Sciencers.org returns with another blog post series written by high school students, this time on Biomedical Engineering!
These are original mini-review articles written by high school students as part of my Biomedical Engineering class at the Stanford Summer Online Institutes.
Are Electrochemical Biosensors the Future of Alzheimer’s Disease Diagnosis?
By SunJae Lee
About the Author
SunJae (Sunny) Lee is a senior at the International School of Beijing. She is fascinated by chemistry and biology (particularly Alzheimer’s disease) and genuinely passionate about service and giving back to the local community. In the future, she hopes to pursue a career in which she can combine these two interests.
Introduction
You most likely know someone that had been affected by the ever-terrifying Alzheimer’s disease. Maybe not a near family member or friend, but perhaps one of the following people: former US president Ronald Reagan, civil rights activist Rosa Parks, and author E.B. White [1]. All of these heroes, from the political or literature world, were affected by Alzheimer’s disease that led to the end of their careers.
Alzheimer’s disease is an irreversible neurodegenerative disease that “is predicted to affect 1 in 85 people globally by 2050” [2]. This disease is believed to be caused by a wide range of different factors, including old age, family history, genetic mutation, and head injury [3]. However, to this date researchers are still investigating the disease, as the exact reason for developing it is unknown. Once affected, Alzheimer’s disease aggravates at an alarming rate that leads to not only memory loss and cognitive impairments, but also several psychological impacts such as depression, stress, and anxiety [4]. The most threatening fact of all is that there is not yet an available cure or a reliable method of timely and accurate diagnosis [4].
To diagnose Alzheimer’s disease in a patient, doctors often examine their blood or urine samples for biomarkers that indicate presence of the disease. The main issue with this, however, is that bodily fluids have low concentrations of biomarkers that can be detected via traditional assays. The traditional assay method of enzyme-linked immunosorbent assay (ELISA), as well as magnetic resonance imaging (MRI) and positron emission tomography (PET) scan, have several disadvantages: time-consuming procedures, potential hazards to health, expensive instruments and need of highly trained professionals [5]. Though certain drugs have been demonstrated to slow down the progression of Alzheimer’s disease, it is usually too late by that point due to the difficulty of diagnosis at an early stage [6]. Hence, it is crucial to develop a simple, safe, and accurate method to diagnose Alzheimer’s disease, especially in the early stages of the disease. The new technology of biosensors, particularly electrochemical biosensors which is the focus of this article, present a desirable solution to the issues above and may be the future of early Alzheimer’s disease diagnosis.
What are Biosensors?
A biosensor is an analytical device that converts a biochemical signal into a quantifiable signal in the form of a current, light, or frequency [5]. Though there are various types, most biosensors integrate these three essential components: a bioreceptor, transducer, and signal output [5]. The bioreceptor utilizes biomolecules such as enzymes, lipids, antibodies, to bind to analytes of interest, which, in this case, would be proteins responsible for Alzheimer’s disease. A signal is created during this interaction, which the transducer then transforms into measurable data [7].
Figure 1: General layout of a biosensor. Molecules of analytes of interest bind with a bioreceptor, which produces a signal that is transformed by a transducer into a measurable signal [7].
Why a biosensor would be a useful tool for diagnosis of Alzheimer’s disease
Scientists have found over the years that aggregation of the biomarkers amyloid-beta (Aβ) peptide and tau protein in the brain are responsible for the onset and progression of Alzheimer’s disease. However, with its complicated structure, they require highly sensitive and selective detection methods – biosensors satisfy precisely that [4]. The nature of biosensors allows for high sensitivity, easy fabrication, and effective miniaturization, which make them especially suitable for biomarker detection [4]. In the case of biosensors integrated with nanomaterials, its high surface area to volume ratio allows their electrical properties to be more susceptible to external influences. These biosensors can also efficiently interact with its target biomolecules that are comparable in size, resulting in higher sensitivity and accuracy of measurements [8].
Special features of electrochemical biosensors
The general process by which electrochemical biosensors operate is similar to that of the standard biosensor. However, electrochemical biosensors are unique in that they can produce an electrical signal proportional to the concentration of an analyte of interest [9]. This is done by measuring the electrical response generated as the reaction occurs between an analyte and the surface of the working electrode of the biosensor [5]. This feature is crucial in monitoring levels of bodily substances like glucose and may be especially useful in tracking concentrations of Alzheimer’s-linked amyloid-beta (Aβ) peptide and tau protein [9].
