Photonic crystal gas sensors based on metal-organic frameworks and polymers.

A photonic crystal (PC) is an optical microstructure with an adjustable dielectric constant. The PC sensor was deemed a powerful tool for gas molecule detection due to its excellent sensitivity, stability, online use and tailorable optical performance. The detection signals are generated by monitoring the changes of the photonic band gap when the sensing behavior occurs. Recently, many efforts have been devoted to improving the PC sensor's detection performance and reducing technical costs by selecting and refining functional materials. In this case, metal-organic frameworks (MOFs) with a large specific surface, tunable structural properties and polymers with unique swelling properties have attracted increasingly attention. In this review, a systematic review of PC gas sensors based on MOFs and polymers was carried out for the first time. Firstly, the optical properties and gas sensing mechanism of PCs were briefly summarized. Secondly, a detailed discussion of the structural properties and rapid preparation methods of distributed Bragg reflectors (DBRs), opals and inverse opals (IOPCs) was presented. Thirdly, the recent advances in MOF, polymer and MOF/polymer-based PC sensors over the past few years were summarized. It should be noted that the sensitivity and selectivity enhancement strategy by appropriate material species selection, organic ligand functionalization, metal-ion doping, diverse functional material arrays, and multi-component compounding were analyzed in detail. Finally, prospects on PC gas sensors are given in terms of preparation methods, material functionalization and future applications.

Au- ZnFe2O4 hollow microspheres based gas sensor for detecting the mustard gas simulant 2-chloroethyl ethyl sulfide.

Mustard gas, a representative of blister agents, poses a severe threat to human health. Although the structure of 2-chloroethyl ethyl sulfide (2-CEES) is similar to mustard gas, 2-CEES is non-toxic, rendering it a commonly employed simulant in related research. ZnFe2O4-based semiconductor gas sensors exhibit numerous advantages, including structural stability, high sensitivities, and easy miniaturization. However, they exhibit insufficient sensitivity at low concentrations and require high operating temperatures. Owing to the effect of electronic and chemical sensitization, the gas-sensing performance of a sensor may be remarkably enhanced via the sensitization method of noble metal loading. In this study, based on the morphologies of ZnFe2O4 hollow microspheres, a solvothermal method was adopted to realize different levels of Au loading. Toward 1 ppm of 2-CEES, the gas sensor based on 2 wt.% Au-loaded ZnFe2O4 hollow microspheres exhibited a response sensitivity twice that of the gas sensor based on pure ZnFe2O4; furthermore, the response/recovery times decreased. Additionally, the sensor displayed excellent linear response to low concentrations of 2-CEES, outstanding selectivity in the presence of several common volatile organic compounds, and good repeatability, as well as long-term stability. The Au-loaded ZnFe2O4-based sensor has considerable potential for use in detecting toxic chemical agents and their simulants.

Synthesis and Application of Polymer SXFA in the Detection of Organophosphine Agents with a SAW Sensor.

The effective detection of isopropyl methylfluorophosphonate (GB, sarin), a type of organophosphine poisoning agent, is an urgent issue to address to maintain public safety. In this research, a gas-sensitive film material, poly (4-hydroxy-4,4-bis trifluoromethyl)-butyl-1-enyl)-siloxane (SXFA), with a structure of hexafluoroisopropyl (HFIP) functional group was synthesized by using methyl vinylpropyl dichlorosilane and hexafluoroacetone trihydrate as initial materials. The synthesis process products were characterized using FTIR. SXFA was prepared on a 200 MHz shear surface wave delay line using the spin-coating method for GB detection. A detection limit of <0.1 mg/m3 was achieved through conditional experiments. Meanwhile, we also obtained a maximum response of 2.168 mV at a 0.1 mg/m3 concentration, indicating the much lower detection limit of the SAW-SXFA sensor. Additionally, a maximum response standard deviation of 0.11 mV with a coefficient of variation of 0.01 and a maximum recovery standard deviation of 0.22 mV with a coefficient of variation of 0.02 were also obtained through five repeated experiments. The results show that the SAW-SXFA sensor has strong selectivity and reproducibility, good selectivity, positive detection ability, high sensitivity, and fast alarm performance for sarin detection.

Fast and Selective Detection of Trace Chemical Warfare Agents Enabled by an ESIPT-Based Fluorescent Film Sensor.

