) |
(click to enlarge) Scanning electron micrograph of an asymmetric Vivid Plasma Separation Membrane by Pall Life Sciences (Ann Arbor, MI).(Photo courtesty Pall Life Sciences)
|
IVDs based on traditional immunoassay procedures and immunochromatographic test strip materials have long been a hallmark of the biotechnology industry. But recent scientific discoveries, the identification of novel biomarkers indicative of disease, and the increased sensitivity of new detection systems have spurred expansion of the IVD market beyond core technologies and procedures. Also, molecular diagnostics has become a critical technology for disease detection, characterization, and susceptibility identification, and can help us understand drug responses and interactions. With the world’s population aging, the integration of molecular diagnostics–based test procedures into traditional therapies will become routine.
During the past 20 years, a variety of world events have enlarged the diagnostics market beyond its traditional healthcare realm and into other disciplines such as microbial and veterinary diagnostics. Global concerns regarding the safety of the food supply, the proliferation of zoonotic diseases afflicting humans interacting with various species, and the threat of bioterrorism have transformed these diagnostic disciplines into areas of heightened research interest.
As much as the IVD market grows, and even as new diagnostic disciplines emerge, many of the well-established diagnostic techniques continue to be employed as a basis for new tests. These techniques and test platforms incorporate membranes, filters, and other solid support materials to facilitate diagnostic determination. Microbial and veterinary diagnostics are utilizing traditional immunoassay and nucleic acid test procedures for the identification of pathogens in human, animal, and environmental samples, but with more-stringent requirements for sample purification. With each new diagnostic test, one critical aspect remains constant—the need to generate high-quality samples for analysis. And samples that are becoming more complex demand specialized materials, membranes, and filters for their preparation. Membrane-based sample preparation has become a critical component of the IVD development scheme.
Sample Collection
The first stage of a diagnostic test is collection of the sample. Like sample preparation, sample collection is an area of increasing importance for ensuring the integrity of the sample. For example, protein profiles of key biomarkers may be altered as a result of up- or down-regulation following sample collection. This alteration can have negative consequences for the downstream analysis of the sample. Optimized collection materials, however, can help stabilize the sample and minimize the alteration of protein profiles.
To minimize the amount of manipulation following sample collection, membranes and filter materials, in conjunction with stabilization reagents, are becoming a common platform. They offer an easy-to-use mechanism for collecting and handling a sample before downstream processing. Filter media and papers (polyester, cellulose, depth media) can be used for storing and archiving collected samples for later analysis or long-term storage.
With the migration of some diagnostic testing from clinical laboratories to doctors’ offices and remote field locations, sample-storage needs have expanded. As with collection, it is important to ensure that the conditions of storage of a diagnostic sample do not deleteriously affect the target analytes. Advances in the field of filtration, such as surface modification and material optimization of various sorts, have led to the development of filter materials that can be used as a storage and archival substrate for diagnostic samples without degrading enzymatic, nucleic acid, or protein profiles. These materials have facilitated the expansion of home sample-collection applications. Test users place the sample on cards that are then mailed to physicians’ offices or reference laboratories for testing.
Sample Preparation
Sample preparation has become integral to the performance of diagnostic assays. As the IVD market expands beyond clinical diagnostics to veterinary medicine, environmental and agricultural science, and industrial applications, the types of samples to be assayed are becoming more complex. Typically, they are unfit for processing without a preparation step. Nonclinical samples can be contaminated with dirt, debris, and particulate matter, all of which must be removed in order to obtain a pure sample for analysis. In addition, many clinical samples require a cleanup or complexity reduction step before an analysis can be done. Patient-to-patient variation in whole blood samples, for example, is driving a need to obtain plasma in order to reduce assay variability for clinical analysis.
Traditional laboratory sample-preparation techniques, such as centrifugation, are prevalent, but the demand to minimize dependency on laboratory equipment is driving the industry to consider integrating membrane-based sample-preparation materials upstream of the analytical event. By eliminating the need for centrifugation, membranes and filtration materials are allowing blood-based diagnostics to move to the point of care (POC).
