Chemical Detection Applications Research Articles

Ultra Enhancement of the Resolution of the Divergence Beam-Based SPR Sensor Using a Wavelet Filter

Surface Plasmon Resonance (SPR) sensors are highly sensitive to refractive index variations, making them ideal for biosensing and chemical detection applications. However, their performance can be constrained by noise, resolution limits, and signal distortions, particularly in divergence beam-based configurations. This research presents an ultra-enhancement of the performance of divergence beam-based SPR sensors by employing advanced wavelet filtering techniques. Wavelets, with their multi-resolution analysis capability, are applied to denoise and refine the sensor signal, significantly improving key performance metrics, including resolution, mean square error (MSE), root mean square error (RMSE), signal-to-noise ratio (SNR), sensitivity matrix (SM), and combined sensitivity factor (CSF).The wavelet filter effectively decomposes the SPR signal into distinct frequency bands, separating noise while retaining high-frequency components required for accurate sensing. This results in a significant reduction in MSE and RMSE of 30 and 92.26%, respectively, while simultaneously improving SNR by 54.08%, maintaining signal quality. The wavelet filter significantly improved the resolution of the SPR sensor by 99.95% (1.3772×10-7 RIU), allowing for more precise detection of refractive index changes and boosting diverge beam-based SPR sensor performance. In addition, a sensitivity matrix (SM) and combined sensitivity factor (CSF) were improved by 42 and 41.94%, respectively, allowing for a more thorough evaluation of the sensor's performance across multiple operational parameters. Simulation and experimentation show that wavelet filtering surpasses standard filtering approaches in terms of noise suppression and signal clarity. This technology has considerable potential for improving the accuracy and reliability of SPR sensors in high-sensitivity applications

Effect of wavelength and liquid on formation of Ag, Au, Ag/Au nanoparticles via picosecond laser ablation and SERS-based detection of DMMP.

The present study investigates the effects of input wavelength (1064, 532, and 355 nm) and surrounding liquid environment (distilled water and aqueous NaCl solution) on the picosecond laser ablation on silver (Ag), gold (Au), and Ag/Au alloy targets. The efficacy of the laser ablation technique was meticulously evaluated by analyzing the ablation rates, surface plasmon resonance peak positions, and particle size distributions of the obtained colloids. The nanoparticles (NPs) were characterized using the techniques of UV-visible absorption, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Furthermore, NPs of various sizes ranging from 6 to 35 nm were loaded onto a filter paper by a simple and effective drop-casting approach to achieve flexible surface-enhanced Raman spectroscopy (SERS) substrates/sensors. These substrates were tested using a simple, portable Raman device to identify various hazardous chemicals (malachite green, methyl salicylate, and thiram). The stability of the substrates was also systematically investigated by determining the decay percentages in the SERS signals over 60 days. The optimized SERS substrate was subsequently employed to detect chemical warfare agent (CWA) simulants such as methyl salicylate (a CWA simulant for sulfur mustard) and dimethyl methyl phosphonate (has some structural similarities to the G-series nerve agents) at different laser excitations (325, 532, and 633 nm). A notably higher SERS efficiency for CWA simulants was observed at a 325 nm Raman excitation. Our findings reveal that a higher ablation yield was observed at IR irradiation than those obtained at the other wavelengths. A size decrease of the NPs was noticed by changing the liquid environment to an electrolyte. These findings have significant implications for developing more efficient and stable SERS substrates for chemical detection applications.

A luminescent organic cocrystal for detecting 2,4-dinitroaniline

2,4-dinitroaniline (2,4DNBA), a significant hazardous chemical, is extensively used in industry and agriculture. The chemical accumulates in the environment for a long time, causing irreversible damage to the ecosystem. Currently, it is quite challenging to identify it by common analysis and detection techniques. Herein, a luminescent organic cocrystal (TCNB-8HQ) was prepared using 1,2,4,5-tetracyanobenzene (TCNB) as the electron acceptor and 8-hydroxyquinoline (8HQ) as the electron donor. The prepared TCNB-8HQ was used as a fluorescent probe with a fast and specific response to 2,4DNBA. This detection method possessed a linear range of 0.5–200 μmol/L with a detection limit as low as 0.085 μmol/L to detect 2,4DNBA in real samples with satisfactory spiking recovery. As revealed by fluorescence spectrum and UV–vis absorption spectrum, the detection mechanism involved competitive absorption between cocrystal material and 2,4DNBA. Moreover, the feasibility of the system was explored by preparing portable indicator strips for 2,4DNBA from organic cocrystal (TCNB-8HQ). This study not only provided an environmentally friendly gram–level preparation strategy to synthesize the fluorescent material but also investigated their application in chemical detection.

