Optical Waveguide Spectroscopy Research Articles

Thermoresponsive and Photocrosslinkable Poly(2-alkyl-2-oxazoline) Toolbox - Customizable Ultralow-Fouling Hydrogel Coatings for Blood Plasma Environments.

This study focuses on developing surface coatings with excellent antifouling properties, crucial for applications in the medical, biological, and technical fields, for materials and devices in direct contact with living tissues and bodily fluids such as blood. This approach combines thermoresponsive poly(2-alkyl-2-oxazoline)s, known for their inherent protein-repellent characteristics, with established antifouling motifs based on betaines. The polymer framework is constructed from various monomer types, including a novel benzophenone-modified 2-oxazoline for photocrosslinking and an azide-functionalized 2-oxazoline, allowing subsequent modification with alkyne-substituted antifouling motifs through copper(I)-catalyzed azide-alkyne cycloaddition. From these polymers surface-attached networks are created on benzophenone-modified gold substrates via photocrosslinking, resulting in hydrogel coatings with several micrometers thickness when swollen with aqueous media. Given that poly(2-alkyl-2-oxazoline)s can exhibit a lower critical solution temperature in water, their temperature-dependent solubility is compared to the swelling behavior of the surface-attached hydrogels upon thermal stimulation. The antifouling performance of these hydrogel coatings in contact with human blood plasma is further evaluated by surface plasmon resonance and optical waveguide spectroscopy. All surfaces demonstrate extremely low retention of blood plasma components, even with undiluted plasma. Notably, hydrogel layers with sulfobetaine moieties allow efficient penetration by plasma components, which can then be easily removed by rinsing with buffer.

In Situ Monitoring of Rolling Circle Amplification on a Solid Support by Surface Plasmon Resonance and Optical Waveguide Spectroscopy.

The growth of surface-attached single-stranded deoxyribonucleic acid (ssDNA) chains is monitored in situ using an evanescent wave optical biosensor that combines surface plasmon resonance (SPR) and optical waveguide spectroscopy (OWS). The "grafting-from" growth of ssDNA chains is facilitated by rolling circle amplification (RCA), and the gradual prolongation of ssDNA chains anchored to a gold sensor surface is optically tracked in time. At a sufficient density of the polymer chains, the ssDNA takes on a brush architecture with a thickness exceeding 10 μm, supporting a spectrum of guided optical waves traveling along the metallic sensor surface. The simultaneous probing of this interface with the confined optical field of surface plasmons and additional more delocalized dielectric optical waveguide modes enables accurate in situ measurement of the ssDNA brush thickness, polymer volume content, and density gradients. We report for the first time on the utilization of the SPR/OWS technique for the measurement of the RCA speed on a solid surface that can be compared to that in bulk solutions. In addition, the control of ssDNA brush properties by changing the grafting density and ionic strength and post-modification via affinity reaction with complementary short ssDNA staples is discussed. These observations may provide important leads for tailoring RCA toward sensitive and rapid assays in affinity-based biosensors.

Thin-Film Polyisocyanide-Based Hydrogels for Affinity Biosensors

A new type of hydrogel thin film that can be post-modified with biofunctional molecules is investigated for possible applications in evanescent wave optical affinity biosensors. This material is based on a polyisocyanide (PIC) copolymer that self-assembles into a fibrous polymer network. It is covalently tethered to a solid transducer surface, and its swelling gives rise to a hydrogel layer with a thickness up to several micrometers, as characterized by a combination of surface plasmon resonance and optical waveguide spectroscopy. Thin PIC-based hydrogel films with pendant functional biomolecules can be used in label-free affinity sensing strategies. In this work, we demonstrate the PIC-based affinity binding matrix through an avidin coupling of functional biomolecules and immunoassay-based detection, which can be readily expanded to other types of assays and target analytes. In addition, the stable PIC matrix proves to be resistant to fouling, even in the presence of complex biological fluids such as blood plasma or serum.

