Colorimetric and fluorescent sensor constructing from the nanofibrous membrane of porphyrinated polyimide for the detection of hydrogen chloride gas

Selective measurement of Cl2 and HCl based on dopant-assisted negative photoionization ion mobility spectrometry combined with semiconductor cooling

This study presents an efficient approach for the precise detection of chlorine gas (Cl2) and hydrogen chloride (HCl), harmful pollutants frequently emitted from chlor-alkali and various industrial processes. These substances, even in trace amounts, pose significant health risks. Ion mobility spectrometry (IMS), known for its sensitivity in pollutant detection, traditionally struggles to differentiate between Cl2 and HCl due to the similarity of their product ions, Cl-. To overcome this limitation, we introduce a novel technique combining dopant-assisted negative photoionization ion mobility spectrometry (DANP-IMS) with an automatic semiconductor cooling system. This unique combination utilizes the differential cryogenic removal efficiencies of Cl2 and HCl to segregate these gases before analysis. By applying DANP-IMS, we achieved selective measurement of Cl- ion signal intensities under both standard and cryogenic conditions, facilitating the accurate quantification of total chlorine and Cl2 levels. We then determined HCl concentrations by deducting the Cl2 signal from the total chlorine readings. Our approach demonstrated detection limits of 2.0 parts per billion (ppb) for Cl2 and 0.8 ppb for HCl, across a linear detection range of 0-200 ppb. Moreover, our method's capability for real-time atmospheric monitoring of Cl2 and HCl near industrial sites underscores its utility for environmental monitoring, offering a robust solution for the separate and precise measurement of these pollutants.

Aggregation induced emission and volatile acid vapour sensing in acridine appended poly (aryl ether) based low molecular weight organogelator

Considerable research attention has been devoted to the development of portable and rapid fluorescence sensors that can selectively detect volatile acids, due to the harmful effects of acid vapour on the environment and human health. Although various types of fluorophores have been reported for sensing volatile acid vapours, regulation of the sensory response using aggregation induced emissive (AIE) based gelators has rarely been reported. In this study, we present the design and synthesis of a novel organogelator that is capable of sensing volatile acids through AIE. An acridine-attached poly(aryl ether) dendron molecular system is synthesized through an aldimine coupling reaction, which self-assembles and forms a gel, exhibiting AIE behavior. The synthesized molecule and prepared gel were characterized using NMR, MASS, XRD, HRSEM and rheology techniques. The AIE property of APD was investigated using steady-state absorption and emission spectroscopic techniques. The sensory response of the APD gelator was tested with various analytes, and the results indicated that APD shows rapid response, particularly to acid vapours, where the detection limits (DL) of trifluoroacetic acid (TFA), hydrochloric acid (HCl) and nitric acid (HNO3) vapor were as low as 0.22, 0.9 and 0.30 ppm, respectively. An APD solid film in filter paper shows a visual color change from yellow to red in an aqueous acidic medium, and the effect is reversed in an alkaline medium. These findings suggest that an APD gelator could potentially be utilized to generate a portable acid vapor sensor kit due to its low detection limit and rapid response time, and it could be also be used as a substitute for existing acid indicators.

Chemical Sensors using Single-Molecule Electrical Measurements

Driven by the digitization and informatization of contemporary society, electrical sensors are developing toward minimal structure, intelligent function, and high detection resolution. Single-molecule electrical measurement techniques have been proven to be capable of label-free molecular recognition and detection, which opens a new strategy for the design of efficient single-molecule detection sensors. In this review, we outline the main advances and potentials of single-molecule electronics for qualitative identification and recognition assays at the single-molecule level. Strategies for single-molecule electro-sensing and its main applications are reviewed, mainly in the detection of ions, small molecules, oligomers, genetic materials, and proteins. This review summarizes the remaining challenges in the current development of single-molecule electrical sensing and presents some potential perspectives for this field.

