Copper Immobilized over 2D Hexagonal SBA-15 for Electrochemical and Colorimetric Sulfite Sensing

Sulfite (SO₃^2-) is considered a highly toxic anion for living organisms. Herein, we report the synthesis of copper immobilized over a 2D hexagonally ordered mesoporous silica material CuMS as an electrochemical and colorimetric dual-technique-based sensing platform for sulfite detection. The immobilization of copper on silica was achieved through the bis[3-(triethoxysilyl)propyl]tetrasulfide (TEPTS) ligand. Morphological and physical properties of the material were confirmed by several characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N₂ sorption, and X-ray photoelectron spectroscopy. The CuMS material retained mesoporosity with a narrow pore size distribution (D ≈ 5.4 nm) and a high Brunauer-Emmett-Teller surface area of 682 m² g^-1 after the immobilization of copper. The prepared catalyst shows promising electrocatalytic activity toward sulfite oxidation. A linear variation in the peak current was obtained for SO₃^2- oxidation in the 0.2-15 mM range with a high sensitivity of 62.08 μA cm^-2, under optimum experimental conditions. The limit of detection (LOD) was found to be 1.14 nM. CuMS also shows excellent activity toward colorimetric detection of sulfite anions with an LOD of 0.4 nM. The proposed sensor shows high selectivity toward the sulfite anion, even in the presence of common interferents. The detection of sulfite in white wine with excellent recovery demonstrates the practical applicability of this sensor.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

A novel miniaturized electroanalytical device integrated with gas extraction for the voltammetric determination of sulfite in beverages

Voltammetry and amperometry are inexpensive and high-performance analytical techniques. However, their lack of selectivity limits their use in complex matrices such as biological, environmental, and food samples. Therefore, voltammetric and amperometric analyses of these samples usually require time-consuming and laborious sample pretreatments. In this study, we present a simple and cost-effective approach to fabricate a miniaturized electrochemical cell that can be easily coupled to a head space-like gas extraction procedure in such a way the sample pretreatment and voltammetric detection are performed in a single step. As a proof of concept, we have used the proposed system to quantify sulfite in beverage samples after its conversion to SO_2(g). Despite the simplicity and low cost of the proposed system, it provided good analytical performance and a limit of detection of 4.0 μmol L^-1 was achieved after only 10 min of extraction. The proposed system is quite versatile since it can be applied to quantify any volatile electroactive species. Also, the proposed system provides a unique way to assess real-time extraction curves, which are essential to study and optimize new gas extraction procedures. Therefore, the approach described in this study could contribute to both applied and fundamental Analytical Chemistry.

Structural and morphological tuning of Cu-based metal oxide nanoparticles by a facile chemical method and highly electrochemical sensing of sulphite

A facile one-step chemical method is introduced for the successful synthesis of Cu₂O, CuO and CuNa₂(OH)₄ crystal structures and their electrochemical properties were also investigated. X-ray diffraction studies revealed that these copper-based oxide nanoparticles display different crystal structures such as cubic (Cu₂O), monoclinic (CuO) and orthorhombic [CuNa₂(OH)₄]. The microstructural information of nanoparticles was investigated by transmission electron microscopy. It shows attractive morphologies of different orientation such as rod like structure, nanobeads and well-aligned uniform nanorod for Cu₂O, CuO and CuNa₂(OH)₄, respectively. Electrochemical sensing of sulphite (SO₃²⁻) on these three copper-based oxide modified electrodes was investigated. Among the three different crystal structures, CuO shows promising electrocatalytic activity towards oxidation of sulphite. A linear variation in peak current was obtained for SO₃²⁻ oxidation from 0.2 to 15 mM under the optimum experimental condition. The sensitivity and detection limit were in the order of 48.5 µA cm⁻² mM⁻¹ and 1.8 µM, respectively. Finally, practical utility of CuO modified electrode was demonstrated for the estimation of sulphite in commercial wine samples.

Determination of sulfite in food and beverages using a reliable ratiometric AIE probe

The feasibility of using an “AIE + ICT” probe for a highly accurate and reliable determination of the sulfite level in food and beverages is demonstrated.

Imidazo[1,5-α]pyridine-based fluorescent probe with a large Stokes shift for specific recognition of sulfite

By taking advantage of the intramolecular charge transfer (ICT) process, we presented a novel fluorescent probe IPY-SO₂ based on imidazo[1,5-α]pyridine derivative for detecting SO₃^2- with a low detection limit (70 nM). Combining its favorable turn-on fluorescence feature (75-fold), rapid response (5 min), high selectivity, large Stokes shift (174 nm) and low cytotoxicity, IPY-SO₂ was successfully applied to imaging SO₃² in living MCF-7 cells and zebrafish.