Team:ZJU-China/Hardware
Hardware(ViruDetector)
Introduction
Though approved by FDA, NMPA, and other countries' drug regulatory authorities as legitimate cancer treatments [1], virus therapy remains a risk-taking endeavor as the potential pathogenicity still somehow exists no matter how elaborate the safety system was designed [2]. For instance, other proven genetic engineering techniques like CAR-T therapy are often conducted after the attempt of regular cures like radiotherapy, chemotherapy was made and have not received positive results [3]. Under such circumstances, it is pivotal for our wet lab's project to be conducted after the exact diagnosis of liver cancer to avoid potential physiological and ethical risks of the virus itself. In layman's terms, we have to be sure the patient does have cancer before making any attempt to cure them and our hardware's job is to be sure the patient does get cancer. Moreover, the alarming mortality rate of liver cancer was contributed largely by the absence of efficient early diagnosis methods [4]. Both perspectives discussed above urge us to develop a hardware system (EIS-Analysis System) aiming at early patient self-inspection and clinical definite detection. Aligning with the project constructed by our wet lab group, our team can provide an entire liver cancer solution, tackling from early detection, definite diagnosis to potential cancer treatment.
User Information collection
During the development of our hardware project, we have conveyed several surveys and have interviewed potential users to better improve our hardware project (We have done the research along with our wet lab and please visit our HP page for the Questionnaire survey and other interview Results). Especially the interview with Dr. Hu (See this page) at The First Affiliated Hospital, College of Medicine, Zhejiang University. Dr. Hu has pointed out several problems with our first edition of the hardware and software system. For instance, the first app we developed did not have a doctor-patient communication function and the detection of AFP needs to be conducted in labs (See Fig. 0). Dr. Hu mentioned that such methods provided a huge obstacle to efficient early detection and we begin to develop a portable detection device.
After the first version of hardware was constructed, we invited Dennis (pseudonym, see Fig. 0-C), a student majoring in biological engineering, to test our device. Dennis himself is a type 1 diabetes patient and has to detect his blood glucose regularly. He has given us several suggestions based on his own specialized knowledge and daily experiences of self-detection. According to Dennis, our first-version detection chip requires patients themselves to drop reagents onto the chip, including their blood, meaning they have to possess certain biological experiment skills and take a lot of blood when conducting detecting (See Fig. 0-A). Inspired by the blood sugar test paper and blood-taking needles Dennis mentioned, we improved our second version device again, packaged the chip, minimized the chip size to suit the blood-taking needle, which enables a more user-friendly testing procedure. After few more minor amendments, we launched our final hardware version as followes:
Structure overview
The EIS-Analysis System we developed is a portable, economically viable impedance testing platform based on user-friendly smartphone apps and electrochemical hardware. We use the mobile workstation to measure the impedance of chips and transmit the processed signal to smartphones with a Bluetooth module. The user (Both patients and doctors, see our software website for more details) will have access to their results within a few minutes and the app will enable instant communication between doctors and patients if needed. Moreover, we have designed our platform with great transportability, meaning our platform can be used to measure myriads of proteins, cell concentrations using an antibody, aptamer, or any other biomarkers that suits impedance detection methods. Other igem teams or research groups will only need to change the biomarker in the chip and provide corresponding standard curves in order to use the EIS analysis system (See our contribution page for more details).
Our device is constituted of three parts (see Fig 1):
The portable power supply (any mobile power bank will suit)
The chip
The portable electrochemical station
As mentioned above, the portable electrochemical station is available for EIS analysis for any chip designed and sending the signal to smartphones for later uses. The chips can be replaced with different needs of subsequent igem teams and we have made two examples this year. Under our teams' demand, we have designed two chips with great performance in linearity, specificity, stability, and rapidity aiming at early cancer self-detection for susceptible populations and definite diagnosis with liver cell puncture fluid respectively.
