Chiral porphyrin-SiO2 nano helices-based sensors for vapor enantiomers recognition

The ability of olfaction to distinguish odors is based on many different properties deriving from the molecular structure, including chirality. Even if the electronic nose (e-nose) concept has been widely used in strict analogy with biological systems to implement sensor arrays that recognize and distinguish complex odor matrices, the fabrication of an enantioselective e-nose remains a challenge. This paper introduces an array of quartz microbalances (QMB) functionalized with sensitive materials made of a combination of achiral receptors and silica nanohelices grafted by chiral and achiral porphyrins. In this combination, nanohelices provide a chiral template for the spatial arrangement of porphyrins, while porphyrins act as receptors that can interact differently with analytes. Remarkably, even if single sensors show scarce enantioselectivity, the signals of the overall array achieve recognition of the chiral identity of the five diverse enantiomeric pairs tested when the data are processed with proper multivariate algorithms. Such an innovative and generalizable approach is expected to enable the formation of an extensive library of readily integrable chiral receptors in enantioselective sensor arrays, potentially revolutionizing diverse fields such as agrochemicals, medicine, and environmental sciences.

Chiral Recognition with Broad Selective Sensor Arrays

The detection and discrimination of chiral analytes has always been a topical theme in food and pharmaceutical industries and environmental monitoring, especially when dealing with chiral drugs and pesticides, whose enantiomeric nature assessment is of crucial importance. The typical approach matches novel chiral receptors designed ad hoc for the discrimination of a target enantiomer with emerging nanotechnologies. The massive synthetic efforts requested and the difficulty of analyzing complex matrices warrant the ever-growing exploitation of sensor array as an alternative route, using a limited number of chiral or both chiral and achiral sensors for the stereoselective identification and dosing of chiral compounds. This review aims to illustrate a little-explored winning strategy in chiral sensing based on sensor arrays. This strategy mimics the functioning of natural olfactory systems that perceive some couples of enantiomeric compounds as distinctive odors (i.e., using an array of a considerable number of broad selective receptors). Thus, fundamental concepts related to the working principle of sensor arrays and the role of data analysis techniques and models have been briefly presented. After the discussion of existing examples in the literature using arrays for discriminating enantiomers and, in some cases, determining the enantiomeric excess, the remaining challenges and future directions are outlined for researchers interested in chiral sensing applications.

Tunable Supramolecular Chirogenesis in the Self-Assembling of Amphiphilic Porphyrin Triggered by Chiral Amines

Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D- or L-proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology.

Development of a Colorimetric Sensor for Autonomous, Networked, Real-Time Application

This review describes an ongoing effort intended to develop wireless sensor networks for real-time monitoring of airborne targets across a broad area. The goal is to apply the spectrophotometric characteristics of porphyrins and metalloporphyrins in a colorimetric array for detection and discrimination of changes in the chemical composition of environmental air samples. The work includes hardware, software, and firmware design as well as development of algorithms for identification of event occurrence and discrimination of targets. Here, we describe the prototype devices and algorithms related to this effort as well as work directed at selection of indicator arrays for use with the system. Finally, we review the field trials completed with the prototype devices and discuss the outlook for further development.

p-Type and n-type conductometric behaviors of octachloro-metallophthalocyanine-based heterojunctions, the key role of the metal

In the present work, we determined the electrical properties of octachlorinated metallophthalocyanines with Co(II) and Cu(II) ions as metal centers. We engaged them in heterojunctions, with lutetium bisphthalocyanine as a partner. Surprisingly, cobalt and copper complexes show opposite behaviors, the first being an [Formula: see text]-type material whereas the latter is a [Formula: see text]-type material, as deduced from the response of the heterojunctions towards ammonia; showing the unusual key role played by the metal center. While the LuPc[Formula: see text]/Cu(Cl[Formula: see text]Pc) complex exhibits a negative response to ammonia, the LuPc[Formula: see text]/Co(Cl[Formula: see text]Pc) complex exhibits a positive response to ammonia, with a sensitivity of 1.47% ppm[Formula: see text] at concentrations lower than 10 ppm and a limit of detection of 250 ppb. All the devices operate at room temperature and in real atmosphere.

An electrochemical quartz crystal microbalance study of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization process

The process of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by the quartz crystal microbalance method in different electrodeposition conditions. The films were deposited in two modes: in potentiostatic conditions (at the potential of [Formula: see text]2 V) and in potentiodynamic conditions (CV with the potential scan rate of 20 mV/s). The effect of electrolysis parameters on 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by obtaining films in two modes and using two supporting electrolytes: tetrabutylammonium perchlorate or tetrabutylammonium hexafluorophosphate. The biggest film mass gain was observed on a clean electrode surface. At further film deposition on the polyporphyrin-coated electrode, the film mass growth stopped. The electrodeposition effectiveness was somewhat higher in the potentiodynamic conditions, with the formation of a looser film. The nature of the supporting electrolyte did not have a significant effect on the electrodeposition process. A significant contribution to the deposition was made by the electrode material. The film thickness was 25–80 nm. The films possessed [Formula: see text]-type conductivity; and the flat-band potential for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiodynamic conditions was 0.33 V, for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiostatic conditions it was 0.16 V.

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.

