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Nanotechnology-based lab-on-a-chip devices

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Related terms
Background
Methods
Research
Implications
Limitations
Safety
Future research
Author information
Bibliography

Related Terms
  • Biochip, Biosite® chip, charged-coupled device (CCD), chemiluminescence, immunoassay, ink-jet microarrays, lab-on-a-chip, microbeads, microchannels, microelectromechanical systems (MEMS), microfluidics, microwells, molecular diagnostics, nanochip, nanofluidics, nanomedicine, nanoparticle, nanotechnology, nucleic acid assay, nucleotide, photolithography, photomask, polyacrylamide gel, quartz, robotic contact printing arrayer.

Background
  • General: Genes, or segments of deoxyribonucleic acid/DNA, are considered the building blocks of life because they provide instructions for all cells in the body. Genes, which are located inside of cells, control an organism's development and functions by instructing cells to make new molecules (usually proteins). Proteins are organic compounds composed of amino acids; the sequence of the amino acids in a protein is defined by genes. Proteins are required for the growth and maintenance of the body.
  • DNA is a long, thread-like (double-helix) molecule made up of large numbers of nucleotides. Nucleotides are the building blocks of DNA and are made of nitrogen bases, sugars, and phosphate. Nitrogen bases are of two types: purines, such as adenine (A) and guanine (G), and pyrimidines, such as cytosine (C) and thymine (T). The sequence of DNA bases is the carrier of genetic information. Long strands of nucleotides form nucleic acids. RNA (ribonucleic acid) is a nucleic acid that aids in protein synthesis, which is important for the growth and maintenance of the body. RNA is formed under the direction of DNA, and both help to form amino acids, which are the building blocks of protein.
  • Nanotechnology: Nanotechnology is the field of research that deals with the engineering and creation of things from materials that are smaller than 100 nanometers (one-billionth of a meter) in size, especially single atoms or molecules. Nanotechnology-based materials are promising tools for biomedical analysis. Biomedicine is the field pertaining to those aspects of the natural sciences that relate to medicine. Because of several scientific advances, the global nanotechnology market is expected to be over a trillion dollars by 2015.
  • Lab-on-a-chip (LOC): LOC is a device that combines several laboratory functions on a single chip that is only a few millimeters to a few square centimeters in size, an example of miniaturization. LOC devices reduce the laboratory and all of its capabilities to a microscopic level, thereby helping to provide point-of-care (bedside) medicine. LOC involves the use of extremely small fluid volumes (<1 picoliter, i.e., one trillionth of a liter (10-12)). LOC is a subset of microelectromechanical systems (MEMS devices), which are also known as micro total analysis systems (µTAS). MEMS is a technology of the very minute (small),similar to nanotechnology. MEMS is used to perform chemical analysis by combining laboratory processes on a single chip.
  • Scientists and engineers have borrowed miniaturization (the creation of small objects) from the computer industry to develop laboratory devices and procedures that fit on a wafer or microchip. Biochip is a broad term indicating the use of microchip technology in molecular biology; it can be defined as arrays (collections) of selected molecules produced by a biomolecule (living organism) immobilized on a surface.
  • The chip contains one or more sample deposit areas, measuring devices, mixing chambers, or fluid channels to move the mixtures around, and reaction chambers that are temperature-controlled. The microchannels are manufactured to different sizes, which enable the fluid to flow from one location to another.
  • Microfluidic system (lab-on-a-chip technology): Microfluidics is a broader term used for LOC. Microfluidics involves the handling of minute amounts of fluids. A microfluidic instrument may be used in the field (bedside) by extraction or separation of a target molecule or analyte, preferably a nucleic acid (DNA), from a fluid-based sample, which is then loaded on a glass chip. This technology is called "lab-on-a-chip" because it represents a complete laboratory in microscale (on a chip). This approach may be used for the early detection of several diseases, including cancer, because it provides fast and accurate results.
