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Jundi Shapur University of Technology, Dezful.

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1 Jundi Shapur University of Technology, Dezful.
Optical Biosensors By: M. D. Talebzadeh Jundi Shapur University of Technology, Dezful.

2 What are biosensors? Parts of a Biosensor
A biosensor is an analytical device, used for the detection of an analyte (a substance or chemical constituent that is of interest in an analytical procedure), that combines a biological component with a physicochemical detector. Parts of a Biosensor the sensitive biological element (e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc.), interacts (binds or recognises) the analyte under study (can created by biological engineering). Immobilizer (like carboxymethyl dextran or similar compound). the transducer or the detector element: transforms the signal resulting from the interaction of the analyte with the biological element into another signal. biosensor reader device with the associated electronics or signal processors that are primarily responsible for the display of the results in a user-friendly way (sometimes the most expensive part).

3 A canary in a cage, as used by miners to warn of gas, could be considered a carbon monoxide biosensor. Many of today's biosensor applications are similar, in that they use organisms which respond to toxic substances at a much lower concentrations than humans can detect to warn of their presence.  honey bees : air pollution sensors; bats and swallows: pesticide contamination biosensors due to their diet of insects aquatic animals or their direct predators: water pollution sensors

4 Evolution of the Medical Biosensor
Mid 1950’s - Leland C Clark "Father of Biosensors" invents an electrode that measures dissolved oxygen in the blood of patients undergoing surgery. The Clark electrode is an electrode that measures oxygen on a catalytic platinum surface using the net reaction: O2 + 4 e− + 2 H2O → 4 OH− The voltage differential measured between the two electrodes, gave the rate at which the oxygen was being diffused. Pt- electrode Ag/AgCl-electrode KCl electrolyte Teflon membrane (permeable to gases) rubber ring voltage supply galvanometer



7 Applications in process control: monitoring temperature, concentration, pressure and the acidity. Development in industry can improve manufacturing techniques. In medicine: tumor cells are used as a biosensor to monitor chemotherapeutic drug susceptibilities. manufacturing of pharmaceuticals and replacement organs such as an artificial pancreas for diabetics. to detect substances such as vitamin B12: living microorganisms such as bacteria can be used.

8 (a) The construction of typical biosensors with elements and selected components. The procedures are described as follows: (i) receptors specifically bind the analyte; (ii) an interface architecture where a specific biological event takes place and givesrisetoasignalrecordedby(iii)thetransducerelement;(iv)computersoftwaretoconvertthesignalintoameaningfulphysical parameter; finally, the resulting quantity is displayed through (v) an interface to the human operator.

9 The sizes of nanomaterials (NW and NT) in comparison to some biological entities, such as bacteria, viruses, proteins, and DNA.

10 A common example of a commercial biosensor : blood glucose biosensor
uses the enzyme glucose oxidase to break blood glucose down. glucose oxidase catalyses the oxidation of glucose to hydrogen peroxide and D-glucono-δ-lactone. it first oxidizes glucose and accepting two electrons. Using two electrodes, the resulting current is a measure of the concentration of glucose. In this case, the electrode is the transducer and the enzyme is the biologically active component.


12 Electrochemical biosensors: based on enzymatic catalysis of a reaction that produces or consumes electrons (such enzymes are rightly called redox enzymes). The sensor substrate usually contains three electrodes; a reference electrode, a working electrode and a counter electrode. The target analyte is involved in the reaction that takes place on the active electrode surface, and the reaction may cause either electron transfer across the double layer (producing a current) or can contribute to the double layer potential (producing a voltage). The label-free and direct electrical detection of small peptides and proteins is possible by their intrinsic charges using biofunctionalized ion-sensitive field-effect transistors. the potentiometric biosensor, (potential produced at zero current) gives a logarithmic response with a high dynamic range. Such biosensors are often made by screen printing the electrode patterns on a plastic substrate, coated with a conducting polymer and then some protein (enzyme or antibody) is attached. The signal is produced by electrochemical and physical changes in the conducting polymer layer due to changes occurring at the surface of the sensor. Such changes can be attributed to ionic strength, pH, hydration and redox reactions, the latter due to the enzyme label turning over a substrate .