Model of the planar broadband differential waveguide interferometer as a humidity sensor

The paper presents a model of the planar broadband differential waveguide interferometer. Its response to the change in thickness and refractive index of the waveguide layer due to the change in humidity is presented. The analysis was carried out for the wavelength range from 450 nm to 850 nm. The orthogonal modes TE0 and TM0, which propagate in this wavelength range, are considered. It is shown that by using light near the maximum of the system characteristic, instead of the spectrometer, the total power at the system output can be measured. Full Text: PDF ReferencesM. Kitsara, K. Misiakos, I. Raptis, and E. Makarona, "Integrated optical frequency-resolved Mach-Zehnder interferometers for label-free affinity sensing", Opt. Express 18, 8193 (2010). CrossRef K. Misiakos, I. Raptis, A. Salapatas, E. Makarona, A. Bostials, et al., "Broad-band Mach-Zehnder interferometers as high performance refractive index sensors: Theory and monolithic implementation", Opt. Express 22, 8856 (2014). CrossRef K. Misiakos, I. Raptis, E. Makarona, A. Botsialas, A. Salapatas, et al "All-silicon monolithic Mach-Zehnder interferometer as a refractive index and bio-chemical sensor", Opt. Express 22, 26803 (2014). CrossRef K. Misiakos, E. Makarona, M. Hoekman, R. Fyrogenis, K. Tukkiniemi, et al., "All-Silicon Spectrally Resolved Interferometric Circuit for Multiplexed Diagnostics: A Monolithic Lab-on-a-Chip Integrating All Active and Passive Components", ACS Photonics 6, 1694 (2019). CrossRef E. Makarona, A. Salapatas, I. Raptis, P. Petrou, S. Kakabakos, et al., "Broadband Young interferometry for simultaneous dual polarization bioanalytics", J Opt Soc Am B 34, 1691 (2017). CrossRef K. Gut, "Broad-band difference interferometer as a refractive index sensor", Opt. Express 25, 3111 (2017). CrossRef K. Gut, "Study of a Broadband Difference Interferometer Based on Low-Cost Polymer Slab Waveguides", Nanomaterials 9, 729 (2019). CrossRef W. Lukosz, "Integrated optical chemical and direct biochemical sensors", Sensor Actuat. B-Chem. 29, 37 (1995). CrossRef W. Knoll, O. Azzaroni, H. Duran, J. Kunze-Liebhäuser, K. Lau, et al. "Nanoporous thin films in optical waveguide spectroscopy for chemical analytics", Analytical and Bioanalytical Chemistry 412, 3299 (2020). CrossRef A. Bucciarellia, V. Mullonib, D. Maniglio, R.K. Pal, V.K. Yadavalli, at al., "A comparative study of the refractive index of silk protein thin films towards biomaterial based optical devices", Optical Materials 78, 407 (2018). CrossRef V.Prajzler, K. Min, S. Kim, and P. Nekvindova, "The Investigation of the Waveguiding Properties of Silk Fibroin from the Visible to Near-Infrared Spectrum", Materials 11, 112 (2018). CrossRef Q. Li, N. Qi, Y. Peng, Y. Zhange, L.Shi, et al. "Aggregation induced red shift emission of phosphorus doped carbon dots", RSC Advances 7, 178889 (2017). CrossRef P. Giovanni, Z. Yuji, N. Deboki, P. Nereus, D. Kaplan, et al. "The optical properties of regenerated silk fibroin films obtained from different sources", App. Phys. Lett. 111, 103702 (2017). CrossRef M. Procek, Z. Opilski, A. M. Maquenda, X.M. Berbel, S.Aznar-Cervantes et al., "Silk fibroin thin films for optical humidity sensing", Proceedings of SPIE 11204,1120409 (2019). CrossRef https://www.thorlabs.com/thorproduct.cfm?partnumber=M595F2 DirectLink

Dually Cross‐Linked Supramolecular Hydrogel as Surface Plasmon Resonance Sensor for Small Molecule Detection

Dually cross-linked supramolecular hydrogels (DCSH) are designed to show responsive properties while maintaining the gel structure by introducing two different kinds of cross-links. This is realized by utilizing a photo-cross-linker for permanent cross-linking and β-cyclodextrin (β-CD) and ferrocene (Fc) as host-guest recognition pair. The DCSH shows increased swelling in the presence of the small target molecule adamantane amine (Ada). Ada can break the non-covalent bonding between β-CD and Fc through competitive molecular guest interaction with β-CD. By using a combination of surface plasmon resonance and optical waveguide spectroscopy, it is possible to use this behavior to construct a reversible sensor for specific small molecule detection.

