Elevating Charge Transport Layer for Stable Perovskite Light-Emitting Diodes.

Ion migration is a major factor affecting the long term stability of perovskite light-emitting diodes (LEDs), which limits their commercialization potential. The accumulation of excess halide ions at the grain boundaries of perovskite films is a primary cause of ion migration in these devices. Here, it is demonstrated that the channels of ion migrations can be effectively impeded by elevating the hole transport layer between the perovskite grain boundaries, resulting in highly stable perovskite LEDs. The unique structure is achieved by reducing the wettability of the perovskites, which prevents infiltration of the upper hole-transporting layer into the spaces of perovskite grain boundaries. Consequently, nanosized gaps are formed between the excess halide ions and the hole transport layer, effectively suppressing ion migration. With this structure, perovskite LEDs with operational half-lifetimes of 256 and 1774 h under current densities of 100 and 20 mA cm-2 respectively are achieved. These lifetimes surpass those of organic LEDs at high brightness. It is further found that this approach can be extended to various perovskite LEDs, showing great promise for promoting perovskite LEDs toward commercial applications.

In Situ Halide Exchange of Cesium Lead Halide Perovskites for Blue Light-Emitting Diodes.

3D perovskites are promising to achieve efficient and bright deep-blue light-emitting diodes (LEDs), which are required for lighting and display applications. However, the efficiency of deep-blue 3D perovskite-based LEDs is limited by high density of defects in perovskites, and their deep-blue emission is not easy to achieve due to the halide phase separation and low solubility of chloride in precursor solutions. Here, an in situ halide exchange method is developed to achieve deep-blue 3D perovskites by spin-coating an organic halide salts solution to treat blue 3D perovskites. It is revealed that the halide-exchange process is mainly determined by halide ion diffusion targeting a concentration equalization, which leads to homogeneous 3D mixed-halide perovskites. By further introducing multifunctional organic ammonium halide salts into the exchange solution to passivate defects, high-quality deep-blue perovskites with reduced trap density can be obtained. This approach leads to efficient deep-blue perovskite LEDs with a peak external quantum efficiency (EQE) of 4.6% and a luminance of 1680 cd m-2 , which show color coordinates of (0.131, 0.055), very close to the Rec. 2020 blue standard. Moreover, the halide exchange method is bidirectional, and blue perovskite LEDs can be achieved with color coordinates of (0.095, 0.160), exhibiting a high EQE of 11.3%.

Efficient and Bright Deep-Red Light-Emitting Diodes based on a Lateral 0D/3D Perovskite Heterostructure.

Bright and efficient deep-red light-emitting diodes (LEDs) are important for applications in medical therapy and biological imaging due to the high penetration of deep-red photons into human tissues. Metal-halide perovskites have potential to achieve bright and efficient electroluminescence due to their favorable optoelectronic properties. However, efficient and bright perovskite-based deep-red LEDs have not been achieved yet, due to either Auger recombination in low-dimensional perovskites or trap-assisted nonradiative recombination in 3D perovskites. Here, a lateral Cs4 PbI6 /FAx Cs1- x PbI3 (0D/3D) heterostructure that can enable efficient deep-red perovskite LEDs at very high brightness is demonstrated. The Cs4 PbI6 can facilitate the growth of low-defect FAx Cs1- x PbI3 , and act as low-refractive-index grids, which can simultaneously reduce nonradiative recombination and enhance light extraction. This device reaches a peak external quantum efficiency of 21.0% at a photon flux of 1.75 × 1021 m-2 s-1 , which is almost two orders of magnitude higher than that of reported high-efficiency deep-red perovskite LEDs. Theses LEDs are suitable for pulse oximeters, showing an error <2% of blood oxygen saturation compared with commercial oximeters.

Proximity hybridization triggered rolling-circle amplification for sensitive electrochemical homogeneous immunoassay.

