High-Resolution Graphene Films for Electrochemical Sensing via Inkjet Maskless Lithography

Abstract

Solution-phase printing of nanomaterial-based graphene inks are rapidly gaining interest for fabrication of flexible electronics. However, scalable manufacturing techniques for high-resolution printed graphene circuits are still lacking. Here, we report a patterning technique [i.e., inkjet maskless lithography (IML)] to form high-resolution, flexible, graphene films (line widths down to 20 μm) that significantly exceed the current inkjet printing resolution of graphene (line widths ∼60 μm). IML uses an inkjet printed polymer lacquer as a sacrificial pattern, viscous spin-coated graphene, and a subsequent graphene lift-off to pattern films without the need for prefabricated stencils, templates, or cleanroom technology (e.g., photolithography). Laser annealing is employed to increase conductivity on thermally sensitive, flexible substrates [polyethylene terephthalate (PET)]. Laser annealing and subsequent platinum nanoparticle deposition substantially increases the electroactive nature of graphene as illustrated by electrochemical hydrogen peroxide (HO) sensing [rapid response (5 s), broad linear sensing range (0.1-550 μm), high sensitivity (0.21 μM/μA), and low detection limit (0.21 μM)]. Moreover, high-resolution, complex graphene circuits [i.e., interdigitated electrodes (IDE) with varying finger width and spacing] were created with IML and characterized via potassium chloride (KCl) electrochemical impedance spectroscopy (EIS). Results indicated that sensitivity directly correlates to electrode feature size as the IDE with the smallest finger width and spacing (50 and 50 μm) displayed the largest response to changes in KCl concentration (∼21 kΩ). These results indicate that the developed IML patterning technique is well-suited for rapid, solution-phase graphene film prototyping on flexible substrates for numerous applications including electrochemical sensing.

Printed Graphene Electrochemical Biosensors Fabricated by Inkjet Maskless Lithography for Rapid and Sensitive Detection of Organophosphates

“…and Materials). 37 The PGEs used herein were first fabricated through our previously reported IML technique 32 that includes inkjet printing a polymer mask, spin-coating a graphene flake solution, thermal postbaking the printed graphene, and finally performing an acetone rinse lift-off to form well-defined electrode patterns with a 5 mm diameter disk-shaped working electrode (Figure 1a). After the graphene patterning process, a laser diode engraver was used to anneal the graphene and remove nonconductive ink surfactants (Figure 1b).…”

“…40 Additionally, this laser annealing process, performed in ambient air, increases the number of superficial defects while adding oxygenated species (COOH, −CO, and −OH) to the said defects as previously reported. 42 The increase of graphene superficial defects has been shown to significantly increase the nucleation density of PtNPs during electrodeposition. 43 Such superficial oxygen species are well-suited for subsequent enzymatic biofunctionalization via glutaraldehyde cross-linking as hydroxyl groups on the graphene surface bind to the aldehyde groups in glutaraldehyde.…”

“…Graphene electrodes were printed and patterned through a recently developed thin film manufacturing technique called inkjet maskless lithography (IML). 32 Next, the printed graphene electrodes (PGEs) were laser-annealed and electrochemically deposited with platinum nanoparticles (PtNPs) to create a nano/microstructured surface that is highly conductive/electroactive with a high surface area for increased enzyme loading and heterogeneous charge transport during electrochemical sensing. The graphenebased electrode was consequently biofunctionalized with the enzyme PTE through covalent cross-linking with glutaraldehyde.…”

Flexible Laser-Induced Graphene for Nitrogen Sensing in Soil

“…5,27 This facile LIG manufacturing protocol also eliminates the need for ink preparation, ink printing, and post-print annealing processes associated with solution-phase printed graphene. 9,[28][29] The utility of LIG has been displayed in numerous applications including supercapacitors, 14,22,[30][31] non-biofouling surfaces, 32 transparent heaters 33 , and more recently, electrochemical sensors. [25][26][34][35] For example, a non-enzymatic amperometric glucose sensor comprised of LIG functionalized with Cu nanocubes was used to selectively measure glucose over a wide concentration range (25 µM-4 mM), which is physiologically relevant to glucose levels in saliva, tears, and blood.…”

Advances in nanomaterial application in enzyme-based electrochemical biosensors: a review

“…Graphene electrodes can be created either by direct printing of graphene ink or by printing a sacricial polymer pattern followed by the graphene deposition. 140,141 On the other hand, graphene electrodes can be produced from carbon-based polymers (i.e., polyimide) by CO 2 laser irradiation. 142 In both cases the electrodes of relatively complex pattern (e.g., interdigitated) can be easily obtained in large quantities suitable for the creation of amperometric, impedimetric or other types of biosensors.…”