Biomolecule Sensor Based on Azlactone-Modified Hydrogel Films.

A 3D hydrogel layer is probed by combining surface plasmon resonance with optical waveguide spectroscopy to detect biomolecules. A template terpolymer P(DMAAm-co-DMIAAm-co-VDMA) is synthesized via reversible addition-fragmentation chain-transfer polymerization. The terpolymer is then modified with an amino group bearing biotin to enable biomolecular recognition for streptavidin. A hydrogel thin layer is prepared onto a gold surface after spin-coating and photo-crosslinking of the modified polymer. Finally, the hydrogel is utilized to quantitatively detect streptavidin by using surface plasmon resonance-optical waveguide spectroscopy measurements.

Shedding Light on the Dark Corners of Metal-Organic Framework Thin Films: Growth and Structural Stability of ZIF-8 Layers Probed by Optical Waveguide Spectroscopy.

Metal-organic framework (MOF) thin films are promising materials for multiple technological applications, such as chemical sensing. However, one potential limitation for their widespread use in different settings is their stability in aqueous environments. In the case of ZIF-8 (zeolitic imidazolate framework) thin films, their stability in aqueous media is currently a matter of debate. Here, we show that optical waveguide spectroscopy (OWS), in combination with surface plasmon resonance (SPR) spectroscopy, offers a convenient way for answering intriguing questions related to the stability of MOF thin films in aqueous solutions and, eventually provide a tool for assessing changes in MOF layers under different environmental conditions. Our experiments relied on the use of ZIF-8 thin films grown on surface-modified gold substrates, as optical waveguides. We have found a linear thickness increase after each growing cycle and observed that the growing characteristics are strongly influenced by the nature of the primer layer. One of our findings is that substrate surface modification with a 3-mercapto-1-propanesulfonate (MPSA) primer layer is critical to achieve ZIF-8 layers that can effectively act as optical waveguides. We observed that ZIF-8 films are structurally stable upon exposure to pure water and 50 mM NaCl solutions but they exhibit a slight swelling and an increase in porosity probably due to the permeation of the solvent in the intergrain mesoporous cavities. However, OWS revealed that exposure of ZIF-8 thin films to phosphate-buffered saline solutions (pH 8) promotes significant film degradation. This poses an important question as to the prospective use of ZIF-8 materials in biologically relevant applications. In addition, it was demonstrated that postsynthetic polyelectrolyte modification of ZIF-8 films has no detrimental effects on the structural stability of the films.

Interpretation of Absorption Spectra of Some Bisazomethine Dyes in a Crystalline State in Terms of Conformational Change and Exciton Interaction

Abstract Absorption properties of 13 bisazomethine dyes in a crystalline state were studied by optical waveguide spectroscopy. Their solid-state absorption spectra were found to shift bathochromically relative to those in solution with no remarkable change in a spectral shape. The observed spectral shifts were characterized in terms of two intermolecular interactions, conformational change and exciton interaction, on the basis of the crystal structure. Solid-state fluorescence properties of the diethylamino derivatives were also examined for their electronic characterization. The characteristic two-dimensional staircase structure, one of the proposed structures of J-aggregates, was found to play a significant role in the bathochromic spectral shift of all the bisazomethine derivatives.

Free-standing hydrogel-particle composite membrane with dynamically controlled permeability.

