Changes In Electrochemical Signals Research Articles

Unique G4-nanowires-mediated switch-modulated electrochemical biosensing for sensitive detection of nickel ion and histidine

Herein, we reported a unique G4-nanowires-mediated switch-modulated electrochemical biosensing platform for sensitive nickel ion (Ni2+) and histidine (His) detection. The as-proposed electrochemical strategy got the utmost out of the peculiar characteristics including addressable and highly stable DNA-tetrahedron substrate; Terminal deoxynucleotidyl transferase (TdT)-generated stochastic G4-nanowires with unique peroxidase-mimic DNAzyme activity; freewheeling and interesting electrochemical switch modulated by Ni2+ and His. As expected, the direct effect of Ni2+ on the peroxidase-mimic DNAzyme activity of the G4-nanowires could be associated with the inhibition and decrease of the signal significantly. Moreover, the emerging His gave rise to a resurgence of electrochemical signal owing to the affinity between Ni2+ and His. In view of these, the proposed biosensor displayed a suitable detection limit of 0.15nM for Ni2+ or 1.2nM for His, respectively (S/N=3). More importantly, taking on Ni2+ and His as the model inputs, representative NOT, YES and IMPLICATION logic gates had been accomplished and outputted by readable electrochemical signal change. It is expected to that the unique G4-nanowires-based electrochemical assay hold huge potentials in applications including environmental monitoring, pharmaceutical analysis and clinical diagnosis.

Hierarchically porous Zr-MOFs labelled methylene blue as signal tags for electrochemical patulin aptasensor based on ZnO nano flower

In this work, the feasibility of a novel sensitive electrochemistry aptasensor for the detection of patulin (PAT) using hierarchically porous metal organic framework@methylene blue connection aptamer as signal tags was demonstrated. The substrate electrode of the aptasensor was prepared by electrodeposited gold nanoparticles (AuNPs) on chitosan-zinc oxide nano flower-modified electrode. Subsequently, the complementary single-stranded DNA was attached to the surface of the modified electrode by Au-S bond. Signal tags self-assemble on the surface of modified electrodes by aptamer-cDNA binding, while methylene blue as mediator for electrochemical detection. Thanks to the large specific surface area provided by zinc oxide nano flower, the electrode can load more signal tags and AuNPs to achieve signal amplification. In presence of PAT, Apt preferentially binds to PAT, causing dissociation of some Apt-cDNA and releasing some signal tags leading, resulting in decreased electrical signals. Under optimal conditions, the change in electrochemical signal was proportional to the logarithm of PAT concentration, from 5 × 10−8-5 × 10-1 μg mL−1, and the detection limit was estimated to be 1.46 × 10-8 μg mL-1. The aptasensor exhibited aceptable reproducibility, renewability, long-term stability and specificity. Moreover, aptasensor was reliable in determination of PAT in spiked apple juice samples.

Dual-signal aptamer sensor based on polydopamine-gold nanoparticles and exonuclease I for ultrasensitive malathion detection

A highly sensitive dual-signal aptamer sensor based on polydopamine-gold nanoparticles (PDA-AuNPs) and exonuclease I (Exo I) was developed for detection of malathion. Compared with traditional sensing elements, aptamer has many advantages, such as high affinity, superior specificity, strong stability and easy modification. The electrodeposition synthesis of PDA-AuNPs gave excellent biocompatibility and electrical conductivity on the sensor. With the addition of malathion, the specific interaction between malathion and its aptamer forced the aptamer to detach from the electrode surface and induced the capture probe to form a hairpin structure on the electrode surface. Exo I was added to motivate the autocatalytic target cycling which remarkably increased the current change of electrochemical signal over 2 times. Therefore, the promising strategy gave rise to an optional dual-signal current readout in both the signal-on of Fc and the signal-off of Tn. In this work, the prepared biosensor exhibited high sensitivity to malathion via the combination of dual-signal design and autocatalytic target cycling amplification. Under the optimized conditions, the proposed sensor showed a wide linear range from 0.5 to 600 ng/L malathion. It also exhibited excellent specificity, acceptable repeatability and good stability. The application of real samples obtained satisfactory recovery results, demonstrating a promising potential in food safety analysis.