Figure 2: Sequence of an electrochemical biosensor [1]. a) An analyte of interest binds to b) a bioreceptor on a biosensor, which reacts and produces a signal. c) The signal transducer converts this signal to a measurable signal through various methods and d) displays it on an analysis system [10].Electrochemical techniques are widely used because it allows for convenient, miniaturized, and portable devices to be made. To further increase sensitivity (more specifically, electrode response magnitude), scientists frequently apply methods to increase the electrode surface, incorporate more conductive material onto the coating of the electrode, or catalyze the reaction. Likewise, the selectivity of the biosensor can be increased by attaching antibodies that target specific biomolecules onto the electrode surface. [5]
Application of electrochemical biosensors in biomarker detection was found to be successful with cortisol, a biomarker of psychological stress [8]. When a nanosized electrode was integrated with nanosized sensing material and a miniaturized transducer, the electrochemical biosensor was shown to be capable of detecting cortisol at pg/mL levels within just 40 minutes [8]. This is faster than the MRI or PET scan, which can take up to 90 minutes, and certainly more efficient than the ELISA test, which can take days, even weeks, and sometimes lead to no result [11, 12, 13].
A similar process could be used to develop a biosensor capable of detecting amyloid-beta (Aβ) peptide and tau protein. Researchers have already begun to create a biosensor that incorporates nucleic acid aptamer bioreceptors, which are single-stranded DNA or RNA oligonucleotides [14]. This technology is attractive for biomarker detection because aptamers are incredibly versatile, hence capable of binding with a variety of biomolecules with high affinity and specificity [14, 15]. Though still in its developmental stages, such biosensor can soon potentially enable doctors to do quick screening and monitoring of Alzheimer’s disease in patients [8]. This could even allow them to diagnose the disease at an earlier stage and move onto treatments aimed to slow progression.
Challenges
Electrochemical biosensors demonstrate an ideal solution for early diagnosis of Alzheimer’s disease. However, for this technology to enter industries and begin commercialization and production at a large scale, it still has a long way to go. Costly materials, potential risks of operating at the nanoscale, and difficulty of storage are among the many factors scientists must consider before bringing them to be manufactured and used in real life [5].
Another step that must be taken before releasing electrochemical biosensors to actual hospitals is validating its effectiveness through multiple clinical trials. Though the design and idea behind using electrochemical biosensors in Alzheimer’s detection seem promising, this research is still at laboratory stages, and the method cannot officially be carried out until it has been ensured to work entirely [5].
Conclusion
To summarize, electrochemical biosensors function by producing an electrical signal proportionate to the concentration of an analyte of interest, thereby providing an excellent feature for monitoring levels of specific substances within the body. This particular type of biosensor is especially sensitive and selective due to its conductive and mechanical properties and thus is suitable for amyloid-beta (Aβ) peptide and tau protein detection. Although this technology is not yet polished and readily available, further research is expected to lead to a successful “Alzheimer’s sensor” that can be used clinically. Based on current progress, it is safe to anticipate a bright future for the involvement of electrochemical biosensors in early diagnosis of Alzheimer’s disease [5].
Discussion & Speculation
In the future, Alzheimer’s disease will become increasingly widespread, with the elderly population (age 65 or over) expected to grow from 8.5% to 17% of the world’s population by the year 2050 [16]. The likelihood of developing Alzheimer’s disease doubles every 5 years after the age of 65, meaning every elder who reaches this age may begin to worry about losing precious memories of their families and friends [3]. All of this stress and worry can be eliminated if we can find a way to develop a biosensor that lasts a lifetime for in vitro use. Today, infants and children receive vaccinations to build protection from various diseases that could infect them in the future. In the same way, we should aim towards developing a long-lasting biosensor that we could insert into our body well before we reach the age at which we become susceptible to the disease. This way, we would know immediately if and when we start aggregating amyloid-beta (Aβ) peptide and tau protein for Alzheimer’s disease. Although this is not a proposal for an ultimate cure for Alzheimer’s disease, I believe finding a way to diagnose Alzheimer’s disease early is the first and vital step in tackling this disease.
