Ceylon Graphite Corp. announced that Ceylon graphite achieved new concentration and conductivity records when studied in the manufacture of an adaptable sensing platform for chemical sensing. The research, published in the Royal Society of Chemistry's "Nanoscale" Journal, was conducted by partners at the Molecular Sciences Research Hub at Imperial College London and specifically incorporated Ceylon's vein graphite to produce a low-surface-tension sprayable graphene ink that was key to the sensor's functionality.

A summary of the test results, completed in January 2023 is highlighted: Ceylon graphite was used to create high concentration, graphene/polyvinylpyrrolidone inks, with record-breaking concentrations as high 3.2 mg mL-1. Raman spectroscopy was used to show high-quality graphene flakes produced via liquid phase exfoliation. The Ceylon-based graphene device was successfully used to detect for pH within the range of pH 3 - 11. These results demonstrate the potential of high-quality graphite to empower the next generation of nano-based diagnostics for biological and chemical sensing.

Results in Summary: Graphene ink formulation: Graphene inks have emerged as a new revolutionary element for high-performance printed, flexible and wearable electronics. Among the various methods available for preparing graphene ink, sonication-assisted liquid-phase exfoliation (LPE) has been chosen due to its simplicity and compatibility with low-boiling solvents. This process involves subjecting graphite (in powder or flakes) and low-boiling point solvents, such as 2-propanol (IPA), along with small amounts (20 mg) of the polymer stabiliser, resulting in a graphene ink with desired electronic propertied for printed electronics and significantly enhanced shelf life of the ink.

IPA was selected as the solvent for the graphene ink as it has a boiling point of 82 degC and impressively low surface pressure of only 20.34 mN m-1, satisfying the criteria for a scalable spray-coating as well as inkjet printing of the optimised ink. The sonication process lasts for 9 hours, ensuring thorough exfoliation of the graphite flakes. Centrifugation at 2.000 - 13,000 g is then employed to further refine the ink and effectively eliminate any remaining unexfoliated flakes.

The optical absorption spectrum (OAS) of the graphene ink, exhibits the characteristic profile associated with the profile associated with the potential of graphene flakes. The optical absorption spectrum (OAS) of the graphene ink exhibits the characteristic profile associated with graphene inks, a flat absorption pattern in the visible spectrum and a distinctive peak in the UV region, confirms the ink is mainly composed by high-quality graphene flakes. The concentration of graphene flakes in the ink is estimated to be ~ 1 mg mL-1 when centrifuged at 13,000 g and as high as 3.2 mg mL-1 when centrifuged at 2,300 g. This concentration surpasses those reported in the literature for graphene inks stabilised by polyvinylpyrrolidone (PVP) by an order of magnitude, underscoring the exceptional quality and potential of this formulation.

Application: A graphene field-effect transistor as a scalable and low-cost high-performance biosensor. The EG-GFET channel is formed using an automatic spray-coating process, ensuring consistent and scalable deposition of the graphene ink onto the PCB test strip. The graphene ink exhibits excellent wetting properties that contribute to film uniformity.

As the individual ink droplets merge into a thin film before evaporating, this wetting behaviour plays a vital role in achieving uniformity. While the addition of PVP stabilizer enhances the concentration and stability of the ink, it is important to note that PVP is known to adversely affect the electrical conductivity of nanostructured graphene thin films due to its insulating properties. However, a solution has been found by utilizing a xenon intense pulsed light (IPL) source, which effectively degrades the PVP polymer without subjecting the PCB substrate to temperatures exceeding its decomposition threshold.

This method proves to be the most suitable for this specific application. The spray coated graphene ink achieved an approximate channel resistivity of 100 O after IPL annealing suitable for flexible and plastic electronics and currently used in industry.