- Email: [email protected]
Amorphous magnetoelastic sensors for the detection of biological agents
Intermetallics 17 (2009) 270–273
Contents lists available at ScienceDirect
Intermetallics journal homepage: www.elsevier.com/locate/intermet
Amorphous magnetoelastic sensors for the detection of biological agents Fei Xie, Hong Yang, Suiqiong Li, Wen Shen, Jeihui Wan, Michael L. Johnson, Howard C. Wikle, Dong-Joo Kim, Bryan A. Chin* Materials Research and Education Center, Auburn University, Auburn, AL 36849, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 May 2008 Received in revised form 28 July 2008 Accepted 28 July 2008 Available online 22 January 2009
Freestanding amorphous magnetoelastic (ME) biosensors were fabricated by two ways. One type with larger size, 2000 400 15 mm, 1000 200 15 mm and 500 100 15 mm, was made from an ME Fe40Ni38Mo4B18 ribbon, the other with smaller size 200 40 4 mm was manufactured by dual beam sputtering and non-traditional microelectronic fabrication techniques. Both platforms were immobilized with JRB7 phage and were developed for the real-time in vitro detection of Bacillus anthracis spores. The experimental results show that the measured sensitivity of the ME sensors agrees with theoretical predictions and the specificity of ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. The 200 40 4 mm biosensor was found to have a detection limit of 102 cfu/ml and sensitivity of 13.1 kHz/decade. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: A. Intermetallics, miscellaneous G. Biomedical applications B. Elastic properties C. Vapour deposition C. Thin films
1. Introduction In 2001, US Citizens were terrorized by deliberate exposure to Bacillus anthracis spores that are the causative agent for anthrax during terrorist attacks targeting the US Postal Service. This attack led to the exposure of 16 people and death of 5. Mass panic amongst the general public led to the realization that bioterrorism could greatly disrupt both the commercial and agricultural sectors of the US economy. Thus it is critical for national security to detect early those biological warfare agents in very small amounts or very low concentrations. When an alternating magnetic field is applied to an amorphous magnetoelastic (ME) material, it undergoes a corresponding oscillating shape change that gives rise to a mechanical vibration with a characteristic resonance frequency. This frequency is a function of the shape, physical dimensions, and mass of the sensor platform. If B. anthracis spores bind to the surface of a platform made of ME material (attachment of mass), a drop in the platform resonance frequency will be induced. Changes in the frequency can be measured wirelessly and remotely both in air and in liquid. Based upon this, freestanding ME sensors for the detection of B. anthracis spores can be developed. These sensors are not only accurate, fast, and inexpensive but are also more sensitive and can be used in the
* Corresponding author. E-mail address: [email protected] (B.A. Chin). 0966-9795/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2008.07.024
field, unlike traditional identification methods, including plate culture, polymerase chain reaction, and enzyme-linked immunosorbent assays [1–5]. Binding of the target analyte can be achieved by immobilizing a selective and specific functional layer on the outer surface of the platform for sensor. The principle for this type of sensor is shown in Fig. 1. In this article we report on the fabrication and characterization of freestanding wireless amorphous magnetoelastic sensors for the detection of B. anthracis spores that are the causative agent for anthrax. 2. Experimental 2.1. Sensor fabrication 2.1.1. Sensors made from ME ribbon Commercially available ME materials (Metglas alloy 2826 MB) in ribbon form from Metglas, Inc. (Conway, SC) were employed to fabricate one type of ME sensor. The average composition of the ribbon was Fe40Ni38Mo4B18. A small piece was cut from the ribbons and hand polished to a thickness of 15 mm by standard metallographic preparation techniques. The ME material pieces were then washed ultrasonically with ethanol, and then diced into rectangular particles of three different sizes, 2000 400 mm, 1000 200 mm and 500 100 mm, using a micro-dicing saw. The particles were then annealed at 200 C for 2 h in a vacuum furnace to relieve residual stress. After annealing these pieces were coated
F. Xie et al. / Intermetallics 17 (2009) 270–273
271
Fig. 1. Diagram of the operating principle of a magnetoelastic particle (MEP) biosensor.
