Mechanism of UV Photoreactivity of Alkylsiloxane Self-Assembled Monolayers

Superhydrophobic Paper-Based Microfluidic Field-Effect Transistor Biosensor Functionalized with Semiconducting Single-Walled Carbon Nanotube and DNAzyme for Hypocalcemia Diagnosis

Hypocalcemia is caused by a sharp decline in blood calcium concentration after dairy cow calving, which can lead to various diseases or even death. It is necessary to develop an inexpensive, easy-to-operate, reliable sensor to diagnose hypocalcemia. The cellulose-paper-based microfluidic field-effect biosensor is promising for point-of-care, but it has poor mechanical strength and a short service life after exposure to an aqueous solution. Octadecyltrichlorosilane (OTS), as a popular organosilane derivative, can improve the hydrophobicity of cellulose paper to overcome the shortage of cellulose paper. In this work, OTS was used to produce the superhydrophobic cellulose paper that enhances the mechanical strength and short service life of MFB, and a microfluidic field-effect biosensor (MFB) with semiconducting single-walled carbon nanotubes (SWNTs) and DNAzyme was then developed for the Ca²⁺ determination. Pyrene carboxylic acid (PCA) attached to SWNTs through a non-covalent π-π stacking interaction provided a carboxyl group that can bond with an amino group of DNAzyme. Two DNAzymes with different sensitivities were designed by changing the sequence length and cleavage site, which were functionalized with SPFET/SWNTs-PCA to form Dual-MFB, decreasing the interference of impurities in cow blood. After optimizing the detecting parameters, Dual-MFB could determine the Ca²⁺ concentration in the range of 25 μM to 5 mM, with a detection limit of 10.7 μM. The proposed Dual-MFB was applied to measure Ca²⁺ concentration in cow blood, which provided a new method to diagnose hypocalcemia after dairy cow calving.

Hierarchical porous zeolitic imidazolate frameworks (ZIF-8) and ZnO@N-doped carbon for selective adsorption and photocatalytic degradation of organic pollutants

Removing organic contaminants such as dyes from water is essential to purify wastewater. Herein, zeolitic imidazolate framework-8 (ZIF-8) and ZnO@N-doped C are reported as effective adsorbents and photocatalysts for the adsorption and degradation of organic dyes. The materials showed effective and selective adsorption toward anionic dyes such as methyl blue (MeB) dye in the presence of fluorescein (FLU) dye. The adsorption capacities of ZnO@N-doped C for MeB and FLU dyes are 900 mg g-1 and 100 mg g-1, respectively. According to UV-Vis diffuse reflectance spectroscopy (DRS) data, ZnO@N-doped C has a lower bandgap (2.07 eV) than ZIF-8 (4.34 eV) and ZnO (3.12 eV). Thus, ZnO@N-doped C serves as an effective photocatalyst for the degradation of both dyes under UV exposure. The degradation efficiency capacity of the dye (50 mg L-1) is >90% using 200 mg L-1 of the photocatalyst. The mechanism of adsorption and photocatalysis is investigated. The photodegradation pathway of the dye involved the generation of oxidative hydroxy radicals (OH˙), which can degrade the dyes. The degradation products of FLU were recorded using mass spectrometry.

Surface Patterning of Closed Nanochannel Using VUV Light and Surface Evaluation by Streaming Current

In nanofluidics, surface control is a critical technology because nanospaces are surface-governed spaces as a consequence of their extremely high surface-to-volume ratio. Various surface patterning methods have been developed, including patterning on an open substrate and patterning using a liquid modifier in microchannels. However, the surface patterning of a closed nanochannel is difficult. In addition, the surface evaluation of closed nanochannels is difficult because of a lack of appropriate experimental tools. In this study, we verified the surface patterning of a closed nanochannel by vacuum ultraviolet (VUV) light and evaluated the surface using streaming-current measurements. First, the C₁₈ modification of closed nanochannels was confirmed by Laplace pressure measurements. In addition, no streaming-current signal was detected for the C₁₈-modified surface, confirming the successful modification of the nanochannel surface with C₁₈ groups. The C₁₈ groups were subsequently decomposed by VUV light, and the nanochannel surface became hydrophilic because of the presence of silanol groups. In streaming-current measurements, the current signals increased in amplitude with increasing VUV light irradiation time, indicating the decomposition of the C₁₈ groups on the closed nanochannel surfaces. Finally, hydrophilic/hydrophobic patterning by VUV light was performed in a nanochannel. Capillary filling experiments confirmed the presence of a hydrophilic/hydrophobic interface. Therefore, VUV patterning in a closed nanochannel was demonstrated, and the surface of a closed nanochannel was successfully evaluated using streaming-current measurements.

