Fast Response Oxygen Micro-Optodes Based on Novel Soluble Ormosil Glasses

 A new type of phenyl substituted ormosils as a matrix for oxygen-sensitive micro-optodes is described. The new ormosils combine features of classical polymers such as solubility in organic solvents and those of sol–gel glasses such as mechanical stability and a porous structure. They make possible a simple and fast fabrication of microsensors with reproducible properties. The influence of the conditions during the polymerisation process (precursor composition and thermal treatment) on the sensing properties has been studied in detail. Oxygen-sensitive films with ruthenium(II)–tris-(4,7-diphenyl-1,10-phenanthroline) and platinum(II)–octaethylporphyrin as indicators were characterised with respect to their mechanical and photophysical properties. Photostability, oxygen sensitivity, response behaviour and signal intensities of the sensing films and the micro-optodes were examined. Micro-optodes based on the new sensing materials are fast responding, photostable and can be produced with a sufficient batch to batch reproducibility. Compared to previously described oxygen micro-optodes, where polystyrene was used as immobilisation matrix, the new sensors can be autoclaved and show favourable properties such as a faster response and a higher sensitivity. They possess many potential applications in medical and biological research. Received June 12, 1998. Revision December 10, 1998.     

Portable Fibre Optic Oxygen Sensor Based on Room-Temperature Phosphor escence Lifetime

 A portable fibre optic instrument for oxygen sensing based on luminescence lifetime is presented. The instrument is based on measurement of the quenching by oxygen of the room temperature phosphorescence (RTP) emitted by aluminium tris(8-hydroxy-7-iodo-5-quinolinesulfonic acid) chelate incorporated in an inorganic matrix by sol–gel technology. The comparatively long RTP lifetime of this sensing material (450 μs) and the large singlet–triplet splitting (λ_exc 390 nm, λ_em 590 nm) allow the use of simple opto-electronic circuits and low-cost processing electronics. Standard electronic components have been applied in development of the low-cost lifetime-measurement instrumentation presented here. Two optical sensor configurations, “flow-through cell” and “probe”, have been designed and evaluated for the determination of very low levels of oxygen, in gaseous argon streams and in waters. The basic technology, design parameters and performance characteristics of the optical sensors are discussed. Applications to determination of dissolved oxygen in river, tap and sewage waters are described. The advantages of luminescence lifetime measurements over conventional RTP intensity measurements for oxygen sensing are discussed. Received April 1, 1999. Revision November 4, 1999.     

FT-Raman-Spectroscopic Study on the Luminescence of Synthetic and Mineral Apatites

 Strong luminescence bands can be present in NIR-excited FT-Raman spectra of certain inorganic materials like hydroxyapatite. Since the origin of these emissions exclusively occurring on NIR-excitation is still unclear, a variety of synthetic and mineral apatites and related calcium salts was studied by means of Stokes and anti-Stokes FT-Raman spectroscopy, X-ray diffraction, and geochemical analyses. The results indicate that the occurrence of the luminescence is in some way related to foreign ion contents. However, a direct correlation to a specific ion could not be found on the basis of available data.     

A Fiber Optode for p-Nitrophenol Based on Covalently Bound 9-Allylaminoacridine

 Using 9-allylaminoacridine synthesized in this laboratory as the fluorescent agent an fiber optode for p-nitrophenol (p-Np) has been prepared. 9-Allylaminoacridine has a polymerizable olefin unit and can be copolymerized with hydrophilic monomer 2-hydroxypropyl methacrylate (HPMA) under UV irradiation. On silanized activated glass surface a 9-allylaminoacridine containing HPMA membrane has been covalently bound forming a stable optode membrane free of leaching problem. The analytical performance characteristics including reversibility, reproducibility, short-term stability and interference have been evaluated. The optode has relatively long lifetime with the spectral response characteristics not changing after one month use. The plot of log(I ₀/I − 1) versus logarithm of the p-NP solution concentration can piecewise be fitted with the straight line of the form of Stern-Volmer equation, with a detection limit of 9.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation obtained from eight separate determinations for two p-NP concentrations, 1.0 × 10⁻⁵ and 4.0 × 10⁻⁴ mol L⁻¹, are 2.36% and 1.34%, respectively. p-Np can be determined in water samples with satisfactory recoveries. Received April 13, 2000. Revision September 28, 2000.     

