Sensitive Chemical Sensors Research Articles

Theoretical Perspective on the Sensing Mechanism of a Pyrazinium‐Based Fluorescent Probe Towards 2,4,6‐Trinitrophenol

ABSTRACTRapid detection of chemical explosives plays a critical role in national security and public safety. An in‐depth study of the sensing mechanism is particularly urgent for the development of highly efficient, sensitive, and selective chemical sensors for the precise detection of chemical explosives. Density functional theory (DFT) and time‐dependent DFT approaches were used in this work to examine the sensing mechanism of a novel fluorescent probe 1‐benzyl‐3,5‐di (thiophen‐2‐yl)pyrazin‐1‐ium bromide (BTPyz) for the detection of 2,4,6‐trinitrophenol (TNP). A comprehensive theoretical exploration was carried out, and a different interaction mode between the probe and TNP from that in the original experiment was proposed. The π–π stacking was established to be the recognition interaction between BTPyz and TNP anion, and the active site was determined from the three potential sizes according to the Gibbs free energy analysis results. The rationality of the reaction mode and the π–π stacking product between the BTPyz and TNP (BTN) was further confirmed by the fluorescence properties (absorption and emission spectra). According to the findings of frontier molecular orbitals (FMOs), photoinduced electron transfer (PET) is the intrinsic mechanism through which TNP quenches the probe's fluorescence.

Highly sensitive photonic crystal fiber chemical sensor for detecting carbon disulfide and bromoform in the THz regime

In this study, an innovative photonic crystal fiber (PCF) designed specifically for the detection of carbon disulfide and bromoform liquid chemicals within the THz frequency range was introduced. The PCF’s structural design was achieved using the Finite Element Method (FEM) and Perfectly Matched Layer (PML) boundary conditions within COMSOL Multiphysics, ensuring precision through appropriate numerical parameters. Six distinct configurations were developed, incorporating circular, square, rectangular slotted, benzene-shaped circular, and two elliptical core designs, as well as an eight-elliptical core design. The PCF models were constructed utilizing the dielectric material TOPAS for accurate simulation and analysis. Various crucial parameters of the proposed PCF were examined across a wide THz spectrum spanning from 0.2 to 1.2 THz. The PCF model exhibited a peak output at the operating frequency of 0.8 THz for the square-shaped core design, achieving a relative sensitivity of 96.891% for bromoform and 95.603% for carbon disulfide. Remarkably low material losses of 0.0081104 cm−1 for bromoform and 0.006703 cm−1 for carbon disulfide were observed, along with a core power fraction of 93.107% for bromoform and 94.263% for carbon disulfide. The effective area was determined to be 1.77 × 10−07 μm2 for bromoform and 1.70 × 10−07 μm2 for carbon disulfide, while the confinement loss measured 2.25 × 10−17 dB/cm for bromoform and 4.76 × 10−17 dB/cm for carbon disulfide. These superior attributes strongly suggest that this model will be crucial in applications like supercontinuum generation, sensing, and biomedical imaging.

A europium-based CP fluorescent probe for sensing malachite green, ascorbic acid and uric acid

Lanthanide (such as Eu and Tb) coordination polymers (CPs) having various coordination modes and unique fluorescence properties can be used as highly sensitive chemical sensors. We synthesized a europium-based CP of Eu2(PEDA)3(H2O)4 (referred to as Eu-PEDA, PEDA = 1,2-phenylenediacetic acid group), and investigated its application in fluorescence detection. Eu-PEDA can be considered as a multifunctional fluorescent probe for sensing malachite green (MG), ascorbic acid (AA) and uric acid (UA) to achieve rapid fluorescence quenching response, and Eu-PEDA exhibited high quenching efficiency Ksv (6.21 × 105 M−1 for MG; 1.16 × 104 M−1 for AA; 1.02 × 104 M−1 for UA), low detection limit (MG: 0.050 μM; AA: 0.705 μM; UA: 0.965 μM). Furthermore, Eu-PEDA suspension dipping test strips, the Eu-PEDA test strips are obtained. The resultant test strip, shows the potential for directly visual detection of MG, AA and UA just by dripping the analytes on it. This work thus offers a facile and efficient strategy for rapid and visual detection of MG, AA and UA by Eu-based coordination compounds. In addition, the possible mechanisms of fluorescence quenching were studied by absorption spectra, the emission and excitation spectra.

