http://www.nano.org.uk/articles/index.php?article=22 08 December 2009 NANO Magazine - Issue 7

Squeezing the medical laboratory onto a chip

Image Credit: NANO Magazine.

Having early access to accurate and reliable diagnostic information is a crucial part of medical treatment; it can improve the prognosis for patients by identifying diseases or conditions at a much earlier and more treatable stage; it can provide information on the ongoing effectiveness of therapies; and it can reduce the costs for increasingly cash-strapped healthcare systems by reducing the time spent in expensive hospital stays. For many patients, for example those with conditions like diabetes, it can be an important part of daily routine and essential self-testing. In-vitro diagnostic devices (IVDs) in many ways lend themselves to the application of nanotechnology. The devices are normally remote from the patient and any utilized nanomaterials, that otherwise might require extensive biological safety testing, do not come into direct contact with the body. The application of nanotechnology can come from the use of such materials, from the ability to engineer at the nanoscale and from the combination of different nanoscale disciplines in an integrated manner. The development of the lab-on-a-chip Since the early 1990s the term lab-on-a-chip (LOC) has become more and more familiar, even provoking interest in the popular press. The concept was invented, and the first LOC system developed at Stanford University, USA, in the mid-1970s, but it was not until some 15 years later that microfluidic engineering and sensor technologies developed sufficiently to allow new generations of LOCs to be developed. Now, further advances mean that engineering at the nanoscale can also be applied to add a new range of new functionalities.

The term lab-on-a-chip, sometimes also called micro-total analysis system (TAS), is usually applied to devices that integrate a variety of functions on a single chip or slide, usually of a few square centimetres or less, and that are capable of analysing very small fluid volumes down to picolitre levels. LOCs comprise a convergence of micro-, or in the latest versions, nano-fluidic engineering, electronics

and small-scale fabrication, often using techniques such a photolithography, in silicon, glass, plastics, ceramics or metal. LOCs will frequently integrate processes such as sample introduction and handling, preprocessing (e.g. dilution, cell lysis, filtering), separation (e.g. by electrophoresis or chromatography) and measurement/detection onto a single chip with associated electronic or optical systems. The microfluidic elements of the chip can include pumps, mixing areas, capillary channels, valves, heaters/coolers and, in some cases, miniaturised bioreactors.

Some of the advantages of LOCs include:

- extremely low consumption of reagents and analytes - fast heating or cooling - high surface to volume ratios - very fast analysis times due to the very small distances substances have to move or diffuse - a greatly improved control of analytical parameters - the possibility of carrying out large number of analyses in parallel - extreme compactness allowing the creation of desktop standalone modular and automated analytical systems - a reduction in fabrication costs, allowing mass production of disposable chips - a safer platform for chemical, radioactive or biological studies because of the integration of functions, the smaller volumes or masses of potentially hazardous materials and biological analytes, and lower stored energies

The extreme compactness of LOC designs could have an added importance in developing highly portable systems that could be used in some parts of the developing world that have a high prevalence of diseases but very limited access to modern, reliable testing tools.

Lab-on-a-chip appoaches are currently being applied in a wide range of medical uses including:

- the measurement of a wide range of biomolecules in blood and other body fluids immunoassays - the detection of bacteria, viruses and cancers DNA testing

Some new lab-on-a-chip approaches incorporating nanotechnology During the late 1980s and 1990s, developments in microfluidics and techniques like photolithography, driven also by initiatives such as the human genome project and the emerging need for early detection systems for hazards such as chemical and biological warfare agents, led to features being developed at smaller and smaller scales in lab-on-a-chip applications. In parallel with developments elsewhere, e.g. computer chip design, nanotechnology is now also being applied to LOCs bringing new functionalities due to the novel characteristics of materials at the nanoscale. These developments include:

- nanopores, e.g. of 1-2 nm diameter, for electrophoretic DNA sequencing - other nanoscale surface features or scaffolds, e.g. to faciliate the behaviour of fluids or to promote the immobilisation adhesion and growth of cells in integrated microbioreactors (-bioreactors) or cell arrays on a cell chip for protein studies and cell-membrane ion-channel studies.

Such -bioreactors or cell arrays will normally also include microfluidic systems designed to deliver nutrients and remove waste products to keep such cells in optimal conditions.

One current example of a cell array under development (CEA Grenoble: ToxDrop Project) utilises a system with a glass surface containing hydrophilic and hydrophobic areas and 800 drops per slide,

each drop containing 100 cells of different types that may be cultured for up to 5 days . Up to 50 parameters can be measured individually for each cell and the system is ultimately expected to be used for high throughput toxicity testing.

- superhydrophobic surfaces, e.g. to facilitate the movement, separation and mixing of tiny aqueous droplets and samples, e.g. by using magnetofluidics - nanoscale actuators, e.g. for valves, mixing or switches - nanowire, e.g. silicon or polymer, and carbon nanotube based biosensors - other new biosensor technologies, e.g. those based on protein nanoimprinting and nanopatterning, direct affinity sensing, resonating beam sensing, surface plasmon sensing and ion-channel sensing - micro- or nano-fluidic systems that can model some of the physiological conditions or stresses that cells are subjected to in-vivo, or which can facilitate cell-to-cell signalling interactions - novel detection systems based on field-effect sensors, electrical conductance, electrochemistry, magnetic fields, optical output (e.g. fluorescence, quantum dots) or acoustic signals, e.g. using piezoelectrics

The large variety of parameters that can be measured using different detection systems, and the large quantity of data that can arise from the individual assays undertaken on a LOC, also necessitate the development and integration of powerful bioinformatics tools, including adaptive and smart software into LOC-based systems.

While there is much progress in developing smaller, more highly integrated and more efficient LOC systems there are still many challenges to be overcome. As one approaches the nanoscale, physical and chemical effects change and become more complex. Some features cannot yet be scaled down and there are size limits below which cells cannot interact effectively which means designing new systems that can model, for example, metabolic processes in the mitochondria or other sub-cellular organelles.

The future evolution of lab-on-a-chip technologies The further development of LOC technology brings closer the possibility of developing systems that can be implanted into the body and that can sample and measure physiological and metabolic parameters in-vivo in real time, allowing doctors to continually monitor patients and track the progression of diseases and conditions, possibly with direct feedback to drug delivery systems or other implanted devices.

A further aim is the development of systems that are increasingly simple to use without specialist training and which can carry out a variety of accurate analyses very quickly using tiny samples, e.g. in emergency or field situations, or at home, e.g. smart and more patient-friendly diabetes monitoring devices. Other integrated systems capable of detecting down to single important marker biomolecules, individual bacteria or viral particles are also under development

The development of LOC systems based on human cells, possibly the patients own cells or even differentiated tissues in some cases, promises to contribute to the development of higher-throughput, more predictive and cheaper alternatives to animal test models for pharmaceutical development, screening and testing and in toxicity studies, e.g. those required under the amended Cosmetics Directive and the REACH Regulation of chemicals.

Richard Moore is Manager of Nanomedicine and Life Sciences at the Institute of Nanotechnology.

Source: NANO Magazine - Issue 7 /...