Forming microstructured alkanethiol self-assembled monolayers on gold by laser ablation

A process to form microstructured alkanethiol self-assembled monolayers (SAMs) on gold is described. It is well known that alkanethiols spontaneously form homogenous SAMs on gold surfaces. By means of laser ablation, the exposed areas of alkanethiol monolayers can be removed from the gold surface. Free gold is obtained which can react further with second and third thiols. By this technique, structured alkanethiol SAMs are obtained reliably and easily. In a rather narrow window of pulse intensities, in our example 120$hboxMW/cm^2pm hbox10%$from a frequency-doubled Nd : YVO$_4$laser with 6-ns pulsewidth operating at a repetition rate of 20 kHz, ablation of alkanethiol monolayers is obtained without causing any damage to the gold substrate. Examples are presented where lines down to 10$muhbox m$in width were laser ablated into an SAM formed either from a hydrophilic or a hydrophobic alkanethiol and filled with a monolayer of a second alkanethiol of opposite hydrophilicity. The patterned structures were examined by optical and fluorescence microscopy as well as by lateral force microscopy. The presented method enables the preparation of microstructured SAMs on gold and probably on a wide variety of other substrates.     

Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.     

Interaction control between endohedral metallofullerene and metal substrate by introducing alkanethiol self-assembled monolayer

The interaction control between endohedral metallofullerenes and a metal substrate has been demonstrated by introducing hexanethiol, octanethiol, and decanethiol self-assembled monolayers (SAMs) as the interlayer. We observe the electric properties of terbium endohedral metallofullerenes (Tb@C82) on alkanethiol SAMs with different chain lengths by scanning tunneling microscopy (STM) and spectroscopy (STS). Based on the comparison of the high-resolution STM images of a Tb@C82 molecule on hexanethiol and octanethiol SAMs, the interaction between Tb@C82 and a hexanethiol SAM is found to be larger than that between Tb@C82 and an octanethiol SAM; this is because at 68 K, the rotational states of Tb@C82 terminate only on the hexanethiol SAM. Furthermore, we find that the tunneling current-voltage characteristics of Tb@C82 on the hexanethiol SAM show the rectifying effects that are also caused by the molecular energy level shifts of Tb@C82 molecules due to the large interaction.     

Molecule counting with alkanethiol and DNA immobilized on gold microplates for extended gate FET

Several molecule counting methods based on electrochemical characterization of alkanethiol and thiolated single-stranded oligonucleotide (HS-ssDNA) immobilized on gold microplates, which were used as extended gates of field effect transistors (FETs), have been investigated in this paper. The surface density of alkanethiol and DNA monolayers on gold microplates were quantitatively evaluated from the reductive desorption charge by using cyclic voltammetry (CV) and fast CV (FCV) methods in strong alkali solution. Typically, the surface density of 6-hydroxy-1-hexanethiol (6-HHT) was evaluated to be 4.639 molecules/nm², and the 28 base-pair dsDNA about 1.226–4.849 molecules/100 nm² on Au microplates after post-treatment with 6-HHT. The behaviors on surface potential and capacitance of different aminoalkanethiols on Au microplates were measured in 0.1 mol/L Na₂SO₄ and 10 mmol/L Tris–HCl (pH = 7.4) solutions, indicating that the surface potential increases and the double-layer capacitance decreases with the length of carbon chain increased for the thiol monolayers, which obey a physics relationship for a capacitor. Comparably, a simple sensing method based on the electronic signals of biochemical reaction events on DNA immobilization and hybridization at the Au surface of the extended gate FET (EGFET) was developed, with which the surface density of the hybridized dsDNA on the gold surface of the EGFET was evaluated to be 1.36 molecules per 100 nm², showing that the EGFET is a promising sensing biochip for DNA molecule counting.     

最小二乘法拟合校准标准曲线火焰原子吸收法测定酱油中钠不确定度的评定

通过对测定酱油中钠含量的不确定度评定分析,找出引起不确定度产生的主要因素,评定确认由最小二乘法拟合校准标准曲线及测量重复性是影响结果的最主要因素,使用标准物质(标准储备液)及稀释过程引入的不确定度也应引起重视,此方法对类似的火焰原子吸收法测定样品中待测元素含量有借鉴和参考作用。     

Continuum-source atomic absorption spectroscopy with an echelle spectrometer adapted to a charge injection device

An instrumental system for continuum-source atomic absorption spectroscopy has been developed for simultaneous multielement determinations. The system consists of an electrothermal atomizer and a charge injection device adapted to an echelle spectrometer to achieve multiplex detection. A continuous 40-nm spectral range in the two-dimensional echelle spectrum was acquired simultaneously through the capability of the charge injection device to integrate signals in its MOS capacitors. Novel methods were developed to compute absorbances by "scanning" through all orders in the entire echelle spectrum or selecting absorption lines randomly. In the range 300-430 nm, characteristic concentrations (1% absorption) were 1.6, 2.6, 2.9, and 3.8 ng mL-1 respectively for Cu, Mn, and two Cr lines; these values are similar to those (1.3, 2.2, 1.2, and 3.6 ng mL-1) obtained for single-element detection with an image-dissector system.     