A hydroxyl-rich covalent organic framework for the precisely selective fluorescence sensing of explosives with high sensitivity

Covalent organic Frameworks (COFs) have become a new platform for functional research and material design. A novel covalent organic skeleton (DHB-TFP COF) was synthesized from 2-hydroxybenzene-1,3,5-tricarbaldehyde and 3,3′-dihydroxybenzidine using Schiff base reaction. DHB-TFP COF is a highly stable porous crystalline material and exhibits exceptional thermal and chemical resistance. DHB-TFP COF exhibited a selective and sensitive “turn-off” fluorescence response to 4-NP in ethanol, and TNP not only significantly quenched the fluorescence of DHB-TFP COF but also caused the obvious red-shift. The fluorescence intensity of DHB-TFP COF exhibited a linear correlation with the concentration of 4-NP with a detection limit of 0.40 μM. Furthermore, the maximum fluorescence peak observed for DHB-TFP COF demonstrated a linear relationship with TNP concentration with a detection limit of 11.15 μM. DHB-TFP COF exhibited satisfactory recovery in the detection of 4-NP and TNP in actual water sample indicating its practical application potential. The O atoms of rich hydroxyl and N atoms of C = N present on the surface of DHB-TFP COF scaffold can establish strong hydrogen bonds with 4-NP and TNP, facilitating their mutual interaction. The spectra studies indicated that the fluorescence quenching mechanism can be attributed to the absorption competitive quenching (ACQ) and fluorescence resonance energy transfer (FRET) mechanism. This study not only proposed the approach for synthesizing novel structured organic frameworks, but also developed a highly selective and sensitive fluorescence chemical sensor for identifying and detecting 4-NP and TNP.

Chiral Metal-Organic Frameworks with Spectroscopic Methods: Towards Chemical Sensor Devices.

Chiral Metal-Organic Frameworks (CMOFs) are a rapidly growing field reflecting their potential as selective and sensitive chemical sensors for chiral analytes. The highly tuneable nature of CMOFs enables the size, shape, and non-covalent interactions to be optimised towards specific analytes to engender strong intermolecular interactions and sensing responses. While CMOFs as chiral chemical sensor devices have been explored with electrochemical methods including differential pulse voltammetry (DPV), bipolar and chemiresistive sensing techniques, the CMOFs as chiral chemical sensors using spectroscopic methods has received significantly less attention. This review examines the synthesis of CMOFs for chemical sensors with spectroscopic methods such as photoluminescence, circular dichroism, and solid-state nuclear magnetic resonance with a view towards their incorporation into chemical sensor devices. Future directions of the field are highlighted for the generation of functional devices.

Photonic crystal nanolasers in polydimethylsiloxane thin film for sensing quantities leading to strain

We propose and realize a 1D photonic crystal nanocavity laser embedded in a polydimethylsiloxane (PDMS) thin film. The nanolaser in PDMS exhibits a significant optical response to structural deformation. It can be attached to object surfaces or integrated into different configurations, enabling the detection of different quantities that induce strain in the film. In experiments, this nanolaser can detect temperature variations or micrometer-scale bending degrees by attaching it to a temperature-controllable or bendable plate, respectively. Moreover, we further utilize the film as a diaphragm of a chamber to demonstrate its potential as a highly sensitive pressure gauge and chemical sensor. By adjusting the thickness of the PDMS thin film and the position of the nanolaser, we experimentally achieved a minimum detectable gas pressure variation of 0.12 kPa and a sensing dynamic range of 46 dB. We also investigate the optical response of the nanolaser to the swelling of the PDMS thin film induced by different organic solvents in experiments. The experimental wavelength shift rates over time are proportional to different chemical vapors’ PDMS swelling ratios, which can be used to identify specific chemical vapors within the chamber that induce PDMS swelling. Based on the experimental results and the capability of reattaching to different objects or configurations, we believe that our PhC nanolaser demonstrated herein holds significant potential as a highly sensitive mechanical and chemical sensor.