13 A DNA field-effect transistor (DNAFET)
It is similar to that of MOSFETs with the exception of the gate structure which is replaced by a layer of immobilized ssDNA (single-stranded DNA) molecules which act as surface receptors. When complementary DNA strands hybridize to the receptors, the charge distribution near the surface changes, which in turn modulates current transport.

14 Silicon nanowire field-effect transistor-based biosensors for biomedical diagnosis and cellular recording investigation, K-I Chen et al. , Nano Today (2011) 6, 131—154 available at



17 MEMS Biosensors devices manufactured in XLIM Lab
This recent activity is born from a collaboration with a Limoges Faculty of Medecine research group (Homéostasie cellulaire et Pathologie EA 3842) in which the main idea was to propose new generation of biosensors especially designed for the biocellular characterization and identification at microwave frequencies. Hence this work has permitted up to now to develop devices specifically designed at the cell scale thanks to micro-machined technologies. These biosensors are able to discriminate different cellular type without any specific labeling and so avoid the contamination of the biological media and the influence of the marker on the cell properties.

18 Piezoelectric sensors utilise crystals which undergo an elastic deformation when an electrical potential is applied to them. An alternating potential (A.C.) produces a standing wave in the crystal at a characteristic frequency. This frequency is highly dependent on the elastic properties of the crystal, such that if a crystal is coated with a biological recognition element the binding of a (large) target analyte to a receptor will produce a change in the resonance frequency, which gives a binding signal. In a mode that uses surface acoustic waves (SAW), the sensitivity is greatly increased. This is a specialised application of the Quartz crystal microbalance as a biosensor. Thermometric and magnetic based biosensors are rare.

19 But, Optical Biosensors:
An optical Biosensor Measures changes in optical properties of substances. – Absorbance in chemical reaction – Fluorescence – Reflectance – Refractive index – Phase shift – Light Energy (wavelength) – Reaction will cause Luminescence

20 For biosensor development, a number of aspects need to be considered :
Transduction signal generation (increase of signal, decrease of noise, etc.) Fluidics design (sample injection and drainage, reduction of sample consumption, increase) of analyte transport, reduction in detection time, etc.) Surface immobilization chemistry (analyte capture efficiency, elimination of non-specific binding, etc.) Detection format (direct binding, sandwich-type binding, competitive binding, etc.) Data analysis (extraction of information regarding analyte concentration, binding kinetics, etc.) we will focus mainly on the transduction part with the emphasis on optical structures and their interactions with the analyte.

21 Label-free detection:
Fluorescence-based Detection: either target molecules or biorecognition molecules labeled by fluorescence tags Label-free detection: target molecules are not labeled or altered, and are detected in natural forms some label-free detection mechanisms measure refractive index (RI) change induced by molecular interactions, which is related to the sample concentration or surface density, instead of total sample mass.

22 Nanobiosensors use an immobilized bioreceptor probe that is selective for target analyte molecules. Nanomaterials are exquisitely sensitive chemical and biological sensors. Nanoscale materials demonstrate unique properties. Their large surface area to volume ratio can achieve rapid and low cost reactions, using a variety of designs. (A) An example of a DNA molecule used as a starter for larger self-assembly. (B) An atomic force microscope image of a self-assembled DNA nanogrid. Individual DNA tiles self-assemble into a highly ordered periodic two-dimensional DNA nanogrid.

23 Only this is an schematic diagram.
- When target analytes bind to the biorecognition molecules, they replace buffer solution molecules within nanometers from the surface. - The target analytes have different RI than that of the buffer solution (for example, the RI for protein is 1.5 vs for buffer solution) - RI change can be detected optically as the sensing transduction signal. Only this is an schematic diagram. Optical biosensor transducers divides into sub- divisions.