Acknowledgments
I owe many thanks to my professor, Dr. Jagannath Padmanabhan from Stanford University, for providing me with the knowledge, as well as the inspiration and excellent opportunity to write this research article. Through the nanobiomaterials course that he designed, I was able to gain insights into a completely new aspect of biological sciences. Additionally, Dr. Padmanabhan’s enthusiastic, engaging, and ever-encouraging approach to teaching drove me to explore beyond the scope of the course and incorporate nanobiomaterials into a field that I am personally interested in.
References.
Kennard, Christine. “Famous People with Alzheimer’s Disease and Other Types of Dementia.” Verywell Health, About, 19 Dec. 2017, www.verywellhealth.com/famous-people-with-alzheimers-98082. Accessed 23 Aug. 2018.
Li, S.-S., Lin, C.-W., Wei, K.-C., Huang, C.-Y., Hsu, P.-H., Liu, H.-L., … Ma, C.-C. M. (2016). Non-invasive screening for early Alzheimer’s disease diagnosis by a sensitively immunomagnetic biosensor. Scientific Reports, 6, 25155. Retrieved from http://dx.doi.org/10.1038/srep25155
“Risk Factors.” Alzheimer’s Association, www.alz.org/alzheimers-dementia/what-is-alzheimers/risk-factors. Accessed 23 Aug. 2018.
Kaushik, A., Jayant, R. D., Tiwari, S., Vashist, A., & Nair, M. (2016). Nano-biosensors to detect beta-amyloid for Alzheimer’s disease management. Biosensors and Bioelectronics, 80, 273–287. https://doi.org/https://doi.org/10.1016/j.bios.2016.01.065
Pasinszki, Tibor, et al. Carbon Nanomaterial Based Biosensors for Non-Invasive Detection of Cancer and Disease Biomarkers for Clinical Diagnosis. National Center for Biotechnology Information, 20 Aug. 2017.
Rushworth, J. V, Ahmed, A., Griffiths, H. H., Pollock, N. M., Hooper, N. M., & Millner, P. A. (2014). A label-free electrical impedimetric biosensor for the specific detection of Alzheimer’s amyloid-beta oligomers. Biosensors and Bioelectronics, 56, 83–90. https://doi.org/https://doi.org/10.1016/j.bios.2013.12.036
Shukla, S. K., Govender, P. P., & Tiwari, A. (2016). Chapter Six – Polymeric Micellar Structures for Biosensor Technology. In A. Iglič, C. V Kulkarni, & M. B. T.-A. in B. and L. S.-A. Rappolt (Eds.) (Vol. 24, pp. 143–161). Academic Press. https://doi.org/https://doi.org/10.1016/bs.abl.2016.04.005
Grieshaber, Dorothee et al. “Electrochemical Biosensors – Sensor Principles and Architectures.” Sensors (Basel, Switzerland)3 (2008): 1400–1458. Print.
Hammond, Jules L. et al. “Electrochemical Biosensors and Nanobiosensors.” Ed. Pedro Estrela. Essays in Biochemistry1 (2016): 69–80. PMC. Web. 23 Aug. 2018.
Abdulbari, H. A., & Basheer, E. A. M. (2017). Electrochemical Biosensors: Electrode Development, Materials, Design, and Fabrication. ChemBioEng Reviews, 4(2), 92–105. https://doi.org/10.1002/cben.201600009
Davis, Charles Patrick. “ELISA Tests.” Edited by John P. Cunha. MedicineNet, www.medicinenet.com/elisa_tests/article.htm.
“How It’s Performed.” NHS, 10 July 2015, www.nhs.uk/conditions/mri-scan/what-happens/. Accessed 23 Aug. 2018.
“PET Scan: Test Details.” Cleveland Clinic, my.clevelandclinic.org/health/diagnostics/10123-pet-scan/test-details.