A novel ethylene linkage-based covalent organic framework for turn-on fluorescence sensing for Al3+ with excellent selectivity and sensitivity

Covalent organic Framework (COFs) has become a new platform for functional research and material design. A novel covalent organic framework (CN-COF) was first synthesized with p-xylylene dicyanide and 2-hydroxy-1,3,5-benzenetrialdehyde through the Knoevenagel condensation reaction. CN-COF is a porous crystal material with strong thermal and chemical stability. CN-COF exhibits a selective “turn-on” fluorescence response to Al3+ in ethanol with blue-shifted emission spectra over the other tested metal ions. The color changes from pink to earth yellow, and the fluorescence effect is clearly visible. The fluorescence intensity of CN-COF was linearly related to the concentration of Al3+, and the detection limit was 1.815 μM. Importantly, CN-COF exhibits a satisfactory recovery for detecting Al3+ in drinking water and fish samples. CN-COF also showed the intuitive semi-quantitative detection ability for Al3+ via the color change with the naked eyes. The special pore structure is conducive to allow Al3+ enter to coordinate with O and N atoms on the wall of CN-COF scaffold. The revisable fluorescence change upon the selective addition of Al3+ and XRD, EDTA, XPS and DFT results demonstrated the complex process. The inhibition of the photoinduced electron transition from O atoms to Al3+ induced the fluorescence enhancement. This study not only presents a synthesis idea for a new structural organic framework, but also offers a highly selective and sensitive fluorescence chemical sensor for the identification and detection of Al3+.

Highly sensitive fiber-optic chemical pH sensor based on surface modification of optical fiber with ZnCdSe/ZnS quantum dots

The pH value plays a vital role in many biological and chemical reactions. In this work, the fiber-optic chemical pH sensors were fabricated based on carboxyl ZnCdSe/ZnS quantum dots (QDs) and tapered optical fiber. The photoluminescence (PL) intensity of QDs is pH-dependence because protonation and deprotonation can affect the process of electron-hole recombination. The evanescent wave of tapered optical fiber was used as excitation source in the process of PL. To obtain higher sensitivity, the end faces of fiber were optimized for cone region. By lengthening the cone region and shrinking the end diameter of optical fiber, evanescent wave was enhanced and the excitation times of QDs were increased, which improved the PL intensity and the sensitivity of the sensor. The sensitivity of sensor can reach as high as 0.139/pH in the range of pH 6.00–9.01. The surface functional modification was adopted to prepare sensing films. The carboxyl groups on the QDs ligands are chemically bonded to the fiber surface, which is good for response time (40 s) and stability (decreased 0.9 % for 5 min). These results demonstrated that ZnCdSe/ZnS QDs-based fiber-optic chemical pH sensors are promising approach in rapid and precise pH detection.

Highly Sensitive and Selective Defect WS2 Chemical Sensor for Detecting HCHO Toxic Gases

The gas sensitivity of the W defect in WS2 (VW/WS2) to five toxic gases—HCHO, CH4, CH3HO, CH3OH, and CH3CH3—has been examined in this article. These five gases were adsorbed on the VW/WS2 surface, and the band, density of state (DOS), charge density difference (CDD), work function (W), current–voltage (I–V) characteristic, and sensitivity of adsorption systems were determined. Interestingly, for HCHO-VW/WS2, the energy level contribution of HCHO is closer to the Fermi level, the charge transfer (B) is the largest (0.104 e), the increase in W is more obvious than other adsorption systems, the slope of the I–V characteristic changes more obviously, and the calculated sensitivity is the highest. To sum up, VW/WS2 is more sensitive to HCHO. In conclusion, VW/WS2 has a great deal of promise for producing HCHO chemical sensors due to its high sensitivity and selectivity for HCHO, which can aid in the precise and efficient detection of toxic gases.

Wearable Devices: Implications for Precision Medicine and the Future of Health Care.

