(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing

Abstract

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterialfraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔE p = 28 mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and β-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1 µM, L.R. 0.5-150 µM; NADH: LOD = 0.6 µM, L.R. 2.5-200 µM) at low overpotential (+ 0.15 V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.

Freestanding laser-induced two dimensional heterostructures for self-contained paper-based sensors

“…The different structure and the higher exfoliation degree of the rGO-based HTs are further confirmed by the absence of the 2D peak in the only-GO film. 36…”

“…53 Fig. 5c depicts the selectivity study performed with the rGO–MoS 2 at −0.3 V; the aim was to assess both the direct effect of potentially interfering species 36 and test the perturbation of concomitant species on the H 2 O 2 detection (interferents are listed in the caption). No interferents tested returned detectable amperometric responses; more captivating the H 2 O 2 amperometric signals, obtained in the solution containing the spiked interferents, are similar to those before interference addition (H 2 O 2 signal recovery ≥ 96%).…”

Carbon Black Functionalized with Naturally Occurring Compounds in Water Phase for Electrochemical Sensing of Antioxidant Compounds

“…Further, it could be seen that the linear relationship obtained between anodic and cathodic peaks vs. the scan rate ( Figure S1C ) proved that electron transfer was confined to the surface of the CB-RA modified electrode. The amount of RA attached to the CB surface was estimated using the Sharp approach [ 31 , 49 ], and thus a CB surface coverage (Г) of 1.95 × 10 −4 mol cm −2 was obtained (the equation used is detailed in the caption of Figure S1 ).…”

“…The observations led to the discovery of a mechanism behind CB-RA stabilization and the reduction in the moieties’ surface functionalization, which can be summarized as follows: (i) the ultrasound induces the untangling of bulk CB aggregates and agglomerates to nanosized particles; (ii) the aromatic skeleton of RA gives rise to π–π interactions within the C-C sp 2 domains of CB units; (iii) the residual RA polar moieties ensure hydrogen bonds with an aqueous phase; (iv) the reducing power of the RA cathecolic groups [ 27 , 31 ] drive AuNPs’ formation on the CB surface. Similarly, for SC, the steroid ring interacts with the CB surface, and the polar moieties (hydroxylic groups and carboxylic charged group) ensure the nanospheres’ colloidal dispersion in water [ 22 , 23 ]; further, the slightly bent but rigid structure of SC favors the interaction with the spherical shape of the CB nanoparticles [ 56 ].…”

“…Interestingly, some biological/natural molecules have demonstrated a stabilizing ability towards 1D and 2D nanomaterials of which some are, among others, bile salt sodium cholate [ 22 , 23 , 24 , 25 ] and naturally derived polyphenols [ 26 , 27 , 28 , 29 , 30 ]. Recently, our research group proved how the rational selection of the stabilizing agent can give rise to functional nanomaterials with peculiar/additional electrochemical features [ 30 , 31 ]. In this respect, aqueous-dispersed/stabilized CBs have not been deeply investigated [ 32 , 33 , 34 ]; in particular, despite the exceptional electrochemical features, N220 CB has not yet been studied with this approach.…”