Multplexed frequency spectrum analyzer nstrumentaton for the characterzaton of multple QCM-based bosensors Atman Jbar, Larb Bellarb 2, Nada Zne 4, Chrstopher A. Mlls 4, Josep Samter 3,4, Abdelhamd Errachd 3,4,2 Laboratore de Géne Electrque, ENSET-RABAT, 3 Unverstat de Barcelona,Martí Franquès,, 08028, Barcelona, 4 Insttut de Boengnyera de Catalunya (IBEC), Parc Centífc de Barcelona, C/ Josep Samter -5, 08028 Barcelona E-mal : atmjbar@yahoo.fr, aerrachd@pcb.ub.es Abstract In ths contrbuton, we present novel multplexed frequency spectrum analyzer nstrumentaton to extract operatonal parameters and completely characterze the frequency response of an array of quartz crystal mcrobalance sensors. The effectveness of the proposed nstrumentaton s proven by expermental measurements over a range of frequences.. Introducton The bo-detecton or measure of nano-parameters represent an mportant way n scentfc nvestgatons and s appled n varous domans: ADN Hybrdzng, proten-proten nteracton, bosensors development, corroson and absorpton studes, electrochemcal deposton, dthenothophene-based polymers [-6]. Several types of sensors are used; the partcularty of pezoelectrc sensors s to traduce the varaton of mass to the varaton of resonant frequency wth hgh senstvty [7]. Therefore, the mcrobalance technque s a good practcal motvaton n bosensors doman and ther applcatons. Several commercal mcrobalances (for example QCA922, QCM00, QCM200) measure only the seres frequency and resstance at resonance. In ths contrbuton, we present the development of nstrumentaton that gves a complete characterzaton of a set of quartz sensors and the soft system for acquston and treatment. Ths paper s organzed as follows: In secton 2, we present the prncples of mcrobalance, quartz model, and measurement methods. In secton 3 we trat and we choce the electronc component of dfferent blocs of the proposed nstrumentaton system. Secton 4 present the set of measures effected n order to valdate our system. Fnally, we conclude on global performances and advantages of our system. 2. Quartz mcrobalance prncples 2. Mcrobalance prncples The quartz crystal mcrobalance (QCM) explots the phenomenon of pezoelectrcty present n some natural and artfcal materals. The drect pezoelectrc effect descrbes the property of a delectrc materal to create a voltage, or varaton of potental, when t s subjected to a mechancal deformaton. As a consequence, t s possble to use ths effect to measure several physcal parameters, such as acceleraton, pressure etc., whch can be used for a pezoelectrc sensor. The nverse pezoelectrc effect, or electrostrcton, descrbes the opposte effect where the pezoelectrc materal deforms under an appled electrcal potental. The resonant frequency of AT cut quartz crystals (low senstvty to temperature) changes as a functon of mass deposted on ts surface, and can be represented by the Sauerbrey equaton [8]: F 2 F 2 m () A Q where, ΔF : frequency varaton due to mass loadng, F : quartz crystal resonant frequency, Δm : mass varaton, ρ Q : densty of quartz, μ : shear modulus, A : pezoelectrc actve area. 2.2 Quartz mcrobalance sensors The equvalent electrcal crcut for the quartz crystal s presented n fgure.
Fgure : Equvalent electrcal crcut of the QCM. where, C 0 : statc capacty, R : Resstance (vscosty), C : dynamc capacty, L : Inductance of quartz (energy gan) The seres resonance frequency, F s, s: F (2) s 2π L C F s changes as a functon of mass and elastcty, and measurement of Fs allows the quartz crystal parameters to be determned. Complex admttance, Y, can be wrtten as: Y( j ) jc0 R jl jc (3) The conductance, G =Re(Y(jω)), and suceptance, B=Im(Y(jω)), are related by: 2 2 2 ( G ) ( B C0 ) ( ) (4) 2R 2R These equatons can be used to model the frequency relatonshp of a crystal. For example, fgures 2 and 3 model a quartz crystal wth, C 0 =22 pf; R =00 Ω; L =22 μh; C =22 nf. The quartz crystal resonance s therefore characterzed by ts resonance frequency (9.95 MHz, 0.2 ms, 2 ). Fgure 3 : Quartz phase Admttance vs. Frequency 2.3 Measurement methods: There are two possble measurement methods: ) Actve method: The quartz crystal s placed n oscllator crcut (Mller or Collpts). The oscllatons are mantaned by a reacton loop and the frequency fluctuatons represent a varaton of mass, elastcty or vscosty, whch s measured by a frequency-meter devce. Ths prncple s smple but the extracton of the crystals parameters s mpossble. ) Passve method: The quartz crystal receves a snusodal exctaton (voltage or current). A network analyzer estmates and represents the equvalent admttance and capactance (L, C ) values. 3. Mcrobalance nstrumentaton The proposed mcrobalance nstrumentaton must have the followng characterstcs: Fgure 2 : Quartz Modulus Admttance vs. frequency. a) Multple sensors analyss b) Frequency measurement up to 00MHz c) Complete characterzaton of sensor (ncludng resonant frequency, resstance and admttance) d) Possblty to effect frequency sweep or sngle frequency analyss. e) Frequency resoluton 0. Hz f) Tme sweep s g) Low electrcal power consumpton.