Impedimetric aptasensor for kanamycin by using carbon nanotubes modified with MoSe2 nanoflowers and gold nanoparticles as signal amplifiers.

An aptamer based impedimetric method is described for the determination of kanamycin. A hydrothermal route was applied to synthesize molybdenum selenide nanoflowers (MoSe2) which are promising materials for use in sensing interfaces due to their high specific surface and excellent electrical conductivity. Carbon nanotubes were then decorated with the MoSe2 nanoflowers and gold nanoparticles (AuNP/CNT/MoSe2) and placed on a glassy carbon electrode to serve as a signal amplifier. An amino-terminal kanamycin-specific aptamer was covalently linked to carboxy groups of acid-oxidized CNTs on the electrode to act as the signalling probe. The various steps during the construction of the modified electrode were monitored by scanning electron microscopy, wavelength-dispersive and energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The change in electrochemical signal was quantified by electrochemical impedance spectroscopy, typically at a working voltage of 0.22V vs. Ag/AgCl. The calibration plot is linear in the 1 pM-0.1nM and 100nM-10μM kanamycin concentration range and has a 0.28 pM detection limit. The assay is outstandingly selective, sensitive, stable and reproducible. Graphical abstract ᅟ.

A label-free electrochemical biosensor for microRNAs detection based on DNA nanomaterial by coupling with Y-shaped DNA structure and non-linear hybridization chain reaction

DNA nanomaterials have been widely used in bioassays due to their promising properties for sensitive and specific detection of biomolecules. Herein, a label-free electrochemical method was developed for quantitative detection of microRNAs by integrating Y-shaped DNA (Y-DNA) structures with non-linear hybridization chain reaction (non-linear HCR). The Y-DNA structures consisting of three sequences (Y1, Y2 and Y3) serve as stable and specific probes for recognizing target miRNAs. In the presence of target miRNA, competitive hybridization occurs between miRNA and Y-DNA, resulting in the release of Y3 and the disintegration of the Y-DNA structure. The triggers, which were blocked by Y3 previously, were exposed and initiated the non-linear HCR. Remarkable electrochemical signal changes were produced after the isothermal amplification reaction. Therefore, the proposed biosensor achieved sensitive detection of microRNAs (miRNAs). Under optimal conditions, the limit of detection (LOD) was reduced to 0.3334 fM and linear range was from 1 fM to 10 pM. The special design of Y-DNA helped the biosensor obtain the ability to distinguish between single base mutations. What's more, this biosensor was capable of detecting miRNAs in clinical serum samples. We hope that this developed biosensor would provide a potential application for DNA nanomaterials in the field of microRNAs detection and inspire more interests in the development of DNA nanomaterial biosensors.

Competitive electrochemical platform for ultrasensitive cytosensing of liver cancer cells by using nanotetrahedra structure with rolling circle amplification

In this work, a competitive and label-free electrochemical platform was performed for the ultrasensitive cytosensing of liver cancer cells based on DNA nanotetrahedron (NTH) structure and rolling circle amplification (RCA) directed DNAzyme strategy. The multifunctional nanoprobes were fabricated through a DNA primer probe, carboxyfluorescein (FAM) functionalized TLS11a aptamer and horseradish peroxidase (HRP) immobilized on the surfaces of the platinum nanoparticles (PtNPs). Then the NTH-based complementary DNA (cDNA) probe, complementary to the TLS11a aptamer, was attached on a disposable screen-printed gold electrode (SPGE) for increasing the reactivity and accessibility with the prepared nanoprobes. Due to the primer probe and the circular probe with G-quadruplex sequences for RCA, it can lead to the formation of numerous G-quadruplex/hemin DNAzyme, thus generating a remarkable electrochemical response. When the target cells were present, the nanoprobes were released from the SPGE due to the specific recognition of TLS11a aptamers for HepG2 cells, resulting in the electrochemical signal changes. The cytosensor was ultrasensitive for HepG2 tumor cell detection with a detection limit of 3 cell per mL. Furthermore, this strategy was also demonstrated to be applicable for cancer cell imaging. In summary, this electrochemical cytosensor holds great potential for circulating tumor cell detection in the early cancer diagnose.

