Design and Inspiration

PFAS, known as per(poly)-fluoroalkyl substances, commonly referred to as “forever chemicals” present major health risks to humans and the environment. With a rise in environmental health concerns, there is a major demand for sensors to selectively detect environmental markers.


With the intrinsic goal of detection of PFAS, I aimed to target rapid, selective PFAS detection through the use of Lateral Flow Assays and Filters. My goal for extending my original focus to filters was to target the capture and detection of PFAS, which can present a possible solution for PFAS removal from water supplies at homes and industries.

While point-of-care diagnostic (POC) treatment employs lateral flow assays for the colorimetric and fluorometric sensing of biological and environmental analytes, few studies have employed conductive polymers for the quantitative sensing of environmental analytes. This final project aims to employ a series of conductive polymers fabricated onto a sensing device for the quantitative detection of environmental markers. As the conductive polymers exhibit an extended pi-conjugated backbone, facile reduction, and oxidation upon introduction to the analyte will encourage selective limits of detection. Through employing the Fusion360 Software, the sensor prototype will be modeled, built, and enhanced throughout the course of this semester.

The e-LFA will contain a sample loading and absorbent pad, that through capillary action drives the fluid through the nitrocellulose membrane to deliver the PFAS to the F-PANi fabricated test lines, which are proposed to induce an increase in conductivity upon introduction to PFAS. In the polymer synthesis lense, the selectivity of a library of functionalized F-PANi polymers for e-LFA will be fabricated onto the sensor.

For my final project, the overall goal is to design am electronic-conductive polymer fabricated sensing device that can quantify PFAS Concentration in water with reference to the EPA limits of detection of 4 ppt. My main three goals for the final project include: 1. Selectivity for PFAS of all chain lengths over non-fluorous compounds Synthetically, the fluorophilic and hydrophobic effect will be targeted to yield covalent and ionic perfluoroalkyl moieties incorporated into the polymer network for selective PFAS detection.

2. Reusable and Cost-Effective Device The cartridges for the sensor will be targetted through laser-cutting PMMA poly(methyl methacrylate).

3. Rapid and Wireless Readout of PFAS Concentration Copper Electrodes with 20-30 resistors will be fabricated onto the PMMA cartridge to measure the average conductivity of the polymeric films. From here, the conductivity can be extrapolated with reference to the bulk resistivity of the film.

Conductivity = σ = 1/(bulk resistivity*film thickness)

- Wireless signal will be employed by incorporating the ESP 32-C3 microcontroller into the electronics board design. From here, with Arduino IDE C++ Code, the wireless readout of the conductivity can be programmed and communicated with devices.

- Output screen on the sensor cartridge will display the PFAS Concentration in the Water and indicate whether the PFAS Concentration is above the EPA Limits of Detection.

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Vinyl Cutting

With an interest in creating a label for my sensor, I decided to target "Enviro Sensing Technology." In order to design my label, I employed Inkscape Software. Particular commands of interest and assistance included Object-Mask-SetInverseMask in order to cut the designs.

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Laser Cutting

Learning to employ Fusion360 for 3D design was a fun and challenging endeavor. With an interest in designing a bridge platform with two arches, I first sketched the base of the bridge. After measuring a thickness of 4.48 mm with the caliper, I went on to begin my drawing. Through this journey, I learned the l feature in order to begin my sketch along with the importance of parameterizing each feature and the mirror image feature for future replication. The base of the arch included rectangular slits for assembly, which were achieved through the rectangular pattern with a slit width of 10 mm and thickness of 4.48 mm. The split cell feature was also employed to create a new document.

In order to encourage arch flexibility with a cardboard material, I chose to extrude the cyclohexane rings onto the arch plane. The kerf chosen was 0.2540 mm, and the dimensions of the base were 100 mm x 50 mm.

Upon yielding Fusion Sketches of the base and arch, both sketches were saved as DXF files. Interestingly, the printer did not accept the DXF files, so an SVG file was employed instead.

This week, I focused on employing Arduino IDE and PythonScript for the prgramming of a seeed Studio Xiao RP 2040 circuit board. With an interest in the wireless readout of PFA concentration for my final project, the goal of this week was to develop program that reports flashes red (indicating PFOA concentration above EPA limits), and a program that flashes green (indicating PFOA concentrations below EPA limits).

The Xiao RP2030 has 32 GPIL ports, by which only 14 are accessible. With respect to the the schematic for the RFP, one can note the LED light locations:
Blue: GPL25
Green: GPL 16
Red: GPL 17

To factory reset the circuit board, press:
R = rest, runs code from scratch
B = factory reset mode

In Arduino, a part of the system employed a bootloader to convert the Arduino code onto Micropython from the circuit to the server. Thus the Arduino code was running on Python and alerts were reported.

