Evaluation of graphite sheets for production of high-quality disposable sensors

Flexible graphite sheets or graphite paper are conductive substrates produced in large scale for use in a wide range of applications, such as in telecommunications, lighting, computer and peripherals, power conversion, and heat generating semiconductors (low-cost material). In this paper we show, for the first time, that commercially available graphite sheets can be used in the as-received condition for the construction of disposable electrodes with excellent performance for electroanalysis (comparable to glassy carbon). Nine different graphite sheets were evaluated by different techniques, such as scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, square wave voltammetry, and amperometry. The obtained results revealed the existence of large variations between different commercially available materials (not all the sheets work well as sensors in the as-received condition). Our studies have shown that there are commercial flexible graphite sheets with higher electrical conductivity and superior homogeneous composition, which are ideal for use as disposable unmodified or modified sensors. The quality of the results obtained with graphite sheets are dependent on the type of material selected as substrate. However, repetitive results are obtained if the same material is always used. The graphite sheets were coupled to low cost 3D-printed cells forming easy to use disposable devices. The performance of the disposable devices was evaluated using ferri-ferrocyanide and ferrocene probes, dopamine (LOD = 0.7 mu mol L-1), catechol (LOD = 0.8 mu mol L-1), ciprofloxacin (LOD = 5.9 mu mol L-1), cadmium (LOD = 0.013 mu mol L-1), and lead (LOD = 0.07 mu mol L-1) as model analytes. According to our knowledge, the electroanalytical performance of graphite sheets demonstrated here surpasses previously reported results.