Hydrophilic Glass Substrates Research Articles

Unlocking the potential of supramolecular polymers with bimodal molecular weights for instant and strong underwater adhesion

Developing adhesives suitable for underwater environments remains a formidable challenge due to the barrier presented by water, hindering contact between the adhesive and adherend. In this work, supramolecular adhesives prepared by mixing low and high molecular weight poly(butyl acrylate)-based copolymers are manifested to function effectively for underwater adhesion regardless of substrates’ affinity to water. Optimization of adhesion performance is achieved by manipulating the copolymer composition, resulting in the remarkable adhesion strengths of 1290 N m-1 and 1047 N m-1 to hydrophobic PET and hydrophilic glass substrates, respectively. The observed high underwater adhesion is attributed to a synergistic effect: instant and efficient removal of the hydration layer facilitated by the low molecular weight polymer strands, and mechanical resilience conferred by the high molecular weight strands featured by chain entanglements. Adequate interfacial interactions are attained by the supramolecular interactions including cation-π and π-π bonding. Notably, owing to its inherent hydrophobicity, the adhesive can be stored underwater for over a week and still displays 842 N m-1 peel strength to glass substrate. This work unlocks the potential of supramolecular adhesives with bimodal molecular weight distribution for instant and strong underwater adhesion, providing a straightforward yet scalable strategy to produce high-performance underwater adhesives.

Effect of Particle-Substrate Interactions on Colloidal Layer Structure Prepared by Convective Self-Assembly Using Polyelectrolyte-Grafted Silica Particles.

Cationic and anionic polyelectrolytes, poly(vinylbenzyl trimethylammonium chloride) (PVBTA) and poly(sodium styrene sulfate) (PSSS), were grafted on the surface of the silica particles, respectively, and then these two types of polyelectrolyte-grafted silica particles were applied to the colloidal layer preparation by convective self-assembly (CSA) using hydrophilic or hydrophobic glass substrates to investigate the effect of the interactions between the particles and the substrate surface on the resultant layer structures. When the PVBTA-grafted silica particle (PVBTA-Si) was used, the colloidal monolayers with a non-close-packed (NCP) structure were formed on both hydrophilic and hydrophobic glass substrates, where the NCP colloidal layers on the hydrophobic glass substrate have a somewhat more ordered structure than those on the hydrophilic glass substrate. In the case of the PSSS-grafted silica particle (PSSS-Si), on the other hand, stripe patterns with close-packed (CP) colloidal layers were obtained on both types of the glass substrates. The number of layers of the stripes on the hydrophilic glass substrate was less than that on the hydrophobic glass substrate, while the spacing and width of the stripes on both substrates were similar to each other. The difference in the structures of the colloidal layers obtained here indicates that an attractive interaction, such as an electrostatic attraction and a hydrophobic interaction, between the particle and the substrate surface is necessary to achieve the NCP structure by the CSA process using polyelectrolyte-grafted silica particles.

Selective visual detection of multiplex PCR amplicon using magnetic microbeads

Nucleic acid amplification tests (NATs), such as genetic tests using polymerase chain reaction (PCR), are sensitive methods for detecting pathogens and food contamination. The rapid, easy, and inexpensive detection of amplicons, DNA, or RNA is key to realizing on-site NATs. We have previously developed a novel amplicon detection method using magnetic microbeads based on the hydrophobicity of DNA in deionized water. In this study, we aimed to expand the method for the detection of multiplex DNA amplicons. Tagged primers and probes for selective attachment were used to detect amplicons from two strawberry pathogens. The amplicon-labeled magnetic microbeads were placed in the round-bottom well of a hydrophilic glass substrate. The attachment of amplicons to the magnetic microbeads changed their surface from hydrophilic to hydrophobic. The magnetized microbeads concentrated at the bottom when the substrate was placed on a permanent magnet, and the concentrated microbeads were easily recognizable by the naked eye. Microbeads without amplicons were adsorbed over a broad area of the bottom of the glass well owing to their hydrophilicity. The appropriate tag probe was attached to specific amplicons for detection, and each amplicon from multiplex PCR was selectively detected within approximately 15 min. Notably, this method requires no electric power and contributes to the realization of on-site NAT detection. This study presents a simple and rapid method for the selective detection of multiplex PCR amplicons using DNA–DNA hybridization.