Filtration and membrane-based platforms are well accepted sample-preparation methods because they can be integrated into a variety of assay schemes. In addition, specialized membranes and filters have been developed that are designed for integration into an assay, which can help IVD manufacturers optimize product performance.
For clinical applications, membranes are available that isolate specific populations of cells for analysis. These membranes can also perform selective removal, to prevent interference with the assay itself. Another advancement is the development of materials that generate high-quality plasma from whole blood samples with minimal levels of hemolysis. Specialized materials for plasma separation allow assay developers and clinicians to shift their focus away from the central laboratory and its reliable electrical supply and consider the provision of diagnostic services in remote locations. Filtration industry advances such as these are facilitating the expansion of IVD technology beyond its traditional settings and markets.
Molecular diagnostic technology increasingly is being used as an IVD testing platform. The quality of any diagnostic protocol, including those that use molecular detection methodologies such as polymerase chain reaction, multiplexing, and mass spectroscopy, depends very much on the quality of the sample that is introduced into the test. An inherent aspect of molecular-based techniques is that the original sample typically is unfit for direct processing. Often, the assay requires a highly purified nucleic acid or protein sample to be generated prior to analysis. Without the presence of a high-quality target molecule, any molecular diagnostic analytical technique is likely to fail. The use of membranes, filters, and activated-solid support materials allows for the specific isolation and concentration of minute quantities of target analytes. These separation materials can also remove contaminants to ensure that the sample is free from interfering substances.
Support for Downstream Analysis
Sample preparation procedures, methodologies, and materials are growing in importance for diagnostic assay development. Also increasing at a rapid pace is the development of next-generation instrumentation for determining diagnostic test results. Each year, advances in instrument sensitivity are pressuring the clinician to ensure that clean samples are introduced into the detection system.
These advances in both test and instrument sensitivity have changed the requirements for sample preparation. The incorporation of membranes and filters into sample preparation devices generates robust mechanisms that result in highly purified samples free from contaminants. This allows for assay sensitivity levels to increase and ultimately reduces the amount of starting sample that is required.
Sample manipulation should be kept to a minimum in order to maintain the sample’s integrity and not jeopardize assay sensitivity. Separation materials and membranes to address these concerns are available. They can be designed into IVD devices, test strips, and platforms to create an integrated device that minimizes sample handling and prevents sample loss. Sample-preparation applications in which filters can be used include prefiltration and clarification, target capture through the immobilization of analyte-specific ligands to a membrane, selective isolation of cells or subsets of cell populations, and specialized separation of blood components.
Solutions are available to address the problem of nonspecific binding. Filters and membranes for a variety of sample-preparation applications have been optimized to minimize sequestering of samples and target analytes while maximizing sample recovery. Manufacturers of membranes and filters for IVDs are going beyond traditional protein binding data and demonstrating that the materials do not bind key diagnostic biomarkers either. Continuing advancement in the development of specialized membranes for critical sample-preparation procedures in diagnostic analysis helps assay developers lower the limits of detection and increase the overall sensitivity of the assay.
POC Capabilities
The primary use for lateral-flow and dipstick-style IVDs has been routine testing for pregnancy and glucose in the over-the-counter (OTC) sector. These formats have served as well as replacements for standard immunoassays in a clinical setting.
Numerous factors have been driving the expansion of both the OTC and clinical POC testing platforms. These include the number of target analytes, infectious diseases, and chronic illnesses that are now able to be tested by traditional lateral-flow technology. The decentralization of healthcare from hospitals to satellite offices, pharmacies, and other patient-care sites, along with the demand for rapid diagnosis, has increased the call for more-integrated IVD devices that require no additional sample handling and preparation.
