Radio Frequency Identification (RFID)-Based Systems for Monitoring Sterilization Processes

Abstract

According to the present disclosure, there is provided a biological indicator system for determining the effectiveness of a sterilization process. The biological indicator system of the present disclosure includes a radio frequency identification sensing board, the radio frequency identification sensing board including a radio frequency identification tag, a microcontroller / digital electronics device, a sensing pad, and a circuit connected to the sensing pad and configured to measure the impedance or resistance level of the sensing pad when exposed to a volatile organic compound. The radio frequency identification tag has a radio frequency integrated circuit and an antenna, and transmits measurement data measured by the sensing pad to a radio frequency reader. The measurement data can be transmitted in real time during incubation, and can be transmitted to a user interface when the biological indicator system is placed in a sterilization chamber during a sterilization process to determine the effectiveness of the sterilization process.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 412,002, filed September 30, 2022, the disclosure of which is incorporated herein by reference.

[0002] (Technical field) The present invention relates generally to systems used to verify the effectiveness of a sterilization process. [Background technology]

[0003] Sterilization is a process that produces products free of viable microorganisms (e.g., Geobacillus or Bacillus bacteria). Sterilization must be routinely monitored to ensure the safety of sterilized products (e.g., medical devices and instruments). Common sterilization monitoring devices include physical indicators, chemical indicators, and biological indicators. Physical indicators monitor the time, temperature, and pressure of the sterilization process to ensure the physical environment is suitable for successful sterilization. Chemical indicators are non-biological indicator testing systems that reveal changes in one or more predefined process variables based on chemical or physical changes caused by exposure to the sterilization process. Biological indicators (BIs) are process monitoring devices with a known population of spores (durable cells) that can verify the effectiveness of the sterilization process. Biological indicators (BIs) tend to provide a more accurate assessment of the success or failure of the sterilization process compared to physical and chemical indicators. However, determining the success or failure of a sterilization process using biological indicators (BIs) requires prolonged incubation to confirm the presence or absence of bacterial growth. The presence of bacterial growth indicates a sterilization failure, while the absence of bacterial growth indicates a sterilization success. For example, depending on the manufacturer and the technology used, biological indicator (BI) incubation times can be 48 hours or longer. Therefore, to ensure the safety and effectiveness of various sterilization processes (e.g., those using steam, vaporized hydrogen peroxide, or ethylene oxide (EtO)), there is a need for a biological indicator system that can provide near-real-time biological indicator results during incubation. Summary of the Invention [Means for solving the problem]

[0004] Aspects and advantages of the invention will be set forth in part in the description that follows, or will be obvious from the description, or may be learned by practice of the invention.

[0005] In one embodiment of the present invention, a biological indicator system for determining the effectiveness of a sterilization process is provided. The disclosed biological indicator system includes a radio frequency identification sensing board including a radio frequency identification tag having a radio frequency integrated circuit and an antenna, a microcontroller / digital electronics, a sensing pad, and a circuit coupled to the sensing pad and configured to measure the impedance or resistance level of the sensing pad when exposed to a volatile organic compound. For example, the circuit may include a resistance circuit coupled to the sensing pad and configured to measure the resistance level of the sensing pad when exposed to a volatile organic compound.

[0006] In another embodiment, the biological indicator system of the present disclosure further comprises a biological indicator and a growth medium, wherein the radio frequency identification sensing board, the biological indicator, and the growth medium are sealed within the container by a cap.

[0007] The headspace distance between the growth medium and the cap can range from about 4 millimeters to about 16 millimeters. A filter is disposed between the radio frequency identification sensing board and the growth medium. The filter includes a polymer coating having a thickness ranging from about 0.01 micrometers to about 5 micrometers.

[0008] In another embodiment, the sensing pad is disposed on the underside of the radio frequency identification sensing board, and the sensing pad is in contact with a gap electrode or interdigital electrode covered with a film, and the gap electrode defines a gap ranging from about 0.01 millimeters to about 0.3 millimeters, and the film includes a polymer and metal nanoparticles.

[0009] In another embodiment, the biological indicator system of the present disclosure further comprises an array of sensing pads.

