Cryoconcentration of flavonoid extract for enhanced biophotovoltaics and pH sensitive thin films.

Flavonoids are important value added products for dye sensitized solar cells biosensors, functional foods, medicinal supplements, nanomaterial synthesis, and other applications. Brassica oleracea contains high levels of anthocyanins in leaf sap vacuoles, and there are many viable extraction techniques that vary in terms of simplicity, environmental impact, cost, and extract photochemical/electrochemical properties. The efficiency of value added biotechnologies from flavonoid is a function of anthocyanin activity/concentration and molecule stability (i.e., ability to retain molecular resonance under a wide range of conditions). In this paper, we show that block cryoconcentration and partial thawing of anthocyanin from B. oleracea is a green, facile, and highly efficient technique that does not require any special equipment or protocols for producing enhanced value added products. Cryoconcentration increased anthocyanin activity and total phenol content approximately 10 times compared with common extraction techniques. Cryoconcentrated extract had enhanced electrochemical properties (higher oxidation potential), improved chroma, and higher UV absorbance than extract produced with other methods for a pH range of 2-12, with minimal effect on the diffusion coefficient of the extract. As a proof of concept for energy harvesting and sensor applications, dye sensitized solar cells and pH-sensitive thin films were prepared and tested. These devices were comparable with other recently published biotechnologies in terms of efficacy, but did not require expensive/environmentally detrimental extraction or concentration methods. This low cost, biorenewable, and simple method can be used for development of a variety of value added products. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:206-217, 2018.

pulSED: pulsed sonoelectrodeposition of fractal nanoplatinum for enhancing amperometric biosensor performance.

For the first time, we combine pulsed electrodeposition with out-of-phase pulsed sonication for controlled synthesis of fractal nanoplatinum structures as the transducer layer in electrochemical sensing. We develop and test this technique, called bimodal pulsed sonoelectrodeposition (pulSED), as a simple approach for creating highly conductive transducer nanometals for use in sensing and biosensing. We first compared the efficiency of pulSED nanoplatinum to other pulsed electrodeposition techniques, and then explored the effect of duty cycle and plating time on electroactive surface area and nanoparticle size/morphology. The developed pulSED nanoplatinum displayed fractal features with a relatively homogenous size distribution (26.31 ± 1.3 nm) and extremely high electroactive surface (0.28 ± 0.04 cm(2)) relative to other electroplating techniques (up to one order of magnitude higher). A high duty cycle (900 mHz) promotes formation of stable nanostructures (including fractal nanostructures) and reduces amorphous structure formation due to bubble cavitation and enhanced mass transport of metal ions to the electrode surface. To demonstrate the applicability of the pulSED technique, non-enzymatic and enzymatic sensors were developed for measuring hydrogen peroxide and glucose. The sensitivity for non-enzymatic peroxide sensing (3335 ± 305 µA cm(-2) mM(-1)), non-enzymatic glucose sensing (73 ± 14 µA cm(-2) mM(-1)) and enzymatic glucose biosensing (155 ± 25 µA cm(-2) mM(-1)) was higher than, or similar to, other nanomaterial-mediated amperometric sensors reported in the literature. The pulSED technique is a one pot method for tunable synthesis of nanometal structures as a transducer layer in electrochemical sensing and biosensing that requires no precursors or capping agents, and can be carried out at room temperature with inexpensive hardware.

A comparative study of graphene-hydrogel hybrid bionanocomposites for biosensing.

Hydrogels have become increasingly popular as immobilization materials for cells, enzymes and proteins for biosensing applications. Enzymatic biosensors that utilize hydrogel as an encapsulant have shown improvements over other immobilization techniques such as cross linking and covalent bonding. However, to date there are no studies which directly compare multiple hydrogel-graphene nanocomposites using the same enzyme and test conditions. This study compares the performance of four different hydrogels used as protein encapsulants in a mediator-free biosensor based on graphene-nanometal-enzyme composites. Alcohol oxidase (AOx) was encapsulated in chitosan poly-N-isopropylacrylamide (PNIPAAM), silk fibroin or cellulose nanocrystals (CNC) hydrogels, and then spin coated onto a nanoplatinum-graphene modified electrode. The transduction mechanism for the biosensor was based on AOx-catalyzed oxidation of methanol to produce hydrogen peroxide. To isolate the effect(s) of stimulus response on biosensor behavior, all experiments were conducted at 25 °C and pH 7.10. Electroactive surface area (ESA), electrochemical impedance spectroscopy (EIS), sensitivity to methanol, response time, limit of detection, and shelf life were measured for each bionanocomposite. Chitosan and PNIPAAM had the highest sensitivity (0.46 ± 0.2 and 0.3 ± 0.1 µA mM(-1), respectively) and electroactive surface area (0.2 ± 0.06 and 0.2 ± 0.02 cm(2), respectively), as well as the fastest response time (4.3 ± 0.8 and 4.8 ± 1.1 s, respectively). Silk and CNC demonstrated lower sensitivity (0.09 ± 0.02 and 0.15 ± 0.03 µA mM(-1), respectively), lower electroactive surface area (0.12 ± 0.02 and 0.09 ± 0.03 cm(2), respectively), and longer response time (8.9 ± 2.1 and 6.3 ± 0.8 s, respectively). The high porosity of chitosan, PNIPAAM, and silk gels led to excellent transport, which was significantly better than CNC bionanocomposites. Electrochemical performance of CNC bionanocomposites were relatively poor, which may be linked to poor gel stability. The differences between the Chitosan/PNIPAAM group and the Silk/CNC group were statistically significant (p < 0.05) based on ANOVA. Each of these composites was within the range of other published devices in the literature, while some attributes were significantly improved (namely response time and shelf life). The main advantages of these hydrogel composites over other devices is that only one enzyme is required, all materials are non-toxic, the sensor does not require mediators/cofactors, and the shelf life and response time are significantly improved over other devices.

A nanoceria-platinum-graphene nanocomposite for electrochemical biosensing.

Most graphene-metal nanocomposites for biosensing are formed using noble metals. Recently, development of nanocomposites using rare earth metals has gained much attention. This paper reports on the development of a nanoceria-nanoplatinum-graphene hybrid nanocomposite as a base transducing layer for mediator-free enzymatic biosensors. The hybrid nanocomposite was shown to improve detection of superoxide or hydrogen peroxide when compared to other carbon-metal hybrid nanocomposites. Based on this finding, the nanocomposite was applied for biosensing by adding either a peroxide-producing oxidase (glucose oxidase), or a superoxide-producing oxidase (xanthine oxidase). Material analysis indicated that nanoceria and nanoplatinum were equally distributed along the surface of the hybrid material, ensuring detection of either superoxide or hydrogen peroxide produced by oxidase activity. Glucose biosensors demonstrated a sensitivity (66.2±2.6µAmM(-1)cm(-2)), response time (6.3±3.4s), and limit of detection (1.3±0.6µM) that were comparable to other graphene-mediated electrodes in the current literature. Remarkably, XOD biosensor sensitivity (1164±332µAmM(-1)), response time (5.0±1.5s), and limit of detection (0.2±0.1µM) were higher than any reported biosensors using similar metal-decorated carbon nanomaterials. This material is the first demonstration of a highly efficient, diverse nanoceria/nanoplatinum/graphene hybrid nanocomposite for biosensing.