Superhydrophobic Glass Microfiber Filter as Background-Free Substrate for Quantitative Fluorometric Assays

We have discovered herein that commonly used laboratory glass microfiber filters can be functionalized as background-free superhydrophobic substrates for quantitative fluorometric assays. In particular, glass microfiber filters (Whatman GF/A) can be treated with low-concentration (20 mM) methyltrichlorosilane/toluene solution to be superhydrophobic (water contact angle >150°) in less than 5 min; the modified glass microfiber filter can be readily patterned with UV/ozone irradiation to create hydrophilic reaction zones on the otherwise superhydrophobic substrate. Compared with traditional cellulose filter paper, the glass microfiber filter has extremely low fluorescence background, which makes it an excellent substrate for preparing quantitative fluorometric assays. In conjunction with smartphone imaging and color analysis, we have showcased a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based fluorometric assay for copper quantitation on these patterned, superhydrophobic glass microfiber filter substrates. Both the limit of detection and linear response range are comparable with the standard spectrophotometric quantitation in solution and commercial copper detection kits, which augments the application potential of superhydrophobic glass microfiber filters as ideal (e.g., background-free) substrates for the preparation of multiplex microassays and other advanced microanalytical devices based on fluorescence readout.

Successive four-phase liquid separation using hierarchical microcube-nanohole structure and controlled surface wettability meshes

The chemical industry needs filter systems with selective wetting properties for environmental protection and effective liquid separation. Current liquid-separation systems are mainly based on the surface energy of the meshes used to separate liquid particles; the smaller the difference between the surface tension of the liquids to be separated, the lower the separation efficiency of these systems. Sophisticated control of the surface wettability of a separation system is necessary to separate liquids with small differences in their surface tension. We precisely adjusted the surface-energy threshold of aluminium meshes used for separation by simply coating their hierarchical microcube and nanohole structures with different materials. We also applied patterning technology to create a single mesh with a heterogeneous distribution of surface tension to successively separate four liquids. Under the force of gravity, the hybrid system of meshes effectively separated the mixture of four liquids, yielding a perfect collection rate (≥98%) and high content ratio (≥96%). Even multiphase mixtures of immiscible liquids with surface tension differences as small as 10.4 mN/m could be effectively separated. Thus, multiphase liquid-separation systems can be used for the efficient and economical separation of various liquid mixtures in many industrial and environmental fields.

Robust Operation of Mesoporous Antireflective Coatings under Variable Ambient Conditions

Generating mesoporous films with adequate film thickness and refractive index is a common method to achieve amplitude and phase matching in low-cost interference-based antireflective coatings (ARCs). For high-surface-energy materials, pores on the 2-50 nm (i.e., on the subwavelength scale) are subject to capillary condensation by surrounding gas phase water molecules, which hampers their functioning. In this work, we examine the effect of relative humidity on mesoporous ARCs and present a simple method for the preparation of ARCs with robust operation under variable conditions. The materials route is based on the generation of well-defined porous aluminosilicate networks by block copolymer co-assembly with poly(isobutylene)- block-poly(ethylene oxide) and postsynthesis grafting of trichloro(octyl)silane molecules to the pore walls. The functionalized films exhibited a maximum transmittance value of 99.8%, with an average transmittance of 99.1% in the visible wavelength range from 400 to 700 nm. Crucially, the antireflection performance was maintained at high humidity values, with an average transmittance decrease of only 0.2% and maximum values maintained at 99.7%. This compared to maximum and average losses of 3.6 and 2.7%, respectively, for nonfunctionalized reference samples. The ARCs were shown to retain their optical properties within 50 humidity cycles, indicating long-term stability against fluctuating environmental conditions.