[0010] In another embodiment, the biological indicator system of the present disclosure further comprises an array of radio frequency identification tags.

[0011] In another embodiment, the biological indicator system of the present disclosure further comprises a radio frequency identification reader connected to the user interface. The radio frequency identification reader also provides power to the radio frequency identification sensing board. The radio frequency identification tag also transmits data to the radio frequency identification reader at a frequency ranging from about 300 megahertz to about 3 gigahertz. Alternatively, the radio frequency identification tag transmits data to the radio frequency identification reader at a frequency ranging from about 3 megahertz to about 30 megahertz.

[0012] In another embodiment, the radio frequency identification sensing board does not have a battery.

[0013] In another embodiment, the biological indicator system of the present disclosure further comprises a temperature sensor.

[0014] Another embodiment of the present invention provides a method for determining the effectiveness of a sterilization process using a biological indicator system including a radio frequency identification sensing board and a radio frequency identification reader. The disclosed method includes exposing a sensing pad of the radio frequency identification sensing board to vapor from the headspace of a container containing a growth medium and a biological indicator, measuring an impedance or resistance level of the sensing pad, and transmitting data related to the impedance or resistance level to a radio frequency identification tag. If the impedance or resistance level is higher than a predetermined baseline impedance or resistance level of the sensing pad, it is determined that a volatile organic compound is present. The presence of a volatile organic compound indicates a failure of the sterilization process.

[0015] In one embodiment, the method of the present disclosure further comprises transmitting the measurement data to a radio frequency identification reader.

[0016] In another embodiment, the method of the present disclosure further comprises transmitting the measurement data from the radio frequency identification reader to a user interface.

[0017] In another embodiment, the method of the present disclosure further comprises measuring the temperature within the container with a temperature sensor.

[0018] In another embodiment, a radio frequency identification sensing board includes a radio frequency identification tag having a radio frequency integrated circuit and an antenna, a microcontroller or digital electronics, and an electrical circuit configured to measure the impedance or resistance level of the sensing pad, and further includes an array of radio frequency identification tags.

[0019] Also, in some embodiments, the radio frequency identification tag transmits the measurement data to the radio frequency identification reader at a frequency ranging from about 300 megahertz to about 3 gigahertz, or alternatively, at a frequency ranging from about 3 megahertz to about 30 megahertz.

[0020] In another embodiment, the radio frequency identification detection board, biological indicator, and growth medium are sealed within the container by a cap, and the headspace distance between the growth medium and the radio frequency identification detection board is in the range of about 4 millimeters to about 16 millimeters.

[0021] In another embodiment, a filter is disposed between the radio frequency identification sensing board and the growth medium, and the filter includes a polymer coating having a thickness ranging from about 0.1 micrometers to about 5 micrometers.

[0022] In another embodiment, the sensing pad is in contact with a gap or interdigitated electrode coated with a film including a polymer and metal nanoparticles, and the gap electrode defines a gap ranging from about 0.01 millimeters to about 0.3 millimeters.

[0023] In another embodiment, the radio frequency identification sensing board includes an array of sensing pads.

[0024] A radio frequency identification reader is also connected to the user interface.

[0025] In another embodiment, the radio frequency identification reader provides power to the radio frequency identification sensing board.

[0026] In another embodiment, the radio frequency identification sensing board does not have a battery.

[0027] Sterilization processes can also use steam, hydrogen peroxide, or ethylene oxide.

[0028] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0029] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in this specification, which makes reference to the accompanying drawings, in which:

