Swellable colorimetric microneedles for glucose detection based on glucose oxidase-like gold nanoparticles.

BACKGROUND: Regular blood glucose monitoring is very important for diabetic patients. The composition of skin interstitial fluid (ISF) is similar to that of blood, which can be used for daily blood sugar detection and disease care. However, most methods of ISF extraction have complicated steps, may cause skin damage, and can only extract a limited amount of ISF, resulting in low detection efficiency. Therefore, it is very necessary to develop a detection method that can not only extract a large amount of ISF safely, efficiently, and conveniently, but also realize rapid detection of glucose level in ISF. RESULTS: Here, we developed a gold nanoparticle (AuNP)-based swellable colorimetric MN patch with minimally invasive sampling function and real-time ISF glucose analysis ability. The MN patch could quickly absorb a large amount of skin ISF, and 60.2 mg of ISF was extracted within 10 min in vitro. It was divided into two layers: the tip layer was embedded with AuNPs with glucose oxidase (GOx)-like activity, which catalyzed the oxidation of glucose extracted from ISF and produced hydrogen peroxide (H2O2); horseradish peroxidase (HRP) encapsulated in the backing layer catalyzed the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) by H2O2 to produce oxTMB, which led to a visible color shift in the backing layer. The ISF glucose level was judged by naked eyes and further quantified by color analysis with Image J software. As a result, the colorimetric MN patch successfully identified the normal blood sugar and hyperglycemia state in vivo. SIGNIFICANCE: The colorimetric MN patch combined in-situ colorimetric sensing based on AuNP nanozyme with MN patch, which detected glucose level without blood drawing, increasing patients' compliance and reducing detection steps and time. Compared with the detection methods based on natural nanozymes, our method had better stability and sensitivity to complex environments (extreme pH and high temperature, etc.) in actual detection.

A swellable hydrogel microneedle based on cerium-metal organic frame composite nanozyme for detection of biomarkers.

Skin interstitial fluid (ISF) has been an alternative source in the field of biomarkers analysis. This work developed swellable hydrogel microneedles (MNs) composed of polyvinyl alcohol and sodium alginate by chemical crosslinking (PVA/SA). Here, PVA/SA was firstly used to fabricate hydrogel MNs, achieving a swellable ratio of 150 % and a rapid extraction of 6.4 mg ISF in 15 min. To replace expensive and non-reusable test kits, hydrogel MNs based on composite nanozyme with high oxidase-like activity were successfully developed to recover and detect biomarkers. The nanozyme was composed of MnO2-modified mixed valence cerium-metal organic frame (MCM). MCM was characterized by multiple techniques to further confirm its composition and structure. MCM combined with the reduction reaction of glutathione (GSH) with oxidized substrate to achieve a colorimetric GSH detection, which had a detection limit (LOD, 0.36 µM) of GSH. The hydrogel MNs based on MCM (MCM-MNs) were firstly applied to the rapid detection of GSH in ISF. All in all, this method combines the advantages of nanozyme and hydrogel MNs to achieve a timely and minimally invasive analysis, which provides a new dimension for the in vivo detection of GSH by skin ISF and holds great implications in biomedical and bioanalysis fields.

The adsorption and release mechanism of different aged microplastics toward Hg(II) via batch experiment and the deep learning method.

Aged microplastics are ubiquitous in the aquatic environment, which inevitably accumulate metals, and then alter their migration. Whereas, the synergistic behavior and effect of microplastics and Hg(II) were rarely reported. In this context, the adsorptive behavior of Hg(II) by pristine/aged microplastics involving polystyrene, polyethylene, polylactic acid, and tire microplastics were investigated via kinetic (pseudo-first and second-order dynamics, the internal diffusion model), Langmuir, and Freundlich isothermal models; the adsorption and desorption behavior was also explored under different conditions. Microplastics aged by ozone exhibited a rougher surface attached with abundant oxygen-containing groups to enhance hydrophilicity and negative surface charge, those promoted adsorption capacity of 4-20 times increment compared with the pristine microplastics. The process (except for aged tire microplastics) was dominated by a monolayer chemical reaction, which was significantly impacted by pH, salinity, fulvic acid, and co-existing ions. Furthermore, the adsorbed Hg(II) could be effectively eluted in 0.04% HCl, simulated gastric liquids, and seawater with a maximum desorption amount of 23.26 mg/g. An artificial neural network model was used to predict the performance of microplastics in complex media and accurately capture the main influencing factors and their contributions. This finding revealed that aged microplastics had the affinity to trap Hg(II) from freshwater, whereafter it released the Hg(II) once transported into the acidic medium, the organism's gastrointestinal system, or the estuary area. These indicated that aged microplastics could be the sink or the source of Hg(II) depending on the surrounding environment, meaning that aged microplastics could be the vital carrier to Hg(II).