*We adopted the blood-taking needle designed for diabetes patients for blood sampling
Detecting Principle
Impedance
"Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current."[5] Impedance measures the resistivity to alternating current presented by the combined effect of resistance and reactance in a circuit [6].
The impedance of a two-terminal circuit element is represented as a complex quantity $|Z|$. The polar form conveniently captures both magnitude and phase characteristics as:
\begin{equation} Z=|Z|e^{j\arg(Z)} \end{equation}
where the magnitude |Z| represents the ratio of the voltage difference amplitude to the current amplitude, while the argument arg(Z) (commonly given the symbol $\Theta$) gives the phase difference between voltage and current. j is the imaginary unit, and is used instead of i in this context to avoid confusion with the symbol for electric current. In Cartesian form, impedance is defined as:
\begin{equation} Z=R+jX \end{equation}
where the real part of impedance is the resistance R and the imaginary part is the reactance X. [7]
Thus, through measuring the R and X we are able to infer the consistent of a certain solution or material.
Ohm's law
The meaning of electrical impedance can be understood by substituting it into Ohm's law. Assuming a two-terminal circuit element with impedance Z is driven by a sinusoidal voltage or current as above, there holds:
\begin{equation} V = IZ = I|Z|e^{j \arg(Z)} \end{equation}
The magnitude of the impedance |Z| acts just like resistance, giving the drop in voltage amplitude across an impedance Z for a given current I. The phase factor tells us that the current lags the voltage by a phase of arg(Z) (i.e., in the time domain, the current signal is shifted $\left( \frac{\theta}{2 \pi} \right)T$ later with respect to the voltage signal) [7].
Electrochemical impedance spectroscopy (EIS)
Electrochemical impedance spectroscopy (EIS) is a powerful technique that utilizes a small amplitude, alternating current (AC) signal to probe the impedance characteristics of a cell. The AC signal is scanned over a wide range of frequencies to generate an impedance spectrum for the electrochemical cell under test.
Electrochemical impedance can be measured using a small excitation signal, so that the system response is pseudo-linear. In a pseudo-linear system, the current response to a sinusoidal potential will be a sinusoid at the same frequency but shifted in phase (see Fig 2).
The excitation signal, expressed as a function of time, has the form
\begin{equation} E_t = E_0 \sin(\omega t) \end{equation}
where $E_t$ is the potential at time t, E0?is the amplitude of the signal, and $\omega$ is the radial frequency. The relationship between radial frequency $\omega$(expressed in radians/second) and frequency $f$ (expressed in hertz) is:
\begin{equation} \omega = 2 \pi f \end{equation}
In a linear system, the response signal, $I_t$, is shifted in phase ($\Phi$) and has a different amplitude than $I_0$.
\begin{equation} I_t = I_0 \sin(\omega t + \phi) \end{equation}
An expression analogous to Ohm's Law allows us to calculate the impedance of the system as:
\begin{equation} Z = \frac{E(t)}{I(t)} = \frac{|E|\sin(\omega t)}{|I|\sin(\omega t + \theta)} =|Z| \frac{sin(\omega t)}{\sin(\omega t + \theta)} \end{equation}
The impedance is therefore expressed in terms of a magnitude, $Zo$, and a phase shift, $\Phi$. [8] [9]
Nyquist plot
Therefore, by measuring magnitude, Zo, and a phase shift, $\Phi$ discussed above in (3) under different frequencies, we are able to plot the Z in (1) on a complex plain, forming what is called Nyquist plot:
As we can see from Fig 3, the Nyquist plot contains two parts, a hemi-circle and an approximate line. Through fitting equivalent circuits (For example the one in Fig 4 below), we are able to reproduce the Nyquist plot using different Rct and Cd in the equivalent circuit.
So far, we have managed to create a relationship between a measurable value (the Rct in the fitted equivalent circuit) and the original impedance (or components in the solution). Through constructing Rct Standard Curve of known concentration solutions we will able to tell the concentration of unknown solutions using the formula derived from the Standard curve.