[0030] [Figure 1] 1 is an exploded view of one embodiment of a biological indicator system of the present disclosure, the biological indicator system including an RFID sensing board. [Figure 2] FIG. 2 is a perspective view showing the top surface of the RFID detection board of FIG. [Figure 3] FIG. 3 is a perspective view showing the underside of the RFID detection board of FIG. [Figure 4] FIG. 4 is a schematic diagram illustrating one embodiment of a biological indicator system of the present disclosure. [Figure 5]FIG. 5 is a schematic diagram illustrating a portion of the biological indicator system of FIG. [Figure 6] FIG. 6 is an enlarged view of one embodiment of a sensing pad used in the biological indicator system of the present disclosure. [Figure 7] FIG. 7 is a flow chart illustrating a method for determining the effectiveness of a sterilization process using the biological indicator system of the present disclosure. [Figure 8] FIG. 8 is an enlarged view of a portion of another embodiment of an RFID sensing board contemplated by the present invention that uses multiple interdigitated electrodes, sensing pads, antennas, and radio frequency integrated circuits (RFICs) as part of an array of RFID tags to enable multiple measurements. [Figure 9] FIG. 9 is a graph showing the relationship between the electrical conductivity of the nanocomposite material and the volume fraction of nanoparticles, which are fillers contained in the film. [Figure 10] FIG. 10 is a graph showing the relationship between the electrical conductivity of nanocomposites containing gold nanoparticles and the volume fraction of gold nanoparticles contained in the film. DETAILED DESCRIPTION OF THE INVENTION

[0031] Various embodiments of the present invention and one or more examples thereof are described in detail below. Each example is provided to explain the invention, not to limit it. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations insofar as they come within the scope of the appended claims and their equivalents.

[0032] As used herein, the terms "about," "approximately," or "approximately," when used to modify a value, indicate that values ​​within ±5% of that value are within the scope of the disclosed embodiments. Furthermore, when multiple ranges are provided, any combination of the minimum and maximum values ​​set forth in the ranges is also contemplated by the present invention. For example, when a range of "about 20% to about 80%" and a range of "about 30% to about 70%" are provided, the range of "about 20% to about 70%" or "about 30% to about 80%" is also contemplated by the present invention.

[0033] Generally, the present invention relates to a biological indicator system for determining the effectiveness of a sterilization process. The biological indicator system includes a self-contained biological indicator (SCBI) with a radio frequency identification sensing board. The radio frequency identification sensing board includes a passive radio frequency identification tag, a microcontroller, a sensing pad, and a measurement circuit (electrical circuit) connected to the sensing pad to measure the level of an electrical characteristic (e.g., resistance, capacitance, and / or impedance) of the sensing pad when exposed to a volatile organic compound. The radio frequency identification tag has a radio frequency integrated circuit and an antenna that wirelessly communicates with a radio frequency identification reader to transmit data related to the impedance or resistance level of the sensing pad measured by the measurement circuit. The integrated SCBI is a self-contained, battery-free biological indicator configured by containing a culture medium necessary for the growth of a test microorganism and a radio frequency identification sensing board 104 within an incubation vessel. Data measured by the measurement circuit is transmitted in real time when the biological indicator system is placed in an incubator / autoreader. Thereafter, when the biological indicator system is placed in the sterilization chamber after sterilization, the data measured by the measurement circuit is transmitted to a user interface for determining the effectiveness of the sterilization process. In this manner, manual steps for tracking and reporting the results of the sterilization process can be eliminated, thereby improving efficiency and accuracy in determining the effectiveness of the sterilization process.

[0034] The present invention also relates to a method for determining the effectiveness of a sterilization process using a biological indicator system including an integrated SCBI. The integrated SCBI is a self-contained biological indicator configured to contain a culture medium necessary for the growth of a test microorganism, a radio frequency identification sensing board 104, and a radio frequency identification reader within a culture vessel. The method includes exposing a sensing pad of the radio frequency identification sensing board to vapor from the headspace of a vessel containing the growth medium and the biological indicator, measuring the impedance or resistance level of the sensing pad, and transmitting data related to the impedance or resistance level to a radio frequency identification tag. If the impedance or resistance level is higher than a predetermined baseline impedance or resistance level of the sensing pad, it is determined that a volatile organic compound is present. The presence of a volatile organic compound indicates a sterilization failure.