Shui, D. Tao, A. Florea, J. Cheng, Q. Zhao, Y. Gu, W. Li, N. JaffrezicRenault, Y. Mei, Z. Guo, Biosensors for Alzheimer’s disease biomarker detection: A review, Biochimie (2018), doi: 10.1016/j.biochi.2017.12.015
“What Is an Aptamer? – Aptamers and SELEX.” Base Pair Biotechnologies, www.basepairbio.com/what-is-an-aptamer/. Accessed 24 Aug. 2018.
“World’s Older Population Grows Dramatically.” National Institutes of Health, 28 Mar. 2016, www.nih.gov/news-events/news-releases/worlds-older-population-grows-dramatically.
Austin Taylor: Austin is a rising senior from the Seattle, Washington area (Snohomish). Austin goes to public school where he runs for the Cross Country and Track teams. Aside from sports, Austin is the President of his school’s NHS, the Vice-President of the Science Club at his school, and a member of the City Youth Council. He likes just about everything in school (besides art) and plans to major in Chemistry in college, and go to medical school to become a surgeon.
Alex Dalrymple: Alex is a rising junior from New Bern, a small town in Eastern North Carolina. Alex attends a high school where she is a member of Science Olympiad, an officer for the Environmental Club, and a varsity volleyball player. In the summers, Alex enjoys participating in undergraduate research in an Inorganics Lab at a near university. Alex is very involved in her local hospital and is currently volunteering with the Oncology Department with hopes to pursue Oncology Research following college.
Dahlia Björklund: Dahlia is a rising senior from London, in the United Kingdom. Dahlia attends a secondary school where she is a member of Economics Society and is part of her school’s fundraising and linking program with the African Science Academy. She also enjoys writing and editing for her school’s magazine, and being head of marketing for the school charity shop. Outside of school Dahlia is very involved in the volunteering tutoring organization that she co-founded with her friends. She is passionate about all of her subjects and hopes to major in both Economics and Physics in college.
Introduction
In a world in which conflict is frequent and devastating, the further development of military clothing is essential to defend troops and limit the loss of life. One avenue to protect soldiers is to integrate nanobiomaterials into the fabric of military clothing to provide both increased strength and antibacterial attributes. Fabrics have been produced that have either great strength and protective qualities or antibacterial benefits, but creating materials that possess both of these qualities would be extremely beneficial for military applications [1].
Nanoparticles have already been implemented into the textile industry through the coating of textile fabrics such as cotton, polyester, and nylon with silver nanoparticle films [2]. Silver nanoparticles have been found to have excellent antibacterial qualities that inhibit the multiplication and growth of bacteria and fungi that cause infection and disease [3]. They have been utilized in fabrics for socks to prohibit the growth of bacteria and are also used in wound dressings for burns, cuts, and skin donor and recipient sites. Carbon nanofibers have also been a source of research in the textile industry [3]. Weaving carbon nanofibers into fabric can allow for increased strength of the fabric [4]. Instead of focusing on the use of nanobiomaterials for regenerative processes, this research focuses on the prevention of possible harm, whether that be from a bullet, an infection, or both. This article will explain the benefits and the defensive opportunities that could be created through a military suit that is able to reduce infection and provide ballistic protection as well as discuss the methods that are available to produce the fabric.
Target of Research
Based on research of the properties of nanomaterials and prior knowledge about them, this research is proposing a fabric that can be infused with nanomaterials to produce a protective armor for defensive purposes. The prospective armor will be made using a fabric that has nanomaterials integrated into its fibers to increase its ballistic protection against bullets. Carbon fibers can be integrated and could also be coated in silver nanoparticles. The purpose of using these nanobiomaterials is that silver nanoparticles contain antibacterial properties, allowing them to stop bacteria from getting in the suit and also help fight possible infection in the case of a bullet puncturing the suit. The goal is to use the findings of previous scientific articles and experiments to propose a body armor that is lightweight and breathable, both nanomaterials properties, that can also be worn under military clothing to increase protection from injury, infection, and disease.
