FABRICATION OF ENCODED MICROPARTICLES FOR ANTI-COUNTERFEITING APPLICATIONS

Abstract

The number of counterfeiting crimes, such as counterfeiting of banknotes, drugs, and even liquors, has steadily grown in the global marketplace. Although a lot of anti-counterfeiting methods are applied to products, advanced technologies are required in order to deal with increasingly sophisticated counterfeit crimes. An anti-counterfeiting technique based on microparticles is difficult to copy because they are very small to detect and many different particles can be integrated, but few technologies using microparticles have been developed. In this thesis, I fabricate encoded microparticles and demonstrate applications of this anti-counterfeiting tool, especially suitable for use with banknotes and drugs. First, shape-coded microparticles are fabricated and applied to banknotes. The size of fabricated polymeric microparticles range from 50㎛ to 500㎛. Special letters are encoded on the different shapes of particles and three different fluorescent dyes are used to realize color information. Since microparticles should be mixed with the paper pulp and printing inks used in the production of banknotes, fabricated polymeric microparticles are silica coated to protect them from the physical stress during the formulation process. Silica-coated microparticles, which have thicknesses from 15㎛ to 40㎛, are successfully integrated into the paper regardless of their size. Such shape-coded microparticles can provide a high level of added security because they are small and information is coded on a particle by both the shape and the fluorescence. Therefore, they could be utilized as a new anti-counterfeiting tool for banknotes. Second, QR-coded microparticles, which can be decoded using a smartphone QR code reader application, are synthesized for the anti-counterfeiting of drugs. A fluorescent acrylic monomer is utilized to minimize diffusion of the fluorescent dye from the particle as well as provide high color contrast between the code and backgrounds. According to the simulation results of propagation of the projected ultraviolet light inside the microfluidic channel, the module size of QR code is set at less than 40㎛ with a channel height greater than 25㎛ to prohibit separation of island patterns which exist inside the particle. The encoding capacity of fabricated QR-coded microparticles mainly depends on both the version of QR code and error correction level. Version 7 microparticles with maximum error correction levels are capable of encoding 93 characters, which is sufficient for storing specific drug information such as the name of the manufacturer, the production date, and the expiration date. At the maximum error correction level, damaged codes with up to approximately 20% of the data area degraded are successfully recovered. Also, the code is successfully decoded without alignment between the particle and the decoding device with the assistance of position detection patterns. The authentication process is demonstrated using a drug capsule containing QR-coded microtaggants and cytotoxicity tests verify that fabricated microparticles are not toxic to cells. Since presented QR-coded microparticles feature high encoding capacities as well as error correction capabilities that were difficult to implement in previous microtaggants, they could be widely used as a part of a highly effective anti-counterfeiting method for drugs.