Enhancement of the response of poly(dimethylsiloxane) hollow prisms through air mirrors for absorbance-based sensing

The hollow prisms are photonic lab-on-a-chip systems with a high degree of monolithic integration that consist of micro-optical (prism and microlenses), microfluidics and structural elements (self-alignment systems) obtained in PDMS by soft lithography. Despite their interesting optical and sensing properties, their working principle, based on the absorption of the working wavelength (lambda=460 nm) by the different substances that can fill the hollow prisms, always involves at least one reflection at the walls of the hollow prism. Due to the low refractive index contrast between the PDMS and the phosphate buffer that fills the hollow prism, the reflectivity at this interface is very low, requiring long integration times. In this paper, we tackle this severe limitation with the definition of an air mirror, which solves the low reflectivity problems: with the appropriate design, the working wavelength matches with the condition of total internal reflection (TIR) only at the air mirror and is reflected back to the hollow prism. Experimental results have shown that the use of air mirrors enhances the sensing properties of the hollow prisms due to several reasons: first, the integration time is strongly reduced, from 2.5s to 80 ms. Second, although the integration time is reduced, the signal-to-noise ratio (SNR) is increased from 12 dB to 19.5 dB. Third, an important improvement of the LOD (with values close to 1 microM and 400 nM for fluorescein and methyl orange diluted in phosphate buffer, respectively) has been experimentally measured. Finally, as compared to the system without the air mirror, the sensitivity is increased by a factor between 1.32 and 2.49 (depending on the geometry used), respectively when this simple, however effective element is included into the system.     

A multireflection cell for enhanced absorbance detection in microchip-based capillary electrophoresis devices

The design, fabrication and testing of a photolithographically fabricated, glass-based multireflection absorbance cell for microfluidic devices, in particular microchip-based capillary electrophoresis (CE) systems is described. A multireflection cell was fabricated lithographically using a three-mask process to pattern aluminum mirrors above and below a flow channel in a chip, with 30 microm diameter optical entrance or exit apertures (one in each mirror) positioned 200 microm apart. Source and detector were positioned on opposite sides, and the metal mirrors were made 1 cm square, to reduce stray light effects. Calibration curves using bromothymol blue (BTB) with a 633 nm source (He:Ne laser) were linear to at least 0.5 absorbance units, with typical r2 values of 0.9997, relative standard deviations in the slopes of +/- 1.3%, and intercepts of zero within experimental error. Effective optical pathlengths of 50-272 microm were achieved, compared to single-pass pathlengths of 10-30 microm, corresponding to sensitivity enhancements (i.e., optical path length increase) of 5 to 10-fold over single-pass devices. Baseline absorbance noise varied within a factor of two in almost all devices, depending only weakly on path length. This device can give much higher absorbance sensitivity, and should be much easier to manufacture than planar, glass-based devices previously reported.     

基于液芯波导原理的微流控芯片长光程光度检测系统

提出了一种基于液芯波导(Liquidcorewaveguide,LCW)原理的微流控芯片吸收光度检测系统.通过芯片与外界接口技术实现液芯波导管与芯片的耦合,建立了芯片上长光程(毫米至厘米级)吸收光度检测池.采用邻菲啉-铁(Ⅱ)显色体系验证系统分析性能,以5.5cm外覆TeflonAF液芯波导管作为检测池(检测池体积240nL)时,芯片系统的检测线性范围为0.03～50μmol/L,对邻菲啉-铁(Ⅱ)配合物的检出限为8nmol/L,检测池有效光程达1.7cm,分析精度RSD(n=5)为0.8%.     

Tactile UV‐ and Solar‐Light Multi‐Sensing Rechargeable Batteries with Smart Self‐Conditioned Charge and Discharge

A tactile, UV‐ and solar‐light multi‐sensing smart rechargeable Zn–air battery (SRZAB) with excellent cell performance, self‐conditioned charge/discharge, and reliable environmental responsivity is made by using multi‐scale conjugated block‐copolymer–carbon nanotube–polyurethane foam assemblies as both a self‐standing air electrode and a sensing unit. Multiscale engineering fully exploits the multi‐synergy among components to endow the newly designed metal‐free multi‐sensing air electrode (MSAE) with bifunctional oxygen reduction and evolution activities, pressure sensitivity, and photothermal and photoelectric conversion functions in a single electrode, enabling effective regulation of interface properties, electronic/ionic transport, or redox reactions in SRZAB upon various stimulations and establishing multiple working principles. MSAE‐driven SRZAB can be used as compressible power sources, self‐powered pressure and optical sensors and light‐to‐electrochemical energy systems.     

