Validation of the mass response of a quartz crystal microbalance coated with Prussian Blue film for ac electrogravimetry

Prussian Blue (PB) films have been considerably studied for many research applications such as electrochromic material development, new material for batteries, etc. Many analytical techniques were employed for examining PB electrochemical behaviour in solution and the quartz crystal microbalance (QCM) used in the alternative regime (ac electrogravimetry) appeared as an attractive in situ mass sensor due to its low cost and its high mass sensitivity. Unfortunately, the validity of the common Sauerbrey equation was questionable with these films or in other terms if the QCM was used as a pure mass sensor. In this work PB film is examined through acoustic measurements and the response can be interpreted as a pure mass change if the thickness is around 0.15 μm. Over this limit, film viscoelastic contributions can affect drastically the mass change estimation: if the thickness is two times larger, the mass error reaches 40%.     

Towards Syntheses and Structures of Heterometallic Clusters Containing Tantalum-tetrachalcogenato Building Blocks

An approach to tackle the synthesis of mixed-transition metal tantalum chalcogenide clusters is described. The synthesis of 1/_∞[Li₃(TaSe₄)(MeCN)₄]_∞ (1) will in future allow the construction of Ta–Se-transition metal clusters. The potential of this route was demonstrated by the synthesis of the mixed-metal Ta–S–Fe and Ta–S–Cu complexes (Et₄N)₃[Fe₂(SPh)₄(TaS₄)] (2) and [Cu₃(TaS₄)(PPh₃)₄] (3). Dedicated to Professor Günter Schmid on the occasion of his 70th birthday.     

In memoriam

Prof. Ing. Zdeněk Šolc, CSc (21 September 1931–30 September 2006) Prof. Zdeněk Šolc was born in 1931. After finishing his university studies, he joined the University of Pardubice where he remained for more than 50 years. He started to work at the Department of Physical Chemistry. His main fields of interest were: preparation of monocrystals, crystallization from solutions, measuring of physical and chemical properties of solutions. In the 1960's he turned to inorganic technology, studying inoranic pigments and he moved to the Department of Inorganic Technology. In this vast area of science, he achieved his greatest successes, and pigments became his ever-lasting passion up to the end of his life. The research in the field of crystallisation was oriented to development of liquid crystals for use in temperature indication, and materials for integrated circuits; besides that a school of inorganic pigments was formed (M. Trojan, Z. Šolc, D. Brandová) whose main orientation is mixed oxide materials for use in ceramics and enamels. A predominant part of the mentioned research activities was pursued at KAnT in 1990–1996, when the Department was headed by Professor Ing. Zdeněk Šolc. Most of Prof. ŠolcŠs projects were focused on the reactivity of inorganic pigments and powder materials, research of their high-temperature syntheses and rating of their physical and chemical properties. He applied mainly simultaneous thermal analytical techniques: thermogravimetry, differential thermal analysis using dynamic measuring conditions and quasi-isothermal and quasi-isobaric ones, moreover emanation thermal analysis and thermal conductivity measurements. Prof. Zdeněk Šolc was a creative scientist. He published more than 50 scientific papers in international journals and wrote 10 textbooks. He was the author of almost 100 lectures of conferences held in the Czech Republic and foreign countries. He had a silent but a very kind personality and he will be missed very much both by the local and the international communities. Requiescat in pace     

Bimetallic Cluster Provides a Higher Activity Electrocatalyst for Methanol Oxidation

The cluster complex Pt₂Ru₄(CO)₁₈ was used as a precursor to prepare a 60 wt% 1:2 Pt:Ru nanoparticles on carbon (PtRu/C) for use as an electrocatalyst for methanol oxidation. This bimetallic carbonyl cluster complex was found to provide smaller, more uniform bimetallic nanoparticle that exhibited higher electrocatalytic activity than a 60 wt% 1:1 Pt:Ru commercial catalyst from E-Tek. Using bimetallic cluster precursors simplifies the synthetic procedures by reducing the need for high temperature reduction and assures a more intimate mixing of the two different metals. Transmission electron microscopy (TEM) images of the catalyst obtained from the cluster precursor showed bimetallic nanoparticles having a narrow size range of 2–3 nm that were dispersed uniformly over the surface of the support. Images of the commercial catalyst showed particles 3–4 nm in diameter that tended to agglomerate near the edges of the carbon support particles. Cyclic voltammograms of methanol oxidation from the two catalysts showed significantly higher activity for the cluster-derived catalyst. The onset potential for methanol oxidation for the cluster-derived catalyst was approximately 170 mV lower than that of the commercial catalyst at 100 A/g Pt, and approximately 250 mV lower at 400 A/g Pt. ^* This report is dedicated to Prof. Günter Schmid on the occasion of his 70th birthday.     