Design of the portable electrochemical station
Our portable electrochemical station is mainly based on Arduino UNO (providing consistent 5V output) and the expansion circuit board we designed. (See Fig 5)
The impedance detection board
In order to realize impedance detection function of electrochemical station, we used the AD5933 chip [10] to generate the detection and have designed the corresponding circuit (See Fig 6, Downloads of layout files available on This page).
Other parts
We use HC-05 Bluetooth module to transmit the signal onto the smart phone and a three-electrode system interface to connect the chip. The entire flow chart is shown below:
The shell
The shell of portable detection was made by laser cutting acrylic plate, the square opening at the front and rear was for the interface and the battery (See Fig 9, Downloads of AutoCAD File available on This page).
Arduino programs
The programs in Arduino are relatively simple which main function is initiating the detection and sending the results to spart phone through Bluetooth module. (More details and downloads are presented on this page)
Assembling all parts above we have the completed detection station:
Budgets
| Item | Quantity | Cost per Unit(USD) | Cost(USD) |
|---|---|---|---|
| Arduino UNO | 1 | 10.69 | 10.69 |
| Circuit board printing | 1 | 0.5 | 0.5 |
| AD 5933 Chip | 1 | 17.8 | 17.8 |
| HC-05 | 1 | 1.55 | 1.55 |
| Wires | 2 | 0.093 | 0.186 |
| LM368DR | 1 | 0.02 | 0.02 |
| ADF4001 | 1 | 5.42 | 5.42 |
| ADG884 | 1 | 1.6 | 1.6 |
| Acrylic?plate (2mm) | 0.3 | 1.55 | 0.465 |
| ''Zensor'' Electrodes | 2 | 8.52 | 17.04 |
| HDR1X8-2.54 | 2 | 2.015 | 4.03 |
| HDR1X6 | 2 | 2.1 | 4.2 |
| Chip resistors and capacitances (As a whole) * | 1 | 1.05 | 1.05 |
| Interface | 1 | 0.75 | 0.75 |
| Total Amount | 65.301 |
Chip design
Corresponding chips for the EIS analyses hardware we have introduced above mainly functions with a biomarker. The selected biomarker (Typically antibody or aptamer) was embedded on the electrode and subsequently dropping with solutions to be assayed. Attached with different concentrations of target molecules, the impedance of the whole electrode-biomarker-target molecule system will differ from each other and can be measured respectively. As mentioned above, our chip design focuses on early patient self-inspection (using AFP) and clinical definite detection (using GPC-3) so as to ensure the necessity of conducting out wet lab treatment.
Functioning along with our EIS analyses hardware, we hope to reach the following results.
We have designed two chips for APF & HCC detection respectively
Please click on each bottom below with chip name to view the corresponding chip design
* For the reporduction of chips, please use "Zensor" Chips (or any Three-electrode chips) and follow our protocol provided below to reconstruct
Chip design for AFP detection
This part of the chip design aims at early self-detection of liver cancer susceptible populations. The target molecule and biomarker we chose, Alpha-Fetoprotein (AFP, and its corresponding anti-AFP antibody), will only be highly expressed in infants'' liver cells and hepatoma carcinoma cells [11]. AFP can be detected within serums and thus, the self-detection process can be conducted using patients' blood samples. Since the AFP has been studied and applied as biomarkers comparatively thoroughly, we will omit the preliminary experiments and present the chip design and results directly.
Electrode processing (immobilization of anti-AFP antibody, See Fig. 12)
Activate electrode with PBS, CV scan for 20 turns, voltage range -1~1V, scan rate 0.1V/s
Slim reduces GO (graphene oxide) on the electrode surface: 150Ul 1mg/ mL GO dispersion, voltage range 0~-1.8V, scan rate 0.05V/s, and number of turns 10.
drip 3ul of 1% chitosan solution and dry it
drop 4ul of AFP antibody onto the surface of the electrode and let it sit for half an hour.
