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Mass Detection Sensor Using Cantilever Beam Engineering Essay

In this paper we are traveling to discourse about a micromachined cantilever beam which is used for the sensing of smaller multitudes. This type of cantilever beam is chiefly used for the biological detection applications. The developed biosensor was capable of rapid and ultrasensitive sensing of bacterium ‘s. The detector was used to observe the little multitudes bacteria ‘s like listeria innocua, MRSA bacterium. Biosensor of these engineerings proves to be the promising solution mensurating the little multitudes. With sweetening in the detectors type the sensitiveness and the distant detection can be increased. The decrease in the size of the detectors from micro to Nano besides proves to be greater consequence for mensurating the smaller multitudes of attogram size.

The micromachined Si cantilever is designed utilizing merged epitaxial sidelong giantism ( MELO ) method. In order to manufacture a low emphasis and thin cantilever chemical mechanical shining method is used. Here two methods were used for the adhesion of the smaller mass on the cantilever beam: 1 ) direct adhesion of the little mass bacteriums 2 ) lodging a bed over the Si beam for the adhesion of mass. The detector calculates the alteration in resonating frequence of the cantilever beam with the mass burden and without mass burden at normal atmospheric conditions. The quiver of the cantilever beam which was excited due to thermic and ambient noise was measured utilizing a scanning investigation microscope. In this paper we will besides demo the theoretical design for the cantilever beam utilizing COMSOL which provide us with the unsmooth thought for the resonance and warp of the beam on the deposition of thin beds on the beam.


Micro and Nanotechnology applications are huge and they have the capableness to decide the challenges of the chemical, environmental and biological analysis. One of the attacks towards the executions of these engineerings is the usage of micro and Nano mechanical resonating chambers which may work as the ultrasensitive transducers in chemical and biological detectors. Merging of Si micro and nanofabrication with surface functionalization of biochemistry offers new exciting chances in developing microscopic biomedical analysis devices with alone features. [ 1 ] Sing the instance for cantilever beam detectors which were introduce to nanotechnology with their usage in the atomic force microscope ( AFM ) . [ 2 ] Cantilever beam links between the physical kingdom in micro and Nanoscale governments. [ 2 ] Due to easy fiction procedure and simple construction cantilever beams have attracted the MEMS and NEMS community attendings towards it. Micro and Nano graduated table cantilevers have proved to be the highly sensitive biosensors. [ 2 ] [ 3 ] [ 4 ] [ 5 ]

Over the past decennaries assorted methods have tried for observing and mensurating DNA-DNA, antibody-antigen and ligand-receptor interaction forces so as to help the bimolecular reorganisation. Well many methods and detectors were developed for mensurating the smaller multitudes and forces, biosensors utilizing cantilever beam were one of the solution to these challenges. Out of which cantilever used in AFM were the greater discovery for analyzing the bio-interaction [ 7 ] , mensurating antibody interaction [ 8-10 ] & A ; hybridisation of complementary DNA strands interactions. [ 1 ] [ 11 ] There have a been a cogency survey made on incorporating magnetic staff of life and scanning AFM for biosensors. [ 12 ] In past few old ages biosensors have attracted considerable involvements in the applications from medical analysis to environmental analysis and besides for industrial procedure. [ 1 ] In the industrial procedure they are used to mensurate the assorted gaseous analyte in the french friess, it can used to observe the quicksilver vapor which are the immediate relevancy applications for air pollution sensing and industrial hygiene monitoring. [ 4 ] [ 6 ] A biosensor chiefly can be divided into three chief constituents: [ 1 ]

Detector: It can be used to recognize the concern signal ( immune detectors or enzymatic detectors )

Transducers: it can be used to change over the signal into more utile end product more likely electronic signal ( amperometric or piezoelectric )

Read out: it can be used to filtrate, magnify, show, record or convey the transduced signal.