Wearable devices are integrated analytical units equipped with sensitive physical, chemical, and biological sensors capable of noninvasive and continuous monitoring of vital physiological parameters. Recent advances in disciplines including electronics, computation, and material science have resulted in affordable and highly sensitive wearable devices that are routinely used for tracking and managing health and well-being. Combined with longitudinal monitoring of physiological parameters, wearables are poised to transform the early detection, diagnosis, and treatment/management of a range of clinical conditions. Smartwatches are the most commonly used wearable devices and have already demonstrated valuable biomedical potential in detecting clinical conditions such as arrhythmias, Lyme disease, inflammation, and, more recently, COVID-19 infection. Despite significant clinical promise shown in research settings, there remain major hurdles in translating the medical uses of wearables to the clinic. There is a clear need for more effective collaboration among stakeholders, including users, data scientists, clinicians, payers, and governments, to improve device security, user privacy, data standardization, regulatory approval, and clinical validity. This review examines the potential of wearables to offer affordable and reliable measures of physiological status that are on par with FDA-approved specialized medical devices. We briefly examine studies where wearables proved critical for the early detection of acute and chronic clinical conditions with a particular focus on cardiovascular disease, viral infections, and mental health. Finally, we discuss current obstacles to the clinical implementation of wearables and provide perspectives on their potential to deliver increasingly personalized proactive health care across a wide variety of conditions.

Probing robust electrochemical monitoring of dimetridazole using nanocrystalline hydroxyapatite-graphene oxide decorated Mn3O4 nanocomposite

Developing low-cost electrocatalysts with efficient, long-lasting electrode materials is of significant interest and presents a considerable challenge for electrochemical sensing applications in food contamination, particularly in the monitoring of dimetridazole (DMZ). In this study, we introduce a novel ternary nanocomposite, namely hydroxyapatite-intercalated graphene oxide-decorated manganese oxide (HAp/GO@Mn3O4), synthesized through straightforward hydrothermal and ultrasonication methods. The nanocomposite is subjected to thorough physicochemical and electrochemical characterization and utilized as an electrode material to enhance DMZ sensors. The ternary nanocomposite of HAp/GO@Mn3O4 delivers improved electrocatalytic activity because the synergistic features offer an enhanced electron transfer rate compared to the other GCE-modified electrodes. The developed sensitive chemical sensor probe exhibits optimized electrochemical conditions and significantly improves the electrode/electrolyte system. It demonstrates wide linear ranges (0.005–440.3 μM), a low limit of detection (LOD, 0.86×10−9 M), and excellent sensitivity (23.12 μA μM−1 cm−2). The sensor also displays reliable reproducibility, repeatability, selectivity, and cycle stability. Moreover, the developed sensor demonstrates its ability to accurately monitor DMZ food contamination samples with an excellent recovery rate in trace-level detection.

Study on the roughen process of branches of AuAg nanostars for the improved surface-enhanced Raman scattering (SERS) to detect crystal violet in fish

The techniques used to precisely tune the morphologies of noble metal nanoparticles are of vital importance as complex three-dimensional nanostructures can generate many “hot spots” for Surface-enhanced Raman Scattering (SERS). Especially, the SERS properties of star-shaped nanoparticles are closely related to the position, number and morphology of branches, making the control over the final morphology of them more important. By adding different reducing agents during the growth process of AuAg nanostars, we accurately controlled the morphology of branches, and synthesized three kinds of hyperbranched star-shaped nanostructures: Lamellar nanostars, Sea urchin-shaped nanostars and Serrated nanostars. The SERS performance of the hyperbranched nanostars were all stronger than that of common AuAg nanostars. Among them, Lamellar nanostars gained the best SERS enhanced factor about 1 × 107 due to the built-in nanogaps and sharp edges. The SERS detection probes prepared with purified Lamellar nanostars had high uniformity and stability, and showed excellent sensitivity in detecting crystal violet in fish, with detection range of 0.01–10 nM and detection limit of 0.015 nM. The results of this work not only provide guidance for the construction of complex Au and Ag bimetallic nanostructures, but also supply a superior material to develop highly sensitive optical chemical sensors and biosensors.

Detection of hazardous greenhouse gases and chemicals with topological edge state using periodically arranged cross-sections

This study investigates a sensitive chemical and hazardous greenhouse gas sensor using ternary phononic crystals composed of periodic tubes. The sensing mechanism depends on the localization of the topological edge state at the interface between phononic crystals. The impact of the structure’s geometry and concentration of a specific gas in air are discussed. Further, the effect of temperature on the position of topological edge state and the sensitivity of the proposed sensor will be studied. This model has shown good sensitivity of 1.58 Hz m−1 s and a figure of merit of 33.7 m−1 s to distinguish different chemical and hazardous greenhouse gas. Furthermore, the proposed detector is low-cost and simple because it does not require a complicated procedure to fabricate multilayers with different mechanical properties.