Photothermally Activated Nanocrystalline Oxynitride with Superior Performance in Flexible Field-Effect Transistors

Photochemical reactions in inorganic films, which can be promoted by the addition of thermal energy, enable significant changes in the properties of films. Metaphase films depend significantly on introducing external energy, even at low temperatures. We performed thermal-induced, deep ultraviolet-based, thermal-photochemical activation of metaphase ZnO_xN_y films at low temperature, and we observed peculiar variations in the nanostructures with phase transformation and densification. The separated Zn₃N₂ and ZnO nanocrystalline lattice in amorphous ZnO_xN_y was stabilized remarkably by the reduction of oxygen defects and by the interfacial atomic rearrangement without breaking the N-bonding. On the basis of these approaches, we successfully demonstrated highly flexible, nanocrystalline-ZnO_xN_y thin-film transistors on polyethylene naphthalate films, and the saturation mobility showed more than 60 cm² V^-1 s^-1.

Superhydrophobic Substrates from Off-the-Shelf Laboratory Filter Paper: Simplified Preparation, Patterning, and Assay Application

Off-the-shelf laboratory filter paper of different pore sizes and thicknesses can be modified with fluorine-free organosilanes to be superhydrophobic, patternable, and ready for quantitative assay applications. In particular, we have demonstrated that the cellulose filter paper treated with a binary hexane solution of short (methyltrichlorosilane) and long (octadecyltrichlorosilane) organosilanes exhibits remarkably high water contact angles (>150°) and low wetting hysteresis (∼10°). Beyond the optimized ratio between the two organosilanes, we have discovered that the thickness rather than the pore size dictates the resulting superhydrophobicity. Scanning electron microscopy images showed that silanization does not damage the cellulose microfibers; instead, they are coated with uniform, particulate nanostructures, which should contribute to the observed surface properties. The modified filter paper is chemically stable and mechanically durable; it can be readily patterned with UV/ozone treatment to create hydrophilic regions to prepare chemical assays for colorimetric pH and nitrite detections.

Monitoring Photochemical Reactions Using Marangoni Flows

We evaluated the sensitivity and time resolution of a technique for photochemical reaction monitoring based on the interferometric detection of the deformation of liquid films. The reaction products change the local surface tension and induce Marangoni flow in the liquid film. As a model system, we consider the irradiation of the aliphatic hydrocarbon squalane with broadband deep-UV light. We developed a numerical model that quantitatively reproduces the flow patterns observed in the experiments. Moreover, we present self-similarity solutions that elucidate the mechanisms governing different stages of the dynamics and their parametric dependence. Surface tension changes as small as Δγ = 10-6 N/m can be detected, and time resolutions of <1 s can be achieved.

Preparation, characterization, and protein-resistance of films derived from a series of α-oligo(ethylene glycol)-ω-alkenes on H–Si(111) surfaces

Films on Si(111) were prepared by photo-activated grafting of CH₂&#xe001;CH(CH₂)m(OCH₂CH₂)nOCH₃ (m = 8, 9; n = 3–7) by using different vacuum conditions. High vacuum produced a higher thickness (40 Å) and <0.8% fibrinogen adsorption (C₁₀EG₇). Films were stable even after 28 days.

Chemical conversion of self-assembled hexadecyl monolayers with active oxygen species generated by vacuum ultraviolet irradiation in an atmospheric environment

Vacuum ultraviolet (VUV, λ = 172 nm) irradiation of alkyl self-assembled monolayers (SAMs) in the presence of dry air alters their surface properties. In this work, UV photochemically prepared hexadecyl (HD)-SAMs on hydrogen-terminated silicon substrates were irradiated by VUV light in dry air, which generated active oxygen species upon excitation of the atmospheric oxygen molecules. These active oxygen species converted the terminal methyl groups of the SAMs to polar functional groups, which were examined quantitatively by X-ray photoelectron spectroscopy (XPS) and chemical labeling. At the first stage of VUV irradiation, the surface of SAMs was functionalized, and the ratios of the generated polar functional groups markedly increased. With the elongation of the irradiation period, the SAMs gradually degraded, and the total polar group percentages gradually decreased. The difference between the oxygenated carbon components derived by the deconvolution of the XPS carbon (C1s) spectrum and the chemical labeling of polar groups revealed enormous quantities of ethereal and ester groups that cannot react with the labeling reagents but are included in the C1s spectral envelope. These modifications were reflected on morphological structures of SAMs, which were gradually distorted until a complete amorphous structure was obtained after the complete elimination of HD-SAMs.

