Plasmonic Gas Sensor Research Articles

New Parameter for Benchmarking Plasmonic Gas Sensors Demonstrated with Densely Packed Au Nanoparticle Layers.

Localized surface plasmon resonance (LSPR) gas sensitivity is introduced as a new parameter to evaluate the performance of plasmonic gas sensors. A model is proposed to consider the plasmonic sensors' surface sensitivity and plasmon decay length and correlate the LSPR response, measured upon gas exchange, with an equivalent refractive index change consistent with adsorbed gas layers. To demonstrate the applicability of this new parameter, ellipsoidal gold nanoparticles (NPs) arranged in densely packed hexagonal lattices were fabricated. The main advantages of these sensors are the small and tunable interparticle gaps (18-29 nm) between nanoparticles (diameters: 72-88 nm), with their robust and scalable fabrication technology that allows the well-ordered arrangement to be maintained on a large (cm2 range) area. The LSPR response of the sensors was tested using an LSPR sensing system by switching the gas atmosphere between inorganic gases, namely He/Ar and Ar/CO2, at constant pressure and room temperature. It was shown that this newly proposed parameter can be generally used for benchmarking plasmonic gas sensors and is independent of the type and pressure of the tested gases for a sensor structure. Furthermore, it resolves the apparent disagreement when comparing the response of plasmonic sensors tested in liquids and gases.

Black phosphorus/waveguide terahertz plasmonic structure for ultrasensitive tunable gas sensing

In this study, we propose a black phosphorus (BP)/waveguide terahertz plasmonic sensing structure comprising vertically stacked crystal quartz, polymethylpentene (TPX), BP, crystal quartz, and TPX layers on a germanium prism. Sharp Fano-type resonance is induced by strong coupling between the surface plasmon polariton and planar waveguide modes, and it generates imaging sensitivity of up to 9.978 × 103 RIU−1 for gas detection, with better sensing performance than other terahertz plasmonic gas sensors. Due to the in-plane anisotropic plasmonic property of BP, the proposed sensing structure exhibits optically tunable detection sensitivity and the imaging sensitivity is highly dependent on the direction. In addition, we investigated the changes in the Fano resonance and surface plasmon resonance, as well as the figure of merit for the imaging sensitivity according to structural parameters such as the thicknesses of the crystal quartz and TPX layers. Our results suggest that the proposed structure may have potential applications in gas detection in the terahertz band.

Design of a near-infrared plasmonic gas sensor based on graphene nanogratings

In this work, a gas sensor based on the plasmonic double-layer graphene nanograting (GNG) structure with an enhanced figure of merit (FoM) is presented in the near-infrared region. This structure includes double periodic graphene nanoribbon arrays, separated by a dielectric. The wavelength interrogation method is employed to accurately investigate the behavior of the proposed structure for various physical and geometrical parameters, including the array pitch, graphene nanoribbon width, refractive index of the intermediate dielectric between the GNGs, and the chemical potential of the graphene. A sharp dip is achieved by the guided-mode resonance between the two GNG layers, due to their near-field coupling. For the optimized design, obtained sensitivity and FoM are 430.91 nm/RIU and 174.68 R I U − 1 , respectively, when the finite-element method is used for the simulations. The high FoM is a result of the field enhancement at the edges of the graphene nanoribbons, as well as the narrow resonance linewidth achieved by the sharp transmission dip. In addition to the high performance and FoM, the structure is robust to the misalignment of two GNG layers, offering a solution for practical gas sensing applications. To the best of our knowledge, the proposed GNG-based structure enjoys a boosted FoM compared to the previously proposed integrated gas sensors, as well as a practically feasible design for fabrication.

On-chip readout plasmonic mid-IR gas sensor

Gas identification and concentration measurements are important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. Here a novel mid-IR plasmonic gas sensor with on-chip direct readout is proposed based on unity integration of narrowband spectral response, localized field enhancement and thermal detection. A systematic investigation consisting of both optical and thermal simulations for gas sensing is presented for the first time in three sensing modes including refractive index sensing, absorption sensing and spectroscopy, respectively. It is found that a detection limit less than 100 ppm for CO₂ could be realized by a combination of surface plasmon resonance enhancement and metal-organic framework gas enrichment with an enhancement factor over 8000 in an ultracompact optical interaction length of only several microns. Moreover, on-chip spectroscopy is demonstrated with the compressive sensing algorithm via a narrowband plasmonic sensor array. An array of 80 such sensors with an average resonance linewidth of 10 nm reconstructs the CO₂ molecular absorption spectrum with the estimated resolution of approximately 0.01 nm far beyond the state-of-the-art spectrometer. The novel device design and analytical method are expected to provide a promising technique for extensive applications of distributed or portable mid-IR gas sensor.

Miniaturized nanohole array based plasmonic sensor for the detection of acetone and ethanol with insights into the kinetics of adsorptive plasmonic sensing.

