Resonance Optical Sensor Research Articles

Double‐layer silver nanoparticle arrays‐based localised surface plasmon resonance optical sensor for sensitive detection of concanavalin A

A localised surface plasmon resonance (LSPR) optical sensor with double-layer silver nanoparticle (Ag NP) arrays has been developed for the sensitive detection of concanavalin A (ConA). Based on the principle of carbohydrate–protein interactions, double-layer dextran capped Ag NP arrays were initially constructed. The increase of adsorption apparent mass and LSPR coupling between the two Ag NP arrays can effectively enhance the LSPR spectral shift response. Compared with the single-layer Ag NP arrays configuration, the double-layer Ag NP arrays configuration improves the limitation of detection of ConA concentration from 3.42 to ∼1.14 µg/ml.

Surface plasmon resonance optical sensor and antibacterial activities of biosynthesized silver nanoparticles

Silver nanoparticles were prepared using aqueous fruit extract of Ananas comosus as reducing agent. These silver nanoparticles showed surface plasmon peak at 439nm. They were monodispersed and spherical in shape with an average particle size of 10nm. The crystallinity of these nanoparticles was evident from clear lattice fringes in the HRTEM images and bright circular spots in the SAED pattern. The antibacterial activities of prepared nanoparticles were found to be size-dependent, the smaller nanoparticles showing more bactericidal effect. Aqueous Zn2+ and Cu4+ selectivity and sensitivity study of this green synthesized nanoparticle was performed by optical sensor based surface plasmon resonance (SPR) at room temperature.

Self-Referencing Optofluidic Ring Resonator Sensor for Highly Sensitive Biomolecular Detection

The noise-suppression techniques of label-free optical ring resonator sensors are crucial to improve their practical sensing capabilities for biochemical analysis and detection in extremely small detection concentration. We have developed a self-referencing optofluidic ring resonator (SR-OFRR) to vastly improve its sensing capability as a label-free optical biosensor. By monitoring the mode-splitting separation generated on a coupled ring resonator system, the common-mode noise is suppressed by 2 orders of magnitude without any external noise-suppression techniques. In this work, we first carried out theoretical analysis to elucidate the sensing principle and then applied the SR-OFRR biosensor to experimentally detect bovine serum albumin with a concentration detection limit on the order of 1 pg/mL (~15 fM).

Design of simultaneous high-Q and high-sensitivity photonic crystal refractive index sensors

Sensitivities (S) and quality factors (Q) have been trade-offs in label-free optical resonator sensors, and optimal geometry that maximizes both factors is under active development. In this paper, we demonstrate that the nanoslotted parallel multibeam cavity possesses unexplored high S and high Q. We achieve S>800  nm/RIU (refractive index unit) and Q>107 in liquid at telecom wavelength range when absorption is neglected. To the best of our knowledge, this is the first geometry that features both high S and Q factors, and thus is potentially an ideal platform for refractive index-based biochemical sensing.

Utilization of Chitosan-Based Sensor Thin Films for the Detection of Lead Ion by Surface Plasmon Resonance Optical Sensor

Chitosan-based sensor thin films were fabricated to detect trace amounts of lead ion using surface plasmon resonance (SPR) optical sensor. The gold surface used for SPR measure- ments was modified with chitosan and chitosan-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (chitosan-BCAT). Both chitosan and chitosan-BCAT layers were deposited on the gold surface by spin coating technique. The experiment has been carried out to monitor the SPR signals for lead ion with sensitive enhancement by chitosan and chitosan-BCAT layers. For both layers, the change in resonance angle (Δθ) is directly proportional to the concentration of lead ion solution. The higher amounts of Δθ were obtained for chitosan-BCAT film due to a specific binding of BCAT with lead ion. The chitosan-BCAT film enhanced the sensitivity of detection down to 0.03 ppm. Data analysis also has been done by Matlab software using Fresnel formula for multilayer system.