  • Uses: LOC has widespread applications in various fields. LOC may be used for detecting disease-causing organisms, such as bacteria and viruses. It is commonly used for bedside diagnostics or in the field because the chip is so small that it can be easily carried anywhere to conduct the tests. The need for transportation of samples to a remote testing facility is also avoided by using LOC, thus saving time. Hence, LOC facilitates the determination of the cause of the infection or disease at the bedside itself, thereby assisting in early the initiation (start) of treatment and preventing complications related to the infection or disease.
  • LOC is also used for immunoassays and nucleic acid analysis. An immunoassay is a test that uses the binding of antibodies to antigens to identify and measure certain substances, such as hormones. A hormone is a chemical released by a gland or tissue that has a specific effect on tissues elsewhere in the body. An antigen is a substance that is capable of causing an immune response in the body. Antibodies are proteins manufactured by the body in response to an antigen; they bind with the antigen to inhibit or destroy it. Immunoassays may be used to diagnose diseases; the test results may provide information about a disease that may help in planning treatment.
  • Nucleic acid analysis is used for examining DNA or RNA samples to detect any variation in the gene sequence (i.e., a mutation) that in turn may lead to the development of diseases such as cancer. LOC has also been used for clinical diagnostics (the detection of disease), monitoring disease states, and biochemical analysis by qualitative (i.e., determining the nature) and quantitative (numerical) analysis of chemical substances or proteins from the sample of interest (e.g., cancer markers in blood).
  • LOC can be applied to analyze DNA, proteins, etc., as in DNA microarrays and protein microarrays. A microarray is a collection of miniaturized tests arranged on a surface that permits many tests to be performed simultaneously, or in order to achieve higher throughput (output). The sample spot sizes in microarrays are usually less than 200 micrometers in diameter. Gene expression microarrays can analyze the expression of many genes at once. This genetic method has been used to identify new genes associated with certain diseases, to classify cancerous tumors (growths), and to predict patient outcomes.

Methods
  • General: Genes, or segments of deoxyribonucleic acid/DNA, are considered the building blocks of life because they provide instructions for all cells in the body. DNA is a long, thread-like (double-helix) molecule made up of large numbers of nucleotides. Nucleotides are the building blocks of DNA and are made of nitrogen bases, sugars, and phosphate. Nitrogenous bases are of two types: purines, such as adenine (A) and guanine (G), and pyrimidines, such as cytosine (C) and thymine (T). Long strands of nucleotides form nucleic acids. Proteins are organic compounds composed of amino acids; the sequence of the amino acids in a protein is defined by a gene. Proteins are required for the growth and maintenance of the body. Antibodies are an important part of the immune system because they identify harmful substances that enter the body and trigger other immune cells to destroy the invading substance.
  • Lab-on-chip (LOC) or microfluidic devices perform operations on small bodies of fluids and/or on particles suspended in a fluid, for example, a colloidal suspension. Colloids are collections of atoms or molecules in a submicroscopic state (finely divided), dispersed in a gas, liquid, or solid. Commonly employed fluids include whole blood samples, bacterial cell suspensions, protein or antibody solutions, and various buffers and reagents. A solution is the incorporation of a solid, liquid, or gas into a liquid, resulting in a homogeneous single phase. A reagent is any substance added to a solution of another substance to participate in a chemical reaction. A buffer is a chemical used to maintain the hydrogen-ion concentration (pH) within limits by neutralizing both acids and bases. Suspension is a condition or state of a substance in which particles are dispersed but not dissolved in a liquid.
  • Microfluidic chip: A microfluidic chip is made of fused silica called quartz. This technology uses a network of channels and wells that are engraved or etched onto glass to build minilabs. The microfluidic chip contains one or more sample deposit areas, measuring devices, mixing chambers, or fluid channels to move the mixtures around, and reaction chambers that are temperature-controlled. The microchannels are manufactured to different sizes, which enable the fluid to flow from one location to another.
