Surface Of Glass Substrate Research Articles

Fabrication of water-resistant and abrasion- resistant superhydrophilic coatings

Superhydrophilic coatings show promising applications in the anti-fogging and self-cleaning fields. However, the application of transparent superhydrophilic coatings faces two challenges: abrasion and water immersion leading to loss of superhydrophilicity. Herein, we contribute Halloysite nanotubes (HNTs) to enhancing abrasion resistance by integrating into network-like structures within coatings, and water resistance by adsorbing sodium alkenyl sulfonate (AOS) facilitated by the positive charge within their cavities, respectively. Hydrolyzed tetraethyl orthosilicate (TEOS) as crosslinking agents combines with the abundant hydroxyl groups (Si-OH) on the surface of HNTs nanotubes and glass substrate to form a three-dimensional network structure. The results demonstrate that the designed HNTs tube coatings have strong abrasion and water resistance accompanied by anti-fogging and self-cleaning properties, which can withstand 800 cycles of Taber abrasion under a load of 250 g, and 90 min of immersion in boiling water. Furthermore, the coated surface exhibited negligible contamination after 153 days in an outdoor environment, which indicates a commendable long-term self-cleaning capability. Therefore, the introduction of HNTs nanotubes can provide a useful strategy for the development of superhydrophilic coatings for anti-fogging and self-cleaning with excellent abrasion and water resistance.

Comparing silver and gold nanoislands’ surface plasmon resonance for bisacodyl and its metabolite quantification in human plasma

Gold and silver nanoparticles have witnessed increased scientific interest due to their colourful colloidal solutions and exceptional applications. Comparing the localized surface plasmon resonance (LSPR) of gold and silver nanoparticles is crucial for understanding and optimizing their optical properties. This comparison informs the design of highly sensitive plasmonic sensors, aids in selecting the most suitable nanoparticles for applications like surface-enhanced infrared spectroscopy (SEIRA) and biomedical imaging, and guides the choice between gold and silver nanoparticles based on their catalytic and photothermal properties. Ultimately, the study of LSPR facilitates the tailored use of these nanoparticles in diverse scientific and technological applications. Two SEIRA methods combined with partial least squares regression (PLSR) chemometric tools were developed. This development is based on the synthesis of homogeneous, high-dense deposited metal nanoparticle islands over the surface of glass substrates to be used as lab-on-chip SEIRA sensors for the determination of bisacodyl (BIS) and its active metabolite in plasma. SEM micrographs revealed the formation of metallic islands of colloidal citrate-capped gold and silver nanoparticles of average sizes of 29.7 and 15 nm, respectively. BIS and its active metabolite were placed on the nanoparticles’ coated substrates to be directly measured, then PLSR chemometric modelling was used for the quantitative determinations. Plasmonic citrate-capped gold nanoparticle substrates showed better performance than those prepared using citrate-capped silver nanoparticles in terms of preparation time, enhancement factor, PLSR model prediction, and quantitative results. This study offers a way to determine BIS and its active metabolite in the concentration range 15–240 ng/mL in human plasma using inexpensive disposable glass-coated substrates that can be prepared in 1 h to get results in seconds with good recovery between 98.77 and 100.64%. The sensors provided fast, simple, selective, molecular-specific and inexpensive procedures to determine molecules in their pure form and biological fluid.

Laser cleaning of RTV coating on the insulator surface by using millisecond pulse lasers.

High-efficiency and high-quality removal of sulfurized silicone rubber from insulator surfaces is paramount for high-voltage power systems. To address this issue, and aiming to achieve precise and nondestructive cleaning of room temperature vulcanized (RTV) coatings, we selected millisecond laser cleaning technology in this study. Successful and efficient cleaning of the RTV coating was performed by adjusting laser parameters. Characterization techniques, including scanning electron microscopy, energy-dispersive x-ray spectroscopy, and confocal microscopy, were employed to comprehensively assess the cleaning effects and ensure the integrity of the substrate surface. The results indicate that by adjusting the scanning power combination of the high power of the millisecond pulse laser to 200W and the low power of 150W, the glass substrate surface maintains excellent roughness and micro-morphological features after laser cleaning, providing optimal conditions for subsequent processing and utilization. This research contributes an efficient and cost-effective solution to the insulation treatment process in high-voltage power systems.

