Optical leaky waveguide sensor for detection of bacteria with ultrasound attractor force

An integrated, sensitive, and rapid system was developed for the detection of bacteria. The system combined an optical metal-clad leaky waveguide (MCLW) sensor with ultrasound standing waves (USW). The performance of a MCLW sensor for the detection of bacteria has been increased (>100 fold) by using USWs to drive bacteria onto the sensor surface. By forming the USW nodes at or within the surface of the MCLW, the diffusion-limited capture rate has been replaced by fast movement. Immobilized anti-BG antibody on the MCLW sensor surface was used to capture Bacillus subtilis var. niger (BG) bacterial spores driven to the surface. This combination of sensor and attractor force combination has been tested by detecting the evanescent scattering from bacterial spores at the sensor surface. Application of ultrasound for 3 min gave a detection limit for BG bacterial spores of 1 x 10(3) spores/mL.     

Highly sensitive detection of proteins and bacteria in aqueous solution using surface-enhanced Raman scattering and optical fibers

We report the detection of the proteins lysozyme and cytochrome c as well as the live bacterial cells of Shewanella oneidensis MR-1 in aqueous solutions with sensitivities order(s) of magnitude higher than those previously reported. Two highly sensitive surface-enhanced Raman scattering (SERS)-based biosensors using optical fibers have been employed for such label-free macromolecule detections. The first sensor is based on a tip-coated multimode fiber (TCMMF) with a double-substrate "sandwich" structure, and a detection limit of 0.2 μg/mL is achieved in protein detections. The second sensor is based on a liquid core photonic crystal fiber (LCPCF) with a better confinement of light inside the fiber core, and a detection limit of 10(6) cells/mL is achieved for the bacteria detection. Both SERS biosensors show great potential for highly sensitive and molecule-specific detection and identification of biomolecules.     

Ultrasensitive detection of 1,4-Bis(4-vinylpyridyl)phenylene in a small volume of low refractive index liquid by surface-enhanced Raman scattering-active light waveguide

This paper reports a novel surface-enhanced Raman scattering (SERS)-active light waveguide method for ultrasensitive detection of a sample dissolved in a small volume of low refractive index liquid. The SERS-active light waveguide demonstrated in this study was constructed via the light-guiding silica capillary. The surface of its inner wall was modified with SERS-active silver nanoparticles that can remarkably enhance Raman signals. The capillary with SERS-active modified layer was filled with the sample solution to form the SERS-active liquid core (LC) fiber. The incident laser beam travels through the waveguide in a totally reflective mode within the fiber wall and penetrates a small distance into the sample solution by the evanescent wave field. The Raman scattering of the analytes adsorbed onto the surface of the SERS-active modified layer can be excited by the laser beam and refracted into the fiber wall. Thus, a sample dissolved in low index liquid, e.g., methanol, can be quantitatively monitored by Raman spectroscopy and detection limit of its concentration is lower than 10(-9) mol/L.     

Near-infrared surface-enhanced-Raman-scattering-mediated detection of single optically trapped bacterial spores

A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of two different Bacillus stearothermophilus variants. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful bacteria. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) surface-enhanced Raman scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of bacterial spores in aqueous media have been measured using SERS substrates based on approximately 60-nm-diameter gold colloids bound to 3-aminopropyltriethoxysilane derivatized glass. The light from a 787-nm laser diode was used to trap and manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the strain discrimination of Bacillus stearothermophilus spores. Comparison of normal Raman and SERS spectra reveals not only an enhancement of the normal Raman spectral features but also the appearance of spectral features absent in the normal Raman spectrum.     

Capillary waveguide optrodes: an approach to optical sensing in medical diagnostics

Glass capillaries with a chemically sensitive coating on the inner surface are used as optical sensors for medical diagnostics. A capillary simultaneously serves as a sample compartment, a sensor element, and an inhomogeneous optical waveguide. Various detection schemes based on absorption, fluorescence intensity, or fluorescence lifetime are described. In absorption-based capillary waveguide optrodes the absorption in the sensor layer is analyte dependent; hence light transmission along the inhomogeneous waveguiding structure formed by the capillary wall and the sensing layer is a function of the analyte concentration. Similarly, in fluorescence-based capillary optrodes the fluorescence intensity or the fluorescence lifetime of an indicator dye fixed in the sensing layer is analyte dependent; thus the specific property of fluorescent light excited in the sensing layer and thereafter guided along the inhomogeneous waveguiding structure is a function of the analyte concentration. Both schemes are experimentally demonstrated, one with carbon dioxide as the analyte and the other one with oxygen. The device combines optical sensors with the standard glass capillaries usually applied to gather blood drops from fingertips, to yield a versatile diagnostic instrument, integrating the sample compartment, the optical sensor, and the light-collecting optics into a single piece. This ensures enhanced sensor performance as well as improved handling compared with other sensors.     

