Novel disposable electrochemical DNA sensors were prepared for the detection of a target DNA sequence on the p53 tumor suppressor (TP53) gene. The electrochemical platform consisted of screen-printed carbon electrodes (SPCEs) functionalized with a water-soluble reduced graphene oxide-carboxymethylcellulose (rGO-CMC) hybrid nanomaterial. Two different configurations involving hairpin specific capture probes of different length covalently immobilized through carbodiimide chemistry on the surface of rGO-CMC-modified SPCEs were implemented and compared. Upon hybridization, a streptavidin-peroxidase (Strep-HRP) conjugate was employed as an electrochemical indicator. Hybridization was monitored by recording the amperometric responses measured at -0.10 V (vs an Ag pseudo-reference electrode) upon the addition of 3,3',5,5'-tetramethylbenzidine (TMB) as a redox mediator and H2O2 as an enzyme substrate. The implemented DNA platforms allow single nucleotide polymorphism (SNP) discrimination in cDNAs from human breast cancer cell lines, which makes such platforms excellent as new diagnosis tools in clinical analysis.

Reduced graphene nanoparticles were prepared from graphene oxide through a two-step covalent modification approach. Graphene oxide was first enriched with reactive epoxy groups by anchoring (3glycidyloxypropyl)trimethoxysilane at the hydroxyl groups located on the nanocarbon basal plane. Modified graphene oxide was further cross-linked and partially reduced by treatment with the fourthgeneration ethylenediamine core polyamidoamine G-4 dendrimer producing graphene nanoparticles with crumpled paper-like morphology. This graphene derivative was employed as a coating material for glassy carbon electrodes and the nanostructured electrode was tested for the preparation of electrochemical biosensors by immobilizing the enzyme tyrosinase through cross-linking with glutaraldehyde. This bioelectrode showed excellent electroanalytical behavior for catechol with a fast response in about 6 s, linear range of 10 nM to 22 mM, sensitivity of 424 mA M À1 , and low detection limit of 6 nM. The enzyme biosensor also showed high stability when stored at 4 C under dry and wet conditions.

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A novel nanostructured architecture for the construction of electrochemical enzyme biosensors is here described. It implies the electrostatic layer‐by‐layer assembly of four‐generation ethylenediamine core polyamidoamine G‐4 dendrimers on glassy carbon electrodes coated with a graphene oxide‐carboxymethylcellulose hybrid nanomaterial. This modified surface was further employed for the covalent immobilization of the model enzyme tyrosinase through a glutaraldehyde‐mediated cross‐linking. The prepared enzyme electrode allowed the amperometric detection of catechol in the 2–400 nM range. The biosensor showed excellent analytical performance with high sensitivity of 6.3 A/M and low detection limit of 0.9 nM. The enzyme electrode retained over 93 % of the initial activity after 40 days at 4 °C.

A novel hybrid nanomaterial was synthesised by covalent attachment of O‐carboxymethylcellulose to reduced graphene oxide. Graphene oxide was first anchored with (3‐aminopropyl)triethoxysilane moieties to provide reactive primary amino groups at the basal plane. Periodate‐oxidised O‐carboxymethylcellulose was further covalently attached to this aminated nanomaterial through reductive alkylation with NaBH4. Stable aqueous dispersions were obtained with the resulting hybrid nanomaterial, which was used to coat glassy carbon electrodes. Furthermore, the enzyme tyrosinase was covalently immobilised and the nanostructured enzyme electrode was successfully employed for the amperometric detection of catechol in the 20 nM–56 μM range. The biosensor showed excellent analytical performance with a high sensitivity of 270 mA M−1 and a low detection limit of 0.2 nM.

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