Following anticancer drug activity in cell lysates with DNA devices

There is a great need to track the selectivity of anticancer drug activity and to understand the mechanisms of associated biological activity. Here we focus our studies on the specific NQO1 bioactivatable drug, ß-lapachone, which is in several Phase I clinical trials to treat human non-small cell lung, pancreatic and breast cancers. Multi-electrode chips with electrochemically-active DNA monolayers are used to track anticancer drug activity in cellular lysates and correlate cell death activity with DNA damage. Cells were prepared from the triple-negative breast cancer (TNBC) cell line, MDA-MB-231 (231) to be proficient or deficient in expression of the NAD(P)H:quinone oxidoreductase 1 (NQO1) enzyme, which is overexpressed in most solid cancers and lacking in control healthy cells. Cells were lysed and added to chips, and the impact of β-lapachone (β-lap), an NQO1-dependent DNA-damaging drug, was tracked with DNA electrochemical signal changes arising from drug-induced DNA damage. Electrochemical DNA devices showed a 3.7-fold difference in the electrochemical responses in NQO1+ over NQO1− cell lysates, as well as 10–20-fold selectivity to catalase and dicoumarol controls that deactivate DNA damaging pathways. Concentration-dependence studies revealed that 1.4 µM β-lap correlated with the onset of cell death from viability assays and the midpoint of DNA damage on the chip, and 2.5 µM β-lap correlated with the midpoint of cell death and the saturation of DNA damage on the chip. Results indicate that these devices could inform therapeutic decisions for cancer treatment.

Graphene Oxide Signal Reporter Based Multifunctional Immunosensing Platform for Amperometric Profiling of Multiple Cytokines in Serum.

Cytokines are small proteins and form complicated cytokine networks to report the status of our health. Thus, accurate profiling and sensitive quantification of multiple cytokines is essential to have a comprehensive and accurate understanding of the complex physiological and pathological conditions in the body. In this study, we demonstrated a robust electrochemical immunosensor for the simultaneous detection of three cytokines IL-6, IL-1β, and TNF-α. First, graphene oxides (GO) were loaded with redox probes nile blue (NB), methyl blue (MB), and ferrocene (Fc), followed by covalent attachment of anti-cytokine antibodies for IL-6, IL-1β, and TNF-α, respectively, to obtain Ab2-GO-NB, Ab2-GO-MB, and Ab2-GO-Fc, acting as the signal reporters. The sensing interface was fabricated by attachment of mixed layers of 4-carboxylic phenyl and 4-aminophenyl phosphorylcholine (PPC) to glassy carbon surfaces. After that, the capture monoclonal antibody for IL-6, IL-1β, and TNF-α was modified to the carboxylic acid terminated sensing interface. And finally a sandwich assay was developed. The quantitative detection of three cytokines was achieved by observing the change in electrochemical signal from signal reporters Ab2-GO-NB, Ab2-GO-MB, and Ab2-GO-Fc. The designed system has been successfully used for detection of three cytokines (IL-6, IL-1β, and TNF-α) simultaneously with desirable performance in sensitivity, selectivity, and stability, and recovery of 93.6%-105.5% was achieved for determining cytokines spiked in the whole mouse serum.