Facile Synthesis of High Nuclearity Silver–Ferrocenyldiselenolate Clusters

1,1′-Bis(trimethylsilylseleno)ferrocene has been used to prepare the silver–ferrocenyldiselenolate clusters Ag₈(Se₂fc)₄(PnPr₃)₄ 1 and Ag₁₆(Se₂fc)₈(PPh₂Et)₆ 2 in good yield. The structures of the frameworks in 1 and 2 have been determined by single crystal X-ray diffraction analysis. This work is dedicated to Prof. Dr. Günter Schmid in celebration of the 70th anniversary of his birthday and in recognition of his pioneering and inspirational work in the arena of metal cluster chemistry.     

Extension of the measuring range of balances

The basic principle of comparing the sample mass with the mass of a reference body in equilibrium gives the equal-armed beam balance a unique accuracy. Main parameters characterising the suitability of the instrument are measuring range, resolution and relative sensitivity (resolution/maximum load). The historical development of the values of these parameters achieved depended strongly on the practical need in those times. Technically unfavourable scales of the oldest Egyptian dynasties (~3000 BC) could resolve mass differences of 1 g and had a relative sensitivity of at least 10^–3. More sophisticated instruments from the 18^th Dynasty (~1567–1320 BC) achieved a relative sensitivity of 10^–4 independent of the size of the instrument. In 350 BC Aristotle clarified the theory of the lever and at about 250 BC Archimedes used the balance for density determinations of solids. The masterpiece of a hydrological balance was Al Chazini’s 'Balance of Wisdom’ built about 1120. Its relative sensitivity was 2⋅10^–5. Real progress took place when scientists like Lavoisier (1743–1794) founded modern chemistry. At the end of the 19^th century metrological balances reached a relative sensitivity of 10^–9 with a maximum load of several kilogrammes. That seems to be the high end of sensitivity of the classical mechanical beam balance with knife edges. Improvements took place by electrodynamic compensation (Emich, Gast). In 1909 Ehrenhaft and Millikan could weigh particles of 10^–15 g by means of electrostatic suspension. In 1957 Sauerbrey invented the oscillating quartz crystal balance. By observing the frequency shift of oscillating carbon nanotubes or of silica nanorods, masses or mass changes in the attogram or zeptogram have been observed recently.     

QCM study of microbiological activity during long-term exposure to atmosphere—aluminium colonisation by <Emphasis Type="Italic">Aspergillus Niger</Emphasis>

The study demonstrated a possibility to sense the activity of microorganisms on metals in situ under atmosphere conditions using a quartz crystal microbalance (QCM) as a sensitive mass change detector. Other innovative aspects of the QCM application include long-term monitoring (over month), taking count of the influence of atmospheric pressure and application of Al-glued foil electrodes. The research subject was aluminium colonisation by Aspergillus niger Tiegh., a filamentous ascomycete fungus. The difference between the QCM data for abiotic and biotic samples reflected microbiological activity, which resulted in exponential mass gain during exposure. The increase in mass was due to various phenomena, i.e. development of biomass, secretion of metabolites, water uptake by the colony and microbially induced corrosion. The glued foil method demonstrated a possibility to expand the scope of the QCM studies from evaporated, sputtered or electroplated materials to those, from which thin foils may be produced. Dedicated to Professor Dr. Algirdas Vaškelis on the occasion of his 70th birthday.     

Use of polyclonal antibodies to ochratoxin A with a quartz–crystal microbalance for developing real-time mycotoxin piezoelectric immunosensors

A piezoelectric immunosensor was tested for ochratoxin A (OTA) mycotoxin detection through the immobilization of OTA–bovine serum albumin (OTA–BSA) conjugate on gold-coated quartz crystals (AT-cut/5 MHz). Immunoassays were performed in a flow-injection system through frequency decreases in a quartz–crystal microbalance (QCM) because of a mass increasing during immunoreaction with anti-OTA antibodies. Three immobilization procedures for OTA–BSA (direct adsorption and covalent attachment to two alkane thiol self-assembled monolayers) were characterized with QCM in real time. Covalent attachment of the OTA–BSA conjugates through gold nanoparticles was also tested for amplifying the signal. Binding of the excess of antibodies to the immobilized OTA in an indirect competitive analysis decreased linearly the resonant frequency in the range of the OTA concentration from 10 to 128 ng/mL, with a detection limit of 8 ng/mL (signal/noise ratio of 3). A pepsin 2 mg/mL (pH = 2.1) solution was used to release antigen–antibody complexes, regenerating the biorecognition surface.     