Hydrophilic/hydrophobic film patterning by photodegradation of self-assembled alkylsilane multilayers and its applications

While the photopatterning of self-assembled monolayers (SAMs) has been extensively investigated, much less attention has been given to highly ordered multilayer systems. By being both thicker (0.5-2 μm) and more stable (cross-linked) than SAMs, patterned hybrid multilayers lend themselves more easily to the development of technology-relevant materials and characterization. This paper describes a facile two-step UV approach to patterning an alkylsilane multilayer by combining photoinduced self-assembly for multilayer synthesis and photodegradation through a mask for creating patterns within the film. In this second stage, a spatially resolved removal of the alkyl tail via a photooxidation mechanism took place, yielding regular and uniform silica microdomains. The result was a regular array of features (alkylsiloxane/silica) differing in chemical composition (hybrid/inorganic), ordering (crystal-like/disordered), and wettability (hydrophobic/hydrophilic). Such a photopatterned film was of utility for a range of applications in which water droplets, inorganic crystals, or aqueous polymer dispersions were selectively deposited in the hydrophilic silica microwells.

Microfluidic immunoassay with plug-in liquid crystal for optical detection of antibody

Recent advance in liquid crystal (LqC) based immunoassays enables label-free detection of antibody, but manual preparation of LqC cells and injection of LqC are required. In this work, we developed a new format of LqC-based immunoassay which is hosted in a microfluidic device. In this format, the orientations of LqC are strongly influenced by four channel walls surrounding the LqC. When the aspect ratio (depth/width) of the channel is smaller than 0.38, LqC orients homeotropically inside the microchannel and appears dark. After antigens bind to immobilized antibodies on the channel walls, a shift of the LqC appearance from dark to bright (due to the disruption of LqC orientation) can be visualized directly. To streamline the immunoassay process, a tubing cartridge loaded with a sample solution, washing buffers and a plug of LqC is connected to the microfluidic device. By using pressure-driven flow, the cartridge allows antigen/antibody binding, washing and optical detection to be accomplished in a sequential order. We demonstrate that this microfluidic immunoassay is able to detect anti-rabbit IgG with a naked-eye detection limit down to 1 μg mL(-1). This new format of immunoassay provides a simple and robust approach to perform LqC-based label-free immunodetection in microfluidic devices.

Cell patterning using a template of microstructured organosilane layer fabricated by vacuum ultraviolet light lithography

Micropatterning techniques have become increasingly important in cellular biology. Cell patterning is achieved by various methods. Photolithography is one of the most popular methods, and several light sources (e.g., excimer lasers and mercury lamps) are used for that purpose. Vacuum ultraviolet (VUV) light that can be produced by an excimer lamp is advantageous for fabricating material patterns, since it can decompose organic materials directly and efficiently without photoresist or photosensitive materials. Despite the advantages, applications of VUV light to pattern biological materials are few. We have investigated cell patterning by using a template of a microstructured organosilane layer fabricated by VUV lithography. We first made a template of a microstructured organosilane layer by VUV lithography. Cell adhesive materials (poly(d-lysine) and polyethyleneimine) were chemically immobilized on the organosilane template, producing a cell adhesive material pattern. Primary rat cardiac and neuronal cells were successfully patterned by culturing them on the pattern substrate. Long-term culturing was attained for up to two weeks for cardiac cells and two months for cortex cells. We have discussed the reproducibility of cell patterning and made suggestions to improve it.

Nano/microstructural effect of hydroxyapatite nanocrystals on hepatocyte cell aggregation and adhesion

Hepatocyte cell aggregation and adhesion to HAp nanocrystals covered with SU-8 polymer micropatterns by nano/microfabrication techniques is demonstrated. The surface roughness and wettability of the HAp nanocrystals are significantly different from those of the SU-8 polymer. QCM-D and microscopic observation clearly reveal that the cells realize the surface properties to form aggregation and preferentially adhere to the HAp nanocrystals at 2 h after seeding, indicating the importance of the microstructures as well as the interfacial phenomena at a nanometer scale.