Aptamer based electrochemical assay for protein kinase activity by coupling hybridization chain reaction

The present work reported a simple, lable-free and sensitive electrochemical method for the detection of protein kinase A (PKA) activity. This method was based on the specific recognition of aptamer and the aptamer-induced hybridization chain reaction (HCR) amplification strategy. The aptasensor was constructed by immobilizing capture probe on a gold electrode via an Au–S bond. When adenosine triphosphate (ATP) aptamer was introduced, its one terminus hybridized with capture probe and the other hybridized with the complementary region of an auxiliary probe, which other region triggered HCR between two hairpin DNA (H1 and H2) to form a long DNA concatamer. At last a large number of electroactive methyle blue (MB) molecules were assembled on the dsDNA concatamer, which generated a significantly amplified electrochemical signal. In the presence of ATP, the HCR would not be performed because the aptamer specifically bond to ATP and the electrochemical response would decrease. However, when ATP and PKA coexisted, the electrochemical response would recovery because that ATP had been translated into ADP by PKA. So the activity of PKA could be effectively monitored according to the change of electrochemical signal. Based on the HCR amplification strategy, the aptasensor showed a wide linear range (4 − 4 ×105 U L−1) and a low detection limit (1.5 U L−1) for the detection of PKA. Furthermore, the method was applied to study the inhibitory effect of H-89 on PKA activity. The developed aptasensor was also used to the analysis of drug-induced PKA activity in cell lysates, indicating the potential application of the developed method in the fields of clinical diagnostics and discovery of new targeted drugs.

A novel psychoanalytical approach: An electrochemical ligand-binding assay to screen antipsychotics

Schizophrenia treatment may see a paradigm shift due to development of new atypical antipsychotic drugs (APDs), with better tolerability due to more selective dopamine (DA) receptor blockade. Monitoring of these APD candidates in biological fluids is of great importance to reduce the development cost, to clarify the mechanism of action and ultimately to support the demonstration of efficacy of these molecules. Electrochemical approaches have attracted great attention for monitoring DA and APD levels but none of the methods developed so far aimed to screen APD candidates. Herein, by this work, we propose for the first time an electrochemical ligand-binding approach for antipsychotic drug screening where competitive binding of a novel APD and DA to a dopamine D3 receptor (D3R) was investigated by looking at electrochemical signals of DA and drug before and after D3R interaction. D3R peptide was incubated with DA and/or drug first and then changes in electrochemical oxidation signals of free DA and the drug was measured by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Circular Dichroism spectroscopy was used to investigate the secondary structure of the peptide upon binding with either drug and/or DA.

Electrochemical behavior of hemin binding with human centrin 3

The electrochemical responses of human centrin 3 (HsCen3) binding with hemin were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using glassy carbon electrodes (GCEs). In CV, the formal potential (E0′) of hemin with the addition of HsCen3 shifted from −0.51 to −0.36V (versus saturated calomel electrode, SCE), indicating that a new species of hemin-HsCen3 had formed. Upon binding with HsCen3, the redox current of hemin in CV and DPV decreased significantly. Based on their titration curves, the association constant of HsCen3 with hemin was obtained with a logK of approximately 4, which was consistent with that obtained from spectroscopy. Combining UV–Vis, fluorescence emission, and electrochemical methods, His100 located on the α-helix between the two domains of HsCen3 was identified as the ligand binding residue of hemin. The protein binding-induced change in electrochemical signal was thus used to construct the diffusion coefficient (D=1.43×10−7cm2/s), the charge-transfer coefficient (α=0.49), and electron transfer standard rate constant (ks=2.54×10−2s−1) in the presence or absence of HsCen3. The electrochemical investigation of hemin bound with HsCen3 may provide useful data for understanding the biological processes of calcium-binding protein.

Effect of a Dual Charge on the DNA-Conjugated Redox Probe on DNA Sensing by Short Hairpin Beacons Tethered to Gold Electrodes.

