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.     

Full-field surface plasmon resonance sensor for high resolution refractive index measurement using common-path heterodyne interferometer

This study presents a full-field surface plasmon resonance (SPR) sensor induced by attenuated total reflection (ATR)-couple for liquid refractive index measurement. The system adopts a common-path heterodyne interferometer to measure the phase difference between P- and S-wave after passing through the SPR sensor. In order to realize the full-field measurement, it adopts a three-frame integrating-bucket method. The experimental results show great consistency profile between single point and full-field liquid refractive index measurement from 1.330 to 1.340 RIU. It shows that the best sensitivity and resolution of a single pixel in charge couple device (CCD) for liquid refractive measurement are 3.3 × 10⁴ (deg/RIU) and 3.53 × 10⁻⁶ (RIU), respectively. As compared with traditional single-point method, the proposed method with a regular CCD has no degradation. Therefore, the system has many applications in chemistry and biology.     

Determination of 3-nitrotyrosine in human urine samples by surface plasmon resonance immunoassay

This paper describes the detection of a low-molecular weight molecule, 3-nitrotyrosine (3-NT) (∼226 Da), in human urine by coupling indirect inhibition assay with a surface plasmon resonance (SPR) sensor. 3-NT antibody (anti-3-NT Ab, mouse IgG) was used in this assay. An optimal antibody concentration has been measured at 27.9 μg/mL in order to obtain the best performance of the sensor surface. The lowest detection limit for 3-NT with this method is 4.7 ng/mL (S/N = 3). Sensor reliability was demonstrated by good specificity, intra-assay and inter-assay relative standard deviations <8%, average recovery of 107.68 ± 19.4% and sensor surface (self-assembled monolayer) stability through more than 200 regeneration cycles and 15 days of repeated measurement. This is the first SPR biosensor assay of 3-NT in human urine. The high stability of the SPR sensor surface underlies the potential of the SPR method as a low cost diagnostic tool for clinical detection of 3-NT.     

Non-aggregation based label free colorimetric sensor for the detection of Cr (VI) based on selective etching of gold nanorods

Gold nanorods (GNRs) exhibit strong longitudinal surface plasmon resonance absorption (LPA), which is highly dependent on its aspect ratio (length/width). The strong oxidization of Cr (VI) enables it to etch GNRs selectively at tips. The redox etching causes the aspect ratio of GNRs to decrease, resulting in the LPA blue shifts and the color of GNRs distinctly changes. Besides, the blue shift is linear to the concentration of Cr (VI) in the range of 0.1-20 μM. Thus, a non-aggregation based label free colorimetric sensor for the detection of Cr (VI) has been developed based on the selective etching of GNRs. The proposed colorimetric sensor is responsive, simple, sensitive (detection limit is 8.8 × 10⁻⁸ M) and selective, and it has been successfully applied to the detection of Cr (VI) in drinking water and sea water. Moreover, the mechanism of colorimetric sensor for the detection of Cr (VI) was also discussed.     

Dynamically modulated intensity interrogation scheme using waveguide coupled surface plasmon resonance sensors

An electro-optically modulated intensity interrogation method based on tunable waveguide coupled surface plasmon resonance sensors has been proposed. It has been theoretically and experimentally demonstrated that the proposed scheme can enable sensitive measurement of measurand variations. By modulating the refractive index in the waveguide layer, this interrogation method yields modulated signal whose amplitude is related to measurand's refractive index. This amplitude modulated signal offers a higher signal to noise ratio and eliminates additive noise in the sensor system. A preliminary investigation using saline buffers with different NaCl concentrations shows a resolution of 2.3 × 10^?6 refractive index unit by our approach. Resolution can be controlled by the amplitude of the applied modulation voltage and can be further enhanced by optimizing the device structure or improving the electro-optical (E-O) coefficient of the E-O material. This approach is simple, stable, and promising for low-cost or multi-channel SPR biosensor applications.     

