The electroluminescence characteristics of pristine and degraded organic light‐emitting diode (OLED) devices are studied using the time‐resolved electroluminescence (TREL) technique. It is found that materials degradation results in notable changes in the temporal profile of TREL curve, which involves a shorter onset time, a longer rise time, and a longer decay time of electroluminescence. It is found that these temporal characteristics are affected by trapped charges formed during the OLED operation. More detailed analysis reveals that there are two types of charge traps. The longer decay time is found to be due to the excitons produced by weakly bound charges trapped in the organic layer that are released by thermal energy even without applying the voltage pulse. In contrast, the shorter onset time of electroluminescence is due to the excitons from strongly bound charges that can be released only when a voltage pulse is applied. It is demonstrated that TREL can be used to investigate the underlying mechanisms of OLED degradation. The presence of different types of charge traps found in this study may prove useful for more elaborate design of OLED devices toward enhanced durability against degradation and higher duty cycle of device operation.

Cerium oxide nanoparticles, also called nanoceria, have recently gained much attention as oxidase-mimicking nanozymes that catalyze the oxidation of chromogenic substrates for color generation without the addition of H2O2. Herein, we have developed a unique colorimetric biosensor for thrombin in human blood plasma, which relies on thrombin-binding aptamer (TBA)-mediated inhibition of the oxidase activity of nanoceria and its restoration by very selective interactions of TBA with target thrombin. In this system, nanoceria were first incubated with TBA, resulting in quick reduction of the oxidase activity of nanoceria via the adsorption of single-stranded (ss)DNA-type TBA on nanoceria. By the addition of sample solutions containing target thrombin, TBA bound on the nanoceria would strongly interact with free thrombin and be detached from the nanoceria, thereby increasing the available surface area of the nanoceria and consequently enhancing the oxidase activity. Using this strategy, target thrombin was successfully detected at concentrations as low as 100 pM over a wide linear range from 0.1 to 10 nM. The diagnostic capability of this method has been demonstrated by detecting thrombin in human blood plasma, showing its great potential in the practical applications.