Encrypted Oligonucleotide Arrays for Molecular Authentication

A Canvas of Spatially Arranged DNA Strands that Can Produce 24-bit Color Depth

Nucleic acid microarray photolithography combines density, throughput, and positional control in DNA synthesis. These surface-bound sequence libraries are conventionally used in large-scale hybridization assays against fluorescently labeled, perfect-match DNA strands. Here, we introduce another layer of control for in situ microarray synthesis─hybridization affinity─to precisely modulate fluorescence intensity upon duplex formation. Using a combination of Cy3-, Cy5-, and fluorescein-labeled targets and an ensemble of truncated DNA probes, we organize 256 shades of red, green, and blue intensities that can be superimposed and merged. In so doing, hybridization alone is able to produce a large palette of 16 million colors or 24-bit color depth. Digital images can be reproduced with high fidelity at the micrometer scale by using a simple process that assigns sequence to any RGB value. Largely automated, this approach can be seen as miniaturized DNA-based painting.

An 8-bit monochrome palette of fluorescent nucleic acid sequences for DNA-based painting

The ability to regulate, maintain and reproduce fluorogenic properties is a fundamental prerequisite of modern molecular diagnostics, nanotechnology and bioimaging. The sequence-dependence of the fluorescence properties in fluorophores commonly used in nucleic acid labelling is here being exploited to assemble a color scale in 256 shades of green Cy3 fluorescence. Using photolithography, we synthesize microarrays of labeled nucleic acids that can accurately reproduce 8-bit monochrome graphics by mapping color to fluorescence intensity and sequence. This DNA-based painting approach paves the way for a full RGB scale array fabrication process.

l-DNA Duplex Formation as a Bioorthogonal Information Channel in Nucleic Acid-Based Surface Patterning

Photolithographic in situ synthesis of nucleic acids enables extremely high oligonucleotide sequence density as well as complex surface patterning and combined spatial and molecular information encoding. No longer limited to DNA synthesis, the technique allows for total control of both chemical and Cartesian space organization on surfaces, suggesting that hybridization patterns can be used to encode, display or encrypt informative signals on multiple chemically orthogonal levels. Nevertheless, cross-hybridization reduces the available sequence space and limits information density. Here we introduce an additional, fully independent information channel in surface patterning with in situ l-DNA synthesis. The bioorthogonality of mirror-image DNA duplex formation prevents both cross-hybridization on chimeric l-/d-DNA microarrays and also results in enzymatic orthogonality, such as nuclease-proof DNA-based signatures on the surface. We show how chimeric l-/d-DNA hybridization can be used to create informative surface patterns including QR codes, highly counterfeiting resistant authenticity watermarks, and concealed messages within high-density d-DNA microarrays.

Multi-level patterning nucleic acid photolithography

The versatile and tunable self-assembly properties of nucleic acids and engineered nucleic acid constructs make them invaluable in constructing microscale and nanoscale devices, structures and circuits. Increasing the complexity, functionality and ease of assembly of such constructs, as well as interfacing them to the macroscopic world requires a multifaceted and programmable fabrication approach that combines efficient and spatially resolved nucleic acid synthesis with multiple post-synthetic chemical and enzymatic modifications. Here we demonstrate a multi-level photolithographic patterning approach that starts with large-scale in situ surface synthesis of natural, modified or chimeric nucleic acid molecular structures and is followed by chemical and enzymatic nucleic acid modifications and processing. The resulting high-complexity, micrometer-resolution nucleic acid surface patterns include linear and branched structures, multi-color fluorophore labeling and programmable targeted oligonucleotide immobilization and cleavage.