[0035] The inventors have discovered that the biological indicator system and method for determining the effectiveness of a sterilization process using the same can improve detection of the growth phase or biological activity of hardy microorganisms (e.g., spores (endospores or bacterial spores). Examples of spores include, but are not limited to, Bacillus subtilis, Bacillus atrophaeus, and Geobacillus stearothermophilus) by focusing on the detection and measurement of volatile organic compounds (VOCs). Upon successful or unsuccessful sterilization, specific volatile organic compounds are produced and rapidly detected in the growth medium and in the headspace of the container containing the biological indicator. After measuring the concentration of the volatile organic compounds (VOCs), a user interface (UI) can analyze the growth or biological activity results after the sterilization process by noting the change in impedance or resistance when the volatile organic compounds (VOCs) come into contact with a film that is part of the biological indicator system, and transmit the analysis results to the end user. This allows the time required to detect and report growth or biological activity after sterilization to be reduced to less than about 30 minutes, e.g., less than about 15 minutes. This time is much faster than conventional methods that require culturing the growth medium for turbidity, which can take 2 to 7 days to confirm successful sterilization if turbidity is lacking. Furthermore, fluorescence measurements, which can take several hours depending on the measurement system, are also unnecessary. Fluorescence measurements, however, introduce complications and room for error due to the use of various reagents and enzymes in the multiple process steps that must be performed. The disclosed biological indicator system can be used in the sterilization of medical devices, such as medical device sets, stacked trays, and mixed loads in current sterilization packaging systems (e.g., sterilization wraps, rigid containers, pouches). Furthermore, the disclosed biological indicator system provides rapid and sensitive detection of volatile organic compounds (VOCs) in microorganisms.The biological indicator system of the present disclosure also allows for wireless reporting using RFID technology to track the status of the biological indicator during testing. Additionally, RFID readers can detect and receive data from multiple RFID tags or an array of RFID tags simultaneously, thereby creating a multiplexed detection system.

[0036] Specific volatile organic compounds (VOCs) that can be detected by the system and method of the present invention, which determine the success or failure of a sterilization process based on the impedance or resistance level of a sensing pad due to the presence of spores in the growth medium, include ketones, alcohols, esters, and furans. Specifically, VOCs that can be detected in the presence of spores, regardless of the type of growth medium used, include ketones such as 2-pentanone, methyl isobutyl ketone, and 4-methyl-2-heptanone; alcohols such as 2-methyl-2-propanol, amylene hydrate, and 2-methyl-1,3-pentanediol; esters such as 3-hydroxy-2,4,4-trimethylpentyl 2-methylpropanoate and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; and furans such as tetrahydro-2,2,5,5-tetramethylfuran. It should further be understood that the systems and methods of the present invention may include an algorithm that subtracts baseline VOC levels emitted from the growth medium to distinguish between VOCs released from spores during germination and VOCs present only in the growth medium.

[0037] The present invention will now be described in more detail with reference to the accompanying drawings.

[0038] Referring first to FIG. 1 , an exploded view of one embodiment of a biological indicator system 100 of the present disclosure is shown. The biological indicator system 100 of the present disclosure includes a radio frequency identification (RFID) detection board 104. The RFID detection board 104 is disposed between a headspace 146 of a container 108 and a cap 102 of the container 108. A growth medium 110 is contained within the container 108. A biological indicator 112 is disposed within the growth medium 110. Furthermore, the headspace distance, i.e., the distance D between the growth medium 110 and the cap 102 when the container 108 is sealed, can be in the range of about 4 millimeters to about 16 millimeters, such as in the range of about 5 millimeters to about 15 millimeters, or, for example, in the range of about 6 millimeters to 14 millimeters. The biological indicator 112 can be any suitable microorganism that exhibits growth in the event of an unsuccessful (i.e., failed) sterilization process, whether the sterilization process is dynamic air removal steam (pre-vacuum and gravity), hydrogen peroxide, or ethylene oxide-based. For example, the microorganism can be a spore (endospore or bacterial spore), including, but not limited to, Bacillus subtilis, Bacillus atrophaeus, Geobacillus stearothermophilus, etc. Furthermore, the growth medium 110 can be any suitable medium used to verify the effectiveness of a sterilization process. For example, the growth medium can be any growth medium that meets the growth-promoting capacity requirements set forth in ANSI / AAMI / ISO 11138-1:2006 / (R)2010. Specific, non-limiting examples of growth media include tryptic soy broth and modified soy-casein digest broth.

