电磁超声换能器新型线圈阻抗及匹配电容的计算

为提高电磁超声换能器(EMAT)的换能效率及信噪比,研究了EMAT线圈阻抗匹配的方法。考虑到检测材料属性、线圈提离以及线圈在高频激励下的集肤和邻近效应等因素会影响线圈的阻抗大小,线圈的分布电容也会对线圈的匹配产生影响,针对EMAT线圈的等效电路,采用有限元方法计算了不同提离情况下的线圈阻抗和分布电容,以此为基础,对线圈的匹配电容进行了计算,并通过实验验证了计算方法和结果的正确性。计算和实验结果表明,线圈电阻随提离增大而减小,线圈电感随提离增大而增大,线圈分布电容随提离增大而减小,变化规律均符合指数规律。     

Cancer biomarker detection in serum samples using surface plasmon resonance and quartz crystal microbalance sensors with nanoparticle signal amplification

Early detection of cancer is vital for the successful treatment of the disease. Hence, a rapid and sensitive diagnosis is essential before the cancer is spread out to the other body organs. Here we describe the development of a point-of-care immunosensor for the detection of the cancer biomarker (total prostate-specific antigen, tPSA) using surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) sensor platforms in human serum samples. K(D) of the antibody used toward PSA was calculated as 9.46 × 10(-10) M, indicating high affinity of the antibody used in developing the assay. By performing a sandwich assay using antibody-modified nanoparticles concentrations of 2.3 ng mL(-1) (Au, 20 nm) and 0.29 ng mL(-1) (8.5 pM) (Au, 40 nm) tPSA in 75% human serum were detected using the developed assay on an SPR sensor chip. The SPR sensor results were found to be comparable to that achieved using a QCM sensor platform, indicating that both systems can be applied for disease biomarkers screening. The clinical applicability of the developed immunoassay can therefore be successfully applied to patient's serum samples. This demonstrates the high potential of the developed sensor devices as platforms for clinical prostate cancer diagnosis and prognosis.     

Conductance oscillations in molecularly linked Au nanoparticle film-superconductor systems

Charge transport across a disordered normal-superconductor (DN-S) interface was studied using a macroscopic, molecularly linked Au nanoparticle film as the DN component. Low-temperature conductance versus voltage and magnetic field exhibit zero-bias and zero-field peaks, respectively. Importantly, the latter typically exhibit superimposed oscillations. Such oscillations are rarely seen in other DN-S systems and are remarkable given their robustness in these macroscopic films and interfaces. A number of observations indicate that conductance peaks and oscillations arise due to a 'reflectionless tunnelling' process. Scattering length scales extracted from the data using a reflectionless tunnelling picture are consistent with literature values. Factors resulting in the observation of oscillations in this system are discussed.     

Chemiluminescence immunoassay based on dual signal amplification strategy of Au/mesoporous silica and multienzyme functionalized mesoporous silica

A chemiluminescent dual signal amplification strategy for the determination of α-fetoprotein (AFP) was proposed based on a sandwich immunoassay format. Monoclonal antibody of AFP immobilized on the gold nanoparticles doped mesoporous SiO₂ (Au/SiO₂) were prepared and used as a primary antibody. Horseradish peroxidase (HRP) and HRP-labeled secondary antibody (Ab₂) co-immobilized into the mesoporous SiO₂ nanoparticles (HRP-Ab₂/SiO₂) were used as the labeled immunological probe. Due to the high ratio surface areas and pore volumes of the mesoporous SiO₂, not only the amount of AFP monoclonal antibody but also the amount of the modified HRP and Ab₂ in HRP-Ab₂/SiO₂ were largely increased. Thus the chemiluminescent signal was amplified by using the system of luminol and H₂O₂ under the catalysis of HRP. Under the optimal conditions, two linear ranges for AFP were obtained from 0.01 to 0.5 ng mL⁻¹ and 0.5 to 100 ng mL⁻¹ with a detection limit of 0.005 ng mL⁻¹ (3σ). The fabricated signal amplification strategy showed an excellent promise for sensitive detection of AFP and other tumor markers.     