with chromium and gold thin films by a magnetron sputtering system. The Cr thin film works as an adhesive interlayer between the gold and the ME material. The gold surface improves the sensor resistance to corrosion and provides a ready surface for bio-probe immobilization. 2.1.2. Sensors made from ME films In order to achieve detection of low spore/cell counts, ME particles with smaller size, 200 40 4 mm, were fabricated using microelectronic processes including a co-sputtering and a nontraditional lift-off process. Amorphous-thick films with compositions near to 80/20 at.% iron/boron were magnetron sputtered by a Discovery-18 sputter system from Denton Vacuum USA (Moorestown, NJ) onto silicon wafers at a base pressure 7 10 7 Torr. The fabrication process starts with a plain silicon wafer that was sputter coated with a layer of Cr and Au, each at a thickness of 30–40 nm. Then the wafer was patterned with rectangular particles of 200 40 mm using photolithography processes. A thin gold film was then deposited onto the substrate, which works as a bottom protective layer for the particles. Fe (DC) and B (RF) targets, on separate cathodes, were used simultaneously to deposit the iron– boron alloy onto the wafer. A DC power of 42 W and a RF power of 101 W were used for depositing amorphous-thick films with compositions around 80/20 at.% iron/boron. An average film
iAC
2.2. Phage immobilization The bio-recognition element used was a filamentous phage selected specifically for B. anthracis spores, clone JRB7. JRB7 was developed by the Department of Pathobiology at Auburn University [9]. This JRB7 phage was immobilized onto the gold surface of the measurement sensor by immersing the gold-coated ME particles in the JRB7 phage solution (1011 vir/ml) for 1 h. Then the sensors were
Bar Magnet (HDC) DC Magnetometer (w/ probe)
HDC
HAC
Rel. Impedance
Coil (HAC)
Network Analyzer
thickness of 4 mm was achieved with a deposition rate of about 4.2 nm/min. A final gold thin film was coated on the substrate as the top protective layer for the particles. This layer also functions as a ready surface for biological immobilization. A lift-off process employing a wash with solvent was used to remove the particles from the wafer. These particles were cleaned with acetone. The assputtered particles were annealed in a vacuum oven at 200 C for about 3 h. This temperature was chosen because it is high enough such that the as-sputtered defects may be healed within a reasonable time, yet it is still far below the Curie temperature of 374 C [6], as well as the recrystallization temperature, which may vary between 390 and 460 C, depending on exact boron content [7,8].
fo
frequency Fig. 2. Diagram of the characterization method for the determination of magnetostrictive particle resonance frequency.
Fig. 3. Mass sensitivity of ME sensor for a flowing analyte.
272
F. Xie et al. / Intermetallics 17 (2009) 270–273
Table 1 Specificity of ME sensor over a range of Bacillus species. Bacillus species
Df (Hz)
Spore capture (vir)