Guide-mode resonance characteristics of periodic structure on base of diamond-like carbon film

We present the study based on rigorous coupled-wave analysis and the S-matrix method to evaluate guide-mode resonance characteristics in the visible range of periodic subwavelength structure fabricated by holographic lithography. This structure consists of a single one-dimensional grating dry etched in a diamond-like carbon film on fused silica substrate. It is shown that reflection spectra of such structure have single peak at normal incidence and two peaks at oblique incidence. Peak positions strongly depend on the grating period and thickness of the waveguide layer. Moreover, the simulation results show that the shift of the second peak in the spectral reflectance is less sensitive to the change of certain structural parameters and is more sensitive to the change of the refractive index of the surrounding medium. It is shown that the simulation results can be employed for the interpretation of optical response obtained from guide-mode resonance optical sensors.

基于调频光谱原理的在线式表面等离子体共振光纤传感器

基于调频光谱原理的在线式表面等离子体共振光纤传感器

Fabrication of broad area optical nanostructures for high throughput chemical sensing

In this work, we implement an optical resonant sensor with high throughput capabilities to act as chemical or biosensor. We optimized the diffraction grating structures by FDTD simulations. Based on this study, we produced dielectric diffractive gratings in 1cm2 areas by laser interference lithography (LIL) and interrogated them with white light. The reflected single wavelength shifted with changes of the external medium's refractive index (RI), resolving variations of 7.3×10−5 refractive index units (RIU). To exploit the broad active areas fabricated, we developed a custom instrument to acquire spatial maps of the resonance. We called the technique broad area resonance scan (BARS) and used it to characterize the geometric and material uniformity of the surfaces. We suggest this as an in situ practice to characterize photonic crystals and also as a method to scan highly parallelized analysis on a single chip in real time. In addition to a refractometric label-free application, we demonstrated a fluorescent-based measurement with the same readout and found state of the art sensitivities. Thus, the multimethod platform presented is able to double prove an assay with a single experiment in addition to its ability to screen large numbers of interactions using low volume of reagents.

Lossy mode resonance optical fiber sensor to detect organic vapors

A transmission sensor able to detect Volatile Organic Compounds (VOCs) has been developed using optical fiber with Plastic Cladding (PCS). Specifically, 1.5cm of the cladding was removed in order to deposit an organometallic compound whose chemical structure is [Au2Ag2(C6F5)4(C6H5CCC6H5)2]n along this section. This complex reacts reversely in presence of organic vapors such as alcohols, therefore, it is used as sensing material. The compound was altered to show a negative charge, so it can be deposited combined with a positive charged polymer by means of the Layer-by-Layer (LbL) method. In this manner, as the nanolayers were deposited, Lossy Mode Resonances (LMRs) were induced and shifted. The polymer nanolayers doped with the organometallic material accelerated the LMRs appearance with respect to the nanolayers without additive and so, it enhanced the spectral shift. Once the construction process was completed, two LMRs were observed, choosing the second one to study the sensor behavior when it was placed at 663.57nm. The sensor was exposed to different concentrations of ethanol, methanol and isopropanol vapors, showing sensitivities of 0.417, 0.520 and 263nmppm−1, respectively. In the case of methanol, the second LMR peak shows a remarkable blue shift of 100nm. The interference with water vapors is minor to 1nm below 60%, whereas the effect of temperature is insignificant between 20°C and 60°C.

A Lossy Mode Resonance optical sensor using silver nanoparticles-loaded films for monitoring human breathing

This work is focused on the fabrication of a human breathing sensor based on the in situ synthesis of silver nanoparticles (Ag-NPs) inside a polymeric coating previously deposited on an optical fiber core by means of the Layer-by-Layer self-assembly. The Ag-NPs were created using a synthesis protocol consisting of a loading step of the Ag+ cations into the polymeric film and a further reduction step using dimethylamine borane (DMAB). The morphology and distribution of the Ag-NPs inside the polymeric coating have been studied using atomic force microscopy (AFM). Furthermore, UV–VIS spectroscopy and energy dispersive X-ray (EDX) were also used to confirm the synthesis of the Ag-NPs within the resultant coating. The amount of Ag-NPs increases when the number of loading/reduction cycles is higher. Therefore the incorporation of the Ag-NPs affects the refractive index of the overlay promoting the observation of a resonant attenuation band in the infrared region (NIR), known as Lossy Mode Resonance (LMR), which can be used as a sensing signal to monitor the human breathing. The quality of the device has been experimentally tested with good sensitivity (0.455nm per RH%) and fast response time (692ms and 839ms for rise/fall).

