Search

We describe a highly sensitive, substrate-specific, label-free, and multiplexed protease assay which reports proteases activities as an optical bar chart, allowing test results to be easily assessed by laymen with the naked eye. First, an oligopeptide microarray having six rows of immobilized oligopeptides, with well-controlled orientations and concentration gradients, is immersed in a buffer solution containing proteases. Then, a thin layer liquid crystal is supported on the microarray to transduce the oligopeptide cleavage event into an optical bar chart of different colors and lengths. This type of optical bar chart provides very rich information such as protease concentration, incubation time, surface densities of oligopeptides, etc. Both trypsin and chymotrypsin can be detected by using this assay within 3 h. The capability of the multiplexed protease assay opens up possibilities for detecting toxins such as botulinum neurotoxins which are known to cleave proteins and affect the docking and fusing synaptic vesicles.

In this article, we report a quartz crystal microbalance (QCM)-based detection method which allows the identification and quantification of two neonicotinoid pesticides, imidacloprid and thiacloprid, in aqueous solutions and celery juice. To achieve high selectivity, molecular imprinted monolayers (MIMs), which can either recognize 1 [micro]M of imidacloprid or 1 [micro]M of thiacloprid, are prepared from alkanethiols self-assembled on QCM sensor chips with preadsorbed templates (either imidacloprid or thiacloprid). Our experimental results show that the detection limit can be improved by using alkanethiols having longer hydrocarbon chains. For example, MIMs prepared from hexadecanethiol have dissociation constants 2-5 times smaller than those prepared from octanethiol. To detect two neonicotinoids in vegetable samples simultaneously, we also develop a new type of MIM with two different templates. A single QCM decorated with this MIM can respond to 10 [micro]M of imidacloprid and 10 [micro]M thiacloprid in celery juice in a real-time manner.

Electrospun polymer-liquid crystal (PLC) fibers have potential applications such as wearable sensors and adaptive textiles because of their rapid response and high flexibility. However, existing PLC fibers only have a narrow responsive range and poor resistance to heat and chemicals. Herein, a new type of PLC fiber is prepared by using a coaxial electrospinning process. The core solution is 4'-pentyl-4-biphenylcarbonitrile (5CB), and the sheath solution is a mixture containing 13 wt % PVP and 10 wt % reactive mesogen (RM). After UV exposure of the fibers, 5CB in the core and RM diffusing from the core are cross-linked into an LC polymer. The fibers have a highly uniform morphology with an average diameter of 3.2 ± 0.5 μm, and mesogens inside the fibers align unidirectionally with the long axis of the fibers. The fibers show a broad phase-transition temperature range between 13.5 and 155.5 °C and have a response time of less than 10 s. The temperature range can also be controlled by adjusting components in the electrospun fibers and UV exposure time. The core-sheath fibers prepared in such a manner exhibit excellent heat and chemical resistance with reversible optical responses. Moreover, when the fibers are exposed to volatile organic compounds (VOCs) such as toluene, the fibers show a rapid optical response to toluene vapor within 25 s. This study demonstrates that the fibers are potentially useful for preparing flexible temperature and chemical sensors.

Millifluidic devices decorated with enzymes have been used for enzymatic reactions in continuous processes, but low enzymatic activity and enzyme leaching remain as challenges. Herein, we develop a strategy to embed cross-linked enzyme aggregates (CLEAs) on the surfaces of millifluidic devices to achieve higher enzymatic activity and better stability. Catalase was chosen as a model enzyme to degrade H 2 O 2 in wastewater samples. First, CLEA of catalase (153 ± 10 nm) was formed by simultaneous precipitation and cross-linking with 25.0 wt % acetonitrile containing 0.025 wt % glutaraldehyde in a millifluidic device. To immobilize CLEA, we first swell a piece of plastic tubing by using 5.0 wt % acetonitrile and then immerse it in an aqueous solution with 5.0 wt % (3-aminopropyl)triethoxysilane (APTES) and 5.0 wt % dextran polyaldehyde (DPA) subsequently. After CLEA is absorbed inside the expanded polymer network of the tubing, the tubing is tightened by using a vacuum to secure the immobilized CLEA. The millifluidic device decorated with CLEA of catalase has total activity of 660 U for degradation of H 2 O 2 , and it shows good stability under a flow rate of 200 μL/min. The tubing can be used to degrade 0.1 wt % H 2 O 2 solution continuously for 3 h or remove 2 wt % residual H 2 O 2 in wastewater for 2 h. The technique is general enough and can be applied to other types of enzymes for continuous enzymatic reactions.