The Photocatalytic Activity of the Bi2O3-B2O3-ZnO-TiO2 Glass Coating

Due to the low melting temperature, the glazes based on the Bi2O3-B2O3-ZnO system are used as coatings on the surface of industrial glass substrates. Moreover, the composition of these coatings does not contain PbO, meeting the optical and environmental properties requirements. In this study, TiO2 was used in the Bi2O3-B2O3-ZnO glaze system to improve its photocatalytic ability. This can be considered a four – component glass system Bi2O3-B2O3-ZnO-TiO2. The heating microscopy results show that the melting temperature of the glaze system is 606 °C. The Fourier transform infrared spectroscopy results show that the TiO2 polyhedra are located independently in the structure without participating in forming a glass network. Thanks to that, the photocatalytic properties of TiO2 are maintained. The X-ray diffraction patterns results show that the formed TiO2 nanocrystals are rutile and anatase crystals. The results of determining the band gap energy using UV-Vis show that the band gap energy of the base glaze system increases with the addition of TiO2. The methylene blue decomposition results also showed that the ability to decompose organic increased when TiO2 was added to the glaze coating. The characteristics such as melting temperature, microstructure, and photocatalytic capacity of Bi2O3-B2O3-ZnO-TiO2 white glazes (5 and 10 % weight of TiO2) also were indicated in this paper.

Arresting Tollens’ reagent's reaction on a glass surface as the easiest method to fabricate Ag nanocluster-based SERS substrates for glucose sensing

The fabrication of Ag nanoclusters-based SERS substrates generally needs high-end processing equipment. On the contrary, here, they are easily fabricated by arresting Tollens’ reagent’s reaction on the surface of a typical glass substrate.

The Influence of UV-Ozone, O2 Plasma, and CF4 Plasma Treatment on the Droplet-Based Deposition of Diamond Nanoparticles.

Surface treatment is critical for homogeneous coating over a large area and high-resolution patterning of nanodiamond (ND) particles. To optimize the interaction between the surface of a substrate and the colloid of ND particles, it is essential to remove hydrocarbon contamination by surface treatment and to increase the surface energy of the substrate, hence improving the diamond film homogeneity upon its deposition. However, the impact of substrate surface treatment on the properties of coatings and patterns is not fully understood. This study explores the impact of UV-ozone, O2 plasma, and CF4 plasma treatments on the wetting properties of the fused silica glass substrate surface. We identify the optimal time interval between the treatment and subsequent ND coating/patterning processes, which were conducted using inkjet printing and ultrasonic spray coating techniques. Our results showed that UV-ozone and O2 plasma resulted in hydrophilic surfaces, while CF4 plasma treatment resulted in hydrophobic surfaces. We demonstrate the use of CF4 plasma treatment before inkjet printing to generate high-resolution patterns with dots as small as 30 μm in diameter. Ultrasonic spray coating showed homogeneous coatings after using UV-ozone and O2 plasma treatment. The findings of this study provide valuable insights into the hydrocarbon airborne contamination on cleaned surfaces over time even in clean-room environments and have a notable impact on the performance of liquid coatings and patterns. We highlight the importance of timing between the surface treatment and printing in achieving high resolution or homogeneity.

