Multifunctional dendritic molecular probe for selective detection of Cu2+ ions using potentiometric and fluorometric techniques.

We have designed and synthesized a multifunctional dendritic molecular probe that selectively detects Cu2+ ions via potentiometric and fluorometric techniques with low detection limits (3.5 µM in potentiometry, 15 nM in fluorometry). The selective and reversible binding of the molecule with the Cu2+ ion was used to make a solid-state microsensor (diameter of 25 µm) by incorporating the molecular probe into the carbon-based membrane as an ionophore for Cu(II). The Cu(II) microelectrode has a broad linear range of 10 µM to 1 mM with a near Nernstian slope of 30 mV/log [aCu2+] and detection limit of 3.5 µM. The Cu(II) microsensor has a fast response time (1.5 s), and it has a broad working pH range from 3.5 to 6.0. The incorporation of the hydrophobic dendritic moiety makes the ionophore less prone to leaching in an aqueous matrix for potentiometric measurement. The cinnamaldehyde component of the molecule helps detection of Cu2+ ions fluorometrically, as indicated by a change in fluorescence upon selective and reversible binding of the molecular probe to the Cu2+ ions. The strategic design of the molecular probe allows us to detect Cu2+ ions in drinking water by using this novel dendritic fluoroionophore and solid-state Cu2+ - ion-selective microelectrode.

Electrochemical Column Cell for Continuous Oxidative Inactivation of Pathogens and Reductive Removal of Toxic Heavy Metals.

A solar-driven electrochemical column (EC) was developed for cathodic sequestration remediation of heavy metals (HMs) and anodic electroporative inactivation of pathogenic bacteria (PB) with continuous flow capacity for sustainable production of drinking water from wastewater. The method produces "revitalized drinking water" by keeping its natural mineral nutrients boosted with dissolved oxygen. The EC was constructed with graphene oxide (GO) synthesized via photoassisted electrochemical oxidation of CF (PEGO-CF) as the cathode and phytoreduced GO (RPEGO-CF) as the anode. In the EC, effluent is passed upward through the microchannel of CF electrodes to obtain a higher contact time with water molecules, enabling deposition of HMs and oxidative inactivation of PB, collectively termed electroadsorptive dialysis (EAD). PEGO-CF and RPEGO-CF stacked inside the EC resulted in the increased surface area and thereby the removal efficiency. Reactive oxygen species (ROS) produced at the anode damaged the bacterial cell sheath, while the oxygen functional group and the cathodic negative potential had a concurrent effect in "sequestration" of HMs. Density functional calculations showed that PEGO might transfer an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) under applied negative potential leading to internal system crossing to the vacant d-orbitals of HMs, allowing for simultaneous coordination and deposition. The EC produced 313 L of revitalized water from wastewater augmented with 500 µg L-1 HMs and 107 CFU mL-1 pathogenic bacteria (Escherichia coli and Staphylococcus aureus). Only a 3.6 J energy investment produced 1 L of revitalized water, which is ∼2000 times less than the usual energy consumption by electroporation and the lowest value obtained to date for bacterial inactivation with heavy metal removal. Laboratory-to-industrial scale-up calculations were performed for this water-purifying technology involving a water-energy nexus, promising high-efficiency bacterial inactivation, and HM remediation to obtain energy-efficient clean and revitalized water.

Flexible Nanogenerator from Electrospun PVDF-Polycarbazole Nanofiber Membranes for Human Motion Energy-Harvesting Device Applications.

