Evaluation and Testing

Methods

Normal wild-type blood has been tested to have a redox-potential of -250 to -270 mV, while sickled blood is estimated to have a redox potential of -220 mV. The basis of our design uses a disposable printed circuit board on which a sample of treated blood is placed. The PCB is inserted into a potentiostat which runs cyclic voltammetry by Arduino code, which is then transferred to a computer via connector USB and analyzed by MATLAB. After analysis is finished, the code will return if the presence of Hemoglobin S in the blood sample is found.

The potentiostat was fabricated and assembled from PCBway, and the code to run the potentiostat was borrowed from the KickStat publication "KickStat: A Coin-Sized Potentiostat for High-Resolution Electrochemical Analysis" doi: https://doi.org/10.3390/s20082407. 

This design was finished and prototyped before Bioengineering Day, however it was not completed before the end of Winter Quarter. Our mentor delegated the task of leading to Carlos Munoz who has done a wonderful job of keeping our group on task. As a group, we have more experience in the lab, and have more training to be able to work in that environment. Our device costs less than $500 for all testing and parts, however, the device for consumer use would be about $30 per device. Single uses with this device after the initial purchase are around $6 per sample. We created a device that uses cyclic voltammetry to find whether or not a blood sample is positive for HbS. We took into account the safety of our team and the safety of the users.

Our design goals were to be able to accurately quantify HbS with an inexpensive, rapid, and easily operable method. This device is able to identify HbS by seeing the redox signal strength at -220mV versus regular blood at -250 to -270mV. It is easily affordable with an initial production cost of $30 for the device and $6 per electrode to test each sample. It is very rapid, with cyclic voltammetry able to be completed in minutes. The operator simply has to prep the blood for testing, insert a disposable PCB into the device and run the device’s code on a computer. 

Results

The users will be able to get rapid results for the amount of HbS present, and therefore be able to receive treatment immediately. Usually the treatment is administered days later, due to laboratory delays, but with instant testing, the patient can get immediate help for their condition. The following table shows the testing process used for the device. Figures 1 and 2 in the table show the redox potentials of the gold electrode with the phosphate buffer solution. The range of peaks shown in figure 1 depict the different cycles, with the lowest currents being the initial runs and the higher current peaks being the later runs, indicating that the electrode is primed for use. Figure 2 shows a single averaged curve from the 7 total cycles. Figures 3, 4, 5, and 6 show the results of the same 10% hemoglobin solution run at different times, with figures 3 and 5 being the 7-cycle scans and 4 and 6 being the single, averaged cycles. This shows that the peaks became more defined after the number of cycles increased.

Current results from our testing show that the device can be used for reading redox potentials as indicated by the peaks shown in the buffer cleaning curves and 10% Hemoglobin solution curves. Over a period of 7 cycles through voltages -450mV to 450mV, visible results show an increase in gold surface electron exchange which can be seen as increasing oxidation peaks for the buffer cleaning curve. The buffer cleaning single curve shows the sixth cycle which indicates a clean electrode.

There is a difference in peak definition for the initial and final scans of the electrode. The initial scan tends to have more noise, as can be seen in the initial 7 cycle 10% Hemoglobin solution scan. As the scans continue, peak shape becomes more defined, as can be seen in the final 7 cycle 10% Hemoglobin solution scan. However, despite the differences in clarity in the multiple cycles, both the initial and final scans can be used to estimate the oxidation and reduction peak currents, although the final scan may be more accurate.

Testing Discussion and Conclusions

Current results are showing fairly consistent scans with the phosphate buffer. Peak values tend to be around -125mV, with varying current amplitudes based on the cycle number. These show only the gold redox reactions, which chemically cleans the electrodes before use. Although we are currently seeing consistent readings for the 10% hemoglobin solution, the peak values do not match the expected values for hemoglobin. Values from literature31 state that the oxidation curve should be in the range of -276mV to -250mV, and current values from our device have been shown to be accurate for both sickle and wild-type hemoglobin, however, more optimization is needed for consistency.

We are reaching the expected values of the literature redox potentials, however they do not always occur. A future direction may be to statistically analyze if the correct values occur enough to be significant. For now, the device is able to read the redox potentials and show graphically the peaks, wherever they land, and mostly show the redox potentials within expected values.