Carbon Nanofiber Strength
When looking at possible materials for fiber integration, many different options were considered. After careful thought, the consensus was that using carbon nanofibers would be the ideal method. Carbon nanofibers have the ability to fortify materials and provide increased strength, even up to 100 times that of steel at one-sixth the weight [5]. The nanofibers are also 17 times stronger than Kevlar®, the material traditionally used to fabricate bullet-proof vests[5]. Carbon nanofibers can be safely and effectively created through electrospinning, in which a carbon polymer solution is passed through a spinneret and is extruded using a high voltage shock to overcome the surface tension of the polymer solution. The result is a mass of long fibers created from a polymer solution, in this case carbon [6]. To maximize strength and produce straight fibers, the carbon nanofibers are pulled along a rotating spool and stretched [7]. The tensile strength of carbon nanotubes is around 80 GPa [6]. To put this into perspective, the pressure inside an average car tire is around 0.0002 GPa. The integration of nanofibers into clothing gives a breathable and lightweight quality, a very attractive feature for the more mobile fields of the military [8]. Carbon nanotubes can also be coated with particles to supply additional qualities such as antibacterial properties.
Use of Silver Nanoparticles to Give Fabrics Antibacterial Qualities
Silver nanoparticles have antibacterial qualities that can help prevent infection and accelerate wound healing, both of which could be of great use to military fabrics [9]. Silver nanoparticles in the size range of 1-100 nm are the most efficient as they have an increased surface area, allowing them to possess greater antibacterial properties [10]. They currently have existing uses as bactericide in sanitizing sprays, toothpastes, and many other antimicrobial consumer goods [11]. The complete details of how silver nanoparticles destroy bacteria are not yet known, but experiments have shown that silver ions arrest the metabolic activity of bacterial cells and inhibit several other cell functions that damage the bacterial cells [10]. Also, when bacterial cells come into contact with silver nanoparticles, nanoparticles accumulate and enter the cells where they generate reactive oxygen species. These reactive oxygen species are released and then attack the bacterial cell itself. Silver is also a soft acid which reacts with the nitrogenous bases to destroy the DNA of a cell, leading to cell death. Silver nanoparticles can adhere to bacterial cell walls and penetrate them, affecting the permeability of the cell membrane and also causing death of bacterial cells (Figure 1) [9]. Wound-healing with silver is attributed to increased death of neutrophils within wounds as well as reduced levels of anti-inflammatory agents. Reducing levels of anti-inflammatory agents within wounds helps accelerate wound healing. Fabrics loaded with silver nanoparticles also possess excellent antibacterial action against E. coli bacteria, as well as other multidrug resistant (MDR) bacteria [11,12].
Figure 1- Process of Silver Causing Death of Bacteria Cell [5]Carbon nanofibers (CNFs) can be functionalized with silver nanoparticles to then be woven in with Kevlar fibers to make a stronger and more flexible fabric. To create these compounds, the silver ions are deoxidized and dispersed in a solution of ethanol. Silver particles are then formed under pressure in supercritical carbon dioxide (SC CO) fluid which possesses unique properties such as low viscosity and minimal surface tension. This enables the SC CO to deliver the silver nanoparticles to the carbon nanofibers. Higher SC CO pressures mean that a larger number of small silver crystals can quickly be deposited onto the CNFs under magnetic stirring and homogeneously coat the fiber, thus avoiding aggregation of the silver nanoparticles. Transmission electron microscopy (TEM) is used to show the morphology of the silver nanoparticles wrapped around the carbon nanofibers (Figure 2) (Figure 3) [6]. This complicated process is only one of many different methods that could be used to functionalize carbon nanofibers with silver nanoparticles, but it is the most effective in this case, as being able to adjust the pressure of the SC COmeans that the nanoparticles can be homogeneously deposited over the material. This is important as the antibacterial qualities of the nanoparticles should be evenly distributed throughout the fabric so that the antibacterial protection is uniform throughout the material.
Figure 2- CNF without Silver Coating (A) and CNF with Silver Coating (B)
Figure 3- Silver Deposition onto CNF Using SC CO [6]
Conclusion
The end result of this research is to manufacture a strong and antibacterial fabric for military use through the creation of protective bodysuits. The proposed method involves carbon nanofibers that are woven into Kevlar® Fabric to greatly increase the strength of the fabric as carbon nanotubes have 17 times the strength of Kevlar® alone (see Figure 4) [13]. The carbon nanotubes and Kevlar® fabric make this protective clothing more effective at preventing wounds inflicted from bullet as well as make it suited for ballistic conflict. However, the material is not suited for wounds inflicted by cutting the fabric. Therefore, any cuts in the fabric that penetrate the skin will allow the antibacterial qualities of the silver particles wrapped around the carbon nanofibers to be active. The silver nanoparticles will disinfect the wound by killing bacteria cells capable of causing infection, thereby improving defense capabilities on multiple fronts. With multiple applications and defensive capabilities, a protective military bodysuit made out of carbon nanofiber-infused Kevlar® offers a unique and effective means of enhancing survivability of military fabrics.
