Microcantilever-basedBiosensors

1、Micromechanical Cantilever-based Biosensors國家自然科學基金NSFC青年基金資助項目1 Introduction to Biosensors2 Micromechanical Cantilever & Its Applications3 Mechanism of the Amplification v of Analyte Mass4 Main Research Topics and Schemes1 Introduction to BiosensorsAs any other sensing device, a biosensor can b

2、e divided into three main components: a detector which recognizes the signal of interest, a transducer which converts the signal into a more useful output, typically an electronic signal, and a read-out system which filters, amplifies, displays, records, or transmits the transduced signal.What Is Bi

3、osensorsSchematic setup of a (bio)chemical sensorThe species to be detected pass through a filter and hit the chemically sensitive layer. The interaction between the analyte molecules and this layer causes a change in the physico-chemical properties of the layer (e.g. changed mass, optical propertie

4、s, and so on). These changed properties are converted by the transducer to an electronic signal, which can be analysed.Types of BiosensorsvClassified by the detector type: - immunosensors - enzymatic sensors - cell sensorsv Classified by the transducer type: - amperometic - piezoelectric - microcant

5、ilevervClassified by the application: - clinical - environmentalDifferent principles of biosensing and typical interfaces(1)Bioaffinity sensors. The analyte (e.g. antibody, antigen) is recognised by immobilised recognition units R (e.g. antigen, antibody and DNA). A: the analyte; T and the arrow: th

6、e transducer; S: the recorded signal. b) Enzymatic sensors. The analyte is converted by immobilised enzymes (E) to products (P).A: the analyte; T and the arrow: the transducer; S: the recorded signal. Different principles of biosensing and typical interfaces(2)c) Transmembrane sensors. (i) Transport

7、 or channel proteins or (ii) receptor proteins are incorporated into a membrane (M). These structures either (i) move the analyte through the membrane, (ii) bind the analyte and open a channel for another species, or iii) subsequently activate a separate enzymatic cascade. A: the analyte; T and the

8、arrow: the transducer; S: the recorded signal. Different principles of biosensing and typical interfaces(3)A: the analyte; T and the arrow: the transducer; S: the recorded signal. Different principles of biosensing and typical interfaces(4)Cell sensors. Immobilised living cells (C) either (i) conver

9、t or (ii) bind the analyte.Different types of biosensor transducers(1)Mass-sensitive detection: - mass changes, m, lead to frequency changes, Af.Measurements of electrochemical impedance or related electrochemical properties: - changes of capacitance, resistance, etcetera, by measurements of current

10、s, I, and voltages, (c) Grating couplers: - intensity changes from I0 to I after the interaction and, - phase changes for different changes in optical thickness i.e. n, film thickness.(d) Surface plasmon resonance: - The graph on the right hand shows typical measurement curves before and after analy

11、te interaction.Different types of biosensor transducers(2)(e) Reflectometric interference: - Measure the intensity changes. The graph on the right hand shows typical measurement curves before and after analyte interaction. (f) Mach-Zehnder interferometer: - intensity and phase changes are measured.

12、A, analyte; R, recognition units.Different types of biosensor transducers(3)2 Micromechanical Cantilever & Its ApplicationsGet an impression of the microcantileversWhat can a microcantilevermeasure possibly?Schematics of possible uses for a microcantilever: AFM force sensor; Temperature, heat se

13、nsor; Medium viscosity sensor; Mass sensor; Stress sensor;(a) Magnetic sensor.Advantages of Microcantilever Transducer?vHigh sensitivity and resolution limits.vSmall quantities (few l) of substance required for analysis(saving money).vPossibility to creat miniaturized, portable, and implantable sens

14、or devices.vMicrocantilever are batch fabricated, so that, cheap and disposable sensors are possible.vArray of cantilevers can be easily fabricated.vIntegration with CMOS circuitry and fluid hading systems.vCould be operated remotely, fully-automated.vCompact, and rugged.How a microcantilever respon

15、se is detected?vStatic method (surface stress) - resolution: mN/m (single monolayer)vResonant frequency method - resolution: 10-15 g3 Mechanism for the Amplification of Analyte MassWhy to Amplify the Analyte Mass- Detection limits: 0.67ng/cm-2, comparable to 10-15 By analyte mass amplification, it c

16、an reach 10-18g- Application in liquids not feasibleK: microcantilever spring constant F0 and f1: the resonant frequencies before and after adsorption of analyte, respectively.How to Amplify Analyte MassIntroduction to FABS (force amplified biological sensor )David R. Baselt, Gil U Lee, and Richard

17、J. ColtonNaval Research Laboratory, Washington, DC 20375-5342, USASystem ConstructionHow the force is amplified?How to Bind the (Gold) Beads to the MicrocantileverExisting ProblemsvMagnetic beads will stick to each other.vMagnetic beads require Helmholtz coils for the signal detection. - the complex

18、ity of the detection system; - the difficulty to shield the coil current.vChemistry: - difficult to bind the biological detector to magnetic bead surface reliably.v Magnetic beads are not commercially available.Advantages of using gold beadsvHigher density, higher mass amplification factor. vMature

19、chemistry to bind biological detector to the gold surface.vMature methods to produce gold beads.vGold beads will not stick to each other.vGold beads do not require Helmholtz coils for the signal detection. 4 Main Research Topics & Scheme微懸臂梁在液體中振動的理論與實驗研究v 微懸臂梁在液體中振動的理論與實驗研究: 由于液體中阻尼的增加，微懸臂梁的振動變