For this week’s 3D scanning design, I was excited to carry out self-portrait scans with Char and Gayuri. We employed the Artec LEO 3D Laser Scanner in the CBA shop and scans were tuned with the Artec LEO software for further tuning of designs through tuning the mesh and scaling. Creality was utilized to prepare the STL files for 3D printing. Unfortunately, the first scan inaccurately accounted for my eyes and facial structure. Thankfully, Char and Gayuri took another scan of me, which looked more representative! I will admit my curls were not fully captured, but I am excited for more scanning in store!

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In an effort to target a cartridge prototype for the quantitative detection of environmental analytes, I targeted a Lateral Flow Assay Cartridge this week. During my designing phase, I employed Autodesk Fusion 360 Software. Features of Autodesk Fusion 360 that I found quite useful included the parametric design of the diameters of the circular holes and dimensions of the test strip and the base cartridge.

Lateral Flow Assay nitrocellulose test strip
D1 = 20 mm
D2 = 40 mm

The base cartridge has dimensions of 40mm x 60 mm.

The sweep feature was helpful in order to secure the lateral flow assay with a Teflon ring. The dimensions of the curve:
CL1= 46 mm
Cl2 = 32 mm
Arc = 8 mm

The mirror feature allows for symmetry of the sketch and was quite useful when drawing the circular holes for the screws with diameters of 1.2 mm and 2.0 mm, respectively. The tangent feature allowed for the constraint of the circles to the polymer film outline, encouraging the security of the sample in place. In extrusion, the bottom part of the cartridge was extruded to a thickness of 3 mm, while the top of the cartridge was extruded to a thickness of 2 mm. In assembly, the M2 and M3 screws will be utilized to secure the polymer film to the cartridge.

The Fillet feature was employed to generate curved edges of the cartridge with a dimension of 2 mm. The base cartridge has dimensions of 40mm x 60 mm.
Thank you to Alfonso for helpful guidance in Fusion tools!

As the original polymer choice was a recycled PLA, I believe the 3D printer was heating above the glass transition temperature of the polymers and led to some defects in the prototype. For this reason, the polymer chosen was a homopolymer of PLA and produced a structurally-sound prototype to be assembled with M3 and M2 screws.

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Despite a quite hectic two weeks with fellowship applications and my first group meeting, I was eager to begin my circuit board design this week. With complex final project aims to measure the resistance of a polymer coating over time to measure the conductivity, my primary goal of this week was to develop a stronger understanding of the electronics design in Eagle which offered a smooth transition from my use of Fusion 360. This week my project focus was to incorporate a button and LED light into a Seeed XIAO RP2040 microcontroller and circuit layout.

Within my electronics design scheme, I focused on employing a resistor in order to control the flow of current to the button and the LED light. Furthermore, I also employed a pull up resistor set up for the button with the grounds connected. Both approaches are preferred as they prevent the buildup of current and a potential shortage.

As I plan to extend my design for further sensing applications, I employed a connector with pins in order to encourage further output sensing in the future.

Notably, the RP 2040 exhibits 2 processor cores with 30 multifunctional general purpose input and output ports, alongside a 4 channel ADS with an internal temperature sensor.

A few key pieces of terminology that I have learned include:
GND = external ground
SMD = Surface Modified Device

Key Features to Eagle Fusion 360, which aided me in my work include:
- Naming connections for clear board diagrams
-Add feature with access to priorly downloaded fab class circuit components
-Starting with a simple board layout including an LED light and switch. From here, I made iterative edits with an increase in complexity with the pin connections.

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This week, I aimed to target a PCB board that contains a few targeted components for my final project, namely:

1. LED Light, which blinks upon introduction to PFAS followed by an output message to the consumer.
2. Button, which functions to turn on/off the LED light, mimicking a light on a potential LFA detector or filter.
3. Microcontroller, XIAO RP2040, which will eventually have to be upgraded to a ESP 32, in order to allow for Bluetooth wireless, quantitative sensing readouts.
4. Connector for further incorporation of output devices including resistivity sensor, Bluetooth.