3. Mcrobalance nstrumentaton functon Fgure 4 llustrates the functonal dagram for the proposed mcrobalance nstrumentaton. A DDS crcut, controlled by a reference oscllator, generates the snusodal exctatons to a sensor selected by an analog swtch. An nstrumentaton amplfer receves the voltage from the quartz sensor and presents t to the nput of a Ampltude/Phase detecton block. After analog to dgtal (A/D) converson, a computer acqures the sgnal through an Input/Output USB nterface. Quartz sensors Quartz sensor Q v e v q q VCO M M 2 v m v m2 v flter F flter F 2 V f V f2 v M 3 v m3 flter F 3 V f3 Instrument amplfer Cables Analog swtch R r GN D Fgure 5: Instrumentaton block dagram A/Phase detecton DDS Reference oscllator Voltage expressons : Exctaton voltage: v e (t) = v e cos ω e t = v e cos 2π f e t Resstance voltage: v (t) = v cos (ω e t + Φ ) = R r q (t) A/D Converson I/O Interface USB Acquston/treatment computer Fgure 4 : Mcrobalance nstrumentaton functonal dagram. 3.2 Electroncs The electroncs are composed of an nstrumentaton amplfer and a measurement block: ampltude, current and phase. The amplfer must solate the requred sensor and measure the measurement block. For measurement block, we use the synchronous detecton method represented n fgure 5. v re : reference voltage, v e : sensor exctaton voltage, v q : sensor voltage, q : sensor current, v : voltage of reference resstance R r (current mage q), v m, v m2, v m3 : outputs of multplers M, M 2 et M 3, V f, V f2, V f3 outputs of flters F,F 2 et F 3. outputs : M : v m (t)= K m v 2 2 e (t) = K m V e ( + cos 2ω e t ) /2 M 2 : v m2 (t)= K m2 v e (t) v (t) = K m2 V e V (cos Φ + cos (2ω e t +2Φ )) /2 M 3 : v m3 (t)= K m3 v 2 2 (t) = K m3 V ( + cos (2ω e t + 2Φ )) /2 Flter outputs : F : V f (t)= K m V e 2 /2 F 2 : V f2 (t)= K m2 V e V cos Φ /2 F 3 : V f3 (t)= K m3 V 2 /2 The quartz mpedance, Z, s, Vq Rr ( Vq V ) Z( j ) (5) I V Then we have, Z( j q R V r e ) Rr (6) V Ve Re ( Z) Rr ( cos ) (7) V V Im( Z) R sn (8) e r V
As the common rejecton rato rejecton mode must be 60 db, the frequency band analyss 00 MHz and the slew rate, Sr >628 V/μs, we have chosen AD829 (nstrumentaton amplfer), AD835 (multpler), MAX038 (reference oscllator), AD9850 (DDS), AD 7655 (4bts Analog to dgtal converter), NI-USB 625(USB-I/O nterface) for use. The DDS AD9850 allows frequency control at 0.029 Hz resoluton (reference: 25 MHz). flter: In order to reject the harmonc frequences, 2ω e, we use a second order low-pass flter, RC. Ths flter assures stablty and suppresses waves caused by fast varaton of the ampltude. In addton, the flter must be rapd and able to allow rapd frequency sweeps. We wll work at frequences of MHz, therefore we use R = 0 kω; C = 2.2 nf. 4. Results and dscusson Fgure 7: Increasng frequency, F mn = 8.9 MHz, F max = 8.99MHz; Ts = 500ms. The resonant peak can be clearly seen n ths tme perod near to ascendant trgger pulse. In order to demonstrate the effectveness of the proposed nstrumentaton unt, several experments are presented usng a 9 MHz quartz crystal (fgures 6-9). In all measurements, the voltage exctaton s snusodal wth an ampltude, Ve = V. The square wave reference sgnal trgger, v t, s also gven whch controls the lnear sweep frequency. Note: F mn : Mnmal frequency analyzer, F max : Maxmal frequency analyzer (ΔF= F max- F mn ), F res : quartz resonant frequency, Ts : Seep perod whch corresponds to the sgnal perod v t. Fgure 8: Reducng the frequency, F mn = 8.96 MHz, F max = 8.99MHz, T s = 500ms. Fgure 6: F mn = 8.0MHz, F max = 9.0MHz, ΔF =MHz, Ts = 500 ms. F res = 8,98 MHz. The resonant peak can be clearly seen n ths tme perod. Fgure 9: Ampltude and Phase, F mn = 8.95MHz, F max = 8.99MHz, ΔF =MHz, Ts = 500 ms.