B. B. B. B. B. B.
5250 54 57 132 37 89
6980 72 76 175 49 118
anthracis megaterium paratyphosus cereus subtilis licheniformis
taken out of the phage solution and washed gently 3 times with PBS solution and 2 times with sterile distilled water. The control sensors without phage solution immersing were directly washed following the same procedure as the measurement ones. Afterwards, both kinds of sensors were placed in a tube filled with 100 mL of tween20 solution (0.05%) with 1% BSA for blocking. Thirty minutes later, the sensors were rinsed 5 times by sterile distilled water and were ready for spore testing. 2.3. Sensor characterization Sensors made from ME ribbon were tested in 108 vir/ml solution of B. anthracis Sterne strain spores flowing at 200 ml/min. The sensor mass sensitivity and specificity were tested. The mass sensitivity of the sensor was measured by taking the average mass change caused by spore binding over the corresponding resonance frequency change. Six Bacillus spore species were tested with 500 100 15 mm sensors to evaluate the JRB7 phage-coatedsensor specificity. Low concentration spore solution testing was carried out on 200 40 4 mm-size sensors (both measurement and control sensors) in diluted spore solutions containing 102–108 cfu/ml. Each of the sensors was first tested with sterile distilled water. The resonance frequency of the sensor was retrieved by a computer every 60 s on a continuous basis for 30 min. Afterwards, the sensor was taken out without washing and put in B. anthracis spore solution with a concentration of 102 cfu/ml for another test of 30 min. The same procedure was applied repeatedly for each concentration of spore solution, increasing spore concentration by one decade until the 108 cfu/ml was reached. The measurement method for determining the resonance frequency of a sensor is schematically depicted in Fig. 2. SEM was used to help identify the spore’s binding to sensor as well as examine other surface features of the sensors. 3. Results and discussion 3.1. The mass sensitivity The mass sensitivity of the sensors made from ME ribbon and the theoretically calculated sensitivity are shown in Fig. 3. A
Fig. 4. The response curve as a function of time and concentration of both measurement sensor and control sensor.
detailed discussion of the theoretical predictions can be found in Refs. [10–12]. The experimentally measured sensitivity of the ME sensor agrees with predictions based upon theory. The measured sensitivity is 10 times greater than PZT cantilever sensors. 3.2. The specificity The resonance frequency change and the corresponding spore capture of sensors to six Bacillus spore species, as measured by counting captured spores on the surface of the sensor revealed by SEM, are listed in Table 1. The result indicates that the specificity of the ME sensors for B. anthracis spore species is excellent. 3.3. Low spore concentration detection Fig. 4 shows the resonance frequency responses of the 200 40 4 mm sensors in B. anthracis spore suspensions. Each type consists of one measurement sensor with phage-coating and one control sensor without phage-coating. It was found that both the resonance frequency and the amplitude of the measurement sensor decreased with time after the sensors were immersed in sterile distilled water. The resonance frequency reached a stable value in a couple of minutes, and this was taken as the baseline for comparison. Some fluctuations were observed at the beginning of some of the 30-min tests, but a steady state was reached quickly. Fig. 4 indicates the resonance frequency drops with the increase of spore concentration. The resonance frequency of the sensor decreased by a total of 48 kHz and reached a saturated state at the end of the test. The sensor detection limits are 102 cfu/ml, and the detection sensitivity is 13.1 kHz. In contrast, the resonance frequency of the control sensor remained stable without considerable change.
Fig. 5. SEM morphology of the 200 40 4 mm sensor surface at the end of the experiment (a) measurement sensors, (b) control sensors.
F. Xie et al. / Intermetallics 17 (2009) 270–273
SEM examination further confirms the extent of bonding of spores to the 200 40 4 mm measurement sensor and control sensor (Fig. 5). 4. Conclusions (1) The measured sensitivity of the amorphous ME sensor made from amorphous ME ribbon is very close to the theoretical one, which is 10 times greater than PZT cantilevers. And the specificity of the ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. (2) Standard microelectronic fabrication techniques have been used for producing 200 40 4 mm amorphous ME particles with a composition of around 80/20 at.% iron/boron for use as biosensor platforms. The 200 40 4 mm biosensor was found to have a detection limit of 102 cfu/ml and sensitivity of 13.1 kHz/decade. References [1] Inglesby TV, O’Toole T, Henderson DA, Bartlett JG, Ascher MS, Eitzen E, et al. Anthrax as a biological weapon, 2002: updated recommendations for management. JAMA 2002;287:2236–52.