Design and synthesis of metal-free ethene-based covalent organic framework photocatalysts for efficient, selective, and long-term stable CO2 conversion into methane

The efficient and selective photocatalytic CO₂ conversion into higher-valued hydrocarbon products (e.g., methane and ethane) over covalent organic frameworks (COFs) remains a challenge, with all previously reported attempts producing carbon monoxide as the dominant product. Herein, we report a new ethene-based COF, through polycondensation of electron-rich (E)-1,2‑diphenylethene and 1,3,6,8‑tetraphenylpyrene units. The synthesized ethene-based COF functioned as an efficient metal-free photocatalyst for the conversion of CO₂ into methane under visible light irradiation, with a selectivity of 100 %, a production rate of 14.7 µmol g^-1h^-1, and an apparent quantum yield of c.a. 0.99 % at 489.5 nm, which are the most promising values reported for CO₂ conversion by a metal-free COF photocatalyst, without any support from a co-catalyst. The carbon origin of CH₄ product is confirmed by isotope tracer ¹³CO₂ experiment. Moreover, the photocatalytic system consistently produces methane for > 14 h with recyclability.

Simultaneous Cryogenic Radical and Oxidative Coupling Polymerizations to Polyaniline/Polyacrylamide Conductive Cryogels for Gas Sensing

The macro-porous structure of polymer cryogels provides an appropriate channel for the adsorption and transport of substances, endowing its application in the field of electrochemical sensing. The combination mode of a polymer matrix and electro-active substance, particularly the distribution of an electro-active substance in the matrix, has an important effect on the overall performance of the sensor. In this work, through the simultaneous oxidation coupling polymerization of aniline (ANI) and radical polymerization of acrylamide (AAm) under cryogenic condition, conductive composite cryogels were prepared, aiming for the uniform distribution of PANI in the PAAm matrix. The possibility of simultaneous polymerizations was symmetrically investigated, and the obtained PANI/PAAm cryogels were characterized. Due to the acid-doping of PANI, the electrical conductivity of PANI/PAAm cryogels could be modulated with acidic and basic gases. Thus, the performance of the gas sensor was studied by making conductive PANI/PAAm cryogel sheets as resistive sensor electrodes. We found that the content of PANI, the sheet thickness and the dry/wet state of the cryogel influenced the response sensitivity and rate as well as the recovery properties. The response duration for HCl and NH₃ gas was shorter than 70 and 120 s, respectively. The cyclic detection of HCl gas and the alternate detection of NH₃/HCl were achieved. This gas sensor with advantages, including simple preparation, low cost and high sensitivity, would have great potential for the application to monitor the leakage of acidic and basic gases.

Volatile Organic Compound Sensing Array and Optoelectronic Filter System using Ion-Pairing Dyes with a Wide Visible Spectrum

An ideal dye-based sensing array has essential design requirements, including facile preparation methodology, tolerance to water vapor, a broad range of color-responsive changes, and a simple readout system. Here, a brief synthetic route is developed for ion-pairing dyes exhibiting unusual chromatic changes across the entire visible spectrum. It requires only mixing and precipitation under mild conditions. The dyes are applied to a sensing array containing 12 sensing elements with different initial states. Owing to the numerous color variations of the dyes, the color map generated by the array is highly simple yet sufficiently accurate to distinguish among the different functional groups (such as amines, aldehydes, and carboxylic acids) as well as carbon chain lengths. Principle component analysis (PCA) demonstrates that volatile organic compounds (VOCs) can be well classified according to the color changes of the sensing array. The ion-pairing dyes are embedded into 3D stacked nanofibers via electrospinning, and function as effective harmful-gas (e.g., formaldehyde) sensors with sub-ppm theoretical detection limits (0.15 ppm). Finally, the 3D stacked nanofibers can be employed in an optoelectronic filter system that automatically checks for formaldehyde in the surroundings and also confirms the effective removal of the detected formaldehyde by the gas filter cartridge.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

Advanced applications of chemo-responsive dyes based odor imaging technology for fast sensing food quality and safety: A review