Stilbene ligand‐based metal–organic frameworks for efficient dye adsorption and nitrobenzene detection

AbstractThe technological developments of metal–organic framework (MOF) for selective adsorption and sensing have been achieved in recent years. Herein, we report two stilbene‐based MOFs, denoted as Zn3(SDC)3(bpy) (1) and Zn(SDC)(bpy)·2DMF (2). MOFs 1 and 2 were synthesized in pure form by controlling the organic linker ratio and were used for the adsorptive removal of dye molecules. Despite their low adsorption capacities, the MOFs were more selective toward cationic dye (methylene blue) than anionic dye (methyl orange). The unique fluorescent property of the MOFs was harnessed for the sensing of harmful organic molecules. Interestingly, the fluorescence of 1′ was quenched by aromatic analytes containing amine and nitro functional groups. However, 2′ only showed modest fluorescence quenching by nitrobenzene. The quenching efficiency of nitrobenzene had a low detection limit for 1′ and 2′ (14.28 and 25.42 μM, respectively). These MOFs can be used as adsorbents and highly sensitive chemical sensors.

Synthesis and Integration of Hybrid Metal Nanoparticles Covered with a Molecularly Imprinted Polymer Nanolayer by Photopolymerization.

Interfacing recognition materials with transducers has consistently presented a challenge in the development of sensitive and specific chemical sensors. In this context, a method based on near-field photopolymerization is proposed to functionalize gold nanoparticles, which are prepared by a very simple process. This method allows in situ preparation of a molecularly imprinted polymer for sensing by surface-enhanced Raman scattering (SERS). In a few seconds, a functional nanoscale layer is deposited by photopolymerization on the nanoparticles. In this study, the dye Rhodamine 6G was chosen as a model target molecule to demonstrate the principle of the method. The detection limit is 500 pM. Due to the nanometric thickness, the response is fast, and the substrates are robust, allowing regeneration and reuse with the same performance level. Finally, this method of manufacturing has been shown to be compatible with integration processes, allowing the future development of sensors integrated in microfluidic circuits and on optical fibers.

A correlation between fractal growth, water contact angle, and SERS intensity of R6G on ion beam nanostructured ultra-thin gold (Au) films

Introduction: This study focuses on the detection of rhodamine-6G using surface-enhanced Raman scattering (SERS) on gold nanostructures (AuNS) of different sizes. Ion beam irradiation has been carried out to tune the size of AuNS and investigate the underlying mechanisms of sputtering and diffusion that govern their growth. Additionally, the study established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. The results of this study offer new insights into the mechanisms of SERS detection on roughened metallic surfaces.Methods: Thermal evaporation was used to deposit an Au thin film on a glass substrate. Subsequent 10 keV Ar+ irradiation was done on Au thin film for fluences ranging from 3×1014 to 3×1016 ions/cm2 to tune the size of AuNS. Rutherford backscattering spectroscopy (RBS) was used to confirm that the decrease in Au concentration under ion beam sputtering was responsible for the tuning in size and structure of AuNS. Fractal dimension (Df) and interface width (w) were used as statistical parameters to control the wettable characteristics of the AuNS surfaces.Results and discussion: The researchers found that the growth of AuNS was governed by ion beam induced sputtering and diffusion mechanisms. They established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. They found that a higher surface coverage area of Au NPs with lower fractal dimensions and water contact angles favoured the SERS detection of R6G. This study provides new insights into the mechanisms of SERS detection on roughened metallic surfaces. It is found that the growth of AuNS was governed by ion beam-induced sputtering and diffusion mechanisms, and established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. The findings of this study may have applications in the development of more sensitive and efficient SERS-based chemical sensors.

