How A Lab On A Chip Can Revolutionize Disease Diagnostics
Our fingernails grow pretty slowly. The average fingernail grows 0.6mm a week. But look down at your fingernails right now. At this very second, they are growing. At a rate of 1 nanometer per second.
1 nanometer is the amount your fingernail grows in a second, 2.5 nanometers make up a strand of human DNA, 100,000 make up the width of a human hair, and over 25 million make up a single inch.
But the most mindblowing part is that we have materials at this scale that have revolutionized industries, especially technology sectors. These nanostructures are over a hundred times stronger than steel, have an incredibly high surface area to volume ratio, a high porosity, and exceptional mechanical benefits.
Nanostructures, materials less than 100 nm in size in at least one dimension, are considered to be a nanostructure, ranging in the size of most biomolecules such as nucleic acids, small proteins, and viruses.
Over the past decade, we have begun to rapidly develop nanotubes, nanoparticles, and nanosensors specifically engineered to perform and improve a variety of processes, from improving carbon capture to targeted drug delivery.
While nanotechnology is well on its way to revolutionizing countless different industries, scientific research, and the backbone of society, it also has a humongous lever in the healthcare sector, especially within medical diagnostics.
Designing Nanostructures
Nanotechnology-based diagnosis techniques chart a path for many opportunities, including rapid diagnostic testing and treatment monitoring.
Through in vitro diagnostics (systems in contained environments outside of the body), nanostructures identify biological changes in the form of measuring the activity or concentrations of a specific biomolecule, by using a transducer to convert the biochemical signal from a biosensor into a quantifiable signal.
Materials and sensors are designed and characterized particularly by their specificity and sensitivity. In order to develop nanotechnology-based diagnostic tests, various nanomaterials, including metallic and magnetic nanoparticles, quantum dots, silica nanospheres, carbon nanotubes, silicon nanowires, and nanostructured surfaces have all been explored.
Metallic Nanoparticles
In particular, metals (especially gold and silver) prove to be extremely advantageous in the design of nanostructures as they can interact with external fields, such as light, radio frequencies, and x-rays.
The bonding of metals consists of many negatively charged electrons, which oscillate around the positively charged nuclei. The collective oscillation of these free electrons, respective to the nuclei, makes up plasmons, which are essentially quasi-particles defined by the quanta of plasma oscillation (organized movement of electrons).
Plasmonic metallic nanoparticles exhibit a property calls surface plasmon resonance (SPR), where the free surface electrons collectively oscillate, induced by a specific wavelength of light.
When an incoming electromagnetic wave matches the frequency of the oscillation of the electron cloud, SPR resonance occurs, and the light is absorbed.
This property allows them to be combined with methods such as absorption spectroscopy, which can quantify and determine the amount of a substance within a solution by the interaction of a sample with different wavelengths of radiation.
One of the most common uses of metallic nanoparticles is within pregnancy tests, as silver and gold nanoparticles are used as a color marker in a process known as Lateral Flow Assays.
Metallic nanoparticles are also used in a process called surface-enhanced Raman spectroscopy (SERS). SERS occurs when molecules are in close proximity to a metal surface, and their electromagnetic field increases dramatically. This is due to a process called Raman scattering, in which there is an inelastic scattering of photons by matter. This essentially means that there is both an exchange of energy and a change in the light’s direction. SERS substrates are most often used to find the presence of biomolecules that are low in abundance, such as proteins within bodily fluids. They can also detect molecular interactions and reveal structural information within a massive variety of applications; including environmental analysis, pharmaceuticals, forensic science, and food quality analysis.
A use case of this technology was in the early detection of pancreatic cancer biomarkers, using a SERS-based immunoassay. In a study published in 2017, researchers looked at how a SERS-base protein biomarker detection platform can be engineered within a microfluidic chip to detect several protein biomarkers and predict the type of disease. The study concluded that the use of gold nanoparticles with specific parameters lead to a significant improvement of SERS signals, and concluded that there was great potential in using SERS as a low-cost, high-sensitivity, and rapid approach for emerging liquid biopsy diagnostics within pancreatic cancer.
Carbon Nanotubes
Carbon nanotubes (CNTs) are small, electrically insulated tubes or pores, that can detect singular molecules when they pass through. They provide to be beneficial within nanosensors due to their extremely high strength (117x stronger than steel!), low mass density, nearly perfect geometrical structure, and electrical conductivity.
The detection of the molecule is based on the change of the ionic current of the electrolyte solution that contains the molecules of interest, resulting in the change of the electrical current.
The incorporation of biochips and nanofluidics with nanotubes has the potential to replace current DNA sequencing methods, as each DNA base has a unique molecular structure. thus, causing different changes in electrical current. Moreover, we can develop nanofluidic devices that employ multiple measurements on single molecules to enhance our ability to size DNA molecules.
