Superhydrophilicity Regulation of Carbon Nanotubes Boosting Electrochemical Biosensing for Real-time Monitoring of H2O2 Released from Living Cells.

Dynamic and accurate monitoring of cell-released electroactive signaling biomolecules through electrochemical techniques has drawn significant research interest for clinical applications. Herein, the functionalized carbon nanotubes (f-CNTs) featuring with gradient surface wettability from hydrophobicity to hydrophilicity, and even to superhydrophilicity, were regulated by thermolysis of an ionic liquid for exploration of the dependence of surface wettability on electrochemical biosensing performance to a cell secretion model of hydrogen peroxide (H2O2). The superhydrophilic f-CNTs demonstrated boosting electrocatalytic reduction activity for H2O2. Additionally, the molecular dynamic (MD) simulations confirmed the more cumulative number density distribution of H2O2 molecules closer to the superhydrophilic surface (0.20 vs 0.37 nm), which would provide a faster diffusional channel compared with the hydrophobic surface. Thereafter, a superhydrophilic biosensing platform with a lower detectable limit reduced by 200 times (0.5 vs 100 µM) and a higher sensitivity over 56 times (0.112 vs 0.002 µA µM cm-2) than that of the hydrophobic one was achieved. Given its excellent cytocompatibility, the superhydrophilic f-CNTs was successfully applied to determine H2O2 released from HeLa cells which were maintained alive after a 30 min real-time monitoring test. The surface hydrophilicity regulation of electrode materials presents a facile approach for real-time monitoring of H2O2 released from living cells and would provide new insights for other electroactive signaling targets at the cellular level.

Untangling the Effects of Doping Carbon with Diverse Heteroatoms on the Bioelectrochemistry of Glucose Oxidase.

Great enthusiasm for doping carbon materials with nonmetallic heteroatoms for promoting electrical contact of redox enzymes with electrodes in bioelectronics has been aroused. However, systematic studies of different heteroatoms on enzyme activities are still lacking. Herein, choosing glucose oxidase (GOD) as a model enzyme, carbon nanotubes (CNTs) are used as electron carriers to evaluate the effects of heteroatoms' species on the direct electron transfer and catalytic activities of GOD. Experimental data demonstrate that phosphorus (P)-doped CNTs provide the most intimate electrical contact with GOD compared to other elements (B, N, and S) doping, delivering a 3-fold increase in rate constant (ks, 2.1 s-1) and an enhanced turnover rate (kcat, 2.74 × 10-9 M cm-2 s-1) in comparison with CNTs. Meanwhile, theoretical modeling clarifies that the active center of GOD interacts more strongly with P-doped CNTs and maintains their conformation well compared to other CNTs. This study will help to understand the mechanism of heteroatom doping of carbon on the enzymatic electron transfer and shed light on the design of efficient bioelectrocatalytic interfaces.

Surface Hydrophobicity Engineering of Pt-Based Noble Metal Aerogels by Ionic Liquids toward Enhanced Electrocatalytic Oxygen Reduction.

Modulating the surface properties of electrocatalysts with ligands could effectively regulate their catalytic properties, while limited in-depth understanding of the surface ligands restricted their rational combination. Herein, ionic liquids (ILs) with different lengths of hydrophobic side chains were employed to regulate the surface hydrophobicity of noble metal aerogels, for comprehending the relationship between surface hydrophobicity and oxygen reduction reaction (ORR) activity and enhancing electrocatalytic ORR. The volcano-like trends between the hydrophobicity and the ORR activity for various Pt-based aerogels indicated that a suitable hydrophobic surface constructed by ILs was most favorable for contacting with oxygen molecules and the desorption of oxygen intermediates. Typically, the PtPd aerogel modified by ILs (PtPd aer-[MTBD][PFSI]) exhibited an inspiring ORR activity, with a 70 mV increase in half-wave potential and a 7.1-fold mass activity compared to the commercial Pt/C. Therefore, the regularity between the surface hydrophobicity and ORR activity of noble metal aerogels was uncovered and will facilitate the modulation of electrocatalysts for practical applications.

Controllable assembly of three-dimensional porous graphene-Au dual aerogels and its application for high-efficient bioelectrocatalytic O2 reduction.