273
[2] Ivnitski D, O’Neil DJ, Gattuso A, Schlicht R, Calidonna M, Fisher R. Nucleic acid approaches for detection and identification of biological warfare and infectious disease agents. Biotechniques 2003;35:862–9. [3] Papaparaskevas J, Houhoula DP, Papadimitriou M, Saroglou G, Legakis NJ, Zerva L. Ruling out Bacillus anthracis. Emerg Infect Dis 2004;10:732–5. [4] Peruski AH, Peruski Jr LF. Immunological methods for detection and identification of infectious disease and biological warfare agents. Clin Diagn Lab Immunol 2003;10:506–13. [5] Cheng Z-Y. Applications of smart materials in the development of high performance biosensors. Mater Res Soc Symp Proc 2006;888:185–95. [6] du Tremolet de Lacheisserie E. Magnetostriction: theory and applications of magnetoelasticity. Boca Raton, FL, USA: CRC Press; 1993 [chapter 3]. [7] Fish GE. Soft magnetic materials. Proc IEEE June 1990;78:947–72. [8] Cowlam N, Carr GE. Magnetic and structural properties of Fe–B binary metallic glasses I: variation of magnetic moment with composition. J Phys F Met Phys 1985;15:1109–16. [9] Brigati J, Williams D, Sorokulova IB, Nanduri V, Chen I-H, Turnbough C, et al. Diagnostic probes for Bacillus anthracis spores selected from a landscape phage library. Clin Chem 2004;50:1899–906. [10] Lakshmanan R, Guntupalli R, Hu J, Petrenko VA, Barbaree JM, Chin BA. Detection of Salmonella typhimurium in fat free milk using a phage immobilized magnetoelastic sensor. Sens Actuators B 1 October 2007;126(2):544–50. [11] Wan J, Shu H, Huang S, Fiebor B, Chen I-H, Petrenko VA, et al. Phage-based magnetoelastic wireless biosensors for detecting Bacillus anthracis spores. IEEE Sensors J March 2007;7(3):470–7. [12] Guntupalli R, Hu J, RamjiLakshmanan S, Huang TS, JamesBarbaree M, Chin Bryan A. A magnetoelastic resonance biosensor immobilized with polyclonal antibody for the detection of Salmonella typhimurium. Biosensors Bioelectron February 2007;22(7):1474–9.
Contents lists available at ScienceDirect
Intermetallics journal homepage: www.elsevier.com/locate/intermet
Amorphous magnetoelastic sensors for the detection of biological agents Fei Xie, Hong Yang, Suiqiong Li, Wen Shen, Jeihui Wan, Michael L. Johnson, Howard C. Wikle, Dong-Joo Kim, Bryan A. Chin* Materials Research and Education Center, Auburn University, Auburn, AL 36849, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 May 2008 Received in revised form 28 July 2008 Accepted 28 July 2008 Available online 22 January 2009
Freestanding amorphous magnetoelastic (ME) biosensors were fabricated by two ways. One type with larger size, 2000 400 15 mm, 1000 200 15 mm and 500 100 15 mm, was made from an ME Fe40Ni38Mo4B18 ribbon, the other with smaller size 200 40 4 mm was manufactured by dual beam sputtering and non-traditional microelectronic fabrication techniques. Both platforms were immobilized with JRB7 phage and were developed for the real-time in vitro detection of Bacillus anthracis spores. The experimental results show that the measured sensitivity of the ME sensors agrees with theoretical predictions and the specificity of ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. The 200 40 4 mm biosensor was found to have a detection limit of 102 cfu/ml and sensitivity of 13.1 kHz/decade. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: A. Intermetallics, miscellaneous G. Biomedical applications B. Elastic properties C. Vapour deposition C. Thin films
1. Introduction In 2001, US Citizens were terrorized by deliberate exposure to Bacillus anthracis spores that are the causative agent for anthrax during terrorist attacks targeting the US Postal Service. This attack led to the exposure of 16 people and death of 5. Mass panic amongst the general public led to the realization that bioterrorism could greatly disrupt both the commercial and agricultural sectors of the US economy. Thus it is critical for national security to detect early those biological warfare agents in very small amounts or very low concentrations. When an alternating magnetic field is applied to an amorphous magnetoelastic (ME) material, it undergoes a corresponding oscillating shape change that gives rise to a mechanical vibration with a characteristic resonance frequency. This frequency is a function of the shape, physical dimensions, and mass of the sensor platform. If B. anthracis spores bind to the surface of a platform made of ME material (attachment of mass), a drop in the platform resonance frequency will be induced. Changes in the frequency can be measured wirelessly and remotely both in air and in liquid. Based upon this, freestanding ME sensors for the detection of B. anthracis spores can be developed. These sensors are not only accurate, fast, and inexpensive but are also more sensitive and can be used in the