Synthesis of Aptes-Capped Self-Adsorption Pd Nanoparticles and Application in Metallization on Glass Substrate with High Adhesion

Palladium is the most used catalysts in the electroless deposition process. The technology that use the amino silane compound (3-Aminopropyl) Triethoxysilane (APTES) as surface modifier is quite mature. Therefore, an innovative idea that one step palladium catalyst APTES-Pd with APTES as capping agent and surface modifier appeared. APTES-Pd is capable to adsorb on surface of glass substrate by forming Si-O covalent bond. Comparing to commercial palladium catalysts, the process is complex and need to work at high concentration, APTES-Pd has easier process and able to work at low concentration. The particle size of APTES-Pd is characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The configuration of APTES-Pd as well as the effect of modification on glass substrate is explained by X-ray photoelectron spectroscopy (XPS).Glass substrate is a good option as an interposer substrate. It has serval advantages, such as low k, high resistivity, high stability, low coefficient of thermal expansion (CTE) mismatch with copper material and good mechanical properties. However, because glass substrate (SiO2) is stable and surface is smooth, it’s hard to electroless deposit Cu layer with high adhesion on it. The adhesion that using commercial palladium catalysts Sn/Pd for electroless copper deposition is too low to pass tape test. Because interaction between Sn/Pd and substrate is electrostatic adsorption which is lower than covalent bond. Using APTES-Pd for electroless copper deposition is capable to improve the interaction between glass and Cu layer. APTES-Pd can pass tape test on glass substrate. But its adhesion is still too low to be measured by T-Peel. To enhance the adhesion of the metal films on glass substrates, we coat titanium dioxide (TiO2) as adhesion promoter. TiO2 can not only bond to glass substrate but increase surface roughness. After coating TiO2 film, the adhesion of metal film increases to 122 gf/cm.

A method for preparing and investigating anti-/de-icing surface by integration of laser-induced graphene (LIG) with a silica sol adhesive (SMP@M-SiO2)

The ice accumulation has a significant negative impact on device/system functions, and the emergence of anti−/de-icing coatings has greatly improved this problem. However, the ideal ice-free state cannot be achieved by hydrophobic properties alone. In this study, we developed a method for developing a composite electro/photo-thermal (active) and superhydrophobic (passive) anti-/de-icing coating by laser-induced graphene (LIG) and post-modification with silica sol adhesive on selected underlying substrates. The composite coating consisted of the bottom layer of LIG, which played a role in constructing a porous skeleton structure and photothermal-electrothermal conversion; and a top layer of silica sol adhesive (SMP@M-SiO2) was used for bond strength enhancement and hydrophobic modification of the LIG. At −10 °C, the freezing time of water droplets on the SMP@M-SiO2@LIG surface was delayed about 14 times, and the ice adhesion strength decreased by 69.8 % when compared with the glass substrate surface. In addition, under one solar irradiation, the SMP@M-SiO2–5@LIG surface temperature rose to 56.5 °C in 900 s, which led to 21.5 times increase in delaying icing time when compared to the bare substrate. At a low DC voltage of 15 V, the temperature of the coating reached 177.1 °C in 60 s. At −20 °C, the developed surface showed no signs of freezing and achieved rapid de-icing and de-frosting in 6 s. The wide applicability of the SMP@M-SiO2–5@LIG surface was demonstrated on glass, plastics, metals, and ceramic substrates.The developed surface combining superhydrophobic passive anti-icing and electro/photo-thermal active de-icing properties is expected to be further applied in various prospective applications.

Enhanced Diffuse Reflectance of Photons in Molybdenum Back Electrode Films Achieved via Surface Texturing for Thin Film Solar Cells