The preparation and investigation of a free-standing membrane made from a composite of thermoresponsive poly(N-isopropylacrylamide) (pNIPAAm) and polystyrene nanoparticles (PS NP) with temperature-controlled permeability is reported. The method exploits the light-induced crosslinking of the photo-reactive pNIPAAm-based polymer and mechanical reinforcement of the membrane structure by the polystyrene nanoparticles. About micrometer thick layers were either directly attached to a gold surface or prepared as free-standing layers spanning over arrays of microfluidic channels with a width of about hundred microns by using template stripping. Diffusion of liquid medium, low molecular weight molecules, and large molecular weight proteins contained in blood through the composite membrane was observed with combined surface plasmon resonance (SPR) and optical waveguide spectroscopy (OWS). The swelling ratio, permeability, and nonspecific sorption to these composite membranes were investigated by SPR and OWS as a function of molecular weight of analyte, loading of PS NP in the composite film, and temperature. The authors show successful preparation of a defect-free membrane structure that acts as a thermoresponsive filter with nanoscale pores spanning over an area of several square millimeters. This membrane can be reversibly switched to block or allow the diffusion of low mass molecules to the sensor surface by temperature-triggered swelling and collapsing of the hydrogel component. Blocking of diffusion and low unspecific sorption of proteins contained in blood serum is observed. These features make this platform interesting for potential future applications in continuous monitoring biosensors for the analysis of low molecular weight drug analytes or for advanced cell-on-chip microfluidic studies.

In situ Observation of Direct Electron Transfer Reaction of Cytochrome c Immobilized on ITO Electrode Modified with 11-{2-[2-(2-Methoxyethoxy)- ethoxy]ethoxy}undecylphosphonic Acid Self-assembled Monolayer Film by Electrochemical Slab Optical Waveguide Spectroscopy

To immobilize cytochrome c (cyt.c) on an ITO electrode while keeping its direct electron transfer (DET) functionality, the ITO electrode surface was modified with 11-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}undecylphosphonic acid (CH3O (CH2CH2O)3C11H22PO(OH)2, M-EG3-UPA) self-assembled monolayer (SAM) film. After a 100-times washing process to exchange a phosphate buffer saline solution surrounding cyt.c and ITO electrode to a fresh one, an in situ observation of visible absorption spectral change with slab optical waveguide (SOWG) spectroscopy showed that 87.7% of the cyt.c adsorbed on the M-EG3-UPA modified ITO electrode remained on the ITO electrode. The SOWG absorption spectra corresponding to oxidized and reduced cyt.c were observed with setting the ITO electrode potential at 0.3 and -0.3 V vs. Ag/AgCl, respectively, while probing the DET reaction between cyt.c and ITO electrode occurred. The amount of cyt.c was evaluated to be about 19.4% of a monolayer coverage based on the coulomb amount in oxidation and reduction peaks on cyclic voltammetry (CV) data. The CV peak current maintained to be 83.4% compared with the initial value for a M-EG3-UPA modified ITO electrode after 60 min continuous scan with 0.1 V/s between 0.3 and -0.3 V vs. Ag/AgCl.

Dynamic Analysis of Adsorption-Desorption Equilibrium of Sublimed Aromatic Molecules Using Polarized Optical Waveguide Spectroscopy

The adsorption-desorption equilibrium of sublimed molecules has been analyzed dynamically by optical waveguide (OWG) spectroscopy. Dynamic change of the transition moment during adsorption behavior was successfully detected using polarized incident light. With this technique, sublimed planer aromatic molecules, such as azobenzene, were revealed to stack parallel to the solid surface at the initial stage followed by adsorption with relatively random orientation.

In situ Observation of Desorption Reaction of Cytochrome c from Solid/Liquid Interfaces with Slab Optical Waveguide Spectroscopy.

An automated solution exchange (SE) mechanism has been introduced to slab optical waveguide spectroscopy to estimate the protein immobilizing ability of a slab optical waveguide (SOWG) surface. In each SE process, SOWG spectral change in absorbance at peak position of cytochrome c (cyt.c) Soret band at 409 nm was observed to analyze the desorption ratio of cyt.c adsorbed on SOWG surface. Continuous SE processes for 100 times have successfully brought us a kind of master desorption curve of cyt.c, which was well fitted by a double exponential equation, indicating the existence of three kinds of adsorbed states, including weakly adsorbed, strongly adsorbed, and immobilized cyt.c. The present results showed that around 30 times SE processes were enough to anticipate the ratio of desorbed and immobilized amounts of cyt.c adsorbed on SOWG surface.