Influence of hydrophobic particles on the film drainage during bubble–solid interaction

In this article, we investigate the complex drainage behavior of liquid (“dimple”) films entrapped between hydrophilic glass substrates and air bubbles in water and aqueous suspensions of polystyrene (PS) particles. The film drainage was monitored by capturing the evolution of spatial-temporal thicknesses using interferometry. Faster drainage of the entrapped film is observed in the PS colloid suspensions compared to the water. The film drainage strongly depends on the interface boundary conditions. Our experiments reveal that the air–liquid interface of the entrapped film becomes partially mobile in the PS suspensions, which results in faster drainage. The hydrophobic PS particles tend to migrate toward the air–water interface and form an ordered layer. We argue that the adsorbed layer of PS particles makes the bubble surface elastic, delaying the formation of the immobile interface.

Assessing the Influence of Polymer-Based Anti-Drift Adjuvants on the Photolysis, Volatilization, and Secondary Drift of Pesticides after Application

One practice to reduce spray drift during pesticide application is the addition of certain chemical adjuvants to spraying solutions, which change their physicochemical properties and result in larger droplets. The environmental impact of these agrochemicals continues however also after application, depending on surface processes occurring upon treated surfaces. While the impact of anti-drift adjuvants has been studied regarding spray drift, their impact on the fate of deposited pesticides has received little attention. Here, the effect of a polymer-based adjuvant (polyacrylamide) on the photolysis and evaporation rates of pyrimethanil (common fungicide) from dry films were investigated under controlled laboratory conditions and during two field studies. The laboratory results indicate that the adjuvant enhances the volatilization and photolysis rate both on hydrophobic lemon leaves and hydrophilic glass substrates. These results can be attributed to an increase in the geometrical area of residual film and a widening of its circumference rim, where solutes are likely to concentrate, when generated from adjuvant-containing droplets. Such morphological differences may enhance the exposure of deposited pesticides to interact with the overlaying atmosphere and incident radiation. The field data was less conclusive, suggesting a small impact of the anti-drift adjuvant on the fungicide’s secondary drift from crops and an even lower effect on volatilization from bare soil.

Periodic stacking of two dimensional Bismuth bi-layers in Bismuth stearate thin films

Investigations of single and bilayers of bismuth are one of the most thrusting areas of research in contemporary condensed matter physics and material sciences. This is because such ultrathin layers of bismuth host interesting exotic electronic properties, which are important from both fundamental science and future application perspectives. In the past, many inorganic processes for the synthesis of single and bi-layers of bismuth were reported using physical and chemical vapor deposition techniques. The ultrathin films deposited are found to interact electronically with the substrates due to their proximity to the substrate surface. We introduce a new and easy organic channel for the synthesis of the bismuth multi-bilayers in ambient conditions. Bismuth stearate multi-bilayer thin films are deposited on the hydrophobic silicon and hydrophilic glass substrates using the Langmuir-Blodgett technique. Optical absorption spectroscopy measurements in the infrared region provided information on various bond structures present in those bismuth stearate thin films. Specular x-ray reflectivity (XRR) experiments and their analysis of such thin films unambiguously show the highly periodic stacking of bismuth bilayers along the surface-normal directions within the multilayer film structure. Model-based microstructural analysis of the XRR data further shows that each bilayer of bismuth is well separated (3.5 nm) from other bismuth bilayers by hydrocarbon chains. At these separations, the electronic states of the bismuth bilayers are expected to be non-interacting with each other. The morphology of the surface obtained from field emission scanning electron microscopy supports the XRR analysis. A bandgap of 3.2 eV was obtained for such bismuth stearate thin films from the optical spectroscopy measurements in the UV-visible range. The large separations between the bismuth-bilayers and between the substrate and the bismuth bilayers are expected to minimize the electronic interactions between them.

Healthy and Pathological Porcine Blood Drop Evaporation: Effect of the Temperature.