A Novel Ion-Selective Sensor for Procaine Hydrochloride Based on a Piezoelectric Quartz Crystal Coated with a Procaine Tetraphenylborate PVC Membrane

 A novel ion-selective sensor for procaine hydrochloride has been proposed and applied successfully to analysis of pharmaceutical preparations. The sensor is based on modification of the Ag-electrode of an AT-cut piezoelectric quartz crystal with a PVC membrane containing procaine tetraphenylborate. A linear relation between the logarithm of the response frequency and the logarithm of the procaine hydrochloride concentration was found experimentally and could be explained by combination of a modified Sauerbrey equation and the Freundlich isotherm. The detection range was from 8.3 × 10⁻⁸ to 5.0 × 10⁻³ M with a detection limit of 8.3 × 10⁻⁸ M. The selectivity of the sensor and the influence of experimental parameters such as solution pH and detection time were investigated. Received February 10, 1999. Revision October 10, 1999.     

基于荧光寿命机理的光纤温度传感器研究

为了实现恶劣环境下温度的测量,设计了一种基于荧光寿命机理的光纤温度传感系统.温度传感系统选用415 nm LED作为光源,以稀土荧光材料Y2O2S:Eu作为温度敏感材料,通过探测放大器和信号采集模块测量了敏感材料的荧光寿命,并由荧光寿命与温度的单调关系最终实现了温度的测量.采用油浴加热的方法进行温度实验,实验结果表明,温度传感系统在25~80℃实现了温度的测量,分辨率为0.5℃.     

Localized Visualization of Chemical Cross-Talk in Microsensor Arrays by Using Scanning Electrochemical Microscopy

 An investigation of an array of four Pt microband electrodes 25 μm wide and spaced 25 μm apart was performed with the scanning electrochemical microscope (SECM). Where possible the SECM measurements were confirmed with conventional electrochemical measurements. It is shown how the sensiti- vity of the SECM recycling current to the activity of the underlying surface can be used to probe the homogeneity of enzyme-modified microelectrodes. The diffusion of H₂O₂ between these micro enzyme- electrodes and unmodified electrodes was investigated and it was demonstrated how the SECM can be a powerful tool in the elucidation of the properties of these electrodes. Received June 8, 1998. Revision November 12, 1998.     

Optical Sensor Arrays Based on Microtiterplate Dimensions

 Multi-analyte and multi-sample sensing requires highly parallel analysis. This paper compares biomolecular interaction analysis based on direct optical detection, with microtiterplate-based assays using labelled reagents. Depending on the method and the application, assays in either a homogeneous or a heterogeneous phase are possible. Their feasibility in different applications is discussed. Two approaches with highly parallel detection devices are demonstrated in the area of environmental analysis as well as in high-throughput screening of drugs. An outlook on the limits of detection using affinity reactions is given. First results of the transfer to nanotiterplates are presented. Received July 14, 1998. Revision November 10, 1998.     

Ultrasensitive Biosensing Platform Based on the Luminescence Quenching Ability of Plasmonic Palladium Nanoparticles

An ultrasensitive biosensing platform for DNA and protein detection is constructed based on the luminescence quenching ability of plasmonic palladium nanoparticles (PdNPs). By growing the particles into large sizes (ca. 30 nm), the plasmonic light absorption of PdNPs is broadened and extended to the visible range with extinction coefficients as high as 10⁹ L mol^?1 cm^?1, enabling complete quenching of fluorescent dyes that emit at diverse ranges and that are tagged to bioprobes. Meanwhile the nonspecific quenching of the dyes (not bound to probes) is negligible, leading to extremely low background signal. Utilizing the affinity of PdNPs towards bioprobes, such as single‐stranded (ss) DNA and polypeptide molecules, which is mainly assigned to the coordination interaction, nucleic acid assays with a quantification limit of 3 pM target DNA and protein assay are achieved with a simple mix‐and‐detect strategy based on the luminescence quenching‐and‐recovery protocol. This is the first demonstration of biosensing employing plasmonic absorption of nanopalladium, which offers pronounced sensing performances and can be reasonably expected for wide applications.     

A Bulk Acoustic Wave Viscosity Sensor for Determination of Lysozyme Based on Lysis of Micrococcus Lysodeikeicus

 A method for determination of lysozyme with a Bulk Acoustic Wave (BAW) viscosity sensor is presented. It is based on the bacteriolytic action of lysozyme on Micrococcus lysodeikeicus (M. lysodeikeicus) and the response of the sensor to the viscosity and density change of this process. There was a good correlation between the frequency shift and the concentration of lysozyme in the range 10–100 μg/ml. The content of lysozyme in human saliva was determined by this method and the results obtained were in good agreement with those from the conventional turbidimetric method. This method has an advantage over the conventional turbidimetric method in that the amount of sample needed is smaller, the procedure is simpler and the concentration range of the bacterium suspension which can be used in the detection was extended. Received September 11, 1998. Revision March 15, 1999.     

