USTC scientists have developed biocompatible contact lenses that convert near-infrared light into visible colors, offering an unprecedented sensory dimension.

Human vision has always been confined to a narrow band of visible light between 400 and 700 nanometers. Beyond one end of this visible range lies a wealth of near-infrared light, rich with thermal and chemical information, but previously entirely imperceptible to the naked eye.

Now, a team led by Professor Tian Xue at the University of Science and Technology of China (USTC) has pushed this boundary. Their recent Cell study demonstrates that humans can push past this sensory limit to perceive the otherwise invisible near-infrared (NIR) light¹.

Scientists embedded engineered upconversion nanoparticles into the selected polymer, creating soft, transparent and biocompatible contact lenses. These lenses, known as ‘upconversion contact lenses’ (UCLs), can convert multiple near‑infrared wavelengths into corresponding visible light.

“Our design enables the naked eye to directly distinguish NIR information such as temporal codes and spatial patterns,” says Xue. “This paves the way for enhanced perception in low-visibility settings and new forms of secure optical communication.”

Beyond the visible spectrum

Detecting infrared light has relied on devices such as night-vision goggles. But these tools are often bulky, require external power, and cannot distinguish between multiple infrared spectral bands.

Furthermore, they are distant from the natural visual process, providing an artificial and less intuitive viewing experience. Xue’s team aimed to create a lightweight, power-free and multispectral NIR vision system.

In 2019, the team reported in Cell that they had, for the first time, showed that mammals could gain naked-eye near-infrared vision using photoreceptor-binding upconversion nanoparticles (pbUCNPs)². These nanoparticles were designed to attach to photoreceptor cells in the retina, where they absorb invisible NIR photons and emit visible light photons in their place.

When injected into the eyes of mice, pbUCNPs enabled the animals to recognize shapes and patterns illuminated solely by NIR light. Electrophysiological recordings confirmed that this stimulation activated the visual cortex, proving the converted signals were processed through the eye’s natural visual pathway.

Despite its scientific significance, the invasive nature of this method made it impractical for human subjects. “The challenge was how to non-invasively and flexibly extend the human eye’s spectral sensitivity — even to grant it near-infrared vision,” says Xue.

The breakthrough came when Xue’s team turned to a familiar, wearable solution: contact lenses. Using soft polymeric materials already used for vision correction, they engineered biocompatible lenses that turn multiple NIR wavelengths between 800 to 1,600 nanometers into visible red, green and blue light — enabling humans to experience near-infrared spatiotemporal colour vision.

Illustration of the human eye enhanced by USTC’s new contact lenses, which convert invisible near‑infrared light into visible colour.

A materials breakthrough

At the core of the new technology are upconversion nanoparticles — special materials that perform a rare optical phenomenon called anti-Stokes emission. Put simply, they take in two or more low-energy photons, typically in the near-infrared range, step the energy up through a series of internal transfers, and release a single higher-energy photon in the visible or ultraviolet spectrum.

To convert multispectral NIR light, Xue’s team collaborated with team of Fan Zhang at Fudan University in Shanghai, China, the latter further developed trichromatic orthogonal upconversion nanoparticles (tUCNPs). These rare-earth-doped nanostructures feature a core–shell–shell structure where each layer filters a specific NIR wavelength and emits a distinct visible colour.

Under three distinct NIR excitations, where wavelength at 980, 808 and 1,532 nanometers, the tUCNPs respectively emit blue, green and red light — three primary colours covering the full red‑green‑blue (RGB) colour range.

Incorporating these nanoparticles into contact lenses required balancing high upconversion efficiency with excellent optical performance. This meant ensuring the nanoparticles were concentrated enough to work effectively without compromising transparency. Furthermore, to ensure clarity, matching the refractive index — a measure of how much a transparent material bends light — between the nanoparticles and the polymer matrix was also critical.

To achieve this balance, the team modified the surface chemistry of the UCNPs and screened dozens of polymers before selecting poly(2-hydroxyethyl methacrylate) (pHEMA), a hydrogel material already used in commercial contact lenses.

By balancing particle loading and transparency, they achieved lenses with a UCNP concentration of 7% by mass — much higher than typical nanocomposite reports — while maintaining over 90% light transmittance across most of the visible spectrum.

A new sensory layer

UCLs open a new channel of perception, say the researchers. In mouse experiments, the lenses enable the detection of NIR temporal signals, such as distinguishing different flicker frequencies.

When applied in humans, the lenses enable people to sense patterns encoded in NIR light — these include time-based patterns in NIR signals, the ability to identify the direction of NIR light coming from specific visual quadrants, and the ability to distinguish multispectral NIR light at three primary colour wavelengths.

Remarkably, both human and mice could perceive these NIR signals even with their eyes closed, due to the strong penetration of NIR light through eyelids.

Currently, fine NIR image perception through UCLs alone is limited by the scattering of converted light, so Xue’s team designed a wearable eyeglass system that restores spatial resolution to a level comparable with normal vision.

Future material innovations, such as “directional light-emitting nanoparticles or embedded micro-optical channels”, might allow direct, high-resolution NIR imaging through the contact lenses themselves, says Yuqian Ma, the first author of the paper.

Rather than replacing normal colour vision, the converted NIR signal is overlaid on the visible spectrum, functioning like an augmented reality filter. This design minimizes sensory competition and cognitive interference, allowing both visible and NIR information to be perceived in parallel.

The lenses also allow recognition of so-called NIR “reflective colours.” Many objects that appear identical under visible light show distinct reflective properties in the NIR range, effectively creating a parallel colour world. These reflective NIR light represent enriched material physiochemical properties. For example, we use visible red colour to tell whether an apple is ripe. In the future, we may use the naked eye to see the reflective NIR colour of a subject and tell its material composition adds Ma.

However, for now, UCLs can only detect NIR light through active illumination from an external source, and fine-resolution imaging depends on supplemental optics. Further, widespread deployment will require interdisciplinary collaboration among neuroscientists, materials scientists, and optical experts to enhance the system’s infrared sensitivity threshold and adaptability, say the researchers.

The breakthrough is already paving the way for practical applications. Possible uses being investigated, include enhanced navigation under conditions of smoke or fog, search-and-rescue operations, secure optical communications, and new methods of industrial inspection.

Xue’s team is also working to boost performance by developing higher-efficiency upconversion nanoparticles with a broader near-infrared detection range, while also exploring applications such as colour-blindness–correcting contact lenses.

“When we extend the range of the visible spectrum, we can capture more information from the natural world, and our understanding of the environment gains another dimension,” says Xue.

Reference

1.Ma, Y. et al. Cell, 188(13), 3375-3388. (2025). 

2.Ma, Y. et al. Cell, 177(2), 243-255. (2019).