Gold Nanoparticles-Coated SU-8 for Sensitive Fluorescence-Based Detections of DNA

SU-8 epoxy-based negative photoresist has been extensively employed as a structural material for fabrication of numerous biological microelectro-mechanical systems (Bio-MEMS) or lab-on-a-chip (LOC) devices. However, SU-8 has a high autofluorescence level that limits sensitivity of microdevices that use fluorescence as the predominant detection workhorse. Here, we show that deposition of a thin gold nanoparticles layer onto the SU-8 surface significantly reduces the autofluorescence of the coated SU-8 surface by as much as 81% compared to bare SU-8. Furthermore, DNA probes can easily be immobilized on the Au surface with high thermal stability. These improvements enabled sensitive DNA detection by simple DNA hybridization down to 1 nM (a two orders of magnitude improvement) or by solid-phase PCR with sub-picomolar sensitivity. The approach is simple and easy to perform, making it suitable for various Bio-MEMs and LOC devices that use SU-8 as a structural material

Diffractive encoding of microparticles for application to bead-based biological assays

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Microparticle encoding technologies for high-throughput multiplexed suspension assays

The requirement for analysis of large numbers of biomolecules for drug discovery and clinical diagnostics has driven the development of low-cost, flexible and high-throughput methods for simultaneous detection of multiple molecular targets in a single sample (multiplexed analysis). The technique that seems most likely to satisfy all of these requirements is the multiplexed suspension (bead-based) assay, which offers a number of advantages over alternative approaches such as ELISAs and microarrays. In a bead based assay, different probe molecules are attached to different beads (of a few tens of microns in size), which are then reacted in suspension with the target sample. After reaction, the beads must be identifiable in order to determine the attached probe molecule, and thus each bead must be labelled (encoded) with a unique identifier. A large number of techniques have been proposed for encoding beads. This critical review analyses each technology on the basis of its ability to fulfil the practical requirements of assays, whilst being compatible with low-cost, high-throughput manufacturing processes and high-throughput detection methods. As a result, we identify the most likely candidates to be used for future integrated device development for practical applications

Microfabricated barcodes for particle identification

Microfabricated barcodes formed in SU8 photopolymer are presented as a method for identifying individual particles based on their diffraction patterns. Two designs of barcoded particles are considered; a single layer SU8 process and a two layer SU8 process. Theoretical data shows that for ideal barcoded particles it should be possible to obtain several million uniquely identifiable codes for particles as small as 50 microns in length

Fabrication of diffraction-encoded micro-particles using nano-imprint lithography

A nano-imprint lithography technique is described for fabrication of optically encoded microparticles (diffractive barcodes). The particles are fabricated from SU8 - a material which can be processed lithographically, and which can be used for attachment of molecular tags. The barcodes are identified by their unique diffraction pattern

Holographically encoded microparticles for bead-based assays

We demonstrate a re-writable, high capacity holographic encoding technique for multiplexed bead-based suspension assays. The microparticles are made from SU8 doped with a photochromic diarylethene dye and manufactured using multilayer photolithography and dry etching. Each particle is encoded with a unique hologram, whose diffraction pattern consists of bright and dark regions, representing a binary number that identifies the particle. Theoretically up to 1024 unique codes are available on a 100 µm particle using this method, when the code is read with a standard 2/3" CMOS camera. Encoding capacities of 512 unique codes have been demonstrated on a 500 µm SU8 particle. The code is thermally stable for 3 days at 25 °C, and once written, the code can be erased and re-written once whilst still remaining readable. The code can be written into the particle during an assay experiment (no pre-encoding is required) and requires simple optics for reading