Research Projects In Nano-Technology

Research Projects in Nano-TechnologyIbrahim AbdulhalimOur research is multidisciplinary combining nanostructures, liquid crystals,devices and methods for biosensing and biomedical optical imagingapplications. Here is a short summary of the main projects.Plasmonic and photonic nanostructures for biosensing:In this activity we use surface Plasmon resonance in Kretschmannconfiguration both in the angular and the spectral modes, Fluorescencemicroscopy and Raman scattering from metallic nanosculptured thin films,and grating based structure, see figure below:SPR in KretschmannincidentlightEnhanced Transmission via etalfilmxNano dielectriclayerλ, θanalyteOther Grating StructuresRMetallic sculptured thin filmsSEF, SERS, SPRλAnalytedWaveguideSubstrateλTαh(b)We have recently demonstrated surface Plasmon resonance (SPR) sensorwith enhanced sensitivity by adding a nm-thick dielectric layer with highdielectric constant to the metal (see Amit Lahav et.al., Optics Letter2008).50Sireflectedlight2nd Siinterface40Electric Field ilm30analyte202nd 0150200250Distance from the prism-metal interface (nm)

In the spectral mode we found recently that the figure of merit of thesesensor is enhanced particularly in the infrared. This fact is being used fordetecting large biological entities in water (Shalabney and Abdulhalim,Optics Letters 2012). See figure ayerSF11glassP-polarized beamCollimated beamCollimation objective0.4SF11prismSPR0.2IndexmatchingfluidWhite lightOptical fibersource05001000150020002500Wavelength (nm)A special SPR imaging approach was developed using a diverging beamand the fast Radon transform for line detection. This approach improvesthe precision of the sensor and allows multichannel sensing (AlinaKarabchevsky et.al. Sensors and Actuators B 2011, J. Nanophotonics2011). Small concentration of BPA in water was detected ( 1ng/L). Seefigure below.100( a)0x 10(b )40x 0050x 10( c)0050(d ction %800200150yρ0θ0100 y12400-5044200Multiple channel ental404003020020400600x40424446480θ505254

Another type of nano-photonic structures being investigated in our groupis the metallic sculptured thin films (STFs) which are made of nanocolumns of metal with controlled porosity and orientation.IOM-LeipzigAs nano-rods like structures the surface Plasmon wave is localized neartheir tips and hence the electromagnetic wave density is enhanced. As aresult we have demonstrated recently the enhancement of fluorescencesignal from fluorophores near these structures (see Abdulhalim et.al.,Appl.Phys.Lett., 2009) and used it for detecting bacteria in water asshown in the figure below.500Ag nanorod STF immersed in aqueoussolution of luminescent E. coli(fluorescence image)Ag-STF200nmAg dense film immersed in aqueoussolution of luminescent E. coli(fluorescence image)Signal (counts)400300200AgAg-RefAlAl-Ref1000550Ag dense filmAg nanorod STF600650700750Wavelength (nm)800850 dilution: 1/100 (antibody to PBS) Antibody: Anti-Rabbit IgG (whole molecule)FITC Catalog number from Sigma: F7512990ul PBS 10ul antibodyRaman signal enhancement is another promising technique we areworking on for sensing because it provides specificity, that is it can tellalso the type of the pollutant not only its concentration.A SERS

,J.Counts x10Counts (subtract background) 10 33Nanophotonics 2012). See figure below:After dipping for 24h in solution of1% aminothiophenol in ethanol908070100nm Ag slantedcolumns onSi(100) aman shift (1/cm)Since the STFs are porous then when used as SPR sensors in theKretschmann configuration they exhibit enhanced sensitivity due to theincrease of the surface to volume ratio (see Atef Shalabney et.al., J.Photonics and Nanostructures 2009, Sensors and Actuators B 2011).250Incident lightSensitivity (deg/RIU)225P1 0prismP1 0.1200Reflected lightSTFP1 0.2P1 0.3175analyte150125P1 P2 010000.050.10.150.2Porosity of 2nd layer0.250.3Another promising structure for sensing is the use of resonant enhancedtransmission through nano-holes in metals. Presently we are optimizingone-dimensional array of metal nanoslits for Biosensing in water (see

Alina Karabchevsky et.al., J. Photonics and Nanostructures, 2009).Ourmain goal in these studies is to come up with a highly sensitive andreliable sensor that can be easily integrated in water to monitor smallquantities of pollutants. In parallel to the fundamental studies that we areperforming, we also design and build prototype sensors that will be usedin a true water purifying system.TransmissionTM%80 (a)DI10% Ethanol20% Ethanol30% Ethanol40% Ethanol50% m)TransmissionTM%0660670680λ(nm)750800850slope 435.3nm/RIU670660690(c)1.341.35n1.36Recently (Olga Krasnykov et.al., Optics Communications 2010) we haveincreased the penetration depth inside the analyte by using infraredwavelengths in order to increase the sensitivity and be able to detectlarge bioentities such as cells.IncidentTM polarization(a)Reflectedbeamkˆx1180 nm50 nm20 nmAnalytez950 PMMAAg24 nm950PMMAAgSiO2950PMMAAgTransmitted beam1825Sensitivity (µm/RIU)16λ - first resonance (µm)Sensitivity (µm/RIU)(b)1215108106452000510Pitc h (µm)1520Wavelength (µm)2014

