A hydrogel-based biosensor for stable detection of glucose.

Glucose detection is vital in the food industry for safety and quality management. As a healthy ingredient, the flavor of honey is frequently impacted by the crystallization of glucose. Therefore, determining the glucose level can offer precise reference data for the manufacture of honey. Various approaches have been tried, and the enzyme-based electrochemical analytical method is one of the most important and widely used strategies. However, there are still challenges for most electrochemical methods to achieve stable detection resistant to temperature variation due to the easy inactivation of the enzyme, the poor anti-interference capacity of the detection techniques and other influences from the external environment. Herein, a hydrogel-based electrochemical biosensor is proposed to stably detect glucose even at wide ranges of temperatures via electrochemical impedance spectroscopic (EIS) measurement. The key factor for stable detection relies on the metal-organic framework nanoparticles' protective layer to guarantee the robustness of glucose oxidase (GOx), thereby achieving stable and specific detection for glucose. Moreover, a cascade reaction-induced hydrogel formation in a 3D structure can be used as an impedance readout, which not only amplifies but also further stabilizes the GOx-induced response. The prepared hydrogel-based electrochemical biosensor showed a linear response to the glucose concentration in the range of 0.75-4 mg/mL. Furthermore, the biosensor has excellent anti-interference and temperature stability. High performance liquid chromatography analysis also validated the accuracy of this biosensor in detecting glucose in the honey sample.

Liquid Metal pH Morphology Sensor Used for Biological Microenvironment Detection.

pH is one of the important parameters of a biological microenvironment, which is closely related to cell growth, development, vitality, division, and differentiation. Monitoring the pH of a microenvironment is helpful to monitor the cell metabolism as well as to understand the cellular life cycle. The sensitivity of liquid metals (LMs) to hydrogen ions has aroused our interest. Here, we propose a novel but facile pH sensor using liquid gallium (LM for short) droplet morphological change as the readout. The pH sensing characteristics of the LM droplet were examined, especially the shape response. LM can form solid native oxide skin rapidly in oxygenated solution, and the oxide layer will be removed in acidic or alkaline solutions, which will cause a great change in surface tension. The phenomenon is the change of LM morphology from macroscopic observation. We explored the electrochemical characteristics of LM at different pH values, explained the mechanism of surface change, and calibrated the relationship curve between LM morphology and pH and the interference of impurity ions on the sensor. Finally, we proposed a detection algorithm for the LM pH morphology sensor and tried to automatically detect pH with a mobile app, which was applied to the pH detection of cell culture solution. We believe that the response characteristics of LM to hydrogen ions have great potential in microenvironment detection.

A double-layered liquid metal-based electrochemical sensing system on fabric as a wearable detector for glucose in sweat.

Integrated electrochemical sensing platforms in wearable devices have great prospects in biomedical applications. However, traditional electrochemical platforms are generally fabricated on airtight printed circuit boards, which lack sufficient flexibility, air permeability, and conformability. Liquid metals at room temperature with excellent mobility and electrical conductivity show high promise in flexible electronics. This paper presents a miniaturized liquid metal-based flexible electrochemical detection system on fabric, which is intrinsically flexible, air-permeable, and conformable to the body. Taking advantage of the excellent fluidity and electrical connectivity of liquid metal, a double-layer circuit is fabricated that significantly miniaturizes the size of the whole system. The linear response, time stability, and repeatability of this system are verified by resistance, stability, image characterization, and potassium ferricyanide tests. Finally, glucose in sweat can be detected at the millimolar level using this sensing system, which demonstrates its great potential for wearable and portable detection in biomedical fields, such as health monitoring and point-of-care testing.

Dynamic Covalent C═C Bond, Cross-Linked, Injectable, and Self-Healable Hydrogels via Knoevenagel Condensation.

Hydrogels have a wide range of applications in the fields of biomedicine, flexible electronics, and bionics. In this study, injectable and self-healable hydrogels were first prepared based on a dynamic covalent C═C bond formed via the Knoevenagel condensation reaction between poly(ethylene glycol) dicyanoacetate and water-soluble poly(vanillin acrylate). Three kinds of catalysts (phosphate buffer, zeolitic imidazolate framework-8, and tertiary amine) were used in Knoevenagel condensation for preparing hydrogels. All hydrogels in this study could be formed in situ, and their gelation time ranged from seconds to minutes. The properties and application of hydrogels could be customized according to the type of catalyst employed. 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) results indicated that all the components and hydrogels exhibited low toxicity, and the hydrogels could be used as 3D cell culture scaffolds. Because of the dynamic covalent C═C bond formed by Knoevenagel condensation, the resultant hydrogels were found to be dynamic and showed good self-healing properties. This work presents a new dynamic covalent chemistry for the preparation of self-healable materials.

Mild polyaddition and polyalkylation based on the carbon-carbon bond formation reaction of active methylene.

The Michael addition and alkylation reaction of active methylene compounds (AMCs) with two active hydrogens had been investigated extensively in organic chemistry, while the polymerization of AMCs had few studies. Herein, we reported active methylene-based polyaddition and polyalkylation catalyzed via an organic superbase under ambient conditions. A model polymerization was first conducted between ethylene glycol diacrylate (EGDA) and methyl cyanoacetate (MCA). The molecular weight (M w) of the model polymer was up to 50 500 g mol-1 with a high yield (99%). Eight AMCs were selected and a high-throughput parallel synthesizing instrument (HTPSI) was used to synthesize semi-library polymers of AMCs and EGDA via a Michael type polyaddition. The obtained AMC-based polymers had low cell cytotoxicity. Elastomers with cyanogen groups could be prepared using trimethylolpropane triacrylate (TMPTA) as a crosslinker. Furthermore, three dihalogen compounds were explored to polymerize with MCA and malononitrile via alkylation reactions. The pendent cyanogen or ester groups of the polymers could be reduced by lithium aluminum hydride. Novel polymer families were constructed based on the polyaddition and polyalkylation of AMCs.