* Corresponding author. E-mail address: [email protected] (B.A. Chin). 0966-9795/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2008.07.024
field, unlike traditional identification methods, including plate culture, polymerase chain reaction, and enzyme-linked immunosorbent assays [1–5]. Binding of the target analyte can be achieved by immobilizing a selective and specific functional layer on the outer surface of the platform for sensor. The principle for this type of sensor is shown in Fig. 1. In this article we report on the fabrication and characterization of freestanding wireless amorphous magnetoelastic sensors for the detection of B. anthracis spores that are the causative agent for anthrax. 2. Experimental 2.1. Sensor fabrication 2.1.1. Sensors made from ME ribbon Commercially available ME materials (Metglas alloy 2826 MB) in ribbon form from Metglas, Inc. (Conway, SC) were employed to fabricate one type of ME sensor. The average composition of the ribbon was Fe40Ni38Mo4B18. A small piece was cut from the ribbons and hand polished to a thickness of 15 mm by standard metallographic preparation techniques. The ME material pieces were then washed ultrasonically with ethanol, and then diced into rectangular particles of three different sizes, 2000 400 mm, 1000 200 mm and 500 100 mm, using a micro-dicing saw. The particles were then annealed at 200 C for 2 h in a vacuum furnace to relieve residual stress. After annealing these pieces were coated
F. Xie et al. / Intermetallics 17 (2009) 270–273
271
Fig. 1. Diagram of the operating principle of a magnetoelastic particle (MEP) biosensor.
with chromium and gold thin films by a magnetron sputtering system. The Cr thin film works as an adhesive interlayer between the gold and the ME material. The gold surface improves the sensor resistance to corrosion and provides a ready surface for bio-probe immobilization. 2.1.2. Sensors made from ME films In order to achieve detection of low spore/cell counts, ME particles with smaller size, 200 40 4 mm, were fabricated using microelectronic processes including a co-sputtering and a nontraditional lift-off process. Amorphous-thick films with compositions near to 80/20 at.% iron/boron were magnetron sputtered by a Discovery-18 sputter system from Denton Vacuum USA (Moorestown, NJ) onto silicon wafers at a base pressure 7 10 7 Torr. The fabrication process starts with a plain silicon wafer that was sputter coated with a layer of Cr and Au, each at a thickness of 30–40 nm. Then the wafer was patterned with rectangular particles of 200 40 mm using photolithography processes. A thin gold film was then deposited onto the substrate, which works as a bottom protective layer for the particles. Fe (DC) and B (RF) targets, on separate cathodes, were used simultaneously to deposit the iron– boron alloy onto the wafer. A DC power of 42 W and a RF power of 101 W were used for depositing amorphous-thick films with compositions around 80/20 at.% iron/boron. An average film
iAC
2.2. Phage immobilization The bio-recognition element used was a filamentous phage selected specifically for B. anthracis spores, clone JRB7. JRB7 was developed by the Department of Pathobiology at Auburn University [9]. This JRB7 phage was immobilized onto the gold surface of the measurement sensor by immersing the gold-coated ME particles in the JRB7 phage solution (1011 vir/ml) for 1 h. Then the sensors were
Bar Magnet (HDC) DC Magnetometer (w/ probe)
HDC
HAC
Rel. Impedance
Coil (HAC)
Network Analyzer
thickness of 4 mm was achieved with a deposition rate of about 4.2 nm/min. A final gold thin film was coated on the substrate as the top protective layer for the particles. This layer also functions as a ready surface for biological immobilization. A lift-off process employing a wash with solvent was used to remove the particles from the wafer. These particles were cleaned with acetone. The assputtered particles were annealed in a vacuum oven at 200 C for about 3 h. This temperature was chosen because it is high enough such that the as-sputtered defects may be healed within a reasonable time, yet it is still far below the Curie temperature of 374 C [6], as well as the recrystallization temperature, which may vary between 390 and 460 C, depending on exact boron content [7,8].