An intein-mediated site-specific click conjugation strategy for improved tumor targeting of nanoparticle systems

The ability to modify and directly target nanoparticulate carriers has greatly increased their applicability in diagnostic and therapeutic studies. Generally essential to the targeting of nanoparticles is the bioconjugation of targeting ligands to the agent's surface. While bioconjugation techniques have steadily improved in recent years, the field is still plagued with inefficient conjugations reactions and/or the lack of site-specific coupling. To overcome these limitations, click chemistry and expressed protein ligation (EPL) are combined to produce a highly efficient, site-specific reaction. This new EPL-click conjugation strategy is applied to create superparamagnetic iron oxide nanoparticles (SPIO) labeled with HER2/neu affibodies. These HER2-SPIO nanoparticles prove to be highly potent and receptor-specific in both in vitro cell studies and murine tumor models. Moreover, when EPL-click-derived HER2-SPIO are compared with SPIO that had been labeled with HER2 affibodies using other popular bioconjugation methods, they produce a statistically significant improvement in contrast enhancement upon cell binding. The EPL-click system is also successfully extended to other nanoparticle platforms (i.e., liposomes and dendrimers) highlighting the versatility of the approach.     

Cation exchange in ZnSe nanocrystals for signal amplification in bioassays

ZnSe nanocrystals (NCs), possessing low native luminescence but high biocompatibility, were employed as labeling tags in bioassays. They were able to amplify each target recognition event thousands of times through a cation-exchange reaction (CXAmp) that released over 3000 encapsulated Zn(2+) from one single NC. The freed cations in turn triggered strong fluorescence from the Zn-responsive dyes. The present study demonstrated that CXAmp with ZnSe delivered superior detection performance in comparison to the conventional labeling methods. The overall fluorescence intensity of CXAmp using 5 nM ZnSe NCs was 30 times higher than that from 5 nM core-shell CdSe/ZnS quantum dots (QDs). The limit of detection (LOD) obtained with ZnSe-based CXAmp was 10-fold lower than with horseradish peroxidase (HRP) labeling, and the detection sensitivity, represented by the slope of the signal-versus-concentration curve, was 20-fold higher. When applied to detect immunoglobulin E (IgE) in a sandwich format, a LOD of 1 ng/mL was achieved. The highly sensitive CXAmp also allowed detection of the total IgE content in dilute human serum, in which the abundant matrix proteins exhibited less interference and more accurate quantification could be performed. Besides high signal amplification efficiency and good biocompatibility, CXAmp with ZnSe could be easily adapted to common laboratory settings and act as a universal labeling system for reliable detection of low-abundance targets.     

Metal nanoparticle deposition for TOF-SIMS signal enhancement of polymers

A novel technique for improved time-of-flight secondary ion mass spectra of polymer ions is presented. This technique is a simple preparatory method, which involves deposition of a submonolayer coverage of metal nanoparticles on the surface of a polymer sample enabling an overall increase in characteristic polymer ions. This procedure gives spectra with enhanced intensity, a larger number of characteristic polymer peaks, and peaks of higher mass. Both Au and Ag nanoparticles were employed to facilitate the ionization of the polymer characteristic secondary ions. Moreover, these experiments demonstrate that the nanoparticles allow localization of high-mass fragment ions during imaging experiments utilizing focused ion beams. In general, we show that the metal nanoparticle deposition method is effective for time-of-flight secondary ion mass spectrometry examination of polymers.     

Use of negative capacitance to provide voltage amplification for low power nanoscale devices

It is well-known that conventional field effect transistors (FETs) require a change in the channel potential of at least 60 mV at 300 K to effect a change in the current by a factor of 10, and this minimum subthreshold slope S puts a fundamental lower limit on the operating voltage and hence the power dissipation in standard FET-based switches. Here, we suggest that by replacing the standard insulator with a ferroelectric insulator of the right thickness it should be possible to implement a step-up voltage transformer that will amplify the gate voltage thus leading to values of S lower than 60 mV/decade and enabling low voltage/low power operation. The voltage transformer action can be understood intuitively as the result of an effective negative capacitance provided by the ferroelectric capacitor that arises from an internal positive feedback that in principle could be obtained from other microscopic mechanisms as well. Unlike other proposals to reduce S, this involves no change in the basic physics of the FET and thus does not affect its current drive or impose other restrictions.     

