Memo
Date: February 17, 2015
To: Inst. Trott and GTA Mohini Dutt
From: Joshua Epperson, Brooke Ott, Luisa Parish, and Ben Weisman
Subject: Detection Circuit Lab___________________________________________________
Introduction
This memo is going to discuss the reasons in which nano-materials are useful for
chemical sensing. It will also discuss why an increased surface area is better for active sensor
materials as well as some advantages of sensor miniaturization. In addition, the disadvantages of
the ways to create nanoporous films of Titania will be addressed. Top-down and bottom-up
manufacturing will be defined and example will be given. The minimum feature that can be
patterned with photolithography with visible light will also be addressed. Lastly, scholarly
articles on nanotechnology were researched and the number of articles produced in the last 4
years compared to the last 6 to 7 years were stated as well as the difference of the engineering
databases compared to the medical data bases.
NTM Questions
Nano-materials are especially useful for applications such as chemical sensing because
they offer complete control over the qualities of a material. If they have a high surface area, they
offer a higher quality reading because there is more space to detect a substance and improves
accuracy. This technology offers useful applications because it could be used to detect particular
dangerous chemicals while maintaining a small scale that could go unnoticed. The nanomaterials would be useful as a sensor to determine the existence of a chemical or material
without interfering with the material and area where it is scanning because they take up such a
small amount of space to measure without interfering.
Sensor miniaturization would be beneficial for multiple reasons. They would be
advantageous because they could be implemented into other products to serve multiple purposes.
This would be helpful for military purposes because it could be built into soldier’s uniforms in
order to scan for uses of chemical during battle in order to protect themselves. Another
advantage of smaller chemical sensors would be in medicine in order to scan for the presence of
particular chemicals. These would allow for scans to receive the same data without harming the
individual that the tests are being done on. It would lead to less possible damage and impact the
person on a smaller scale. A third advantage of smaller chemical sensors would be that they
could analyze smaller quantities of chemicals because of their smaller scale. These could be
helpful when identifying chemicals that have a low concentration or quantity. This would be
helpful allowing for smaller samples to be tested that would give the same result. The surface
area of the sensor should be increased in order to offer more area for the chemical to be
discovered. The sensor has to come in contact with the chemical in order for the sensor to tell
the user that there was a chemical present. The more surface area present in the sensor the more
likely it is for the sensor to sense the chemical.
The disadvantages of the different manufacturing methods available for nano-chips have
several flaws. The major disadvantage in this process especially the top down manufacturing
method is that the cuts have to be done on a small scale. While the problem for bottom down
manufacturing is that the material is not made on a scale that does not have imperfections that
would not be bigger than the scale of the product. This leads that the major problem in
manufacturing of nano technology is that the scale of the product is smaller than can be
produced.
Top-down manufacturing is a form of creation where an object is created from
conventional means—the pieces of the object are manually connected. Examples of this include
building skyscrapers, sewing a shirt, and manufacturing cars. All of the examples include
manual labor, large expenses, and often large amounts of material. Bottom-up manufacturing,
meanwhile, is a form of creation wherein atomic-level energies are relied upon to connect/form
the components of an object. Examples of this include the creation of cell membranes of
organisms higher than viruses, the use of quantum dots, and self-aligning attachments of circuits
to a circuit board. All of these examples use interactions of micron or nano sized
components/energy—membranes are self-assembled structures of lipids that energetically favor
assembly because of their composition, quantum dots fluoresce at a specific wavelength of light
based upon their structure/features, and self-aligning attachments utilize the capillary forces of
molten solder.
There are two separate techniques for photolithography; however, for both, the pattern
produced is limited to roughly one-half the wavelength of light used for exposure. The
wavelength of red, orange, yellow, green, blue, indigo and violet light is 665 nm, 630 nm, 600
nm, 550 nm, 470 nm, 425 nm, and 400 nm, respectively. Therefore, the minimum feature that
can be patterned with the same colors is roughly 332.5, 315, 300, 275, 235, 212.5, and 200
nanometers, respectively.