[0039] As shown, the RFID sensing board 104 can be separated from the headspace 146 of the container 108 by a filter 106. The filter 106 helps prevent moisture from the growth medium 110 in the container 108 from contacting the RFID sensing board 104 and potentially damaging it. The filter 106 includes a coating formed from a water-repellent polymer, such as a fluorinated or perfluorinated compound. This allows only volatile organic compound (VOC) vapors to reach the sensing elements (sensing pads 132) of the RFID sensing board 104, as described below. The coating of the filter 106 can have a thickness ranging from about 0.01 micrometers to about 5 micrometers, such as from about 0.05 micrometers to 4 micrometers, or from about 0.1 micrometers to 3 micrometers. Furthermore, in some embodiments, the filter can be in the form of a film.

[0040] 1-5, the RFID detection board 104 will be described in detail. The RFID detection board 104 has an upper surface 114 and a lower surface 116. A radio frequency identification (RFID) tag 121 having an antenna 118 and a radio frequency integrated circuit (RFIC) 120 is disposed on the upper surface 114. A microcontroller / digital electronics 122, a signal processing unit 124, circuitry 126, and a temperature sensor 128 are also disposed on the upper surface 114. Meanwhile, one or more sensing pads 132 are disposed on the lower surface 116. Each of the sensing pads 132 has or is in contact with a gap electrode 130 for detecting specific VOCs generated by the biological indicator 112 and collected in the headspace 146 of the container 108 if the sterilization process is unsuccessful (i.e., has failed). How each of these components detects the presence or absence of specific VOCs to determine whether the sterilization process was successful will be described in detail below.

[0041] First, VOCs released from the biological indicators 112 in the growth medium 110 after sterilization collect in the headspace 146 of the container 108. Subsequently, the VOC vapors pass through the filter 106 and reach the sensing pad 132 disposed on the underside 116 of the RFID sensing board 104. Referring to FIGS. 5 and 6 , the volatile organic compounds (VOCs) that reach the sensing pad 132 come into contact with a film 138 on the gap electrode 130 present on the sensing pad 132. The gap G of the gap electrode 130 can be in the range of about 0.01 millimeters to about 0.3 millimeters, for example, in the range of about 0.05 millimeters to about 0.25 millimeters, or, for example, in the range of about 0.1 millimeters to about 0.2 millimeters. The film 138 can include metal nanoparticles 142 having ligands 144 embedded in a polymer 139 forming the film 138. When the VOC 131 to be detected contacts the film 138 of each sensing pad 132, the film 138 expands due to the interaction between the VOC 131 and the film 138 containing the metal nanoparticles 142 and the ligands 144. This results in a change in impedance or resistance of the film 138 associated with the VOC 131 bound to the metal nanoparticles 142 via the ligands 144, thereby enabling the detection of the presence of the VOC 131. Referring to the biological indicator system 200 shown in FIG. 4 , the impedance or resistance change is measured by the circuit 126. The impedance or resistance data measured by the circuit 126 is transmitted to the microcontroller 122 via the signal processing unit 124. The microcontroller 122 can interact with the RFIC 120 of the RFID tag 121. The microcontroller 122 converts the signal (data) received from the circuit 126 from analog to digital and then transmits the signal to the RFIC 120 of the RFID tag 121, which stores the received data. The microcontroller 122 also stores algorithms for determining accurate impedance and / or resistance measurements.

[0042] The antenna 118 is connected to the RFIC 120. The antenna 118 backscatters a radio signal 134 that can be detected by an RFID reader 136, which receives the impedance or resistance data. The antenna 118 can communicate with the RFID reader 136 up to about 10 meters away from the antenna 118, such as about 7.5 meters away from the antenna 118, or for example about 5 meters away from the antenna 118. The RFID reader 136 can transmit the impedance or resistance data received from the antenna 118 to a user interface 148 for further analysis to determine the presence or absence of specific VOCs based on the measured impedance or resistance levels. The RFID tag 121 and the RFID reader 136 can operate at ultra-high frequencies (e.g., frequencies ranging from about 300 megahertz to about 3 gigahertz) or high frequencies (e.g., frequencies ranging from about 3 megahertz to about 30 megahertz). Additionally, it is important to note that because the enclosure 108 housing the RFID detection board 104 is exposed to high temperatures ranging from about 120° C. to about 135° C. or higher, the RFID detection board 104 does not include a battery. Instead, power is provided by the RFID reader 136.