In memoriam Professor Zhen-Rong Lu (8 January 1946–5 January 2007)

Professor Zhen-Rong Lu, passed away on 5^th January 2007. Zhen-Rong Lu was born in Changshu in Jiangsu Province on 8^th January 1946. He received his B.Sc. in 1968 and M.Sc. in 1981 from Nanjing University. He worked for Suzhou Research Institute of Chemical Engineering (1968–1979); Department of Chemistry, Suzhou University (1981–1988); Department of Chemistry, The University of Melbourne, Australia (1988); Department of Chemistry, Monash University, Australia (1989); Testing and Analysis Center, Suzhou University, China (1990–2007). Main fields of interest have been: kinetics; relationship between thermal behavior and structure of complexes; crystal and molecular structure using thermal analysis and X-ray diffraction. He was awarded the third award of STA in 1995. Number of publications was 84 and the number of citations was 115. He was the writer of different chapters, i.e. Handbook of Thermal Analysis, Chapter 3–6, Published by John Wiley & Sons, Chichester 1998; Thermal Analysis Kinetics (in Chinese), Chapter 1, Science Press, Beijing 2001. Professional activities were: Member of the Chemical Thermodynamics and Thermal Analysis Committee (CTTA), Chinese Chemical Society (CCS) (1998–2007), Editorial Board of the Journal of Thermal Analyis and Calorimetry (2003–2007), Chairman of the Thermal Analysis Committee of Jiangsu Province (1991–2007), Chairman 3^rd Chinese Symposium on Thermoanalysis Kinetics and Thermokinetics Shihezi, China (2003). Professor Lu was a good and a cordial man always. He was extremely generous, always willing to see the positive side of life. He was a famous teacher and an outstanding researcher on a local and an international level as well. Besides his academic endeavors, he enjoyed his life spending quality time with his family and friends. We have suffered a great loss. We will miss him a lot as we have lost a true friend. May he rest in peace.     

Immunodetection by quartz crystal microbalance

Biodetection is one of the most important challenges for the twenty-first century: many fields are concerned, mainly environmental and medical. The quartz crystal microbalance (QCM) may offer great possibilities for this purpose: a direct response signal, which characterizes the binding event between a sensitive layer, immobilized onto the surface transducer, and the analyte to be detected, can be obtained. However, for the detection of small biomolecules such as antigens, it is quite difficult to obtain an observable signal that corresponds directly to the binding event. In general, this is owing to the lack of mass sensitivity of the commonly used QCM, with 5- to 10-MHz quartz crystals. For improving this mass sensitivity, a 27-MHz quartz resonator was developed and incorporated in a flow-through microcell. Two biospecies, IgG rabbit and peroxidase enzyme, were studied with this ultra-sensitive QCM in terms of specificity, detection limit, and calibration curve.     

Dual and tetraelectrode QCMs using imprinted polymers as receptors for ions and neutral analytes

Polymers as coating materials were combined with quartz crystal microbalances (QCMs) to design sensor devices for the detection of both ionic and neutral analytes in liquid phase. The design and geometry of dual and tetraelectrode QCMs have been optimized to reduce electric field interferences. An unusual Sauerbrey effect was observed while exposing potassium salt solution to 10- and 20-MHz QCMs, i.e. increase in the frequency shifts by a factor of seven, which is attributed to electro-acoustic phenomena. Non-functionalized sol-gel materials were synthesized by templating with hydrophobic salt such as tetraethyl ammonium picrate. Imprinting with these ions of low charge density leads to sensitive layers, and UV–Vis spectroscopy was used to check re-inclusion of this analyte. In the next strategy, functionalized polyurethane for potassium ions and sol-gel materials with aminopropyl group as ligand were generated to tune selectivity and sensitivity towards Ni²⁺ and Cu²⁺. Methacrylic acid polymers were optimized for the detection of atrazine by hydrogen bonding; double molecular imprinted polyurethane approach was followed for pyrene recognition. Finally, these imprinted polymers were combined with tetraelectrode QCM to develop sensor platform.     

