Polymorph-Dependent Electrogenerated Chemiluminescence of Low-Dimensional Organic Semiconductor Structures for Sensing

Fluorescence lifetime imaging for explosive detection

In this Letter, a time-resolved 120 × 128 pixel single-photon avalanche diode (SPAD) sensor is used in conjunction with an array of organic semiconductor films as a means of detecting the presence of explosive vapors. Using the spatial and temporal resolution of the sensor, both fluorescence intensity and fluorescence lifetime can be monitored on a pixel-by-pixel basis for each of the polymer films arranged in a 2 × 2 grid. This represents a significant improvement on similar systems demonstrated in the past, which either offer spatial resolution without the temporal resolution required to monitor lifetime or offer only a single bulk measurement of lifetime and intensity without the spatial resolution. The potential of the sensing system is demonstrated using vapors of DNT, and differing responses for each of the four polymer films is observed. This system has clear applications as the basis of a portable chemical fingerprinting tool with applications in humanitarian demining and security.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Highly Efficient Aggregation-Induced Enhanced Electrochemiluminescence of Cyanophenyl-Functionalized Tetraphenylethene and Its Application in Biothiols Analysis

Exploring new electrochemiluminescence (ECL) luminophores with high ECL efficiency and good stability in aqueous solution is in great demand for biological sensing. In this work, highly efficient aggregation-induced enhanced ECL of cyanophenyl-functionalized tetraphenylethene (tetra[4-(4-cyanophenyl)phenyl]ethene, TCPPE) and its application in biothiols analysis were reported. TCPPE contains four 4-cyanophenyl groups covalently attached to the tetraphenylethene (TPE) core, generating a nonplanar three-dimensional twisted conformation structure. TCPPE nanoparticles (NPs) with an average size of 15.84 nm were prepared by a precipitation method. High ECL efficiency (593%, CdS as standard) and stable ECL emission (over one month) were obtained for TCPPE NPs in aqueous solution. The unique properties of TCPPE NPs could be ascribed to the efficient suppression of nonradiative transition, the decrease of the energy gap, and the increase of anionic radical stability, which were proved by theoretical calculation and electrochemical and fluorescence methods. Contrasting aggregation-induced ECL chromic emission was first observed for TCPPE NPs. As a proof-of-methodology, an ECL method was developed for three biothiol assays with detection limits of 6, 7, and 300 nM for cysteine, homocysteine, and glutathione, respectively. This work demonstrates that TCPPE NPs are promising ECL luminophores, and the incorporation of appropriate substituents into luminophores can improve ECL efficiency and radical stability.

Hydrogen Bond Organic Frameworks as a Novel Electrochemiluminescence Luminophore: Simple Synthesis and Ultrasensitive Biosensing

Nowadays, continuous efforts have been devoted to searching highly efficient electrochemiluminescence (ECL) emitters for applications in clinical diagnosis and food safety. In this work, triazinyl-based hydrogen bond organic frameworks (Tr-HOFs) were synthesized by N···H hydrogen bond self-assembly aggregation, where 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) (phenyDAT) was prepared via the cyclization reaction and behaved as a novel ligand. Impressively, the resulting Tr-HOFs showed strong ECL responses with highly enhanced ECL efficiency (21.3%) relative to the Ru(bpy)₃²⁺ standard, while phenyDAT hardly showed any ECL emission in aqueous phase. The Tr-HOFs innovatively worked as a new ECL luminophore to construct a label-free biosensor for assay of kanamycin (Kana). Specifically, the ECL response greatly weakened upon assembly of captured DNA with ferrocene (cDNA-Fc) onto the Tr-HOFs-modified electrode, while the ECL signals were adversely recovered by releasing linked DNA (L-DNA) from double-stranded DNA (dsDNA, hybridization of aptamer DNA (aptDNA) with L-DNA) due to the specific recognition of Kana with the aptDNA combined by the linkage of L-DNA and cDNA-Fc on the electrode. The as-built sensor showed a broadened linear range (1 nM-10 μM) and a limit of detection (LOD) down to 0.28 nM, which also displayed satisfactory results in the analysis of Kana in the milk and diluted human serum samples. This work offers a novel pathway to design an ECL emitter with organic molecules, holding great promise in biomedical analysis and food detection.