Charges of redox species can critically affect both the interfacial state of DNA and electrochemistry of DNA-conjugated redox labels and, as a result, the electroanalytical performance of those systems. Here, we show that the kinetics of electron transfer (ET) between the gold electrode and methylene blue (MB) label conjugated to a double-stranded (ds) DNA tethered to gold strongly depend on the charge of the MB molecule, and that affects the performance of genosensors exploiting MB-labeled hairpin DNA beacons. Positively charged MB binds to dsDNA via electrostatic and intercalative/groove binding, and this binding allows the DNA-mediated electrochemistry of MB intercalated into the duplex and, as a result, a complex mode of the electrochemical signal change upon hairpin hybridization to the target DNA, dominated by the "on-off" signal change mode at nanomolar levels of the analyzed DNA. When MB bears an additional carboxylic group, the negative charge provided by this group prevents intimate interactions between MB and DNA, and then the ET in duplexes is limited by the diffusion of the MB-conjugated dsDNA (the phenomenon first shown in Farjami , E. ; Clima , L. ; Gothelf , K. ; Ferapontova , E. E. Anal. Chem. 2011 , 83 , 1594 ) providing the robust "off-on" nanomolar DNA sensing. Those results can be extended to other intercalating redox probes and are of strategic importance for design and development of electrochemical hybridization sensors exploiting DNA nanoswitchable architectures.

Ultrasensitive electrochemical detection of miRNA-21 by using an iridium(III) complex as catalyst

The ultrasensitive electrochemical detection of miRNA-21 was realized by using a novel redox and catalytic “all-in-one” mechanism with an iridium(III) complex as a catalyst. To construct such a sensor, a capture probe (CP) was firstly immobilized onto the gold electrode surface. In the presence of miRNA-21, a sandwiched DNA complex could form between CP and a methylene blue (MB) labeled G-rich detection probe modified onto a gold nanoparticle (AuNP) surface (DP-AuNPs). Upon addition of K+, the structure of DP changed to a G-quadruplex. Then, the iridium(III) complex could selectively interact with the G-quadruplex, catalyzing the reduction of H2O2, which was accompanied by an electrochemical signal change using MB as an electron mediator. Under optimal conditions, the electrochemical signal of MB reduction peak was proportional to miRNA concentration in the range from 5.0 fM to 1.0 pM, with a detection limit of 1.6 fM. In addition, satisfactory results were obtained for miRNA-21 detection in human serum samples, indicating a potential application of the sensor for bioanalysis.

Immobilization-free electrochemical DNA detection with anthraquinone-labeled pyrrolidinyl peptide nucleic acid probe

Electrochemical detection provides a simple, rapid, sensitive and inexpensive method for DNA detection. In traditional electrochemical DNA biosensors, the probe is immobilized onto the electrode. Hybridization with the DNA target causes a change in electrochemical signal, either from the intrinsic signal of the probe/target or through a label or a redox indicator. The major drawback of this approach is the requirement for probe immobilization in a controlled fashion. In this research, we take the advantage of different electrostatic properties between PNA and DNA to develop an immobilization-free approach for highly sequence-specific electrochemical DNA sensing on a screen-printed carbon electrode (SPCE) using a square-wave voltammetric (SWV) technique. Anthraquinone-labeled pyrrolidinyl peptide nucleic acid (AQ-PNA) was employed as a probe together with an SPCE that was modified with a positively-charged polymer (poly quaternized-(dimethylamino-ethyl)methacrylate, PQDMAEMA). The electrostatic attraction between the negatively-charged PNA–DNA duplex and the positively-charged modified SPCE attributes to the higher signal of PNA–DNA duplex than that of the electrostatically neutral PNA probe, resulting in a signal change. The calibration curve of this proposed method exhibited a linear range between 0.35 and 50nM of DNA target with a limit of detection of 0.13nM (3SDblank/Slope). The sub-nanomolar detection limit together with a small sample volume required (20μL) allowed detection of <10fmol (<1ng) of DNA. With the high specificity of the pyrrolidinyl PNA probe used, excellent discrimination between complementary and various single-mismatched DNA targets was obtained. An application of this new platform for a sensitive and specific detection of isothermally-amplified shrimp's white spot syndrome virus (WSSV) DNA was successfully demonstrated.