[0043] Additionally, the RFID sensing board 104 can measure the temperature inside the container 108 via the temperature sensor 128. As with the impedance or resistance data, the temperature data measured by the temperature sensor 128 is transmitted to the microcontroller 122, where it is converted from an analog signal to a digital signal before being transmitted to the RFIC 120. Furthermore, it should be understood that the microcontroller 122 is not limited to storing information related to impedance, resistance, and temperature, but can also be used to store other sensor signals and data. The microcontroller 122 is also configured to measure these sensor data simultaneously.

[0044] Additionally, the user interface 148 can simultaneously display measured sensor data (e.g., impedance, resistance, temperature, etc.) and calibrate the displayed sensor data based on the type of sterilization process performed (e.g., steam, hydrogen peroxide, ethylene oxide, etc.) since different types of sterilization processes release different VOCs, resulting in different impedance or resistance levels depending on the VOCs released.

[0045] As shown in FIG. 5, the RFID tag 121 includes an antenna 118 and an RFIC 120. As shown in FIG. 2, the antenna 118 is positioned along the periphery of the top surface 114 of the RFID sensing board 104 to obtain a sufficient signal. Furthermore, to maximize the antenna surface area, the antenna 118 may be formed with a circular pattern along the periphery of the RFID sensing board 104, as shown. It should be appreciated that multiple RFID tags 121 may be arranged in an array on the RFID sensing board 104 to receive data from each sensing pad 132 regarding the impedance and / or resistance levels associated with each sensing pad 132, thereby enabling the detection and identification of multiple VOCs.

[0046] Referring now to FIG. 7, a flowchart illustrating a method 300 for determining the effectiveness of a sterilization process using the biological indicator system 100, 200 of the present disclosure is shown. The method 300 for verifying (determining) the effectiveness of a sterilization process after placing the container 108 of the biological indicator system 100, 200 in a sterilization chamber along with the product to be sterilized and completing the sterilization process includes the following steps: First, the sensing pad of the radio frequency identification sensing board 104 is exposed to steam from the headspace (e.g., a self-contained integrated biological indicator) in the container (step 302). It should be understood that the self-contained integrated biological indicator (SCBI), whether steam, hydrogen peroxide, or ethylene oxide-based, is exposed to the sterilization process. Next, the impedance or resistance level of the sensing pad is measured (step 304). The measurement data is then transmitted to a radio frequency identification reader (step 306). If the impedance or resistance level is higher than a predetermined baseline impedance level or a predetermined baseline resistance level of the sensing pad, it is determined that a volatile organic compound is present. The presence of a volatile organic compound indicates a sterilization failure. The measurement data is then transmitted from the radio frequency identification reader to a user interface (step 308). The temperature within the container is then measured by a temperature sensor (step 310). The temperature data is transmitted to the RFID reader in the same manner as transmitting impedance or resistance level data. It should be understood that any of the above steps may be applied in any suitable order or combined, as would be understood by one skilled in the art.

[0047] 8, on the other hand, is an enlarged view of a portion of another embodiment of an RFID sensing board 104 contemplated by the present invention, which uses multiple interdigital electrodes 130 and sensing pads 132 (measurement pads) to enable multiplexed measurements. In this embodiment, four interdigital electrodes 130 are shown in an array 105, and the RFID sensing board 104 has a border 133 for ink deposition around the interdigital electrodes 130 in the array. It should be understood that the interdigital electrodes 130 are coated with a film 138, as described above. The distance, or gap G, between adjacent arms or fingers 135 of the interdigital electrode 130 can be in the range of about 0.01 millimeters to about 0.3 millimeters, such as in the range of about 0.02 millimeters to about 0.25 millimeters, or, for example, in the range of about 0.03 millimeters to about 0.2 millimeters. The average resistance of each interdigitated electrode 130 after ink deposition can be in the range of about 2 megaohms to about 5 megaohms, such as in the range of about 2.25 megaohms to about 4.75 megaohms, or such as in the range of about 2.5 megaohms to about 4.5 megaohms.