Reusable hydroxyapatite nanocrystal sensors for protein adsorption

The repeatability of the adsorption and removal of fibrinogen and fetal bovine serum on hydroxyapatite (HAp) nanocrystal sensors was investigated by Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance with dissipation (QCM-D) monitoring technique. The HAp nanocrystals were coated on a gold-coated quartz sensor by electrophoretic deposition. Proteins adsorbed on the HAp sensors were removed by (i) ammonia/hydrogen peroxide mixture (APM), (ii) ultraviolet light (UV), (iii) UV/APM, (iv) APM/UV and (v) sodium dodecyl sulfate (SDS) treatments. FTIR spectra of the reused surfaces revealed that the APM and SDS treatments left peptide fragments or the proteins adsorbed on the surfaces, whereas the other methods successfully removed the proteins. The QCM-D measurements indicated that in the removal treatments, fibrinogen was slowly adsorbed in the first cycle because of the change in surface wettability revealed by contact angle measurements. The SDS treatment was not effective in removing proteins. The APM or UV treatment decreased the frequency shifts for the reused HAp sensors. The UV/APM treatment did not induce the frequency shifts but decreased the dissipation shifts. Therefore, we conclude that the APM/UV treatment is the most useful method for reproducing protein adsorption behavior on HAp sensors.

Photoimaging with singlet oxygen at the solid-air interface

Films of anthracene carboxylic acids were irradiated through photomasks and oxidized at the exposed regions by singlet oxygen upon sensitization. The efficiency of a photomask to protect the material underneath was investigated by optical and infrared spectroscopy. As the thickness of the film is reduced, the efficiency of the mask drops. This is explained by the migration of singlet oxygen at the solid-air interface, which in turn reacts at the masked area. For films with a thickness of <15 nm, the efficiency of the mask approaches zero; sufficient efficiency is achieved at thicknesses > 100 nm. From the investigations, it will become clear that the contrast between the irradiated and masked area of an image is affected by reduction of the film thickness. On the other hand, the resolution of an image, which relates to the minimum feature size of an image, is not dependent on the thickness of the film. The contributions of "inside" and "outside" reactions are examined separately, and a quantitative approximation of the spatial range of both modes of the oxygenation is given. We set up an approximate relation between mask efficiency and experimental conditions comprising internal and external oxygen diffusion, film thickness, and mask dimensions. These results give a deeper insight into the limits of resolution and contrast in singlet oxygen lithography.

Regulation of pattern dimension as a function of vacuum pressure: alkyl monolayer lithography

Photopatterning of a hexadecyl (HD) monolayer has been demonstrated using vacuum ultraviolet (VUV; lambda = 172 nm) light under controlled vacuum pressure with the objective of minimizing the pattern dimension. X-ray photoelectron spectroscopy (XPS) and lateral force microscopy (LFM) studies reveal that photodegradation of the HD monolayer not only is limited to the regions exposed to VUV but also spreads under the masked regions. The strong oxidants generated by VUV irradiation to atmospheric oxygen and water vapor diffuse toward the masked regions through the nanoscopic channels and photodissociate the monolayer under the masked area, near the photomask apertures, resulting in broadening of the photopattern. Such broadening decreases with decreased vacuum pressure inside the VUV chamber, associated with a decrease of oxidant concentration and reduction of their diffusion. Gold nanoparticles (AuNPs) were immobilized on the VUV patterned features to probe the dimension of the chemically active pattern. Field emission electron microscopy reveals the construction of 565 nm wide pattern features at a vacuum pressure of 10 Pa. This pattern widens to 1,030 nm at 10 (4) Pa using the same size apertures (500 nm) as printed on the photomask. This study provides insight for fabricating submicron patterns with high reproducibility and its exploitation for different applications, which includes the patterning of nanoparticles, biopolymers, and other nano-objects at submicron dimensions.

Polar and azimuthal alignment of a nematic liquid crystal by alkylsilane self-assembled monolayers: effects of chain-length and mechanical rubbing

Alkylsilane self-assembled monolayers (SAMs) on oxide substrates are commonly used as liquid crystal (LC) alignment layers. We have studied the effects of alkyl chain length, photolytic degradation, and mechanical rubbing on polar and azimuthal LC anchoring. Both gradient surfaces (fabricated using photolytic degradation of C18 SAMs) and unirradiated SAMs composed of short alkyl chains show abrupt transitions from homeotropic to tilted alignment as a function of degradation or chain length. In both cases, the transition from homeotropic to tilted anchoring corresponds to increasing wettability of the SAM surfaces. However, there is an offset in the critical contact angle for the transition on gradient vs unirradiated SAMs, suggesting that layer thickness is more relevant than wettability for LC alignment. Mechanical rubbing can induce azimuthal alignment along the rubbing direction for alignment layers sufficiently near the homeotropic-to-planar transition. Notably, mechanical rubbing causes a small but significant shift in the homeotropic-to-tilted transition, e.g., unrubbed C5 SAMs induce homeotropic anchoring, but the same surface after rubbing induces LC pretilt.