This study aims to understand and compare the evaporation dynamics of drops of healthy and pathological porcine blood (glomerulonephritis disease) evaporated on hydrophilic glass substrates at different surface temperatures (Ts): 23, 37, 60, and 90 °C. Subsequently, the different induced phenomena are characterized and described. Additionally, drops of water were evaporated at these four surface temperatures to better understand the difference between healthy and pathological porcine blood. Statistical studies were performed to analyze the evaporation rate, the maximum and average values of Marangoni numbers (Ma), and the evaporated specific time. The statistical tests showed significant differences in these parameters between healthy and pathological blood for each surface temperature. The mean and the maximum of the Ma increase with the increase in Ts caused by the increase in the temperature differences between the edge and the center of the drop. When comparing healthy and diseased blood, the Ma maximum and mean of healthy blood were higher than those of diseased blood for all Ts. Besides, this study emphasizes the influence of temperature on blood evaporation and the pattern caused by the Marangoni effect. These results demonstrate that differences between the two blood types are related to the disease and pave the way to developing a new methodology for medical decision-making.

Coacervation and adhesion mechanism of PEI/TA hydrogel revealed by molecular dynamics simulations.

Coacervate-derived polyethyleneimine (PEI)/thioctic acid (TA) hydrogels can efficiently repel interfacial water and achieve robust underwater adhesion on diverse substrates, thus representing a promising material for a wide range of biomedical uses such as wound dressings, hemostatic agents, drug carriers, and tissue repair. Understanding the cohesion and adhesion dynamics in this coacervate-to-hydrogel strategy is critical for the development of underwater bioadhesive. However, these mechanisms remain obscure due to the difficulty of obtaining the atomic details. In this work, we first applied quantum calculations and classical mechanics models to obtain accurate force field parameters for PEI and TA. Based on the refined force field, we employed microsecond-long all-atom molecular dynamics (MD) simulations to investigate the coacervation of PEI/TA complex and its adhesion on glass and polypropylene. Our simulations revealed that the phase transition in PEI/TA coacervation was jointly achieved by two types of aggregation, i.e., TA-TA aggregation through hydrophobic associations and PEI-TA aggregation driven by electrostatic interactions. In addition, MD simulations further depicted the distinct adhesion modes of PEI/TA on the two substrates. TA assembled on top of the hydrophobic polypropylene substrate, replacing the interfacial water, whereas PEI amines penetrated the interfacial water to directly bind to the silanols of the hydrophilic glass substrate. The tight adhesion of PEI/TA hydrogel was then quantified by the diffusion coefficient of molecular moieties, which reflected the extremely low mobility of the bound moieties. These findings deepen our understanding of the formation and adhesion of PEI/TA hydrogel at the atomic level and provide guidance for the future design of advanced bioadhesive for potential clinical applications.

Semicrystalline Polymer Micro/Nanostructures Formed by Droplet Evaporation of Aqueous Poly(ethylene oxide) Solutions: Effect of Solution Concentration.

Deposits formed after evaporation of sessile droplets, containing aqueous solutions of poly(ethylene oxide), on hydrophilic glass substrates were studied experimentally and mathematically as a function of the initial solution concentration. The macrostructure and micro/nanostructures of deposits were studied using stereo microscopy and atomic force microscopy. A model, based on thin-film lubrication theory, was developed to evaluate the deposit macrostructure by estimating the droplet final height. Moreover, the model was extended to evaluate the micro/nanostructure of deposits by estimating the rate of supersaturation development in connection with the driving force of crystallization. Previous studies had only described the macrostructure of poly(ethylene oxide) deposits formed after droplet evaporation, whereas the focus of our study was the deposit micro/nanostructures. Our atomic force microscopy study showed that regions close to the deposit periphery were composed of predominantly semicrystalline micro/nanostructures in the form of out-of-plane lamellae, which require a high driving force of crystallization. However, deposit central areas presented semicrystalline micro/nanostructures in the form of in-plane terraces and spirals, which require a lower driving force of crystallization. Increasing the initial concentration of solutions led to an increase in the lengths and thicknesses of the out-of-plane lamellae at the deposits' periphery and enhanced the tendency to form spirals in the central areas. Our numerical study suggested that the rate of supersaturation development and thus the driving force of crystallization increased from the center toward the periphery of droplets, and the supersaturation rate was lower for solutions with higher initial concentrations at each radius. Therefore, periphery areas of droplets with lower initial concentrations were suitable for the formation of micro/nanostructures which require higher driving forces, whereas central areas of droplets with higher initial concentration were desirable for the formation of micro/nanostructures which require lower driving forces. These numerical results were in good qualitative agreement with the experimental findings.

