How to transform the ink of a marker into a graphene-based electric circuit. The latest frontier of innovation has been published in Advanced Science

It is the first case of electric circuit created using a simple marker and a laser beam. Simple and sustainable materials to generate innovative applications on any surface, such as a coffee cup.
A research group coordinated by Francesco Greco, associate professor of bioengineering at the Sant'Anna School of Advanced Studies in Pisa, has transformed the ink of a red marker pen into a graphene-based electrical circuit. The study, published in the scientific journal Advanced Science, is the result of a collaboration between the Sant'Anna School, Graz University of Technology, CSGI - Center for Colloid and Surface Science, the University of Florence and Istituto Italiano di Tecnologia.

"Passing a laser beam over the ink transforms it into a form of porous and conductive carbon called 'laser-induced graphene' (LIG). So far, we belived that it was possible to obtain this LIG only from particular plastic materials and polymers, and this somehow limited its applications. An ink or paint, on the other hand, can be used easily and anywhere, to coat other objects. They also represent an economically advantageous alternative, says Francesco Greco.

From ink to... graphene. The role of the dye called Eosin

The study published in Advanced Science - as part of the European project 5DNanoprinting - was born from an everyday object: a red marker, like those you buy in stationery shops and are used for writing on whiteboards. This red marker contains a specific dye called Eosin, which has a chemical structure similar to that of graphene and is highly temperature stable.

The first to notice the particular characteristics of the Eosin dye was Alexander Dallinger, post-doc at the Institute of Solid State Physics (University of Graz). Dallinger observed the strange behaviour of the inks when irradiated by a laser.

‘The initial discovery happened by chance. I was trying laser writing on other materials, without success: none of them were transformed into conductive graphene. I had written on one of the samples its name with a red marker to recognise it. By mistake (or luck?) the laser beam passed over the writing: right at that point I saw a black trace appear. Intrigued, I immediately analysed it: the trace was conductive and it was graphene! This led to many questions: what is the marker ink made of? Why does that marker work and others don't? What is the ‘secret ingredient’? These questions were the starting point for the whole study and the discoveries that led to this publication,’ says Alexander Dallinger.

The ‘Paint & Scribe’ approach: an electric circuit can be created on any surface

To transform the colour into a circuit, the first steps taken by the research group were to define the design of the electronic circuit on a computer and trace the colour on a surface of their choice (it could be a sheet of paper, a coffee cup or a pair of glasses, for example). Once these actions had been defined, a laser machine traced the computer-generated design onto the coloured surface. When exposed to the laser, the Eosin dye was chemically transformed into graphene, a conductive material.

“This approach, called ‘Paint & Scribe’, integrates a graphene-based electrical circuit on any surface, induced by a laser: paint an object, then pass the laser over it and you get a circuit. It is an innovative system considering that, until now, graphene-based electrical circuits were only obtained on polymeric precursors” explains Greco.

Pisa-Firenze-Graz: the innovation triangle

Rodorico Giorgi and Rachel Camerini, respectively associate professor and post-doc at the Department of Chemistry ‘Ugo Schiff’ of the University of Florence and the CSGI - Center for Colloid and Surface Science, also played a fundamental role in the study. Their experience in the field of colours and pigment chemistry was essential for analysing the composition of the inks and identifying the dyes responsible for the formation of graphene.

‘We work in the field of Cultural Heritage, studying the matter and tis transformations. It's surprising how knowledge of the properties of organic dyes suddenly turns out to be the key to interpreting a phenomenon never seen before. You know a lot of things but you can't explain everything. Then one day you put two pieces of a puzzle together and take a step forward. That's the beauty of science!’ explains Rodorico Giorgi.

Possible applications

‘I believe that our study is an example of how scientific curiosity can unexpectedly lead to practical and applicative implications. In fact, this study, besides analysing why only some dyes are suitable for transformation into LIG, aims to propose this method for the realisation of circuits and sensors on any surface. Instead of installing circuits or sensors (often heavy, expensive and bulky) on the objects to be sensorised, we can now think of ‘writing’ them directly where they are needed. This could give a boost to applications in many sectors: printable electronics, biomedical sensors, robotics, automation, environmental sensors. We are already working on some of these applications. We have also started to study other dyes derived from natural materials, with to the aim of creating green electronics,’ Francesco Greco concludes.