  • Many different techniques may be used to pump the fluids from one location on the chip to another. For instance, capillary force is the ability of a substance to draw another substance into it. Electrophoresis, a technique that uses electrical current to separate and analyze proteins and DNA by electrical charge, may also be used.
  • Biosite® chip: Biosite chip is a commercial brand of a microfluidic chip that is manufactured by Biosite, Inc., San Diego. In this system, a drop of a patient's blood is placed on the chip. Capillary force is used to pull the drop of blood inside the microfilter; it is separated later by a microseparator. A microcomputer analyzes the data and gives results within 15 minutes. The system is not completely integrated (the computer is not present on the chip), but it is small and portable. This test is conducted to check if an individual has suffered a heart attack by detecting three proteins released from the heart muscle in cases of heart attack. The proteins are present in abnormal quantities only in case of heart diseases such as heart attack. Hence, the identification of the presence of the proteins helps in early diagnosis, facilitating quicker treatment.
  • Microarray chips: A microarray is a collection of miniaturized tests arranged on a surface that permits many tests to be performed simultaneously in order to achieve higher output. The commonly used solid or physical support materials for the microarray chips include glass slides, silicon, microwells/nanowells (extremely small wells), nitrocellulose membranes, and microbeads. A nitrocellulose membrane is a thin layer formed by a mixture of pulpy or cotton-like polymer (large chains of molecules) of cellulose (a form of glucose), nitric acid, and sulfuric acids.
  • It is important that the chip surface should have certain properties, which include: the ability to immobilize the target molecules such as proteins; the ability to maintain the conformation (structural arrangement) and functionality of the target molecules; chemical stability (i.e., it should not break down) before and after the coupling procedures (the joining of target molecules on the physical support surface); the ability to achieve the maximum binding capacity to the target molecules; and compatibility with different standard microarray equipment and detection systems.
  • DNA microarray: DNA microarrays, or DNA chips, are miniaturized chemical reaction areas or spots affixed to a solid supporting material or substrate in a regular pattern for genetic analysis. This is used to test DNA or RNA fragments by immobilizing or fixing the target sequence along with a fluorescent marker onto the surface of the chip and hybridizing (binding) them with a probed sample. A probe is a sequence complementary to the target sequence (e.g., DNA). When the specific target is hybridized with the probe, the fluorescent marker releases colored light, which is scanned; the data analyzed by a computer to identify the target sequence. Hybridization refers to the binding of the probe with the target complementary sequence, forming a hybrid. The advantage of microarray technology is that multiple markers or thousands of DNA sequences may be detected and identified in a single reaction, thus assisting in timely treatment decisions and management of the disease.
  • Microarray chip construction: The LOC fabrication may be an automated or manual process, involving imprinting of externally manufactured and purified molecules on an array or a slide surface. The spacing of the target molecule (e.g., protein) spots on the slide surface or microwells depends on the size of the molecular sample. For example, antibody arrays typically have 375 micrometer spacing. Unlike the microfluidic chip, microarrays involve the imprinting of externally manufactured molecules on a slide surface.
  • Printing extremely small quantities of molecules on a slide surface is challenging, as it needs to have required densities (the concentration of the mass of the substance per unit volume), excellent reproducibility, and good binding capacity. These have been simplified with the help of automated capture molecule imprinting methods, which include robotic contact printing, ink-jetting, piezoelectric spotting, and photolithography.
  • Robotic contact printing arrayers have very tiny pins that deliver subnanoliter (lesser than one billionth of a liter) target molecule volumes directly on the surface of microchips. The contact printing robots have certain limitations, i.e., they are unable to align their pins to prefabricated structures and need to touch the array surface. Ink-jetting involves noncontact robotic array printers that deposit nanoliters (one billionth of a liter) to picoliters (one trillionth of a liter) of protein droplets to polyacrylamide gel packets and microwells. Polyacrylamide is a large compound that is formed from several small molecules (polymers) of the chemical acrylamide and is used to form a gel matrix (medium) in electrophoresis. A matrix is a surrounding or binding substance within which something else (other particles or a solution) is contained or embedded. Because of its capacity to separate molecules with high resolution, polyacrylamide is also used to separate nucleic acids that are small or those that differ in length by as little as one base pair. A base pair includes two nucleotide sequences located on opposite complementary DNA or RNA strands that are connected by hydrogen bonds.
