Recently, three-dimensional carbon nanostructures have attracted significant attention for biosensing applications. We have prepared highly porous three-dimensional graphene (3DG) structures (90% porosity) by templateassisted chemical vapor deposition technique and enhanced their electrocatalytic activity through in situ electrochemical deposition of rose-like yttrium hexacyanoferrate particles on their struts. The 3DG structure has an average channel size of ∼500 μm, and the microflowers have lateral sizes in the range of 2−10 μm. The performance of the 3DG-based electrode in efficient detection of ascorbic acid was investigated after transferring on a gold screen printed electrode (SPE). The sensor exhibits an electrocatalytic response as low as <5 s, a detection limit of 0.5 μM within a wide linear range up to 1.5 mM, and a fairly high sensitivity of 43.3 μA μM −1 cm −2 . These electrochemical responses are superior to many other electrodes, particularly carbon materials, utilized for ascorbic acid detection. The developed sensor also shows good selectivity for ascorbic acid detection; no interference with other common electroactive inferences such as glucose, sucrose, and uric acid is obsereved. The potential application of the Y-modified 3DG sensor for detection of ascorbic acid in commercial juices as real samples is also shown. This novel nanocomposite structure may open a novel approach for the expansion of efficient electrochemical sensors based on commercial SPE.

Owing to the exceptional properties of graphene and the crucial role of substrate on the performance of electrochemical biosensors, several graphene-based hybrid structures have recently emerged, yielding improved selectivity and sensitivity. To date, most of the reported biosensors utilize solution-driven graphene flakes with drawbacks of low conductivity (due to high inter-junction contact resistant) and structural fragility. Herein, we present a conductive three-dimensional CeO 2 semiconductor nanoparticles/graphene nanocomposite, as a platform for sensitive detection of hydrogen peroxide, an important molecule in fundamental biological processes. The 3D conductive graphene architecture is fabricated by chemical vapor deposition on nickel foam. The fabricated biosensor displays high sensitivity (60 μA.mM −1 ) at a low negative potential of −0.25 V, a low detection limit (<1.0 μM at S/N = 3), and a fast response (<5 s) in the range of 2.8 to 160 μM. Furthermore, density functional theory simulations show that the improved detection is not only related to the catalytic effect of ceria nanoparticles, but also to more efficient charge transfer from nanoparticles to the 3D graphene network. Moreover, it is established that the amperometric response of the biosensor is insensitive to interfering molecules such as glucose, sucrose, and potassium chloride, indicating its potential for practical applications.

No abstract

This work presents a novel melatonin sensor based on unfunctionalized macroporous graphene networks decorated with gold nanoparticles for the differential pulse voltammetric detection of melatonin in pharmaceutical products. Highly porous graphene structures were prepared by metallic template-assisted chemical vapor deposition, and their active surface area and electrocatalytic activity were improved by electrochemical deposition of gold nanoparticles (50−250 nm) on their struts. The graphene-gold electrodes present a highly sensitive performance toward electro-oxidation of melatonin with a wide linear range of 0.05−50 μM, a low detection limit of 0.0082 μM (3σ/m), and a significant sensitivity of 16.219 μA μM −1 cm −2 . Therefore, the performance of the sensor regarding the obtained figures of merit is better than many other electrodes utilized for melatonin detection. The electrochemical active surface area of the glassy carbon electrode was multiplied by 18, and the high conductivity of gold-graphene composites and their synergistic catalytic effect lowered electron transport resistance by 87%. Moreover, long-term signal stability for about 14 days, acceptable reproducibility (relative standard deviation (RSD) of 4.70%), repeatability (RSD of 0.14%), and selectivity of the electrodes with various interfering materials are demonstrated. The valid potential application of the sensors for the determination of melatonin in pharmaceutical samples is shown.

No abstract