This later sensor is being developed further in fiber form for real timeblood analytes sensing within a catheter.Nanophotonic liquid crystal devices for biomedical imaging:In this activity liquid crystals (LCs) are combined with nanostructures inorder to come up with miniature devices to control the optical propertiesof the light such as producing tunable filters and polarizations controllers.These devices can be controlled with a small voltage in a high speed.Recently we have combined such novel LC devices into spectropolarimetricskin imaging system being evaluated at Soroka hospital for skin cancerdiagnosis. In the figure below a wide dynamic range filter is demonstrateusing a novel concept (O. Aharon et.al., Optics Express 2009, OpticsLetters 2009, J. Biomedical Optics 2011).Polarization control deviceswere also developed and integrated into the same system. The idea is bygrabbing images at many polarization states and many wavelengths theinformation content on the tissue structure is enhanced and the reliabilityof the devices increases (Avner Safrany et.al., Optics Letters 2009, J.Biomedical Optics 2010).

Lab setupPrototype in action atSoroka University HospitalIn combining LC with nano-porous Si photonic crystal structure we aretrying to create a narrow band tunable filter.Recently we havediscovered that the molecules get ordered within the cylindrical nanopores in a special way. Applying a voltage to the composite caused thefilter peak to split into two polarization dependent peaks, thus indicatingthat the composite is biaxial (Shahar Mor et.al., Applied Physics Letters2010). In the figure below: (a) Atomic force microscope image of the toplayer of the P-Si 1D structure used, (b) schematic cross section view ofthe layered structure where AL stands for alignment layer; (c) and (d) are20x polarized microscope images of the two samples, showing theircorresponding filter color of green and red; (e)-(h) schematic drawings toillustrate some of the LC configurations inside the pores showing the UA,homeotropic, PR and ER configurations respectively.(a)(b)(c)250 nm(f)(g)Glass substrateALLCPSi 1DPCSi substrate(e)(d)(h)

Recently we have discovered the possibility of photoalignment of liquidcrystals on nano dimensional chalcogenide glass films (Miri Gelbaor,Appl.Phys.Lett. 2011) and we have shown that it is a result of thephotoinduced anisotropy in these materials even for such thin films as thinas 20nm (I. Abdulhalim et.al., Optical Materials Express, 2011).Polarizationmicroscope imagesat different voltages0V1.6V1.9VTransmission spectra at different voltages for 5µmcell at 45o between 2 crossed polarizers(a) x70,000 SEM micrograph of a typicalnonirradiated chalcogenide AS2S3 thin filmprepared for this study. (b-d) x10 microscopeimages of LC device oriented at 45º between twocross polarizers: (b) shows the transition betweenirradiated and non irradiated areas, (c) irradiatedarea alone, (d) nonirradiated area alone. (e-f) x10micrograph images of LC device oriented atextinction position between two crossed polarizersin irradiated (e) and in nonirradiated (f) areas.LC cell response at 537nm near the Friederickszthreshold showing Vth 0.99V in agreement withthe theoretical value:Chalcogenide glasses act also as semiconductors and a photocurrent isgenerated when light is shined on them.Using this property we havedemonstrated writing an image in the blue and reading it with the red intransmission (Miri Gelbaor et.al., to be published 2013).Another important activity involves the incorporation of liquid crystaldevices into full field optical coherence tomography system.With theassistance of a single retarder incorporated into FF-OCT system based onthe Linnik microscope, Ph.D student Avner Safrani has succeeded toobtain high resolution 3D images of cell nuclei both in the axial and thelateral directions (A. Safrani and I. Abdulhalim, Appl.Optics 2011, OpticsLetters, 2012).

OCT image 20 µm below topsurface of Onion cell nucleaλ 710nm ; λ 10nm ; NAeff 1.05200lp/mmA new project just started involves developing OASLMs for night vision.The figure below shows the principle of such device as well as preliminaryresults on image conversion from the blue to the red using chalcogenideglass nanolayer ( 100nm thick) (Miri Gelbaor et.al., to be published2013).This optically addressed spatial light modulator (OASLM) hasmany applications in image processing, conversion, correlation, andoptical computing.Modulated red beamGlass substrate withTransparent electrodeand alignment layerLC layerAlignment layerPhotosensor layerSubstrate withtop electrode layerBlue writing beamRed Reading beam

Photonics and Nanostructures 2009, Sensors and Actuators B 2011). Another promising structure for sensing is the use of resonant enhanced transmission through nano-holes in metals. Presently we are optimizing one-dimensional array of metal nanoslits for Biosensing in water (see 0 10 20 30 40 50 60 70 80 90 250 750 1250 1750 2250 Raman shift (1/cm)