Electrochemical biosensing platform based on AuNWs/rGO-CMC-PEDOT:PSS composite for the detection of superoxide anion released from living cells

Detection of superoxide anion (O2·-) levels holds significant importance for the diagnosis and even clinical treatments of oxidative stress-related diseases. Herein, we prepared a composite electrode material to encapsulate copper-zinc superoxide dismutase (SOD1) for biosensing of O2·-. The sensing material consists of gold nanowires (AuNWs), reduced graphene oxide (rGO), carboxymethyl cellulose (CMC) and PEDOT:PSS. CMC provides abundant -COOH to bind SOD1, with a high adsorption coverage of 1.499 × 10-9 mol cm-2 on the sensor surface. rGO and PEDOT endow the composite with significant conductivity, whereas PSS has antifouling capability. Moreover, AuNWs exhibit excellent electrical conductivity and a high aspect ratio, which promotes electron transfer, and ultimately enhances the catalytic performance of the enzyme. Meanwhile, SOD1(Cu2+) catalyzes the dismutation of O2·- to O2 and H2O2, and H2O2 is then electrochemically oxidized to generate amperometric signals for determination of O2·-. The sensor demonstrates outstanding detection performance for O2·- with a low detection limit of 2.52 nM, and two dynamic ranges (14.30 nM-1.34 μM and 1.34 μM-42.97 μM) with corresponding sensitivity of 0.479 and 0.052 μA μM-1cm-2, respectively. Additionally, the calculated apparent Michaelis constant (Kmapp) of 1.804 μM for SOD1 demonstrates the outstanding catalytic activity and the surface-immobilized enzyme's substrate affinity. Furthermore, the sensor shows the capability to dynamically detect the level of O2·- released from living HepG2 cells. This study provides an inovative design to obtain a biocompatible electrochemical sensing platform with plenty of immobilization sites for biomolecules, large surface area, high conductivity and flexibility.

Selective response of dopamine on 3-thienylphosphonic acid modified gold electrode with high antifouling capability and long-term stability

In this work, an Au electrode modified with self-assembled monolayers (SAMs) of 3-thienylphosphonic acid (TPA) was used as a novel functional interface to selectively sense dopamine (DA) in the presence of excess ascorbic acid (AA). Ellipsometry, X-ray photoelectron spectroscopic (XPS) and electrochemical measurements proved the immobilization of TPA on the gold surface. Interestingly, the Au electrode modified with TPA substantially improved the antifouling and renewal capabilities towards the oxidation of dopamine (DA) after 15 days of storage in undeoxygenated phosphate buffer solution (PBS pH 7.4). Moreover, the TPA-SAMs modified Au electrode could afford a selective electrochemical response for the DA oxidation in the presence of ascorbic acid (AA). Based on this result, a high sensitive detection limit of 2.0 × 10^-7 M for DA could be obtained in the presence of high concentration of AA.

Evaluation of biochar-ultrafiltration membrane processes for humic acid removal under various hydrodynamic, pH, ionic strength, and pressure conditions

The performance of an ultrafiltration (UF)-biochar process was evaluated in comparison with a UF membrane process for the removal of humic acid (HA). Bench-scale UF experiments were conducted to study the rejection and flux trends under various hydrodynamic, pH, ionic strength, and pressure conditions. The resistance-in-series model was used to evaluate the processes and it showed that unlike stirred conditions, where low fouling resistance was observed (28.7 × 10¹² m^-1 to 32.5 × 10¹² m^-1), higher values and comparable trends were obtained for UF-biochar and UF alone for unstirred conditions (28.7 × 10¹² m^-1 to 32.5 × 10¹² m^-1). Thus, the processes were further evaluated under unstirred conditions. Additionally, total fouling resistance was decreased in the presence of biochar by 6%, indicating that HA adsorption by biochar could diminish adsorption fouling on the UF membrane and thus improve the efficiency of the UF-biochar process. The rejection trends of UF-biochar and UF alone were similar in most cases, whereas UF-biochar showed a noticeable increase in flux of around 18-25% under various experimental conditions due to reduced membrane fouling. Three-cycle filtration tests further demonstrated that UF-biochar showed better membrane recovery and antifouling capability by showing more HA rejection (3-5%) than UF membrane alone with each subsequent cycle of filtration. As a result of these findings, the UF-biochar process may potentially prove be a viable treatment option for the removal of HA from water.