A new homogeneous electrochemical immunoassay strategy was developed for ultrasensitive detection of carcinoembryonic antigen (CEA) based on target-induced proximity hybridization coupled with rolling circle amplification (RCA). The immobilization-free detection of CEA was realized by the use of an uncharged peptide nucleic acid (PNA) probe labeled with ferrocene (Fc) as the electroactive indicator on a negatively charged indium tin oxide (ITO) electrode. In the presence of a target protein and two DNA-labeled antibodies, the proximate complex formed in homogeneous solution could unfold the molecular beacon, and a part of the unfolded molecular beacon as a primer hybridized with the RCA template to initiate the RCA process. Subsequently, the detection probe modified Fc (Fc-PNAs) hybridized with the long amplified DNA products. The consumption of freely diffusible Fc-PNAs (neutrally charged) resulted in a significant reduction of the Fc signal due to the fact that long amplified DNA/Fc-PNA products were electrostatically repelled from the ITO electrode surface. The reduction of the electrochemical signal (signal-off) could indirectly provide the CEA concentration. Under the optimal conditions, CEA detection was implemented in a wide range from 1 pg mL-1 to 10 ng mL-1, with a low detection limit of 0.49 pg mL-1. The proposed strategy exhibited advantages of good selectivity, high sensitivity, acceptable accuracy, and favorable versatility of analytes. Moreover, the practical application value of the system was confirmed by the assay of CEA in human serums with satisfactory results.

Proximity hybridization triggered hemin/G-quadruplex formation for construction a label-free and signal-on electrochemical DNA sensor.

We describe a novel label-free and signal-on electrochemical DNA sensing platform via proximity hybridization triggered hemin/G-quadruplex formation based on the direct electron transfer of hemin. The thiolated modified G-DNA1 was first immobilized onto the Au electrode surface. In the presence of target DNA, Y-junction-structure ternary complex can be formed to trigger the proximity assembly of G-DNA1, hemin, and G-DNA2, which leads to the formation of hemin/G-quadruplex for generation an amplified electrochemical signal by differential pulse voltammetry. The observed signal gain was sufficient to achieve a demonstrated detection limit of 54 fM, with a wide linear dynamic range from 10-13 to 10-9 M and discriminated mismatched DNA from perfect matched target DNA with a high selectivity. Benefiting from the one step proximity dependent hemin/G-quadruplex formation, the assay method is extremely simple and can be carried out within 40min. The advantages of free of any label conjugation step, and versatility make it a promising candidate for point-of-care testing and commercial application.

Proximity hybridization-regulated catalytic DNA hairpin assembly for electrochemical immunoassay based on in situ DNA template-synthesized Pd nanoparticles.

Novel hybridization proximity-regulated catalytic DNA hairpin assembly strategy has been proposed for electrochemical immunoassay based on in situ DNA template-synthesized Pd nanoparticles as signal label. The DNA template-synthesized Pd nanoparticles were characterized with atomic force microscopic and X-ray photoelectron spectroscopy. The highly efficient electrocatalysis by DNA template synthesized Pd nanoparticles for NaBH4 oxidation produced an intense detection signal. The label-free electrochemical method achieved the detection of carcinoembryonic antigen (CEA) with a linear range from 10-15 to 10-11 g mL-1 and a detection limit of 0.43 × 10-15 g mL-1. Through introducing a supersandwich reaction to increase the DNA length, the electrochemical signal was further amplified, leading to a detection limit of 0.52 × 10-16 g mL-1. And it rendered satisfactory analytical performance for the determination of CEA in serum samples. Furthermore, it exhibited good reproducibility and stability; meanwhile, it also showed excellent specificity due to the specific recognition of antigen by antibody. Therefore, the DNA template synthesized Pd nanoparticles based signal amplification approach has great potential in clinical applications and is also suitable for quantification of biomarkers at ultralow level.

A sensitive sandwich-type electrochemical aptasensor for thrombin detection based on platinum nanoparticles decorated carbon nanocages as signal labels.

In this work, a novel and sensitive sandwich-type electrochemical aptasensor has been developed for thrombin detection based on platinum nanoparticles (Pt NPs) decorated carbon nanocages (CNCs) as signal tags. The morphological and compositional of the Pt NPs/CNCs were examined using transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results showed that the Pt NPs with about 3-5nm in diameter were well dispersed on the surface of CNCs. The thiolated aptamer was firstly immobilized on the gold electrode to capture the thrombin molecules, and then aptamer functionalized Pt NPs/CNCs nanocomposites were used to fabricate a sandwich sensing platform. Then, the high-content Pt NPs on carbon nanocages acting as hydrogen peroxide-mimicking enzyme catalyzed the reduction of H2O2, resulting in significant electrochemical signal amplification. Differential pulse voltammetry is employed to detect thrombin with different concentrations. Under optimized conditions, the approach provided a good linear response range from 0.05 pM to 20nM with a low detection limit of 10fM. This Pt NPs/CNCs-based aptasensor shows good precision, acceptable stability and reproducibility, which provided a promising strategy for electrochemical aptamer-based detection of other biomolecules.