Figure 4- Bodysuit with Integration of CNF (red) Wrapped with Silver Nanoparticles (yellow) and Kevlar® Fibers(black) *Not Drawn to scale as Kevlar® Fibers are Larger in Diameter than Carbon Nanofibers
Possible Difficulties
It is important to conduct further research on the properties of silver nanoparticles as well as the mechanism behind the ability of silver nanoparticles to impart antibacterial properties. As stated previously, there are many ways in which scientists believe that silver nanoparticles actively kill bacteria, but it is important to thoroughly understand the mechanism behind the antibacterial quality of silver nanoparticles to explore the longevity of the nanoparticles on this fabric. The amount of nanoparticles on the suit may be reduced over time, leading to a need for bodysuit replacement, or possible re-application of nanoparticles. Further research would be needed to determine the lifespan of silver nanoparticles in the suit. Another issue presented is the heat sensitivity of Kevlar®fabrics. These fabrics will not work optimally when exposed to continuous heat. However, the carbon nanofibers that are woven into the Kevlar®material can possess thermal properties to prevent heat from affecting the material as severely. Another avenue for further exploration would be the benefits of using carbon nanofibers compared to carbon nanotubes. Research has indicated that both carbon nanofibers and nanotubes are effective for several properties of this military suit such as ballistic protection, additional strength, and the ability to be functionalized with silver nanoparticles. However, nanofibers were chosen in this case as they are very flexible, unlike nanotubes, and can easily be woven into a fabric. They are also easy to produce through electrospinning. Furthermore, as the carbon nanomaterials would be used for such specific purposes, we could test whether carbon nanofibers or carbon nanotubes are the most effective in terms of the specific qualities of this suit that are required such as ballistic protection, flexibility, thermal properties, and breathability.
Future Applications and Questions
When studying nanobiomaterials, it can be easy to get caught up in the hypothetical and stray away for what is currently possible. While these ideas are what further science in the present and the future, it remains important to focus on the things that are possible now when considering things like funding from a source like the Department of Defense. That being said, the process of turning an original idea like this into reality is dependent on asking the questions that stimulate achievable answers and solutions.
Without actually receiving funding and running experiments, it is hard to tell what the limitations of this design are. It is believed in this article that the suit would be fit around the whole body, but is that necessarily so? Furthermore, could the fabric even be created in a way that covers the whole body without limiting functionality and flexibility, not to mention all the things soldiers have to carry in the field? Additionally, what preliminary test would have to be run and what results would have to be acquired to garner support from the Department of Defense or other research-funding sources? All of these are questions that would have to be considered in great depth if this idea is ever to become reality, however, none of these questions touch on the principal problem when considering research ideas. This vital problem is simply the cost of producing such a material. While nanomaterial integration does not project as being extremely expensive, scaling up the design of the defensive suit could be costly.
Acknowledgements
As we come to the end of this article and course, we would like to thank our great peers, chill counselors Ana and Hailey, and wonderful professor Jagannath. Two weeks prior to finishing this article, Jagan made a promise to his class that we would walk away from this course with the knowledge and ability to learn any topic in just 14 days. At the time it seemed like quite the statement and possibly hyperbole; however, the style and approach Jagan took to teaching this class made all the difference. By asking the right questions and encouraging us to form original thought, Jagan was able to not only teach us about Nanobiomaterials but how to learn and really excel in anything we set our minds to. Thank you Jagan for creating an environment where learning was enjoyable once again.
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To kick off this blog, we will start with a series of blog posts on “Nanobiomaterials” – written by high school students aka tomorrow’s scientists.
I am teaching a course on Nanobiomaterials at the Stanford Summer Institute and this blog post series features original articles written by the students in the class.