Electron and phonon transport in Au nanoparticle decorated graphene nanoplatelet nanostructured paper

Monodispersed Au nanoparticles are synthesized on the surface of exfoliated graphene nanoplatelets (GNP) in the presence of polyethyleneimine (PEI) with microwave assisted heating. A highly structured layered Au/GNP "paper" with good flexibility and mechanical robustness is prepared by vacuum assisted self-assembly. The thermal and electrical conductivity of the hybrid paper with and without the Au nanoparticles are investigated after different experimental processing conditions including thermal annealing and cold compaction. Annealing effectively decomposes and removes the adsorbed PEI molecules and improves thermal contact between Au/GNP particles, whereas cold compaction reduces porosity and induces stronger alignment of the Au/GNP within the hybrid paper. Both approaches lead to improvement in electrical and thermal conductivity. It is also found that adjacent GNP particles are electrically connected by the Au nanoparticles but thermally disconnected. It is believed that phonons are scattered at the Au/GNP interfaces, whereas electrons can tunnel across this interface, resulting in a separation of electron and phonon transport within this hybrid paper.     

Non-lithographic SERS substrates: tailoring surface chemistry for Au nanoparticle cluster assembly

Near‐field plasmonic coupling and local field enhancement in metal nanoarchitectures, such as arrangements of nanoparticle clusters, have application in many technologies from medical diagnostics, solar cells, to sensors. Although nanoparticle‐based cluster assemblies have exhibited signal enhancements in surface‐enhanced Raman scattering (SERS) sensors, it is challenging to achieve high reproducibility in SERS response using low‐cost fabrication methods. Here an innovative method is developed for fabricating self‐organized clusters of metal nanoparticles on diblock copolymer thin films as SERS‐active structures. Monodisperse, colloidal gold nanoparticles are attached via a crosslinking reaction on self‐organized chemically functionalized poly(methyl methacrylate) domains on polystyrene‐block‐poly(methyl methacrylate) templates. Thereby nanoparticle clusters with sub‐10‐nanometer interparticle spacing are achieved. Varying the molar concentration of functional chemical groups and crosslinking agent during the assembly process is found to affect the agglomeration of Au nanoparticles into clusters. Samples with a high surface coverage of nanoparticle cluster assemblies yield relative enhancement factors on the order of 10⁹ while simultaneously producing uniform signal enhancements in point‐to‐point measurements across each sample. High enhancement factors are associated with the narrow gap between nanoparticles assembled in clusters in full‐wave electromagnetic simulations. Reusability for small‐molecule detection is also demonstrated. Thus it is shown that the combination of high signal enhancement and reproducibility is achievable using a completely non‐lithographic fabrication process, thereby producing SERS substrates having high performance at low cost.     

Contact capacitance effect in measurement of a.c. impedance spectra for hydrating cement systems

An attempt is made to clarify an argument related to the utilization of a.c. impedance spectroscopy for hydrating cement systems. The question relates to which electrode configuration, 2-point, 3-point or 4-point measurement, is pertinent for impedance spectrum measurement. Theoretical analysis and experiment indicate that these electrode configurations should in principle give the same results. The impedance spectra from 3- or 4-point measurement are, however, strongly influenced by the contact areas between the specimen and potential sensors. This influence is attributed to the potential sensor-specimen contact capacitance effect. The experiment indicates that when contact capacitance, or area, between the specimen and potential sensor is small enough the impedance spectrum in the Nyquist plot is characterized by an almost perfect semi-circle and negligible high frequency offset resistance. These are the typical characteristics of the spectra obtained from 3- and 4-point measurements with point contact between the potential sensors and specimen. The 2-point and 4-point measurements give the same spectra when contact capacitance approaches a sufficiently large value. It is apparent that the impedance spectra from 3- and 4-point measurements with point contact cannot reflect true information about hydrating cement systems. They are experimental artifacts. The 2-point measurements, however, can give more reliable results.     

