Team:ZJU-China/Human Practices
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OVERVIEW
Lianjun Lin, Director of the IVDs department of MDST.
Is our diagnostic device biosafe? Is it good for our community? Does it meet the demands of public? Can it be truly applied to our truly life? To complete the investigation of the big background where our ideas were born, we visited experts in related area and performed questionnaires in order to evaluate the public acceptance of our device.
A Public investigation concerning about the public acceptance of our device:
Biosecurity & Ethics ConsiderationBiosecurity is the most important and a basic consideration of our product since we chose to develop an in-vitro medical device. MDST (Zhejiang Institute of Medical Device Testing) is a supervisor department of government responsible for regulating medical device. Hence, we thought the suggestions from this department would make a great difference to our final product. Here, we applied a filed visit to their lab and interview the department charge, Lianjun Lin to consult his advice and opinions about the biosecurity and our medical device. We summarize his points of view which do make great impact on our project designing and list them below:
questionariesQ: How to promise the security of a medical diagnostic device?
A: It’s hard to define the word “security” while it related to many other concepts. The first thing you should concern about you device security is the national standard of in-vitro medical device. It represents the minimum level of safety that a product can be allowed to produce. Particularly for your device, I recommended you to focus on the basic security concerning about the Cell-Free Biosensor.
Generation one - A Detector IA Detector Iare formed by the working electrode, the counter electrode and the reference electrode. The task of the working and counter electrodes is to provide places where reactions take place (same as an electrolytic cell), and the reference electrode provides a “zero point”, which is necessary for numerical results (results presented by numbers). By using these all together, we can detect the catalyzation on the electrode surface and transfer it to the workstation. Electrochemical workstations are often utilized in the process of preparing sensors, which can accurately and conveniently describe characteristics of various solutions. One of the common uses is to plot CV curves and I-T curves.
In CV (Cyclic Voltammetry Curve), the electrochemical workstation forces reactions to move to the oxidation end and the reduction end successively by applying periodically and oscillating voltages to the electrodes. During these cycles, the changes of the current will tell us plenty of characteristics about the occurring reaction For an enzyme electrode sensor, the value of the oxidation peak or the value of the reduction peak of the cyclic voltammogram is linearly related to the concentration of reactant (of course, within a certain range of concentration). After getting the CV curve and plotting a standard cure, this linear relationship allows us to convert the current result of an unknown solution into a concentration result.
The I-T diagram (current-time change) is also important. By given a constant voltage (the voltage that push the current to peak in the CV diagram.), the catalyzing reaction will approach a specific steady state at last. Through the I-T diagram, we can get some information that CV curve can't provide, for instance--how long does it take for the reaction to reach equilibrium, which determines how long it takes to give an accurate feedback after adding the tested substance.
The I-T diagram (current-time change) is also important. By given a constant voltage (the voltage pushes the current to peak in the CV diagram.), the catalyzing reaction will approach a specific steady state. Through the I-T diagram, we can learn what CV curve can't provide, for instance--how long does it take for equilibrium, which determines how long it takes to give an accurate feedback after adding the tested substance.
By analyzing the CV curve or the I-T curve, we got the most practical graph - the relationship between the peak value of current and the concentrations of substances-that is, the standard curve. By analyzing substances in a concentration gradient, we knew where the detection had a good linear correlation, which is necessary for real-world detection. In this way, detecting a substance in an unknown concentration only needs to read the peak value of current and calculate the concentration by referring to the standard curve simply.
Single Enzyme TestAt the very beginning, we used a single enzyme sensor to detect the actual function of A Detector Ⅰ. We measured the function of three enzymes separately (glucose oxidase, horseradish peroxidase and lactate dehydrogenase, which are components of designed logical gate). The characteristics of each enzyme provided useful information for further experiments.
Test results were quite satisfactory. This indicated that there was still a large degree of retention of the enzyme activity after modification of the Tag/Catcher system. Figure 4, Figure 5, and Figure 6 illustrate that these three enzyme electrodes worked well.
Fig. 3
The activity test of the Glucose Oxidase (GOx）sensor. (A) The Cyclic Voltammetry Curve of glucose oxidase had a distinct oxidation peak around 0.3-0.4V, and its height increased with increasing substrate concentrations. (B) Picture B is a partial enlargement of Picture A. The relationship between the height of the peak and the concentration of the substrates could be observed more clearly on the Fig B. (C) Fig. C shows the linear relationship between substrate concentrations and peak currents. The correlation coefficient of 0.9966 indicates that the sensor had a fairly good capability within this concentration range.
Fig. 4
The activity test of the Horseradish Peroxidase (HRP) sensor. (A) Similar to the glucose oxidase sensor, the horseradish peroxidase sensor had a distinct oxidation peak (around 1.0-1.3V) that can be used as an “indicator” of substrate concentrations. (B) Picture B is a partial enlargement of Picture A. (C) Picture C shows a high correlation between peak currents and substrate concentrations, thus it is a satisfactory standard curve.
Fig. 5
The activity test of the Lactate Dehydrogenase(LDH) (A) The oxidation peak of the LDH sensor was not very obvious, but after calculating, we found that its peak current values still had a satisfactory relationship with the substrate concentrations. (B) Picture B is a partial enlargement of Picture A. Although this oxidation peak was relatively inconspicuous, we could still see it. (C) The relatively high correlation coefficient indicates that our sensor had good detection capability in the concentration range of 0.5-6mmol.
Enzyme Complex (Logical Gate) test
As we explained in the multi-enzyme complex part, part, glucose oxidase and horseradish peroxidase can be used together to construct an AND gate, while lactate dehydrogenase, glucose oxidase and horseradish peroxidase can be used to construct an XOR gate. Figure 7 and 8 show that both have been successfully constructed. Our project ideas have been implemented.
Fig. 6
Current-time diagram (I-T) of the AND gate. (A) Picture A shows the I-T curve for different input conditions (0/0, 0/1, 1/0, 1/1). The current was stable at about 80s. In theory, the 1/1 input had the highest current output, and the actual result met this expectation. (B) Picture B is a partial enlargement of Picture A. We could find that the sensor clearly distinguished between different input conditions. The 1/1 input had the highest current output, followed by the 0/1 input, and the other two inputs lower. Different inputs were clearly distinguished, indicating that the AND gate met our expectations.
Fig. 7
Current-time diagram (I-T) of the XOR gate. (A) Figure A shows the I-T curve for different input conditions (0/0, 0/1, 1/0, 1/1). The current was stable at about 90s. (B) Picture B is a partial enlargement of Picture A. The output of 0/1 and 1/0 were significantly different from (higher than) those of 1/1 and 0/0, which was in line with the characteristics of the XOR gate.
Future Plan
We were satisfactory with the results from the first generation of products, A Detector I. However, we cannot DIY our hardware, and the electrodes themselves need to rely on the huge electrochemical workstation, which let us think about the possibility of exploring the next portable generation of products----A Detector II
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