Mr. Amay Bandodkar, a Ph.D. candidate in the laboratory of Professor Joseph Wang at the University of California in San Diego, is the recipient of the 2016 Metrohm Young Chemist Award. His work on wearable electronics was selected from a field of 70 submissions. Robert Stevenson had an opportunity to interview Amay at Pittcon.
RLS: Thank you for meeting me. I want to congratulate you on winning the award. Please tell me about yourself.
AB: I was born and raised in Mumbai, India. In college, I started to focus on chemistry since I was fascinated by the fact that chemistry dictates the properties of everything in the universe. I was especially enticed by the field of nanotechnology and the impact it has on modulating the properties of materials. During my undergraduate work, I found the field of biosensors of particular interest since these devices have immense applications in healthcare, environmental protection and even defense. So I worked as an undergraduate researcher in my department, and also had the opportunity to work at national labs in India and Germany. Professor Wang’s work in electrochemical sensors is unparalleled, and I knew it would be the best place to pursue my Ph.D. I asked if he would be interested in taking me as his graduate student, and he agreed.
RLS: How did you get started on your research?
AB: Wearable devices have become a hot topic; knowing the impact they would have, Professor Wang entrusted me with developing these devices. I worked with my team toward this goal under Professor Wang’s valuable guidance. We started with simple, flexible, paper-based wearable chemical sensors that could detect important metabolites—such as glucose and lactate—and electrolytes—such as sodium and ammonium—directly on the human body. Thereafter, we focused on giving the sensors more “skinlike” properties such as stretchability and the ability to self-heal. We spent a considerable amount of time identifying the best ratio of elastomeric binder, conductive filler and solvent to obtain printed devices that could stretch up to 500% without having much of an effect on their electrochemical properties (see Figure 1).
Figure 1 – All-printed PEDOT:PSS and Ag/AgCl ink-based stretchable electrochemical devices.We worked on developing self-healing printed devices since mechanical damage-induced device failure is the Achilles’ heel of printed electronics (see Figure 2). First, micro-capsules loaded with the healing agent (an organic solvent) were synthesized. These capsules were then dispersed within an acrylic-based carbon ink. The prepared inks were used to print self-healing devices. When the printed trace is damaged, the capsules along the crack also rupture, leading to the release of encapsulated organic solvent, which dissolves the binder. This results in rearrangement of the conductive particles, which restores the mechanical and electrical contact across the crack. Our experiments showed that this restoration takes places within 3–5 sec.
Figure 2 – Image illustrating the self-healing ability of a carbon trace when completely severed by a knife. The trace was printed using microcapsules-based carbon ink.Wearable sensors need to be in contact with the skin. The devices must be soft and stretchable like human skin, and also robust and nontoxic. I started working with several materials and eventually selected a silicone-based elastomer that is widely used for prosthetics, masks and toys as the stretchable binder. I found that by carefully manipulating the ink composition and device design, I could stretch the printed device as much as 500% without breaking it. Our research is still in the initial phase; we are actively looking for better ink components that will allow us to fabricate inexpensive devices that possess even more striking properties.
RLS: Can circuits be created on the membrane?
AB: Yes, we can use conductive inks to print circuits.
RLS: What kinds of sensors have you developed and how do they work?
AB: I worked with my team to develop wearable electrochemical sensors for noninvasive detection of glucose (for diabetes), lactate, sodium, ammonium and pH (for fitness monitoring). These devices leverage electroanalytical techniques such as amperometry and potentiometry. We functionalize the printed sensors with specific enzymes and chemical reagents to detect the desired chemical species with high selectivity. These sensors thus generate signal (current or potential) proportional to the concentration of the chemical species.
RLS: What about cost? I can see that these could be expensive, at least at first.
AB: Not really—the flexible/stretchable substrate and conductive ink are not expensive. If this technology is expensive, no one will use it. My goal is for the cost to be less than $1, which would make the devices disposable. We rely heavily on screen-printing technology, since it allows large-scale, low-cost fabrication of high-fidelity sensors.
