Fiber-optic chemical and biochemical probes based on localized surface plasmon resonance

A novel reflection-based localized surface plasmon resonance fiber-optic probe for chemical and biochemical sensing is reported. The sensor is based on intensity measurement of the internal reflected light at a fixed wavelength from an optical fiber where the extinction cross-section of self-assembled gold nanoparticles on the unclad portion of the optical fiber changes with different refractive index of the environment near the gold surface. The reflection-based localized surface plasmon resonance fiber-optic probe has been shown to be capable of direct sensing of the “spectroscopically silent” Ni²⁺ ion and label-free detection of streptavidin and staphylococcal enterotoxin B at the picomolar level.     

Development of silver nanorod array based fiber optic probes for SERS detection

The development of intrinsic SERS fiber optic sensors, i.e., fiber optical sensors that also serve as SERS active platforms, is challenging in that an easy, robust method that integrates the SERS active platform with fiber optics is still largely missing. There is a trade-off between implementing optimal morphology of SERS active nanostructures for best enhancement effect and preserving optical transparency that allows maximum transmission of the excitation radiation and the detected signals. In the present work, highly sensitive and reproducible silver nanorod arrays (AgNRs) have been integrated to a fiber optic probe for SERS detection. The films underlying the AgNR coating have been tailored to allow maximum light transmission while maintaining optimal SERS activity. The intense spectral background from the probe fiber core is largely eliminated by using a GRIN lens to produce a tight focus of the incident radiation at the AgNR coating. The performance of the AgNR fiber optic probes has been evaluated in a forward scattering optical configuration using BPE and adenine. The low detection limit of BPE and adenine is 10⁻⁷ M. Reproducibility and sampling methods are also discussed.     

Tethered DNA scaffolds on optical sensor platforms for detection of hipO gene from Campylobacter jejuni

DNA biosensors have gained increased attention over traditional diagnostic methods due to their fast and responsive operation and cost-effective design. The specificity of DNA biosensors relies on single-stranded oligonucleotide probes immobilized to a transduction platform. Here, we report the development of biosensors to detect the hippuricase gene (hipO) from Campylobacter jejuni using direct covalent coupling of thiol- and biotin-labeled single-stranded DNA (ssDNA) on both surface plasmon resonance (SPR) and diffraction optics technology (DOT, dotLab) transduction platforms. This is the first known report of the dotLab to detect targeted DNA. Application of 6-mercapto-1-hexanol as a spacer thiol for SPR gold surface created a self-assembled monolayer that removed unbound ssDNA and minimized non-specific detection. The detection limit of SPR sensors was shown to be 2.5 nM DNA while dotLab sensors demonstrated a slightly decreased detection limit of 5.0 nM (0.005 μM). It was possible to reuse the SPR sensor due to the negligible changes in sensor sensitivity (∼9.7 × 10⁻⁷ ΔRU) and minimal damage to immobilized probes following use, whereas dotLab sensors could not be reused. Results indicated feasibility of optical biosensors for rapid and sensitive detection of the hipO gene of Campylobacter jejuni using specific ssDNA as a probe.     

Ultrasensitive immunosensing of tuberculosis CFP-10 based on SPR spectroscopy

An antigen (Ag), CFP-10, found in tissue fluids of tuberculosis (TB) patients may be an ultimate candidate for use as a sensitive TB marker with a sensing method for early simplified diagnosis of TB. In this study, chemical and optical optimizations were carried out using novel immuno-materials for establishment of a self-assembled surface plasmon resonance (SPR) optical immunosensor system for detection of CFP-10, which is valuable for pre-clinical work, prior to conduct of massive clinical observations. For creation of a simple sensing interface, a monoclonal antibody (anti-CFP-10) was immobilized directly on a gold surface, followed by blocking with cystamine. Orientation and accessibility of anti-CFP-10 were assessed by the selective binding of CFP-10. Recent results indicate that the reusability of the sensor chip adopting the cystamine method was found to be preferable to other immobilization methods. A linear relationship was well correlated between SPR angle shift and CFP concentrations in the range from 100 ng mL⁻¹ to 1 μg mL⁻¹. Modification of the SPR chip with antibody provides a simple experimental platform for investigation of isolated proteins under experimental conditions resembling those of their native environment.     