石墨炉原子吸收光谱法测定痕量金—测量方式对分析准确度的影响

本文报道了用不同厂家的仪器、不同种类的石墨管,不同测量方式对石墨炉原子吸收测定地球化学样品中痕量金分析准确度的影响,研究了其影响的主要原因。     

原子吸收光谱分析中干扰消除与校正进展

原子吸收光谱分析由于使用锐线光源,是一种选择性比较好的分析方法,但在实际工作中仍存在化学干扰和物理干扰,应采取适当措施予以消除。本文简要地介绍了原子吸收光谱分析中各类干扰的消除和化学计量学在原子吸收光谱分析中的应用情况。     

Attenuated total reflection surface-enhanced infrared absorption spectroscopy of carboxyl terminated self-assembled monolayers on gold

A new recipe for surface-enhanced infrared absorption (SEIRA) active island Au films with improved adhesion in aqueous solution, low resistivity, and enhancement of the infrared (IR) absorption of about 300 was developed. The Au films prepared were utilized in studies of the ionization of self-assembled monolayers of 11-mercaptoundecanoic acid in Na2SO4 aqueous solutions by attenuated total reflection surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy. It was found that the carboxyl end groups of the self-assembled monolayer turn into carboxylate anions on going from anodic to cathodic potentials or from acidic to alkaline pH. The water molecules close to the self-assembled monolayer in acidic solutions or at anodic potentials are preferentially aligned with their dipole moments parallel to the interface. This type of alignment can be ascribed to the dipole-dipole interaction between the carboxyl groups and the water molecules. On the other hand, in alkaline solutions or at cathodic potentials the structure of water close to the self-assembled monolayer is essentially bulk-like, with randomly oriented water molecules. This observation suggests that in alkaline solutions or at cathodic potentials the charge of the carboxylate anions is almost completely compensated for by strongly adsorbed counter cations. As a result, the electric field close to the surface of the ionized self-assembled monolayer is weak and has little influence on the orientation and hydrogen bonding of the water molecules.     

Electrothermal atomic absorption spectrometric determination of gold by vapor formation and in situ trapping in graphite tubes

Gold was determined in ore samples following generation, separation, collection on a graphite cuvette inner wall, and atomization of its volatile species formed by combining an acidified sample solution with an aqueous sodium tetrahydroborate solution at room temperature. A detection limit of 2.6 microg L(-1) (3sigma) was obtained with a 5.0 mL sample volume. Precision of replicate measurements was typically 10% RSD. The overall efficiency of the volatile species generation, transport, and trapping process was 0.4%. Atomization of gold from Pd, Ir, Cu, Ag, and W coated graphite cuvettes, following by trapping of the gaseous volatile gold species on these surfaces, has been investigated. Pd coating was found to decrease the sensitivity. Five microg of Ir, 20 microg of Cu, 20 microg of Ag, and 5 microg of W were chosen as optimum masses. W treatment was the best one for sensitivity enhancement, having an improvement factor of 2.4. Silanization of glass surfaces significantly decreased memory effects; improved peak shapes were thus obtained for flow injection vapor generation atomic absorption spectrometry (FI-VGAAS). The method described in this study was used for the determination of gold in an ore reference material, Gold Ore (MA-1b), Canadian Reference Materials Program.     

Colloidal gold filtrates as metal substrates for surface-enhanced infrared absorption spectroscopy.

A new method for obtaining surface-enhanced infrared absorption (SEIRA) spectra of antibodies and antibody/antigen complexes has been developed. Antibodies attached to colloidal gold particles and then collected by filtration onto porous polyethylene membranes show enhanced spectral bands at 1080 and 990 cm-1 regardless of the antibody specificity. Attachment of a model antigen, glucose oxidase, to its specific antibody/colloid complex prior to collection produces enhanced bands at 1540, 1395, and 1250 cm-1. Similarly, when the antigen Salmonella is attached to its specific antibody/colloid complex prior to collection, a new enhanced band is observed at 1015 cm-1. Similarities and differences of the SEIRA spectra obtained on gold colloid are compared to previous work on gold films.     