Nonlabeled quartz crystal microbalance biosensor for bacterial detection using carbohydrate and lectin recognitions

High percentages of harmful microbes or their secreting toxins bind to specific carbohydrate sequences on human cells at the recognition and attachment sites. A number of studies also show that lectins react with specific structures of bacteria and fungi. In this report, we take advantage of the fact that a high percentage of microorganisms have both carbohydrate and lectin binding pockets at their surface. We demonstrate here for the first time that a carbohydrate nonlabeled mass sensor in combination with lectin-bacterial O-antigen recognition can be used for detection of high molecular weight bacterial targets with remarkably high sensitivity and enhanced specificity. A functional mannose self-assembled monolayer in combination with lectin concanavalin A (Con A) was used as molecular recognition elements for the detection of Escherichia coli W1485 using a quartz crytsal microbalance (QCM) as a transducer. The multivalent binding of Con A to the E. coli surface O-antigen favors the strong adhesion of E. coli to the mannose-modified QCM surface by forming bridges between these two. As a result, the contact area between cell and QCM surface that increases leads to rigid and strong attachment. Therefore, it enhances the binding between E. coli and the mannose. Our results show a significant improvement of the sensitivity and specificity of the carbohydrate QCM biosensor with a experimental detection limit of a few hundred bacterial cells. The linear range is from 7.5 x 10(2) to 7.5 x 10(7) cells/mL, which is four decades wider than the mannose-alone QCM sensor. The change of damping resistances for E. coli adhesion experiments was no more than 1.4%, suggesting that the bacterial attachment was rigid, rather than a viscoelastic behavior. Little nonspecific binding was observed for Staphylococcus aureus and other proteins (fetal bovine serum, Erythrina cristagalli lectin). Our approach not only overcomes the challenges of applying QCM technology for bacterial detection but also increases the binding of bacteria to their carbohydrate receptor through bacterial surface binding lectins that significantly enhanced specificity and sensitivity of QCM biosensors. Combining carbohydrate and lectin recognition events with an appropriate QCM transducer can yield sensor devices highly suitable for the fast, reversible, and straightforward on-line screening and detection of bacteria in food, water, and clinical and biodefense areas.     

Polymeric dual-slab waveguide interferometer for biochemical sensing applications

A polymer based dual-slab waveguide Young's interferometer was demonstrated for biochemical sensing. Evanescent field is utilized for probing the binding events of biomolecules on the waveguide surface. Refractive index sensing in analyte and protein adsorption on the sensing surface were investigated with glucose de-ionized water solution and bovine serum albumin, immunoglobulin G solutions in phosphate buffered saline buffer. A detection limit of 10(-5) RIU and 4 pg/mm(2) was achieved for homogeneous and surface sensing, respectively. Also, the influence of water absorption inside the polymeric device on the measurement stability was evaluated. The results indicate that the waveguide polymer sensor fabricated with the spin coating technique can achieve a satisfactory sensitivity for homogeneous refractive index sensing and, as well, for monitoring molecular binding events on the surface.     

基于TSL256x的助航灯光监控系统设计

针对目前机场助航灯检测系统存在的耗时、耗力等问题,设计了一种基于TSL256x光强传感器以及单片机控制器的监控系统.该监控系统以单片机为主控制器,利用TSL256x测量光照强度并将其转换成数字信号,输入单片机进行数据分析处理,进一步对助航灯的开关进行控制,实现了助航灯自动监控系统.研究认为,该系统能够对整个机场的助航灯进行自动监控.     

Long-range surface plasmon-enhanced fluorescence spectroscopy biosensor for ultrasensitive detection of E. coli O157:H7

A new biosensor platform for the detection of bacterial pathogens based on long-range surface plasmon-enhanced fluorescence spectroscopy (LRSP-FS) is presented. The resonant excitation of LRSP modes provides an enhanced intensity of the electromagnetic field, which is directly translated to an increased strength of fluorescence signal measured upon the capture of target analyte at the sensor surface. LRSPs originate from a coupling of surface plasmons across a thin metallic film embedded in dielectrics with similar refractive indices. With respect to regular surface plasmon-enhanced fluorescence spectroscopy, the excitation of LRSPs offers the advantage of a larger enhancement of the evanescent field intensity and a micrometer probing depth that is comparable to the size of target bacterial pathogens. The potential of the developed sensor platform is demonstrated in an experiment in which the detection of E. coli O157:H7 was carried out using sandwich immunoassays. The limit of detection below 10 cfu mL(-1) and detection time of 40 min were achieved.     

