Team:ZJU-China/Hardware

At the very beginning of hardware construction, all biological products and other auxiliary reagents (like Au nanoparticles and Nafion) have to immobilized on the electrode. To meet the need of large-scale manufacturing and high accuracy, we used a 2D printer to print these materials onto IDEs (InterDigital Electrode) to modify the Au-surface. Then we assembled IDEs, amplifier, convertor and digital interface to an entire circuit. The signal from the circuit is transmitted to an iPhone through Bluetooth. Several blood samples from a qualified Hospital were collected for access our hardwares and enzyme IDEs.

2D printer

Our 2D printer consists of a constant-flow pump, motors, an Arduino Uno microcontroller. The printer’s user interface is based on a Windows software by Steamduino which support several file formats like CAD scripts or normal pictures. Imported files will be converted to 2D routes and transmitted to the microcontroller. The speed of motors and flow rate of the "ink" are controllable in the panel. Since the space between lead feet of IDEs is about 4 mm, the printer can reach an accuracy of 3 mm. The path-programmable printer offers more possibilities for developers to design on the level of electrodes. For example, separated areas of the chip can be modified with different enzymes.

Fig. 1 Real picture of a 2D printer and its control panel

IDE (interdigital electrode) design

IDE (interdigital electrode) is composed of two interdigital electrodes with two connection tracks, on an insulative substrate. IDE is cheaper than normal electrodes and can work with low volumes of sample. The interdigitated configuration typically enhances sensitivity and detection limits.

The IDE circuit is planted on a PET (Polyethylene terephthalate) platform. And circuits itself are covered with copper, nickel and gold (in a manner from inside to surface) to enhance the conductivity. The current in side IDEs are led out through a FPC (Flexible Printed Circuit) connector which fits to the size of IDE lead feet.

二级标题！First generation of IDE

Taking our 2D-printer’s precision into consideration, we designed our first generation of IDE (see Fig. 1). The part with black lines is 6×interdigital working electrodes, the green part is a counter electrode and the red part is a reference electrode. But in the first design, two interdigital electrodes in pair are linked to the same lead foot which significantly lower the space for further DIY.

Fig. 2 First generation of IDE. The part with black lines is 6×interdigital working electrodes, the green part is a counter electrode and the red part is a reference electrode.

To make it easier to adjust hardware for the above IDE and to print enzyme solution, we modify our IDE and create the second generation of IDE (see Fig.2). We design thicker working electrode and electrical contact, working electrode reaching the thickness of 0.44mm. And 0.48mm gap is left to avoid short circuit. And we separate each pair of interdigital electrode, following the principle of IDE design.

Fig. 2 Second generation of IDE

Integration

To accurately describe the results of protein production, simplify user operations and save time, we developed a complete system consisting of two parts. That is converter and amplifier, reporter.

We connect a Transimpedance Amplifiers together with a Bluetooth module an expansion on arduino nano board.

We printed the ink containing modified enzymes on IDE. IDE’s output ports are connected to the in-port of the second part with a very low electronic current which can accordingly form a voltage big enough that is sufficient to be detected by our detector. The detector is just an arduino nano board with an blueteeth board which, we use analog pin to detect the voltage and using blueteeth board to transfer the data to mobile phone running the WeChat mini-program which can show the data it received by blueteeth. In last part the reporter receives the voltage and transfer them with our algorithm into an actual current value, and then sends processed user-readable results to the applets on the user’s mobile phone. This app is developed in the WeChat Platform, here are some screen shoots in the app.

The hardware implementation not only solves the need to report wet experiment results, but also is much more user friendly, especially for non-professionals.

In order to verify the stability and accuracy, we conducted dozens of tests in the hospital using real blood samples and contacted the experts to evaluate the hardware.

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