Study of FRET between Zn-Cu-In-S/ZnS core/shell quantum dots-Cresyl violet dye system

This study reports the fluorescence resonance energy transfer between Zn-Cu-In-S/ZnS core–shell quantum dots and Cresyl Violet dye. The quenching of Zn-Cu-In-S/ZnS core–shell QD (donor) emission and lifetime and simultaneous enhancement in Cresyl Violet (acceptor) emission validates and confirms the non-radiative resonance energy transfer from Zn-Cu-In-S/ZnS QDs to Cresyl violet. The values of spectral overlap, Förster distance, the distance between donor and acceptor pair and FRET efficiency were determined using the steady state as well as time-resolved fluorescence spectroscopic techniques. This study demonstrates that this systemexhibits efficient FRET and can act as a very sensitive chemical sensor. Since Zn-Cu-In-S/ZnS QDs are nontoxic compared to popular cadmium-based quantum dots, the application of FRET in biological systems will be advantageous. It can find vast applications in photonics and biomedical applications.

High performance UV-LED activated gas sensors based on ordered carbon mesoporous materials loaded with ZnO nanoparticles

Carbon mesoporous materials (CMMs) with various ZnO loading concentrations have been fabricated as sensitive chemical sensors for nitrogen dioxide (NO2) and ammonia (NH3) detection. Mesostructured carbon with high surface area (>1000 m2/gr) is prepared using a template replication method, and zinc oxide (ZnO) nanoparticles are loaded through a facile solution impregnation. The sensors are operated at room temperature (∼25 °C) and activated by UV irradiation of a 365 nm wavelength and 25 mW/cm2 irradiance emitted from a UV-LED. SEM, TEM, XRD, XPS, and BET characterizations are carried out to study the physico-chemical properties of the prepared materials. The sensors with 57 wt% and 70 wt% ZnO loadings have exhibited superior gas sensing for the detection of NO2 and NH3, respectively. The maximum response values in optimal loading concentrations are 1.91 (NO2) and 1.35 (NH3), which are significantly higher than those of pristine ZnO nanoparticles reported previously. This improvement in response could be attributed to the high surface area, as well as the extended separation and restrained recombination rate of the photo-induced electron-hole pairs in ZnO/CMM sensing material. Furthermore, loading on CMMs produces more oxygen vacancies (OVac) induced by C-dopant, which increases the number of active sites and results in a large number of photo-induced oxygen ions on the surface, thus enhancing gas sensing activity.

Fluorescent sensor array based on Janus silica nanoflakes to realize pattern recognition of multiple aminoglycoside antibiotics and heavy metal ions

The development of highly sensitive and selective chemical sensor arrays that can be used for the recognition of multiple organic and inorganic compounds has been a pressing demand and persistent challenge. We combined the Pickering emulsion and quantum dots (QDs) doping technology to fabricate Janus silica nanoflakes–based fluorescence sensor arrays for the pattern recognition of multiple heavy metal ions and aminoglycoside antibiotics. Janus silica nanoflakes were embedded with green and red light–emitting CdTe QDs as signal sensing units. The aptamer and sulfhydryl-specific recognition elements were modified and attached to the sides for the simultaneous recognition of heavy metal ions and aminoglycosides. The thiol groups chelated the target metal ions, resulting in the fluorescence quenching of the QDs. The aptamers provided specific recognition sites for aminoglycosides, and the fluorescence intensities of the QDs were enhanced in the presence of aminoglycosides. The parameters characterizing the fluorescence sensor array were optimized, and by analyzing the fluorescence response patterns following the linear discriminant analysis method, we observed that the sensor array could discriminate between the target compounds successfully. Finally, Cu2+ and Co2+ were detected in crayfish samples, and the results were confirmed following the inductively coupled plasma atomic emission spectroscopy technique.

Electrochemical Enzyme Sensor Based on the Two-Dimensional Metal–Organic Layers Supported Horseradish Peroxidase

Metal-organic frames (MOFs) have recently been used to support redox enzymes for highly sensitive and selective chemical sensors for small biomolecules such as oxygen (O2), hydrogen peroxide (H2O2), etc. However, most MOFs are insulative and their three-dimensional (3D) porous structures hinder the electron transfer pathway between the current collector and the redox enzyme molecules. In order to facilitate electron transfer, here we adopt two-dimensional (2D) metal-organic layers (MOLs) to support the HRP molecules in the detection of H2O2. The correlation between the current response and the H2O2 concentration presents a linear range from 7.5 μM to 1500 μM with a detection limit of 0.87 μM (S/N = 3). The sensitivity, reproducibility, and stability of the enzyme sensor are promoted due to the facilitated electron transfer.