SPR enhanced ellipsometric gas monitoring on thin iron doped tin oxide layers

In this work, thin iron doped tin oxide layers (3–6 nm) were investigated with regard to gas sensitivity by means of surface plasmon resonance (SPR) effect with ellipsometric readout. The experimental set-up was a Kretschmann configuration with gold as metal layer. The sensor system was exposed to different concentrations of methane in the low ppm range and the sensor response of an uncoated gold layer compared to a gold layer coated with iron doped tin oxide. The additional layer effects stability with regard to drift behavior of the sensor and an increase in sensitivity. Furthermore, the sensor is able to detect the toxic gas carbon monoxide in low concentration range (down to 0.5 ppm). The thin layers were investigated by X-ray photoelectron spectroscopy, secondary electron microscopy and spectroscopic ellipsometry. The possible mechanisms taking place on the surface are discussed.     

An optical sensor for nitrogen dioxide based on a copper phthalocyanine Langmuir—Blodgett film

A copper phthalocyanine Langmuir—Blodgett film has been incorporated in an optical gas sensor which exploits the phenomenon of surface plasmon resonance. For the detection of nitrogen dioxide, a significant improvement over previous work is demonstrated. The use of an ultra-thin layer of nickel to protect the underlying silver layer is also reported.     

Thin film temperature sensor for real-time measurement of electrolyte temperature in a polymer electrolyte fuel cell

This paper describes a technique for the measurement of the electrolyte temperature in an operating polymer electrolyte fuel cell (PEFC). A patterned thin film gold thermistor embedded in a 16 μm thick parylene film was laminated in the Nafion^® electrolyte layer for in situ temperature measurements. Experimental results show that the sensor has a linear response of (3.03 ± 0.09) × 10⁻³ °C⁻¹ in the 20–100 °C temperature range and is robust enough to withstand the electrolyte expansion forces that occur during water uptake. An electrolyte temperature increase of 1.5 °C was observed in real-time when operating the fuel cell at 0.2 V and a current density of 0.19 A/cm². The temperature sensitivity of the present sensor is in an order of magnitude better than the conventional micro-thermocouples that have been reported. Additionally, use of micro-fabrication techniques allows for an accurate placement of the temperature sensor within the fuel cell. Simulation results show that the sensor has no significant effect on the local temperature distribution.     

Cross-sensitivity evaluation for ammonia sensing using absorption spectroscopy in the UV region

This paper describes an optical sensor for the monitoring of ammonia gas. An open path optical technique is used to analyze the absorption lines of ammonia within the ultra-violet region. The optical sensor shows absorption lines comparable to the theoretical ammonia spectra. Cross-sensitivity with carbon dioxide and oxygen gas has been tested and clearly shows that these two gases have no effect on ammonia measurement in the ultra-violet region, between 200 nm and 230 nm. The optical sensor is able to detect ammonia down to 9 ppm with an average error less than 2%. The optical sensor system also shows a fast response time which is less than 4 s.     

Resonance wavelength-dependent signal of absorptive particles in surface plasmon resonance-based detection

We describe the resonance wavelength-dependent signal of absorptive particles in surface plasmon resonance (SPR)-based detection using both modeling and experimental results. The particles, gold nanocages, have a significant absorption cross-section in the nearinfrared (NIR), resulting in a wavelength-dependent refractive index as measured by SPR. The SPR signal due to the nanocages varies by 4-fold over resonance wavelengths from 650 nm to 950 nm. The greatest SPR signal occurs at the longest resonance wavelengths; its magnitude is due to the inherent increase in sensitivity of SPR on gold with increasing wavelength and the optical absorption properties of the nanocages.     

Development of a molecular imprinting thick film electrochemical sensor for cholesterol detection

A combined molecular imprinting and thick film electrochemical sensor for cholesterol concentration detection had been developed. The ferro-ferric cyanide coupled redox reaction was used as the means to quantify the cholesterol presented in the test medium. This electrochemical sensor employed a modified gold working electrode, a platinum counter electrode and an Ag/AgCl reference electrode. The alkanethiol was used to form the self-assembled monolayer (SAM) on the gold working electrode. The SAM was then used with the cholesterol as the template forming the molecular imprinting layer. This sensor prototype could detect cholesterol concentrations between 66 and 700 nM and only a 1 μL of the sample volume was required.     