Footed hangs the electrodes above a solution of 25% glutaraldehyde for half an hour, then takes them out and washes the surface with deionized water.
AFP detection and chip properties
The detection of AFP can be done through dropping serum containing different concentrations of AFP onto the processed electrode and incubating for less than 5 minutes before reading.
2.1 Short incubating time
We have tested the relationship between incubating time and Rct readings (See Fig. 13), the results turned out that our chip are able to reach the highest testing value (most measurable place) within a short time period. And rapidness is a pivotal part of user experiences, especially for at-home detecting situations.
2.2 Linearity
Linearity is the fundamental of AFP detection since the standard curve is derived from a set of Linear concentration. See Fig. 14 for our chip''s linearity for AFP detection.
2.3 Stability
The detection system must provide consistent results in order to be used for real-world detection. We have tested our device repeatedly using the same solution at two different concentrations and received relatively stable results. See Fig 15.
2.4 Selectivity
The serum content constitutes of various disturbing proteins and other molecules. Our device should have the ability to ensure the selectively by responding only to the target molecule AFP. Fig 16. Portrays our results and from the figure we can see that our detecting device provides low Rct response to disturbing materials and only gives out high response to AFP.
2.5 Transportability
Lastly, we examined the feasibility of transplanting the electrode system onto our portable devices by conducting the experiment under the same concentration. (See Fig 17.) And the result provided two almost-overlapping curve indicating the high transferability.
Chip packaging
In order to facilitate patient usage and other igem teams, we have packaged our chip so that they can be used directly without conducting electrode processing procedures. We will use the first Chip as an example as all packaging steps are similar to each other.
Since the in-lab detection of chips were conducted using electrochemical station in an environment of K3[Fe(CN)6]/ K4[Fe(CN)6] redox system. We have sprayed the K3[Fe(CN)6]/ K4[Fe(CN)6] dry powder onto one side of the chip which will resolve into the blood sample during the test. The reaction chamber of the chip confined the total volume so as to recreate the same concentration of K3[Fe(CN)6]/ K4[Fe(CN)6] system with the given amount of K3[Fe(CN)6]/ K4[Fe(CN)6] powder. The structure is shown below (Fig. 18).
References
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[2] Kootstra, N. A. and I. M. Verma. Gene Therapy with Viral Vectors. Annual Review of Pharmacology and toxicology 43: 413-39 (2003)
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[4] Volk, M.L., Marrero, J.A. Early detection of liver cancer: Diagnosis and management. Curr Gastroenterol Rep 10, 60-66 (2008). https://doi.org/10.1007/s11894-008-0010-2
[5] "Electrical Resistivity And Conductivity - Wikipedia". En.Wikipedia.Org, 2021, https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity.
[6] Slurzberg; Osterheld (1950). Essentials of Electricity for Radio and Television. 2nd ed. McGraw-Hill. pp. 360 - 362
[7] "Electrical Impedance - Wikipedia". En.Wikipedia.Org, 2021, https://en.wikipedia.org/wiki/Electrical_impedance.
[8] "Basics Of EIS: Electrochemical Research-Impedance". Gamry.Com, 2021, https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-spectroscopy/.
[9] "Basics Of EIS: Electrochemical Research-Impedance". Gamry.Com, 2021, https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-spectroscopy/.
[10] "AD5933 Datasheet And Product Info | Analog Devices". Analog.Com, 2021, https://www.analog.com/en/products/ad5933.html#product-documentation.
[11] June, Carl H. et al. "CAR T Cell Immunotherapy For Human Cancer". Science, vol 359, no. 6382, 2018, pp. 1361-1365. American Association For The Advancement Of Science (AAAS), https://doi.org/10.1126/science.aar6711. Accessed 10 Oct 2021.
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