Fluorescent nanocomposites based on gold nanoclusters for metal ion detection and white light emitting diodes.

Gold nanoclusters (AuNCs) are among the most promising organic-inorganic hybrid luminescent materials for various applications. The current development of AuNCs majorly focuses on controlling their luminescence properties. Herein, we report a new strategy to facilely construct two different nanocomposites featuring enhanced photoluminescence based on mercaptopropionic acid-protected AuNCs (MPA-AuNCs). Through co-assembly with Zn2+ and 2-methylimidazole (2M-IM), the weak luminescence of MPA-AuNCs evolved into either intense blue-green or orange emission at different concentration ratios of additives. HR-TEM and spectroscopic characterization studies revealed that the intense blue-green emission was ascribed to the formation of ZnS quantum dots (QDs) on the outer surface of AuNCs (AuNCs@ZnS), while the strong orange emission originated from the primitive MPA-AuNC core encapsulated by a cubic ZIF-8 shell (AuNCs@ZIF-8). The AuNCs@ZnS nanocomposite was further applied as an exceptional chemical sensor for selective detection of Pb2+ and Fe3+via different quenching mechanisms, and the AuNCs@ZIF-8 composite was applied for fabricating light-converting devices. The co-assembly of AuNCs with Zn2+ and imidazole derivatives provides a facile strategy for acquiring differentiated nanomaterials that have versatile potential applications in chemical detection and light-converting devices.

Chemiluminescent carbon dots: Synthesis, properties, and applications

• Chemiluminescent properties and synthetic route of carbon dots are discussed. • Possible mechanism and recent advance in related applications of chemiluminescent carbon dots are identified. • Challenge and prospect in the future development of chemiluminescent CDs are considered. As one of important approaches of light emission, chemiluminescence (CL) induced by chemical reactions has evoked considerable interest for its potential applications in chemical detection, bioanalysis, and cold light source. Carbon dots (CDs) are one kind of emerging carbon nanomaterials for promising CL due to their unique luminescent properties, such as high fluorescence quantum yield, tunable emission wavelength, high photostability, etc . With the special physicochemical property, CDs can take part in the CL reaction as oxidants, emitting species, energy acceptors of chemical reaction energy or even catalysis involving in different CL systems. With these novel influences in CL reaction, these CD-related CL systems have been applied in a broad range of areas. For the reason, CL CDs and their applications such as CL emitting species, catalyst, sensor, information encryption, photodynamic therapy and in-vitro and in-vivo bioimaging/biosensor are reviewed and discussed in this paper. Meanwhile, the challenges and future prospects of the CL CDs have been discussed and proposed.

Quantification of Analyte Concentration in the Single Molecule Regime Using Convolutional Neural Networks.

Single molecule (SM) detection represents the ultimate limit of chemical detection. Over the years, many experimental techniques have emerged with this capacity. Yet, SM detection and imaging methods produce large spectral data sets that benefit from chemometric methods. In particular, surface enhanced Raman scattering spectroscopy (SERS), with extensive applications in biosensing, is demonstrated to be particularly promising because Raman active molecules can be identified without recognition elements and is capable of SM detection. Yet quantification at ultralow analyte concentrations requiring detection of SM events remains an ongoing challenge, with the few existing methods requiring carefully developed calibration curves that must be redeveloped for each analyte molecule. In this work, we demonstrate that a convolutional neural network (CNN) model when applied to bundles of SERS spectra yields a robust, facile method for concentration quantification down to 10 fM using SM detection events. We further demonstrate that transfer learning, the process of reusing the weights of a trained CNN model, greatly reduces the amount of data required to train CNN models on new analyte molecules. These results point the way for unambiguous analysis of large spectral data sets and the use of SERS in important ultra low concentration chemical detection applications such as metabolomic profiling, water quality evaluation, and fundamental research.