A Subnanosecond Time-Resolved Fluorescence Lifetime Spectrometer Applying Laser Diodes

Summary.  Since the first application of laser diodes (LD) for the determination of fluorescence lifetimes in our group in 1995, great technical improvements have been made to increase the time resolution of the apparatus. Using the phase fluorometric method, measurements down to 100 ps are now possible. Values can be measured in steps of 10 ps with good reproducibility using a high-frequency signal generator and a GHz digital storage oscilloscope. No additional optical equipment is necessary for this new method. Following an easy calibration procedure, results are available within one minute without any adjustments. The components of the new apparatus including light source, sample chamber for standard fluorescence cuvettes, and detection unit are situated in a 12 × 13 × 9 cm setup. The apparatus was tested with different fluorophores, and the results correlate very well with known values in the range of 0.1 to 1000 ns. Received February 16, 2000. Accepted March 13, 2000     

基于发光共振能量转移的比率型上转换荧光纳米探针检测次硝酸

次硝酸（Nitroxyl,HNO）由一氧化氮（NO）经单电子还原和质子化作用产生,在生理和病理过程中都有着重要作用.本工作构建了一种基于发光共振能量转移（Luminescence resonance energy transfer,LRET）的比率型上转换纳米探针用于检测生物体系中HNO含量.该探针以上转换纳米颗粒（Upconversion nanoparticles,UCNPs）为能量供体,有机染料Fl-TP为能量受体构建.Fl-TP能特异性识别HNO并与之反应生成Fl-HNO,Fl-HNO在400～500 nm处具有明显的吸收峰,与UCNPs的蓝色发射光谱重叠,从而发生LRET过程.随着HNO浓度增加,Fl-HNO的荧光强度（F_{525 nm}）逐渐增强,UCNPs的荧光强度（F_{480 nm}）逐渐下降,比率信号（F_{525 nm}/F_{480 nm}）逐渐增加,并与HNO浓度对数呈良好的线性关系,该探针的线性检测范围为3～100 μmol·L^－1,检出限23.4 nmol·L^－1.实验结果表明该比率探针特异性强,灵敏度高,并可成功实现在活细胞和生物组织中HNO的检测.     

Luminescence in Organic Silicons Prepared from Organic Precursors in Plasma Discharges

Summary.  The photoluminescence of plasma-prepared polysilanes during the change from linear 1D Si chains to an amorphous 3D Si network was studied. The excitonic absorption band with a maximum at 353 nm in 1D Si experiences a blue shift and broadening upon introduction of branching and networking defects. With the gradual transition from 1D to 3D structure, an extensive redistribution of oscillator intensity along the absorption edge, accompanied by a decrease of the resolution of the σ-σ^* band, was observed. In the short wavelength region of the excitation spectra there is an enormous increase of excitonic emission at 328 nm. This effect is tentatively attributed to the excitation of the phenyl group or to the phenyl-silicon bond as confirmed by effusion spectra of the phenyl species. Received July 10, 2000. Accepted (revised) September 8, 2000     

Luminescence and energy transfer of Ce~(3+) and Dy~(3+) in BaLaB_9O_(16)

Under the excitation of UV light, the composition dependence of luminescence properties of Ce3+ and Dy3+ in BaLaB9O16 has been studied. The mechanisms of energy transfer from Ce3+ to Dy3+ and of concentration quenching of Dy3+ emission under the excitation of UV light have been presented as well.     

Utility of Certain σ and π-Acceptors for the Spectrophotometric Determination of Sildenafil Citrate (Viagra)

 The molecular interaction between sildenafil citrate as electron donor and each of iodine; 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); tetracyanoethylene (TCNE); 2,4,7-trinitro-9-fluorenon (TNF); chloranilic acid (CLA); chloranil (CL) and bromanil (BL) as acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Beer’s law was obeyed in a concentration limit of 10–260 μg/mL for sildenafil citrate. For more accurate analysis, Ringbom optimum concentration range was found to be between 20–240 μg/mL. The limits of detection and determination were calculated and found to be 1.5 and 5.2 μg/mL, respectively. The standard deviations were calculated for different concentrations of sildenafil citrate using various acceptors. A Job’s plot of the absorbance versus the molar ratio of the sildenafil citrate to each of acceptors under consideration indicated (1:1) ratio. The proposed methods were found to be rapid, accurate, precise and sensitive and could be applied for determination of sildenafil citrate in pharmaceutical dosage forms (Viagra) without interferences from common additives encountered. Received August 30, 2000. Revision January 5, 2001.     