Preparation of a sewage sludge laboratory quality control material for butyltin compounds and their determination by isotope-dilution mass spectrometry

The characterisation of a laboratory quality control material (QCM) for dibutyltin (DBT) and tributyltin (TBT) in sewage sludge is described. The reference values were determined by the use of two different types of isotope-dilution mass spectrometry: gas chromatography–mass spectrometry and gas chromatography–inductively coupled plasma mass spectrometry. To avoid possible analytical errors such as non-quantitative extraction and species degradation during sample preparation, different extraction methods were tested (microwave- and ultrasound-assisted extraction and mechanical stirring). The reference values were based on the unweighted means of results from the homogenisation and characterisation studies. The reference values obtained were 1,553 ± 87 and 534 ± 38 ng Sn g^-1 for DBT and TBT, respectively. In the uncertainty budget estimation, the sample inhomogeneity and between-method imprecision were taken into account. The concentrations of DBT and TBT in QCM are similar to those in the harbour sediment certified reference material PACS-2. Likewise, the levels of DBT and TBT are in the range of these compounds normally present in sewage sludge worldwide. In the future, the QCM will be used for an intercomparison study on DBT and TBT in sewage sludge, and as a day-to-day QCM during studies concerning the application of sewage sludge as an additive to artificial soil or as a raw material in civil engineering construction.     

Gravimetric measurement in redox polymer electrodes with the EQCM beyond the Sauerbrey limit

Gravimetric measurements during electrochemical redox switching of an Os-containing hydrogel film in contact with aqueous electrolyte have been obtained beyond the Sauerbrey rigid mass limit of the electrochemical quartz crystal microbalance (EQCM). For an acoustically non-rigid film the frequency-to-mass Sauerbrey relationship is not valid and the mass has been obtained from the experimental electroacoustic impedance data collected simultaneously with electrochemical experiments interpreted using Martin's viscoelastic model.     

Errors induced in quartz crystal mass uptake measurements by nongravimetric effects: Considerations beyond the EerNisse caution

We report frequency changes in AT‐cut quartz crystals for glassy polymers subsequent to temperature and carbon dioxide pressure changes. Anomalous frequency shifts are observed for the crystal subsequent to such changes. Since, the Sauerbrey equation has been applied routinely for mass uptake measurements in glassy polymers, using the quartz crystal microbalance fitted with AT‐cut quartz crystals, it is important that nongravimetric effects that impact the frequency change be well understood. In the present work, we provide a quantitative analysis of the breakdown of the Sauerbrey equation for viscoelastic materials by using the Johannsmann (Macromol Chem Phys 1999, 200, 501) treatment of the response of AT‐cut crystals. Clearly, there exist significant errors in mass uptake measurements for materials deposited on AT‐cut quartz crystals when precautions pertaining to film thickness and viscoelastic compliance are ignored. We show that while the early caution of EerNisse on stress effects in AT‐cut quartz crystals can be important in mass uptake measurements, for polymers, the major source of error arises from viscoelastic effects in the coating. We conclude that mass uptake measurements for films of compliant materials and polymers above their glass transition cannot be performed with accuracy, using AT‐cut quartz crystals if the results are not corrected for frequency shifts due to viscoelastic effects of the overlayer unless the films are extremely thin, that is, less than 100 nm. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 801–814, 2006     

Ruthenium Nanoparticles Intercalated in Hectorite: A Reusable Hydrogenation Catalyst for Benzene and Toluene

The cationic organometallic aqua complexes formed by hydrolysis of [(C₆H₆)RuCl₂]₂ in water, mainly [(C₆H₆)Ru(H₂O)₃]²⁺, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with molecular hydrogen (50 bar, 100°C) with decomposition of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9–18 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyses the hydrogenation of benzene and toluene in ethanol (50 bar H₂, 50°C), the turnover frequencies attaining 7000 catalytic cycles per hour. Dedicated to Professor Günter Schmid, pioneer of nanocluster chemistry, on the occasion of his 70th birthday     

Nobelpreise für Chemie und Medizin 1999

Ahmed H. Zewail, California Institute of Technology, Pasadena, USA, erhielt für seine Studien des Übergangszustands chemischer Reaktionen mit Hilfe der Femtosekundenspektroskopie”︁ den Nobelpreis für Chemie M99. Der Deutschamerikaner Günter Blobel ist für die von ihm entwickelte „Signalhypothese”︁ und den Nachweis, daß „Proteine eingebaute Signale besitzen, die ihren Transport und die Lokalisation in der Zelle steuern”︁, mit dem diesjährigen Nobelpreis für Medizin oder Physiologie ausgezeichnet worden.     