Inhomogeneous Growth of Micrometer Thick Plasma Polymerized Films.

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers plasma polymers as homogeneous and continuous structures.

Synthesis and Characterization of New Functional Photo Cross-Linkable Smart Polymers Containing Vanillin Derivatives.

The synthesis of new functional monomers based on vanillin is reported. The monomers further were used in the synthesis of different temperature-responsive photo cross-linkable polymers via free radical polymerization with N-isopropyl acrylamide and a maleimide photo cross-linker. These polymers were characterized by NMR, FTIR and UV spectroscopy, as well as gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Critical solution temperatures were determined by UV spectroscopy. Hydrogel thin films were formed by spin coating of a polymer solution over gold with adhesion promotor followed by cross-linking by UV irradiation. The swelling properties were determined by surface plasmon resonance coupled with optical waveguide spectroscopy. The swelling behavior of the hydrogel films was determined as a function of temperature. The incorporation of a dialkyl amino group compensated the hydrophobic effect of the vanillin monomer. Transition temperatures in the physiological range could be obtained.

Long-range surface plasmon resonance sensors fabricated with plasma polymerized fluorocarbon thin films

A rapid and simple approach to prepare the dielectric buffer layers is of crucial importance for the development of long-range surface plasmon resonance (LRSPR) sensors. In this regard, we describe for the first time the use of plasma polymerized fluorocarbon thin films as the dielectric buffer layers for the construction of LRSPR sensors. The fluorocarbon films were achieved by radio frequency plasma polymerization of perfluorooctyl ethylene (PFOE) at continuous wave mode with an input power of 60 Watts. The resulting ppPFOE exhibited good adhesion with both the glass substrate and the gold superstrate, and also remained relatively stable in aqueous solutions as seen by optical waveguide spectroscopy (OWS). The obtained LRSPR sensor consisting of a SF11-ppPFOE-Au structure was employed for the detection of both the bulk refractive index variation and the protein adsorption.

<i>In situ</i> Observation of Direct Electron Transfer Reaction of Cytochrome <i>c</i> Immobilized on ITO Electrode Modified with 10-carboxydecylphosphonic Acid by Slab Optical Waveguide Spectroscopy and Cyclic Voltammetry

<i>In situ</i> Observation of Direct Electron Transfer Reaction of Cytochrome <i>c</i> Immobilized on ITO Electrode Modified with 10-carboxydecylphosphonic Acid by Slab Optical Waveguide Spectroscopy and Cyclic Voltammetry

Optical waveguide sensor based on silica nanotube arrays for label-free biosensing.

Label-free biosensing based on optical waveguide spectroscopy of silica nanotube (SNT) arrays is realized with high sensitivity. The SNT arrays fabricated using a porous anodic alumina (PAA) template assisted by surface sol-gel (SSG) method showed a high value of 552 reciprocal refractive index unit as the sensing figure of merit by exchanging the sensing environment with water and ethanol. A standard biotin-streptavidin affinity model was tested using the SNT arrays which support a TM1 mode and the fundamental response of the system was investigated. Results show that the response of the SNT arrays for adsorption of streptavidin is higher than the one using substrate without removing the PAA template due to the larger surface area and the stronger electromagnetic field. The limit of detection (LOD) of the SNT arrays for detection of streptavidin was estimated as 93 pM, with the detection time of 40 min. Additionally, the Fresnel calculations suggested higher potential sensitivity of the current system compared to that of the conventional SPR sensors. Thus, the SNT arrays may be used as a versatile platform for high-sensitive label-free optical biosensing due to the high performance and the large potential of the surface functionality.