A multichannel surface plasmon resonance sensor using a new spectral readout system without moving optics

Surface plasmon resonance (SPR) sensors with spectral interrogation provide a high refractive index resolution, a large dynamic range and a fixed optical detection module. In this work, we propose a new multichannel spectral detection unit that uses only one spectrometer to measure the reflection spectrum from multiple sensing spots serially without any mechanical movement. This spectral detection unit is designed based on a spatial light modulator (SLM) configured as a programmable optical aperture for the spectrometer. To demonstrate this concept, a five-channel laboratory SPR prototype was built based on the proposed multichannel detection unit, and we evaluated the device's sensitivity and resolution using a refractive index test. Refractive index resolution of 1.4 × 10⁻⁶ refractive index units (RIU) can be reached using the five-channel prototype. This sensor is suitable for low-cost multichannel biosensing applications that do not contain fast kinetics.     

A microfluidic based differential plasmon resonance sensor

A new type of differential surface plasmon (SPR) sensor integrated with a microfluidic system is presented. The working principle of the microfluidic device is based on hydrodynamic modulation of two laminar streams inside a microchannel to provide periodic changes of the environment on the SPR sensor. The modulated reflectance is then demodulated using a lock-in amplifier. The presented sensor provides sensitivities of index of refraction about 4 × 10⁻⁸ RIU together with a 4 orders of magnitude dynamic range. This method demonstrates a sensitive detection scheme which could be used for label-free detection.     

ZnO modified gold disc: A new route to efficient glucose sensing

Surface of a gold disc was modified by depositing ZnO film electrochemically. AFM analysis of the film shows c-axis oriented pillar like structures grown normal to the surface. Sensor surface was prepared by immobilizing glucose oxidase (GOD) on the ZnO modified gold disc. Different concentrations of glucose (50-1000 ng/ml) were taken to monitor the sensor response. Sensor was found to be highly sensitive to low concentrations of glucose and sensitivity increases linearly in the range of 50-250 ng/ml. The high sensitivity of the ZnO modified gold disc may be attributed to the SPR induced electron transfer between the two systems (i.e. Au and ZnO). The work indicates promising application of the system as a tool for studying sensitive bio-specific interactions, with further development of highly sensitive and selective bio-molecular and chemical SPR based optical sensors.     

Design and performances of immunoassay based on SPR biosensor with Au/Ag alloy nanocomposites

A novel method for detecting human IgG is reported, which is based on Au/Ag alloy nanocomposites for amplifying surface plasmon resonance response. Au/Ag alloy nanocomposites were characterized in detail by transmission electron microscopy (TEM), UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). Covalent immobilization of about 24 nm diameter of Au/Ag alloy nanocomposites on the Au film results in a large shift in resonance wavelength, which is due to the increase of the thickness of the sensing membrane, high dielectric constant of Au/Ag nanoparticles, and electromagnetic coupling between Au/Ag alloy nanocomposites and Au film. The SPR biosensor based on Au/Ag alloy nanocomposites exhibits a satisfactory response for human IgG in the concentration range of 0.15-40.00 μg mL⁻¹. While the biosensor based on Au nanoparticles shows a response in the concentration range of 0.30-20.00 μg mL⁻¹ and the biosensor based on Au film shows a response for human IgG in the concentration range of 1.25-20.00 μg mL⁻¹.     

An interferometric biosensor composed of a prism-chamber assembly and a composite waveguide with a Ta2O5 nanometric layer

A highly sensitive integrated polarimetric interferometer biosensor with improved long-time stability and simple operation was prepared by using a novel prism-chamber assembly and an inexpensive waveguide made by sputtering a tapered nanometric layer of Ta₂O₅ on a single-mode glass waveguide. By comparing the measured refractive-index (RI) sensitivities with those simulated based on a four-layer homogeneous waveguide, both the equivalent thicknesses (T_eq) for the tapered Ta₂O₅ layers and a severe dependence of RI sensitivity on T_eq were obtained. Addition of 1 g of water in 100 g of a Chinese liquor (alcohol concentration = 46% (v/v)) was easily detected by the sensor. Monitoring of anti-human IgG adsorption with a waveguide of T_eq = 31.99 nm indicates that the antibody coverage required for inducing a phase-different change of Δ? = π is less than 0.012 monolayer. The same waveguide presents a quasi-linear dependence of Δ? on water temperature with the slope of d(Δ?)/dT = −28.50°/°C to which the contribution by the thermo-optical effect of the waveguide is 4.24°/°C, equivalent to a liquid RI change of Δn_c = 1.41 × 10⁻⁵. The interferometer exhibits the promising potential for chemical and biological analyses because of its outstanding characteristics.     

