Electrogenerated chemiluminescence 73: acid–base properties, electrochemistry, and electrogenerated chemiluminescence of neutral red in acetonitrile

Dual-Mode Immunoassay Constructed by Water-Induced Perylene Diimide Supramolecular Self-Assembly and Enzymatic Biocatalytic Precipitation Strategy

A water-induced electron-deficient dye, the supramolecule perylene diimide (PDI), has been identified recently. PDI possesses advantages such as easy reduction, nontoxicity, low cost, and simple preparation, making it a promising candidate for electrochemiluminescence (ECL) sensing platforms. In this study, a series of PDI supramolecular systems with morphological changes were prepared by utilizing water molecules to induce PDI self-assembly. This method improves the π-π stacking interactions between PDI molecules and effectively mitigates the aggregation-caused quenching (ACQ) effect on the luminous efficiency of the coplanar polycyclic aromatic hydrocarbon PDI. It is noteworthy that excellent ECL emission performance of the PDI supramolecular system was observed at -0.4 V. This low excitation potential aids in preserving antigen-antibody bioactivity and ensures accurate identification of the immune response. As a proof of concept, a dual-mode immunosensing platform for carcinoembryonic antigen (CEA) detection was constructed using an enzymatic biocatalytic precipitation (EBCP) strategy. The dual-mode immunosensor exhibited good detection performance in the concentration range of 0.001-80 ng·mL-1, presenting an advanced bioprotective analytical method for CEA detection.

Phase-Resolved Electrochemiluminescence with a Single Luminophore

Multiphase chemical systems are greatly different than bulk solutions, as they provide a unique environment for reactions to proceed and have unique physicochemical properties. Thus, new tools need to be developed to gain a more detailed understanding of these systems. Here, we use electrogenerated chemiluminescence (ECL) to elucidate phase boundaries precisely and comprehensively between aqueous droplets and an organic continuous phase owing to ECL's unprecedented spatial resolution (a few micrometers) confined at the electrode surface. Phase-resolved mapping was accomplished by selecting a luminophore that is soluble in both phases while selecting two coreactants that are exclusively soluble in one phase or the other. This type of system allows us to map the complex liquid|electrode and the liquid|liquid interfaces in a multiphase system. We show that electrical connectivity is not conserved throughout solvent inclusions, which result from neighboring droplet coalescence, indicating an unexpected initial lack of electronic communication. These results have great importance to energy storage and conversion devices and wearable/implantable sensors, which are dominated by complex, multiphase environments.

Ionic liquid-based hollow fiber-supported liquid-phase microextraction enhanced electrically for the determination of neutral red

A method of ionic liquid-based hollow fiber liquid-phase microextraction enhanced electrically was successfully developed and applied to the extraction and determination of neutral red (NR) dye, which was selected as the model analyte. A room temperature ionic liquid, 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]), was placed in the pores of a polytetrafluoethylene hollow fiber, which acts as a liquid membrane and the acceptor solution. The extraction parameters affecting the enrichment factor of NR, such as pH, extraction time, elution time, stirring rate, and the voltage were optimized. In addition, UV–Visible (UV–Vis) or electrochemiluminescence spectra were also determined. The extraction rate and capacity of NR could be improved significantly by cathodic polarization. Under the optimized extraction conditions (organic liquid microextraction phase [C₈mim][PF₆], pH 7, stirring rate 300 rpm, extraction time 20 minutes, ultrasonic-assisted elution time 3 minutes, voltage −70 V), the detection limit of 0.38 μg/L and linear correlation coefficient of r > 0.99 were obtained. The established method was successfully applied to the analysis of three soft drink samples, which were spiked with NR standards at the concentrations of 0.1, 1.0, and 5.0 mg/L, and satisfactory results were obtained.