Public attention to foodquality and safety has been increased significantly. Therefore, appropriate analytical tools are needed to analyze and sense the food quality and safety. Volatile organic compounds (VOCs) are important indicators for the quality and safety of food products. Odor imaging technology based on chemo-responsive dyes is one of the most promising methods for analysis of food products. This article reviews the sensing and imaging fundamentals of odor imaging technology based on chemo-responsive dyes. The aim is to give detailed outlines about the theory and principles of using odor imaging technology for VOCs detection, and to focus primarily on its applications in the field of quality and safety evaluation of food products, as well as its future applicability in modern food industries and research. The literatures presented in this review clearly demonstrated that imaging technology based on chemo-responsive dyes has the exciting effect to inspect such as quality assessment of cereal , wine and vinegar flavored foods , poultry meat, aquatic products, fruits and vegetables, and tea. It has the potential for the rapid, reliable, and inline assessment of food safety and quality by providing odor-image-basedmonitoring tool. Practical Application: The literatures presented in this review clearly demonstrated that imaging technology based on chemo-responsive dyes has the exciting effect to inspect such as quality assessment of cereal , wine and vinegar flavored foods, poultry meat, aquatic products, fruits and vegetables, and tea.

Ultra-Highly Sensitive Hydrogen Chloride Detection Based on Quartz-Enhanced Photothermal Spectroscopy

Combining the merits of non-contact measurement and high sensitivity, the quartz-enhanced photothermal spectroscopy (QEPTS) technique is suitable for measuring acid gases such as hydrogen chloride (HCl). In this invited paper, we report, for the first time, on an ultra-highly sensitive HCl sensor based on the QEPTS technique. A continuous wave, distributed feedback (CW-DFB) fiber-coupled diode laser with emission wavelength of 1.74 µm was used as the excitation source. A certified mixture of 500 ppm HCl:N2 was adapted as the analyte. Wavelength modulation spectroscopy was used to simplify the data processing. The wavelength modulation depth was optimized. The relationships between the second harmonic (2f) amplitude of HCl-QEPTS signal and the laser power as well as HCl concentration were investigated. An Allan variance analysis was performed to prove that this sensor had good stability and high sensitivity. The proposed HCl-QEPTS sensor can achieve a minimum detection limit (MDL) of ~17 parts per billion (ppb) with an integration time of 130 s. Further improvement of such an HCl-QEPTS sensor performance was proposed.

QCM-Based HCl Gas Sensors Using Spin-Coated Aminated Polystyrene Colloids

Hydrogen chloride (HCl) gas is highly toxic to the human body. Therefore, HCl gas detection sensors should be installed at workplaces where trace HCl gas is continuously generated. Even though various polymer-based HCl-gas-sensing films have been developed, simpler and novel sensing platforms should be developed to ensure the cost effectiveness and reusability of the sensing platforms. Therefore, we present a simple strategy to fabricate reusable HCl-gas-sensing platforms using aminated polystyrene (a-PS) colloids and investigate their sensitivity, reusability, and selectivity using a quartz crystal microbalance (QCM). The reusable a-PS(1.0) colloidal sensor with a high degree of amination (DA) exhibited the highest binding capacity (102 μg/mg) based on the frequency change (Δf) during the HCl gas adsorption process. Further, its sensitivity and limit of detection (LOD) were 3.88 Hz/ppm and 5.002 ppm, respectively, at a low HCl gas concentration (<10 ppm). In addition, the sensitivity coefficient (k*) of the a-PS(1.0) colloid sensor with respect to HCHO was higher than that in the case of HF because of the lower binding affinity of the former with the a-PS(1.0) colloids. Based on these results, highly sensitive and reproducible a-PS colloids could be reused as an HCl-gas-sensing platform and used as an HCl sorbent in a gas column filter.