fo
frequency Fig. 2. Diagram of the characterization method for the determination of magnetostrictive particle resonance frequency.
Fig. 3. Mass sensitivity of ME sensor for a flowing analyte.
272
F. Xie et al. / Intermetallics 17 (2009) 270–273
Table 1 Specificity of ME sensor over a range of Bacillus species. Bacillus species
Df (Hz)
Spore capture (vir)
B. B. B. B. B. B.
5250 54 57 132 37 89
6980 72 76 175 49 118
anthracis megaterium paratyphosus cereus subtilis licheniformis
taken out of the phage solution and washed gently 3 times with PBS solution and 2 times with sterile distilled water. The control sensors without phage solution immersing were directly washed following the same procedure as the measurement ones. Afterwards, both kinds of sensors were placed in a tube filled with 100 mL of tween20 solution (0.05%) with 1% BSA for blocking. Thirty minutes later, the sensors were rinsed 5 times by sterile distilled water and were ready for spore testing. 2.3. Sensor characterization Sensors made from ME ribbon were tested in 108 vir/ml solution of B. anthracis Sterne strain spores flowing at 200 ml/min. The sensor mass sensitivity and specificity were tested. The mass sensitivity of the sensor was measured by taking the average mass change caused by spore binding over the corresponding resonance frequency change. Six Bacillus spore species were tested with 500 100 15 mm sensors to evaluate the JRB7 phage-coatedsensor specificity. Low concentration spore solution testing was carried out on 200 40 4 mm-size sensors (both measurement and control sensors) in diluted spore solutions containing 102–108 cfu/ml. Each of the sensors was first tested with sterile distilled water. The resonance frequency of the sensor was retrieved by a computer every 60 s on a continuous basis for 30 min. Afterwards, the sensor was taken out without washing and put in B. anthracis spore solution with a concentration of 102 cfu/ml for another test of 30 min. The same procedure was applied repeatedly for each concentration of spore solution, increasing spore concentration by one decade until the 108 cfu/ml was reached. The measurement method for determining the resonance frequency of a sensor is schematically depicted in Fig. 2. SEM was used to help identify the spore’s binding to sensor as well as examine other surface features of the sensors. 3. Results and discussion 3.1. The mass sensitivity The mass sensitivity of the sensors made from ME ribbon and the theoretically calculated sensitivity are shown in Fig. 3. A
Fig. 4. The response curve as a function of time and concentration of both measurement sensor and control sensor.
detailed discussion of the theoretical predictions can be found in Refs. [10–12]. The experimentally measured sensitivity of the ME sensor agrees with predictions based upon theory. The measured sensitivity is 10 times greater than PZT cantilever sensors. 3.2. The specificity The resonance frequency change and the corresponding spore capture of sensors to six Bacillus spore species, as measured by counting captured spores on the surface of the sensor revealed by SEM, are listed in Table 1. The result indicates that the specificity of the ME sensors for B. anthracis spore species is excellent. 3.3. Low spore concentration detection Fig. 4 shows the resonance frequency responses of the 200 40 4 mm sensors in B. anthracis spore suspensions. Each type consists of one measurement sensor with phage-coating and one control sensor without phage-coating. It was found that both the resonance frequency and the amplitude of the measurement sensor decreased with time after the sensors were immersed in sterile distilled water. The resonance frequency reached a stable value in a couple of minutes, and this was taken as the baseline for comparison. Some fluctuations were observed at the beginning of some of the 30-min tests, but a steady state was reached quickly. Fig. 4 indicates the resonance frequency drops with the increase of spore concentration. The resonance frequency of the sensor decreased by a total of 48 kHz and reached a saturated state at the end of the test. The sensor detection limits are 102 cfu/ml, and the detection sensitivity is 13.1 kHz. In contrast, the resonance frequency of the control sensor remained stable without considerable change.