Engineering databases return similar results as medical databases, however, engineering
databases contain articles on a much wider range of nanotechnology applications than medical
databases. For example, when nanotechnology was searched in the medical databases
ClinicalKey and Biosis Citation Index the results focused on the medical applications of
nanotechnology. The articles produced had titles such as “Developing DNA nanotechnology
using single molecule fluorescence” (found using ClinicalKey database) and “Laser-based
nanotechnologies for tissue engineering applications” (found using Biosis Citation Index
database). Engineering databases produced many similar medically based articles. For example,
the engineering database Compendex produced articles such as “Structural DNA nanotechnology
for intelligent drug delivery”. However, engineering databases also produced nanotechnology
articles that were much different than the medical databases. Ceramic Abstracts, another
engineering database, produced articles such as “Use of Nanotechnology in Solar PV Cell”,
which focused on nanotechnologies’ applications in solar cells, a topic that was not found in any
medical database.
The number of nanotechnology articles published in the recent years appears to be
increasing compared to the number of nanotechnology articles published in the last six to seven
years. When search results using the database Compendex were limited to the past four years,
58250 articles were found. When the search was limited to the past six and seven years, 90600
and 103375 articles were found for each respective year. This means that of 90600
nanotechnology articles written in the last 6 years written 64% of them were written in the last
four years; and 56% of the articles written in the past seven years were written within four years.
This trend also holds true when the same time constraints were applied when searching
nanotechnology in the Ceramic Abstracts engineering database. 70% of nanotechnology articles
written in the past 6 years were from at most 4 years ago and 69% of the articles written in the
past 7 years were written within four years ago.
Conclusion
In this experiment a binary voltmeter circuit was built and then modified by attaching a
DAD unit to the circuit to create a fluorescein detection circuit. Binary readings were taken at
various voltages to calibrate the circuit. Error may have played a role in these readings. Internal
resistance of various circuit parts may have caused voltage readings to be greater than theoretical
values predicted by equations such as Ohms Law. Also, flickering LEDs made taking some
binary voltage readings difficult. This was corrected, however, by making slight adjustments to
the resistance applied by the trim pot and by changing out dysfunctional LEDs for functional
ones. The circuit created in this lab will be used during future experimentation as means to detect
fluorescein in a chip.
The lab on a chip device relates heavily to the reading associated with this experiment.
The reading describes a sensor as a device that changes properties in response to a stimulus. This
is a valid description of the fluorescein detection circuit created during lab. When fluorescein is
excited by blue light, its emission signal is detected by a photodetector which acts as a sensor by
changing its properties by creating a signal. The circuit converts this signal from an analog
reading to a digital reading and changes its properties by displaying a binary number that
corresponds to the amount of fluorescein present.
The chip design process is contains both top down and bottom up manufacturing
processes. Top down manufacturing is more of the traditional style of manufacturing; it is a labor
intensive process that involves the fabrication of parts to be put together to create a final product
(similar to the assembly of a vehicle or building). This process is how the chip is being created.
The chip is being designed, then fabricated from the top down with a milling machine, and
finally assembled and tested. Bottom up manufacturing utilizes self-assembly properties of
various materials. It generally occurs on a very small scale and depends on small amounts of
energy to drive an assembly that basically creates itself. The chip does contain some aspects of
bottom up manufacturing. For example, by making the channels running between wells small,
capillary forces will help move liquids through the chip as well as prevent back flow into other
wells.
Appendix:
Table A1: Capillary Testing Data
Capillary A: Inside Diameter = 2.26 mm
Trial 1
Δh: -0.0069 m ΔP: 68 kg/m-s2
Trial 2
Δh: -0.0091 m ΔP: 89 kg/m-s2
Trial 3
Δh: -0.0052 m ΔP: 51 kg/m-s2
Capillary B: Inside Diameter = 1.03 mm
Trial 1
Δh: -0.0031 m ΔP: 30 kg/m-s2
Trial 2
Δh: -0.0065m ΔP: 64 kg/m-s2
Trial 3
Δh: -0.0050 m ΔP: 49 kg/m-s2
Sample Calculations:
Change in
Pressure
∆𝑃 = −𝜌𝑔∆ℎ
∆𝑃 = −(998.2 𝑘𝑔/𝑚3 )(9.81𝑚
/𝑠 2 )(−0.0050𝑚)
∆𝑃 = 49 𝑘𝑔/(𝑚 ∗ 𝑠 2 )
Change in Pressure= (density)*(gravity)*(change in
height)
(1)