Bio MEMS Class -1 st week

Transcription

1 Bio MEMS Class -1 st week Jang, Jaesung Ref: Bashir ADDR Review paper,

2 Introduction Bio-MEMS: devices or systems, constructed using techniques inspired from micro/nano-scale fabrication, that are used for processing, delivery, manipulation, analysis, or construction of biological and chemical entities. Lab-on-a-chip (micro-tas) Applications: Diagnostics, Therapeutics, Tissue Engineering, Implantable Bio-MEMS etc. Biology -> Micro/Nano System Micro/Nano System -> Biology 2

3 Materials 1. Microelectronics related materials Silicon, glass, and related materials used for microelectronics and MEMS Established techniques in microelectronics, relatively high cost 2. Plastic and polymeric materials PDMS (poly)dimethylsiloxane, SU-8, etc. Low cost, rapid prototyping, ease in fabrication 3. Biological materials and entities Proteins, cells, and tissues. Relatively unexplored, tissue engineering, new possibilities 3

4 BioChips BioChips: BioMEMS for diagnostic applications Detect cells, microorganisms, viruses, proteins, DNA and related nucleic acids, and small molecules of biochemical importance and interest Advantages (i) reducing the sensor element to the scale of the target species and hence providing a higher sensitivity, (ii) reduced reagent volumes and associated costs, (iii) reduced time to result due to small volumes resulting in higher effective concentrations, (iv) amenability of portability and miniaturization of the entire system. Biosensors: analytical devices that combine a biologically sensitive element with a physical or chemical transducer to selectively and quantitatively detect the presence of specific compounds in a given external environment 4

5 Sensing Methods in BioChips Mechanical Detection Surface Stress Change Detection 2 L t z ( 1 ν ) ( σ ) l z = 4 1 σ t E 2 Measurement Volume Z (bulk) Measurement electrodes Electrical Detection Conductometric Detection Z (interface) Measurement electrodes Optical Detection Capture Fluorescence probes detection Target Probes DNA detection on chip surfaces z = deflection of the free end of the cantilever L = cantilever length t = cantilever thickness E = Young s modulus ν = poison s ratio σ 1 change in surface stress on top surface σ 2 change in surface stress on bottom surface Amperometer Detection Reference electrode - Reference electrode Capture probes Fluorescence detection Target Probes Mass Change Detection GOD Working Electrode Glucose e Protein detection on chip surfaces Potentiometric Detection 1 k f = 2π m m = k π f 1 f o k = spring constant m = mass of cantilever f 0 = unloaded resonant frequency f 1 = loaded resonant frequency (a) ISFET Source Reference electrode Capture/ sensor layer Current flow Drain (+ve voltage) (b) Reference electrode Current flow Ions or analytes Capture probes Cell detection on chip surfaces (c) 5

6 Mechanical Detection One of the most typical structure used in MEMS and BioMEMS for mechanical detection is cantilever (diving board type structure). Measured quantities: deflection (bending) and frequency Label-free detection Deflection measurement based sensors Biochemical reaction is performed selectively on one side of the cantilever. -> A change in surface free energy results in a change in surface stress, which induces measurable bending of the cantilever. The bending of the cantilever can then be measured using optical means (laser reflecting from the cantilever surface into a quad position detector (PD), like in an AFM) or electrical means (piezoresistor incorporated at the fixed edge of the cantilever). Deflection vs. mass Frequency measurement based sensors A mass added onto a cantilever surface, which induces a shift in the natural frequency of cantilever. The frequency shift can be measured electrical or optical means Frequency shift vs. mass 6

7 Mechanical Detection (Example) 7

8 Electrical Detection Electrical Detection: amperometric, potentiometric, and conductometric Detection Portability and miniaturization Amperometric biosensors: Electric current associated with the electrons involved in redox ( 산화환원 ) processes. Ex: Glucose detection with glucose oxidase (GOD) Potentiometric biosensors: Potential at electrodes due to ions or chemical reactions at an electrode (such as an ion Sensitive FET). Conductometric biosensors: Conductance (impedance) changes associated with changes in the overall ionic medium between the two electrodes. Simplicity and ease of use Cell-based biosensors 8

9 Electrical Detection (Example) Ref. 9

10 Optical Detection Optical Detection: Fluorescence or chemiluminescence Fluorescence detection: This technique is based on fluorescent markers that emit light at specific wavelengths and the presence and enhancement, or reduction in optical signal can indicate a binding reaction Proper attachment of DNA, proteins, and other molecules is very critical to efficient capture of the target species. Majority of the detection schemes in microarray and numerous lab-on-a-chip devices and applications Chemiluminescence It is the generation of light by the release of energy as a result of a chemical reaction ex. firefly Bioluminescence: Light emission from a living organism (sometimes called biological fluorescence) Electrochemiluminescence: light emission by passage of electrical current Challenges: integrate the photo-detectors in a miniaturized portable format. 10

11 Micro-Array DNA micro-array The techniques used to define patterns on semiconductor surfaces were utilized to construct arrays of single-stranded DNA. Once single strands of known sequences (capture probes) are placed at specific known sites on a chip surface, hybridization with molecules of unknown sequence (target probes) can reveal the sequence. Nucleic acid hybridization is the process of joining two complementary strands of DNA. Forming the DNA arrays Optical: masking steps but higher density of molecules Electrical: electrophoretically transported to specified locations on chip surfaces and it is based on the fact that oligonucleotides and DNA have a negative charge Protein and antibody arrays Soft lithography and micro-contact printing Detection is typically done by optical means (fluorescence) 11

12 Lab on a chip and Microfluidic devices Lab on a chip: sensors and devices with some level of integration of different functions and functionality. Integrating sample handling and preparation, mixing, separation, lysing of cells, and detection. All functions shown in this schematic (Fig. 12) might not always be used, rather only some of these may be integrated to achieve a specific aim. For example, for the case of DNA detection, the cells might be lysed and then an on-chip PCR device might be used to perform amplification and detection using specific primers. The fluorescence detection was performed with on-chip photo-diode detectors. Many of these devices are being developed for onetime use assays (to prevent cross-contamination) and, hence, the use of plastic biochips is very prevalent. Micro-mixing, flow sequencing, and metering using balanced centrifugal and capillary forces in CD-type plastic biochip has been described, as shown in Fig.14 12