Optical Properties of Three Crystal Modifications of a 2,3-Dicyanopyrazine Dye

Some pyrazine dyes are known to display strong fluorescence not only in solution but also in the solid-state. 5-t-Butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]pyrazine (1) is a 2,3-dicyanopyrazine dye synthesized for an examination of substituent effects on thin-film growth [1]. Dye 1 was found to exhibit three crystal modifications with different color appearance (I: red, II: black, III: reddish purple). Modification I is a solvate crystal including one chloroform per one dye molecule [2], and modifications II and III are polymorphs. In this work, optical properties of these three modifications were interpreted on the basis of their crystal structures. The absorption spectra of the modifications were measured using optical waveguide spectroscopy. The absorption maxima of modifications I, II and III were found at 559 nm, 462 nm and 571 nm, respectively. A bathochromic absorption shift of reddish modifications I and III from that of 1 in toluene was 79 nm (-2944 cm-1) and 91 nm (-3320 cm-1), respectively. On the other hand, a hypsochromic absorption shift of 18 nm (812 cm-1) was observed in modification II. The fluorescence maxima of modifications I, II and III were found at 619 nm, 734 nm and 668 nm, respectively. The energy displacement corresponding to the observed spectral shifts was characterized in terms of an exciton interaction. The exciton interaction for a dimer was estimated using the extended dipole model, and the nearest-neighbor approximation was applied for evaluating a total energy displacement due to crystallization. The calculation results were qualitatively in good agreement with the observed spectral shifts. The result also revealed that molecular pairs in two-dimensional stacking structure in these modifications play a significant role in the total energy displacement.

Adsorption of a Carboxylic Acid-Functionalized Aminoxyl Radical onto SiO2

Silicon wafers both without and with silicon(IV) oxide surface coverage were covered with benzene solutions of stable organic radical 3-(N-tert-butyl-N-aminoxyl)benzoic acid (mNBA). X-ray photoelectron spectroscopy supported the presence of the radical on both surface-cleaned (oxide-reduced) and oxide-covered surfaces. Optical waveguide spectroscopy showed that the radical retained its structure while adsorbed to the surface of the wafers, without noticeable decomposition. AFM and MFM imaging showed that the radical formed blocky particles with a change in rms roughness from 0.3 nm premodification to 1.7 nm postmodification on the surface-cleaned silicon. Similar experiments using oxide-coated silicon showed that the radical adsorbed to form much smoother layers, with a small change in rms roughness from 0.2 to 0.3 nm. Contact angle measurements of water on the premodified and postmodified samples showed a large, hydrophobic change in the silicon oxide surface but only a modest change in the surface-cleaned silicon surface. Samples of mNBA adsorbed onto silica gel showed strong electron-spin resonance signals from the aminoxyl spin, even years after production. The results demonstrate the prospects for treating and coating oxide-covered silicon wafers and silicon oxide-coated particles with a paramagnetically active organic substrate, without major chemical modification of the pretreatment surface; the resulting organic spin sites can be stable for years.

Swelling and Water Uptake Behavior of Nanofilms Obtained by a Magnetron Enhanced Plasma-Polymerization Process

This work deals with the water uptake and swelling behavior of magnetron-enhanced plasma-polymerized nanofilms in an aqueous medium. Those coatings are used in biomedical applications such as implants or contact lenses. The role of water in biomaterial surface science is considered to be of great importance. Water is not only the major molecule in most living organisms (70%) and the carrier of cells but it is also the medium in which biochemical processes take place. Because of its small size and mobility, water is the first molecule to come in contact with a biomaterial in any clinical application.[1] It is believed, that the degree of polymer swelling strongly affects the interaction of proteins with the surface of the polymer, which determines its biocompatibility. Polymers with a high swelling degree show weak enthalpic interactions with proteins, resulting in a protein-repellency.[2] A new approach is applied, which combines three characterization techniques: dynamic contact angle measurements, optical waveguide spectroscopy, and electrochemical impedance spectroscopy. A relation between the composition of the films and the water and salt transport phenomena through the nanofilm was observed. A higher amount of oxygen in the precursor gas ratio in the polymerization process leads to a higher wettability as well as a higher water and salt intrusion. Based on this observation an electrical model was introduced and helped to interpret the experimental results.