A White cell type multiple reflection system for tropospheric research

Summary A White cell type multiple reflection system (MRS) for long path absorption measurements is reported which makes use of the reinjection technique. The set-up of this MRS system was optimized by model calculations and compared with other suggested designs in field measurements. In pilot tests the performance of the system and the applicability to troposheric measurements were tested. Using a 6 m mirror system an absorption path length of 1.2 km was realized under field condition just despite of the open path set-up. No problems with atmospheric fluctuations affected the measurements for the chosen path length. In the laboratory an optical path length of 2.5 km was achieved. Thus, this MRS design is very interesting for applications both inside and outside the laboratory.     

Capillary electrophoretic separation of dsDNA under nonuniform electric fields

Improved sensitivity for the analysis of DNA by capillary electrophoresis has been achieved, based on simultaneous increases in optical path length and injection volume. To increase the optical path length, bubble cells with diameters ranging from 150 to 450 microm have been fabricated and tested. In terms of resolution and sensitivity, a bubble cell of 300 microm diameter is appropriate when using 75-microm capillaries. To allow greater injection volumes, we performed on-line concentration of DNA in the presence of electroosmotic flow (EOF) using 2.0% poly(ethylene oxide) (PEO). With a 300-microm bubble cell, a 170-fold improvement in the sensitivity for the 89-bp fragment has been accomplished when injecting about 0.33 microL DNA. In the presence of the bubble cell, the resolution for the large fragments improves while that for the small ones (<124 base pair) decreases. The effect of bubble cells was further investigated by conducting DNA separation in the absence of EOF, showing that improvements in resolution are mainly due to increased migration differences when DNA migrated at low electric field strengths in the bubble region. We have suggested that such an effect is more profound using shorter capillaries, leading to complete separation of phiX 174 RF DNA-Hae III digest in 2 min.     

Capillary scale light emitting diode based multi-reflection absorbance detector

We describe a light emitting diode (LED) based multi-reflection capillary scale absorbance detector based on both square and round capillaries and compare their performance with a conventional single-pass on-tube detector. The optical path length is extended by silver coating, the external surface of the capillary. The reflective geometry has been reported to be less prone to artifacts induced by refractive index changes; we do find this to be true. Although the detection volume/illuminated volume is increased some, a multi-reflection cell based on a 180 μm bore capillary with a ∼2-cm long illuminated volume shows over a 50-fold gain in signal-to-noise (S/N) compared to a single-pass on-tube configuration with the same capillary. The limit of detection (LOD) is 4.4 fmol (2.6 pg, 1 μL of 22.0 nM injected dye) BTB under pulseless (pneumatic) flow conditions. The cells behave as multipath devices where the effective path lengths are greater at low absorbance values. In our experiments, where non-coherent light is launched through optical fibers that are large compared to capillary bore dimensions, increase in the effective path length of the cell do not occur in a predictable fashion with the angle of incidence of the light beam. Although the effective path length almost linearly increases with increasing distance between the light entry and exit windows, the absolute values of the effective path lengths are always lower than this physical distance, suggesting that after some passage through the solution, light largely travels through or along the glass wall. Square capillaries have better light transmission and offer some performance advantages. Multi-reflection cells can indeed be of value for sensitive detection in microflow systems.     

Micro-impedance cytometry for detection and analysis of micron-sized particles and bacteria

The sensitivity of a microfluidic impedance flow cytometer is governed by the dimensions of the sample analysis volume. A small volume gives a high sensitivity, but this can lead to practical problems including fabrication and clogging of the device. We describe a microfluidic impedance cytometer which uses an insulating fluid to hydrodynamically focus a sample stream of particles suspended in electrolyte, through a large sensing volume. The detection region consists of two pairs of electrodes fabricated within a channel 200 μm wide and 30 μm high. The focussing technique increases the sensitivity of the system without reducing the dimensions of the microfluidic channel. We demonstrate detection and discrimination of 1 μm and 2 μm diameter polystyrene beads and also Escherichia coli. Impedance data from single particles are correlated with fluorescence emission measured simultaneously. Data are also compared with conventional flow cytometry and dynamic light scattering: the coefficient of variation (CV) of size is found to be comparable between the systems.     

Ultra-sensitive UV detection in micro separation

Most UV detectors used in micro separation techniques today suffer from an enormous loss in sensitivity due to the small cell volume necessary to avoid peak dispersion. Flow cells with volumes between 10-100 nl are normally constructed of fused silica tubing. With typical path lengths of between 50-320 μm, a tremendous loss in sensitivity results, consistent with Beer-Lambert's law. We have successfully constructed an ultrasensitive UV flow cell. Its total volume does not exceed 90 nl and yet its optical path length is nearly 2 cm (20,000 μm). Due to its special design, dead volume is minimized and is comparable to that of a 3 nl capillary flow cell (on-column). Sensitivity enhancement of 100-500 times can easily be realized in comparison with on-column detection. The potential of this ultra-sensitive UV flow cell in micro separations is illustrated by applications using Capillary LC and Pakked Capillary SFC.     

