The present application relates to radiation sensors, and specifically to radiation sensors using a biological organism reaction to radiation in order to control a warning mechanism.
This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
Many forms of radiation are commonly used for health care, power plants, and food sterilization. Excessive exposure to ionizing radiation can pose health risks that may be detrimental or fatal to those affected; thus, it is important to monitor/measure radiation exposure among individuals who work in high-risk environments (e.g., nuclear plant operators) or are exposed to nuclear accidents (e.g., Fukushima disaster). Nevertheless, even low levels of high-energy radiation exposure (e.g., gamma rays) pose significant health risks (e.g., cancer) for radiation workers. Although high-risk working sites (e.g., hospitals, laboratories, power plants) are typically equipped with large-scale radiation monitoring systems, workers lack precise effective personal monitoring. Wearable personal dosimeters consisting of diodes and solid-state devices are commercially available; however, they are not cost effective and are thus limited to very high-risk industrial usage. Furthermore, the traditional radiation sensors do not directly correlate with biological damage of the ionizing radiation (i.e., DNA damage, mutation, and cell death).
Although many studies have demonstrated the lethal effect of radiation on living matter, no dosimeter up to now has taken advantage of such sensitivity for creating a direct indicator of radiation-induced biological damage.
There is therefore an unmet need for a novel radiation sensor that can be manufactured at ultralow cost and can correlate to damage to biological systems when exposed to radiation.
For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended.
An ultralow cost novel radiation sensor which can correlate to damage to biological systems when exposed to radiation is disclosed herein. In particular, to facilitate personal radiation exposure measurements, in one embodiment a low-cost, film-type, disposable radiation dosimeter that utilizes a micro-organic material (e.g., Saccharomyces Cerevisiae) is disclosed. The use of such micro-organic material (e.g., yeast which genetically is closely homologous to humans) aids in predicting biological damage of the ionizing radiation. A change in resistance can be used to quantitatively measure exposure to radiation.
In another embodiment according to the present disclosure, a novel low-cost wearable radiation sensor is disclosed that combines a micro-electromechanical systems (MEMS) structure with a microorganism (e.g., yeast) which utilizes the dose-response effect of ionizing radiation on the microorganism cells as a biologically relevant surrogate to measure radiation. When exposed to radiation, yeast suffers DNA damage, mutations, and/or death, resulting in their decreased viability and ability to ferment a sugar solution. As a result, the microorganism provides a physical response (i.e., gas generation) to radiation that is biologically significant (DNA damage). The radiation sensor according to the present disclosure provides the microorganism housed in a low cost wearable MEMS structure as a biologically sensitive radiation indicator. The dose response viability of yeast cells and the resulting gas generation in presence of sucrose solution is used to deflect a polydimethylsiloxane (PDMS) membrane and activate a Light emitting diode (LED) indicator. The sensor allows radiation detection with sensitivity in the range of −0.195 mm/decade-rad (1-1000 rad). Alternatively, the deflection can be used to measure a change in capacitance that can be used to quantitatively measure the amount of exposure to radiation.
An exploded view of the radiation sensor 100 according to the first embodiment is depicted in
The sensor can be fabricated using rapid prototyping techniques, depicted in
In operation, ethanol (CH3CH2OH) and CO2 are produced by yeast fermentation when the yeast begins fermenting in presence of glucose. CO2 reacts with water to form carboxylic acid (H2CO3). The generated acid serves as an electrolyte, which alters the electrical conductivity of the solution, which is measured over time. To evaluate the effect of radiation on the electrical properties of yeast, various sensors were exposed to different doses of radiation (0, 10, 100 and 1000 rad) using a Co-60 (1.13 MeV) source. After exposure, each sensor was provided with 0.1 mL of de-ionized water (e.g., using a 30 G hypodermic needle or based on a wicking principal); this sets the yeast concentration inside the sensor to 100 g/L. The sensors were then connected directly to an LCR meter (e.g., LCR-821, GW INSTEK), and the electrical conductivity was measured over time (60 min) at a frequency of 1 kHz, as shown in
In order to begin the fermentation process, deionized (DI) water is added to the sensor, by a wicking process or by injecting DI water into the sensor using a hypodermic needle. Once all DI water was evaporated or consumed after an hour, the capacitance reading is infinite, similar to the beginning of the experiment, and the resistance is at its maximum value. The measurement data as shown in
The second embodiment of the radiation sensor according to the present disclosure is based on deformation of flexible membranes that can provide both a pass/fail as well as quantitative results. A plan view of the radiation sensor 200 according to the second embodiment is shown in
The fermentation process produces carbon dioxide and ethanol. The rate of CO2 gas generation during fermentation correlates with the activity of the yeast population, which is impaired by radiation exposure; thus gas generation rate is indicative of the radiation dose.