The origin and global distribution of second order variability in satellite ocean color and its potential applications to algorithm development

Empirical algorithms based on first order relationships between ocean color and the chlorophyll concentration ([Chl]; mg m^? 3) are widely used, but cannot explain the statistical dispersion or “anomalies” around the mean trends. We use an empirical approach that removes the first order effects of [Chl] from satellite ocean color, thus allowing us to quantify the impact on the ocean color signal of optical anomalies that vary independently of the global mean trends with remotely sensed [Chl]. We then present statistical and modeling analyses to interpret the observed anomalies in terms of their optical sources (i.e. absorption and backscattering coefficients). We identify two main sources of second order variability for a given [Chl]: 1) the amount of non-algal absorption, especially due to colored dissolved organic matter; and 2) the amplitude of the backscattering coefficient of particles. The global distribution of the anomalies displays significant regional and seasonal trends, providing important information for characterizing the marine optical environment and for inferring biogeochemical influences. We subsequently use our empirically determined anomalies to estimate the backscattering coefficient of particles and the combined absorption coefficient for colored detrital and dissolved materials. This purely empirical approach provides an independent assessment of second order optical variability for comparison with existing methods that are generally based on semi-analytical models.     

Absorption-based fiber optic surface plasmon resonance sensor: a theoretical evaluation

In this paper, an optical absorption based fiber optic surface plasmon resonance (SPR) sensor has been studied theoretically. The theoretical treatment is based on Kretschmann’s SPR theory and the Lorentz model that expresses a damped harmonic oscillator is included in the treatment for optical absorption in the sensing layer. The optical source considered is an un-polarized collimated beam. The light is coupled to the fiber using a microscope objective that focuses the beam at the center of the input face of the fiber. The effects of the parameters related to the sensing region, the light source and the optical fiber on the sensitivity and the operating range of the SPR sensor have been studied with the help of numerical calculations and computer simulations. It has been found that the excitation frequency in absorption-based fiber optic SPR sensor is an important parameter. The sensitivity is better for the lower off-resonance excitation frequency. The sensitivity and the operating range of the sensor are better for large value of the core diameter. The optimization of numerical aperture of the fiber, film thickness and the length of the sensing region is required to achieve the maximum sensitivity. Further, the increase in the extinction coefficient of the sample increases the sensitivity of the sensor while the decrease in the width of its absorption spectrum increases the sensitivity. The sensitivity and the operating range of the sensor are better for small values of the refractive index of the absorbing sample.     

Improve the refractive index sensitivity of gold nanotube by reducing the restoring force of localized surface plasmon resonance

The core refractive index sensitivity of a gold nanotube was investigated by calculating the shift of local surface plasmon resonance (LSPR). It was found that the core refractive index sensitivity can be improved by reducing the wall thickness or the surrounding refractive index. The sensitivity increases exponentially with decreasing wall thickness, but increases linearly with decreasing surrounding refractive index. This multi-factor controlled sensitivity of gold nanotube enlarges the ability of optimizing the refractive index sensors. The physical origin of this tunable refractive index sensitivity of gold nanotube was also investigated based on the plasmon hybridization and repulsive effects on the restoring force of plasmon oscillation. This physical mechanism can be used for designing core-shell metallic nanostructures for effective LSPR chemical and biological sensing.     

Surface plasmon resonance study on the optical sensing properties of nanometric polyimide films to volatile organic vapours

The optical sensing properties of nanometric polyimide films towards ethanol and methanol vapours have been investigated by surface plasmon resonance technique. To this purpose polyimide sensing layers have been deposited onto gold/glass substrates by glow-discharge-induced vapour deposition polymerization technique. The sensible layer shows reversible and stable responses to different concentrations of methanol and ethanol vapours. A linear dependence between the change in reflectivity and the vapours concentration is observed being the sensitivity to both vapours similar, however, the response is larger in presence of ethanol vapours. Numerical fitting routines on surface plasmon resonance curves indicate that optical changes are motivated by an absorption process of the analyte. This produces a detectable increase of the real refractive index and a swelling process in the polyimide layer.     