RLS: What applications do you envision?
AB: My lab is mostly focused on developing printed chemical sensors for various healthcare, defense and environmental applications. However, we are now venturing into new avenues, such as printed energy devices. We like to explore radical ideas. For example, we are working on wearable biofuel cells that can harvest electricity from human sweat. Recently we were able to power a wristwatch and a light-emitting diode (LED) using these devices. Although these could be powered for only a short time, the results are quite promising and, with the advances in materials science, enzymology and electronics, one day such devices may turn out to be viable for harvesting energy.
RLS: How does the sweat-powered LED work?
AB: Human sweat contains considerable levels of lactate. Fortunately, there is an enzyme—lactate oxidase—that can selectively oxidize lactate to generate electricity. We exploited this enzymatic reaction to develop a wearable biofuel cell where the anode was fabricated by immobilizing the enzyme along with a mediator (for obtaining efficient electron transfer between the redox site of the enzyme and the anode) and carbon nanotubes (for enhancing the current generated). The cathode is made of platinum, which reduces oxygen to water. When you bring both these electrodes together in the presence of lactate, the lactate molecule becomes oxidized at the anode to generate electrons that flow from the anode through the external load (for example, LED); the electrons are consumed at the cathode, where the oxygen is reduced to water.
RLS: You mentioned that wearable circuits would be more versatile if the energy could be stored. Do you foresee suitable batteries?
AB: Indeed, wearable batteries are going to play a crucial role in the budding field of wearable electronics. Several researchers, including us, are now working on thin, flexible/stretchable batteries that can be easily integrated with the human body to continuously power various wearable devices. The scope for wearable batteries is huge.
RLS: The Internet of Things is creeping into chemical and life science laboratories. Do you see your inventions changing the lab workflow?
AB: Having a host of chemical sensors at various chemical and life science laboratories is bound to have a major impact. Such sensors will provide us with unprecedented levels of vital information and enable us to continuously and remotely monitor several parameters at the same time.
RLS: Please explain the unique team approach in Professor Wang’s laboratory.
AB: We have a goal-driven approach for each project. Professor Wang likes to entrust his students to work on multiple projects simultaneously. His lab always attracts talented, self-motivated students and this helps us put together high-performance teams that can achieve tough milestones within limited timeframes. Professor Wang allows new students to work on existing projects to teach them important skills and the working principles of the lab. Students are then given the opportunity to lead projects. There is a continuous exchange of ideas between Professor Wang and his students.
RLS: Are the teams multidisciplinary? Do you recruit members from outside of Prof. Wang’s lab?
AB: Indeed. Our project goals mandate that we have a cross-disciplinary research approach. In several projects we collaborated with groups that have expertise in electrical engineering, batteries, thermoelectrics and the medical field.
RLS: You’ve served as a project leader. How did this go?
AB: I started as a team member working with senior graduate students and post-docs in various projects to learn skills that I would need later when I would be a team leader. I gradually worked my way up and started leading projects. I will forever be indebted to the Wang lab for teaching me important leadership skills that allow me to handle multiple projects at the same time without compromising on the quality of any project. Over the years I have learned to handle high-performance teams, efficient time management, effective communication skills and resource management. I am confident that these skills will be quite useful for me in future when I become a professor and have to handle a big research group.
RLS: What do you see in your future?
AB: My dream is to be a successful professor running a multidisciplinary research group. I’ve accepted a post-doctoral position in Prof. John Rogers’ group at Northwestern University. His lab is renowned for developing soft, stretchable electronics for wearable/implantable devices. Eventually, I wish to combine the knowledge I’ve acquired from both groups (Professors Wang and Rogers) to address the most pressing needs in the wearable devices field.
RLS: Thank you for sharing your views. I can see that you are passionate about your work, and I look forward to seeing your solutions to wearable devices.
AB: Thank you, Dr. Stevenson, for showing interest in my work and for your kind words. Such appreciation motivates me to push myself harder.
Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]