Enhanced Persistent Luminescence and Uniformity of ZGGO Nanoparticles via Nonstoichiometric Reactions for Advanced Bioimaging and Biosensing Applications

Persistent Luminescence Nanoparticles (PLNPs) are distinguished by their ability to retain and emit light long after the excitation source has been removed, a property that finds versatile applications ranging from bioimaging to photocatalysis. Traditional synthesis methods, however, often result in particles with irregular shapes and sizes, limiting their practical application. The novel approach employed by the research team involves adjusting the Ge/Ga ratio in Cr-doped zinc gallogermanate (ZGGO) PLNPs, transforming their morphologies into highly uniform nanocubes while simultaneously increasing their persistent luminescence intensity by approximately 3.7 times.

A new study published in ACS Applied Materials & Interfaces conducted by Miss Shuting Yang, Miss Wenjing Dai, Dr. Jie Wang from the Soochow University alongside Dr. Man Tang from Wuhan Textile University, the researchers synthesized zinc gallogermanate ZGGO PLNPs with enhanced uniformity and persistent luminescence. The experiments, aimed at overcoming limitations in existing synthesis methods and broadening the application spectrum of PLNPs. The team synthesized a series of ZGGO PLNPs by solvothermal methods, varying the Ge/Ga ratio in a nonstoichiometric approach. The experiments were designed to investigate how alterations in the electronic structure via stoichiometric adjustment could influence the morphological and luminescent properties of the nanoparticles. The authors characterized the morphology of the nanoparticles using scanning electron microscopy and transmission electron microscopy. The authors’ analysis showed that by adjusting the Ge/Ga ratio, it was possible to transform a mixture of nanocubes and nanospheres into highly symmetrical and uniform nanocubes. This morphological transformation was accompanied by an increase in the size of the nanocubes. Additionally, they evaluated the persistent luminescence properties using spectroscopic methods and found that the adjustment of the Ge/Ga ratio led to a significant enhancement of the persistent luminescence intensity. Specifically, the luminescence intensity increased by about 3.7 times at an optimized Ge/Ga ratio.  Moreover, the authors investigated the mechanism behind the enhanced luminescence. By employing electron spin resonance spectroscopy and other analytical techniques, the researchers determined that the enhanced luminescence was due to the increased density of lattice defects, such as oxygen vacancies and interstitial ions, which were introduced by the nonstoichiometric reactions. These defects acted as traps for excitation energy, contributing to the persistent luminescence.

A critical part of the study was to evaluate the PLNPs’ responsiveness to ROS. The team demonstrated that the persistent luminescence of ZGGO PLNPs could be quenched by ROS, a property they exploited to develop a method for autofluorescence-free serum ROS detection. This finding has significant implications for biosensing and bioimaging applications. Leveraging the ROS responsiveness, the researchers designed a biosensing assay for detecting glucose oxidase activity based on the interaction between ZGGO PLNPs and H₂O₂ produced by the enzymatic reaction of GOx with glucose. This assay exhibited potential for the development of novel biosensing platforms for monitoring glucose metabolic disorders.

The authors successfully demonstrated that nonstoichiometric reactions could be used to control the size and morphology of ZGGO PLNPs, significantly enhancing their persistent luminescence. The enhancement in luminescence was attributed to the increased density of lattice defects introduced by adjusting the stoichiometry, which facilitated the trapping of excitation energy. The PLNPs’ sensitivity to ROS was harnessed for developing innovative biosensing methods for ROS and glucose oxidase activity, showcasing the potential of these nanoparticles in bioimaging and biosensing applications devoid of autofluorescence interference.

One of the critical aspects of this study is the relationship between the electronic structure of PLNPs and their luminescent properties. By altering the stoichiometry, specifically the Ge/Ga ratio, the researchers were able to manipulate the density of lattice defects in the ZGGO nanoparticles. These defects play a pivotal role in trapping excitation energy, which is crucial for persistent luminescence. The controlled introduction of nonstoichiometric defects led to an optimized balance between the size and uniformity of the PLNPs and their luminescent efficiency. The enhanced persistent luminescence of these nanoparticles, coupled with their responsiveness to reactive oxygen species, opens up new avenues for their application in bioimaging and biosensing. The study successfully demonstrates the use of these optimized PLNPs for autofluorescence-free detection of serum ROS and as a biosensing platform for monitoring glucose oxidase activity. This latter application is particularly promising for the development of non-invasive diagnostic tools for glucose metabolic disorders. In conclusion, the work of Miss Yang, Miss Dai, Dr. Wang, and Dr. Tang advances the synthesis techniques for producing PLNPs with improved properties. By leveraging nonstoichiometric reactions to control the electronic structure of ZGGO PLNPs, they have developed nanoparticles with superior uniformity, size control, and enhanced persistent luminescence. The new work successfully addresses previous limitations in PLNP synthesis and significantly broadens the potential applications of PLNPs in the medical and environmental fields. Future research will likely focus on further refining the synthesis process, exploring the full range of potential applications of these nanoparticles, and potentially scaling up production for commercial use. This study exemplifies the power of interdisciplinary research in materials science and nanotechnology, offering promising solutions to longstanding challenges in the field.