Surface plasmon resonance optical sensor for detection of Pb2+ based on immobilized p-tert-butylcalix[4]arene-tetrakis in chitosan thin film as an active layer

Abstract Surface plasmon resonance (SPR) optical sensor, for sensitive and selective detection of Pb2+, was developed in this study based on p-tert-butylcalix[4]arene-tetrakis (BCAT) immobilized in chitosan thin film as an active layer. Pb2+ can be detected by measuring the SPR signal when BCAT immobilized chitosan thin film is exposed to Pb2+ in aqueous solution. The BCAT immobilized chitosan thin film was coated on a gold layer by spin coating technique. The measurements were carried out for Pb2+ concentration ranging from 30 ppb to 5 ppm. A linear relationship between the shift of SPR angle and concentration of Pb2+ up to 1 ppm, with sensitivity of 0.045° ppm−1 has been observed. Pb2+ can also be selectively detected when present in mixtures of heavy metal ions containing Cu2+, Hg2+, Zn2+ and Mn2+ ions.

Analysis of Pb(II) ion sensing by crosslinked chitosan thin film using surface plasmon resonance spectroscopy

The crosslinked chitosan thin film had been studied as a sensor element of surface plasmon resonance (SPR) optical sensor. Crosslinked chitosan solution was synthesized by homogeneous reaction of medium molecular weight chitosan in aqueous acetic acid solution with glutaraldehyde as crosslinking agent. It was deposited on gold film by spin coating. Using SPR technique, the optical properties of crosslinked chitosan thin film before and after contacting with different concentration of Pb(II) ion in a range of 0.5–100ppm had been obtained by fitting. The resonance angle shifted to lower value as the Pb(II) ion concentration increased. Changes in the resonance angle (Δθ) are directly proportional to the concentration of Pb(II) ion solution. X-ray photoelectron spectroscopy (XPS) had been employed to confirm chemical elements and their bonding of the thin film prior to adsorption, as well as chemical interactions involved between Pb(II) ion and the thin film.

Flow-enhanced transient response in whispering gallery mode biosensors

Whispering gallery mode (WGM) optical resonator sensors are an extremely sensitive label-free technology for detecting the binding of biomolecules in solution. To better understand the fast transient response observed with these devices, we model mass transfer to spherical and toroidal WGM sensors of identical outer radius. Finite element simulations predict a 3-10 fold higher binding frequency for toroidal sensors. These results agree to within an order of magnitude with experimental data from the literature and suggest a design strategy to improve the transient response of a sensor by making the device small only in the dimension that governs boundary layer development.

Application of dynamic line narrowing in resonant optical sensing

We propose a dynamic operational mode and the resulting dynamic line narrowing as a method for enhancing the resolution and the detection limit of high-quality (high-Q) resonant optical sensors. Using a silica microtoroid as an experimental platform, we demonstrate that dynamic line narrowing through the thermo-optic effect can significantly improve the detection limit in both resonant shift and resonance splitting operating modes.

Surface Plasmon Resonance Optical Sensor for Detection of Essential Heavy Metal Ions with Potential for Toxicity: Copper, Zinc and Manganese Ions

In this work, surface plasmon resonance (SPR) spectroscopy had been studied for detection of essential heavy metal ions with potential for toxicity: copper, zinc and manganese ions (Cu2+, Zn2+ and Mn2+). The sensitivity of SPR optical sensor had been enhanced by introducing a thin crosslinked chitosan layer on a gold film. Crosslinked chitosan solution was synthesized by homogeneous reaction of medium molecular weight chitosan in aqueous acetic acid solution with glutaraldehyde as crosslinking agent. It was deposited on gold film by spin coating. From the results we found that the change in the resonance angle (Δθ) is directly proportional to the concentration of heavy metal ions solution (0.5-100 ppm). The sensitivity of this optical sensor for the studied heavy metal ions are in following order: Cu2+ > Zn2+ > Mn2+. The gold/chitosan interface in SPR technique is highly sensitive for these heavy metal ions with detection limit as low as 0.5 ppm.