Study on design and application of fully automatic miniature surface plasmon resonance concentration analyzer

A fully automatic miniature surface plasmon resonance (SPR) concentration analyzer having high performance and low cost and developed using a Spreeta™ sensor was designed for field applications and concentration analysis. As in the case of Biacore™ instruments, the automatic sampling system of this device can introduce air segments between the sample/regeneration solution and buffer solution in the pipeline, which effectively prevents mixing of the solutions. A temperature sensor (AD 590) and temperature compensation method are used, which make the device insensitive to temperature fluctuations. A real-time data-smoothing algorithm for the SPR detection data is adopted; this can reduce the noise level to 5 × 10⁻⁷ RIU (refractive index units). The noise level of the sensorgram is 3.5% of the original level. Two types of self-prepared sensing chips—SMX-BSA (bovine serum albumin coated with sulfamethoxazole) and SMX-CM5 (carboxymethyl dextran coated with sulfamethoxazole)—are used to analyze the concentrations of sulfamethoxazole (SMX) standard solutions. Each chip's SMX calibration curve is established within the measurement range of 0-2000 ng/ml, and both limits of detection (LOD) are 2 ng/ml. One cycle of assay time is less than 15 min.     

Ochratoxin A immunoassay with surface plasmon resonance registration: Lowering limit of detection by the use of colloidal gold immunoconjugates

An immunoanalytical system was developed for the determination of ochratoxin A with the use of a surface plasmon resonance (SPR) sensor amplified by the anti-species antibody-colloidal gold particle (CGP) conjugate. The use of the binding of immune complexes to the CGP-anti-species antibody conjugate leads to the SPR signal amplification by a factor of more than 10 and results in the 60 pg/mL limit of detection of ochratoxin A with an assay time of 30 min. These characteristics are superior to those obtained both in the conventional enzyme immunoassay with the use of the same reagents and the SPR assay with unmodified antibodies and specific antibodies conjugated to colloidal gold.     

A novel photometric glucose biosensor based on decolorizing of silver nanoparticles

A novel glucose biosensor based on chromophore (silver nanoparticles) decolorizing for the photometric determination of glucose was developed. Silver nanoparticles are directly synthesized in the sol-gel matrix by a one-step method based on the reduction of the inorganic precursor AgNO₃ and were used for the preparation, characterization and calibration of a highly sensitive and cost-effective localized surface plasmon resonance-based glucose biosensor. In the presence of glucose oxidase (GOx) and due to the enzyme-substrate (glucose) reaction, H₂O₂ was produced and silver nanoparticles in the sol-gel glass have the ability for the decomposition of hydrogen peroxide. Due to the degradation of silver nanoparticles a remarkable change in the localized surface plasmon resonance absorbance strength could be observed which have been monitored as a suitable signal for determination of substrate concentration. Beer's law is obeyed in the range from 50 to 800 mg/L glucose and the limit of detection is 23 mg/L. The proposed optical biosensor has been successfully applied to the determination of glucose in various real samples.     