Inhibiting Au nanoparticle aggregation in freeze-thawing by presence of various additives

After freezing aqueous suspensions of gold nanoparticles (AuNPs) in the presence of various substances, the resulting aggregation of the nanoparticles was evaluated and the anti-aggregation effects of the different additives were compared. Many of the additives exhibited an anti-aggregation effects during freeze-thawing, the extent of which was greater at higher additive concentrations and the effects were 5 ~ 35% less than during the actual freeze-drying. Dextran and polyvinylpyrrolidone highly inhibited the aggregation even at markedly low additive concentrations (2 µg/mL). The use of a combination of a disaccharide (2 mg/mL of sucrose) and a sugar ester (20 µg/mL of sucrose palmitate) successfully preserved the redispersibility of the product after freeze-thawing while using each separately did not. Regarding the influence freezing and thawing conditions, a higher thawing temperature (from 4˚C to 60˚C) resulted in 10 ~ 20% better redispersibility of the AuNPs whereas the freezing temperature had no significant affect. The effect of freezing/thawing cycles of suspensions of AuNPs was also examined. The concentration of additive molecules on the surfaces of the frozen particles was monitored by In-situ Fourier transform IR spectroscopy. The collective findings of this study indicate that the additives essentially exert an anti-aggregation effect by slowing down the movement of the AuNPs.     

Charging effect in Au nanoparticle memory device with biomolecule binding mechanism

Organic memory device having gold nanoparticle (Au NPs) has been introduced in the structure of metal-pentacene-insulator-silicon (MPIS) capacitor device, where the Au NPs layer was formed by a new bonding method. Biomolecule binding mechanism between streptavidin and biotin was used as a strong binding method for the formation of monolayered Au NPs on polymeric dielectric of poly vinyl alcohol (PVA). The self-assembled Au NPs was functioned to show storages of charge in the MPIS device. The binding by streptavidin and biotin was confirmed by AFM and UV-VIS. The UV-VIS absorption of the Au NPs was varied at 515 nm and 525 nm depending on the coating of streptavidin. The AFM image showed no formation of multi-stacked layers of the streptavidin-capped Au NPs on biotin-NHS layer. Capacitance-voltage (C-V) performance of the memory device was measured to investigate the charging effect from Au NPs. In addition, charge retention by the Au NPs storage was tested to show 10,000 s in the C-V curve.     

Optical and morphological characterisation of a silver nanoparticle/fluorescent poly(phenylenethynylene) composite for optical biosensors

Thiol silver nanoparticles prepared by the phase transfer method have been mixed with a fluorescent poly(phenylenethynylene) sequenced with dithioester-diethylsulfide moieties in order to develop a nanocomposite for its possible application in optical biosensors for the detection and attack of fungi such as Paecilomyces variotii. Films have been prepared by dipping technique and characterized by AFM, XPS, UV-Visible and fluorescence spectroscopy. Optical Absorption properties of the nanocomposite are similar to those of the polymer with an absorption tail in the visible which supports the presence of silver nanoparticles. Despite the lack of fluorescence of the nanoparticles, the composite emits in the yellow green region and the intensity of the fluorescence of the nanocomposite film decreases after the immersion in the culture thus permitting the detection of the fungus by this technique. The fungus can be deposited on films of both the polymer and nanocomposite, nevertheless only in the latter case, an attack on mycelium is observed revealing the fungicidal effect of silver nanoparticles in the nanocomposite.     

