Ionic Self-assembled Multilayers Research Articles

Fabrication of Localized Surface Plasmon Resonance Fiber Probes Using Ionic Self-Assembled Gold Nanoparticles

An nm-thickness composite gold thin film consisting of gold nanoparticles and polyelectrolytes is fabricated through ionic self-assembled multilayers (ISAM) technique and is deposited on end-faces of optical fibers to construct localized surface plasmon resonance (LSPR) fiber probes. We demonstrate that the LSPR spectrum induced by ISAM gold films can be fine-tuned through the ISAM procedure. We investigate variations of reflection spectra of the probe with respect to the layer-by-layer adsorption of ISAMs onto end-faces of fibers, and study the spectral variation mechanism. Finally, we demonstrated using this fiber probe to detect the biotin-streptavidin bioconjugate pair. ISAM adsorbed on optical fibers potentially provides a simple, fast, robust, and low-cost, platform for LSPR biosensing applications.

Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings

We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LPGs) function effectively as biosensors using biotin–streptavidin as a demonstration bioconjugate pair. Biotin, streptavidin, and anti-streptavidin were deposited onto the ISAM-coated LPG sequentially, each inducing a measurable resonant wavelength shift of the LPG. Control experiments verified the specificity of the biosensor system. Furthermore, we demonstrate that ISAM coated turnaround point LPGs could serve as highly sensitive biosensors that exhibit a change in transmitted intensity rather than resonant wavelength. Experimental measurements confirm that ISAM-coated LPGs provide an attractive platform for building efficient and high-performance optical sensors.

Nanoscale patterning of ionic self-assembled multilayers

Films that are nanostructured in all three dimensions can be fabricated by the templatedgrowth of ionic self-assembled multilayers (ISAMs) on solids that have been patterned bynanografting. Nanografting was used to controllably pattern –COOH surface groups on abackground of –OH groups. Atomic force microscopy (AFM) confirms that ISAMbilayers grow selectively on the –COOH groups and not on the surrounding –OHgroups. The patterned area clearly shows an increase in height with an increase inthe number of bilayers. As compared with other methods of nanofabrication,nanografting with ISAM deposition provides fast and precise control over the size of thepattern region, which remains stable even after repeated washing. This combinationallows the fabricated template to be altered in situ without the need of any kind ofmask, expensive probe, or post-lithography processing/cleaning methods. We havedemonstrated line widths of 75 nm. Ultimately the line width is limited by thewidth of the AFM tip that causes desorption of the thiol, which is typically about25 nm. Smaller line widths should be possible with the use of sharper AFM tips.

Optical intensity-based long-period fiber grating biosensors and biomedical applications [Life Sciences

In this article, we present a novel long-period fiber grating (LPFG) biosensor that can employ the simple and cost-effective optical intensity-based signal process method instead of the complex and expensive optical spectrum-based method. The ionic self-assembled multilayers (ISAM) technique is utilized to immobilize a thin layer of biorecognition film on the surface of a specially designed turnaround-point (TAP) LPFG. The new sensor maintains the optical resonant feature to achieve the desired high sensitivity but can be interrogated using optical intensity-based signal-processing. The new TAP-LPFG biosensor may be used for real-time DNA forensic analysis.

Millisecond switching in solid state electrochromic polymer devices fabricated from ionic self-assembled multilayers

The electrochromic switching times of solid state conducting polymer devices fabricated by the ionic self-assembled multilayer method has been investigated. The devices were composed of bilayers of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) and poly(allylamine hydrochloride) on indium tin oxide substrates. Devices fabricated from 40 bilayer thick films have coloration and decolaration switching times of 31 and 6ms, respectively, with low applied voltage (1.4V) for an active area of 0.6cm2. The switching times have been shown to decrease with the active area of the electrochromic device suggesting that even faster electrochromic switching times are possible for devices with smaller areas.

Solid-State Electrochromic Devices via Ionic Self-Assembled Multilayers (ISAM) of a Polyviologen

A PV was synthesized by polymerization of N,N'-bis(δ-aminopropyl)-4,4'-bipyridinium bromide hydrobromide (APD) and isophthaloyl chloride (ISP). The PV was completely soluble in water as well as in organic solvents. The spectroelectrochemical and EC properties of the resulting ionic self-assembled multilayers of PV/poly-(2-acrylamido-2-methylpropanesulfonic acid) (PAMPs) were examined by cyclic voltammetry, FT-IR spectroscopy, UV-vis spectroscopy, optical switching and current density measurements. Solid state devices made of PV films sandwiched with PANI as a counter electrode have switching times of 100-250 ms. 40 Bilayer films of PV/PAMPs show high contrast (ΔT = 61%) in 0.1 M NaClO 4 liquid electrolyte solution and CE as high as 57 cm 2 . C -1 , one of the highest reported so far for any bipyridinium salt system.

High Contrast Solid-State Devices of Self-Doping Polyaniline Sulfonic Acid (PASA) Based on Ionic-self Assembled Multilayers (ISAM)

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Highly sensitive optical response of optical fiber long period gratings to nanometer-thick ionic self-assembled multilayers

Ionic self-assembled multilayers deposited on long period fiber gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Fine control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition technique for fine-tuning grating properties. In addition a variety of biological and chemical sensing agents can easily be incorporated into these films, which makes this an attractive platform for realization of high-performance LPG-based sensors.