Fig. 5. SEM morphology of the 200 40 4 mm sensor surface at the end of the experiment (a) measurement sensors, (b) control sensors.
F. Xie et al. / Intermetallics 17 (2009) 270–273
SEM examination further confirms the extent of bonding of spores to the 200 40 4 mm measurement sensor and control sensor (Fig. 5). 4. Conclusions (1) The measured sensitivity of the amorphous ME sensor made from amorphous ME ribbon is very close to the theoretical one, which is 10 times greater than PZT cantilevers. And the specificity of the ME sensors coated with JRB7 phage for B. anthracis spore species is excellent. (2) Standard microelectronic fabrication techniques have been used for producing 200 40 4 mm amorphous ME particles with a composition of around 80/20 at.% iron/boron for use as biosensor platforms. The 200 40 4 mm biosensor was found to have a detection limit of 102 cfu/ml and sensitivity of 13.1 kHz/decade. References [1] Inglesby TV, O’Toole T, Henderson DA, Bartlett JG, Ascher MS, Eitzen E, et al. Anthrax as a biological weapon, 2002: updated recommendations for management. JAMA 2002;287:2236–52.
273
[2] Ivnitski D, O’Neil DJ, Gattuso A, Schlicht R, Calidonna M, Fisher R. Nucleic acid approaches for detection and identification of biological warfare and infectious disease agents. Biotechniques 2003;35:862–9. [3] Papaparaskevas J, Houhoula DP, Papadimitriou M, Saroglou G, Legakis NJ, Zerva L. Ruling out Bacillus anthracis. Emerg Infect Dis 2004;10:732–5. [4] Peruski AH, Peruski Jr LF. Immunological methods for detection and identification of infectious disease and biological warfare agents. Clin Diagn Lab Immunol 2003;10:506–13. [5] Cheng Z-Y. Applications of smart materials in the development of high performance biosensors. Mater Res Soc Symp Proc 2006;888:185–95. [6] du Tremolet de Lacheisserie E. Magnetostriction: theory and applications of magnetoelasticity. Boca Raton, FL, USA: CRC Press; 1993 [chapter 3]. [7] Fish GE. Soft magnetic materials. Proc IEEE June 1990;78:947–72. [8] Cowlam N, Carr GE. Magnetic and structural properties of Fe–B binary metallic glasses I: variation of magnetic moment with composition. J Phys F Met Phys 1985;15:1109–16. [9] Brigati J, Williams D, Sorokulova IB, Nanduri V, Chen I-H, Turnbough C, et al. Diagnostic probes for Bacillus anthracis spores selected from a landscape phage library. Clin Chem 2004;50:1899–906. [10] Lakshmanan R, Guntupalli R, Hu J, Petrenko VA, Barbaree JM, Chin BA. Detection of Salmonella typhimurium in fat free milk using a phage immobilized magnetoelastic sensor. Sens Actuators B 1 October 2007;126(2):544–50. [11] Wan J, Shu H, Huang S, Fiebor B, Chen I-H, Petrenko VA, et al. Phage-based magnetoelastic wireless biosensors for detecting Bacillus anthracis spores. IEEE Sensors J March 2007;7(3):470–7. [12] Guntupalli R, Hu J, RamjiLakshmanan S, Huang TS, JamesBarbaree M, Chin Bryan A. A magnetoelastic resonance biosensor immobilized with polyclonal antibody for the detection of Salmonella typhimurium. Biosensors Bioelectron February 2007;22(7):1474–9.