Carbon cloth surface engineering for simultaneous detection of ascorbic acid, dopamine, and uric acid in fetal bovine serum

Carbon cloth (CC) was electrochemically activated using three electrochemical methods in different electrolytes. The gases released during the activation process etched the surface of the CC, thereby increasing its surface area of the activated CC (FCC). Moreover, functional groups such as oxygen-containing groups and N-doping have been introduced. The quantity and type of functional groups introduced during the activation process were related to the anions in the solution. FCC electrodes were used to construct electrochemical sensors for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The PFCC electrode activated by advanced cyclic voltammetry in (NH4)2HPO4 showed linear ranges for AA, DA, and UA concentrations of 0.1 to 2.1 mM, 0.5 to 11 µM, and 0.5 to 11 µM, respectively. The detection limits are 72.93, 0.22, and 0.42 µM, respectively. The good flexibility the PFCC electrode made it suitable for the preparation of flexible sensors. The simultaneous determination of AA, DA, and UA in fetal bovine serum showed a reliable recovery ratio. This study provides a simple and green approach for activating carbon cloth and constructing flexible electrochemical sensors with the potential to simultaneously detect AA, DA, and UA.

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.

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.

Hemin-Functionalized Microfluidic Chip with Dual-Electric Signal Outputs for Accurate Determination of Uric Acid

Herein, we develop a hemin-functionalized microfluidic chip with dual-electric signal outputs for accurate determination of uric acid (UA). Hemin is designed as the catalyst, which could trigger a built-in reference signal. Carbon nanotube (CNT) and alkalinized titanium carbide (alk-Ti₃C₂T_x) are used as attachment substrates to strengthen the signal. Benefiting from the synergistic action of hemin, CNT, and alk-Ti₃C₂T_x, the hybrid functionalized sensor shows prominent electrochemical capacity, desirable catalytic activity, and unique built-in signal ability. Through density functional theory calculations, the structure-reactivity relationship and possible signal output mechanism are deeply investigated. The functionalized sensor is further integrated into a microfluidic chip to prepare a portable electrochemical sensing platform, in which multiple sample processing steps including primary filtration, target enrichment, and reliable analysis can be conducted step-by-step. Based on the abovementioned designs, the developed functionalized microfluidic platform presents desirable performance in UA determination with a detection limit of 0.41 μM. Furthermore, it is capable of accurately detecting UA in urine samples, providing a promising idea for biomolecule monitoring.