Circuit Board Design -Tune Ups
I targeted my circuit board design in Fusion 360, Eagle and particularly included a connection from the button to the LED light, to further encourage connection. It is important to note, that the class “fab” component folder needed to be downloaded to allow access to components available in CBA. The design of my board for this week, while containing additional needed space, was a heart. I will note that the original design from Week V. was modified to include a connection from LED to the button. From here, I downloaded the STL files of the top PC board and outline with Anthony’s line of code, “run singleImages,” which prompts a download of the STL files in Fusion. I then uploaded both my outline and top file to Neil’s MODS by selecting program PCB 2D Mill feature, followed by prompting trace outlines for the top and outline, with the following settings:

Top Trace
• Diameter of Mill Screws = 1/64”, 0.4 mm
• Cut depth = 0.1mm
• Max depth = 0.1 mm
• Offset number = 2

Edge Cut File
• Diameter of Mill Screws = 1/64”, 0.8 mm
• Cut depth = 0.6mm
• Max depth = 1.8 mm
• Offset number = 3

Milling the Board
The program employed for board miling was the Universal G Code software. First, the appropriate screw was fastened after raising the z axis and removing the vacuum adaptor. From here, zeroed the x, y, z plane and loaded the top trace g-code file. It is important to note that during my first trial of milling my PCB board, a major hurdle faced was first connecting the mill to the software with the guidance of Alfonso and Quentin. In addition, the trace of the path was originally set to 6 ml diameter, which led to quite unusable mill jobs. Thus, I further went on to employ a 16 ml route size, which led to a quite pristine board below:

Soldering Fun
From here, I embarked on the next stage of the project, soldering, following the training from Alfonso! For this, I employed the tin metal wire, and carefully positioned my component onto the board. The soldering pen does reach to a temperature of 400 degrees Celsius, so extreme caution was employed. It is important to note, that the data sheets helped to indicate the directionality of the LED, Button, and resistors. While I am still working to finalize the working- product, I have made the following progress shown with the components below:

2 X 3 Header SMD
10 Ohm Resistor with 5V supply voltage and 3V forward voltage
XIAO RP 2040 Microcontroller
Red LLED1206
SW Switch Tactile 6MM

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Molding and Design
This week, I aimed to design an Erlenmeyer flask for both design aesthetic and to eventually expand to a food mold for Erlenmeyer candies after the food-friendly silicone material arrives. To first design the mold, I employed Fusion 360. It is important to note that parameterization was a key component in order to keep track of all different component parameters and change them as needed.

I first employed the revolve featured of half of the Erlenmeyer flask drawing, along with the fillet-feature to smooth the edges. From here, the sketch was extruded with the revolving feature. Next, I targeted a register with a depth of 40 mm, with length and width 160 mm x 180 mm respectively. Further, tightening, I employed spheres along the diagonal axes of the mold to encourage fastening when adding the material for the final product. Moreover, a sprue opening was employed as an outlet to add the material. I do wish that I had employed a vent, in order to prevent bubbling. Then, to make two molds, I copied my first mold and then combined both molds to one body. The final mold was exported as a mesh STL file.

Milling Mold Outline
Cut 3D Software was employed in order to prepare mill trace from the mesh STL file for milling the wax block. The following parameters were used:

• HTMAA Mill Diameter = 0.125 in
• Pass Depth = 0.1 in
• Stepover = 0.015 in
• Spindle Speed = 6000 rpm
• Feed rate = 90.0
• Plunge Rate = 90.0
• Rapid Clearance Gap = 0.2 in

It is important to note that a smoothing feature allowed for a clean finish. The x and y axis were then zeroed with the Shop Bot software, following the z axis zeroed with a z-zero plate. The mold was then milled with frequent vacuum to remove the wax.

Preparing Mold and Casting
I prepared the physical mold with Smooth-On silicone based polymer, with structure described below. Equivolumes of curing agent A and B were employed at 8 each, respectively. It is important to note that in preparation a consistent and slow stirring is needed in order to prevent bubbles from the exothermic reaction. Bubbles that formed on the surface were removed via sonication. From here the mold curing time for the mold was for 75 minutes.
From here, Hydrocal (gypsum cement) plaster material, which consists of calcium sulfate dihydrate. A 2.2:1 ratio of Hydrocal powder to water were combined and then stirred slowly to yield a smooth consistency. From here, the plaster was added to the mold slowly in order to prevent bubbling. It is important to note a sand bath was used to secure the mold in place. (Thank you, Graham!)

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With much anticipation, I was excited to embark on this week’s project to employ computer-controlled machining to design, mill, and assemble a large piece! With an interest in tables for my apartment décor, I set out to design two-tiered nightstands. In my design phase, I first considered a circular base and top shelf, along with modern legs below. My ideal height for the nightstand would be 24 inches.

