See engineering for additional context on how these components were designed with synthetic biology in mind.
Biosensor Applicator
Figure 1: Exploded view of the applicator.
Table 1: Preliminary bill of materials for the applicator. Each item is used once per applicator.
| ITEM NO. | PART NUMBER | DISCRIPTION | LINK FOR DRAWING |
|---|---|---|---|
| 1 | IN-001 | Outer Shell | IN-001 |
| 2 | IN-002 | Inner Shell | IN-002 |
| 3 | IN-003 | Secondary Launcher | IN-003 |
| 4 | IN-004 | Primary Launcher | IN-004 |
| 5 | IN-005 | Monitor | IN-005 |
| 6 | IN-006 | Safety Cap | N/A |
| 7 | - | Large Spring | STOCK |
| 8 | - | Small Spring | STOCK |
Basic Function:
The user will receive the applicator, previously called the injector, with only the safety cap (IN-006) and outer shell (IN-001) exposed; the other components will be internal. To apply the monitor (IN-005), remove the safety cap (IN-006) and press down face A of the inner shell (IN-002) on to the desired location. The safety cap (IN-006) is discarded and assumed to be no longer part of the applicator from this point on. The inner shell (IN-002) will move deeper into the outer shell (IN-001) with the other components (IN-003, IN-004, IN-005, large spring, small spring). A compliant mechanism between face B on the inner shell (IN-002) and face A on the outer shell (IN-001) creates a resistance as the user presses down on face A of the inner shell (IN-002). A compliant mechanism is then tripped between the primary launcher (IN-004) and the outer shell (IN-001). The large spring drives the small spring, primary launcher (IN-004), secondary launcher (IN-005), and the monitor (IN-005) towards the outside of the large and inner shells (IN-001 and IN-002, respectively). Face A of the monitor (IN-005) is pressed against the skin; face A of the monitor (IN-005) contains the adhesive and adheres to the skin. There is a compliant mechanism on the primary launcher (IN-004) that snaps into the inner shell (IN-002) preventing the primary launcher (IN-004), the small spring, and the secondary launcher (IN-003) from leaving the inner shell (IN-002). Prongs extending off of the secondary launcher (IN-003) are pressed up against the skin; this causes them to spread apart, releasing the secondary launcher (IN-003) from the primary launcher (IN-004). The secondary launcher (IN-004) is propelled back into the inner shell (IN-002) by the small spring.
Detailed design parameters
Fluorescence sensor:
Housing
IMAGE 1: Render of the PFOA housing.
The housing blocks out the light to reduce the noise in the system. The STL files for the housing can be found here. An exploded view for assembly of the housing can be found here.
Download top here.
Download slit here.
Download bottom here.
Microfluidic Chip
A Microfluidic chip was designed and a mask fabricated while the team was still focused on using Fluorescence to help firefighter’s carcinogen levels. This microfluidic chip would have housed the aptamer and let a sample of liquid enter the chambers and be lit up and its fluorescence analyzed. We built a chromium mask (on the Heidelberg mask writer) which was used to pattern Su8-2015 onto a silicon wafer, creating 15-micron high structures that follow the above pattern. Had we continued further on this path, we would have poured PMDS over the wafer, with the Su-8 silicon wafer acting as the mold, resulting in a PMDS cylinder structure with 15-micron deep wells. The aptamers would have been put into the wells and sealed shut with a glass slide. When we were ready to analyze, we would create a hole in the center of the well structure and insert the solution we wanted to analyze. We did not get any further past creating the silicon- su8 mold because we decided to switch directions and analyze progesterone with electrochemistry instead of PFOAs with florescence.
Potentiostat
Proposed potentiostat circuit diagram adapted from design in Meloni, G. N.1
Our experiments measuring progesterone levels via aptamers on a gold electrode have all been done using AC Voltammetry using a potentiostat. This means it is essential that we simplify and recreate a potentiostat on a PCB that can be used in the sensor. In order to create this pcb, we are following the circuit design outlined in the above paper. This circuit uses an arduino (which we could switch for another microcontroller) to send voltage sweeps from -0.4 to -0.1 V through the Amplifying Circuit, Electrochemical cell and transimpedence amplifier, mimicking a potentiostat and allowing us to measure the current created at different progesterone levels.
References
- Meloni, G. N. Building a Microcontroller Based Potentiostat: A Inexpensive and Versatile Platform for Teaching Electrochemistry and Instrumentation. J. Chem. Educ. 93, 1320–1322 (2016).