In the followers we will concentrate on mechanical transduction mechanism which is based on the bending of micro-cantilevers due to the surface assimilation of mass on the surface of the beam. Microscale detectors have proved to be highly sensitive biosensor. The alteration in resonance frequence of the beam due to mass burden is the cardinal facet for mensurating the mass of the burden. This method used for mensurating the little mass is non merely sensitive because of simple fiction procedure and less clip devouring but it is more efficient device excessively. These types of detectors can be used for multiple purpose mass sensitive by utilizing the array of cantilever with different analyte harmonizing to the demand of multitudes. Turning a magnetostrictive movie over the silicon beam makes the detectors like remote detection, self – standardization & A ; self – testing, therefore a batch development is need in the MEMS and NEMS engineering.

The chief ground for utilizing Si cantilever is because of the fiction advantages they give over microscale like: [ 2 ]

Dimensions of the device can be control.

Can accomplish Micro to Nano dimensions

Fabrication of arrays of devices possible with Si engineering

Low cost fiction.

Integration of assorted devices on the same platform

High mechanical quality factor

In this paper we will depict about a Si based micromachined cantilever as a resonant biosensor for the sensing of mass of bacteriums cell and antibodies. Listeria Innocua was the bacteria that was taken into consideration as the mass. The mass of the antibody was besides step so as to mensurate the sensitiveness and warp of the beam so as to show the consequence of interaction between the bed and the bacteriums and to mensurate the resonating frequence of before and after the mass burden. [ 2 ] The fiction and the measurement technique for this biosensor are described in this paper below.

Fabrication procedure:

In this technique we are traveling to manufacture the Si cantilever utilizing merged epitaxial lateral over growing ( MELO ) and chemical mechanical shining ( CMP ) .We are traveling to utilize the selective epitaxial growing ( SEG ) , epitaxial sidelong giantism ( ELO ) and chemical- mechanical shining ( CMP ) for the microfabrication of thin individual crystal Si cantilever beam. [ 2 ] [ 13 ] Various signifier of selective Si growing has been besides described antecedently. [ 2 ] [ 14 ] [ 15 ] This type of Si based fiction procedure can be besides used for flow detectors, force per unit area detector, biochemical detector and many more. The procedure of fiction utilizing MELO and CMP consequences in a low emphasis cantilever with a bomber 100nm thickness. [ 15 ]

This technique used for the fiction of Si cantilever does n’t include an oxide bed which reduces the mismatch between the Si and Si dioxide which exist when utilizing SOI as the get downing stuff. We need to bring forth maximal possible emphasis free cantilever, since the residuary emphasis green goods in the beam while fiction affect the vibrational belongings of the beam. The present method can be used for manufacturing arrays of cantilever beam by changing their dimensions. The method is besides capable to bring forth nanometre scope cantilever beam for individual molecule sensing applications. The thin cantilever fiction can be shown in eight following stairss: [ 15 ]


This steps trade with the shaping of the cantilever shapes utilizing a wet etching procedure. In this procedure the Si dioxide bed is grown utilizing the photolithography procedure. Using a buffered hydrated oxide ( BHF ) the oxide bed is wet etched and the cantilever form is obtained. The stairss for the wet etching procedure are shown below in the figure:

Figure 1: ( Image gracious ) surface micromachining of the cantilever beam. [ * ]

Stairss involve in the procedure: [ * ]

A ( a ) The deposition of the sacrificial bed

( B ) Specifying the ground tackle and bushing parts on the Si substrate.

( degree Celsius ) Pattering of the structural bed.

( vitamin D ) Final obtained free standing cantilever beam.

Fig.2: ( Image gracious ) Bulk micromachined by anisotropic etching of Si. [ * ]

Different positions of cantilever beam: [ * ]

( a ) Position for the bottom program of the cantilever beam with pits, stop and holes in the wafer etched figure above.

( B ) Top program position of an anisotropically etched wafer demoing the fiction of a cantilever beam utilizing etch halt bed.

( degree Celsius ) Cross subdivision, AA ‘ in the figure shows the hole, stop, and pit of the cantilever beam.

( vitamin D ) Cross subdivision, BB ‘ , shows the cantilever beam.

In the above procedure we use the Si stuff along & lt ; 100 & gt ; way in ordered to obtain minimal denseness consequence.