Mixed C18 and C1 modification on an optical fiber for chromatographic sensing

An optical fiber-chromatographic sensor, aiming at simultaneous and selective response to multiple components following a chromatographic separation, is described. We report an improved approach for immobilization of octadecyl (C(18)) and methyl (C(1)) moieties as stationary phase on an optical fiber suitable as a sensing phase for organic solutes. By this approach, the stability and lifetime of the sensing layer as well as the detectability and retention behavior of the chromatographic sensor could be improved. Infrared spectroscopy was employed to confirm the presence of C(18) and C(1) moieties on the modified surface of the optical fiber. The chromatographic sensor was applied, with good sensitivity and chemical selectivity, to the simultaneous separation and detection of bromobenzene and toluene, using water as the mobile phase.     

基于石墨烯光子晶体光纤的流体传感器

与传统的传感器设备阵列相比,由于结构更为简单,具有广泛检测兼容性的光纤系统逐渐成为分布式监测的有力候选者。然而,受工作机制的限制,大多数光纤传感器仍局限于对折射率等物理参数进行探测,一种用于环境化学监测的全光纤分布式传感系统亟待研发。本工作中,我们向化学气相沉积法生长的石墨烯光子晶体光纤(Gr-PCF)中引入了一种化学传感机制。初步结果表明,石墨烯光子晶体光纤可以选择性地检测浓度为ppb级的二氧化氮气体,并在液体中表现出离子敏感性。石墨烯光子晶体光纤与光纤通信系统的波分、时分复用技术结合后,将为实现分布式光学传感环境问题提供巨大的潜力和机会。     

Optimisation of an integrated optical evanescent wave absorbance sensor for the determination of chlorinated hydrocarbons in water

The suitability of an integrated optical chemical sensor for the determination of highly volatile chlorinated hydrocarbons in aqueous solutions has been proven. The analytes are detected by NIR absorption spectrometry in the evanescent field of an integrated optical strip waveguide generated in a BGG31 (Schott, Germany) glass substrate, which is coated with a hydrophobic polymer superstrate as sensing layer. It has been shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepared by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t(90)-value) are between five and fourteen minutes for a coating thickness of around 30 microm. The sensor response is totally reversible. The analyte desorbes in air within 2 min. The enrichment of trichloroethene in the polysiloxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step.     

溶胶-凝胶薄膜光纤传感器法测定空气中二氧化氮

以四乙氧基硅烷合成溶胶-凝胶薄膜,包埋偶氮试剂制备得到对二氧化氮具有灵敏响应的传感膜;与分支光纤等元件耦合成光纤传感器,通过累积吸收法能够现场测定空气中的低浓度二氧化氮．其检出限为每小时5ng／L;测定相对标准偏差为4．4％（n=6,C（NO2）=200ng／L,1h）。实验表明,CO2、NO、SO2、NO等共存气体在低浓度下对传感器测定NO2无明显干扰。     

Structure, dynamics, and optical properties of concentrated milk suspensions: an analogy to hard-sphere liquids

A systematic study of the effects of volume fraction increment on the optical properties, the structure, and the dynamics of the casein micelles and fat droplets in milk was performed using diffusing wave spectroscopy. Four types of milk were investigated, NIDO full fat milk, fat-free milk, whey and fat-free milk, and finally lactose and fat-free milk. Independent measurements to calculate the dependence of the viscosity and the index of refraction of the milk serum and casein micelles as a function of the volume fraction were also performed. We compare the experimentally determined quantities photon transport mean free path (l*) and self-diffusion coefficient D(s) with the predictions from theoretical calculations using classical colloidal models such as a hard-sphere fluid. We demonstrate that all types of milk with and without fat content behave, structurally, like colloidal hard-sphere systems up to volume fractions well over 45%. In the case of dynamic measurements, both lactose- and fat-free and whey- and fat-free milk behave also like hard-sphere systems whereas fat-free milk and fat-containing NIDO milk deviate slightly at volume fractions over 35%. Finally, a comparative measurement and theoretical calculation of the casein micelle's size was performed.     

Polymeric nanofilm-coated optical fibre sensor for speciation of aromatic compounds

An optical fibre sensor has been shown to be suitable for monitoring of benzene, toluene and o-xylene (BTX) with both high selectivity and sensitivity. The sensing principle underlying this experimental device is based on the changes of the reflected optical power when BTX vapours are present in the analytical tube containing an optical fibre coated with a thin film of poly[methyl(3, 3, 3-trifluoropropyl)siloxane]. The interaction of organic vapour with the sensitive surface promotes a variation of the light power, proportional to the amount of adsorbed BTX vapour. A set of experiments concerning different operational conditions was performed in order to promote a higher analytical performance and the newly developed BTX sensor showed higher sensitivity and shorter analytical time than a method based on gas chromatography–flame ionisation detector. Furthermore, the proposed sensor also provides the basis for an inexpensive analytical technique with adequate specificity for measurements of BTX at trace levels with appropriate reversibility, repeatability, and reproducibility. Finally, the analytical performance of the developed sensor was also evaluated and found adequate for industrial air samples.     