Molybdenum (Mo) thin film is widely used as the bottom electrode in substrate‐configured thin film solar cells due to its high conductivity and reflectivity. Mo grown onto microtextured substrates increases the diffuse reflection of incident photons via scattering/multiple reflections on the corner/edges, in addition to the contribution from increased surface area. Herein, bilayer Mo is grown using direct current magnetron sputtering onto plain and textured substrates. To texture the glass substrate surface, a periodic array of cross‐linked photoresist structures (SU‐8 2000.5 & SU‐8 2005) is introduced via UV‐lithography process. Characterizations are done using X‐ray diffractometer, optical microscope, scanning electron microscope, and optical profilometer. Angle‐dependent specular reflectance, diffuse reflectance, and electrical measurements done on Mo grown on plain and textured substrates lead to a comprehensive understanding of the advantages of growing Mo films on textured substrates. The electrical resistivity of Mo grown on plain and textured substrates is of the same order, measuring 3.09 × 10−5 Ω cm, 3.25 × 10−5 Ω cm, and 3.87 × 10−5 Ω cm, respectively. A high‐diffuse reflectance of 62.7% is obtained for SU‐8 2005 textured Mo films. Investigations using COMSOL simulations support the optical reflectance analysis.

Fabrication of Hyperbranched Photomechanical Crystals Composed of a Photochromic Diarylethene.

We report the fabrication of hyperbranched hollow crystals of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene on a concave surface of the spherical glass substrate by sublimation and their practical photomechanical behaviors. The number of units of the branched structure of the hollow crystals composed of this compound is proportional to the substrate curvature of the substrate. Compared with the sublimation process of the same compound on the flat glass substrate, two kinds of the thin film domains are generated separately in the center and around the edge of the spherical glass substrate. Especially under the high relative humidity condition, the boundaries between these thin film domains move gradually around the edge through the center during as long as 6 h of sublimation time so that the hyperbranched hollow crystals are densely produced on the entire surface of the substrate. These hyperbranched hollow crystals can be prepared with the highly ordered molecular packing due to the very slow formation process of the crystalline walls of the hollow structures. Furthermore, the photo-induced bending behaviors in the few- and highly-branched hollow crystals have the practical roles in moving and bending the minute objects according to their characteristics of these branched shapes.

Buried Optical Waveguide in Photo-Thermo-Refractive Glass by Ion Exchange Technology

To realize application of functional material Photo-Thermo-Refractive (PTR) glass for integrated photonic device production, PTR glass material is fabricated and employed as matrix material for planar optical waveguide manufacturing. Buried optical waveguide, with a core dimension of 8.7 μm × 9.0 μm (width by height), and its front edge located at approximately 12.5 μm underneath the glass substrate surface, is obtained by using thermal ion exchange (TIE) and subsequent field-assisted ion migration (FAIM). Transmission loss of these waveguides can be reduced to a value as low as 0.08 dB/cm at the operating wavelength of 1550 nm, and the coupling loss to standard single-mode-fiber is measured to be 0.47 dB/facet, demonstrating the feasibility of low-loss integrated photonic devices fabrication on PTR glass materials by ion exchange technology.

Microlens array device for laser light shaping in laser scanning smart headlights.

We present, what we believe to be, a novel microlens array (MLA) scheme for laser light shaping in laser scanning smart headlight. The laser spot has a Gaussian distribution that may reach a high peak power density in the central part, which is called hot spot. When the laser beam is applied to a phosphor plate for luminous conversion, the hot spot of Gaussian beam causes thermal quench and decreases luminous efficacy. To avoid this effect, an MLA is used, so as to achieve a uniform energy distribution. In this study, we propose a laser scanning smart headlight fabricated by a new MLA structure, with an arrangement providing both light uniformity and shaping. The novel MLA is designed by two-dimensional micro-concave lens array yielding a flat-top beam. The flexible fabrication process employs laser drilling to shape the micro-hole array on the glass substrate surface and then etch it to form MLA without requiring any mask lithography process. The full-width half maximum (FWHM) of light output distribution can be adjusted by the glass etching parameters, and the light distribution could be controlled by the arranged layout of the array. Thus, beams with FWHM divergence ranging from 5° to 34° has been fabricated and characterized. The typical pixel shape is a rectangle with two different FWHMs in two orthogonal directions, and the fabrication method achieves this goal as well. This novel design and unique maskless process of the MLAs is a promising tool for development the next generation laser scanning smart headlight.

