Real time detection of adenosine and theophylline in urine and blood samples using graphene modified electrode

Herein, we report the grafting of stable graphene layers on to glassy carbon (GC) electrode by a two-step diazotization strategy using melamine. The resulting graphene modified electrode is used for the selective determination of theophylline (TP) in the presence of inhibitor neurotransmitter antagonist, adenosine (AD). The modified electrode surfaces are characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Bare GC electrode fails to show stable voltammetric signals for TP and AD due to the surface fouling caused by the oxidation products of the analytes. However, the graphene modified electrode showed stable voltammetric signals for the simultaneous detection of TP and AD than the bare GC electrode. Further, the graphene modified electrode is used for the selective determination of TP in the presence of 34-fold excess AD. A linear plot is noticed upon increasing the TP concentration from 3.0 x 10(-8)-1.0 x 10(-4) M. The limit of detection is found to be 5.4 x 10(-9) M (S/N = 3). The practical application of the proposed modified electrode is demonstrated by the simultaneous determination of TP and AD in human blood serum and urine samples.