Cylindrical sensor geometry for absorbance-based fiber-optic ammonia sensors

A novel cylindrical shape geometry is proposed for fiber-optic ammonia sensors based on chromophoric indicator dyes. Sensors are constructed by trapping the internal indicator solution inside a short segment of a gas-permeable tube. Fiber-optic probes are used to supply incident radiation and to collect light that transverses through the internal solution. This cylindrical sensor geometry provides large optical path lengths which permits the use of chromophoric indicator dyes. Unlike the conventional distal tip geometry, the diffusion path is independent of the optical path which results in short response times coupled with high sensitivity and low limits of detection. Our experiments indicate that stray radiation is negligible for this sensor design, and that the optical path length essentially equals the distance between the fiber-optic probes. Sensors constructed with Bromothymol Blue as the indicator dye are evaluated. As part of this evaluation, three different modes of operation are tested. The best analytical performance obtained when a single discrete aliquot of the internal solution is used. Steady-state responses are achieved within 13-16 min for 200 nM levels of ammonia from sensors with limits of detection ranging from 150 to 20 nM.     

Optical fibre sensor for hydrogen sulphide monitoring in mouth air

A reversible optical fibre chemical sensor for hydrogen sulphide monitoring in mouth air based on reflectance measurements has been developed. The active sensing phase has been prepared by immobilising the colorimetric reagent 2,6-dichlorophenolindophenol (DCPI) in a silica gel support. The principle of the determination is based on the increase of reflectance of such solid sensing phase when hydrogen sulphide reduces the colorimetric reagent with the subsequent decolouration process. The addition of 1.26 μg of Cu(II) per gram of solid support improved the response time and reversibility of the sensing phase.The detection limit is 10 ppb (v/v) of hydrogen sulphide. The linear range using the Kubelka-Munk function extends at least up to 1000 ppb (v/v). The sensor exhibits a response time of less than 2 min for hydrogen sulphide concentrations in the linear range and the signal is reversible.The optical sensor has been successfully tested for human malodour monitoring and the results validated by comparison with those obtained for the same individuals using a commercially available electrochemical instrument.     

无透镜数字全息显微成像技术与应用

针对微结构和微光学元件等微小物体的表面定量检测,本文介绍了一种利用无透镜数字全息的快速、无损的显微成像方法。首先介绍了基于球面波的无透镜数字全息显微成像技术的基本原理,采用CCD作为光电转换器件,基于迈克尔逊干涉光路,设计了无透镜数字全息显微成像系统,利用反射镜构成折反式光路,系统结构简单、紧凑,提升了系统便携性。然后利用USAF1951分辨率板对构建的成像系统进行了标定实验,得出其横向分辨率为6.69μm,放大倍率为3.375,系统工作距离为12.0mm。此外,还对晶圆表面结构进行实际测量。实验验证了该系统的可行性和有效性,有望进一步应用于MEMS、微光学元件、光学元件等表面形貌的定量测量中。     

Effect of CO on surface behaviour of U3O8

A total reflection X-ray fluorescence (TXRF) analyzer with a special structure is described. Its short X-ray path (about 15 cm) resulted in a high sensitivity, low power consumption and small volume. The structure with double total reflection path is suitable for easy change of exciting source to cover a large element range. The minimum detection limit (MDL) of 6 pg for Co under Cu exciting source and 22 pg for Sr under Mo tube. Some significant works were done, such as the detemination of sulfur content in fuel oils, the non-destructive analysis of an ancient bronze utensil and the regular analysis of tap water.     

A critical evaluation of a long pathlength cell for flow-based spectrophotometric measurements

Coupling of a flow cell based on a liquid core waveguide (LCW) to flow systems for spectrophotometric measurements was critically evaluated. Flow-based systems with and without chemical reactions were exploited to estimate the increase in analytical signal in comparison to those obtained with a conventional 1-cm cell under different experimental conditions. The Schlieren effect associated to intense concentration gradients in the sample zone was investigated with model solutions that do not absorb visible electromagnetic radiation. The effect of radiation scattering was lower than the expected by considering the increase in the optical path, being the magnitude of the perturbation up to 40% higher for the 100-cm LCW cell. Several alternatives for compensation of the Schlieren effect were experimentally investigated. The potentiality of the LCW for turbidimetric measurements and coupling to monosegmented flow analysis was also evaluated.