  • Ink-jet microarrays or spotters are commonly of two types, namely piezoelectric spotting and thermal spotting. Sample droplets are delivered by electrical stimulation in the piezoelectric spotting method and by thermal stimulation (i.e., caused by heat) in the thermal spotting method. In photolithography, ultraviolet (UV) light is passed through a transparent or translucent membrane, which acts as a photomask (like a stencil) on to the surface of the array slide. The antibody or other capture molecules are imprinted only on to the points on the array slide that are activated by the stenciled image.
  • Detection methods (readout): A number of different detection methods are available to affix the reactive target molecule onto microarray chips: labeling (attaching) the protein or small molecule probes with fluorescent, affinity, or radioisotope tags detected by fluorescent, colorimetric, or chemiluminescent methods. A radioisotope is an isotope that changes to a more stable state by emitting radiation. The chemiluminescence method uses a chemical dye that binds with a protein (e.g., biotin) labeled to the probe; the chemical reaction emits light (luminescence), which is detected by luminescent imager. Similarly, in the colorimetric detection method, a colored staining reagent is detected by a colorimeter.
  • Generally, fluorescent detection is the preferred method, as it is safe, effective, and sensitive, and is compatible with the available charge-coupled device (CCD) cameras or microarray laser scanners. CCDs are devices used to form images electronically with the help of a silicon layer, which when struck by light releases electrons. CCD cameras capture fluorescent images through photoactive signals transmitted as electronic signals. However, affinity tags can also be used to label the microarray probes. Affinity tags or purification tags are short sequence of amino acids that can be detected by colorimetry.
  • Advantages: Some of the advantages of using the lab-on-chip platforms include simplified handling, provision of fast and accurate results, reduced consumption of the sample and reagents with minimal waste production, and low production cost and instrument size. Since only small amount of reagents are required, it helps in reducing the cost. Also, some reaction products may be harmful to humans; lab-on-chip devices reduce human interaction, thereby decreasing the harmful effects of the reagent products. When LOCs are produced in large quantities, it will be cost-effective because they are fabricated using nanotechnology. Nanotechnology is the field of research that deals with the engineering and creation of things from materials that are smaller than 100 nanometers (one-billionth of a meter) in size, especially single atoms or molecules.

Research
  • General: A lab-on-a-chip is a device that combines several laboratory functions on a single chip that is only a few millimeters to square centimeters in size, an example of miniaturization. LOC devices reduce the laboratory and all of its capabilities to a microscopic level.
  • T-cell activation: Scientists have conducted tests to activate T-cells on microfluidic chips to make them available for future treatment purposes. T-cells are types of white blood cells called lymphocytes, which help fight against disease and infection. It was found that T-cells were activated by expressing the T-cell activation marker molecule (CD69). This approach may be used for regulating stem cell differentiation, which could be used for future treatment. Differentiation is a change in a cell resulting in its specialization for specific functions, such as a nerve cell. A microfluidic chip is made of fused silica called quartz. This technology uses a network of channels and wells that are engraved or etched onto glass to build minilabs.
  • Biostatus of astronauts: Scientists are conducting studies to develop lab-on-chip devices to monitor astronauts' health in space. This may help in monitoring several indicators of health such as blood pressure, breathing and heart rates, oxygen and carbon dioxide levels in the blood, calcium concentration in the blood, and the rate of muscle atrophy (a decrease in muscle size) and bone mass loss. Bone mass is a measure of the amount of calcium contained in a certain volume of bone. These tests facilitate the monitoring of the health of the astronauts from the ground and also the determination of the exact effects of a weightless environment on humans.