In research published just this year, researchers concluded that by taking advantage of their high mechanical strength, high transmission efficiency, and easy planar integration, CNTs can break through the limitations of traditional nanofluidic applications. Carbon nanotubes have an extremely high surface area to volume ratio, making it possible to generate clear electrical signals at low concentrations, allowing for extremely small sample size, and the miniaturization of sensors. Moreover, carbon nanotubes have sites at their ends that can be used for purposes such as ion and molecular detection, capture, and manipulation.
Currently, 25.64% of carbon nanotubes in biomedical applications are used within biosensors.
In research published in 2018, researchers used graphene oxide and CNT to develop a reusable, low-cost, and effective immunosensor for lung cancer. The study concluded that the immunosensor developed with the integration of CNTs had high conduction properties, high stability, and could be reproduced. The study concluded that the rapid diagnosis was much more probable, even suggesting that the sensor could provide a diagnosis in just 15 minutes.
Silicon Nanowires
Silicon nanowires, nanoscale channels through which current is passed, have also shown great potential in the engineering of nanobiosensor devices. Silicon nanowires can be constructed from carbon nanotubes or silicon, but require high temperatures in order to be synthesized.
Silicon-based nanowire sensors have gained attraction due to their high sensitivity, label-free, and real-time detection, alongside their manufacturability for mass production. Silicon nanowire sensors are field-effect transistor (FET) based devices, meaning that they have a source, drain, and gate electrodes. The channels are opened and closed in a specific order to detect the target biomolecule.
In most nanowires, antibodies are usually the detectors on the surface of the nanowire, and they interact with the biological target of interest. The change in the shape of the antibody causes a change in the current passed through the nanowire, resulting in the biomolecule. The nanowires can be positioned in an array, where various antibodies correspond with each nanowire. The system can then mass detect different types of disease, or even create a personalized molecular profile for an individual in relation to a singular disease.
Silicon nanowires have been shown to act as ultrasensitive, selective sensors of metal ions, nucleic acids, proteins, protein and DNA interactions, small molecule and protein interactions, cells, and even viruses.
The Next Generation Of Healthcare Monitoring & Disease Diagnostics
Nanobiosensors
Biosensor: a device designed to detect or quantify a biochemical molecule, such as a particular DNA sequence or a particular protein.
Put “nano” in front of that, and we’ve unlocked the next generation of disease diagnostics.
Nanobiosensors and microarrays of biosensors within diagnostics provide an opportunity for the development of nanobiosensor systems, especially nanofluidic platforms, which manipulate fluids at the nano-scale. Both nanobiosensors and microfluidics are technologies most popular in the development of rapid diagnostic tests.
These technologies are specifically constructed for the rapid detection of diseases and pathogens-specific biomolecules or biomarkers, including DNA, proteins, and specific circulating cells.
Nanobiochips chips contain microarrays, essentially mini test sites, which allow for multiple biological tests to be carried out simultaneously by tiny, biologically active artificial structures, which are usually smaller than those of cells.
Thousands of biochemical reactions are performed on a single, nanoscale chip.
Many biosensors use a capture probe, which selectively binds to the target molecule, which transfers the challenge of detecting a target within the solution to the challenge of detecting a minuscule change within a localized surface. The change is measured through a variety of methods, such as surface plasmon resonance (SPR), mechanical motion, or magnetic particles.
Many types of biosensors also exist, such as label-free biosensors, which don’t require a label or a tag to report the detection of a specific molecule. On the other hand, electrical biosensors are dependent on current or voltage measurements to detect the binding of a molecule. However, electrical biosensors are promising for applications where minimizing the device size and cost is crucial, such as within point-of-care applications, due to their low cost and power.
Nanofluidics
As an emerging field, nanofluidics offers unique opportunities in comparison to other microscale devices.
Nanofluidic structures have small fluidic conducts, allowing them to be applied in situations in which there are extremely small quantities of biological samples. They can separate, determine, and size biomolecules, such as DNA and proteins, oncogenes, viruses, and bacteria, furthering the idea of nanofluidic structures as “labs-on-a-chip.”
In nanofluidic chips, a chamber, up to a few hundred nanometers in size, has a liquid sample that is manipulated and analyzed. Considering that the volume of the sample is so low, the chamber allows for a reduction of the substrate needed but provides the advantage of a high surface area to volume ratio and molecular confinement.
Most importantly, nanofluidics provides a tool to investigate singular molecules. However, its properties range from being able to single sequence variations within DNA to optical mapping, a technique that makes ordered, genome-wide, high-resolution maps from single DNA molecules.
Thermoplastic nanofluidics is a branch of nanofluidics that also houses great potential. Thermoplastics are polymers that can be melted and recast almost indefinitely, including polycarbonates and polyethylene terephthalate, or PET. Thermoplastics have shown promise in fluidic applications, due to their diverse yet simple fabrication techniques, which allow for devices to be produced easily and at low costs through techniques such as injection molding.
Applications
While one aspect of the challenge in developing these systems for in vitro diagnostics is the construction of these nanobiosensors and rapid diagnostic tests, making them more effective and innovative test approaches, another challenge is bringing them into point-of-care applications, allowing them to be applicable within everyday clinical practice.
