate a new paradigm to rationally design inexpensive and durable biomimics for electrochemiluminescence quenching strategy, showing great promise in bioanalytical applications.

Sensitive electrochemical detection of NADH and ethanol at low potential based on pyrocatechol violet electrodeposited on single walled carbon nanotubes-modified pencil graphite electrode.

In this work, the electrodeposition of pyrocatechol violet (PCV) was initially investigated by the electrochemical surface plasmon resonance (ESPR) technique. Subsequently, PCV was used as redox-mediator and was electrodeposited on the surface of pencil graphite electrode (PGE) modified with single-wall carbon nanotubes (SWCNTs). Owing to the remarkable synergistic effect of SWCNTs and PCV, PGE/SWCNTs/PCV exhibited excellent electrocatalytic activity towards dihydronicotinamide adenine dinucleotide (NADH) oxidation at low potential (0.2V vs. SCE) with fast amperometric response (<10s), broad linear range (1.3-280 μM), good sensitivity (146.2 μA mM(-1)cm(-2)) and low detection limit (1.3 μM) at signal-to-noise ratio of 3. Thus, this PGE/SWCNTs/PCV could be further used to fabricate a sensitive and economic ethanol biosensor using alcohol dehydrogenase (ADH) via a glutaraldehyde/BSA cross-linking procedure.

Magnetic Zirconium Hexacyanoferrate(II) Nanoparticle as Tracing Tag for Electrochemical DNA Assay

Novel multifunctional magnetic zirconium hexacyanoferrate nanoparticles (ZrHCF MNPs) were prepared, which consisted of magnetic beads (MBs) inner core and zirconium hexacyanoferrate(II) (ZrHCF) outer shell. As an artificial peroxidase, the ZrHCF MNPs exhibited remarkable electrocatalytic properties in the reduction of H2O2 at 0.2 V vs saturated calomel electrode (SCE). On the basis of the bonding interaction between Zr (IV) of the shell ZrHCF framework and phosphonate groups, the 5-phosphorylated ssDNA probes with a consecutive stretch of guanines as a spacer could be incorporated in ZrHCF MNPs easily. Thus, DNA-grafted ZrHCF MNPs could be simply obtained by magnetic separation. The prepared nanoelectrocatalyst was further used as signal nanoprobe for the ultrasensitive electrochemical DNA assay. Under optimal conditions, the proposed biosensor presents high sensitivity for detecting target DNA with a linear range from 1.0 fM to 1.0 nM and a low detection limit of 0.43 fM. Moreover, it exhibits good performance with excellent selectivity, high stability, and acceptable fabrication reproducibility.

Biosensing platform based on graphene oxide via self-assembly induced by synergic interactions

A novel self-assembled glucose biosensor based on graphene oxide (GO) was constructed by using 1-pyrenebutyric acid-N-hydroxysuccinimide ester (PANHS) as linking molecular. The stepwise self-assembly process was performed for PANHS anchoring in N,N-dimethylformamide (DMF) solvent and the further glucose oxidase (GOD) binding in aqueous solution, respectively. The molecular interactions and the morphologic properties were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electronic microscopy (FESEM), and atomic force microscopy (AFM). In addition, the quantitative loadings of anchored PANHS and GOD were well elucidated by surface plasmon resonance (SPR) measurements. The obtained novel glucose sensor exhibited satisfactory analytical performance to glucose: wide linear range (4.0×10(-6) to 4.4×10(-3) M), fast response (10s), high sensitivity (40.5±0.4 mA M(-1) cm(-2)), and low detection limit (2 μM, S/N=3). Furthermore, the biosensor exhibited excellent long-term stability and satisfactory reproducibility.