Implications
  • General: DNA is a long, thread-like (double-helix) molecule made up of large numbers of nucleotides. Nucleotides are the building blocks of DNA and are made of nitrogen bases, sugars, and phosphate. Long strands of nucleotides form nucleic acids. Proteins are organic compounds composed of amino acids; the sequence of the amino acids in a protein is defined by a gene. Proteins are required for the growth and maintenance of the body.
  • Lab-on-a-chip (LOC) is a device that combines several laboratory functions on a single chip that is only a few millimeters to square centimeters in size, an example of miniaturization. LOC devices reduce the laboratory and all of its capabilities to a microscopic level, thereby helping to provide point-of-care (bedside) medicine.
  • The nanotechnology-based LOC devices help in conducting many tests simultaneously or in parallel, in order to achieve higher throughput (output). The tests help in detecting cell-level dysfunctions at an early stage, in addition to disease-causing organisms (pathogens), thus helping in disease diagnosis. This may also help identify and classify (subtype) pathogens, thus facilitating the development of personalized medicine.
  • Detection of disease-causing organisms and diseases: Scientists have invented an inexpensive, portable, and integrated microfluidic instrument that is capable of performing amplification (the production of multiple copies of DNA or RNA) and analysis on a single sample. A microfluidic instrument may be used in the field, separating a target molecule or analyte, preferably a nucleic acid, from a fluid-based sample loaded on a glass chip. The sample may be either water-based or a biological fluid sample. The combination of portability, cost-effectiveness, and high performance helps in easy detection of disease-causing organisms and also has the potential to make healthcare more accessible.
  • Protein characterization: An LOC device is a versatile tool for genetic analysis of proteins and protein characterization, and a protein's interactions with other proteins, nucleic acids, enzymes, small molecules, and drugs, and for comparison of proteins in normal state and disease conditions. This will help in understanding impaired protein pathways, the production of abnormal proteins and chemicals, and the proteins to be targeted for treatment of diseases. An enzyme is a substance that increases the speed of a chemical reaction without being changed in the overall process.
  • Drug development: LOC is widely used, especially in the development of novel drugs targeting particular proteins and pathways, improving existing drugs, and understanding drug response in terms of interactions and toxicity (poisonous reactions). Also, LOC has the potential to screen more drugs for defects in manufacturing in less time, thereby reducing the cost of drug development.
  • Protein biomarkers/tumor markers: A biomarker is a physical, functional, or biochemical indicator. It is a substance introduced into an organism to observe the functions of the organs and other aspects of health. A tumor marker is a substance released into the circulation by tumor tissue, the detection of which indicates the presence of tumor. LOC technology has been used to discover novel protein biomarkers, which may help in the detection and/or diagnosis of a disease, the monitoring the course of a disease, or the indication of the disease stage. Examples include protein biomarkers or tumor markers for breast, intestinal, or skin cancers, etc. The tumor markers can be analyzed and quantified (counted) from very minimal biopsy or tissue extracts, thereby creating new possibilities for monitoring cancer treatment and for therapy. A biopsy is a diagnostic test in which tissue or cells are removed from the body for examination under a microscope.
  • Biochemical warfare agent detection: LOC devices may be used to detect a pathogen in the case of a bioterrorism attack, thereby facilitating immediate treatment. A bioterrorism attack is the deliberate release of viruses, bacteria, or other agents to cause large-scale illness or death in people, animals, or plants. For example, Bacillus anthracis Ames, which is a bacterium that lives in a spore and causes inhalational anthrax, may be used as biochemical weapon. According to the U.S. Centers for Disease Control and Prevention (CDC), anthrax spores were deliberately spread in powder-containing envelopes through the U.S. postal system in 2001, causing widespread panic. In such cases, miniaturized devices help in detecting the pathogens.