In Situ Observation of Electrodeposition of Li on Pt and Ni Substrates in Organic Electrolyte

Li metal has attracted attention as a material of negative electrodes for rechargeable batteries, but has the problem of reversibility due to Li dendrite formation during charge-discharge cycles. The suppression of Li dendrite formation is essential for developing Li metal rechargeable batteries. The morphology of electrodeposited Li and the growth of Li dendrite have been studied extensively; however, the relationship between the growth of Li dendrite and the change of electrochemical signal is still unclear. To clarify this relationship, it is necessary to conduct in situ optical microscopic observation. To investigate the effect of current density on Li deposition morphology, potentiodynamic and galvanostatic polarization measurements were conducted. Pt and Ni substrates were mechanically polished with SiC paper through 1500 grit, and then polished down to 1 µm using diamond paste. The counter electrode was a Pt wire. The reference electrode was Li. 1 M LiPF6 EC:DMC(1:1 vol%) was used as the electrolyte. The electrode surface area was around 95mm2. The current density for the galvanostatic experiment was varied from 0.1 to 2.0 mA/cm2, and the electrochemical deposition of Li was performed at constant charge (3.6 C/cm2). Surface observations were conducted by an optical microscope and a laser microscope. All electrochemical measurements were carried out in a glove box filled with argon. Figure 1 shows the cathodic polarization curves of Pt and Ni substrate. The increases in cathodic current densities were observed at around 0 V(vs.Li/Li+), indicating that the electrodeposition of Li proceeded at the potential range less than 0 V. Figure 2 shows the laser microscope images of the electrode surfaces after the galvanostatic polarization measurements. The surface of Li deposited on Ni was smooth compared with that on Pt. In particular, non-uniform deposition was observed at 0.1 and 2.0 mA/cm2 on the Pt substrate. In the case of the Ni substrate, a more uniform deposition was observed at lower current density. Figure 1

Cyclic voltammetric studies of carbohydrate–protein interactions on gold surface

Abstract A simple electrochemical method for the determination of association constants between carbohydrates and carbohydrate-binding proteins using cyclic voltammetry (CV) is described. The binding of concanavalin A (Con A) and cholera toxin (CT) to their specific α-mannose and β-galactose derivatives self-assembled on gold electrodes is electrochemically monitored with a redox probe of K 3 Fe(CN) 6 /K 4 Fe(CN) 6 . Upon binding of the proteins to the carbohydrate-modified electrodes, the redox current in CV decreases. The binding-induced change in electrochemical signal is thus used to construct Langmuir adsorption isotherm for the carbohydrate–protein interactions and to obtain the association constants. The association constants of carbohydrate–protein interactions determined by CV ((5.8 ± 1.2) × 10 7 M − 1 for mannose–Con A, (2.6 ± 0.5) × 10 8 M − 1 for galactose-CT) were in good agreement with those measured with electrochemical impedance spectroscopy and quartz crystal microbalance.

A Simple, Fast, and Sensitive Assay for the Detection of DNA, Thrombin, and Adenosine Triphosphate Based on Dual-Hairpin DNA Structure

In the present study, based on multifunctional Dual-Hairpin DNA structure, a simple, fast and high sensitive assay for the detection of DNA, thrombin and adenosine triphosphate (ATP) was demonstrated. DNA sequence labeled with methylene blue (MB), which was designed as single-stranded DNA (ssDNA) matching with target DNA, thrombin, or ATP aptamer, hybridized to the adjunct probe and formed the dual-hairpin structure on the electrode. With the hybridization of adjunct probe and the hairpin-like capture probe in the stem region, the dual-hairpin was formed with outer and inner hairpins. By the conjugation of the target probe with the adjunct probe in the outer hairpin, the adjunct probe divorced from the dual-hairpin structure. The adjunct probe with signal molecules MB, attaching near or divorcing far from the electrode, produced electrochemical signal change and efficient electron transfer due to the fact that it was in proximity to the electrode. However, upon hybridization with the perfect match target, the redox label with the target probe was forced away from the modified electrode, thus resulting in the change of the Dual-Hairpin DNA conformation, which enables impedance of the efficient electron transfer of MB and, consequently, a detectable change of the electrochemical response. In addition, another highlight of this biosensor is its regenerability and stability owing to the merits of structure. Also, based on this Dual-Hairpin platform, the detection limits of DNA, thrombin, and ATP were 50 nM, 3 pM, and 30 nM, respectively. Moreover, this pattern also demonstrated excellent regenerability, reproducibility, and stability. Additionally, given to its ease-of-use, simplicity in design, easy operations, as well as regenerability and stability, the proposed approach may be applied as an excellent design prompter in the preparation of other molecular sensors.