Membranes and specialized filters that perform the functions of sample preparation, clarification, blood separation, and cell selection can be integrated into diagnostic devices and test strips to eliminate requirements for laboratory space, equipment, and trained personnel. The use of membranes as the sample-preparation mechanism, in conjunction with the traditional conjugate pads, nitrocellulose membrane (or other reaction membrane), and absorbent pads, is helping to streamline the assay work flow. If a sample is viscous or filled with particulate matter and debris, a filter material or membrane used as a sample pad will remove interfering substances from the sample before it reaches the conjugate pad. Membranes used for prefiltration, when integrated into an immunochromatographic test strip, help minimize background and the likelihood of false positives or negatives due to interfering substances.
Many IVD tests are now requiring plasma as the starting sample. Without the use of centrifugation or other blood separation techniques to process the whole blood sample, plasma-based IVD tests cannot be performed outside of a central laboratory. Membrane manufacturers now have developed products specifically to address this need. High-quality plasma can be generated by means of microporous materials that deliver plasma to the IVD test strip without hemolysis or binding diagnostic biomarkers. Continuing IVD-specific product developments in the field of filtration and separation science are addressing the remaining issues hampering the performance of IVD testing in more decentralized locations.
Out of the Clinic, into the World
The manufacture of test devices that do not require up-front sample handling and processing will drive the expansion of IVDs to more-remote world markets. Diagnostic analysis will then be obtainable regardless of the environmental conditions. Traditionally, the market for IVD testing has been the developed world, but, over the past few years, some movement into the developing world has been seen. To perform IVD testing in regions of the developing world requires overcoming challenges involving sample and reagent stabilization as well as the availability of meters and readers, trained personnel, laboratory equipment, and electricity. The developing world offers IVD manufacturers numerous opportunities, but the assays developed for that market must be simple and cannot require additional sample handling or processing. The use of membranes instead of standard sample-preparation procedures will allow diagnostic testing to be completed in remote settings that previously had limited potential for such a healthcare service.
The diagnostics market has roots planted in the clinical sector, but diagnostic assays are no longer used exclusively for assessing medical conditions in humans. Agricultural and environmental science, veterinary medicine, and industries such as food and beverage have all adopted diagnostic assay technology in some form. A majority of these assays employ traditional immunoassay procedures for detecting the presence or absence of infectious agents, other microbes, yeast or fungus contamination, or chemical contaminants. As the purposes of diagnostic assays have become more diverse, the samples analyzed have grown in complexity and volume. But the goal is still the same—to determine whether a particular sample is contaminated or contains a target analyte or molecule.
Filtration plays an integral role in fostering the development of assays for larger sample volumes with varying degrees of viscosity and debris load. Membranes of several different types are available to handle a variety of industrial samples. For example, asymmetric membranes can be incorporated into diagnostic devices to clarify large volumes of heavily burdened samples rapidly, producing clean samples suitable for analysis. The use of membranes and filter materials for unburdening samples prior to analysis expands the range of sample types that can be analyzed by traditional methods of diagnostic assay.
Membranes Present and Future
For decades, the IVD industry has been using membranes and filter materials in immunochromatographic test strips, which were composed of standard absorbent or conjugate pads and nitrocellulose membranes. As requirements have evolved to encompass more-complex samples and more-sensitive assays, incorporating specialized membrane–based technologies is becoming standard practice.
Filter-based materials are integrated into IVD devices to replace off-line sample-preparation procedures. By removing steps, this integration streamlines the process of sample collection, preparation, and analysis. And, by reducing the handling and processing necessary, membranes and filters designed to perform specialized functions also contribute to lowering overall cost per test.
During the next decade, the number of different clinical and nonclinical diagnostic tests will continue to grow. Furthermore, the expansion of IVD testing into developing regions of the world will rapidly accelerate the need for optimized membrane and filter-based materials. Specialized membranes will be needed in order to address forthcoming challenges associated with new types of sample, more-complex samples, more-sensitive assays, and more widely differentiated places of testing. As demands on the IVD industry to supply specialized filters continue to evolve, membrane manufacturers will address these needs by developing next-generation materials for sample collection, preparation, and analysis.