  • Identification of pathogens affecting environment: Environmental monitoring involves measuring the concentrations of gases and pollutants in a certain area. For example, lab-on-chip devices have been used for the field detection and quantification (counting) of Karenia brevis, a microscopic, single-celled organism (algae) that may cause "algal bloom" in coastal waters. The algal bloom is commonly known as "red tide," as it accumulates rapidly and forms dense, visible patches near the water's surface, leading to discoloration of the water. This phenomenon causes a lot of problems for coastal communities and leads to fish and mammal deaths. Also, tourism and fisheries are affected due to the accumulation of the algae. These devices have been a valuable tool for monitoring Karenia brevis in field environments, thereby ensuring the safety of shellfish harvested for human consumption. Since the tool helps monitor the water, it can help prevent contamination, thereby aiding in protecting the shellfish.

Limitations
  • One limitation is that the sensor in the lab-on-chip (LOC) devices may degrade at the sensing surface, causing difficulty in modifying specific surfaces on the miniaturized device. Advancements made in the manufacture of LOC devices (such as the incorporation of beads as a barrier for reactions in miniaturized devices) have helped overcome this limitation. LOC is a device that combines several laboratory functions on a single chip that is only a few millimeters to square centimeters in size, an example of miniaturization. LOC devices reduce the laboratory and all of its capabilities to a microscopic level, thereby helping to provide point-of-care (bedside) medicine.
  • Other problems may arise as a result of improper immobility (fixing) of the molecules to the microarray surface for the whole procedure, leading to inaccurate results. Some fluorescent labels used for detection may alter the probe's ability to interact with the target proteins, thereby impairing the protein interactions on the microarray, which may lead to incorrect results. A microarray is a collection of miniaturized tests arranged on a surface that permits many tests to be performed at the same time in order to achieve higher throughput (output).

Safety




Future research
  • General: Research is ongoing to develop new powerful applications and improve the fabrication techniques of lab-on-chip (LOC) devices, facilitating an explosive growth in point-of-care (bedside) medicine, wherein simple, inexpensive instruments allow tests to be performed quickly by untrained personnel at the patient's side. LOC is a device that combines several laboratory functions on a single chip that is only a few millimeters to square centimeters in size, an example of miniaturization. LOC devices reduce the laboratory and all of its capabilities to a microscopic (very small) level, thereby helping to provide point-of-care (bedside) medicine.
  • LOC devices are being developed to identify several diseases or infections, such as AIDS, tuberculosis, severe acute respiratory syndrome (SARS), and pneumonia. AIDS (acquired immune deficiency syndrome) is caused by the human immunodeficiency virus (HIV). HIV primarily attacks the immune system, making the patient extremely vulnerable to opportunistic infections, which occur in people who have weakened immune systems. Tuberculosis (TB) is a bacterial infection caused by a bacterium called Mycobacterium tuberculosis. These bacteria usually attack the lungs but can also damage other parts of the body, such as the lymph nodes, kidneys, and bones. SARS is a contagious respiratory infection caused by a virus; it sometimes can cause death. Pneumonia is an infection of one or both lungs, usually caused by bacteria, viruses, or fungi.
  • LOC devices are also likely to be used for the screening and detection of many noncommunicable (non-infectious) diseases, such as cancer, heart diseases, diabetes, leukemia (blood cancer), and several central nervous system-related disorders. Diabetes, also known as diabetes mellitus, is a chronic (long-term) health condition where the body is unable to properly break down glucose (sugar) in the blood, leading to increased blood sugar levels.
  • Oral cancer: Oral cancer, a deadly and disfiguring disease, has a poor prognosis (outcome) and hence early identification of the cancer is important for improving the survival rate among affected individuals. Early detection may be possible with a mass screening that requires a rapid diagnostic test. LOC technology holds the promise of replacing laboratory techniques that require sophisticated equipment and elaborate processing by skilled persons with miniaturized, automated, and inexpensive diagnostic devices.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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