Stability of self-assembled monolayers on titanium and gold

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.

Direct photopatterning and SEM imaging of molecular monolayers on diamond surfaces: mechanistic insights into UV-initiated molecular grafting

We have used X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy, and field-emission scanning electron microscopy (SEM) to investigate the formation of single- and two-component molecular patterns by direct photochemical grafting of alkenes onto hydrogen-terminated diamond surfaces using sub-band gap 254 nm ultraviolet light. Trifluoroacetamide-protected 1-aminodec-1-ene (TFAAD) and 1-dodecene were used as model systems for grafting. Illumination with sub-band gap light can induce several different kinds of excitations, including creation of mobile electrons and holes in the bulk and creation of radicals at the surface and in the adjacent fluid, which induce grafting of the alkenes to the surface. SEM images of patterned molecular layers on nanocrystalline diamond surfaces reveal sharp transitions between functionalized and nonfunctionalized regions consistent with diffraction-limited excitation. However, identical experiments on type IIb single-crystal diamond yield a significantly more extended transition region in the molecular pattern. These data imply that the spatial resolution of the direct molecular photopatterning is affected by diffusion of charge carriers in the bulk of the diamond samples. The molecular contrast between surfaces with different terminations is consistent with the expected trends in molecular electron affinity. These results provide new mechanistic insights into the direct patterning and imaging of molecular monolayers on surfaces.

Strategies for controlled placement of nanoscale building blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others.

Single molecule adsorption at compositionally patterned self-assembled monolayers on gold: role of domain boundaries

This paper examines the single-molecule adsorption of YOYO-I-labeled lambda-DNA at compositionally patterned self-assembled monolayers (SAMs). The interactions of fluorescently labeled lambda-DNA molecule with the patterned SAMs, which are comprised of different functional groups (i.e., amine-, alcohol-, and acid-terminated thiolates), were monitored at optically transparent gold films using total internal reflection fluorescence microscopy. The role of solution pH, lambda-DNA concentration, and domain size was investigated. In addition to delineation of the relative adsorption strength as a function of terminal group identity (NH2 > COOH > OH), the potential importance of structural defects was also revealed. The latter result, found both at the disordered boundaries between domains and at adlayers in which structural order was affected by the length of the alkyl chain, points to the subtle but preferential adsorption of the "sticky ends" of lambda-DNA. These experiments also detected an intriguing dependence of adsorption with respect to domain size.

Micropatterning of biomolecules on glass surfaces modified with various functional groups using photoactivatable biotin

Biomolecule patterning by photolithographic methods has considerable advantages because a large number of different biomolecules can be assembled on a spatial area by a combinatorial method and complex biomolecule patterning can be created in situ in closed environments such as microfluidic channels. Here, a photobiotin was used as the photoactivatable reagent to create patterned arrays of biomolecules. The variability of photobiotin deposition on glass substrates modified with a variety of materials having carboxyl, lysine, aldehyde, amine groups, and BSA (bovine serum albumin) was characterized by subsequent derivatization with Cy3-labeled streptavidin. The fluorescence images of the photobiotin patterned glass surfaces showed that the BSA/aldehyde-coated glass could be considered as the most appropriate substrate to immobilize photobiotin, in view of the homogeneous immobilization of biomolecules with high density in defined regions and the reduction of nonspecific binding to the surface. In streptavidin equilibrium adsorption assays, the maximum amount of streptavidin-Cy3 bound to the BSA/aldehyde-coated glass surface continued to rise with increasing streptavidin-Cy3 concentration until 12.0 microg/mL was reached and the surface then became saturated. Also, a line array of biotin-labeled single-strand probe DNAs was created on the BSA/aldehyde-coated glass by photolysis of photobiotin through a slit-type mask and biotin/streptavidin/biotin chemistry, extended to a quantitative measurement of the concentrations of target DNA. The results of target DNA analysis showed linearity over a wide range from 0.5 ng/mL to 5 microg/mL and were reproducible.