The process of miniaturization in biochip technology has been revolutionized by the introduction of nanotechnol-ogy—a term used for the creation and utilization of materials, devices, and systems through the control of matter on the nanometer-length scale, i.e., at the level of atoms, molecules, and supramolecular structures. The term is applied for the construction and utilization of functional structures with at least one characteristic dimension measured in nanometers (a nanometer is one billionth of a meter (10_9 m). Nanotechnology is applied for healthcare when it is referred to as nanobiotechnol-ogy. The topic is discussed in more detail elsewhere. Nanobiotechnology has also been applied to molecular diagnostics and referred to as nanodiagnostics. The assigned title of the article ''lab-on-a-chip'' indicates focus on nanofluidics. However, several nanotechnologies shown in Table 1 are used for molecular diagnostics and some of these can be applied in the form of nanochips.
Nanoarrays are the next stage in the evolution of miniaturization of microarrays. Whereas microarrays are prepared by robotic spotting or optical lithography, limiting the smallest size to several microns, nanoarrays require further developments in lithography strategies used in nanotechnology and include the following:
• Electron beam lithography.
• Dip-pen nanolithography (DPN).
• Scanning probe lithography.
• Finely focused ion beam lithography.
• Nanoimprint lithography.
High-throughput protein arrays allow the miniaturized and parallel analysis of large numbers of diagnostic markers in complex samples. This capability can be enhanced by nanotechnology. Dip-pen nanolithography technique has been extended to protein arrays with features as small as 45 nm, and immunoproteins as well as enzymes can be deposited. Selective binding of antibodies to protein nanoarrays can be detected without the use of labels by monitoring small (5-15 nm) topographical height increases in atomic force microscopy (AFM) images.
Protein Nanoarrays (BioForce Nanosciences, Ames, IA, USA) contain up to 25 million spots per square centimeter. They can be used to detect protein-protein interactions. BioForce's NanoReader uses a customized AFM to decipher molecules on a NanoArray chip. The company was awarded a grant in 2002 by the U.S. Department of Defense for breast cancer research titled, ''Protein Nano-arrays for Studying Malignant Progression in Breast Cancer Cell Lines.'' The project constructed a nanoscale protein array platform and used it as a basic research tool to study alterations in cellular signaling pathways that accompany breast cancer disease progression.
Table 1 Nanotechnologies with potential applications in molecular diagnostics
Microfluidic chips for nanoliter volumes: NanoChip Optical readout of nanoparticle labels NanoArrays Protein nanoarrays Nanoparticle technologies Gold particles Nanobarcodes
Magnetic nanoparticles: Ferrofluids, supramagnetic particles combined with MRI Quantum dot technology Nanoparticle probes Nanowires Nanopore technology
Measuring length of DNA fragments in a high-throughput manner
Multiple combined tests (such as protein and DNA) to be performed on the same disposable chip Prostate-specific antigen binding to antibody DNA nanomachines for molecular diagnostics Nanoparticle-based immunoassays
DNA-protein and nanoparticle conjugates Nanochip-based single-molecular interaction force assays Resonance light scattering technology Nanosensors
Living spores as nanodetectors Nanopore nanosensors Quartz nanobalance DNA sensor
Probes encapsulated by biologically localized embedding
Nanosensor glucose monitor
Photostimulated luminescence in nanoparticles
Optical biosensors: Surface plasmon resonance technology
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