火焰原子吸收分光光度法测定碳素钢中铜含量的测量不确定度评定

对火焰原子吸收分光光度法测定碳素钢中铜含量的测量不确定度进行了分析,分析了测量不确定度的主要来源,并对各不确定度分量进行了评定,求得合成标准不确定度和扩展不确定度分别为0.00071%和0.0014%.     

火焰原子吸收光谱法测定浸渍液中钾、钙、铜、铁

提出了用空气-乙炔火焰原子吸收光谱法进行镉镍电池浸渍液中钾、钙、铜、铁含量的测定,介绍了钾、钙、铜、铁最佳测定条件及呈良好线性范围的浓度,同时对样品消化处理条件及在测定样品中的干扰因素进行了综合考虑。该方法具有很好的灵敏度和重现性,具有方法步骤简单、操作容易、干扰少等特点。测定样品钾、钙、铜、铁含量的相对标准偏差均小于1.0%。标准加入回收率均在97.0%~100.0%范围内。达到了实验室分析与质量的控制。适用于镉镍电池浸渍液中含有较多共同被测离子钾、钙、铜、铁的生产现场控制分析和样品系统分析。     

In-situ monitoring of alkanethiol self-assembled monolayer chemisorption with combined spectroscopic ellipsometry and quartz crystal microbalance techniques

Self-assembled monolayers (SAMs) formed via chemisorption are important for a variety of surface enhancement and biological applications. We demonstrate that combinatorial spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) provides dynamic, in-situ characterization of the chemisorption process. In agreement with other studies, we find there are two steps for 1-decanethiol, an example alkanethiol SAM, chemisorption onto gold, which are a brief, fast phase followed by one that is long but slower. By using both the optical (SE) and mechanical (QCM-D) techniques, we show that the SAM porosity decreases during the second phase as the coupled ethanol solvent in the disorganized layer is replaced by more alkanethiol.     

Three-photon electromagnetically induced absorption and transparency in an inhomogeneously broadened atomic vapour

We study both theoretically and experimentally three-photon electromagnetically induced transparency and electromagnetically induced absorption resonances in inhomogeneously broadened 85 Rb atomic vapour driven by probe and drive laser radiations. We observe narrow Doppler-free absorption as well as transmission resonances for the probe field when the driving laser field is redshifted from the D₁ or D₂ lines of ⁸⁵Rb; the frequency difference between the drive and probe fields is equal to the hyperfine splitting of the ground state of the atoms, and the probe field is tuned to the centre of the Doppler broadened atomic transition. We theoretically study the spectroscopic effect in both homogeneously and inhomogeneously broadened media. Our numerical simulations are in good agreement with the experimental results.     

Stripe domain analysis of alkanethiol and alkynethiol monolayers self-assembled on the surfaces of gold grains

The self-assembled monolayers (SAMs) of alkanethiols such as 1-dodecanethiol (DDT) on the surface of polycrystalline gold grain on quartz crystal microbalance (QCM) at room temperature and alkynethiols such as phenylethynyl thiol (PET) on the surface of Au(111)/mica under − 65 °C have been fabricated. A multimode scanning probe microscope (SPM) investigation for the first time reveals the formation of stripe domain of DDT SAMs together with roundish domain. This feature was not caused by an annealing treatment but might be induced by coexistence of a few different facets and reconstruction of the surface on the grain. The stripe domain of PET SAMs could also be found on the surface of the grain, which was within the substrate of the gold/mica. It shows that the feature of the stripe domain for organothiol monolayers self-assembled on gold grain surfaces possesses a certain generality. Furthermore, the arrangement of organothiol stripe domain can be well understood from the interpretation of the relationship between the stripe width and width direction, molecule interval distance, molecule length and tilt angles of the thiols.     

Detection of copper in water using on-line plasma-excited atomic absorption spectroscopy (AAS)

A measurement method and apparatus was developed to measure continuously toxic metal compounds in industrial water samples. The method was demonstrated by using copper as a sample metal. Water was injected into the sample line and subsequently into a nitrogen plasma jet, in which the samples comprising the metal compound dissolved in water were decomposed. The transmitted monochromatic light was detected and the absorbance caused by copper atoms was measured. The absorbance and metal concentration were used to calculate sensitivity and detection limits for the studied metal. The sensitivity, limit of detection, and quantification for copper were 0.45 ± 0.02, 0.25 ± 0.01, and 0.85 ± 0.04 ppm, respectively.