Batch preparation of linear Au and Ag nanoparticle chains via wet chemistry

We present a simple, wet-chemical method for fabricating linear chains of Au and Ag nanoparticles by selectively etching alternating segments from striped metal nanowires. Nanowires composed of sacrificial Ni segments as well as Au and/or Ag segments were prepared by templated electrodeposition in the pores of alumina membranes. After removal from the membrane, wires were coated with SiO2, and selective etching revealed the nanoparticle chains. Extinction spectra are presented as a function of interparticle spacing.     

Comparative study of Ag and Au nanoparticles biosensors based on surface plasmon resonance phenomenon

The specific sensitivity of surface plasmon resonance to changes in the local environment of nanoparticles allows their use as platforms to probe chemical and biochemical binding events on their surfaces without any labeling [1], [2], [3], [4]. In this paper, we perform a comparative study of gold and silver nanoparticle based biosensors, prepared within the same conditions, in order to determine which metal seems the best for biological sensing. The prototypical biocytin–avidin interaction is used to study gradual changes over time and with avidin concentration in the absorption spectra bands of biocytinylated 10 nm silver and gold nanospheres. First, the Ag nanoparticles plasmon resonance absorbance signal is about 10 times larger than the Au one. Secondly, for an equivalent concentration of avidin, the optical property modifications are more pronounced for silver nanoparticles than for gold ones of the same geometry. These observations attest the superiority of Ag on Au nanoparticles when optical considerations are only taken into account. Finally, with both biosensors, the specificity of the interaction, checked by replacing avidin with bovine serum albumin, is relatively poor and needs to be improved.     

An Au nanoparticle/bisbipyridinium cyclophane-functionalized ion-sensitive field-effect transistor for the sensing of adrenaline

A film consisting of polyethyleneimine (PEI), Au nanoparticles (12 +/- 1 nm) and coadsorbed cyclobis(paraquat-p-phenylene) (1) was assembled as a sensing interface on the Al2O3 insulating layer of an ion-sensitive field-effect transistor (ISFET). Adrenaline (2) was sensed by the functionalized ISFET with a detection limit of 1 x 10(-6) M. The sensing ability of the nanostructured device for the analysis of adrenaline originates from the preconcentration of the analyte in the cyclophane by pi-pi donor-acceptor interactions. Analysis of adrenaline is accomplished by the measurement of the source-drain current, Isd, or by the gate-source voltage, Vgs. The sensing device is reusable (at least 100 cycles) and exhibits high stability.     

Functionalized periodic Au@MOFs nanoparticle arrays as biosensors for dual-channel detection through the complementary effect of SPR and diffraction peaks

A facile and low-cost method to prepare periodic Au@metal-organic framework (MOF) (MIL-100(Fe)) nanoparticle arrays was developed.The arrays were fabricated in situ using monolayer colloidal crystals as templates,followed by Au deposition on substrates,and annealing.MIL-100(Fe) coatings were applied on the nanospheres using a simple solvent thermal process.The prepared periodic Au@MIL-100(Fe) nanoparticle (NP) arrays were characterized by two peaks in the visible spectra.The first peak represented the surface plasmon resonance (SPR) of the Au nanospheres,and the other peak,or the diffraction peak,originated from the periodic structure in the NP array.After modification with 3-aminophenylboronic acid hemisulfate (PBA),the Au@MIL-100(Fe) NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity.These responses could be due to the strong interaction between PBA and glucose molecules.The diffraction peak was sensitive at low glucose concentrations (less than 12 mM),whereas the SPR peak rapidly responded at high concentrations.The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions.These results can be used to develop a dual-channel biosensor.We also created a standard diagram,which can be used to efficiently monitor blood glucose levels.The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100(Fe) NP arrays functionalized with different recognition agents.     

Ultrasensitive colorimetric DNA detection using a combination of rolling circle amplification and nicking endonuclease-assisted nanoparticle amplification (NEANA)

A combination of rolling circle amplification and nicking endonuclease-assisted nanoparticle amplification (NEANA) is used for the rapid, colorimetric detection of DNA. The integration of rolling circle amplification into the NEANA approach allows for detection of oligonucleotides with arbitrary sequences at ultralow concentrations.