High-sensitive SPR sensing with Indium Nitride as a dielectric overlay of optical fibers

In this work, an Indium Nitride (InN) dielectric overlay has been used to develop a surface plasmon resonance optical fiber sensor. Although InN is a very promising material in electronics industry, this is the first time that this kind of material is used for optical sensing. The obtained results show an improvement of the reliability and long term stability with respect to previous devices made with the same technology. More remarkably, the sensitivity increases up to 11,800 nm/RIU in the range of outer refractive indices between 1.415 and 1.429, the highest sensitivity achieved with this kind of devices. Therefore, a novel application of the InN to optical fiber sensors is demonstrated. The use of this material would be of great interest to produce new SPR-based devices for chemical and biological sensing.

Fabrication of Nano-Grating by Focused Ion Beam / Scanning Electron Microscopy Dual-Beam System

The uniform, well designed nano-gratings have been successfully fabricated by using a dual beam focused ion beam (FIB)/scanning electron microscopy (SEM) system on the silicon substrates coated with 15 nm thick Au layer. The nano-gratings were designed with period of 840 nm, groove of 425 nm and beam of 415 nm. By adjusting the FIB parameters of milling like beam current, dwell time and scanning model, the fabricated nano-gratings were uniform in width and the side wall had good verticality. The currently fabricated nano-gratings using focused ion beam can be adjusted to serve as sub-wavelength optical resonant sensor which can be extended to nano-grating accelerometer with resolution of 10-9g.

Nanoengineered optical resonance sensor for composite material refractive-index measurements

We present an optical resonance sensor capable of measurement of refractive index in highly nonhomogeneous materials. Traditional optical resonance sensors fail when the size of particles is comparable with the wavelength (100 nm and larger). Our new nanoengineered design allows incorporation of a highly delocalized mode into a resonance structure. The sensing depth of the device was measured to be 1 mum, the largest reported in the literature as far as we know, with a quality factor of 500. We demonstrate two applications.

Design guidelines for optical resonator biochemical sensors

We propose a design tool for dielectric optical resonator-based biochemical refractometry sensors. Analogous to the widely accepted photodetector figure of merit, the detectivity D*, we introduce a new sensor system figure of merit, the time-normalized sensitivity S*, to permit quantitative, cross-technology-platform comparison between resonator sensors with distinctive device designs and interrogation configurations. The functional dependence of S* on device parameters, such as resonant cavity quality factor (Q), extinction ratio, system noise, and light source spectral bandwidth, is evaluated by using a Lorentzian peak fitting algorithm and Monte Carlo simulations to provide theoretical insights and useful design guidelines for optical resonator sensors. Importantly, we find that S* critically depends on the cavity Q factor, and we develop a method of optimizing sensor resolution and sensitivity to noise as a function of cavity Q factor. Finally, we compare the simulation predictions of sensor wavelength resolution with experimental results obtained in Ge17Sb12S71 resonators, and good agreement is confirmed.

Optical resonant sensors: a method to reduce the effect of thermal drift

The use of a whispering gallery mode (WGM) resonator with an ultrahigh quality factor Q is promising in highly sensitive, label-free, lab-on-a-chip sensor applications. We investigated a novel method of using the differential frequency of TE and TM modes to reduce the thermal noise baseline, which commonly limits the sensitivity of WGM sensors. We studied the temperature dependence of WGM based sensors and experimentally demonstrated the reduction of temperature fluctuation and thus a significant improvement in the practical sensor detection limit.