Encoded nano-structures/particles have been used for barcoding and are in great demand for the simultaneous analysis of multiple targets. Due to their nanoscale dimension(s), nano-barcodes have been implemented favourably for bioimaging, in addition to their security and multiplex bioassay application. In designing nano-barcodes for a specific application, encoding techniques, synthesis strategies, and decoding techniques need to be considered. The encoding techniques to generate unique multiple codes for nano-barcodes are based on certain encoding elements including optical (fluorescent and non-fluorescent), graphical, magnetic, and phase change properties of nanoparticles or their different shapes and sizes. These encoding elements can generally be embedded inside, decorated on the surface of nanostructures or self-assembled to prepare the nano-barcodes. The decoding techniques for each encoding technique are different and need to be suitable for the desired applications. This review will provide a thorough discussion on designing nano-barcodes, focusing on the encoding techniques, synthesis methods, and decoding for applications including bio-detection, imaging, and anti-counterfeiting. Additionally, associated challenges in the field and potential solutions will also be discussed. We believe that a comprehensive understanding on this topic could significantly contribute towards the advancement of nano-barcodes for a broad spectrum of applications.

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Porous polyurethane films with well-ordered pores were prepared using polystyrene microspheres as a template, and the surface pore sizes were tuned using a new upside-down (USD) method. After polystyrene microspheres were self-assembled on a substrate and the voids between microspheres were infiltrated with a polyurethane prepolymer solution, the samples were placed upside down to allow the prepolymer solution to flow back before it was solidified. The surface pore sizes of the porous films were tuned by changing the time in which the samples were placed upside down. Using microspheres of the same size, we prepared porous polyurethane films with surface pore sizes ranging from 32 to 87% of the templating microsphere size.

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By attaching different biomolecule probes to surface-modified microspheres, a large number of complementary targets labeled with fluorophores can be interrogated simultaneously using the bead-based microarray format. In this work, a new bead-based DNA microarray was fabricated on a porous polymer film with well-ordered array of pores. The well-ordered porous polymer film was prepared using the non-lithographic breath figure method. Different biotinylated DNA probes were conjugated to avidin-modified polystyrene (PS) microspheres. The DNA microarray was fabricated by randomly dispersing DNA probe-conjugated PS microspheres into the pores on the polymer film. Multiplexing detection of DNA was performed using target DNAs labeled with ATTO dyes using a fluorescence microscope imaging system. The Bead-based DNA microarray was constructed for detection of four serotypes of Dengue virus. This technique was demonstrated to be a simple and cost-effective method for rapid detection of DNA targets.