Ratiometric and colorimetric sensors for highly sensitive detection of water in organic solvents based on hydroxyl-containing polyimide-fluoride complexes

Two new hydroxyl-containing polyimides (PIs) with excellent comprehensive performances were designed and synthesized. After PIs react with fluoride ion (F^-), the resulting polyimide-fluoride complexes (PI-1·F and PI-2·F) are exploited as ratiometric and colorimetric sensors for detecting trace water in DMSO/DMF with high sensitivity. Both sensors PI-1·F and PI-2·F exhibit a good naked-eye visual detection as well as an excellent linear relationship between the UV-vis absorbance ratio and the low water content in DMSO/DMF, which constitutes a quantitative method for determining water content in DMSO/DMF. The limits of detection (LOD) of sensor PI-1·F for water in DMSO and DMF are as low as 0.0035% and 0.0031% (v/v), respectively. The sensor PI-2·F shows the higher sensitivity for water detection with extremely low detection limits of 0.00084% and 0.0015% in DMSO and DMF, respectively. Furthermore, PI films have been directly used for the visual sensing of water in acetonitrile, acetone and ethanol, which provides an effective way for fabricating high-performance film-based water sensor devices.

A reversible chromogenic covalent organic polymer for gas sensing applications

A triazine-cored covalent organic polymer (COP) was designed and synthesized via amine linkages under ambient conditions. The novel architecture of the COP was fully characterized via spectroscopic and analytical techniques. The present COP demonstrates a quick, portable and reversible chromogenic response towards noxious HCl vapours.

Multifunctional Gas and pH Fluorescent Sensors Based on Cellulose Acetate Electrospun Fibers Decorated with Rhodamine B-Functionalised Core-Shell Ferrous Nanoparticles

Ferrous core-shell nanoparticles consisting of a magnetic γ-Fe₂O₃ multi-nanoparticle core and an outer silica shell have been synthesized and covalently functionalized with Rhodamine B (RhB) fluorescent molecules (γ-Fe₂O₃/SiO₂/RhB NPs). The resulting γ-Fe₂O₃/SiO₂/RhB NPs were integrated with a renewable and naturally-abundant cellulose derivative (i.e. cellulose acetate, CA) that was processed in the form of electrospun fibers to yield multifunctional fluorescent fibrous nanocomposites. The encapsulation of the nanoparticles within the fibers and the covalent anchoring of the RhB fluorophore onto the nanoparticle surfaces prevented the fluorophore's leakage from the fibrous mat, enabling thus stable fluorescence-based operation of the developed materials. These materials were further evaluated as dual fluorescent sensors (i.e. ammonia gas and pH sensors), demonstrating consistent response for very high ammonia concentrations (up to 12000 ppm) and fast and linear response in both alkaline and acidic environments. The superparamagnetic nature of embedded nanoparticles provides means of electrospun fibers morphology control by magnetic field-assisted processes and additional means of electromagnetic-based manipulation making possible their use in a wide range of sensing applications.

Porous materials applied to biomarker sensing in exhaled breath for monitoring and detecting non-invasive pathologies

Overview of the use of porous materials for gas sensing to analyze the exhaled breath of patients for disease identification.

Fluorescent electrospun PMMA microfiber mats with embedded NaYF4: Yb/Er upconverting nanoparticles

Functional upconverting nanoparticles (UCNPs) can offer new possibilities in fluorescent applications as they exhibit desired characteristic properties like large shift between the fluorescent emission signal and the infrared excitation wavelength, multi- and narrow-band absorption and emission in visible and near infrared - Vis/NIR, together with excellent photostability and low toxicity as opposed to semiconducting quantum dots. The upconversion luminescence emission or quenching characteristics of UCNPs can be altered upon exposure to physical or chemical environmental factors providing thus a functionality that can be utilized for sensing or imaging. Furthermore their functionalization with suitable indicator dyes or recognition elements can extend the range of luminescence response and ratiometric sensing to specific analytes. Synergistically, electrospun nano- and microfibers offering large surface area can enhance the functionality of UCNPs by retaining the fluorescence efficiency and improving the overall responsivity due to dramatically increased surface. For the optimization of this hybrid material system the controllable incorporation of UCNPs is required especially at increased concentration conditions needed for high brightness. Herein, we report the fabrication, morphological and optical characterization of electrospun polymer-based nanocomposite fibers, consisting of poly(methyl methacrylate) (PMMA) and upconverting lanthanide doped nanoparticles of the type NaYF₄ : 20% Yb³⁺/2% Er³⁺ @ NaYF₄. Morphological studies regarding the uniformity and aggregation effects of the UCNP inclusion within the fibers have been implemented followed by upconversion emission characterization by pulsed near-infrared excitation. The study and optimization of such nanocomposite fibrous systems could provide useful insights for the development of efficient upconverting electrospun fiber mats for a number of imaging and sensing applications.