A CO2 sensor based upon a continuous-wave thermoelectrically-cooled quantum cascade laser

A CO₂ sensor based upon a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser operating between 2305 and 2310 cm⁻¹ and a 54.2 cm long optical cell has been developed. Two approaches for direct absorption spectroscopy have been evaluated and applied for monitoring of the CO₂ concentration in gas lines and ambient laboratory air. In the first approach optical transmittance was derived from the single channel laser intensity, whilst in the second approach a ratio of signal and reference laser intensities (balanced detection) was used. The optimum residual absorption standard deviation was estimated to be 1.9 × 10⁻⁴ for 100 averages of 1 ms duration and 0.1 cm⁻¹ scans over the P(46) CO₂ absorption line of the ν₃ vibrational band at 2306.926 cm⁻¹. A CO₂ detection limit (1 standard deviation) of 36 ppb was estimated for 0.1 s average and balanced detection.     

基于SPR的光纤传感器的研究与实验

基于表面等离子体共振（SPR）的光纤传感器不仅具有SPR高灵敏性的特点,还发挥了光纤本身的诸多优点,具有广泛地研究和应用价值。在分析了光纤SPR原理的基础上,设计并实现了光纤SPR传感器,给出了系统结构模型。通过对不同质量分数的甘油溶液进行测试,获得了SPR光谱共振波长等随待测环境介质折射率变化的有效信息,证实了使用这种传感器进行环境介质检测的可行性。     

Rice-like CuO nanostructures for sensitive electrochemical sensing of hydrazine

In this work, a low temperature aqueous chemical growth methodology was used for the fabrication of CuO nanostructures. The as-synthesised nanostructures were then elaborately characterised by number of analytical techniques such as scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The obtained nanostructures were observed to possess interlaced rice-shaped structural features with the length and width of individual rice determined to be in the range of 200–300 nm and 50–100 nm respectively. The unique nanostructures when utilised as electrode material exhibited excellent electro-catalytic potential towards oxidation of hydrazine in alkaline media. The excellent conductive of CuO added by the high surface area of obtained nanorice-like structures enabled development of highly sensitive (3087 µA mM⁻¹ cm⁻²), selective and stable electrochemical sensor for hydrazine. In addition, the successfully application of the developed sensor in spiked tap, bottled and industrial water samples for the detection of hydrazine suggested its feasibility for practical environmental application.

     

光谱吸收硫化氢气体浓度传感器

提出一种基于红外吸收光谱测量法检测硫化氢气体浓度的方法。分析了硫化氢气体近红外光谱吸收特性,为消除光源不稳定及光电器件的热零点漂移、零点漂移对测量准确度的影响,基于差分吸收检测法设计了硫化氢气体浓度传感器,对硫化氢气体浓度检测进行了实验研究,实验表明该传感器的测量灵敏度可达10-5(10ppm)。     

Large-area Raman enhancement substrates using spontaneous dewetting of gold films and silver nanoparticles deposition

We present a cost-effective method for making large-area surface enhanced Raman scattering (SERS) substrates by using spontaneous dewetting of ultrathin gold film. The dewetting of 5-nm-thick gold film formed high-density gold islands ranged from 40 nm to 80 nm. The measured SERS signal was 5 times stronger than synthesised gold nanoparticles. The SERS signals can be further increased by depositing small silver nanoparticles on the dewetted film. The experimental results showed 5-nm-thick silver coating increased SERS signals up to 10 times. The calculations by finite-difference time-domain method verified such SERS enhancement originated from enhanced electric fields between gold islands and silver nanoparticles. In the application, we demonstrated an all-optical measurement of pH values in microfluidic devices by using SERS signals of para-mercaptobenzoic acid.     

Ultra trace mercury(II) detection by a highly selective new optical sensor

This paper presents the development and construction of a sensitive new optical sensor that is highly selective to Hg²⁺ ion in aqueous solution. The sensing element, the newly synthesized (1Z,2Z)-N′¹,N′²-dihydroxy-N¹,N²-dipyridin-2-ylethanediimidamide, incorporated into a plasticized poly(vinyl chloride) membrane, is capable of determining mercury(II) with a high selectivity over a wide dynamic range from 5.78 × 10⁻⁹ to 1.05 × 10⁻³ M at pH 4.0 with a lower detection limit of 1.71 × 10⁻⁹ M. The optode membrane's response to Hg²⁺ is fully reversible and reveals a very good selectivity towards Hg²⁺ ion over a wide variety of other metal ions in solution. Performance characteristics of the sensor evaluated as good reversibility, wide dynamic range, long life span, long-term response stability, and high reproducibility. The proposed optical sensor gives good results for applications in direct determination of mercury(II) in environmental real samples that are satisfactorily comparable with corresponding data from cold-vapor atomic absorption spectrometry.