Fabrication of highly luminescent SiO2–Au nanostructures and their application in detection of trace Hg2+

Photoluminescence of gold nanoclusters (AuNCs) make them attractive in many fields including biological labeling and chemical detection. However, compared with organic dyes or quantum dots, the generally lower fluorescence efficiency of AuNCs limits their application. Here, an efficient and facile strategy is developed to fabricate highly luminescent SiO2–Au NCs nanostructures with a high quantum yield (33.3%) via a three-step procedure involving peptide self-assembly, biomimetic mineralization of silica, and conjugation of AuNCs. Photoluminescence lifetime, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy were used to in-depth explore the mechanism for fluorescence enhancement. The results indicated that the fluorescence enhancement of SiO2–Au NCs is mainly attributed to the suppression of strong Au(I) → ligand charge transfer and non-radiative decay triggered by confinement effect. The SiO2–Au NCs solution presents relatively high fluorescence intensity over a wide range of pH and salt concentration. These superior properties make them an ideal candidate of fluorescent probes with excellent sensitivity and selectivity in the detection of Hg2+ ions. Moreover, the quenched fluorescence of SiO2–Au NCs can be recovered by the introduction of glutathione. Therefore, SiO2–Au NCs can serve as a recyclable fluorescent probe for the detection of Hg2+ and glutathione through the “fluorescence off” or “fluorescence on” process. The results provide a promising step toward the fabrication of highly fluorescent probes of AuNCs and further expand their application in chemical detection.

In-Line Microfiber-Assisted Mach–Zehnder Interferometer for Microfluidic Highly Sensitive Measurement of Salinity

We present a microfluidic U-shaped micro-cavity sensor by splicing a segment of a microfiber of a few hundred micrometers in length tapered from a single-mode fiber (SMF) between two SMFs with a predesigned lateral offset for highly sensitive salinity measurement. The proposed sensing probe serves as an in-line microfiber-assisted Mach–Zehnder interferometer (MAMZI) with an ultra-high refractive index sensitivity of $10^{4}$ nm/RIU. Three Mach–Zehnder interferometer structures with different cavity lengths of 351.82, 242.56, and 181.31 $\mu \text{m}$ are fabricated, by which microfluidic sensing systems are established for in-line measurement of sodium chloride (NaCl) solution. Experimental results indicate that the detection limit of NaCl solution is as low as $4\times 10^{-3}$ wt% and the response time is less than 15 s, which would make the MAMZI-based microfluidic measuring system play an important role in label-free biological and chemical detection applications.

Chip-scale broadband spectroscopic chemical sensing using an integrated supercontinuum source in a chalcogenide glass waveguide

On-chip spectroscopic sensors have attracted increasing attention for portable and field-deployable chemical detection applications. So far, these sensors largely rely on benchtop tunable lasers for spectroscopic interrogation. Large footprint and mechanical fragility of the sources, however, preclude compact sensing system integration. In this paper, we address the challenge through demonstrating, for the first time to our knowledge, a supercontinuum source integrated on-chip spectroscopic sensor, where we leverage nonlinear Ge22Sb18Se60 chalcogenide glass waveguides as a unified platform for both broadband supercontinuum generation and chemical detection. A home-built, palm-sized femtosecond laser centering at 1560 nm wavelength was used as the pumping source. Sensing capability of the system was validated through quantifying the optical absorption of chloroform solutions at 1695 nm. This work represents an important step towards realizing a miniaturized spectroscopic sensing system based on photonic chips.

Detection of volatile-organic-compounds (VOCs) in solution using cantilever-based gas sensors

Micromechanical resonant sensor offers many advantages for chemical detection, but it fails to maintain high quality factor (Q-factor) when working directly in liquid because of the viscous damping. To solve the problem, a gas/liquid separated sensing method is introduced to detect volatile organic compounds (VOCs) in solution with a resonant cantilever gas sensor. With the help of a waterproof and breathable expanded polytetrafluoroethylene (ePTFE) film, the resonant sensor can be physically isolated from the analyte solution. Thus, the sensor can resonate in gas phase environment with a high Q-factor, meanwhile the interference from the solvent emission can be significantly suppressed. Loaded with the sensing-group functionalized mesoporous-silica nanoparticles (MSNs), the resonant cantilever can detect the target VOC molecules that permeate from the flowing solution sample at the other side of the film. Two typical kind of resonant microcantilever VOC sensors are tested to verify the proposed method, which are loaded with carboxyl (–COOH) and amino (–NH2) sensing groups functionalized MSNs, respectively. The sensors exhibit highly sensitive (mg/L level resolution) and reproducible detection ability to aniline and acetic-acid solution, respectively. This gas/liquid separated sensing technique is promising in various on-site chemical detection applications.