Measure 2:

A thin buried bed oxide is grown over the beam in order to obtain the dilutant cantilever beam utilizing an oxidization procedure. The thickness of the beam can be varied utilizing selective cover, etching and oxidization procedure over the inhumed oxide. As shown in figure 3 ( a )


In order to open the seed window a reactive ion procedure ( RIE ) is done over the oxide bed utilizing the CHF3/O2. A sacrificial bed is grown followed by moisture etching and the annealed so as to cut down the harm caused by RIE procedure.

Measure 4: ( epitaxial bed growing )

A epitaxial bed was grown utilizing the Gemini I Pancake type reactor. The obtained end product can be seen the figure 3 ( degree Celsius ) below ( top position ) . The reactor status maintained were T= 9700C, P= 40 Torr. HCl was used to keep the selectivity of the oxide bed, the carier gas was H and the beginning was dichlorosilane ( DCS ) .

Measure 5: ( Chemical mechanical shining )

CMP was performed in two different type of etching procedure over the oxide bed in a combination in order to obtain a faster and finer thin movie of Si. NALCO 2350 was used for faster etching procedure and NALCO2355 was used to execute the finer etching procedure. So as to protect the cantilever from rinsing off there was a demand to smooth the Si down to the wafer level surface. The undermentioned stairss are given below.

FIG 3.1: ( Image gracious ) Micro fiction of thin movie cantilever beam utilizing MELO and CMP ( a-d ) [ 15 ]

Measure 6:

Tetra methyl ammonium hydrated oxide ( TMAH ) was used to etch the Si wafer but a thin bed of 30nm oxide was grown in order to salvage the cantilever from the etching procedure. The etch window was opened with the RIE utilizing CF3/O2.

Measure 7:

The cantilever beam was released after the etching procedure utilizing TMAH as shown in fig 3.2 ( degree Fahrenheit ) . The concluding merchandise of the cantilever beam was obtained by etching off the oxide bed utilizing BHF ( buffered hydrofluoric ) .

FIG 3.2: ( Image gracious ) Micro fiction of thin movie cantilever beam utilizing MELO and CMP ( e-f ) [ 15 ]

Measure 8:

Thought the concluding cantilever was obtained so besides the constructions were deionized in the H2O for 10min and were treated utilizing methyl alcohol in 3 stairss for 10min. the merchandise was eventually air dried.

FIG 4: ( Image gracious ) cantilever beam [ 2 ]

COMSOL design: ( The theoretical design for the Cantilever Beam )

A theoretical simulation on the cantilever beam was performed in order to mensurate it inactive warp on the bed deposition and the Eigen frequence of the beam. The undermentioned consideration done for the beam is shown below in the tabular array:

Table 1: Dimension of the cantilever beam taken under consideration.

The inactive warp of the cantilever beam and the resonance frequence of the cantilever beam as obtained in the COMSOL package is shown below in the figure.

a )

B )

FIG 5: COMSOL DESIGN a ) inactive warp of the beam ( 8.125 e-10 ) B ) Resonance frequence of the beam ( 2.310725 e5 ) .

Measuring Technique:

To execute the mechanical word picture of the cantilever beam obtained from the MELO and CMP procedure a resonating frequence measuring was performed. In order to vibrate the cantilever beam thermal and ambient noise was used, since they were sufficient to vibrate the cantilever beams. In order to mensurate the quiver and to mensurate the resonance frequence of the beam dimension 3100 series ( digital instruments, veeco metrology group ( SPM ) was used. [ 2 ] [ 15 ] The power spectral denseness was so evaluated utilizing the MATLAB package and the thermic information was fit to the amplitude response of the simple harmonic oscillator [ 13 ] [ 16 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ . ( 1 )

Where degree Fahrenheit is the frequence and field-grade officer is the resonating frequence, Q is the quality factor of the Si beam and Adc is the cantilever amplitude at zero frequence.

The resonating frequence of the cantilever beam was given by: [ 16 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.. ( 2 )

Where m is the effectual mass and K is the spring invariable which is given by: [ 16 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ ( 3 )

Where fi is the resonating frequence obtained after the mass burden. While the effectual mass can be calculated utilizing: [ 2 ] [ 16 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.. ( 4 )

The alteration in mass due to alter in resonating frequence can be given by: [ 2 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ . ( 5 )

Whereas n= 1 for the added mass distributed uniformly over the beam and n=0.24 when the mass is distributed indiscriminately over the rectangular cantilever beam.