Selective oxidation with nanoporous silica supported sensitizers: an environment friendly process using air and visible light

Transparent and porous silica xerogels containing various grafted photosensitizers (PSs) such as anthraquinone derivatives, Neutral Red, Acridine Yellow and a laboratory-made dicyano aromatics (DBTP) were prepared. In most cases, the xerogels were shown to be mainly microporous by porosimetry. The PSs were characterized in the powdered monoliths (form, aggregation, concentration) by electronic spectroscopy which also proved to be a useful tool for monitoring the material evolution after irradiation. These nanoporous xerogels were used as microreactors for gas/solid solvent-free photo-oxygenation of dimethylsulfide (DMS) using visible light and air as the sole reactant. All these PSs containing monoliths were efficient for gas-solid DMS oxidation, leading to sulfoxide and sulfone in varying ratios. As these polar oxidation products remained strongly adsorbed on the silica matrix, the gaseous flow at the outlet of the reactor was totally free of sulfide and odorless. The best results in term of yield and initial rate of degradation of DMS were obtained with DBTP containing xerogels. Moreover, as these materials were reusable without loss of efficiency and sensitizer photobleaching after a washing regeneration step, the concept of recyclable sensitizing materials was approved, opening the way to green process.

Studies of the melatonin binding site location onto quinone reductase 2 by directed mutagenesis

Melatonin is a neurohormone implicated in both biorhythm synchronization and neuroprotection from oxidative stress. Its functions are mediated by two G-protein-coupled-receptors (MT1 and MT2) and MT3, which corresponds to quinone oxidoreductase 2 (QR2). To determine the binding site of QR2 for melatonin, point mutations of residues crucial for the enzymatic activity of hQR2 were performed. The substitution of the hydrophobic residues Phe126, Ile128 and Phe178 by tyrosines at the active site significantly increased enzymatic activity and decreased the affinity of a structural analog of melatonin, the 2[(125)I]iodo-MCANAT. The mutation of residues implicated in zinc chelating (His(173); His(177)) had no effect on radioligand binding. Destabilisation of the cofactor FAD by mutation N18E showed that 2[(125)I]iodo-MCANAT binding was closely linked to the conformational integrity of human QR2. Surprisingly, the mutations C222F and N161A, which are distant from the determined binding site of the ligand, increased the affinity of 2[(125)I]iodo-MCANAT for hQR2. What seems to better explain the binding variations among the mutants are the activity recorded with BNAH and coenzyme Q1. Various hypotheses are discussed based on the various parameters used in the study: nature of the substrates and co-substrates and nature of the amino acid changes. This study, which constitutes the first structural analysis of hQR2, should enable to better understand the biological role of melatonin on this enzyme and particularly, the discrepancies between the pharmacologies of the melatonin binding site (MT3) and the QR2 catalytic activity.

A monolithic silicon based integrated signal generation and detection system for monitoring DNA hybridisation

The aim of this work was to develop an integrated solution to DNA hybridisation monitoring for diagnostics on a monolithic silicon platform. A fabrication process was developed incorporating a gold initiation electrode patterned directly onto a PIN photodiode detector. Patterned interdigitated type electrodes exhibited the smallest reduction in photodiode sensitivity, therefore these were chosen as the ECL initiator design. A novel DNA hybridisation assay was developed based on the displacement of a partially mismatched complementary strand by a perfectly matched labelled complementary strand. Pre-hybridised thiolated oligonucleotide and unlabelled 25% mismatched oligonucleotide were assembled on the gold initiation electrode. On addition of the labelled perfectly complementary oligonucleotide, the mismatched strands were displaced and a signal was generated. The sensitivity of the photodiode to light emitted at 620 nm, the ruthenium emission wavelength, was determined and subsequently, the diode current response to light generated by flow addition of ruthenium solution was found to be measurable to a concentration of 10 fM. Pre-hybridised duplex DNA, consisting of thiolated oligonucleotide and ruthenium labelled complementary oligonucleotide, was assembled on the gold initiation electrode. The difference between the current measured during flow of buffer and the ECL co-reactant TPA was three orders of magnitude, indicating that DNA assembled on the surface comprised sufficient ruthenium to generate a measurable signal. Finally, the displacement of unlabelled partial mismatch oligonucleotide from the sensor surface was monitored on addition of the ruthenium labelled perfectly complementary oligonucleotide in TPA flow and the measured photodiode current response was up to 50 times greater.