The current development of these sensors is mainly focused on two areas; the use of the nanoparticles as biomarkers, and the development of novel nanosensors, which can incorporate different types of nanostructures, such as carbon nanotubes or lateral nanostructures.
Nanosensors For Glucose Monitoring
Despite the widespread use of insulin as diabetes treatment, the management of diabetes still comes with a large set of hurdles. In current clinical practices, patients must provide blood samples and self-monitor blood glucose in order to prevent hypoglycemia or hyperglycemia. However, there might be a much faster way to consistently monitor blood glucose in a non-invasive, fast, and sensitive way through nanotechnology.
In miniaturized glucose sensors, nanoscale properties can have immense advantages, including high surface areas, which yield larger currents and faster responses, thus improving the sensitivity of the glucose sensor, with a lower signal-to-noise ratio and higher selectivity of measurement.
The fabrication of a rapid, portable diagnostic test would provide a lot of advantages, especially in the form of an implantable microfluidic biosensor for in vivo glucose monitoring and insulin administration.
Researchers have explored various nanomaterials for the development of these sensors, from CNTs, due to their electron transfer capabilities, graphene nanosheets which can support gold nanoparticles, and nanocomposites, made of nanotubes and polymers (e.g. cellulose) which can create an entrapment matrix for glucose oxidase on the surface of an electrode.
Researchers have also looked into the idea of “smart tattoos,” minimally invasive optical glucose sensors implanted into the skin of the patient. However, unlike regular tattoos, these smart tattoos would be replaced weekly or monthly to account for sensor migration and degradation. In essence, the sensors would change fluorescent properties in response to the levels of blood glucose, which could then be read out using optical interrogation through the skin. This method would eliminate the need for patients to take blood samples and allow data to be collected in a more continuous manner.
Detection of Bacteria and Viruses
Modern detection of pathogens, including bacteria and viruses, is performed using sensitive lab techniques, such as enzyme-linked immunoassays, which detect blood antibodies, PCR testing, or other sequencing techniques. However, these techniques require several steps, from sample preparation, high costs, slow validation times, and require professionals. By taking advantage of the optical, magnetic, electrical, and catalytic properties of nanomaterials, we can offer more sensitive, specific, and cheaper diagnostic assays to detect pathogens.
Pathogens express certain glycoproteins, glycopeptides, lipoproteins, carbohydrates, and lipids on their membranes, thus allowing nanostructures to use antibodies to develop immunoassays. Nanobiosensors can also be conjugated with specific oligonucleotide sequences, short DNA or RNA molecules which are used as probes for detecting specific sequences that are complementary to the oligonucleotides. These oligonucleotides that are attached to the nanostructures can bind with pathogen nucleic acid sequences.
Furthermore, nanofluidic systems might be the next generation of research for the point of care management of microbial infections. There has been limited research about their potential, but researchers have already been able to leverage this technology in various use cases such as CNS infections and bacteria detection in meningitis.
Cancer Diagnostics
The incorporation of nanotechnology within cancer diagnostics can greatly improve the outcome rates of patients through the early detection of disease.
Several nanomaterials, including gold nanoparticles, silicon nanowires, carbon nanotubes, and graphene, have been leveraged to detect various cancer biomarkers, including proteins, DNA, or RNA. For example, silicon nanowires, have been used for the detection of several prostate cancer biomarkers, such as prostate‐specific antigen (PSA) and the prostate biomarker 8‐OHdG by using a silicon nanowire that is functionalized with antibodies against these biomarkers. However, nanobiosensors have also been used in the detection and diagnosis of biomarkers related to breast cancer, pancreatic cancer, lung cancer, and several other cancers over the past few years.
Using developing technologies, provided by companies like NanoString, we can even develop sensors that can simultaneously detect more than one cancer biomarker, and measure a panel of biomarkers in relation to a specific cancer type and individual, creating a personalized cancer diagnosis.
Future Perspectives
While the vast majority of these applications have been limited to early-stage research and development, they show great potential for the next generation of disease diagnostics, alongside treatment monitoring and the generation of molecular profiles in relation to certain diseases or conditions.
Until now, the incorporation of nanostructures within medicine is focused on the development of high-sensitivity diagnostic tools, novel approaches to personalized treatment, and drug delivery vehicles. However, by placing an additional focus on nanosystems, which have benefits ranging from rapid diagnostics to high SA/V ratios, we can soon bring mobile testing devices into everyday clinical practice.
Many of the technologies described within this article also have a versatile role, detecting very specific biomarkers while having the ability to be leveraged for similar biological purposes. In essence, we can take what we know about nanobiosensors solving specific problems, and leverage that knowledge into many more applications, such as hormone monitoring and the diagnosis of reproductive disorders.
Moreover, even within in vitro nanodiagnostics, nanobiosensors and nanofluidic systems allow for new diagnostic platforms to improve point-of-care applications. By improving point-of-care diagnostics, we can create devices that are accessible for patients at home, allow for the integration of diagnostics with therapeutics alongside the development of personalized treatment approaches.
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