Based on the directed assembly technique of nanoxerography, the Nanotech team has developed secured marking stickers also called nanomarkers or nanotags.

It is about reproducing via the electrostatic directed assembly of colloidal nanoparticles, a logo, a pattern or a code of desired geometry whose dimensions can vary from micrometer to millimeter. Assembled nanoparticles have photoluminescent properties that could be activated and observed under certain experimental conditions (magnification, light intensity, light wavelength, filters, …). These nanomarkers are then transferred into or onto a product of interest (plastic cards, official documents, luxury products, etc…).

Depending on targeted applications, few types of nanoparticles are synthesized in the team and then assembled individually or coupled between each other in function of the degree of security/traceability to be reached. To realize it, it is possible to play with the complexity of the nanoparticle synthesis, their quantum yield, but also with the size and the geometry of the pattern or with the complexity of the required reading device.

Here is an example of nanotag representing a 40 µm wide QR code in which two types of core-shell nanoparticles have been assembled: (1) β-NaYF4:Gd3+,Tm3+,Yb3+@NaYF4 and (2) β-NaYF4:Gd3+,Er3+,Yb3+@NaYF4 (Figure. 1). This nanotag is highly secured : (i) the synthesis of these specific nanoparticles is complex and their optical signature is unique and unforgeable (ii) the nanotag is only visible under a dedicated optical characterization set up associated with a powerful laser, the quantum yield of these nanoparticles being very low (a few %) (iii) owing to the assembly of the two types of nanoparticles (1) and (2), it is possible to combine multiple messages that are only appearing under certain conditions. Here, the entire QR code is photoluminescent when a 980 nm laser is employed, it generates an optical response in the blue wavelengths (485 nm) though a short pass 500 nm filter revealing only the emission of the nanoparticles (1) while a second message “31” is readable in green (545 nm) if two filters are used, a high pass 530 nm and a short pass 650 nm to only keep the response of the nanoparticles (2)

Figure 1 : AFM topographical image of a 40 µm x 40 µm QR code made of a binary NC assembly consisting of (i) green-upconverting β -NaYF4:Gd3+,Er3+,Yb3+@NaYF4and (ii) blue-upconverting β -NaYF4:Gd3+,Tm3+,Yb3+@NaYF4 nanoparticles (b)total upconversion photoluminescence mapping of this QR code; (c) blue (485nm) upconversion PL mapping after passing the light through a 500 nm short pass filter and (d) the number “31” hidden within the QR code is revealed in green (545 nm), only when the PL light is passed through 530 nm long pass and 650 nm short pass filters. From [1]

On another hand, the ANR « Nanotaggin » project on which the Nanotech team is presently working on proposes to use such nanotags to secure official documents like ID cards or passports. For this particular application, a choice has been made to have a simple reading device based on a smartphone. Consequently, it was mandatory to synthesize nanoparticles with a high photoluminescence. Figure 2 illustrate an example of 2 mm wide QR code (link to the team section on the lab website) realized in the frame of the Nanotaggin project with semiconductor quantum dots CdSe@CdS featuring a high quantum yield (60-70%). The QR code is lighted with a simple blue LED, observed though a smartphone camera equipped with a x20 lens and read via a common dedicated app.

Figure 2 : Reading example of the millimeter wide QR code nanotag excited with a simple blue LED, observed though a lens added on the smartphone camera

One of the objectives of this activity is to allow mass production of such nanomarkers. Thus, few fabrication techniques are developed in the team in collaboration with companies who produce associated equipments like Innopsys (Fr) or NILT (Dk). Below is an example of hundreds of thousands micrometric QR codes on a 4 inch wafer surface generated by electrical nanoimprint lithography, patented in the team (Figure3).

Figure 3 : Example of fabrication of hundreds of thousands micrometric QR codes in a single step on a large surface. From [2]


[1] N. M. Sangeetha, P. Moutet, D. Lagarde, G. Sallen, B. Urbaszek, X. Marie, G. Viau, L. Ressier, Nanoscale 2013, 5, 9587.

[2] R. Diaz, E. Palleau, D. Poirot, N. M. Sangeetha, L. Ressier, Nanotechnology 2014, 25, 345302.

* A collaboration with the companies Nanolike and SELP allowed to validate the transfer of these markers on flexible substrates owing to an intermediate sacrifical layer and their integration into PVC or PET credit card like supports, on an industrial production line. Nanolike took a license on one of the patent deposited by the Nanotech team to protect this discovery and was working on integrating them on ID documents. A first contract was won by Nanolike to apply this technology to authenticating the engineering diplomas delivered by INSA de Toulouse.

Figure 8 : Smartphone reading under blue LED excitation of 5mm wide securised markers that were composed of CdSe@CdS nanoparticles

* Biocompatible nanomarkers

RoHS europeen standarts requested a limitation over applications that include cadmium or lead –because of their high toxicity-. That’s why the Nanotech team decided to work on alternatives for their historical CdSe@CdS markers: enviro intelligent markers based on nanogels (hydrogel nanoparticles), nanoparticles that are nontoxic and biocompatible. The idea behind this approach is to benefit from the original properties of the high volume changes (swelling/shriking) of nanogels that they preserved once assembled on a substrate by nanoxerography. At that point, nanogels are thus capable of adsorbing, absorbing or desorbing on demand other species that have for instance a specific optical response (like fluorophores). Moreover, the extreme sensitivity of nanogels to electrostatic forces permitted to define a protocol in which they can assemble or disassemble on a same surface without any extra injection step. Finally, the Nanotech team has demonstrated that a same assembled surface can be entirely recycled to make new processes. All the results were smartly combined to propose a new generation of biocompatible markers with improved security and traceability levels (see Figure 9).

Figure 9 : Scenario example in which nanogel based markers are used for the secured traceability of an electronic component

* Infrared nanomarkers

Recently, the research activities of the Nanotech team on this theme focus on new markers emitting in the infrared wavelengths following a hybrid approach with PbS particles. This study funded by the French Army aims at targeting military applications.

* Nanomarkers by UV microstructuration

To answer to a regular request from various companies, the Nanotech team proposed to develop a new assembly approach of colloidal nanoparticles allowing a simple and robust integration on various objects: the UV microstructuration of an epoxy nanocomposite (see figure XXX). This process consists in elaborating a composite material obtained by mixing nanoparticles of interest with a UV cross-linkable epoxy. This nanocomposite epoxy will then be applied locally on a random object of interest and topographically structured through a flexible PDMS stamp by UV nanoimprint.

Figure 10 : Principle of the UV microstructuration of a nanoparticle based epoxy composite

The generic aspect of this method is presently studied by applying it on various types of flat or curved surfaces of all kind (wood, metal, polymer, glass, textile,etc…). The compatibility of the epoxy with different nanoparticles will be also analyzed and the main synthesis criteria along with the adaptation of chemical properties of the epoxy will be identified.

This method might be another alternative to the 3D assembly by nanoxerography. In the case of secured markers, the multilayered 3D assembly is mandatory to obtain an optical response high enough to be readable through a smartphone. By topographically structuring a nanocomposite epoxy featuring luminescent nanoparticles, the optical response of the assembly might benefit from the entire response of all nanoparticles in volume. If this effect is confirmed, a new generation of secured and robust markers easily transferred on any type of object will see the light of day.