The document describes the design of microcantilever sensors for the detection of tuberculosis. Computational models were developed to simulate the behavior of triangular, pi-shaped, and rectangular microcantilevers. Simulation results found that the rectangular microcantilever design had the highest sensitivity, with an eigenfrequency of 4.5078*106 Hz and maximum displacement of 9.3887*10-19m detected for an input of 50 antigens. The rectangular microcantilever sensor was determined to be the most suitable design for sensitive detection of tuberculosis.
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1. DESIGN OF MEMS BASED MICROCANTILEVER FOR
TUBERCULOSIS DETECTION
Saranya R 1
, Saranya K 1
, Ceemati D 1
, Chandra Devi K 1
, Meenakshi Sundaram N 1
1
PSG College of Technology, Department of Biomedical Engineering, Peelamedu, Coimbatore-641 004.
Introduction: Tuberculosis is caused by a bacterium
called Mycobacterium tuberculosis. The fusion protein,
ESAT-6/CFP-10 is secreted by the extended region of
RDX- 1 which encodes ESX-1, a novel protein secretion
system and known to contribute to virulence and
pathogenicity in the host. The most prominent cantilever
type of detection is preferred (figure 1). The objective of
the study was to select the best suited cantilever for
tuberculosis detection.
Computational Models: The three dimensional
geometry of the Cantilever was simulated using COMSOL
Multiphysics 4.3b software (figure 2).The Stoney's formula,
which relates cantilever end deflection 隆 to applied stress
given by:
--- (1)
Where is Poisson's ratio,
E is Young's modulus,
L is the beam length and
t is the cantilever thickness
The total force being applied to the cantilever is much more
related to the number of analyte molecules attaching to the
cantilever. The resonance frequency (f) on a cantilever
working in dynamic mode is given by:
--- (2)
Where k is the spring constant,
meff is the effective or dynamic mass.
Results: The Stationary and Eigen frequency
studies are performed. The simulated results of the
Cantilever structures are given in figures (3) and (4).
The lowering of the resonant frequency is attributed
due to the increase in the mass of analyte over the
thiolated gold surface.
Cantilever
type
Displacement
(袖m)
Eigen
Frequency
(Hz)
Triangular
shape
1.0023*10-13
9.86225
Pi- shape 3.9693*10-21
1.8115*107
Rectangular
shape
9.3887*10-9
4.5078*106
Conclusions: The Eigen frequency and the maximum
displacement were observed for rectangular shaped cantilever
sensor. The sensor is highly sensitive since it can detect even
attomolar concentration of the analyte molecules. For an input
mass of 50 ESX-1 antigens, a maximum displacement of
9.3887*10-19
was observed (figure 5). Thus, a highly sensitive
and selective sensor based on cantilever is simulated using
COMSOL Multiphysics 4.3b.
References:
1.Hemmati M, Expression and Purification of
Recombinant Mycobacterium Tuberculosis Diagnosis
Antigens, ESAT-6, CFP-10, and ESAT-6/CFP-10, and Their
Potential Use in the Diagnosis and Detection of
Tuberculosis, Iranian Red Crescent Medical Journal, Vol.
13, No.8, Pages 558-565,(2011).
2.Danica Helb, Rapid Detection of Mycobacterium
tuberculosis and Rifampin Resistance by Use of On-
Demand Near Patient Technology , Journal of Clinical
Microbiology,Vol. 48, No. 1, Pages. 229237, (2010).
Figure 3. Simulated Results of the Proposed Cantilevers
Figure 5. Displacement Vs Input force for different types of
Cantilever structures
Figure 1. Deflection of the Cantilever upon selective binding
Figure 2: Proposed Geometry of the Cantilever Structures
Figure 3 & 4. Simulation results of the different types of Cantilever