Principles of Electronic Nanobiosensors

Transcription

1 Principles of Electronic Nnoiosensors Unit 3: Sensitivity Lecture 3.10: Cntilever-sed Sensors: Bsic Opertion By Muhmmd A. Alm Professor of Electricl nd Computer Engineering Purdue University A. Shkouri nnohub-u Fll 013 1

2 Outline Introduction Biosensors compred How does mechnicl iosensor work Physics of liner iosensing Dynmic iosensing Conclusion Alm, Principles of Nnoiosensors, 013

3 Three types of sensors Potentiometric Fluid Gte Amperometric Ref. & Aux. Electrode Mechnicl Gte Chrge to current Chemicl to current Mss to frequency Alm, Principles of Nnoiosensors, 013 3

4 Mss of molecules 180 Dlton/molecule (0.3 zepto-grm) 15 Dlton/AA 1 pico-grm 300 Dlton/p (0.5 zepto-grm) MDltons 10s of ttogrm Humn cell ~ 1 nnogrm 10s of zeptogrms possile, in principle 4

5 Why cntilever-sed mechnicl sensors Reference electrodes ovited; cn e miniturized. Free from chrge screening. Liner response expected. Esily implemented sed on MEMS sed technology. Avilility of rod rnge of reserch results Still limited y limits of settling time (diffusion limit) Selectivity is n issue, like potentiometric sensors Interprettion complicted for very smll sensors Alm, Principles of Nnoiosensors, 013 5

6 How does cntilever sensor work W~1um, L~4 um, H~5nm Cntilever rry Alm, Principles of Nnoiosensors, 013 6

7 How to mesure deflection Opticl Resistive Cpcitive 7

8 How to ring the iomolecule to the sensors Diffusion limited response Flow enhnced response Alm, Principles of Nnoiosensors, 013 8

9 Outline Introduction Biosensors compred How does mechnicl iosensor work Physics of liner iosensing Dynmic iosensing Conclusion Alm, Principles of Nnoiosensors, 013 9

10 Equivlent spring-mss system Selective Chemicl Lyer y = y 0 Recting Chemicl Compound y d y dy + γ + ( 0) = F ext m k y y dt dt Alm, Principles of Nnoiosensors,

11 Equivlent spring-mss system H H/ W m I = 0.4ρ LWH k = 3EI L L = WH y = y 0 d y dy + γ + ( 0) = F ext m k y y dt dt m = 0.4 ρ LW ( H + H ) k = 3EI L ( ) 3 1 I = W H + H 3 Alm, Principles of Nnoiosensors,

12 Oscilltion in n idel spring-mss No dmping, simple liner spring, trnsient force pplied m d y dy + γ + ( 0) = F ext m k y y dt dt ( ) d y0 y k y 0 y = dt i 0t Ae ω + + = y y = y y 0 ω ma = ka 0 Before After ω 0 = k / m 0, ω = k m ω 0, = k m Chnge in resonnt frequency signls cpture of iomolecules Alm, Principles of Nnoiosensors, 013 1

13 Si em: An Exmple L=3 um, W=1.5nm H=5nm, E=70 GP, Density=330 Kg/m 3 m = αρv = Kg m m 3 10 m m 3 17 = Kg=63 fg k ( ) N 5 10 m m = αei L = = m m ( 6 ) N m f = ω 1 k π = π m =.47 MHz Alm, Principles of Nnoiosensors,

14 Mss only dynmic response: Idel spring y = y 0 y ω k m = ω k m ω = ω m m Before After ω = k m ω 0, = k / 0, / m k m = α EI L 1 3 = αρwlh I = WH 3 1 m = m + m k = k + k m α E 1 ω = 1αρ WL Multiple vriles to improve nnoiosensor response Alm, Principles of Nnoiosensors,

15 Spring-only Dynmic response Before y = y 0 y 0, k / m After ω = ω 0, = k / m m = m + m k = k + k H = 0 nm, H = 10 nm, A = π (1nm), N = 10 cm t t 1 s ω k m = ω k m k = α EWH /1L dk dh 3 k H dh NAH s t t 3 3 k k N AH H k k 3 s t t 4.7% 15