A gaseous hydrogen chloride chemosensor based on a 2D covalent organic framework

A tetraphenylethene-based 2D covalent organic framework (COF) has been synthesized. It exhibits a very fast response and high sensitivity to the presence of gaseous HCl by way of distinct changes in fluorescence emission and color, which makes the COF a good chemosensor for spectroscopic and naked-eye detection of gaseous HCl.

A novel hydroxyl-containing polyimide as a colorimetric and ratiometric chemosensor for the reversible detection of fluoride ions

A novel hydroxyl-containing polyimide film has been designed and fabricated as a chemosensor for the real-time visualization of F⁻ with high selectivity and sensitivity.

HCl Gas Sensor Coating Based on Poly(N-isopropylacrylamide) Nanoparticles Prepared from Water-Methanol Binary Solvent

Poly(N-isopropylacrylamide) (PNIPAM) nanoparticles formed in water-methanol binary solvent were successfully deposited on a resonator surface at room temperature by exploiting the cononsolvency effect on the phase transition of PNIPAM aqueous solutions. Scanning electron microscopic observation revealed that the nanoparticles were secondary and made up of agglomerated primary spherical particles of about 10-nm diameter, buried in the film. The magnitude of the sensor response toward HCl gas was larger than that of the nanoparticle sensor prepared from pure water solvent, and the sensitivity to 1 ppm of HCl of sensor-coated nanoparticles based on the present method was 3.3 Hz/ppm. The recovery of the sensors was less than 90% at first cycle measurement, but had improved to almost 100% at the third cycle.

Electrospun one-dimensional nanostructures: a new horizon for gas sensing materials

Electrospun one-dimensional (1D) nanostructures are rapidly emerging as key enabling components in gas sensing due to their unique electrical, optical, magnetic, thermal, mechanical and chemical properties. 1D nanostructures have found applications in numerous areas, including healthcare, energy storage, biotechnology, environmental monitoring, and defence/security. Their enhanced specific surface area, superior mechanical properties, nanoporosity and improved surface characteristics (in particular, uniformity and stability) have made them important active materials for gas sensing applications. Such highly sensitive and selective elements can be embedded in sensor nodes for internet-of-things applications or in mobile systems for continuous monitoring of air pollutants and greenhouse gases as well as for monitoring the well-being and health in everyday life. Herein, we review recent developments of gas sensors based on electrospun 1D nanostructures in different sensing platforms, including optical, conductometric and acoustic resonators. After explaining the principle of electrospinning, we classify sensors based on the type of materials used as an active sensing layer, including polymers, metal oxide semiconductors, graphene, and their composites or their functionalized forms. The material properties of these electrospun fibers and their sensing performance toward different analytes are explained in detail and correlated to the benefits and limitations for every approach.

Polyaniline-Functionalized Nanofibers for Colorimetric Detection of HCl Vapor

Hydrogen chloride (HCl) gas is a hazardous byproduct of industrial processes. Colorimetric approaches to facilitate portable and remote detection are especially desirable. We graft polyaniline to the surface of electrospun nylon nanofibers to minimize mass transfer. Using the resulting nanofibers, we demonstrate colorimetric detection of HCl at sub-ppm levels. We investigated the reusability of the fibers and observed a twofold increase in the limit of detection with multiple uses because of dedoping of the PANi indicated by elemental analysis. The limit of detection using visual detection was compared to spectrophotometric analysis. The ΔE from CIE LAB color space analysis via diffuse reflectance spectroscopy enhances the limit of detection by ∼fivefold when compared to visual detection. This analysis is a promising approach for remote detection using simple commercial digital cameras to achieve low limits of detection.