Fgure 9 shows the ampltude and phase sgnals. At resonance, the ampltude can be seen to peak whereas the phase falls rapdly before recoverng. Ths demonstrates the change n mpedance behavor. These measurements present the localzaton of resonant peak for several sweep ntervals and valdate our technque whch can be performed by usng an acquston nterface and treatment system presented n the followng secton. 5. Acquston and treatment software To collate and treat the data, QCMcrobalance software has been developed whch acqures nstrumentaton sgnals and descrbes the functons gven n fgure 0. Fgure 0: Acquston and treatment functons The automatc nstrumentaton functon ensures that the measurements occur wth temporal confnements. It allows us to program the start/stop commands and defne the measurement perod. 6. Concluson The proposed novel nstrumentaton allows the measurement of the parameters that completely determne the quartz crystal behavor n the frequency doman. It can control an array of sensors allowng the possblty of smultaneous experments or smultaneous characterzaton of several dependent parameters. Ths mcrobalance requres an power supply of +5V/-5V. The ampltude of the quartz exctaton voltage s V. In addton, the use of dgtal syntheszer crcut assures a precse analyss of frequency. Ths mcrobalance, wth data explotaton and treatment software, consttute a performance tool for all experments requrng the use of quartz crystal mcrobalance sensors. References : [] A. Jbar, L. Bellarb, A. Errachd, Développement de Bocapteurs Basés sur la mcrobalance à quartz modfée par le transfert du flm Langmur-Blodgett d mmunoglobulne G/amphphle, Congrès de botechnologe-settat 06 ma 2005. [2] C. A. Mlls, J. Beeley, C. Wyse, D. R. S. Cummng, A. Gldle, J. M. Cooper, Polymer-based mcro-sensor pared arrays for the determnaton of prmary alcohol vapors, Sens. Act. B (n press) [3] C. A. Mlls, K. T. C. Cha, M. J. Mlgrew, A. Gldle, J. M. Cooper, D. R. S. Cummng, A Multplexed Impedance Analyzer for Characterzng Polymer-Coated QCM Sensor Arrays, IEEE Sens. J. 6 (2006) 996-002 [4] J. M. Beeley, C. Mlls, P. A. Hammond, A. Gldle, J. M. Cooper, L. Wang, D. R. S. Cummng, All-dgtal nterface ASIC for a QCM-based electronc nose, Sens. Act. B 03 (2004) 3 36 [5] I.A. Marques de Olvera, M.B. Santos, S. Rodrguez, M.T.S.R. Gomes, R. Ertja, J. Samter and A. Errachd, Frst characterzaton of a bosensor for large DNA molecules usng quartz crystal mcrobalance and mpedance spectroscopy, Transducers 04 & Eurosensors XXI, 0-4, June, Lyon France, 2007 [6] S. A. Rodrguez-Segu, I. Bucor, M. M. Burger, J.Samter, A.Errachd and X. Fernandez-Busquets, Aplcaton of a bo-qcm to study carbohydrates selfnteracton n presence of calcum, Transducers 04 & Eurosensors XXI, 0-4, June, Lyon France, 2007 [7] F. Soav,C. Arbzzan and M. Mastragoston, Quart crystal mpedance and EQCM measurements appled to dthenothophene-based polymers. Chem. Phys.,2000 pp- 2993-2998. [8] S. J.Martn, V. E. Granstaff, and G. C. Frye. Characterzaton of a Quartz Crystal Mcrobalance wth Smultaneous Mass and Lqud Loadng. Sanda Natonal Laboratores, Albuquerque, New Mexco 8785.Sauerbrey.