Design
First, I spent much time on YouTube to learn the general design assembly process for Fusion 360 furniture parts. Next, I embarked on the design phase by measuring the thickness of the wood at 11.6 mm with 4 ft x 8 ft width and length, respectively. To start, I defined the parameters of my drawing, through the parameterization feature:

Thickness = 11.6 mm
Height = 609 mm
Top Shelf Diameter = 457.2 mm
Bottom Shelf Diameter = 300 mm
Length of Base = 8 ft
Width of Base = 4 ft


Next, I first began by defining an offset construction plane with the height of the table. This encouraged the three-dimensional drawing, assembly, and modeling of my piece. From here, I began drawing the top shelf on the offset plane with the height of the bottom shelf. Note, after drawing followed by extrusion to the wood thickness of 11.6 mm. Similarly, I defined the offset plane height (parameterized as height/2) for the bottom shelf.

The leg of the chair could then be drawn by drawing on an offset plane perpendicular to the shelves. It is important to note, that a feature of circular pattern was then employed along the z-axis to yield 4 legs of the table. Lastly, I targeted cuts within the top and bottom shelf for assembly through the combine and cut feature. From here, a new base of the BCX plywood board was targeted with 4 ft x 8 ft dimensions, and the joint feature was employed to add each piece of the table to the base. A dxf file was then exported.
The VCarve program was employed with a defined 96 in by 48 in dimensions. Thank you to John for training and guidance! It was important to not employ the offset feature and ensure that 2 in margins were considered to account for screwing the wooden piece in place. From here, the join and close vectors feature was utilized to ensure each piece was closed. I then added the dog bone features to the slots along with tabs.
Stock Cut Thickness = 0.52 in
Depth Cut = 0.26 in
Conventional Cut (clockwise from L to R)
Endmill = 0.25 in


Next, the toolpath was defined to yield the ShopBot file for milling followed by export to the ShopBot file.

Milling
The ShopBot Mill was employed to mill the design. It is important to note that PPE (long pants, goggles, close-toed shoes) is necessary when working with the ShopBot and assembling designs. In addition, a filter vacuum was utilized to collect sawdust particles.

First, the ShopBot file was opened, and the and y zero were previously defined. Thus, the z zero was defined with a z zero metal plate. Upon zeroing in all three dimensions, it is now time to start the spindle by pressing the green button, start. The milling process lasted approximately 30 minutes.

Assembly
Initially, when assembling my table, the bottom shelf assembly cuts did not adequately scale with the size of the top table cuts. Thus, I milled the bottom shelf design. Editing the cut slits to yield my exciting masterpieces below! Overall, I enjoyed this week’s project design and look forward to targeting my tables with more durable wood later this week.

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With a strong interest in building on my final project, I was eager to embark on input design this week. With an interest in monitoring the conductivity change of my conductive polymer films upon introduction to PFAS in order to further quantify the concentration of PFAS, I was eager to design an input device to record the resistance of my polymers.

Design
In order to design my PCB board, I employed Eagle in Fusion 360 Software. The Xiao RP 2040 Microcontroller was employed with particular interest in the A0-A3 ports for input sensing of the resistance. As I monitored the resistance with two electrodes, I employed the A0 port. In order to monitor the voltage of the electrodes over time, a voltage divider was employed, by which:

Voltage Source = 3.3V
Resistance 1 = 20 MOhm
Resistance 2 = 10 MOhm
Output Voltage = 2.475V

Milling and Soldering
The SRM-20 Roland was employed to mill the PCB Board, which was controlled directly through MODs. For the SRM-20 Roland MODS Program, the PNG image must be uploaded to generate a mill-path instead. It is important to note that the x,y,z zero must be manually determined. The traces employed were 16 mills, which offered an intricately milled board at the end.

During the soldering phase, tin metal was employed in order to sadder the XIAO microcontroller, 10 MOhm resistor, and connector to the board. While I am still acclimating to soldering, I eventually was able to establish a connection between each component as confirmed via multimeter detection signals.
Arduino and Input Sensing
For programming the RP Xiao 2040 Microcontroller, I employed Arduino IDE code, by which I defined the input port for the analog pin as A0, the 3.3V reference, which also can be referenced to 1024 counts later in the script. Furthermore, calculations for R1 can be determined from the voltage divider equation:

V out = (Vs*R2)/(R1+R2)

During the sensing phase, I ran the Arduino code and was able to measure the resistance of the polymer films on the order of 3-4 MOhms, which indicates high oxidation of the polymer sample, but also doesn't directly align with the 4-point probe resistance of 20 MOhm. Further tuning must be targetted as a background resistance of 1 MOhm was observed and to yield consistent reading with the four point probe. In the future, I aim to improve the design of the electrodes through vinyl cutting copper tape designs with controlled contact to my polymer films.