Microporous Porphyrin Networks Mimicking a Velvet Worm Surface and Their Enhanced Sensitivities toward Hydrogen Chloride and Ammonia

This work shows that the functions of microporous organic network materials can be enhanced through engineering of the material structure. Mimicking the surface structure of velvet worms, we prepared the aligned 1D structure (rod) of microporous porphyrin networks by the Sonogashira coupling of tetrakis(4-ethynylphenyl)porphyrin with 1,4-diiodobenzene in an anodic aluminum oxide plate. The length of the 1D structure was controlled in the range of 1-5 μm. The velvet worm surface-like microporous porphyrin networks (Velvet-MPNs) showed higher sensitivities to hydrogen chloride and ammonia gases by up to ∼14 and 4.6 times, respectively, compared with a control MPN material without rods.

A novel aggregation-induced-emission-active supramolecular organogel for the detection of volatile acid vapors

A novel supramolecular organogel with AIE properties was synthesized and applied for sensing volatile acid vapors with excellent performance.

Efficient Energy Transfer (EnT) in Pyrene- and Porphyrin-Based Mixed-Ligand Metal-Organic Frameworks

Designing and synthesizing the ordered light-harvesting systems, possessing complementary absorption and energy-transfer process between the chromophores, are essential steps to accomplish successful mimicking of the natural photosynthetic systems. Metal-organic frameworks (MOFs) can be considered as an ideal system to achieve this due to their highly ordered structure, superior synthetic versatility, and tailorable functionality. Herein, we have synthesized the new light-harvesting mixed-ligand MOFs (MLMs, MLM-1-3) via solvothermal reactions between a Zr₆ cluster and a mixture of appropriate ratio of 1,3,6,8-tetrakis(p-benzoic acid)pyrene and [5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrinato]-Zn(II) ligands. The identical symmetry and connectivity of the two ligands of the MLMs was the key parameter of successful synthesis as a single MOF form, and the ample overlap between the emission spectrum of pyrene and the absorption spectrum of porphyrin provided the ideal platform to design an efficient-energy transfer (EnT) process within the MLMs. We obtained the nanoscale maps of the fluorescence intensities and lifetimes of microsize MLM grains for unambiguous visualization of EnT phenomena occurring between two ligands in MLMs. Moreover, due to complementary absorption and energy transfer between the two ligands in the MLMs, our MLMs performed as superior photoinduced singlet-oxygen generators, verifying the enhanced light-harvesting properties of the pyrene- and porphyrin-based MLMs.

Colorimetric sensors for rapid detection of various analytes

Sensor technology for the rapid detection of the analytes with high sensitivity and selectivity has several challenges. Despite the challenges, colorimetric sensors have been widely accepted for its high sensitive and selective response towards various analytes. In this review, colorimetric sensors for the detection of biomolecules like protein, DNA, pathogen and chemical compounds like heavy metal ions, toxic gases and organic compounds have been elaborately discussed. The visible sensing mechanism based on Surface Plasmon Resonance (SPR) using metal nanoparticles like Au, Ag, thin film interference using SiO₂ and colorimetric array-based technique have been highlighted. The optical property of metal nanoparticles enables a visual color change during its interaction with the analytes owing to the dispersion and aggregation of nanoparticles. Recently, colorimetric changes using silica substrate for detection of protein and small molecules by thin film interference as a visible sensing mechanism has been developed without the usage of fluorescent or radioisotopes labels. Multilayer of biomaterials were used as a platform where reflection and interference of scattering light occur due to which color change happens leading to rapid sensing. Colorimetric array-based technique for the detection of organic compounds using chemoresponsive dyes has also been focused wherein the interaction of the analytes with the substrate coated with chemoresponsive dyes gives colorimetric change.

A fluorescent and colorimetric sensor based on a porphyrin doped polystyrene nanoporous fiber membrane for HCl gas detection

A fluorescent and colorimetric HCl gas sensor based on the use of the optical probe 5,10,15,20-tetraphenylporphyrin (TPPH₂) contained in a polystyrene nanoporous fiber membrane was facilely fabricated by electrospinning method.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.