Adhesion of Individual Attachment Setae of the Spider Cupiennius salei to Substrates With Different Roughness and Surface Energy

Dynamic adhesion is a key ability for animals to climb smooth surfaces. Spiders evolved, convergent to geckos, a dry adhesive system made of setae branching into smaller microtrichia ending as spatulae. Several previous studies concentrated either on the whole adhesive claw tuft on the spider´s foot that consists of attachment setae or on the single adhesive contact elements, the microtrichia with spatula-shaped tips. Here, the adhesion of single setae of the spider Cupiennius salei was examined and the morphology of the pretarsus and the fine structure of the setae were studied in further detail. Using individual setae fixed to force sensing cantilevers, their adhesion at different contact angles with a glass substrate was measured as well as their adhesive performance on substrates with different roughness and on smooth surfaces with different surface energies. The results show an individual variability of the adhesive forces corresponding to the seta morphology and especially to the seta tip shape. The tip shapes of the setae vary largely even in neighboring setae of the pretarsal claw tuft that comprises approximately 2,400 setae. Regarding surface energy of the substrate, the adhesion force on hydrophobic polytetrafluoroethylene was 30% of that on a hydrophilic glass substrate, which points to the importance of both van der Waals interactions and hydrogen bonds in spider adhesion.

Long Rod-Like Liquid Crystal Containing Azobenzene and the Applications in Phase-Transition Regulation and Orientation of Nematic Liquid Crystal

Phase-transition and orientation of liquid crystal (LC) are two crucial factors for LC application. In this work, a long rod-like LC compound containing double azobenzene (M1) is successfully designed and synthesized. The combing technologies of nuclear magnetic resonance (1H NMR, 13C NMR) and Fourier transform infrared spectroscopy (FTIR) are used to identify the chemical structure of the molecule. Additionally, the polarized optical microscopy (POM), differential scanning calorimetry (DSC), and one-dimensional wide-angle X-ray diffraction (1D WAXD) experimental results show that M1 exhibits an ultrawide range of LC phases and a stable LC structure even at ultrahigh temperature, which indicates that this LC can be applied in some especial devices. Further, the compound M1 is used to tune the LC temperature range of the commercial LC 4-cyano-4′-pentylbiphenyl (5CB). A series of samples 1–7 are obtained through doping different contents of M1, which show different LC temperature ranges that are dependent on the composition ratio of M1 and 5CB. More interestingly, all resultant samples show spontaneous vertical orientation on the hydrophilic glass substrate. Meanwhile, due to the effect of azobenzene in the compound M1, a reversible transition between homeotropic to random orientation of the LC molecules is achieved when these LC cells are alternately exposed to UV irradiation and visible light, which implies that this material shows potential application in especial display and optical storage technologies.

Design, Fabrication, and Analysis of a Capillary Diode for Potential Application in Water-Oil Separation.

A capillary device is designed and fabricated in glass to work as a fluidic diode with vanishingly small hydrodynamic conductance for imbibition of water within a finite range of immersion depths. This is attained through patterning a section of predefined length on the device surfaces using a single-step laser-based ablation process and without resorting to chemical treatment of the hydrophilic glass substrate. While the studied device works as a fluidic diode for water, it can behave as a conventional capillary slit for the imbibition of oils (e.g., alkanes, silicone oils) with low surface tension. A prototype device with simple geometric design is demonstrated for selective adsorption and separation of water and oil in vertical imbibition experiments at controlled immersion depths. Efficient devices for passive separation of water and oil can be designed based on the demonstrated physical mechanism and the analytical model proposed in this work.

Two-step filter-free phase-shifting interferometry and its application in quantitative phase imaging of a droplet evaporation with different evaporation modes

By combining a dual-channel phase-shifting interferometry (DCPSI) system and two-step filter-free phase-shifting phase retrieval (TFPS) algorithm, we achieve the quantitative phase imaging of a regular droplet evaporation on the hydrophilic glass substrate with low contact, moreover, the relevant physical parameters including the topographic information, contact radius, contact angle, height and volume are accurately calculated under two kinds different evaporation modes (constant contact radius (CCR) and constant contact angle (CCA)). Furthermore, it is found that the proposed TFPS based DCPSI method is also suitable for the quantitative phase imaging of irregular droplet evaporation. Importantly, for random phase shifts and without filtering in advance, this TFPS based DCPSI method reveals high accuracy in phase extraction of dynamic process, and this will supply a powerful tool for the kinetic analysis during a droplet evaporation or fluid flow with micro-scale variation.