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This week, I at first was quite interested in developing a Touch Screen Output Device with a TFT LCD Display Touch Screen, but after some analysis on the complex microcontroller incorporation and soldering needs, I chose to first target an OLED SSD 1396 Display.
I then refined my goal to target the readout of the PFOA Concentration within the analyte along with EPA Limits of detection. A sample OLED Readout would include two cases:

1. PFOA Concentration is above EPA Limits: “Alert! PFOA Concentration = 200 ppt. Warning! Above EPA Limit of Detection.”

2. PFOA Concentration is below EPA Limits: “Alert! PFOA Concentration = 0.03 ppt. Below EPA Limit of Detection.

In order to target my wireless readout of PFOA Concentration, I first targeted my PCB Board with an Xiao RP2040 Microcontroller. In designing my PCB Board, on Fusion 360 Eagle, I solely targeted to incorporate my RP2040 Microcontroller along with a connector to the OLED Display. Important connections to the OLED Display included:

GND: Ground

VCC: Voltage at Common Collector is the power supply which ranges from 3.3V - 5.0V

SCL: Serial Clock Line, which is a digital communication signal for data transmission. Moreover, the Serial Clock Line also confirms that the receiver (microcontroller and OLED) and sender (Arduino Code) receive communication at the synchronously. Note, the SCL and SDA are both employed in the I2C (inter-integrated circuit) communication protocol, which carried data.

SDA: Serial Data Line, which works with the SCL and allows for data to be communicated between devices.


Milling
From here, I went on to embark on a long journey of milling. While, I was relatively content with the simplistic function of my board, I ran into some time demanding milling troubleshooting experiences including:

• Worn out end mills.
• Origin recognition issues on the SRM 20 PCB.
• Leveling and zeroing.

I am extremely grateful to Alfonso and Quentin for helping me in the milling process. Thank you Alfonso for going through a review milling process with me, I appreciate it.


Soldering
The fun continues! I went on to solder my board but noticed a light spark in copper traces upon milling the connector component. I attribute this to potential component failure of the connectors or the melting of the copper traces. Upon attempting to connect my computer to the board with an HDMI, I could not observe any light flashing. Upon attempting to boot and reset the board, I still did not observe a light flicker. I went on to carry out examination with a digital multimeter to determine if current did flow through the copper traces, but unfortunately could not observe current near the adaptor. Despite a time-demanding week, I emphasize a few key learning points:

1. The connections incorporated within an OLED and the RP 2040 microcontroller allow for communication from the Arduino code to the OLED Device via an output function with the inter integrated circuit (I2C) communication.

2. It is important to make a thorough analysis of milling conditions to prevent an over exhaustion in milling time. (6 hours.)

3. One can spark a circuit through soldering, and it is important to always maintain a safe working environment. Including an exhaust fan, tweezers, and caution when handling the soldering pan. Please read SDS sheet before handling the soldering pen.


I did manage to write my Arduino Code for the OLED readout with reference to and hope to further incorporate my output device into my final project.

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For machine building week, my CBA section aimed to build a camera machine for monitoring photos. I contributed to the team project by 3-D printing, and assembling the rotor employed for synergistically rotating the models in front of the camera. This model incorporates a PCB board with a XIAO-RP2040 microcontroller in order to further connect the rotor to a step motor for rotating the models on a platform.
Find out more about our group project below: https://fab.cba.mit.edu/classes/863.23/CBA/machine/index.html

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In the sphere of materials synthesis, I targeted the interfacial polymerization of polyaniline(PANI) nano fibers for my final project. The beauty of PANI coatings is that they exhibit a rigid conjugated backbone, which allows for facile oxidation to the emeraldine salt upon acidification of PFAS.
This polymerization is carried out with an oxidant, ammonium persulfate (APS) and camphorsulfonic acid (CSA), and Dichloromethane. Upon polymerizing polyaniline to yield the emeraldine salt form, the PANI-ES was reduced to PANI-EB with ammonium hydroxide.

While PANI-EB is insoluble in most organic solvents aside from DMF, it can be characterized by Scanning Electron Microscopy (SEM), Fourier Transfer Infrared Resonance (FTIR) Spectroscopy, and Thermal Gravimetric Analysis. The degradation temperature, Td of PANI was determined to be 326.12 °C.
As PANI forms even dispersions in aqueous media, it can be employed as an ink for the lateral flow assay sensors. In addition, PANI can be polymerized homogeneously on cellulosic membranes for the filter sensing devices. This encourages controlled, rapid, and limited-waste preparation of PANI-paper for further commercialization of the PANI devices.