photophysical properties that are potentially useful for different applications. [1-5] One of the many fascinating properties of CDs is its fluorescence. Many reports have shown that the fluorescence of CDs originates from the surface fluorophore and graphitizing core. [6-9] However, the transition between singlet and triplet states occurs with extremely low probability due to the spin-forbidden, hence the room temperature phosphorescence (RTP, T 1 →S 0) and thermally activated delayed fluorescence (TADF, transitions T 1 →S 1 →S 0) are difficult to be achieved under ambient conditions. [10-12] Other than that, afterglow from pure CDs is seldom observed and studied. [13-17] A selfquenching resistance CDs with RTP lifetime of 13.4 ms were induced by polyvinyl alcohol (PVA) chains from Liu's group. [13] Through seeded growth method, Andrey et al. prepared several phosphorescent CDs powders with average decay lifetime ranging from 52 to 419 ms. [14] Yang's group focused on suppressing the nonradiative transitions having achieved the adjustable decays between 188 and 658 ms. [15] Feng and co-workers found that fluorine and nitrogen codoped CDs with RTP could realize the decay lifetime of 141 to 1210 ms by adjusting pH values. [16] It is noteworthy that long-lived emission (LLE) about 1.46 s of CDs powder was successfully achieved via microwave irradiation but with very poor ability to resist moisture that RTP totally disappeared in solution and also quite faint emission intensity only with quantum yield (QY) of 3.53% by Lin et al. [17] As for these pure CDs, phosphorescence that is responsible for the total afterglow without TADF component only lasts for a few seconds accompanied by a relatively low phosphorescent efficiency. Furthermore, these pure CDs have extremely poor stability, thus afterglow of them was completely quenched by oxygen or moisture, causing the RTP to be only captured in powdery CDs rather than solution. [13-17] Nevertheless, a great deal of effort was devoted to improving the afterglow behavior. In some cases, the RTP can be ameliorated by introducing heavy atoms, such as halogens and metals which enhanced the intersystem crossing (ISC) process attributed to the strong spin-orbit coupling. [18,19] Alternatively, embedding CDs in solid matrices that serve Carbon nanodots (CDs) anchored onto inorganic supporter (amorphous nanosilica, SiO 2) like a core-satellite structure have enhanced the room-temperature phosphorescence (RTP) intensity along with ultralong lifetime of 1.76 s. Special and quite stable structure should account for these superiorities, including hydrogen network, covalent bond, and trap-stabilized triplet-state excitons that are responsible for the generation of phosphorescence. These multiple effects have efficaciously protected CDs from being restrained by the external environment, providing such long-lived emission (LLE) that can subsist not only in powdery CDs-SiO 2 but also coexist in aqueous solution, pushing a big step forward in the application prospects of liquid-state phosp...

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Objective. Steady-state visual evoked potential (SSVEP) is an essential paradigm of electroencephalogram based brain–computer interface (BCI). Previous studies in the BCI research field mostly focused on enhancing classification accuracy and reducing stimuli duration. This study, however, concentrated on increasing the number of available targets in the BCI systems without calibration. Approach. Motivated by the idea of multiple frequency sequential coding, we developed a calibration-free SSVEP–BCI system implementing 160 targets by four continuous sinusoidal stimuli that lasted four seconds in total. Taking advantage of the benchmark dataset of SSVEP–BCI, this study optimized an arrangement of stimuli sequences, maximizing the response distance between different stimuli. We proposed an effective classification algorithm based on filter bank canonical correlation analysis. To evaluate the performance of this system, we conducted offline and online experiments using cue-guided selection tasks. Eight subjects participated in the offline experiments, and 12 subjects participated in the online experiments with real-time feedbacks. Main results. Offline experiments indicated the feasibility of the stimulation selection and detection algorithms. Furthermore, the online system achieved an average accuracy of 87.16 ± 11.46% and an information transfer rate of 78.84 ± 15.59 bits min−1. Specifically, seven of 12 subjects accomplished online experiments with accuracy higher than 90%. This study proposed an intact solution of applying numerous targets to SSVEP-based BCIs. Results of experiments confirmed the utility and efficiency of the system. Significance. This study firstly provides a calibration-free SSVEP–BCI speller system that enables more than 100 commands. This system could significantly expand the application scenario of SSVEP-based BCI. Meanwhile, the design criterion can hopefully enhance the overall performance of the BCI system. The demo video can be found in the supplementary material available online at stacks.iop.org/JNE/18/046094/mmedia.