Quartz Crystal Microbalance for Selenite Sensing Based on Growth of Cadmium Selenite Crystals Immobilized on a Monolayer of Phosphorylated 11-Mercapto-1-Undecanol

 A quartz crystal microbalance (QCM) sensor for selenite ions in aqueous solution was constructed based on crystal formation of cadmium selenite, immobilized with a self-assembly monolayer (SAM) of phosphorylated 11-mercapto-1-undecanol (MUD) on a QCM gold electrode surface. The mass change caused by the selective adsorption of selenite ions on the cadmium selenite crystals at the solid/solution interface was detected by the QCM. The response (−ΔF) of the modified QCM oscillator increased with increasing selenite ion concentrations in sample solutions, ranging from 9.7×10⁻⁵ to 9.0×10⁻⁴ M at pH 7.4. The synthetic process of anchoring cadmium selenite crystals on the phosphorylated MUD organic film was also followed by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The atomic concentrations measured by XPS confirmed the crystal growth of cadmium selenite on the phosphorylated MUD SAM at the QCM gold electrode surface. From the AFM images, changes in surface topographic features were followed: the MUD SAM and phosphorylated MUD on the QCM gold electrode had similar surface roughness; however the difference for the cadmium selenite film on the phosphorylated MUD SAM was clearly seen. The observed QCM frequency change of the modified QCM oscillator per unit time was found to be proportional to the square of the supersaturation of cadmium selenite, indicating the crystal growth of cadmium selenite at the solid/solution interface. The modified QCM oscillator exhibited selectively strong QCM response to SeO₃ ²⁻ ion. In contrast, the responses to tested interfering anions were almost negligible. The order of anion selectivities of the present modified QCM sensor was SeO₃ ²⁻≫CO₃ ²⁻>SeO²⁻ ₄, SO₄ ²⁻, Br⁻, I⁻, NO₃ ⁻. These selectivities were basically attributable to the differences in solubility products and solubilities for the salts of each anion with cadmium (II) ion. Received May 12, 1998. Revision December 29, 1998.     

Glassy polymer‐sorption phenomena measured with a quartz crystal microbalance technique

The quartz crystal microbalance (QCM) method is applied to the measurement of CO₂ sorption in glassy poly(ethylene terephthalate) (PET), poly(methyl methacrylate), and polysulfone. Polymer thin films in the thickness range of 350–550 nm are prepared by spin‐casting onto the quartz crystal devices. Sorption isotherms at temperatures below the glass transition are analyzed with the dual‐mode sorption model. As‐cast, quenched, and slow‐cooled thermal‐conditioning protocols yield consistent trends in the sorption level, namely, as‐cast > quenched > slow‐cooled. The sorption levels and model results for the quenched‐conditioned samples measured with QCM compare favorably with those reported from the pressure‐decay and gravimetric methods on thick films. With extended analysis of PET, the QCM technique is also useful for the exploration of the temperature dependence associated with gas sorption in glassy polymer systems. Measured heats of sorption and the collapse of the Langmuir component near the PET glass‐transition temperature agree with those reported previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2109–2118, 2003     

Adsorption of bovine serum albumin onto poly(methyl methacrylate) stereocomplex films with a molecularly regulated nanostructure

Stereoregular poly(methyl methacrylate)s (PMMAs) were stepwise assembled on a quartz crystal microbalance (QCM) substrate after the immersion of the QCM into alternating acetonitrile solutions at ambient temperature. A quantitative QCM analysis at each step showed stereocomplex formation on the substrate surface. The adsorption of bovine serum albumin (BSA) onto stereocomplex films with a molecularly regulated nanostructure was analyzed quantitatively. The adsorption constant and the maximum adsorption amount, calculated by the assumption of Langmuir‐type adsorption, showed that BSA adsorbed with a relatively weak interaction onto the stereocomplex films. The BSA adsorption onto the stereocomplex films occurred in an end‐on manner, with a smaller adsorption constant than for that onto individual spin‐coated films. The amount of BSA adsorbed was significantly affected by the molecular weight of syndiotactic PMMA. Attenuated total reflection spectra indicated that BSA adsorbed onto the films with or without denaturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1807–1812, 2003