Construction of self-enhanced photoelectrochemical platform for L-cysteine detection via electron donor-acceptor type coumarin 545 aggregates

Self-enhanced electron donor-acceptor type coumarin 545 aggregates prepared via an anionic surfactant-assisted reprecipitation method provide an underlying approach for the photoelectrochemical detection of L-cysteine, which can be employed in aqueous solution without the addition of electron donors.

Arousing Electrochemiluminescence Out of Non-Electroluminescent Monomers within Covalent Organic Frameworks

Covalent organic frameworks (COFs) with stable long-range ordered arrangements are promising materials for organic optoelectronics. However, their electrochemiluminescence (ECL) from non-ECL active monomers has not been realized. Here, we report a design strategy for ECL-emitting COF family. The donors and acceptors co-crystallized and stacked into the highly aligned array of olefin-linked COFs, so that electrons can be transported freely. By this means, a tunable ECL is activated from non-ECL molecules with the maximum efficiency of 32.1% in water with the dissolved oxygen as an inner coreactant, and no additional noxious co-reactant is needed any more. Quantum chemistry calculations further demonstrate that this design reduces the COFs' band gaps and the overlap of electrons and holes in the excited state for better photoelectric properties and stronger ECL signals. This work exploits a basis to envisage the broad application potential of ECL-COFs for various biosensors and light-emitting display.

Recent advances in electrochemiluminescence luminophores

Electrochemiluminescence (ECL) has continued to receive considerable attention in various applications, owing to its intrinsic advantages such as near-zero background response, wide dynamic range, high sensitivity, simple instrumentation, and low cost. The ECL luminophore is one of the most significant components during the light generation processes. Despite significant progress that has been made in the synthesis of new luminophores and their roles in resolving various challenges, there are few comprehensive summaries on ECL luminophores. In this review, we discuss some of the recent advances in organic, metal complexes, nanomaterials, metal oxides, and near-infrared ECL luminophores. We also emphasize their roles in tackling various challenges with illustrative examples that have been reported in the last few years. Finally, perspective and some unresolved challenges in ECL that can potentially be addressed by introducing new luminophores have also been discussed. Graphical abstract.

Epitaxial growth of dual-color-emitting organic heterostructures via binary solvent synergism driven sequential crystallization

The controlled construction of organic heterostructured architectures derived from molecules with similar nucleation thresholds and concentrations has been rare and remains a great challenge. Herein, we report a sequential epitaxial growth to synthesize dual-color-emitting organic heterostructures with 9,10-bis(phenylethynyl)anthracene (BPEA) microwire trunks and tris-(8-hydroxyquinoline)aluminium (Alq3) microstructure branches by an anti-solvent induced sequential crystallization strategy. During the epitaxial growth process, the hydrogen-bonding interactions of the anti-solvent and solvent cause a large change in the solubility and crystallization rate of BPEA and Alq3 molecules in the mixed system, which facilitates sequential crystallization of organic molecule pairs with similar nucleation thresholds and concentrations into desired heterostructures by manipulating the synergism of anti-solvents and solvents. The Förster resonant energy transfer process in heterostructures could be modulated by varying the structure of heterostructures, such as the shape, amount and angles of the branches. The present synthesis strategy provides a unique insight into the detailed formation mechanism of complex organic heterostructures, further guiding the construction of more functional heterostructure materials.