Aerogels derived from the colloidal nanoparticles featured with hierarchical interconnected pore-rich networks guarantee their great potentials in various applications. Herein, the controllable assembly of three-dimensional aerogels based on Au nanoparticles (Au NPs) and reduced graphene oxide (rGO) nanosheets as building blocks via a bottom-up approach have been systematically clarified. The difference of building blocks and their assembly sequence were crucially to the final aerogel morphologies and electrochemical properties. Specifically, the highly porous graphene-gold dual aerogels (rGO-Au DAGs) with interconnected rGO nanosheets and Au nanowires showed high conductivity, large surface area and good biocompatibility. Thus, it was employed as an excellent matrix to immobilize enzyme for high-efficient bioelectrocatalysis. Taking bilirubin oxidase as an example, a more positive on-set potential (0.60 V) and a larger catalytic current density (0.77 mA cm-2@0.40 V) than those of other rGO-Au assemblies were achieved for direct bioelectrocatalytic O2 reduction. This study will provide an efficient strategy for unique dual-structural aerogels design and shed light to develop new functional materials for bioelectrocatalytic applications such as biosensors and biofuel cells.

Superhydrophilic edge-rich graphene for the simultaneous and disposable sensing of dopamine, ascorbic acid, and uric acid.

A simple and rapid simultaneous sensing strategy of multiple biomarkers is of great importance but challenging in health diagnosis. In this study, a novel free-standing edge-rich graphene film (fs-ERG) was in situ fabricated via a facile chemical vapor deposition route on a porous Si3N4 substrate. The subsequent superhydrophilic modification of the fs-ERG not only makes it maintain the original abundant edge-rich sites, high conductivity, and hierarchical porosity, but also endows it with collective electrochemical characteristics. Thereafter, the superhydrophilic fs-ERG (S-fs-ERG) demonstrated a fast electron-transfer kinetics towards the oxidation of dopamine (DA), ascorbic acid (AA), and uric acid (UA), which promised a sensitive simultaneous electrochemical determination with low detectable limits of 0.1, 2.5 and 0.5 µM, respectively. Furthermore, this sensing electrode displayed high selectivity in the presence of co-existing interferences as well as excellent reproducibility, and thus performed well in DA, AA and UA detection in real samples. These superior sensing performance metrics combined with the low-cost and scalable fabrication of S-fs-ERG based electrodes bode well for their great potential for the simultaneous and disposable sensing of DA, AA and UA in practical application.

Integrating Highly Porous and Flexible Au Hydrogels with Soft-MEMS Technologies for High-Performance Wearable Biosensing.

Wearable biosensors for real-time and non-invasive detection of biomarkers are of importance in early diagnosis and treatment of diseases. Herein, a high-performance wearable biosensing platform was proposed by combining a three-dimensional hierarchical porous Au hydrogel-enzyme electrode with high biocompatibility, activity, and flexibility and soft-MEMS technologies with high precision and capability of mass production. Using glucose oxidase as the model enzyme, the glucose sensor exhibits a sensitivity of 10.51 µA mM-1 cm-2, a long durability over 15 days, and a good selectivity. Under the mechanical deformation (0 to 90°), it is able to maintain an almost constant performance with a low deviation of <1.84%. With the assistance of a wireless or a Bluetooth module, this wearable sensing platform achieves real-time and non-invasive glucose monitoring on human skins. Similarly, continuous lactic acid monitoring was also realized with lactate oxidase immobilized on the same sensing platform, further verifying the universality of this sensing platform. Therefore, our work holds promise to provide a universal, high-performance wearable biosensing platform for various biomarkers in sweat and reliable diagnostic information for health management.

Highly sensitive and selective turn-on fluorescent chemosensors for Hg2+ based on thioacetal modified pyrene.

This work reports a facile strategy for the synthesis of water-soluble fluorescent probes Pyr1 and Pyr2, which have carboxyl and hydroxyl group in the side chain of thioacetal moiety, respectively. Pyr1-2 exhibit exclusively selective turn-on fluorescence response towards Hg2+ over other cations, based on intramolecular charge transfer (ICT) mechanism. Upon addition of Hg2+, the thioacetal moiety in Pyr1-2 can be converted to aldehyde group, which is confirmed by 1H NMR titrations. The detection limits for Pyr1-2 are less than 1.80nM in aqueous media, lower than the maximum allowable level of Hg2+ in drinking water by EPA. Moreover, Pyr2 have been successfully used for fluorescence imaging of Hg2+ in living cells, demonstrating potential application in biological science.