[0048] Next, FIG. 9 is a graph showing the relationship between nanocomposite conductivity and filler volume fraction of metal nanoparticles 142 contained in a polymer 139 forming a nanocomposite film 138 that is part of an RFID tag 121 contemplated by the present invention. In particular, in the first stage (A), the nanocomposite film 138 has low conductivity because a small number of metal nanoparticles 142 are present and spaced apart within the polymer 139. The conductivity of the nanocomposite film 138 is approximately the same as that of the polymer 139. In the second stage (B), the filler metal nanoparticles 142 are present in greater numbers within the polymer 139, forming clusters of metal nanoparticles 142. In this state, tunneling occurs between adjacent metal nanoparticles 142, gradually increasing the conductivity of the nanocomposite film 138. In the third stage (C), the number of metal nanoparticles 142 approaches the percolation threshold, forming complete electrical paths between the metal nanoparticles 142. During this stage, the conductivity of the nanocomposite film 138 rapidly increases. In the final stage (D), the conductivity of the nanocomposite film 138 gradually increases as more filler metal nanoparticles 142 are added to the polymer 139. The most sensitive sensing response of the nanocomposite film 138 is achieved when the volume fraction of the filler nanoparticles is between the second stage (B) and the third stage (C).

[0049] 10 is a graph showing the relationship between the conductivity of a nanocomposite film 138 containing gold nanoparticles (GnPs) and the volume fraction of gold nanoparticles (AuNPs) contained in the film, with and without chloroauric acid (HauCl4). As is known in the art, the relationship between the conductivity σ (S / cm) of a nanocomposite body or film and its resistance R can be expressed as: R=L / (σ A)

[0050] In the above formula, L is the distance or gap G between the electrodes, and A is the cross-sectional area of ​​the nanocomposite film covering the electrodes. In the present invention, the target conductivity of the nanocomposite film is in the range of about 1E-8 S / cm to about 1E-3 S / cm, which corresponds to a resistance of about 100 kilohms to about 1000 megahms. However, due to accuracy issues in measuring high resistances (e.g., 10 megahms or greater) from leakage current, the target resistance of the films of the present invention can be in the range of about 100 kilohms to about 10 megahms.

[0051] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems, and practicing any methods incorporated herein. The patentable scope of the invention is defined by the claims, and may include other embodiments that occur to those skilled in the art. Such other embodiments are within the scope of the claims if they contain elements that do not differ from the literal language of the claims, or if they contain equivalent elements that do not differ substantially from the literal language of the claims.

Claims

1. 1. A biological indicator system for determining the effectiveness of a sterilization process, comprising: equipped with a radio frequency identification detection board; The radio frequency identification detection board includes: a radio frequency identification tag having a radio frequency integrated circuit and an antenna; A microcontroller; A detection pad; and a circuit connected to the sensing pad and configured to measure an impedance or resistance level of the sensing pad when exposed to a volatile organic compound.

2. 10. The system of claim 1, a biological indicator; a growth medium; The system, wherein the radio frequency identification sensing board, the biological indicator, and the growth medium are sealed within a container by a cap.

3. 3. The system of claim 2, A system wherein the headspace distance between the growth medium and the cap ranges from about 4 millimeters to about 16 millimeters.

4. 3. The system of claim 2, A system wherein a filter is disposed between the radio frequency identification sensing board and the growth medium.

5. 5. The system of claim 4, The system, wherein the filter comprises a polymer coating having a thickness ranging from about 0.01 micrometers to about 5 micrometers.

6. 10. The system of claim 1, The system wherein the sensing pad is disposed on a lower surface of the radio frequency identification sensing board.

7. 7. The system of claim 6, The system wherein the sensing pad is in contact with a film-covered gap electrode or interdigital electrode.