Hierarchical self-assembly flower-like ammonium nickel phosphate as high-rate performance electrode material for asymmetric supercapacitors with enhanced energy density

Ammonium nickel phosphate has a large specific capacitance as an electrode material at low current density, but its capacitance decays fast at high current density, which directly affects the rate performance of supercapacitors. Herein, we demonstrate a facile route for the controllable synthesis of hierarchical self-assembly flower-like ammonium nickel phosphate as a high-rate electrode material for asymmetric supercapacitors, which is an important strategy to enhance the energy density at high power density. The flower-like structures are hierarchically assembled by a mass of rectangular sheets, which can provide fast electron transport and short ion diffusion path, thereby exhibiting excellent electrochemical performance with ultrahigh specific capacitance of 1016 F g^-1 at 1.0 A g^-1. More importantly, the NH₄NiPO₄ · H₂O materials exhibit outstanding rate performance (800 F g^-1 even at large current density of 30 A g^-1) and superior long-term cycle life (83% of capacity retention up to 3000 cycles at 5 A g^-1). Furthermore, the NH₄NiPO₄ · H₂O//AC asymmetric supercapacitors are assembled in aqueous KOH electrolyte, and exhibit high energy density (46.2 Wh kg^-1 at 160 W kg^-1 and 26.7 Wh kg^-1 at a large power density of 4000 W kg^-1, respectively). Due to the outstanding electrochemical performance, the all-solid-state asymmetric supercapacitors are successfully constructed using these materials.

Surface tension driven aggregation of organic nanowires via lab in a droplet

Directing the architecture of complex organic nanostructures is desirable and still remains a challenge in areas of materials science due to their structure-dependent collective optoelectronic properties. Herein, we demonstrate a simple and versatile solution strategy that allows surface tension to drive low-dimensional nanostructures to aggregate into complex structures via a lab in a droplet technique. By selecting a suitable combination of a solvent and an anti-solvent with controllable surface tension difference, the droplets can be automatically cracked into micro-droplets, which provides an aggregation force directed toward the centre of the droplet to drive the low-dimensional building blocks to form the special aggregations during the self-assembly process. This synthetic strategy has been shown to be universal for organic materials, which is beneficial for further optimizing the optoelectronic properties. These results contribute to gaining an insightful understanding on the detailed growth mechanism of complex organic nanostructures and greatly promoting the development of organic nanophotonics.

Tailoring the structures and photonic properties of low-dimensional organic materials by crystal engineering

Low-dimensional organic materials have given rise to tremendous interest in optoelectronic applications, owing to their controllable photonic properties. However, the controlled-synthesis approaches for organic nano-/micro-architectures are very difficult to attain, because the weak interaction (van der Waals force) between the organic molecules cannot dominate the kinetic process of crystal growth. We report a simple method, which involves selective adhesion to the organic crystal plane by hydrogen-bonding interaction for modulating the crystal growth process, which leads either to the self-assembly of one organic molecule into two-dimensional (2D) microsheets with an obvious asymmetric light propagation or one-dimensional (1D) microrods with low propagation loss. The method of tailoring the structures and photonic properties for fabricating different micro-structures would provide enlightenment for the development of tailor-made mini-sized devices for photonic integrated circuits.

Simultaneous structure and luminescence property control of barium carbonate nanocrystals through small amount of lanthanide doping

Rare earth doping has been widely applied in many functional nanomaterials with desirable properties and functions, which would have a significant effect on the growth process of the materials. However, the controlling strategy is limited into high concentration of lanthanide doping, which produces concentration quenching of the lanthanide ion luminescence with an increase in the Ln³⁺ concentration, resulting in lowering the fluorescence quantum yield of lanthanide ion. Herein, for the first time, we demonstrate simultaneous control of the structures and luminescence properties of BaCO₃ nanocrystals via a small amount of Tb³⁺ doping strategy. In fact, Tb³⁺ would partially occupy Ba²⁺ sites, resulting in the changes to the structures of the BaCO₃ nanocrystals, which is primarily determined by charge modulation, including the contributions from the surfaces of crystal nuclei and building blocks. These structurally modified nanocrystals exhibit tunable luminescence properties, thus emerging as potential candidates for photonic devices such as light-emitting diodes and color displays.