Influence of the transition metals central atom nature on the optical and electrophysical properties of phthalocyanine nanowires

In the present work, phthalocyanine nanowires were obtained on the surface of glass substrates with an ITO coating. The presence of α, β, and χ crystalline phases, which are formed in the course of synthesis was demonstrated using XRD. Measurement of the absorption spectra showed that the observed change in the shape of the absorption bands is associated with the formation of phase states and the relationship between the tendency of the central metal ion to leave the phthalocyanine plane and the value of the Davydov splitting. It was found that the high-value conductivity of the nanowires is explained by the possibility of the π-electrons transition depending on the metal ion, over the states of overlapping phthalocyanine rings. An analysis of the obtained results showed that additional energy states are involved in the charge transfer mechanism, which is formed during the coordination interaction of metal ions with an organic ligand.

Silver nanostar films for surface-enhanced Raman spectroscopy (SERS) of the pesticide imidacloprid

Strategies for synthetic control of anisotropic metal nanostructures have grown in recent years in part due to their great potential for application as surface-enhanced Raman scattering (SERS) sensing substrates. It has been shown that SERS using silver substrates is a powerful tool for identification and qualification of trace chemical analysis on the basis of their unique molecular vibrations. In this work, we synthesized star-shaped silver nanostructures and fabricated SERS substrates to use the SERS enhancement of the Raman signal to detect neonicotinoid pesticides. These silver nanostar substrates were prepared by assembling the nanostar particles on a glass substrate surface using a self-assembly technique with various layers of silver nanostars film. The silver nanostar distribution on the solid substrate surface was found to have good reproducibility, reusability and were a stable SERS substrate giving SERS enhancements for pesticide detection at concentrations as low as 10−6 mg/ml. The distribution of these silver nanostars on the surface allowed excellent reproducibility of the detection with a low relative standard derivation (RSD) of SERS intensity of 8%. This work potentially builds a platform for an ultrasensitive detector where samples can be probed with little to no pre-processing and a range of pollutants can be detected at very low levels.

Ag-doped-CuO nanoparticles supported polyaniline (PANI) based novel electrochemical sensor for sensitive detection of paraoxon-ethyl in three real samples

In this paper, a novel nanocomposite is chemically synthesized by reinforcing Ag-doped CuO (Ag@CuO) nanoparticles into the matrix of polyaniline (PANI). This nanocomposite is used as a sensing platform for paraoxon-ethyl (PE) detection. The homogeneous distribution of Ag@CuO nanoparticles onto the PANI matrix provides a smooth and dense surface area, further accelerating the transmission of electrons. The synergistic effect of Ag@CuO and PANI matrix is responsible for the outstanding conductivity, biocompatibility, and catalytic power of the proposed biosensor. For the biosensor fabrication, the nanocomposite is electrophoretically deposited onto the surface of the ITO glass substrate and then the acetylcholinesterase (AChE) enzyme is immobilized onto the fabricated electrode surface by using glutaraldehyde as a crosslinking agent. Under all optimized detection conditions, the proposed biosensor (AChE/Ag@CuO/PANI/ITO) shows a broad linear range from 5 to 100 pM with a low detection limit (LOD) of 11.35 pM. All the electrochemical results confirm the high sensitivity (0.5536 μA (pM)−1 cm−2), high selectivity, good reproducibility, and acceptable stability of the proposed biosensor. Moreover, the proposed biosensor is successfully applied for paraoxon-ethyl (PE) detection in three real samples.