The present work demonstrates development of a miniaturized plasmonic platform comprised of a Au nanohole array (NHA) on a Si/Si3N4 substrate. Plasmonic responses of the NHA platform, which is coated with Cu-benzenetricarboxylate metal organic framework (MOF), are found to be promising even towards 500 nmol mol-1 (ppb) of acetone or ethanol vapors at room temperature. The sensing characteristics are further investigated by varying the operating temperature (296 K to 318 K) of the sensor and the concentrations of vapors (500 nmol mol-1 to 320 μmol mol-1). The plasmonic responses for the sensors are correlated with the adsorption of vapors on the MOF surface and modeled in accordance to Langmuir-type adsorption. Kinetic parameters are estimated for the adsorption of fixed concentrations of acetone and ethanol vapors within the studied operating temperature range. The linear variation of characteristic response time constants with the operating temperature provides Arrhenius activation energies for the adsorption of acetone and ethanol vapors. The comparatively lower activation energy estimated for the adsorption of ethanol results in faster and more sensitive response of the sensor towards that analyte. The plasmonic sensor for the detection of nmol mol-1 level acetone and ethanol vapors at room temperature along with the kinetic correlation on plasmonic response with the adsorption of the analytes described herein offer new insights to existing reports on surface modification and plasmonic detection.

Sol-Gel Thin Films for Plasmonic Gas Sensors.

Plasmonic gas sensors are optical sensors that use localized surface plasmons or extended surface plasmons as transducing platform. Surface plasmons are very sensitive to dielectric variations of the environment or to electron exchange, and these effects have been exploited for the realization of sensitive gas sensors. In this paper, we review our research work of the last few years on the synthesis and the gas sensing properties of sol-gel based nanomaterials for plasmonic sensors.

Fluctuations in transient response of adsorption-based plasmonic sensors

The basic parameters of a sensor element defining its ultimate performance are sensitivity and intrinsic noise. In plasmonic gas sensors both are determined by refractive index changes due to adsorption and desorption (a–d) of target analyte particles to the sensor active area. In this paper we present a general model that can be simultaneously used to determine sensitivity and intrinsic noise of a plasmonic sensor both during transients and in steady-state and is valid for multi-analyte environments. The model utilizes the conventional probabilistic approach. It is derived without any assumptions about the stochastic nature of the fundamental (a–d) process. It reveals how all stochastic properties of the processes with (pseudo) first order kinetics with the initial number of particles equal to zero can be fully determined from the deterministic solution, without any previous stochastic analysis. Based on the proposed model it is possible to establish the optimum moment for readout when fluctuations are minimal. Transients last longer and fluctuations are lower at lower temperatures. The insight into the transient dynamics opens the possibility to use a single element sensor for multiple analyte sensing. Another result is that a–d noise is higher for smaller adsorption areas, which may be important for micro and nanosystems generally, since each of them has to be kept immersed in some kind of environment and thus be subject to contamination by adsorption that can significantly influence their behavior. Besides being applicable for plasmonic sensors of trace amounts of gases and other nanoplasmonic devices used in sensing, the model is applicable for other adsorption-based sensors, as well as for the investigations of stochastic phenomena in micro and nanostructures.

Spectral, amplitude and phase sensitivity of a plasmonic gas sensor in a metallic photonic crystal slab geometry: Comparison of the near and far field phase detection strategies

Using finite-difference time-domain method, we investigate phase and amplitude reflective properties of a metallic photonic crystal slab comprising a two-dimensional array of gold disks placed on top of a thin gold film resting on a dielectric substrate. Photonic crystal slab overcladding is a gaseous analyte. Throughout the paper we discuss prospectives of application of such photonic crystal slabs to sensing of changes in the gas refractive index. We start by studying the field distributions and spectral positions of two types of surface plasmons supported by such PhCs as a function of the photonic crystal lattice period, the gold film thickness, and the gold disk size. First, we find that the spectral positions of plasmon peaks depend almost linearly on the photonic crystal lattice constant, which is a manifestation of the delocalized nature of a plasmon extending over the PhC lattice. This is possible due to connectivity between metallic disks via an underlying thin metallic film. Second, we find that the width of plasmonic peaks is highly sensitive to the relative size of the metallic disks compared to the lattice period. This can be well explained via interaction between the localized plasmons situated at the disc edges in the adjacent unit cells. We therefore find that plasmons in the metallic PhC slabs featuring metallic discs connected by a metallic film exhibit both strong local and non-local properties. Third, we find that, generally, there are two types of plasmons supported by such metallic PhCs. One type is a plasmon with a large fraction of its field located in the gas overcladding, which is most suitable for sensing. In contrast, another plasmon type has its field concentrated at the interface between a thin metal film and a substrate; such plasmons are only weakly sensitive to the refractive index of the sensor overcladding, and, therefore, can serve as convenient references for the sensor measurements. Finally, we report sensor sensitivities to changes in the real part of the gas refractive index when using amplitude and phase-based detection strategies. We start by demonstrating that when measured in the sensor far field, the phase sensitive detection provides much lower detection limit ( 1.8 × 1 0 − 6 RIU) compared to that of the amplitude-based detection ( 1.5 × 1 0 − 4 RIU). We then find that sensor phase and amplitude sensitivities can be considerably enhanced when performing measurements using point detectors placed in the near field of a sensor. Particularly, we have established that both phase and amplitude sensitivities are maximal when measured in the sensor near field along the normal to the sensor surface going through the point of the highest symmetry of a photonic crystal unit cell ( Γ point). Sensor resolution as high as 2.2 × 1 0 − 7 RIU for the phase-based detection and 7.4 × 1 0 − 5 RIU) for the amplitude-based detection are found, with the most dramatic enhancement observed for the phase detection approach. We believe that experimental verification of the sensor sensitivity enhancement using phase detection in the sensor near field can be accomplished by using scanning near-field optical microscopy.