Method of measuring Bacillus anthracis spores in the presence of copious amounts of Bacillus thuringiensis and Bacillus cereus

A sensitive and reliable method for the detection of Bacillus anthracis (BA; Sterne strain 7702) spores in presence of large amounts of Bacillus thuringiensis (BT) and Bacillus cereus (BC) is presented based on a novel PZT-anchored piezoelectric excited millimeter-sized cantilever (PAPEMC) sensor with a sensing area of 1.5 mm2. Antibody (anti-BA) specific to BA spores was immobilized on the sensing area and exposed to various samples of BA, BT, and BC containing the same concentration of BA at 333 spores/mL, and the concentration of BT + BC was varied in concentration ratios of (BA:BT + BC) 0:1, 1:0, 1:1, 1:10, 1:100, and 1:1000. In each case, the sensor responded with an exponential decrease in resonant frequency and the steady-state frequency changes reached were 14 +/- 31 (n = 11), 2742 +/- 38 (n = 3), 3053 +/- 19 (n = 2), 2777 +/- 26 (n = 2), 2953 +/- 24 (n = 2), and 3105 +/- 27 (n = 2) Hz, respectively, in 0, 27, 45, 63, 154, and 219 min. The bound BA spores were released in each experiment, and the sensor response was nearly identical to the frequency change during attachment. These results suggest that the transport of BA spores to the antibody immobilized surface was hindered by the presence of other Bacillus species. The observed binding rate constant, based on the Langmuir kinetic model, was determined to be 0.15 min-1. A hindrance factor (alpha) is defined to describe the reduced attachment rate in the presence of BT + BC and found to increase exponentially with BT and BC concentration. The hindrance factor increased from 3.52 at 333 BT + BC spores/mL to 11.04 at 3.33 x 105 BT + BC spores/mL, suggesting that alpha is a strong function of BT and BC concentration. The significance of these results is that anti-BA functionalized PEMC sensors are highly selective to Bacillus anthracis spores and the presence of other Bacillus species, in large amounts, does not prevent binding but impedes BA transport to the sensor.     

Phage-Based Magnetoelastic Wireless Biosensors for Detecting Bacillus Anthracis Spores

A biosensor for the detection of biological warfare agents (Bacillus anthracis spores) was developed that combines the phage display technique with a magnetoelastic wireless detection platform. The affinity-based biosensor utilizes a phage-derived diagnostic probe as the biomolecular recognition element to capture target agents multivalently. Upon binding of the target agent to the sensor surface, the resonance frequency of the magnetoelastic biosensors decreases due to the additional mass of the target agent. Scanning electron microscopy was used to confirm binding of spores to the sensor surface. The sensitivity of the magnetoelastic acoustic sensor was tested to be 130 Hz per order of magnitude of spore concentration with a detection limit of 10³ spores/ml. The specificity of the sensors was tested against spores of other closely related Bacillus species and a large preferential binding to Bacillus anthracis spores was observed. The longevity of the phage based biosensor was compared to traditional antibody based biosensors and found to exhibit a much longer life     

Modal analysis and device considerations of thin high index dielectric overlay slab waveguides

The effect of adding a thin high index dielectric overlay layer onto a 3-layer slab waveguide demonstrates several interesting features that can be exploited in integrated optical device configurations. A simple modal analysis is employed to examine the behavior of guided light launched from a 3-layer waveguide structure then coupled and propagated in the 4-layer overlay region. Modal properties typically overlooked in conventional slab waveguides are made use of in the design and theoretical analysis of an MMI device and optical index of refraction sensor. The optical structure presented here can form the backdrop waveguide design for more complex and active devices.     

Analysis of biomolecular interactions using a miniaturized surface plasmon resonance sensor

A commercially available miniaturized surface plasmon resonance sensor has been investigated for its applicability to biological interaction analysis. The sensor was found to exhibit excellent repeatability and linearity for high-refractive index solutions and good reproducibility for the binding of proteins. Its detection limit for the monoclonal antibody M1 was found to be 2.1 fmol, which corresponds to a surface concentration of 21 pg/mm2. Simple surface immobilization procedures relying on biotin/avidin or glycoprotein/lectin chemistry have been explored. Equilibrium dissociation constants for the binding of the FLAG peptide to its monoclonal antibody (M1) and for the binding of concanavalin A to a glycoprotein have been determined. The close agreement of these measurements with values obtained by surface fluorescence microscopy and fluorescence correlation spectroscopy helps to validate the use of this device. Thus, this sensor shows promise as an inexpensive, portable, and accurate tool for bioanalytical applications in laboratory and clinical settings.     