Effect of PAA on the structure and transmittance of hollow spherical SiO2 film prepared by sol-gel method

Hollow spherical silica film has been used on glass substrates as an antireflective coating, and PAA is one of the common templates for preparing SiO2 films by sol-gel method. In this paper, the effects of polyacrylic acid (PAA) content on the SiO2 films prepared by the sol-gel method were analyzed using TEM, DLS, XRD, IR, SEM, and the transmission spectrum. The sol containing hollow spherical micelles can be prepared well from tetraethyl orthosilicate (TEOS) as raw material and PAA as water-soluble polymer by improved Stober, and template method. With the increase of PAA content, the particle size of hollow spherical silica colloidal particles increases and the quantity decreases. The sol is attached to the surface of the soda lime glass substrate to form a film by dip-coating method. With the increase of withdrawal speed, the transmittance of the glass increases, and with the increase of PAA content from 0.1g to 0.6g, the sample's transmittance decreases first and then increases.

An Exploration into Damage Repair and Manufacturing Technology of Photomask Glass Substrates

There are strict requirements on the surface-shape accuracy, cracks, scratches, and subsurface damage of photomask glass substrates with the advancement of photo-etching technology. In this study, photomask quartz glass substrates were etched with the hydrofluoric (HF) acid etching method after chemical mechanical polishing (CMP), so that the polishing hydrolysis layer could be completely removed. In addition, the surface scratches caused by CMP were observed with a surface quality detection device and a white light interferometer. Second, the high-efficiency array-type magnetorheological polishing technology was employed to eliminate the surface-shape error on the surface of quartz photomask glass substrates. Finally, the removal function rotation angle based magnetorheological polishing technology was utilized to evenly remove the mid-frequency ripples and scratches caused in the preceding technological process. The experimental results demonstrated that these technologies can be used to realize rapid damage removal and high-quality processing of photomask glass substrates.

Self-assembly strategy to reduce non-specific adsorption for the development of high sensitivity quantitative immunoassay

The development of functionalized surfaces with low non-specific adsorption is important for their biomedical applications. To inhibit non-specific adsorption on glass substrate, we designed a novel optical biochip by modifying a layer of dense negatively charged film (SO32−) on its substrate surface via self-assembly. Compared with the untreated glass substrate, it reduced the adsorption by about 300-fold or 400-fold by poly (styrene sulfonic acid) sodium salt (PSS), or meso-tetra (4-sulfonatophenyl) porphine dihydrochloride (TSPP) on individually the modified glass substrate. Considering the effect of fluorescence resonance energy transfer (FRET) between TSPP and the QDs in solution by mixing, a strategy of 2-layer of TSPP followed by 4-layer of PSS was designed to modify the glass for preparing biochips. Under the optimized conditions, the biochip on functionalized glass substrate co-treated with TSPP and PSS realized the sensitive quantitative detection of C-reactive protein (CRP) based on a quantum dot fluorescence immunosorbent assay (QD-FLISA). The limit of detection (LOD) for CRP achieved 0.69 ng/mL with the range of 1-1,000 ng/mL using TSPP and PSS co-treated glass substrate surface, which was respectively about 1.9-fold and 7.5-fold more sensitive to the PSS-modified biochip and the TSPP-modified biochip. This work demonstrated an effective and convenient strategy to obtain biochips with low non-specific adsorption properties on functionalized surfaces, thus providing a new approach for creating ultra-high sensitivity microchannels or microarrays on glass substrates.

Real Time Nanoscale Cleaning Phenomenon Observation During Enforcing MHz Wave By Evanescent Field

