Microcantilever-basedBiosensors

1、Micromechanical Cantilever-based Biosensors国家自然科学基金NSFC青年基金资助项目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微悬臂梁在液体中振动的理论与实验研究v 微悬臂梁在液体中振动的理论与实验研究: 由于液体中阻尼的增加，微悬臂梁的振动变

20、得比较复杂，需要深入研究其振动特性，特别是频率响应与其弹性常数、有效质量以及液体物性（如密度和粘度）间的关系，以及品质因素Q和液体物性间的关系。这是从理论上搞清微悬臂梁在液体中的工作机理的基础，也是设计微悬臂梁的振动驱动输入的理论需要。Topic 10222222xYAxYEIxcctiemFydtdydtyd*02022yGeeFemFkydtdydtydmititi2/0*022*计算机仿真微悬臂梁在液体中振动的研究。实验理论研究Its Scheme金微球粒度的选择v 金微球粒度选择方法的研究:金微球的粒度指金微球的直径，它决定着金微球的质量，也决定着被测生物分子的质量放大倍数。选择粒度合

21、理的金微球是实现合理的质量放大的关键。Topic 2v金微球粒度的选择方法: - 被测生物分子和生物识别元件间的特异性 结合力的大小； - 微悬臂梁在振动过程中作用在“三明治”式特异性结合体（包括金微球在内）上的最大的力； - 金微球在微悬臂梁振动过程中不会使特异性结合体破裂。 在满足以上条件下，使金微球的粒度达到最大。这既可以保证最大的检测灵敏度，同时，由于分子间非特异性结合力远小于特异性结合力，使用较大的金微球可以通过振动去除因非特异性结合吸附在微悬臂梁上的金微球和被测分子。 Its Scheme微悬臂梁弹性常数的实时标定方法v 研究微悬臂梁弹性常数的实时标定方法: 弹性常数是反映微悬臂梁

22、振动特性的关键参数。由生产厂家提供的微悬臂梁的弹性常数标称值与实际值之间存在最大可达60的误差，因此弹性常数的重新标定至关重要，它是标定微悬臂梁生物传感器的关键所在。目前在AFM中经常采用的静态标定方法是直接通过测量力和微悬臂梁的形变而得到的，实验过程繁琐，不适合在微悬臂梁生物传感器中使用。通过本项目的研究，我们将探索出微悬臂梁弹性常数的实时标定方法，打破目前弹性常数标定对AFM仪器的依赖性，解决微悬臂梁生物传感器的整体标定的关键问题。 Topic 3v微悬臂梁弹性常数实时标定方法的研究 : 通过分别测量微悬臂梁在空气和在物性已知的液体中的共振频率来反算其弹性常数。通过与目前在AFM中经常采用

23、的静态标定方法比较，来修正我们的标定方法。l2204364981KKlIts Scheme开发微悬臂梁品质因数Q控制电路v 研究开发微悬臂梁品质因数Q控制电路 : 品质因数Q控制电路可以提高微悬臂梁在液体中的有效品质因数23个数量级，这不仅使AC检测法在液体中的灵敏度大大提高，克服微悬臂梁在液体中形变漂移对检测的影响，也可以有效地提高传感器的线性范围。品质因数Q控制电路主要包括两个模块，一个正反馈模块和一个锁相环模块。正反馈模块用于增加微悬臂梁的品质因数；锁相环模块跟踪微悬臂梁的振幅、频率和相位，并通过一个可变移相器和一个可变增益放大器控制微悬臂梁振动的品质因数Q。Topic 4v微悬臂梁的品

24、质因数Q控制电路的开发: 品质因数Q控制电路主要包括两个模块，一个正反馈模块和一个锁相环模块。锁相环跟踪微悬臂梁的频率和相位它输出F1=F0eit到压电驱动器。正反馈模块用于增加微悬臂梁的品质因数，并通过一个可变移相器和一个可变增益放大器产生输出F2GAei(t-/2) 到压电驱动器，其中G为放大器增益，为相移值。这样，微悬臂梁的激励将是F1和F2的合成。对于这样两个驱动信号输入，微悬臂梁振动的品质因数Q将受到放大器增益G和相移的控制。 F1F2Its Scheme两种两种Q控制技术控制技术模拟Q控制数字Q控制借助Pspice进行电路的设计与开发。经模块调试、与原子力显微镜联机调试和在传感器上的应用调试完成Q电路的开发。 传感器的结构设计与优化v 传感器的结构设计与优化；以BAS为识别机制 的质量放大型微悬臂梁生物传感器的研制: 包括传感器的整体设计、微悬臂梁的结构设计，微悬臂梁、压电驱动器、支架和样品池的集成与组装；电极连接和前置放大；以及有关抗腐蚀的表面处理等。在此基础之上构