Large fragmentation under drop suspension splashing

In our work, we first experimentally checked whether the existing splashing criteria would work for droplets of dilute suspensions with particles 10 μm in diameter. The suspensions were a mixture of aqueous glucose solution with isodense hydrophilic polystyrene particles. The drop splashing of the suspensions began at lower impact velocities than for pure water under the impact onto hydrophilic flat glass substrates. The splashing of such suspensions could not be described by any of the existing criteria — neither for a pure liquid with effective viscosity nor by using criteria that consider the energy balance of separately escaping particles. Analysis of the escaping fragments showed that their diameter was an order of magnitude larger than the particles’ diameter. Taking into account the size of the escaping fragments in the criterion based on energy balance allowed to predict the splashing of the considered suspensions.

Analysis of profile and morphology of colloidal deposits obtained from evaporating sessile droplets

We experimentally investigate the profile and morphology of the ring-like deposits obtained after evaporation of a sessile water droplet containing polystyrene colloidal particles on a hydrophilic glass substrate. In particular, the coupled effect of particle size and concentration are studied. The deposits were qualitatively visualized under an optical microscope and profile of the ring was measured by an optical profilometer. The profile of the ring resembles a partial torus-like shape for all cases of particles size and concentration. The cracks on the surface of the ring were found to occur only at smaller particle size and larger concentration. We plot a regime map to classify three deposit types - discontinuous monolayer ring, continuous monolayer ring, and multiple layers ring - on particles concentration - particle size plane. Our data shows a possible existence of a critical concentration (particle size) for a given particle size (concentration) at which the monolayer ring forms. For the larger particle sizes, the immersion capillary forces between the particles dominate, aiding the formation of a monolayer ring of the particles. We measure the width and height of the ring and show that they scale with particle concentration by a power law for the multiple layers ring. This scaling corroborates with an existing continuum based theoretical model. We briefly discuss the effect of the interaction of growing deposit with shrinking free surface on the ring dimensions and profile. The present results aid understanding of the ring formation process and will be useful in guiding the design of self-assemblies of the colloidal particles formed by the evaporating droplets.

Reconfigurable and Permanent Wetting Patterns on Polymer Surfaces Obtained Using Plasma Oxidation and Laser Ablation

Abstract Smart surfaces with preferably reconfigurable wetting properties can lead to key applications in labon- a-chip analytical and preparative systems. In this paper, we present our recent results obtained using polymer surfaces whose wetting properties are modified in a permanent manner using laser ablation and in a reconfigurable manner using plasma oxidation. Polydimethylsiloxane (PDMS) diluted in solvent is used as the polymeric material coated over microscope glass slides in our studies. In the first part, the tracks of ~ 70 μm width are defined over the surface by surface oxidation using cold plasma exposure through a microfluidic channel. In the second part, femtosecond laser micromachining is used for selective removal of polymer coating and uncovering the hydrophilic glass substrate. We experimentally demonstrate guiding of water in the form of filaments and droplets over the obtained hydrophilic tracks of ~ 110 μm. We also discuss preliminary experiments to coat light sensitive azobenzene over a glass substrate with the help of a silane in order to achieve reversible isomerization upon periodic exposure to UV/vis radiation. Furthermore, we elaborate advantages, challenges and the significant role of such patterned surfaces in future applications.

Inkjet printing for localized coating and functionalization of medical devices

Abstract Inkjet printing has become essential for pharmaceutical research as well as biomedical applications. It is a promising tool to meet future challenges in patientindividual designed pharmaceuticals and implants. In this context, the main areas of use are high-throughput screening (HTS), drug-loaded microparticles, drug formulation and oral dose development, 3D-printing/bioprinting as well as coating of implants. This study deals with the latter. In view of promising applications for localized coating and functionalization of implant surfaces this work shows preliminary results on inkjet printing of the polymer poly(2- ethyl-2-oxazoline) (PetOx), a protein repellent polymer (PRP). To deposit single droplets with small volumes (~500 pl) of aqueous PetOx solution (50 g/l), printing parameters were determined for the piezo-driven drop-ondemand inkjet printhead NanoTip J, operating in a Nanoplotter 2.1 (both from GeSiM mbH, Germany). Different printing strategies are demonstrated by varying droplet spacing and drying time while printing on hydrophilic glass substrate. Printing and stacking of almost uniform polymer lines (width ~ 200 μm) is demonstrated.

