XPANCEO's additive-free nano-inks let you draw a working sensor with a marker

Conventional electronics are built in specialized factories, etched layer by layer under tightly controlled conditions. In contrast, printed electronic components (a sensor, a circuit, a light-responsive coating) are produced by depositing functional materials onto paper, plastic, or film, much as a printer lays down an image. The approach could yield inexpensive, flexible elements integrated into clothing, applied to skin, or embedded within a smart contact lens. Progress, however, has been held back by a problem: formulating a usable ink from the materials that would give such devices their capabilities. 

The most promising of these materials are only a few atoms thick, built from stacked layers, and valued for their optical and electrical properties. Turning them into a printable liquid is difficult because their particles drift together and settle, and the usual remedy is to add stabilizing chemicals to keep them apart. Those additives leave residues that degrade the material's properties and sit poorly on soft, delicate surfaces. For a device worn on the eye or applied to skin, such residues are not a minor flaw but a question of safety. The field has long had to choose between inks that stay stable and inks that stay clean. 

How the ink is made 

Researchers at XPANCEO have developed a way to avoid this trade-off, using only light. Their method applies extremely brief laser pulses — each lasting femtoseconds, or millionths of a billionth of a second — to a solid target submerged in liquid. Because the pulse ends faster than heat can spread through the material, a fragment is vaporized while its structure is preserved, and the freed fragments cool into a suspension of particles so fine that tens of thousands would span the width of a single hair. 

The particles stay separated due to an electrical charge they carry. As each particle forms, it acquires a faint charge, and since every particle carries a charge of the same sign, they repel one another, remaining evenly dispersed throughout the liquid. The ink is clean, then, not because impurities were removed, but because nothing was ever added. 

Working this way, the team produced inks from six different materials: molybdenum disulfide (MoS₂), molybdenum diselenide (MoSe₂), platinum diselenide (PtSe₂), and palladium diselenide (PdSe₂), together with two members of a metallic, electrically conductive class of materials known as MXenes (Ti₃C₂ and Ti₃AlC₂). Producing inks across so varied a set indicates that the technique is not confined to one material but may apply broadly across this family of compounds. The researchers deposited well-defined patterns using aerosol jet printing, a precision technique that delivers ink as a fine mist, and confirmed the chemical identity of the printed structures through spectroscopic analysis. 

A pen replaces the printer 

The inks can also be applied with far simpler tools. The team filled an ordinary refillable marker with one of the inks and wrote by hand on paper, plastic, foil, and flexible film, without any surface preparation, and the strokes dried within seconds. Once written, the ink acts as an optical magnifying glass for molecules, through a technique called surface-enhanced Raman scattering (SERS). It amplifies the weak signal a molecule produces under laser light, so that a detector can register amounts too small to see otherwise. Where plain paper responded only to a strong dose, the ink-drawn line picked up a trace roughly a thousand times weaker. 

"A smart contact lens is among the most demanding platforms a material can be asked to serve," says Valentyn Volkov, founder and scientific partner at XPANCEO. "It is worn against the eye, so every component within it must be clean, stable, and compatible with a soft, flexible, biocompatible surface. Inks that achieve their stability through added chemistry simply cannot meet that standard. By producing materials that are clean by their very nature, and that can be deposited with precision onto delicate substrates, we open a design space that was previously difficult to access. This is why we invest in fundamental science of this kind: the functional layers that will one day give a lens its capabilities depend on having the right materials to build them from, and that work begins long before the device itself." 

For XPANCEO, a result like this matters beyond the demonstration. It shows these inks can form functional layers that sense chemicals. A smart contact lens could carry layers of exactly this kind, laid down cleanly and precisely onto a soft surface, free of the chemical residues that could compromise a device worn against the eye. The longer-term ambition is a lens that reads the chemistry of tear fluid, which carries markers of health such as glucose, sensing them at the surface of the eye without a blood test.