Ion-Channel – Mimetic Sensors Based on Self-Assembled Monolayers of Phosphate Esters: High Selectivity for Trivalent Cations

 Gold electrodes were chemically modified with a phosphate ester monolayer designed to mimic biological ion-channel membranes. Cyclic voltammograms of Fe(CN)₆ ³⁻ as electroactive marker were measured in the presence of various types of analyte cations. Whereas in the absence of analyte cations the marker reduction was hindered by electrostatic repulsion between the marker anions and phosphate groups of the receptor monolayer, binding of di-and trications to the monolayer resulted in large increases of the reduction current. Trivalent cations could be detected down to the submicromolar concentration range with excellent selectivities over alkali metal ions. Also divalent cations were well discriminated and similar responses as to trivalent cations were only observed if their concentration exceeded that of the trivalent cations by about two orders of magnitudes. Received August 24, 1998. Revision March 10, 1999.     

Chemfet Based Microsensors Covered with Ion-Partitioning Polymeric Membranes

 The development of a new type of microsensors based on chemically sensitive field-effect transistors (CHEMFETs) covered with polymeric bulk ion-partitioning membranes is presented. For the construction of the microsensor, a PVC plasticized membrane containing two ionophores, one selective to protons and the other to the analyte cation of interest, is placed on the gate of a pH sensitive field-effect transistor which acts as the transducer. With the use of thin (5–10 μm) ion-partitioning membranes onto the pH-sensitive ISFET gate, the proton displacement out of the membrane and to the pH sensitive gate is fast and reversible. This displacement generates a signal that is directly related to the analyte concentration found in the test solution. Comparing the performance of CHEMFETs and ISEs selective to the monovalent potassium cation and the divalent calcium ion validates this novel CHEMFET response mechanism.     

A theoretical study of photoinduced electron transfer between tetracyanoethylene and arene

 Ab initio calculations have been performed to investigate the state transition in photoinduced electron transfer reactions between tetracyanoethylene and biphenyl as well as naphthalene. Face-to-face conformations of electron donor–acceptor (EDA) complexes were selected for this purpose. The geometries of the EDA complexes were determined by using the isolated optimized geometries of the donor and the acceptor to search for the maximum stabilization energy along the center-to-center distance. The correction of interaction energies for basis set superposition error was considered by using counterpoise methods. The ground and excited states of the EDA complexes were optimized with complete-active-space self-consistent-field calculations. The theoretical study of the ground state and excited states of the EDA complex in this work reveals that the S₁ and S₂ states of the EDA complexes are charge–transfer (CT) excited states, and CT absorption which corresponds to the S₀→S₁ and S₀→S₂ transitions arise from π−π^* excitation. On the basis of an Onsager model, CT absorption in dichloromethane was investigated by considering the solvent reorganization energy. Detailed discussions on the excited state and on the CT absorptions were made. Received: 30 April 2001 / Accepted: 18 October 2001 / Published online: 9 January 2002     

Luminescence Resonance Energy Transfer Sensors Based on the Assemblies of Oppositely Charged Lanthanide/Gold Nanoparticles in Aqueous Solution

This work demonstrates luminescence resonance energy transfer (LRET) sensors based on lanthanide‐doped nanoparticles as donors (D) and gold nanoparticles as acceptors (A), combined through electrostatic interactions between the oppositely charged nanoparticles. Negatively charged lanthanide‐doped nanoparticles, YVO₄:Eu and LaPO₄:Ce,Tb, with high luminescence quantum yield and good water‐solubility, are synthesized through a polymer‐assisted hydrothermal method. Positively charged polyhedral and spherical gold nanoparticles exhibit surface plasmon resonance (SPR) bands centered at 623 and 535 nm, respectively. These bands overlap well with the emission of the Eu³⁺ and Tb³⁺ ions within the lanthanide nanoparticles. Herein, the gold nanoparticles are synthesized through a seed‐mediated cetyltrimethylammonium bromide (CTAB)‐assisted method. The assemblies of the oppositely charged donors and acceptors are developed into LRET‐based sensors exhibiting a donor quenching efficiency close to 100 %.     

AFM Investigation on Vickers Indents: An Artefact?

 Plastic instability in tensile test has long been discovered and has been studied theoretically and experimentally. More recently the effect was also investigated in torsion mode and in depth sensing Vickers microhardness tests by optical- and scanning electron microscopy. We used atomic force microscopy (AFM) to investigate the effect on a series of indents. Experimental parameters were chosen so, that we should find indents with no, with a few, and with numerous slip lines. We found stripes on the inner surface of indents, but we found stripes even on those indents, where no stairs where expected. Based on considerations made on interference patterns we concluded, that the stripes are caused by multiple light stray in the AFM head, which interference pattern is significantly different from usual interference pattern on AFM images.