During typical use of the sensor 200, the user wears it during radiation exposure. After exposure, the user breaks the thin glass separator 203 by pressing the back of the sucrose chamber 202, thus mixing the yeast cells 204 with the sucrose solution 205. The resulting fermentation produces CO2 that can deflects a PDMS membrane 206 (dashed line indicating deflected state). In the absence of radiation, the generated CO2 is sufficiently large to deflect the membrane (solid line) enough in order to close a switch and turn on an LED indicator. If radiation exposure is large enough to deactivate a significant number of yeast cells, the diminished CO2 byproduct cannot turn on the LED. Thus, this sensor 200 translates the irradiation-induced biological damage of yeast to a visual LED indicator.
One fabrication embodiment is shown in
The sucrose reservoir is fabricated using impermeable materials to prevent evaporation. First, an acrylic ring (ID 15 mm, OD 20 mm, thickness 5.6 mm) is laser cut using CO2 laser engraver system (e.g., PLS6MW, UNIVERSAL LASER SYSTEMS, INC.), as shown in
Two PDMS rings are provided using PDMS cast on a laser-machined acrylic mold (8 mm inner diameter, 15 mm outer diameter, 5.6 mm height), as shown in
The other PDMS ring is bonded to a 5 mm-thick PDMS substrate embedded with a circuit connecting a reed switch (ORD311, STANDEX-MEDER ELECTRONICS), a battery (3V, CR 1216, RADIOSHACK), and a red LED (VISUAL COMMUNICATIONS COMPANY) in series, as shown in
To determine the efficacy of the radiation sensor, the fermentation kinetics of yeast were initially investigated by measuring the gas generation rate at various yeast concentrations (10 g·L−1, 25 g·L−1, 50 g·L−1, and 100 g·L−1). Each yeast sample was placed in a flask with a 50 mM aqueous solution of sucrose and heated at 32° C. (typical human skin temperature) for 30 minutes. The generated CO2 was collected and measured via a standard pneumatic trough setup.
The deflection of the 200 μm PDMS membrane in the radiation sensor in response to pressurized CO2 was investigated by injecting CO2 gas into the PDMS/yeast chamber of the sensor using a 30 G hypodermic needle. Since PDMS is partially permeable to CO2, the membrane deflection saturates after some time for a given gas flowrate (for sufficiently low flowrates). Experiments determined that the membrane bursts when exposed to flow rates greater than 6-7 mL/min. The maximum deflection of PDMS for various flow rates of CO2 in the range 0-5 mL/min was measured and recorded. The results of these experiments and the fermentation characterization were used to select a yeast concentration (100 g·L−1) for use in the sensor for optimum membrane deflection.
The effect of radiation on yeast activity was studied by evaluating their gas generation rate after radiation exposure. Yeast samples were exposed to various doses (0-1 krad) of radiation using a Co-60 (1.13 MeV) source. The yeast were then incorporated into the sensors as described in the fabrication procedure (using 100 g·L−1), and the sensors were activated. The resulting maximum deflection of the PDMS membrane was then measured and recorded.
The results of the membrane deflection investigations are plotted in
The effect of radiation dose on PDMS membrane deflection is shown in the semi-log plot of
Using the radiation and deflection results, the CO2 generation rate inside the sensor can be back-calculated for each radiation dose using a linear equation, W=0.2728Q+0.4315 (W=Deflection and Q=gas generation rate), obtained from a linear fit of the data in
Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. The implementations should not be limited to the particular limitations described. Other implementations may be possible.
The present patent application is related to and claims the priority benefit of U.S. Provisional Patent Application Ser. No. 62/449,307, filed Jan. 23, 2017, the contents of which is hereby incorporated by reference in its entirety into the present disclosure.
Number | Date | Country | |
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62449307 | Jan 2017 | US |