Reliable detection of airborne chemical warfare agents (CWAs) at the site and in real-time remains a challenge due to the rarity of miniaturized analytical tools. Herein, an o-carborane-functionalized benzothiazole derivative (PCBO) with excited-state intramolecular proton transfer (ESIPT) and AIE characteristics was synthesized. The PCBO-based film sensor showed a highly sensitive response to representative simulants of CWAs, and detection limits were found to be 1.0 mg·m-3 for triphosgene, 6.0 mg·m-3 for chloroethyl ethyl sulfide, and 0.2 mg·m-3 for diethyl chlorophosphite. Moreover, the sensor showed great reusability (>100 cycles) and unprecedented response speed (<0.5 s). The excellent sensing performance was ascribed to the microenvironmental sensitivity of the sensing fluorophore, the porous adlayer structure of the film, and the specific binding of the fluorophore to the analytes. Furthermore, discrimination and identification of the examined CWA simulants were realized via the introduction of another fluorophore (HCBO)-based film. Importantly, a portable fluorescent CWA detector was built with the sensor as the key component, and its applicability was demonstrated by the successful detection of a typical CWA sample (Sarin). The present study indicates that fluorescent film sensors could satisfy reliable onsite and real-time detection of harmful chemicals.

Interface and Sensitive Characteristics of the Viscoelastic Film Used in a Surface Acoustic Wave Gas Sensor.

The surface morphology of viscoelastic-sensitive films significantly affects sensing characteristics of surface acoustic wave (SAW) sensors. Uniformity and compactness of the film surface directly influences detectability of the SAW sensor toward target gases. Viscoelastic fluoroalcoholpolysiloxane (SXFA) was prepared in this work using spin coating technology on an SAW delay line of 200 MHz and then used as coating for detection of dimethyl methylphosphonate (DMMP). Polarizing, atomic force, and scanning electron microscopies confirmed the uniformity of the SXFA surface. The particle diameter in the cluster region was 10-15 µm. The contact angle (5.72-26.69°), surface tension (21.053-29.155 mN/m), Gibbs free energy (-160.68 to -153.45 J/m2), and spreading coefficient (0.3028-6.9453 J/m2) of different concentrations of SXFA were obtained through experiments, and their relation was analyzed using the Young T equation and Gibbs adsorption isotherm. The glass transition temperature (-19.7 °C) and elasticity of SXFA were also discussed. The consistency of sensor preparation was confirmed by detecting DMMP with five SAW sensors prepared simultaneously. Seven consecutive tests showed that the SAW sensor presents satisfactory repeatability (standard deviation, s, 1.134; coefficient of variance, v, 0.065; and population mean deviation, δ, 0.913) at a concentration of 1.71 mg/m3 and acceptable linear relationship at a concentration range of 0.058-1.92 mg/m3, with a sensitivity of around 1.21 mv/(mg/m3). The sensor exhibited outstanding sensitivity and satisfactory linearity and repeatability to DMMP. Meanwhile, the sensing mechanism in gas adsorption was also discussed in terms of LSER formulation and hydrogen bonding formation between SXFA and DMMP.

[Research progress of microextraction by packed sorbent and its application in microvolume sample extraction].