24 Technical consideration!
the sensor performance must be improved - For a label-free optical biosensor, the most commonly seen noise is from temperature fluctuations, which results in a thermooptic effect (i.e., temperature-dependent RI changes) and a thermo-mechanic effect (e.g., thermal expansion) in both sensor substrate and buffer solution. A general approach to reduce the thermally induced noise is to implement a temperature control, such as a thermoelectric cooler to stabilize temperature.

25 Types of Optical Biosensor transducers
1) surface plasmon resonance based biosensors; 2) interferometer-based biosensors; 3) Optical waveguide based biosensors; 4) optical ring resonator based biosensors; 5) optical fiber based biosensors; 6) Photonic crystal based biosensors.

26 1) surface plasmon resonance based biosensors;
A surface plasmon wave (SPW) is a charge density oscillation that occurs at the interface of two media with dielectric constants of opposite signs, such as ametal (gold or silver) and a dielectric. There are four basic methods to excite the SPR: prism coupling / waveguide coupling / fiber optic coupling /grating coupling

27 At the resonant angle or resonant wavelength, the propagation constant of the evanescent field matches that of the SPW, the photon will be coupled into the SPW.

28 SPR-based… (through gold nanoparticles) Applications
detection of proteins with a ranging from picomolar to nanomolar detection of DNA molecules as low as 54 fM sensitive and fast detection of cancer biomarkers bacterial detection for environmental monitoring, food safety and homeland security Advantage high throughput detection Difficulties 1) The evanescent field in those basic SPR structures only penetrates into the surrounding medium for about 100 nm, and thus it is very difficult to detect the large target molecules like cells and bacteria. 2) There is only one SPW to detect the RI change. It is impossible to differentiate the surface RI change and the bulk solution RI change.

29 2) interferometer-based biosensors; Mach-Zehnder interferometer
Young’s interferometer Hartman interferometer Backscattering interferometery

30 Interferometery?!

31 Mach-Zehnder interferometer (MZI)
Coherent, single frequency, single polarization light from a laser enters the single-mode input waveguide and is split equally at a Y-junction. The two branches recombine at the output, resulting in interference, and a photodetector measures the intensity. Generally, the waveguide structure must be single polarization and single mode so that multimodal and cross-polarization interference do not appear at the output. A change in the RI at the surface of the sensor arm results in an optical phase change on the sensing arm and a subsequent change in the light intensity measured at the photodetector. One branch has a window over the top of it allowing the evanescent field of that branch to interact with the sample while the reference arm is protected from the sample with a thick cladding layer. Mach-Zehnder interferometer (MZI)

32 Young’s interferometer (YI)
Instead of recombining the arms as in the MZI, the optical output of the two arms combines to form interference fringes on a detector screen, such as a CCD.

33 Hartman interferometer (HI)
Functionalization molecules are patterned in strips on top of a planar waveguide.

34 Interfrometery-based… Applications
antibody for human chorionic gonadotropin (hCG) was detected (MZI). Specific detection of herpes simplex virus type 1 (HSV-1) was performed using an anti-HSV-1 antibody immobilized on the interferometer surface (YI).

35 3) Optical waveguide based biosensors

36 4) optical ring resonator based biosensors

37 5) optical fiber based biosensors;

38 6) Photonic crystal based biosensors

39 References: [1] Xudong Fan, Ian M. White, Siyka I. Shopova, Hongying Zhu, Jonathan D. Suter, Yuze Sun, “Sensitive optical biosensors for unlabeled targets: A review” , analytica chimica acta ( ) 8–26 available at [2] Silicon nanowire field-effect transistor-based biosensors for biomedical diagnosis and cellular recording investigation, K-I Chen et al. , Nano Today (2011) 6, 131—154 available at [3]

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