Ultrasensitive determination of hydrazine using a glassy carbon electrode modified with Pyrocatechol Violet electrodeposited on single walled carbon nanotubes

AbstractA glassy carbon electrode (GCE) was modified with pyrocatechol violet (PCV) that was electrodeposited on single walled carbon nanotubes (SWCNTs) via continuous cycling between 0 and 0.9xa0V (vs. SCE). The resulting electrode exhibits excellent electrocatalytic activity towards the oxidation of hydrazine at 0.3xa0V. The apparent surface coverage of the electrode is at least 24 times higher (2.7u2009×u200910−10xa0molxa0cm−2) than that obtained with a bare GCE (1.1u2009×u200910−11xa0molxa0cm−2). This is attributed to a remarkably strong synergistic effect between the acid-pretreated SWCNTs and the electrodeposited PCV coating. Response is fast (2xa0s) and sensitive (281xa0mAxa0M−1xa0cm−2). Other features include a wide linear range (150 nM to 0.4xa0mM) and a low detection limit (150 nM at an SNR of 3). The sensor has been successfully applied to the determination of hydrazine in water and cigarette samples with good accuracy and precision. In addition, the morphology and the wetting properties of the coating were studied by scanning electromicroscopy and contact angle measurements.n FigureA glassy carbon electrode (GCE) was modified with pyrocatechol violet (PCV) that was electrodeposited on single walled carbon nanotubes (SWCNTs). The resulting electrode exhibits excellent electrocatalytic activity towards the oxidation of hydrazine at 0.3xa0V with fast response, wide linear range and a low detection limit.

Br-PADAP embedded in cellulose acetate electrospun nanofibers: Colorimetric sensor strips for visual uranyl recognition

In this work, a new visual colorimetric strip based on cellulose acetate nanofiber mats modified by 2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol was successfully prepared via electrospinning technology. The prepared colorimetric strip showed high sensitivity towards UO22+ with the yellow-to-purple color change signal. Upon the optimal conditions of solution pH at 6.0 and response time for 80min, the detection limit for UO22+ can reach 50 ppb. Moreover, the strip also exhibited excellent anti-interference ability in the presence of other metal ions. In order to achieve the quantitative detection for UO22+, a color-differentiation map was established, which was prepared from converted H values. Finally, the strip was also used to detect UO22+ in the seawater and showed high sensitivity.

Enhanced Electrochemiluminescence of One-Dimensional Self-Assembled Porphyrin Hexagonal Nanoprisms

In this work, we synthesized the one-dimensional nanostructure of zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP) via a self-assembly technique. Using sodium dodecyl sulfate (SDS) as soft template, the self-assembled ZnTPyP (SA-ZnTPyP) had the morphology of hexagonal nanoprisms with a uniform size (diameter of 100 nm). The SA-ZnTPyP exhibited remarkably different spectral properties compared to those of the original ZnTPyP. The as-prepared SA-ZnTPyP was used to modify glassy carbon electrodes (GCE), and the electrochemiluminescence (ECL) behaviors of the SA-ZnTPyP/GCE were investigated. The hydrophilic carbon dots (C-dots) could efficiently prevent the dissolution of SA-ZnTPyP in DMF containing 0.1 mol L-1 TBAP and, simultaneously, could accelerate electron transfer. Therefore, the enhanced ECL was realized by C-dots/SA-ZnTPyP/GCE by using H2O2 as co-reactant. This amplification of ECL was further studied by ECL spectroscopies and cyclic voltammetry, and the corresponding mechanism was proposed.

Unusual Fe(CN)63–/4– Capture Induced by Synergic Effect of Electropolymeric Cationic Surfactant and Graphene: Characterization and Biosensing Application

Herein, a special microheterogeneous system for Fe(CN)6(3-/4-) capture was constructed based on graphene (GN) and the electropolymeric cationic surfactant, an amphiphilic pyrrole derivative, (11-pyrrolyl-1-yl-undecyl) triethylammonium tetrafluoroborate (A2). The morphology of the system was characterized by scanning electron microscope. The redox properties of the entrapped Fe(CN)6(3-/4-) were investigated by cyclic voltammetry and UV-visible spectrometry. The entrapped Fe(CN)6(3-/4-) exhibited highly electroactive with stable and symmetrical cyclic voltammetric signal. A dramatic negative shift in the half wave potential can be obtained due to the unusual Fe(CN)6(3-/4-) partitioning in in this microheterogeneous system based on poly(A2+GN). Finally, the entrapped Fe(CN)6(3-/4-) was applied in the construction of the enhanced biosensors to hydrogen peroxide and sulfide.