Microextraction is a rapidly developing sample preparation technology in the field of analytical chemistry, which is seeing widespread application. Accurate sample preparation can not only save time but also improve the efficiency of analysis, determination, and data quality. At present, sample pretreatment methods must be rapid, allow for miniaturization, automation, and convenient online connection with analytical instruments. To meet the requirements of green analytical methods and improve the extraction efficiency, microextraction techniques have been introduced as suitable replacements to conventional sample preparation and extraction methods. Microextraction using a packed sorbent (MEPS) is a new type of sample preparation technology. The MEPS equipment was prepared using microsyringe with a volume of 50-500 µL, including MEPS syringes and MEPS adsorption beds (barrel insert and needle, BIN), which is essentially similar to a miniaturized solid phase extraction device. The BIN contains the adsorbent and is built into the syringe needle. A typical MEPS extraction procedure involves repeatedly pumping the sample solution in two directions (up and down) through the adsorbent multiple times in the MEPS syringe. The specific operation course of MEPS includes conditioning, loading, washing, elution, and introduction into the analysis instrument. The conditioning process is adopted to infiltrate the dry sorbent and remove bubbles between the filler particles. The adsorption process is accomplished by pulling the liquid plunger of the syringe so that the sample flows through the adsorbent in both directions multiple times. The washing process involves rinsing the sorbent to remove unwanted components after the analyte is retained. The elution process involves the use of an eluent to ensure that the sample flows through the adsorbent in both directions multiple times, so that elution can be realized by the pumping-pushing action. The target analyte is eluted with the eluent, which can be directly used for chromatographic analysis. However, when processing complex biological matrix samples by MEPS, pretreatment steps such as dilution of the sample and removal of proteins are commonly required. At present, the operation modes of the MEPS equipment are classified into three types: manual, semi-automated, and fully automated. This increase in the degree of automation is highly conducive to processing extremely low or extremely high sample volumes. Critical factors affecting the MEPS performance have been investigated in this study. The conditions for MEPS optimization are the operating process parameters, including sample flow rate, sample volume, number of sample extraction cycles, type and volume of the adsorbent, and elution solvents. It is also necessary to consider the effect of the sample matrix on the performance of MEPS. The MEPS sorbent should be cleaned by a solvent to eliminate carryover and reuse. The sorbent is a core aspect of MEPS. Several types of commercial and non-commercial sorbents have been used in MEPS. Commercial sorbents include silica-based sorbents such as unmodified silica (SIL), C2, C8, and C18. Unmodified silicon-based silica is a normal phase adsorption material, which is highly polar and can be used to retain polar analytes. C18, C8, and C2 materials are suitable for reversed-phase adsorption, while SCX, SAX, APS, and M1 (C8+SCX) adsorbents are suitable for the mixed-mode and ion-exchange modes. Noncommercial sorbents include molecularly imprinted materials, restricted-access molecularly imprinted materials, graphitized carbon, conductive polymer materials, modified silicon materials, and covalent-organic framework materials. The performance of MEPS has recently been illustrated by online with LC-MS and GC-MS assays for the analysis of biological matrices, environmental samples, and food samples. Pretreatment in MEPS protocols includes dilution, protein precipitation, and centrifugation in biological fluid matrices. Because of the small sample size, fast operation, etc., MEPS is expected to be more widely used in the analysis of bio-matrix samples. MEPS devices could also play an important role in field pretreatment and analysis.

Self-made microextraction by packed sorbent device for the cleanup of polychlorinated biphenyls from bovine serum.

Microextraction by packed sorbent, a miniaturized form of the solid-phase extraction, is a new sample pretreatment technology mainly used for bioanalysis. In this work, self-made device was fabricated by packing C18 sorbent into a microinjection needle (50 µL) and then applied for the analysis of polychlorinated biphenyls in bovine serum followed by gas chromatography with mass spectrometry determination. Compared with conventional solid-phase extraction, the developed method bears many intriguing properties such as low consumption of the sample and organic solvent, time-saving and easy operation, which are of great interest and desire for bioanalysis applications. A series of parameters that affect the analytical performance, such as the type of elution, the aspirating/dispensing cycles of sample loading and elution, washing solution, and matrix effects, was investigated in detail. Under the optimized conditions, the proposed method presented a good linearity (R ≥ 0.986) and satisfactory sensitivity and limits of detection (0.06-0.53 ng/mL) and quantification (0.20-1.77 ng/mL), respectively. In addition, satisfactory recoveries (60.0-91.4%) and accuracy (RSD ≤ 5.72%) were achieved after optimizing the conditions when applying the developed method to real sample analysis. The screening of polychlorinated biphenyls residues in bovine serum samples by the developed method demonstrated that the assay is ideally suited as a monitoring method for polychlorinated biphenyls residues in bioanalysis.

Research on the interaction of hydrogen-bond acidic polymer sensitive sensor materials with chemical warfare agents simulants by inverse gas chromatography.

Hydrogen-bond acidic polymers are important high affinity materials sensitive to organophosphates in the chemical warfare agent sensor detection process. Interactions between the sensor sensitive materials and chemical warfare agent simulants were studied by inverse gas chromatography. Hydrogen bonded acidic polymers, i.e., BSP3, were prepared for micro-packed columns to examine the interaction. DMMP (a nerve gas simulant) and 2-CEES (a blister agent simulant) were used as probes. Chemical and physical parameters such as heats of absorption and Henry constants of the polymers to DMMP and 2-CEES were determined by inverse gas chromatography. Details concerning absorption performance are also discussed in this paper.