Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi5O7Br nanostructures were synthesized via a facile, low-temperature thermal treatment procedure, and their photocatalytic activity toward nitrogen fixation was evaluated and compared. Spectroscopic measurements showed that the tubular Bi5O7Br sample prepared at 40 °C (Bi5O7Br-40) exhibited the highest electron-transfer rate among the series, producing a large number of O2 .– radicals and oxygen vacancies under visible-light photoirradiation and reaching a rate of photocatalytic nitrogen fixation of 12.72 mM·g–1·h–1 after 30 min of photoirradiation. The reaction dynamics was also monitored by in situ infrared measurements with a synchrotron radiation light source, where the transient difference between signals in the dark and under photoirradiation was analyzed and the reaction pathway of nitrogen fixation was identified. This was further supported by results from density functional theory calculations. The reaction energy of nitrogen fixation was quantitatively estimated and compared by building oxygen-enriched and anoxic models, where the change in the oxygen vacancy concentration was found to play a critical role in determining the nitrogen fixation performance. Results from this study suggest that Bi5O7Br with rich oxygen vacancies can be used as a high-performance photocatalyst for nitrogen fixation.
Understanding the behavior of biomolecules on nanointerface is critical in bioanalysis, which is great challenge due to the instability and the difficulty to control the orientation and loading density of biomolecules. Here, we investigated the thermodynamics and kinetics of DNA hybridization on gold nanoparticle, with the aim to improve the efficiency and speed of DNA analysis. We achieved precise and quantitative surface control by applying a recently developed poly adenines (polyA)-based assembly strategy on gold nanoparticles (DNA-AuNPs). PolyA served as an effective anchoring block based on the preferential binding with the AuNP surface and the appended recognition block adopted an upright conformation that favors DNA hybridization. The lateral spacing and surface density of DNA on AuNPs can be systematically modulated by adjusting the length of polyA block. We found the stability of duplex on AuNP was enhanced with the increasing length of polyA block. When the length of polyA block reached to 40 bases, the thermodynamic properties were more similar to that of duplex in solution. Fast hybridization rate was observed on the diblock DNA-AuNPs and was increased along with the length of polyA block. We consider the high stability and excellent hybridization performance come from the minimization of the DNA-DNA and DNA-AuNP interactions with the use of polyA block. This study provides better understanding of the behavior of biomolecules on the nanointerface and opens new opportunities to construct high-efficiency and high-speed biosensors for DNA analysis.
In recent years, poly adenine (polyA) DNA functionalized gold nanoparticles (AuNPs) free of modifications was fabricated with high density of DNA attachment and high hybridization ability similar to those of its thiolated counterpart. This nanoconjugate utilized poly adenine as an anchoring block for binding with the AuNPs surface thereby facilitated the appended recognition block a better upright conformation for hybridization, demonstrating its great potential to be a tunable plasmonic biosensor. It’s one of the key points for any of the practical applications to maintaining stable conjugation between DNA oligonucleotides and gold nanoparticles under various experimental treatments. Thus, in this research, we designed a simple but sensitive fluorescence turn-on strategy to systematically investigate and quantified the dissociation of polyA DNA on gold nanoparticles in diverse experimental conditions. DNA desorbed spontaneously as a function of elevated temperature, ion strength, buffer pH, organic solvents and keeping time. What’s more, evaluating this conjugate stability as affected by the length of its polyA anchor was another crucial aspect in our study. With the improved understanding from these results, we were able to control some of our experimental conditions to maintain a good stability of this kind of polyA DNA−AuNPs nanoconjugates.
Aggregation of α-Synuclein (α-Syn) in Lewy bodies is largely responsible for the demise and death of dopamine neurons. Oxidative stress associated with the aggregation-induced oxidative damage is considered as a possible origin of the toxicity. However, the cellular mechanism of H2O2 in the aggregation of α-Syn remains a debate, i.e., whether the aggregation is caused by endogenously secreted or exogenous H2O2 from upstream. Here, we report on the development of an ultrasensitive plasmonic assay with a designed nanoplasmonic probe to unravel the role of H2O2 in the aggregation of α-Syn. The nanoplasmonic probe is composed of a Au nanoparticle with surface-attached double-stranded DNA and horseradish peroxidase (HRP). In the presence of H2O2, HRP initiates the polymerization of aniline, which in turn results in the in situ formation of a layer of conducting polymer on the nanoplasmonic probe. By monitoring the associated plasmonic response, we can sensitively detect H2O2 with a remarkably low detection limit of 8 nM. With this ultrasensitive plasmonic assay, we find that exogenous H2O2 plays a dominant role for the aggregation of α-Syn in vitro, whereas the contribution from endogenously secreted H2O2 is negligible.
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