Poly(vinylidene difluoride) (PVDF) has become the polymer matrix of choice for fabrication of wearable electronics and physiological monitoring devices. Despite possessing a high piezoelectric constant, additives are required to increase the charge transfer from PVDF matrix to connected signal readout units. Many of these additives also stabilize the ß-phase of PVDF, which is associated with highest piezoelectric coefficients. However, most of the additives used are often brittle ceramic-phase materials resulting in decreased flexibility of the devices and offsetting the gain in ß-phase content. Intrinsically conducting polymers (ICP), on the other hand, are ideal candidates to improve the device-related properties of PVDF, due to their higher flexibility than ceramic fillers as well as ability to form conducting network in PVDF membranes. This work reports the performance and device feasibility of PVDF-polycarbazole (PCZ) electrospun nanofiber membranes. A higher ß-phase was observed by FTIR spectroscopy in PVDF/PCZ compared to other PVDF phases. Moreover, a higher open-circuit potential was recorded over PVDF/polyaniline composites, which were studied for comparison. The addition of PCZ reduced the flexibility of pure PVDF nanofibers by 20% only. Besides, the work investigated the bacterial biofouling and cell compatibility of the matrix, as essential properties to examine any putative medical device application. PVDF/PCZ membranes were then used to develop a nanogenerator, which was capable of instantly lighting an entire LED array employing the rectified output power, and charged up a 2.2 µF capacitors using a bridge rectifier through a vertical compressive force applied periodically. Finally, the nanogenerator demonstrated electrical energy harvesting from movements of various parts of the human body, such as toe and heel movement and wrist bending. In conclusion, PCZ can be considered as an attractive, biocompatible, and anti-biofouling conducting polymer for electrical actuation and flexible electronic device applications.

Artificial Bifunctional Photozyme of Glucose Oxidase-Peroxidase for Solar-Powered Glucose-Peroxide Detection in a Biofluid with Resorcinol-Formaldehyde Polymers.

Photozymes or artificial photosynthesis based on alternative natural enzymes is vital for the sustainable development of next-generation healthcare, energy, and materials science. Herein, we report resorcinol-formaldehyde (RF) resins as a solar-driven metal-free bifunctional glucose oxidase-peroxidase stand-alone photozyme for the colorimetric dual detection of hydrogen peroxide and glucose. The π-bond conjugated benzenoid-ortho/para quinoid RF polymers are efficient for glucose oxidation and hydrogen peroxide reduction with concurrent 3,3',5,5'-tetramethylbenzidine oxidation under natural sunlight. The photoinduced colorimetric process could detect H2O2 up to 3.5 µM at 652 nm with the linear range of 0.1-2 mM. A limit of detection of 9.2 µM was exhibited by the system while measuring glucose with a linearity from 0.2 to 8.5 mM. The formation of hydroxyl radicals (•OH) from glucose oxidation reactions was evidenced by spin trapping electron paramagnetic resonance studies conducted herein. The results indicated that RF resins possessed strong intrinsic glucose oxidase and peroxidase (POx)-like activity under natural sunlight with promising storage and operation. This simple photozyme will definitely have potential uses in biomimetic solar-driven catalysis, bioenergy, and biomedicine.

Chemically modified carbon nitride-chitin-acetic acid hybrid as a metal-free bifunctional nanozyme cascade of glucose oxidase-peroxidase for "click off" colorimetric detection of peroxide and glucose.

Hybrid nanomaterials-based artificial enzymes with numerous utilities are necessary to develop future bionic devices in mimicking physiological processes. This paper demonstrates bifunctional enzyme mimicking roles of a metal-free nanozyme hybrid of chemically modified graphitic carbon nitride (MGCN), chitin and acetic acid (AcOH). The MGCN exhibited glucose oxidase-mimicking activity and chitin-AcOH mirrored peroxidase. MGCN-chitin-AcOH when in contact with glucose, oxidised glucose to gluconic acid and hydrogen peroxide (H2O2) while the chitin-AcOH decomposed the generated H2O2, as proved separately, by concurrent oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The super-sensitive colorimetric process produced linear regression equation for H2O2 as A = 0.00105C + 0.0630 (C:µM, R2 = 0.9961) with a detection limit of 0.052 µM, whereas for glucose, the linear relationship was A = 0.00084C + 0.0458 (C:µM, R2 = 0.9952) having a detection limit of 0.055 µM. The developed method was also successfully applied for assessment of H2O2 and glucose in human serum and urine samples. Non-enzymatic glucose test strips from MGCN-chitin-AcOH based hydrogel were reported and verified for semi-quantitative analysis of glucose. These compared well with results from standard enzyme-based colorimetric procedure. The developed hybrid nanozyme provided feasible alternatives to the two natural enzymes (peroxidase and glucose oxidase) realized through real sample analysis. The developed hybrid nanozyme can be successfully used for colorimetric detection of peroxide and glucose in medical diagnostics.