Controlling the hydrophilicity and cohesion during deposition of highly oriented type I collagen films: An approach for biomedical applications

Using the Langmuir-Blodgett (LB) technology we have pioneered a straightforward and low-cost approach to fabricate highly oriented collagen in thin film format (thickness: ~20 nm, surface areas: 2.5 × ~6.0 cm). An important factor for the use of these films is their cohesion under various conditions. Film formation was studied by coating hydrophilic or hydrophobic glass substrates. The fresh or aged (2 1/2 years, −18 °C.) collagen solutions used for this purpose either contained collagen network-stabilizing agents (n-propanol or phosphate ions) or were prepared without these stabilizers. Film formation on the air/water interface was analyzed by pressure-area isotherms. Maximum surface pressures were ~4–7 mN/m and ~10–18 mN/m for isotherms using n-propanol or phosphate buffer saline (PBS), respectively, versus ~0.4–0.8 mN/m without using a stabilizer; with higher surface pressures for the combination fresh solution/n-propanol or aged solution/PBS. Deposited films were studied by optical and electron microscopy and fast Fourier transform analysis. Coatings (to both substrate types) exhibit a defined orientation of collagen aggregates within a matrix of oriented collagen when freshly made or aged collagen solutions were used and n-propanol was present during film formation. The higher degree of hydrophilicity of the aged solution does not adversely affect the cohesion and collagen orientation during film formation. Using physiological phosphate ions shows that deposition of defect-free and oriented collagen (on both substrate types) is only possible using fresh collagen solutions. Unlike n-propanol-containing solutions, films were most stable using hydrophilic glass substrates. Film formation failed in the absence of network stabilizers. Controlling the cohesion via (a) the water accessibility of collagen structures, (b) specific network stabilizers and (c) substrate properties enables tunable film characteristics for future biomedical approaches.

Characterizing self-assembly and deposition behavior of nanoparticles in inkjet-printed evaporating droplets

The self-assembly and deposition mechanisms of nanoparticles in droplets on a substrate are of significant importance in many inkjet printing-based industrial applications such as microelectronics, display systems, and paint manufacturing. However, a comprehensive investigation into the velocity field of fluid and its accompanying particle transport behavior in injected droplets undergoing immediate evaporation has not been conducted. In this study, we describe the underlying mechanisms of the self-assembly and deposition behavior of nanoparticles in inkjet-printed, evaporating droplets by visualizing the internal fluid flows. We additionally characterize the relationship between the internal fluid flows and nanoparticle patterns by changing not only the wettability and temperature of the substrate, but also the chemical composition of nanoparticle suspensions. We verify that Marangoni flow generated on a hydrophobic PDMS substrate with a contact angle (CA) of >90° helps the formation of dome-shaped nanoparticle structures, while radially outward flow generated on a hydrophilic glass substrate with a CA of <10° produces either mono-layered and flat, or ring-shaped nanoparticle structures, depending on the number density of the suspension. The presented characterization results provide not only valuable mechanistic insights, but also practical guidelines for inkjet printing-based nanoparticle applications.

Surface-enhanced Raman spectroscopy substrate based on Ag-coated self-assembled polystyrene spheres

The silver (Ag) films were deposited on the monodispersed polystyrene spheres that were drop-coated on hydrophilic glass substrates in order to form a self-assembled 2D monolayer. Thus prepared Ag films over polystyrene nanospheres (AgFONs) were used to record the surface-enhanced Raman scattering (SERS) spectra of rhodamine 6G (R6G) and pyridine (λex = 514.5 nm). AgFONs were prepared by depositing 120, 180 and 240 nm thick Ag layer on the 1000 nm polystyrene spheres and 80, 120, 160 and 200 nm thick Ag layer on the 350 nm spheres as well as on their mixture (350 + 1000 nm). The silver was deposited by electron beam evaporation technique. The best enhancement of the Raman signal for both test molecules was obtained using 180 nm Ag film deposited on the 1000 nm spheres and using 80 nm Ag film deposited on the 350 nm polystyrene spheres. The lowest detectable concentrations of R6G and pyridine were 10−9 mol L−1 and 1.2 × 10−3 mol L−1, respectively. This study has shown that AgFONs could be regarded as good and reproducible SERS substrate for analytical detection of various organic molecules.