20、得比較復雜，需要深入研究其振動特性，特別是頻率響應與其彈性常數(shù)、有效質(zhì)量以及液體物性（如密度和粘度）間的關系，以及品質(zhì)因素Q和液體物性間的關系。這是從理論上搞清微懸臂梁在液體中的工作機理的基礎，也是設計微懸臂梁的振動驅(qū)動輸入的理論需要。Topic 10222222xYAxYEIxcctiemFydtdydtyd*02022yGeeFemFkydtdydtydmititi2/0*022*計算機仿真微懸臂梁在液體中振動的研究。實驗理論研究Its Scheme金微球粒度的選擇v 金微球粒度選擇方法的研究:金微球的粒度指金微球的直徑，它決定著金微球的質(zhì)量，也決定著被測生物分子的質(zhì)量放大倍數(shù)。選擇粒度合

21、理的金微球是實現(xiàn)合理的質(zhì)量放大的關鍵。Topic 2v金微球粒度的選擇方法: - 被測生物分子和生物識別元件間的特異性 結合力的大??； - 微懸臂梁在振動過程中作用在“三明治”式特異性結合體（包括金微球在內(nèi)）上的最大的力； - 金微球在微懸臂梁振動過程中不會使特異性結合體破裂。 在滿足以上條件下，使金微球的粒度達到最大。這既可以保證最大的檢測靈敏度，同時，由于分子間非特異性結合力遠小于特異性結合力，使用較大的金微球可以通過振動去除因非特異性結合吸附在微懸臂梁上的金微球和被測分子。 Its Scheme微懸臂梁彈性常數(shù)的實時標定方法v 研究微懸臂梁彈性常數(shù)的實時標定方法: 彈性常數(shù)是反映微懸臂梁

22、振動特性的關鍵參數(shù)。由生產(chǎn)廠家提供的微懸臂梁的彈性常數(shù)標稱值與實際值之間存在最大可達60的誤差，因此彈性常數(shù)的重新標定至關重要，它是標定微懸臂梁生物傳感器的關鍵所在。目前在AFM中經(jīng)常采用的靜態(tài)標定方法是直接通過測量力和微懸臂梁的形變而得到的，實驗過程繁瑣，不適合在微懸臂梁生物傳感器中使用。通過本項目的研究，我們將探索出微懸臂梁彈性常數(shù)的實時標定方法，打破目前彈性常數(shù)標定對AFM儀器的依賴性，解決微懸臂梁生物傳感器的整體標定的關鍵問題。 Topic 3v微懸臂梁彈性常數(shù)實時標定方法的研究 : 通過分別測量微懸臂梁在空氣和在物性已知的液體中的共振頻率來反算其彈性常數(shù)。通過與目前在AFM中經(jīng)常采用

23、的靜態(tài)標定方法比較，來修正我們的標定方法。l2204364981KKlIts Scheme開發(fā)微懸臂梁品質(zhì)因數(shù)Q控制電路v 研究開發(fā)微懸臂梁品質(zhì)因數(shù)Q控制電路 : 品質(zhì)因數(shù)Q控制電路可以提高微懸臂梁在液體中的有效品質(zhì)因數(shù)23個數(shù)量級，這不僅使AC檢測法在液體中的靈敏度大大提高，克服微懸臂梁在液體中形變漂移對檢測的影響，也可以有效地提高傳感器的線性范圍。品質(zhì)因數(shù)Q控制電路主要包括兩個模塊，一個正反饋模塊和一個鎖相環(huán)模塊。正反饋模塊用于增加微懸臂梁的品質(zhì)因數(shù)；鎖相環(huán)模塊跟蹤微懸臂梁的振幅、頻率和相位，并通過一個可變移相器和一個可變增益放大器控制微懸臂梁振動的品質(zhì)因數(shù)Q。Topic 4v微懸臂梁的品

24、質(zhì)因數(shù)Q控制電路的開發(fā): 品質(zhì)因數(shù)Q控制電路主要包括兩個模塊，一個正反饋模塊和一個鎖相環(huán)模塊。鎖相環(huán)跟蹤微懸臂梁的頻率和相位它輸出F1=F0eit到壓電驅(qū)動器。正反饋模塊用于增加微懸臂梁的品質(zhì)因數(shù)，并通過一個可變移相器和一個可變增益放大器產(chǎn)生輸出F2GAei(t-/2) 到壓電驅(qū)動器，其中G為放大器增益，為相移值。這樣，微懸臂梁的激勵將是F1和F2的合成。對于這樣兩個驅(qū)動信號輸入，微懸臂梁振動的品質(zhì)因數(shù)Q將受到放大器增益G和相移的控制。 F1F2Its Scheme兩種兩種Q控制技術控制技術模擬Q控制數(shù)字Q控制借助Pspice進行電路的設計與開發(fā)。經(jīng)模塊調(diào)試、與原子力顯微鏡聯(lián)機調(diào)試和在傳感器上的應用調(diào)試完成Q電路的開發(fā)。 傳感器的結構設計與優(yōu)化v 傳感器的結構設計與優(yōu)化；以BAS為識別機制 的質(zhì)量放大型微懸臂梁生物傳感器的研制: 包括傳感器的整體設計、微懸臂梁的結構設計，微懸臂梁、壓電驅(qū)動器、支架和樣品池的集成與組裝；電極連接和前置放大；以及有關抗腐蝕的表面處理等。在此基礎之上構