16 Modultion of `k due to molecule cpture on cntilevers 10-40% chnge in `k Experimentl Vlidtion Dynmic nd sttic response ω ω k k Gupt, Nir, et l., PNAS 006 Ekinci et l., Rev Sci Inst., 007 Wee et l., Biosen. Bioelec

17 Reversl of frequency t nnoscle Amplitude Amplitude efore fter Frequency (MHz) efore fter Frequency (MHz) Gupt, Nir, et l., PNAS dh H E ρ = 1 E ρ c H=5nm, W=1.5 um Lc=5um lnce etween mss nd spring effects Lc=3um 17

18 Composite effects nd frequency reversl dh c m = αρwlh 1 ( ) m = αρwl H + dh 1 c k α = ( ) 3 E H W 3 1L Before After ω ω = 0, k / m ω = 0, k / m 0, = ω0, k m = k m k dh H α + = 1L c 3 E ( H dhc ) W 3 Eρ = 1 E ρ Alm, Principles of Nnoiosensors,

19 Conclusions Cntilever sensors mesures chnges in mss nd stiffness of the em following the cpture of iomolecules. The reversl of frequency is n importnt chrcteristic feture of nnoscle cntilever sensors. Reference or counter-electrode no longer needed; cn e miniturized. Diffusion limits nd selectivity still importnt concerns. Alm, Principles of Nnoiosensors,

20 Review questions Do the cntilever-sed mechnicl sensors suffer from the prolem of electricl screening? Do we need the reference electrode in cntilever-sed mechnicl sensors? Why not? Do you see ny dvntge of using reference cntilever for differentil mesurements? Wht quntity is mesured in dynmic detection: Deflection or chnge in resonnce frequency? Wht does the resonnce frequency of cntilever depend on? Alm, Principles of Nnoiosensors, 013 0

21 Appendix: Moment of Inerti r 0 d d 1 1 r i I x d d = I = ( r ) 0 r i 1 π 4 Alm, Principles of Nnoiosensors, 013 1

22 Frequency chnge due to dmping (in wter) in response to Trnsient Input d y dy + γ + = 0 ext = m ky F dt dt Solution: αω0t y = Ae sin( ω ' t + φ ) γ 1 α = mω Q 0 k γ ω ' = ( ) m 4m 1 The response is dmped nd the nturl frequency chnged. Alm, Principles of Nnoiosensors, 013

23 Appendix: An electricl nlog m d y dy + γ + ky = Fcos( ωt) dt dt di I RI + L( ) + ( )dt = Vcos( ω t) dt C d Q dq Q L + R + = V cos( ω t) dt dt C Q= C V c q y L m C 1/ I V v F R γ k Alm, Principles of Nnoiosensors, 013 3

24 m Forced oscilltion & rodening of response d y dy + γ + ky = Fcos( ωt) dt dt y = A sin( ωt+ φ ) 0 0 A 0 F0 / m F0 /k = = γω ( ω ) ω ω 1 tnφ = ω0 + m + ω0 ω0q ωγ / m 0 ω ω0 Q mω / γ 0 ω 0 = k / m ω / ω = 1/Q = Alm, Principles of Nnoiosensors, 013 4

25 Forced oscilltion & rodening of response y Q= C V c V / V = (1/ jωc) / (R+ jωl j/ ωc) c A 0 V/ ω VC = CVC = = 1 R + ( ω L ) ω / ( ω Q ) + (( ω / ω ) 1) ωc 0 0 Q= Lω /R 0 ω 0 = 1/ LC Alm, Principles of Nnoiosensors, 013 5

26 A 0 = F 0 /k ω ω 1 + ω0 ω0q Pek position Q= mω / γ 0 0 ω = k / m Minimize denomintor to find ω p ω = Q Alm, Principles of Nnoiosensors, 013 6