Counterfeiting is considered a scourge in widespread industries across the globe. The rapid surge of counterfeit products in the market causes economic havoc, which impedes the livelihood of the primary inventor^1,2,3,4,5,6. This was brought to the fore in 2020⁷ on the ongoing concern of emerging counterfeit products as evidenced by the increasing trend of publications consisting of the keyword anticounterfeiting or counterfeiting in their titles. A significant increase can be observed in counterfeit-related publications since last reported in 2019, suggesting that considerable efforts are being made to combat the production and distribution of fraudulent goods. On the other hand, it can also be quite alarming, given that it signifies the progression of the counterfeiting industry, which is expected to persist if not addressed effectively. The textile industry is not insulated from this problem, as the presence of counterfeit textile products has severely impacted the livelihood of genuine sellers, manufacturers and weavers, among others^3,8. For instance, the textile industry in West Africa was long considered one of the leading export markets in the world. However, it was reported⁹ that approximately 85% of the market share is held by smuggled textiles that infringe upon West African textile trademarks. The effects of counterfeiting have also been reported in other continents like Asia, America, and Europe, indicating that this crisis has reached an uncontrollable level and poses a significant threat to the already struggling textile industry^{2,3,4,10,11,12}.

With the rapid advancements of science, technology, and innovation, researchers took upon the role of developing functional materials for the purpose of anti-counterfeiting applications. The use of covert technology is one of the most common and effective approaches to counteract the production of fraudulent goods. It involves utilizing photoluminescent materials as security dyes that exhibit a specific light emission when irradiated by different wavelengths^13,14. However, some photoluminescent dyes available in the market may impose toxicity at high concentrations, thereby posing threats to human health and the environment^15,16.

Turmeric (Curcuma longa) is an essential plant used in myriad applications such as paints, flavoring agents, medicine, cosmetics, and fabric dyes¹⁷. Present in the rhizomes are naturally occurring phenolic chemical compounds called curcuminoids. These curcuminoids include curcumin, demethoxycurcumin, and bisdemethoxycurcumin, among which curcumin is the main constituent responsible for the vibrant yellow to orange coloration and the properties of turmeric¹⁸. Curcumin, otherwise known as 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione^19,20 with an empirical formula of C₂₁H₂₀O₆, has attracted a significant amount of attention in the biomedical and pharmaceutical fields due to its antiseptic, anti-inflammatory, anti-bacterial, and antioxidant properties^{17,18,21,22,23}. Interestingly, curcumin also possesses spectral and photochemical characteristics. Particularly noteworthy is its intense photoluminescent properties when subjected to ultraviolet (UV) excitations which have been explored only by a few studies^19,24,25. Given these characteristics, in tandem with its hydrophobic nature and non-toxic properties, curcumin emerges as an ideal colorant for authentication markings.

The extraction of curcumin from turmeric was first reported in the early 1800s. Over the past centuries, numerous extraction methodologies and techniques have been devised and improved to achieve higher yield^{26,27,28,29,30,31,32,33}. Conventional solvent extraction is a widely used approach as it employs organic solvents such as ethanol, methanol, acetone, and hexane among others, to isolate curcumin from turmeric^34,35. This method has evolved through modifications, coupled with more advanced techniques such as microwave-assisted extraction (MAE)^18,36,37, Soxhlet extraction^38,39, enzyme-assisted extraction (EAE)^39,40, and ultrasonic extraction³⁶, among others to increase the yield. Generally, the solvent extraction method has been applied for natural dye extraction due to its versatility, low energy requirement, and cost-effectiveness making it ideal for scalable industries such as textiles.

Curcumin has been integrated as natural dyes for textiles due to its distinct yellow hue. However, the poor adsorption of natural dyes unto textile fibers pose as a challenge that hinders its commercial viability⁴¹. Mordants, such as metals, polysaccharides, and other organic compounds, serve as common binders to strengthen the affinity of natural dyes unto the fabric. Chitosan, a polysaccharide derived from crustaceans, has been widely utilized as an alternative mordanting agent due to its abundance in nature, biocompatibility, and wash durability⁴². This study reports a facile and straight forward approach in preparing curcumin-based authentication marking. Crude curcumin extracts were obtained via sonication-assisted solvent extraction method. The photoluminescent properties of the extracted curcumin were comprehensively investigated on textile substrates and further enhanced with the introduction of chitosan as a mordanting agent. This demonstrates the significant potential as a naturally derived photoluminescent dye for authentication applications.