Counterfeiting of products is proliferating globally, stimulated by the increasing significance of international and electronic commerce, and boosted
by technological advancements that facilitates the manufacturing of counterfeit goods.[4] They are prevalent across various industries such as
cosmetics, pharmaceuticals, microelectronics, and textiles.[5]
In recent years, our society has prioritized developing a robust anti-counterfeiting system, suitable throughout the supply chain. An effective solution
involves attaching security labels to protected products,[2] namely QR codes, RFID tags, barcodes, holographic labels, and plasmonic labels.
However, their successful implementation is hindered by the ease of imitation due to rapid technological advancements and sometimes the need for
sophisticated equipment.[4, 5]
The integration of optical encoding with security labels significantly enhances the effectiveness of anti-counterfeiting systems. Optical anticounterfeiting
technology has garnered widespread attention due to its relative simplicity and high encoding capability.[6, 7] The use of luminescent
materials (e.g. organic fluorescent dyes, rare earth materials, or semiconductor quantum dots) with good optical properties (high intensity and long
emission duration) is popular because of their easy readout.[2, 7, 8] Carbon quantum dots (C-dots) are particularly promising due to their
size/shape/composition tunable optical properties, low toxicity and ability to be prepared from low-cost precursors.[7] Recently, Li et al. [9] prepared
solid-state C-dots with a bright green color, high quantum yields (QY, 40-67%) and temperature-dependent photoluminescence properties. Their
application to produce a temperature-sensitive (30-150 ºC) flexible anti-counterfeiting code exemplified their utility in creating secure anticounterfeiting
codes.
Only, in 2016, Campos-Cuerva et al. [10] developed user-configurable anti-counterfeiting labels, combining Au and Ag nanoparticles (NPs) with
unique optical signatures and magnetic NPs with a physical signal dependent on their size; in 2017, Deak and Cheng patented a magnetic anticounterfeit
label and the identification system thereof [11]. This highlights the potential of magnetic responses and of their combination with optical
response to provide additional layers of security in anti-counterfeiting technologies. Furthermore, considerable attention has been devoted in recent
years to developing Physically Unclonable Function (PUF) security labels. These labels rely on generating random patterns, resulting in unique
fingerprint-like characteristics that cannot be controlled. Various studies have explored the creation of PUF labels using plasmonic Ag [12, 13] and
Au [14, 15] NPs, with methods ensuring random size or spatial distribution. Multiple security levels have been incorporated, including chromatic,
spectral, and morphological responses,[12] or through three random optical imaging techniques (bright field, Raman imaging, and dark field) [15].
Despite offering robust security, the PUF labels implementation is challenging because requires characterization and storage in a database for
authentication, which entails time and costs.
In the textile industry, addressing the challenge of counterfeiting emerges as a critical concern, exacerbated by the evident insufficiency of current
methodologies, underscoring the imperative for prompt and inventive interventions. This has prompted exploration into diverse strategies such as
impregnating cotton yarn with fluorescein [1] or applying fluorescein to polyester fabrics using microwave irradiation [8]. In both works, the coated
textile substrates kept their original properties and exhibited a yellowish green emission (under UV light), even with a weak yellow coloration of
cotton fiber. However, these approaches are limited by the release of fluorescein during washing cycles, compromising its anti-counterfeiting
function. Jiang et. al [16] used electrospinning to create fluorescent nanofibers based on aggregation-induced emission luminogen, which were used
to weave smart anti-counterfeiting textiles. The fibers exhibited stable fluorescent and mechanical properties, even after being stretched, bent,
washed, and rubbed. Colloidal C-Dots, synthesized at a large scale but using a complex procedure (emission at 520 nm, QY of ~79%), were utilized
to inkjet print a flexible security code on cotton fabric, which remained flexible and with a QY of 42% (62% of this value after 6 months) [7]. A
fluorescence ink based on C-dots produced from natural plant dyes was also employed to print patterns in a cotton substrate, which were almost
invisible under daylight and had clear patterns under 365 and 395 nm light, proving their optical anti-counterfeiting capabilities [17]. Additionally,
water-dispersible ink based on hybrid carbon/silicon dots has been developed for screen-printing patterns (e.g. a logo and a QR code), namely on
cotton fabrics, with t |