A T-shaped triazatruxene probe for the naked-eye detection of HCl gas with high sensitivity and selectivity

A T-shaped Schiff-base triazatruxene derivative (TATNFF) was designed, synthesized, and explored as a sensitive probe to detect HCl gas by the naked eye. The remarkable color change of TATNFF with turn-on behavior in the presence of a trace amount of HCl gas was obviously observed by the naked eye, which opens up a new strategy to explore a novel set of smart responsive materials for sensing applications.

AIE luminogen-functionalised mesoporous nanomaterials for efficient detection of volatile gases

Mesoporous silica nanoparticles functionalised with aggregation-induced emission (AIE) luminogen via a carbon-nitrogen double bond are fabricated into films by a dip-coating method. The as-made films can serve as efficient fluorescent sensors for the naked-eye detection of volatile acid gases by colour and emission changes, as well as for the detection of 2,4-dinitrotoluene vapours by fluorescence quenching.

A porphyrin-based chemosensor for colorimetric and fluorometric detection of cadmium(II) with high selectivity

A new chemosensor (ProE) based on a functionalized porphyrin for colorimetric and fluorometric detection of cadmium ions ( Cd 2+) was outlined. ProE displays a distinct color change, as well as dramatic ratiometric variations in absorption and fluorescent emission spectra upon exposure to Cd 2+. This condition allows the detection of the analyte at concentrations as low as 0.073 μM. The dual chromo- and fluorogenic responses of the probe are attributed to the formation of a 1:1 Cd 2+/ProE complex, which ultimately affects its optical properties. The sensor also exhibited high selectivity and sensitivity toward Cd 2+ over other common metal ions in a moderate pH range, leading to potential fabrication of both "naked-eye" and ratiometric fluorescent detection of Cd 2+.

Porphyrinated polyimide honeycomb films with high thermal stability for HCl gas sensing

Thermally stable films with ordered pores are fabricated from porphyrinated polyimides and they exhibit excellent property in HCl gas sensing.

Synthesis of porphyrin monomers on the basis of meso-mono-hydroxy- and aminophenylporphyrins

The methods for the synthesis of porphyrins containing active vinyl groups on a periphery of the tetrapyrrole macroheterocycle are described. The possibility of their usage as comonomers in a copolymerization reaction with methyl methacrylate is given.

Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

A novel porphyrin-containing polyimide nanofibrous membrane for colorimetric and fluorometric detection of pyridine vapor

A novel zinc porphyrin-containing polyimide (ZPCPI) nanofibrous membrane for rapid and reversible detection of trace amounts of pyridine vapor is described. The membrane displays a distinct color change, as well as dramatic variations in absorption and fluorescent emission spectra, upon exposure to pyridine vapor. This condition allows the detection of the analyte at concentrations as low as 0.041 ppm. The vapochromic and spectrophotometric responses of the membrane are attributed to the formation of the ZPCPI-pyridine complex upon axial coordination. From surface plasmon resonance analysis, the affinity constant of ZPCPI-pyridine complex was calculated to be (3.98 ± 0.25) × 10⁴ L·mol⁻¹. The ZPCPI nanofibrous membrane also showed excellent selectivity for pyridine vapor over other common amines, confirming its applicability in the manufacture of pyridine-sensitive gas sensors.

Functional nanofibers in sensor applications

Over the last decade, the interest in electrospun nanomaterials and their applications has increased. The fascinating and unparalleled properties of electrospun nanomaterials, such as large surface-to-volume ratios and high open porosity, have opened new and unexpected fields of application, especially in ultrasensitive sensors. By exploiting the inherent physical, electrical and mechanical properties of nanomaterials, it is possible to improve the performance of conventional sensors by increasing their sensitivity, selectivity, portability and power efficiency. In this chapter, the recent progress in the development of electrospun nanomaterials is reviewed. In particular, applications in some predominant sensing approaches, such as acoustic wave, resistive, photoelectric, optical and biological, are discussed.