Sampling and quantitative analysis of clean B. subtilis spores at sub-monolayer coverage by reflectance fourier transform infrared microscopy using gold-coated filter substrates

A study was conducted to determine the concentration dependency of the mid-infrared (MIR) absorbance of bacterial spores. A range of concentrations of Bacillus subtilis endospores filtered across gold-coated filter membranes were analyzed by Fourier transform infrared (FT-IR) reflectance microscopy. Calibration curves were derived from the peak absorbances associated with Amide A, Amide I, and Amide II vibrational frequencies by automatic baseline fitting to remove most of the scattering contribution. Linear relationships (R2 >or= 0.99) were observed between the concentrations of spores and the baseline-corrected peak absorbance for each frequency studied. Detection limits for our sampled area of 100 x100 microm2 were determined to be 79, 39, and 184 spores (or 7.92 x 10(5), 3.92 x 10(5), and 1.84 x 10(6) spores/cm2) for the Amide A, Amide I, and Amide II peaks, respectively. Absorbance increased linearly above the scattering baseline with particle surface concentration up to 0.9 monolayer (ML) coverage, with the monolayer density calculated to be approximately 1.17 x 10(8) spores/cm2. Scattering as a function of surface concentration, as estimated from extinction values at wavelengths exhibiting low absorbance, becomes nonlinear at a much lower surface concentration. The apparent scattering cross-section per spore decreased monotonically as concentrations increased toward 1.2 ML, while the absolute scattering decreased between 0.9 ML and 1.2 ML coverage. Calculations suggest that transverse spatial coherence effects are the origin of this nonlinearity, while the onset of nonlinearity in the baseline-corrected absorption is probably due to multiple scattering effects, which appear at a high surface concentration. Absorption cross-sections at peaks of the three bands were measured to be (2.15 +/- 0.05) x 10(-9), (1.48 +/- 0.03) x 10(-9), and (0.805 +/- 0.023) x 10(-9) cm2, respectively. These values are smaller by a factor of 2-4 than expected from the literature. The origin of the reduced cross-section is hypothesized to be an electric field effect related to the surface selection rule.     

邻菲罗啉共振光散射光谱法测定痕量镉的研究

基于镉与KI、邻菲罗啉形成多元配合物导致体系共振光散射强度增强,并且随着Cd2+浓度的加大,共振光散射的强度逐渐增大,建立一种邻菲罗啉共振光散射光谱法测定痕量镉的新方法。室温下,采用邻菲罗啉,pH=7.0条件下,在λ=397.6 nm处,Cd2+的加入浓度与共振光散射强度呈良好的线性关系,方法线性范围为0.01～6.5μg/mL,相关系数r=0.999 1,检出限0.06μg/mL,样品加标回收率为96.0%～102.8%。该法用于实际样品废旧电池中痕量镉的分析,效果较好。     

Pulsed laser deposited ZnO film on side-polished fiber as a gas sensing element

A simple sensor element consisting of a side-polished single-mode fiber and a planar metal oxide waveguide is described. The thin ZnO planar waveguide was produced on the polished fiber surface by pulsed laser deposition at optimized processing parameters. A measurement scheme for in situ control of the film thickness during the deposition process was developed and used. X-ray diffraction measurements and scanning electron microscopy were used to characterize the structure and the surface morphology of the planar waveguide, respectively. The numerical evaluation of the sensor sensitivity predicts the possibility to detect refractive index changes of less than 10(-4). Furthermore, preliminary gas sensor tests were performed by using a mixture of 1.5% butane diluted in N(2) and pure butane. A shift of the spectral position of the resonance points was observed from 3 to 5 s after gas exposure, which corresponds to refractive index changes of 3 x 10(-5) and 1.2 x 10(-3) for 1.5% butane and for pure butane, respectively.     