Fluorescein-labeled “arch-like” DNA probes for electrochemical detection of DNA on gold nanoparticle-modified gold electrodes

In the present study, a gold nanoparticle-modified gold electrode (nanogold electrode) was used to develop a novel fluorescein electrochemical DNA biosensor based on a target-induced conformational change. The nanogold electrode was obtained by electrodepositing gold nanoparticles onto a bare gold electrode. This modification not only immobilized probe oligonucleotides, but also adsorbed fluorescein onto the surface of the gold nanoparticles to form an “arch-like” structure. This article compares the electrochemical signal changes caused by the hybridization of “arch-like” DNA on nanogold electrode and linear DNA on bare gold electrode. The results showed that the adsorption effect of nanogold can enhance the sensitivity of the sensor. The linear range of target ssDNA is from 2.0×10−9M to 2.0×10−8M with a correlation coefficient of 0.9956 and detection limit (3σ) of 7.10×10−10M. Additionally, the specificity and hybridization response of this simple sensor were investigated.

Direct assessment from cyclic voltammetry of size effect on the hydrogen sorption properties of Pd nanoparticle/carbon hybrids

The hydrogen sorption properties of palladium particles synthesized with different sizes (2, 6 and 18nm) dispersed on high surface area graphite powders are studied by both solid/gas and electrochemical methods. We demonstrate that we can directly evaluate by cyclic voltammetry the influence of the particle size on Pd hydride phase formation despite the ohmic losses and capacitive currents associated with powder electrodes. The size-dependent Pd hydride compositions calculated from electrochemical signals and pressure-composition-isotherms under ambient conditions are in good agreement and show the same trend: as the Pd particle size is reduced, the hydrogen content increases in the α phase and decreases in the β phase. Changes in electrochemical signals during cycling are observed when the potential domain covers the Pd oxide region, corresponding to an increase of the mean size of the smallest particles from 2 to ∼12nm (as confirmed by ex situ X-ray diffraction) whereas no modification occurs if it is restricted to the hydrogen region. This highlights that voltammograms can be used to readily detect in situ size modifications of Pd nanomaterials.

Cleavage of Metal-Ion-Induced DNAzymes Released from Nanolabels for Highly Sensitive and Specific Immunoassay

This work reports a novel electrochemical immunoassay protocol with signal amplification for determination of low-abundance protein (free prostate-specific antigen, PSA, used as a model) with high sensitivity and high selectivity by coupling metal sulfide (PbS)-based nanolabels with cleavage of the corresponding lead ion-induced DNAzymes. The assay mainly consists of an antigen-antibody immunoreaction with metal nanolabel in a transparent 96-well polystyrene microplate, the release of metal ions from the nanolabel, and cleavage of metal ion-induced DNAzyme. The signal is amplified by the labeled redox tag (ferrocene) on the DNAzyme-based sensor. In the presence of target analyte, the sandwiched immunocomplex can be formed between the primary antibody on the microplate and the corresponding metal sulfide nanolabel. The carried nanolabel can release numerous metal ions by acid, and induce the cleavage of the corresponding DNAzyme, thus resulting in the change of electrochemical signal. Under optimal conditions, the DNAzyme-based immunoassay presents an obvious electrochemical response for the detection of PSA, and allows detection of PSA at a concentration as low as 0.1 pg mL(-1). Intra-assay and interassay coefficients of variation (CV) were less than 9.5% and 10%, respectively. No significant differences at the 0.05 significance level were encountered in the analysis of 12 clinical serum specimens between the developed immunoassay and a commercially available enzyme-linked immunosorbent assay (ELISA).