In recent years, abrasive nanoparticles (sub Φ50 nm) have been applied in Chemical Mechanical Polishing (CMP) process to realize flattened surface of substrate for multilayer wiring structure and fine wiring width to achieve high performance Large Scale Integration Circuit. Definitely, the highly efficient removal of nanoparticles to be cause of the serious defect which remained on/in substrate in Post-CMP cleaning process is required. Therefore, it is indispensable to investigate the cleaning mechanisms by visualizing the cleaning phenomena that considered as nanoparticles’ behaviors during the process to realize optimal and efficient cleaning technology. However, the cleaning phenomena have not already clearly known because the residual contamination on the wafer surface has been usually inspected only before and after the cleaning process in dry condition, not in wet condition due to the surface scanning methods (e.g., scanning electron microscopy).Generally, cleaning phenomenon is considered as abrasive nanoparticles’ behaviors, which are detached from a wafer surface and occasionally reattach to the surface or remain on the surface to be a residual contamination. These behaviors occurred in a few hundred nm range from the substrate surface. Hence, we have established the real-time visualization method to observe the nanoparticles’ behaviors in wet cleaning phenomena by applying an optical evanescent light that localized less than approx. 200 nm from the surface. Experimentally contact and non-contact cleaning phenomena also have been duplicated on an optical microscope that developed ourself.In this paper, we visualized ultrasonic cleaning phenomena considered as Φ30, 50, 70 nm silica particles’ behaviors and/or cavitation effects movement during enforcing MHz wave by applying an evanescent light. Either Silica nanoparticles or cavitation effects that existing in an evanescent field were limitedly scatter to be the propagating light, which can reach to the optically CMOS area sensor of camera in a microscopy (Figure.1).The typically observation results of the Φ30, 50, 70 nm silica particles’ detachment from the silica glass substrate surface during enforcing 1.1 MHz wave by oscillating piezo actuator with a power density of approx. 0.2 watt per square centimeter with the exposure time of 16 milliseconds in 60 frames per second as shown in Figure.2. The time-varying residual rate of silica particles on the surface was also evaluated by counting the Φ30, 50, 70 nm silica particles that attached on the surface in the observation area of 120 × 40 squared micrometers. Some of each silica nanoparticles were randomly intermittently detached from the surface or remained on the surface during the acoustic cavitation repeatedly irregularly occurs and decays near the surface by enforcing the MHz wave. The nanoparticle residual change rate showed trend that silica nanoparticles detached from the surface when the acoustic cavitation irregularly occurred near the surface.The typically phenomenon was found that the residual silica nanoparticles were detached from the surface within 16 milliseconds (≒1/60 seconds) when the acoustic cavitation effects approached near to the surface that shown by background of high scattering light intensity as shown in Figure.3. Repeated occurrence of acoustic cavitation phenomenon seemed to accelerate the detachment of silica nanoparticles. By using the evanescent field, cleaning phenomena near the surface during enforcing MHz wave were visualized in real time. Figure 1

Quantitative Biosensing Based on a Liquid Crystal Marginally Aligned by the PVA/DMOAP Composite for Optical Signal Amplification.

The working principle for a liquid crystal (LC)-based biosensor relies on the disturbance in the orderly aligned LC molecules induced by analytes at the LC-aqueous or LC-solid interface to produce optical signals that can be typically observed under a polarizing optical microscope (POM). Our previous studies demonstrate that such optical response can be enhanced by imposing a weak electric field on LCs so that they are readily tilted from the homeotropic alignment in response to lower concentrations of analytes at the LC-glass interface. In this study, an alternative approach toward signal amplification is proposed by taking advantage of the marginally tilted alignment configuration without applying an electric field. The surface of glass substrates was modified with a binary aligning agent of poly(vinyl alcohol) (PVA) and dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP), in which the amount of PVA was fine-tuned so that the interfacing LC molecules were slightly tilted but remained virtually homeotropically aligned to yield no light leakage under the POM in the absence of an analyte. Two nematic LCs, E7 and 5CB, were each sandwiched between two parallel glass substrates coated with the PVA/DMOAP composite for the detection of bovine serum albumin (BSA), a model protein, and cortisol, a small-molecule steroid hormone. Through image analysis of the optical appearance of E7 observed under the POM, a limit of detection (LOD) of 2.5 × 10−8 μg/mL for BSA and that of 3 × 10−6 μg/mL for cortisol were deduced. Both values are significantly lower than that obtained with only DMOAP as the alignment layers, which correspond to signal amplification of more than six orders of magnitude. The new approach for signal amplification reported in this work enables analytes of a wide range of molecular weights to be detected with high sensitivity.