Data Analysis

Week 4 was short, but with the end of our program quickly approaching, Ellie and I started planning our poster design and finalizing our data analysis. Wednesday we started creating our graphs from our data collection. We were already under the assumption that very few of our samples were viable and capable of sensing any glucose. We made graphs for all samples tested using chronoamperometry. These graphs helped reveal any trends associated with increasing current with additional glucose. Only one sample revealed a trend as expected.

Next week we will create several more graphs that compile the data using our successful sample that was tested over several days. This will allow us to analyze any see if there was any significant drop in current over continued use/time. We will also go back and look at our cyclic voltammetry graphs and see if we could possibly change the voltage used in our chronoamperometry tests in order to see a greater change between glucose concentrations.

Moving forward, we would like to design more samples, but time is a constraint. Future goals would be to look at what type of paste sketches worked best and try to repeat these results. We would also like to test our samples in a variety of solutions such as sweat and other common liquids that contain sugar.



Glucose Sensor Testing Phase

During week 3, Ellie and I began testing of recently designed glucose sensors. We carried out two tests: cyclic voltammetry (CV) and chronoamperometry. These tests were carried out in various glucose solutions. We designed a serial dilution on a spreadsheet ranging from 0mM to 60 mM, our step size was 6 mM up to 22mM, we then jumped to 10 mM steps. We used dextrose, a synonymous molecule to glucose and PBS solution in order to create our solutions.

Our CV tests allowed us to analyze if we had any current peaks. Surprisingly, many of our samples revealed a linear plot and did not have any peaks. These samples were kept for further analysis but we did not do any chronoamperometry measurements using these samples. Our CV scans were all run for 5 cycles at a scan rate of 200scans/sec.

Our chronoamperometry measurements were set at .15mV, and we then measured current using that constant voltage. We determined the voltage to use by analyzing our CV peaks and at what voltage the peaks were commonly occurring at. The chronoamperometry measurements were each run for 200 seconds. We added a new PBS and glucose solution between each test. We made sure to add the strip simultaneously to the solution as we started the chronoamperometry scan. This stayed consistent for all tests. We also determined that adding the smaller volume of glucose prior to the PBS also helped yield better results. Once we took chronoamperometry measurements for all concentrations for one sample, we were able to look at where each concentration became saturated. The trend that we expected, increased concentration would produce a higher current was seen for most samples. The only discrepancy in this trend was that a lower concentrations (below 14mM) most of our samples did not seem to be sensing the glucose in solution.

Glucose Sensor Design

In week two, Ellie and I worked with Vladimir and Murat to design our glucose biosensor. We are using a commercial electrochemical sensor platform in order to design our glucose sensors.

We used a Prussian Blue (carbon graphite) paste and stencil approach in order to lay down the bottom layer of our working electrode. We used a razor blade in order to apply our paste. We then baked the strips at 80 degrees Celsius.  We then placed the strips in a Phosphate-buffered saline (PBS) solution and used a cyclic voltammeter to obtain a standard curve we could reference in later experiments.  We then let the voltammeter run until our peak curves were standardized. This varied from 10-20 cycles.

The next step in our experiment was to add the our enzyme, glucose oxidase asperigllus (GOx). We prepared the enzyme solution by adding 1mL of 1X PBS solution, 40 mg GOx, and 10mg BSA. We used a vortex to mix the solution and then pipetted 10 µL of the solution on top of the working electrode. This was left to dry under the hood for two hours.

Next we added the crosslinker on top of the enzyme solution. We used two different concentrations (25% and 35%) and applied 10 µL of solution on the working electrode. Strips were again left under the hoof to dry. Due to time constrictions we then left the samples in the fridge over night. The next day, we added a diffusion layer on top of everything. This was again left to dry.

Next week we will use our prepared samples and record their sensing ability of glucose.

Crash course on Biosensors

June 14th

The summer RET at ASSIST is also designed to allow collaboration with the young scholar program. My research experience segment will be a joint project with Ellie McGhee, a high school student from the Durham School of Science and Math. Our project will be carried out in Dr.Daniele’s lab. We are focusing on biosensor design and fabrication, specifically glucose sensors. We are under the direct supervision of Dr. Vladimir Pozdin and Murat Yokus.

Our first two days in the lab were spent looking at a variety of prototype sensors, reading literature and discussing the nuts and bolts of sensor design. There are three main parts to a biosensor: (1) recognition element (input), (2) transducer that converts the recognition event into a measurable sensor, and (3) a signal processing system that converts the signal into a readable form. Our research project will focus on modifying a current recognition element in order to measure a common food product containing glucose.

The recognition element of current glucose sensors predominately fall into second generation (see B in Fig 1). Second generation elements depend upon redox mediators that allow electron transfer from the enzyme to the electrode surface. A variety of electron mediators can be used in order to obtain desired results. Our project will seek to design a second generation sensor.

First generation sensors (see A in Fig. 1) rely on the reduction of oxygen and the detection of hydrogen peroxide, both physiologically active molecules. Drawbacks to this design include; difficulties obtaining high-selectivity, and adverse localized reactions due to concentrated hydrogen peroxide.

Third generation sensors (see C in Fig. 1) are an ideal solution to biosensor design. This type is reagentless and relies on direct transfer of electrons between the enzyme and electrode without mediators. The absence of mediators provides the biosensors with superior selectivity. There are few enzymes that naturally exhibit the ability for direct electron transfer. Most third generation sensors will require designing engineered enzymes that allow for this electron transfer, this has proved very difficult so far.


Fig. 1     Chem. Soc. Rev., 2013,42, 8733-8768

I look forward to learning more about sensor design and how to quantify the electric signals in order to produce a readable signal. Next week will begin learning how to use the voltages produced by sensors in order to obtain a readable value.

Why RET?

This is blog is intended to share and document my summer research experiences spent participating in Dr. Michael Daniele’s lab. As a high school biology teacher, receiving the chance to participate in the Research Experience for Teachers (RET) sponsored by ASSIST (Advanced Self-Powered Systems of Integrated Sensors and Technologies) at NC State University is extremely exciting. I look forward to learning about cutting-edge technologies in nanoscience and sharing these exciting advancements with my students.

ASSIST’s mission to improve health care by cross-linking personal health and environmental data also intrigues me. As an aspiring doctor, I have a high interest in the health aspects of my teaching career.  I will also be able to share these practices with the students at Athens Drive Magnet High School, which is now a center for Medical Sciences and Global Health Initiatives.

This blog will describe my progress and completion of my research project. It will also outline how I plan to translate and implement what I learn from this research experience in my classroom. Enjoy!