Fluorescence resonance energy transfer (FRET) has found widespread uses in biosensing, molecular imaging, and light harvesting. Plasmonic metal nanostructures offer the possibility of engineering photonic environment of specific fluorophores to enhance the FRET efficiency. However, the potential of plasmonic nanostructures to enable tailored FRET enhancement on planar substrates remains largely unrealized, which are of considerable interest for high‐performance on‐surface bioassays and photovoltaics. The main challenge lies in the necessitated concurrent control over the spectral properties of plasmonic substrates to match that of fluorophores and the fluorophore–substrate spacing. Here, a self‐assembled plasmonic substrate based on polydopamine (PDA)‐coated plasmonic nanocrystals is developed to effectively address this challenge. The PDA coating not only drives interfacial self‐assembly of the nanocrystals to form closely packed arrays with customized optical properties, but also can serve as a tailored nanoscale spacer between the fluorophores and plasmonic nanocrystals, which collectively lead to optimized fluorescence enhancement. The biocompatible plasmonic substrate that allows convenient bioconjugation imparted by PDA has afforded improved FRET efficiency in DNA microarray assay and FRET imaging of live cells. It is envisioned that the self‐assembled plasmonic substrates can be readily integrated into fluorescence‐based platforms for diverse biomedical and photoconversion applications.

Objective. Filter bank canonical correlation analysis (FBCCA) is a widely-used classification approach implemented in steady-state visual evoked potential (SSVEP)–based brain computer interfaces (BCIs). However, conventional detection algorithms for SSVEP recognition problems, including the FBCCA, were usually based on ‘fixed window’ strategy. That’s to say, these algorithms always analyze data with fixed length. This study devoted to enhance the performance of SSVEP-based BCIs by designing a new dynamic window strategy which automatically finds an optimal data length to achieve higher information transfer rate (ITR). Approach. The main purpose of ‘dynamic window’ is to minimize the required data length while maintaining high accuracy. This study projected the correlation coefficients of FBCCA into probability space by softmax function and built a hypothesis testing model, which took risk function as evaluation of classification result’s ‘credibility’. In order to evaluate the superiority of this approach, FBCCA with fixed data length (FBCCA-FW) and spatial temporal equalization dynamic window (STE-DW) were implemented for comparison. Main results. Fourteen healthy subjects’ results were concluded by a 40-target online SSVEP-based BCI speller system. The results suggest that this proposed approach significantly outperforms STE-DW and FBCCA-FW in terms of accuracy and ITR. Significance. By incorporating the fundamental ideas of FBCCA and dynamic window strategy, this study proposed a new training-free dynamical optimization algorithm, which significantly improved the performance of online SSVEP-based BCI systems.

Manipulation of the oxidation states of the metal species within metal−organic frameworks leads to compositional, structural, and surface property evolutions, which will impact their performance as sorbents in adsorptive separation processes. In this study, we propose a new low-cost postsynthesis strategy to modify the oxidation states of copper species within the copper-1,3,5-benzenetricarboxylic acid (Cu-BTC) structure employing Na 2 S 2 O 3 as the reducing agent. The compositional and structural evolutions of the modified samples were thoroughly characterized by a series of methods, and the dimethyl disulfide (DMDS) adsorption performance was evaluated. Accurately controlled reduction of Cu(II) to Cu(I) and formation of nanopores in the modified Cu(I)/Cu(II)-BTC samples have been observed and confirmed experimentally. Specifically, the sample 0.46/Cu-BTC/24h with a Cu(I)/Cu(II) molar ratio of 1.79 exhibits both the highest DMDS adsorption capacity (146.66 mg-S/g) and fastest diffusion with D of 7.59 × 10 −13 cm 2 /s at 298 K. Further density functional theory calculations reveal that the modified Cu(I)/Cu(II)-BTC structures exhibit much higher interaction energy, E in , with DMDS (70.65 kJ/mol) than the parent Cu(II)-BTC (20.28 kJ/mol). Controllable reduction of Cu(II) to Cu(I) in Cu-BTC leads to significantly enhanced guest−host interactions as well as the formation of uniform nanoscale porosity leading to effect enhancement for the adsorption of DMDS using modified Cu-BTC materials.

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