Probing antigen-antibody binding processes by impedance measurements on ion-sensitive field-effect transistor devices and complementary surface plasmon resonance analyses: development of cholera toxin sensors

Impedance measurements on ISFET devices are employed to develop new immunosensors. The analysis of the transconductance curves recorded at variable frequencies, upon the formation of antigen-antibody complexes on the ISFET devices, allows determination of the biomaterial film thicknesses. Complementary surface plasmon resonance measurements of analogous biosensor systems, using Au-coated glass slides as support, reveal similar film thicknesses of the biomaterials and comparable detection limits. A dinitrophenyl antigen layer is immobilized on the ISFET gate as a sensing interface for the anti-dinitrophenyl antibody (anti-DNP-Ab). The anti-DNP-Ab is analyzed with a sensitivity that corresponds to 0.1 microg mL(-1). The assembly of the biotinylated anti-anti-DNP-Ab and avidin layers on the base anti-DNP-Ab layer is characterized by impedance measurements. The development of an ISFET-based sensor for the cholera toxin is described. The anti-cholera toxin antibody is immobilized on the ISFET device. The association of the cholera toxin (CT) to the antibody is monitored by the impedance measurements. The detection limit for analyzing CT is 1.0 x 10(-11) M.     

Immunosensor for detection of inhibitory neurotransmitter gamma-aminobutyric acid using quartz crystal microbalance

A piezoelectric immunosensor for sensing the low molecular weight neurotransmitter gamma-aminobutyric acid (GABA), one of two major inhibitory neurotransmitters in the central nervous system, is described. The sensing interface consists of a dextran layer covalently attached to a self-assembled monolayer of thiolamine compound on the surface of gold electrodes of the crystals. The dextran layer is further modified with GABA molecules to act as the biosensing layer. The affinity binding of monoclonal anti-GABA antibody on the modified piezoelectric crystals is studied in real time without any additional labels. The equilibrium association constant, K(eq) for binding between anti-GABA antibody and GABA molecules is 14.5 microg x mL (-1). The detection limit for anti-GABA is approximately 10 nM. The sensitivity of the sensor at a concentration corresponding to half-maximal response is 13.6 ng/mL x Hz. The functionalized sensor substrate is subsequently used for competitive determination of different concentrations of free GABA (range of 5 microM-50 mM) in PBS-BSA buffer. The detection limit of the immunosensor for sensing GABA with maximum sensitivity is approximately 42 microM.     

Guided shear horizontal surface acoustic wave sensors for chemical and biochemical detection in liquids.

The design and performance of guided shear horizontal surface acoustic wave (guided SH-SAW) devices on LiTaO3 substrates are investigated for high-sensitivity chemical and biochemical sensors in liquids. Despite their structural similarity to Rayleigh SAW, SH-SAWs often propagate slightly deeper within the substrate, hence preventing the implementation of high-sensitivity detectors. The device sensitivity to mass and viscoelastic loading is increased using a thin guiding layer on the device surface. Because of their relatively low shear wave velocity, various polymers including poly(methyl methacrylate) (PMMA) and cyanoethyl cellulose (cured or cross-linked) are investigated as the guiding layers to trap the acoustic energy near the sensing surface. The devices have been tested in biosensing and chemical sensing experiments. Suitable design principles for these applications are discussed with regard to wave guidance, electrical passivation of the interdigital transducers from the liquid environments, acoustic loss, and sensor signal distortion. In biosensing experiments, using near-optimal PMMA thickness of approximately 2 microm, mass sensitivity greater than 1500 Hz/(ng/mm2) is demonstrated, resulting in a minimum detection limit less than 20 pg/mm2. For chemical sensor experiments, it is found that optimal waveguide thickness must be modified to account for the chemically sensitive layer which also acts to guide the SH-SAW. A detection limit of 780 (3 x peak-to-peak noise) or 180 ppb (3 x rms noise) is estimated from the present measurements for some organic compounds in water.     

Label-free detection of bacteria by electrochemical impedance spectroscopy: comparison to surface plasmon resonance

The low but known risk of bacterial contamination has emerged as the greatest residual threat of transfusion-transmitted diseases. Label-free detection of a bacterial model, Escherichia coli, is performed using nonfaradic electrochemical impedance spectroscopy (EIS). Biotinylated polyclonal anti-E. coli is linked to a mixed self-assembled monolayer (SAM) on a gold electrode through a strong biotin-neutravidin interaction. The binding of one antibody molecule for 3.6 neutravidin molecules is determined using the surface plasmon resonance (SPR). The detection limit of E. coli found by SPR is 10(7) cfu/mL. After modeling the impedance Nyquist plot of E. coli/anti-E. coli/mixed SAM/gold electrode for increasing concentrations of E. coli (whole bacteria or lysed bacteria), the main parameter that is modified is the polarization resistance RP. A sigmoid variation of RP is observed when the log concentration of bacteria (whole or lysed) increases. A concentration of 10 cfu/mL whole bacteria is detected by EIS measurements while 103 cfu/mL is detected for lysed E. coli.