The planar dimensions and measured values of unloaded cantilever at the normal status with the resonating frequence, quality factor, spring changeless and mass sensitiveness are shown below in the tabular array: [ 2 ]

Table 1: Dimension values [ 2 ]


The sample usage in the procedure was Listeria innocua bacteriums which were grown on the Luria-Bertani ( LB ) stock at 370C placed in a n brooder. The undermentioned parametric quantities were considered for the Listeria Innocua bacteriums growing: [ 1 ]

Initial concentration: 5*10^6 to 5*10^8 cells/ml

Buffer used: phosphate buffered saline ( PBS ) with pH value of 7.4

Antibody: Goat affinity-purified polyclonal

Barricading agent: BSA ( Bovine Serum Albumin ) for forestalling nonspecific binding of bacteriums cell

To take the slackly bound bacteriums PBS was used.

To obtain the effectual dry mass of the bacteriums non-specific binding was performed on the cantilever beam. The resonating frequences were calculated in the air. Doppler vibrometer was used to execute the resonance measurings. In order to avoid the stiction of the beam at the substrate surface they used CPD ( Critical point drying ) for drying the liquid used for the bacterium adhesion. The consequences obtained for the frequence measuring is shown below:

FIG4: ( image courteous ) resonant frequence before and after the mass burden of the bacteriums. [ 2 ]

The mass obtained utilizing the mass equation ( 5 ) was around 85fg.

Another survey was performed utilizing the antibody. BSA and antibody to the bacterium was trapped onto cantilever beam by scattering 10-15Aµl of solution. The resonating frequence of the cantilever beam was measured in air in order to acquire the alteration in frequence due to the antibody and BSA mass. The beam was once more treated with the bacteriums and the alteration in the frequence was observed. The consequence obtained can be seen in the figure below:

FIG 5: ( image courteous ) resonant frequence of the unloaded cantilever beam, after antibody + BSA, after the mass burden. [ 2 ]

Application of Biosensors:

Biochemical procedure are the most complexity procedure as comparison to chemical and physical hence the bio-sensing are more demanding undertaking. Normally bio-sensing devices are carried out in liquid ( aqueous solution ) environment. The cantilever warps are affected by the flowing and commixture of solution caused by turbulency. Several groups have showed how bio-sensing can be implemented utilizing micro cantilever detectors. Measuring the surface emphasis one can supervise broad mass surface assimilation with the micro cantilever, cantilevers can be used for force transducers to observe the presence of receptor coated magnetic beads which would lodge onto the functionalized cantilever surface. [ 1 ] Cantilever based detectors are really versatile they can be used in any natural conditions. They have the capableness of transducing different signals like magnetic, electric, thermic, chemical, mass and flow. [ 1 ] A micrometre transducer can be successfully implemented in the biosensor, it adds several advantages to the bio-sensors like increasing the sensitiveness & A ; bounds, they are inexpensive and easy to manufacture and they can be integrated in CMOS ( complementary metal oxide semiconducting material ) . [ 1 ]

Using the biosensors several bio medical applications can be foreseen such as: [ 1 ]

Monitoring presence

Concentration of the substance in solutions or gases

Calculating specific adhering energy

Monitoring chemical surface reactions

Analyzing adsorption-desorption procedure of substance.

Future work:

Optimization of the cantilever dimensions and forms for maximal emphasis, mass or temperature sensitiveness and the usage of big arrays of cantilevers in parallel development are needed.


The present survey shows the usage of micromachined cantilever beam for biological intent. This present work shows about the biosensor utilizing the MEMS engineering. The present work shows that utilizing the MEMS it is possible to mensurate the mass of few Femtogram or attogram. This theoretical account shows the rapid and sensitive sensing of the bacterial cells. A theoretical simulation was performed for the theoretical account utilizing the COMSOL package. Antigen-antibody was used as the midst bed for the adhesion of the bacteriums. Hence it shows the micromachined cantilever as a resonating mass detector.