Preparation and Characterization of Nano Porous Silicon for Chemical Detection Applications

Preparation and Characterization of Nano Porous Silicon for Chemical Detection Applications

Toward real-time spectral imaging for chemical detection with a digital micromirror device-based programmable spectral filter

Hyperspectral imaging sensors have proven to be powerful tools for highly selective and sensitive chemical detection applications, but they have significant operational drawbacks including slow line-scanning acquisition, large data volume of the resulting images, and a detection time lag due to the computational overhead of the matched-filter analysis. We have recently developed and demonstrated a high-speed, high-resolution, programmable spectral filter based on the Texas Instruments DLP® digital micromirror device (DMD) that is capable of performing matched-filter image processing across a two-dimensional (2-D) field-of-view directly in the optical hardware and will enable real-time chemical detection without slow scanning, large data volumes or expensive postprocessing requirements. Based on traditional optical techniques, our spectral filter encodes the spectral information orthogonal to the spatial image information, enabling the DMD to encode matched-filter information into the spectral content of the scene without disturbing the underlying 2-D image. With this new technology, everything from simple multiband filters to very complicated hyperspectral matched filters can be implemented directly in the optical train of the sensor, producing an image highlighting a target signature within a spectrally cluttered scene in real time without further processing. We will first describe the implementation of a DMD as a multiplexing spectral selector for a 2-D field-of-view, discuss its utility as a multiband spectral filter, and show how the DLP’s® duty cycle-based grayscale capability enables the direct measurement of the adaptive matched filter. We will also show examples of multispectral and hyperspectral matched-filter images recorded with our visible spectrum prototype.

Fabrication and Properties of Large-Area Silicon Nanowire Arrays

Wet chemical etching with dry metal deposition method has been developed to fabricate large-area aligned silicon nanowire (SiNW) arrays. The combination of nanoclusters Ag film with proper interconnection and interspaces (of about 20 nm thick), and proper temperature during etching (from 20 to 80 °C) is vital to successfully fabricating large-area uniform SiNW arrays. Raman and photoluminescence spectra of the SiNW arrays indicated their potential applications in chemical detection and optical devices ,respectively.

Quantum cascade laser: Applications in chemical detection and environmental monitoring

In this paper we consider the structural parameter optimization of the active region of a GaAs-based quantum cascade laser in order to maximize the optical gain of the laser at the characteristic wavelengths, which are best suited for detection of pollutant gasses, such as SO2, HNO3, CH4, and NH3, in the ambient air by means of direct absorption. The procedure relies on applying elaborate tools for global optimization, such as the genetic algorithm. One of the important goals is to extend the applicability of a single active region design to the detection of several compounds absorbing at close wave-lengths, and this is achieved by introducing a strong external magnetic field perpendicularly to the epitaxial layers. The field causes two-dimensional continuous energy subbands to split into the series of discrete Landau levels. Since the arrangement of Landau levels depends strongly on the magnitude of the magnetic field, this enables one to control the population inversion in the active region, and hence the optical gain. Furthermore, strong effects of band non-parabolicity result in subtle changes of the lasing wavelength at magnetic fields which maximize the gain, thus providing a path for fine-tuning of the output radiation properties and changing the target compound for detection. The numerical results are presented for quantum cascade laser structures designed to emit at specified wavelengths in the mid-infrared part of the spectrum.

Mid-infrared vertical-cavity surface-emitting lasers for chemical sensing

The first (to our knowledge) III-V mid-IR vertical-cavity surface-emitting lasers (lambda = 2.9 microm) are demonstrated and show promising characteristics for chemical detection applications. The cw optical-pumping threshold is low (4 mW at 80 K) and efficiency is high (5.6% W/W). Pulsed operation is obtained up to 280 K and cw up to 160 K. Lateral-mode confinement will lead to spectrally pure, single-mode output for chemical identification.

Decision tree for chemical detection applications

Analyse discriminante et par regression de l'augmentation de la fluorescence du (diphenylacetyl-2) indanedione-1,3 ((p-dimethylamino) benzaldazine)-1, reactif analytique possible pour pesticide, aminoacide, composes aliphatiques