Investigation of a Biosensor Based on Phenylalanine Dehydrogenase Immobilized on a Polymer-Blend Film for Phenylketonuria Diagnosis

Studies on Square Wave and Cyclic Voltammetric Behavior of 1,2- and 1,4-Dihydroxybenzenes and Their Derivatives in Acetic Acid, Ethyl Acetate and Mixtures of the Two

An electrochemical investigation of 1,2- and 1,4-dihydroxybenzenes was carried out with platinum macro- and microelectrodes using square wave and cyclic voltammetry techniques. Furthermore, the effect of the two solvents-acetic acid and ethyl acetate-was compared. When using square wave voltammetry, signals only appeared at lower frequencies and only when the supporting electrolyte was in excess, as expected due to the relatively low permittivity of the used solvents. The behavior of hydroquinone and catechol did not differ significantly from that of their derivatives (dihydroxybenzaldehydes, dihydroxybenzoic acids and 2',5'-dihydroxyacetophenone). When the cyclic voltammetric experiments using a microelectrode were extended to higher anodic potentials, electrode fouling was very significant in ethyl acetate after the potential region where steady-state oxidation to the corresponding quinone occurs. The substituent effect was not significant here either, which was proven by using different functional groups in different positions. In contrast, the position had a dramatic influence on the susceptibility to electropolymerization, as 1,2-dihydroxybenzenes-independent of the nature of the substituent on the benzene ring-deactivated the electrode, while 1,4-dihydroxybenzenes did not, possibly due to the different solubilities of the polymers formed from the primary oxidation product (quinones). A user-friendly analytical procedure is also proposed that uses an electropolymerization reaction and does not require frequent cleaning of the electrode via polishing, which is required usually especially with a microelectrode.

Ultrasonic-assisted synthesis and in vitro biological assessments of a novel herceptin-stabilized graphene using three dimensional cell spheroid

In vivo assays of graphene and its derivatives are big challenges in biological evaluations because they require simultaneous long-term stability in aqueous dispersion and controllable systemic toxicity. Bifunctional graphene nanosheets which have key function in biomedical area are expected to address this challenge. Here, novel bifunctional graphene nanosheets were successfully synthesized in the presence of Herceptin, a natural antibody, using a facile ultrasonic-assisted method. Graphite layers were successfully exfoliated which resulted excellent stability of separated layers in herceptin solution. In aqueous solution, graphene concentration was effectively controlled by varying the herceptin content and sonication time. Furthermore, the toxicity of graphene was tested in both 2D and 3D spheroid cultures. The results showed that graphene toxicity were considerably reduced in spheroid culture compared to the 2D culture data. Moreover, the toxicity behavior of graphene was dependent on the exposed concentration of graphene that the mortality rate was significantly decreased when the concentration of graphene was below 1 µg/mL. This bifunctional graphene which possessed long-term stability in aqueous solutions and induced slight toxicity offers a promising nanostructure in tumor-targeted drug delivery, regenerative medicine and tissue engineering. This proof-of-concept study demonstrates the feasibility of ultrasonic assisted method in one-step synthesis of bifunctional nanomaterials and biostructures for clinical applications.

Aptamer-based biosensor for detection of phenylalanine at physiological pH

A simple, sensitive aptamer-based biosensor for the detection of phenylalanine is developed using the electrochemical transduction method. For this proposed aptasensor, a 5-thiol-terminated aptamer is covalently attached onto a gold electrode. At the first time, the electrode was evaluated as an electrochemical aptasensor for determination of phenylalanine in aqueous solutions. This sensor was tested in a Tris-HCl buffer with physiological pH = 7.4 by cyclic voltammetry and differential pulse voltammetry. The detection limit and sensitivity of the modified electrode toward phenylalanine were estimated to be 1 nM (S/N = 3) and 0.367 μA nM(-1), respectively. The linear range of the signal was observed between 1 and 10 nM of phenylalanine with 0.9914 correlation factor. The herein-described approach is expected to promote the exploitation of aptamer-based biosensors for protein assays in biochemical and biomedical studies.