Surface plasmon resonance (SPR) sensors for the rapid, sensitive detection of the cellular response to osmotic stress

Cells regulate their volume in response to changes in osmolarity of both, their extracellular and intracellular environments. As stability of the cell volume is a compelling exigency for cellular integrity, techniques for a sensitive, time-resolved volume measurement of adherently grown mammalian cells attract considerable interest, especially in the field of cell physiology and biology. In this study we apply a surface plasmon resonance (SPR) based biosensor for the comparative analysis of the volume responses of two renal epithelial cell types to non-isotonic challenges. The on-line, label-free and non-invasive biosensor format shows distinct similarities and differences in the reaction kinetics of the two cell types. Furthermore regulatory volume responses to the osmotic stimuli as well as their inhibition by Gd³⁺ ions can be observed with a high time-resolution. Limit-of-detection measurements indicate the high sensitivity of the sensor capable of detecting cellular volume responses of adherently grown mammalian cells to osmotic stimuli well below a bioanalytical relevant value of 5 mOsm/kg.     

Surface plasmon resonance based fiber optic sensor for the detection of low water content in ethanol

A fiber optic sensor utilizing surface plasmon resonance (SPR) has been fabricated for the detection of low content of water in ethanol. The sensor utilizes spectral interrogation technique for operation. The resonance wavelength has been found to vary linearly with water content in the range 0-10% with sensitivity of 1.149 nm per percentage of water. The results are in agreement with the refractive index variation of ethanol-water mixture. The sensor has a water resolution of 0.145% which is better than the evanescent wave absorption sensor reported for the similar study. The sensor will find application in determining the low water content in ethanol which is used as a bio-fuel and in the field of medicine and organic chemistry.     

动态范围可调的波导型SPR传感器模型

表面等离子体共振 (SPR)技术是一种简单直接的传感技术 ,SPR对金属表面附近的折射率的变化极为敏感 ,利用这一性质 ,表面等离子体共振传感器已成为生物传感器研究领域的热点。现提出一种电光调制波导型SPR模型 ,模拟计算表明该模型在不损害灵敏度的条件下 ,扩大了探测的动态范围。     

Free chlorine sensing using an interferometric sensor

A waveguide interferometer based free-chlorine sensing technique has been developed. A polymer film for a specific free chlorine binding was designed, synthesized and applied on the surface of a waveguide. The material is based on cyanuric acid moieties along each repeating unit covalently tethered to poly(norbornene)s. Chlorine sensing was accomplished by measuring the refractive index change of the polymer, as a result of the reaction between cyanuric acid and free chlorine, interferometrically by the evanescent field extended above the waveguide surface. The free chlorine binding to cyanuric acid is reversible and a linear calibration curve from 0.1 to 10 mg L⁻¹ of HOCl concentration was obtained with the level of detection (LOD) and level of quantification (LOQ) of 0.047 and 0.328 mg L⁻¹ of HOCl, respectively. A free chlorine measurement with less interference from combined chlorine than DPD based colorimetric method was developed as a result of the different sensing responses of free and combined chlorine. Free chlorine residual was measured in samples collected from tap water and poultry processing waters by both optical sensor and DPD-based colorimetric method. Good agreement between both methods was observed although the levels for free chlorine measured by the optical sensor are systematically lower than the readings obtained from the DPD method. The difference might be the result of the interference from combined chlorine during the DPD measurement.     

Surface plasmon resonance immunosensor using Au nanoparticle for detection of TNT

In order to develop the fully integrated portable surface plasmon resonance (SPR) system for detection of explosives, the amplification strategy of SPR signal was investigated. Indirect competitive inhibition method allowed the middle-sized SPR sensor to detect trinitrotoluene (TNT) at ppt level. However, this enhanced SPR signal was not high enough to detect TNT at ppt level by a miniaturized SPR sensor. Therefore, localized surface plasmon resonance (LSPR) effect using Au nanoparticle as further signal amplification approach was used. The amplification method of indirect competitive inhibition and LSPR were combined together for fabrication of the immunosurface using Au nanoparticle. TNT detectable range of this immunosurface was from 10 ppt (10 pg/ml) to 100 ppb (100 ng/ml), which was almost comparable to that without Au nanoparticle. The observed resonance angle change due to binding monoclonal TNT antibody (M-TNT Ab) with the immunosurface modified with Au nanoparticle was amplified to four times higher than that in absence of Au nanoparticle.