A novel amidine-based fluorescent probe TPE-4+ for rapid detection of anionic surfactant sodium dodecyl sulfate

An accurate, fast, and simple surfactant detection method is of great significance for monitoring surfactants pollution. Sodium dodecyl sulfate (SDS) is one of the most commonly used anionic surfactants and has been listed as an important monitoring pollutant for surfactant residues. Herein, a novel fluorescent probe named TPE-4+ with four amidines as the recognition functional group and tetraphenylethene as the fluorophore was fabricated. Due to the special intramolecular environment, the probe showed selectively identification towards SDS which made an aggregation induced fluorescence enhencement. Under the optimum conditions, the fluorescence enhencement of TPE-4+ is linearly related to the concentration of SDS in the range of 5.0-60.0 μM with limit of detection (LOD) of 0.010 μM and limit of quantification (LOQ) of 0.034 μM. Relative to the reported methods, the probe in our work showed better selectivity and sensitivity. The proposed method was successfully applied for the SDS determination of disinfecting bowls.

A Perspective on Polythiophenes as Conformation Dependent Optical Reporters for Label-Free Bioanalytics

Poly(3-alkylthiophene) (PT)-based conjugated polyelectrolytes (CPEs) constitute an important class of responsive polymers with excellent optical properties. The electrostatic interactions between PTs and target analytes trigger complexation and concomitant conformational changes of the PT backbones that produce distinct optical responses. These conformation-induced optical responses of the PTs enable them to be utilized as reporters for detection of various analytes by employing simple UV-vis spectrophotometry or the naked eye. Numerous PTs with unique pendant groups have been synthesized to tailor their interactions with analytes such as nucleotides, ions, surfactants, proteins, and bacterial and viral pathogens. In this perspective, we discuss PT-target analyte complexation for bioanalytical applications and highlight recent advancements in point-of-care and field deployable assays. Subsequently, we highlight a few areas of critical importance for future applications of PTs as reporters, including (i) design and synthesis of specific PTs to advance the understanding of the mechanisms of interaction with target analytes, (ii) using arrays of PTs and linear discriminant analysis for selective and specific detection of target analytes, (iii) translation of conventional homogeneous solution-based assays into heterogeneous membrane-based assay formats, and finally (iv) the potential of using PT as an alternative to conjugated polymer nanoparticles and dots in bioimaging.

Machine learning to accelerate screening for Marcus reorganization energies

Understanding and predicting the charge transport properties of π-conjugated materials is an important challenge for designing new organic electronic devices, such as solar cells, plastic transistors, light-emitting devices, and chemical sensors. A key component of the hopping mechanism of charge transfer in these materials is the Marcus reorganization energy which serves as an activation barrier to hole or electron transfer. While modern density functional methods have proven to accurately predict trends in intramolecular reorganization energy, such calculations are computationally expensive. In this work, we outline active machine learning methods to predict computed intramolecular reorganization energies of a wide range of polythiophenes and their use toward screening new compounds with low internal reorganization energies. Our models have an overall root mean square error (RMSE) of ±0.113 eV, but a much smaller RMSE of only ±0.036 eV on the new screening set. Since the larger error derives from high-reorganization energy compounds, the new method is highly effective to screen for compounds with potentially efficient charge transport parameters.

A single molecular sensor for selective and differential colorimetric/ratiometric detection of Cu2+ and Pd2+ in 100% aqueous solution

A novel salicylaldehyde bis-Schiff-base probe decorated with imidazolium ionic liquid moieties at both ends (SAS-IMIs) was designed and facilely synthesized as a colorimetric/ratiometric sensor to visually detect Cu²⁺ and Pd²⁺ in pure aqueous media. Due to the positively charged characters of its head and tail, the SAS-IMIs exhibited high water solubility with a potential advantage in minimizing the self-aggregation. More importantly, simply by varying the solution pH, colorimetric/ratiometric sensing detection of individual metal ion (Cu²⁺ or Pd²⁺) was realized without any mutual interference. Subsequently, sensitive, selective, and differential detections for Cu²⁺ (LOD: 0.080 μM) and Pd²⁺ (LOD: 0.076 μM) in 100% aqueous solutions were achieved, which proved to be applicable for real water samples. Results from density functional theory (DFT) calculations unveiled the Cu²⁺/Pd²⁺-binding properties of SAS-IMIs, which were in accordance with the experimental observations. Furthermore, a SAS-IMIs-based solid phase sensor was fabricated, which manifested satisfactory detection abilities for Cu²⁺ and Pd²⁺.

Surfactant-Triggered Fluorescence Turn "on/off" Behavior of a Polythiophene-graft-Polyampholyte

Polythiophene-graft-polyampholyte (PTP) is synthesized using N,N-dimethylaminoethyl methacrylate and tert-butyl methacrylate monomers by grafting from polythiophene backbone, followed by hydrolysis. The resulting polymer exhibits aqueous solubility via formation of small-sized miceller aggregates with hydrophobic polythiophene at the center and radiating polyionic side chains (cationic or anionic depending on the pH of the medium) at the outer periphery. The critical micelle concentration of PTP in acidic solution (0.025 mg/mL, pH = 2.7) is determined from fluorescence spectroscopy. PTP exhibits reversible fluorescence on and off response in both acidic and basic medium with the sequential addition of differently charged ionic surfactants, repeatedly. The fluorescence intensity of PTP at pH 2.7 increases with the addition of an anionic surfactant, sodium dodecyl benzenesulfonate (SDBS), due to the self-aggregation forming compound micelles. The fluorescence intensity of these solutions again decreases on addition of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), because of assembling of SDBS with CTAB, thus deassembling the PTP-SDBS aggregates. At pH 9.2, these turn on and turn off responses are also shown by PTP with the sequential addition of cationic surfactant (CTAB) and anionic surfactant (SDBS), respectively. This result shows that PTP has potential for surfactant-induced reversible fluorescence turn on and off using ionic surfactant (SDBS and CTAB) through self-assembling and deassembling of the ionic aggregates. The reversible aggregation and disaggregation process of PTP with the surfactants at both acidic and basic pH is supported from dynamic light scattering and Fourier transform infrared spectroscopy. The morphology of the above systems studied by transmission and scanning electron microscopy also supports the above aggregation and disaggregation process.

Water soluble polythiophenes: preparation and applications

Different synthetic procedures for water soluble polythiophenes and their applications in sensing, detection of biomolecules and optoelectronic devices are discussed.

Fluorescent thiophene-based materials and their outlook for emissive applications

An overview of fluorescent thiophene-based materials and their applications, highlighting in particular the various methods employed to achieve highly emissive materials.