A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis

This paper provides a selection of the last two decades publications on the development and application of chemical sensors based on piezoelectric quartz resonators for a wide range of analytical tasks. Most of the attention is devoted to an analysis of gas and liquid media and to industrial processes controls utilizing single quartz crystal microbalance (QCM) sensors, bulk acoustic wave (BAW) sensors, and their arrays in e-nose systems. The unique opportunity to estimate several heavy metals in natural and wastewater samples from the output of a QCM sensor array highly sensitive to changes in metal ion activity in water vapor is shown. The high potential of QCM multisensor systems for fast and cost-effective water contamination assessments “in situ” without sample pretreatment is demonstrated.

Macromolecular hexa-asymmetric zinc(II) phthalocyanines bearing triazole-modified triphenylene core: Synthesis, spectroscopy and analysis towards volatile organic compounds on Surface Acoustic Wave devices

The synthesis and characterization of novel asymmetric zinc(II) phthalocyanines (4–9) and their linking through peripheral and nonperipheral positions on the phthalocyanine ring via click coupling to alkyne-functionalized 2,3,6,7,10,11-hexakis(prop-2-ynyloxy)triphenylene core are described for the first time. These phthalocyanines (Pcs) (4–12) were characterized by elemental analysis and different spectroscopic techniques such as UV-vis, 1H-NMR, FT-IR and mass spectroscopy. Furthermore, the utilization of thin films of novel Pcs as a sensitive layer for detection of lung cancer from exhaled human breath at room temperature under exposure to marker volatile organic compounds (VOCs) are presented. The developed sensors were tested for acetone, ethanol, [Formula: see text]-hexane, toluene, chloroform and isoprene in a range of 300–14560 ppm. The obtained results have confirmed the possibility of utilization of Pc-based Surface Acoustic Wave (SAW) sensors for medical diagnosis based on exhaled breath analysis.

Singlet oxygen generation from porphyrin-functionalized hexahedral polysilicon microparticles

The generation of singlet oxygen (SO), primarily by using a combination of light and photosensitizers in the presence of a dissolved gas, finds applications in both chemistry and medicine. The efficiency of its formation can be enhanced by immobilization of the photosensitizers. In this work, we have explored the covalent functionalization in suspension of hexahedral slab-like polysilicon microparticles ( [Formula: see text]P, with a largest dimension of three microns) with a model photosensitizer, 5-(4-isothiocyanatophenyl)-10,15,20-(triphenyl)porphyrin (ITC-P), and evaluated the singlet oxygen generation of this photosensitizer in solution and after immobilization (ITC-P-[Formula: see text]P) in suspension. The SO-detection experiment on the functionalized microparticles was performed using a hydrogel as the matrix supporting the microparticles (to avoid their settling), and revealed that ITC-P-[Formula: see text]Pin suspension is capable of generating SO more efficiently than free ITC-P in solution.

Synthesis and physico-chemical properties of a H-cardanol triazole zinc porphyrin conjugate

Although a large number of natural and non-natural metalloporphyrins are known, examples with fluorescence and fat-soluble properties are rare. We have achieved the synthesis of a fluorescent and fat-soluble zinc porphyrin incorporating four units of hydrogenated cardanol (H-cardanol). The synthesis is sustainable since the product is derived from cashew-nut shell liquid (CNSL), which is a renewable and bio-waste material. The H-cardanol triazole zinc porphyrin conjugate (HTZPC) was synthesized through applying a copper(i) catalyzed azide–alkyne cycloaddition (CuAAC) reaction between a H-cardanol derived azide and a tetraarylporphyrin derived alkyne. The absorption and emission properties of the hydrocarbon solvent soluble HTZPC were evaluated using UV-vis and fluorescence emission spectra obtained in various solvents. The results were compared with related molecules like a triazole-zinc porphyrin conjugate (TZPC), zinc tetra-C(4)-methoxyphenyl porphyrin (ZP), and a H-cardanol-triazole conjugate (HTC). The results showed that HTZPC undergoes J-type aggregation in both non-polar and highly polar solvents, which is dictated by van der Waals attractive forces between H-cardanol units in polar solvents (e.g. methanol and dimethylformamide) and π–π stacking interactions between porphyrin units in non-polar solvents (hexane). Moreover, the spectra indicated that the triazole units could stabilize the zinc porphyrin via intermolecular coordinate-complex formation. We anticipate that fat-soluble HTZPC could find applications in medical fields (e.g. in the photodynamic therapy of fat tissue).

A fluorescent and fat-soluble zinc porphyrin incorporating four units of hydrogenated cardanol (H-cardanol) was synthesized, and its physico-chemical properties were characterized.

Porphyrin-Functionalized Zinc Oxide Nanostructures for Sensor Applications

Hybrid materials made of wide band gap semiconductors and dye molecules are largely studied mainly for photovoltaic applications. However, these materials also show interesting chemical sensitivity. Zinc oxides (ZnO) and porphyrins are good examples of a metal oxide semiconductor and a dye molecule that give rise to a hybrid material with such interesting properties. ZnO has been studied for sensors, optoelectronics, electronic devices, photo-anodes for dye-sensitized solar cells, and for mechanical energy harvesting. Porphyrins, on the other side, can be synthesized in order to mimic their roles in living systems such as oxygen transport and charge transfer for catalytic processes in animals and photosynthesis in plants. This paper provides a review of the chemical sensing properties of porphyrin-capped ZnO nanostructures. The methodologies to functionalize the ZnO surface with porphyrins are illustrated with emphasis on the relationships between the material preparation and its sensing properties. The development of sensors is described through the application of the hybrid materials to different transducers.

Tailoring of the chlorine sensing properties of substituted metal phthalocyanines non-covalently anchored on single-walled carbon nanotubes

Schematic view of the interaction between Cl₂ and S₁/S₂ hybrid sensor.