8. 8. The system of claim 7, The gap electrode defines a gap in the range of about 0.01 millimeters to about 0.3 millimeters.

9. 8. The stem of claim 7, The system, wherein the film comprises a polymer and metal nanoparticles.

10. 10. The system of claim 1, The system further comprises the array of sensing pads.

11. 10. The system of claim 1, The system further comprises an array of said radio frequency identification tags.

12. 10. The system of claim 1, The system further comprises a radio frequency identification reader connected to the user interface.

13. 13. The system of claim 12, The radio frequency identification reader provides power to the radio frequency identification sensing board.

14. 13. The system of claim 12, The system wherein the radio frequency identification tag transmits data to the radio frequency identification reader at a frequency ranging from about 300 megahertz to about 3 gigahertz.

15. 13. The system of claim 12, The system wherein the radio frequency identification tag transmits data to the radio frequency identification reader at a frequency in the range of about 3 megahertz to about 30 megahertz.

16. 10. The system of claim 1, The radio frequency identification sensing board is battery-free.

17. 10. The system of claim 1, The system further comprises a temperature sensor.

18. 1. A method for determining the effectiveness of a sterilization process using a biological indicator system comprising a radio frequency identification sensing board and a radio frequency identification reader, comprising: exposing the sensing pads of the radio frequency identification sensing board to vapors from the headspace of a container containing a growth medium and a biological indicator; measuring the impedance or resistance level of the sensing pad; transmitting data relating to the impedance level or the resistance level to a radio frequency identification tag; determining that a volatile organic compound is present if the impedance level or the resistance level is higher than a predetermined baseline impedance level or baseline resistance level of the sensing pad; The presence of said volatile organic compounds indicates a failure of the sterilization process.

19. 20. The method of claim 18, The method further comprising transmitting the data to the radio frequency identification reader.

20. 20. The method of claim 19, The method further comprising transmitting the data from the radio frequency identification reader to a user interface.

21. 20. The method of claim 18, The method further comprising measuring the temperature within the container with a temperature sensor.

22. 20. The method of claim 18, The radio frequency identification detection board includes: a radio frequency identification tag having a radio frequency integrated circuit and an antenna; Microcontrollers or digital electronics; and an electrical circuit configured to measure an impedance or resistance level of the sensing pad.

23. 23. The method of claim 22, The method, wherein the radio frequency identification sensing board further includes an array of the radio frequency identification tags.

24. 23. The method of claim 22, The method of claim 1, wherein the radio frequency identification tag transmits the data to the radio frequency identification reader at a frequency ranging from about 300 megahertz to about 3 gigahertz.

25. 23. The method of claim 22, The method of claim 1, wherein the radio frequency identification tag transmits the data to the radio frequency identification reader at a frequency in the range of about 3 megahertz to about 30 megahertz.

26. 20. The method of claim 18, the radio frequency identification sensing board, the biological indicator, and the growth medium are sealed within the container by a cap; The method, wherein the headspace distance between the growth medium and the radio frequency identification sensing board ranges from about 4 millimeters to about 16 millimeters.

27. 20. The method of claim 18, The method, wherein a filter is disposed between the radio frequency identification sensing board and the growth medium.

28. 28. The method of claim 27, The method, wherein the filter comprises a polymer coating having a thickness ranging from about 0.1 micrometers to about 5 micrometers.

29. 20. The method of claim 18, The method, wherein the sensing pad is in contact with a gap electrode or an interdigitated electrode coated with a film comprising a polymer and metal nanoparticles.

30. 30. The method of claim 29, The gap electrode defines a gap in the range of about 0.01 millimeters to about 0.3 millimeters.

31. 20. The method of claim 18, The radio frequency identification sensing board includes an array of the sensing pads.

32. 20. The method of claim 18, The method, wherein the radio frequency identification reader is connected to a user interface.

33. 20. The method of claim 18, The radio frequency identification reader provides power to the radio frequency identification sensing board.

34. 20. The method of claim 18, The radio frequency identification sensing board is battery-free.

35. 20. The method of claim 18, A method wherein the sterilization process uses steam, hydrogen peroxide, or ethylene oxide.

Images