Immobilized enzymes can be used to catalyze biochemical reactions in a batch process, however, it is more difficult to use them in a continuous process. Herein, we develop an enzyme immobilization technique for flexible tubing surfaces, which can be used to catalyze biochemical reactions in a continuous process. In this technique, the tubing is first treated with (3-aminopropyl)triethoxysilane at 50 °C and baked at 100 °C in vacuum to form a network of reactive amine functional group on the inner tubing surface. Subsequently, dextran polyaldehyde, a polymeric cross-linker, is used to immobilize crude protease extract and catalase for hydrolyzing casein and degrading H 2 O 2 , respectively, in a continuous process. The immobilized proteases are highly stable even after a long-term storage at 4 °C. After 12 weeks of storage, 90% of the original protease activity can be preserved. Meanwhile, the immobilized catalase is able to degrade 0.1% H 2 O 2 solution flowing at 5 μL/min. The immobilization technique is potentially useful for bioassays and industrial wastewater treatments when continuous processes are preferred.

Microparticles sitting at interfaces formed by a liquid crystal (LC) and water are known to self-assemble into distinct patterns. In this study, we observed that poly(ethylenimine)- (PEI-) coated microparticles are able to self-assemble at LC/water interfaces decorated with surfactants such as Tween 20 and sodium dodecyl sulfate (SDS). Interestingly, assemblies of microparticles strongly depend on the types of surfactants used and how surfactants adsorb on the PEI-coated microparticles. For example, adsorption of Tween 20 on the PEI-coated microparticles causes the microparticles to form short chains that follow the director field of the LC. In contrast, adsorption of SDS causes the microparticles to assemble into circular rings that encompass domains saturated with SDS. Such surfactant-driven assembly of microparticles offers a possible method for directing the assembly of microparticles. It can also be applied for the visual detection of lipases that hydrolyze Tween 20 in water.

Human chorionic gonadotropin (hCG) is an important biomarker for the diagnosis of pregnancy and cancers. In this study, we report an antibody-free and label-free mechanism for detecting hCG. To replace enzyme-labeled antibodies, we use a short oligopeptide as an hCG receptor to bind hCG. The short oligopeptide sequence, (N-)PPLRINRHILTR(-C), is identified after 5 rounds of screening by use of a phage library. After binding, liquid crystal (LC) is used to transduce the binding event into optical signals. The captured hCG can disrupt a thin layer (~6 μm) of LC covered on the surface. Depending on the initial concentration of hCG, LC gives distinct optical signals visible to the naked eye. The limit of detection (LOD) for this method is approximately 1 IU/mL (2 nM) in both phosphate-buffered saline and urine samples, and only 0.6 μL of hCG solution is required. This means that as little as 45.5 pg of hCG can be detected by this method. Compared to other detection methods for hCG, this detection method does not require the use of antibody and is label-free. It has the potential to become a portable diagnostic kit for hCG.

We report a surface plasmon resonance (SPR) biosensor for online detection of glyphosate. The surface of the sensing element is decorated with an oligopeptide, TPFDLRPSSDTR, which is identified by using phage display library. This oligopeptide shows high binding specificity for glyphosate (KD = 8.6 μM), probably because of the presence of R and D in the oligopeptide. To detect glyphosate in buffer solution, an SPR gold sensor chip is modified by using the oligopeptide with a surface density of 0.6 1/nm(2). The sensitivity of this oligopeptide-functionalized SPR biosensor is 1.02 RU/μM whereas the limit of detection (LOD) is 0.58 μM. This oligopeptide functionalized SPR biosensor also shows good specificity against other analytes such as glycine, thiacloprid, and imidacloprid.

In this paper, we report the integration of liquid crystal (LC) dots on microfluidic channels as microscopic protein sensors. Flexibility of patterning LC dots on a surface to fit small microfluidic channels is achieved by using inkjet printing technology. These LC dots (1 pL) remain stable when they are subjected to flowing buffer solution at a high flow velocity (v ≥ 0.198 cm/s). When the buffer solution contains protein, such as bovine serum albumin (BSA), it causes a change in the orientational ordering of the LC dots as indicated by a distinct dark-to-bright transition in the optical appearance of the LC dots. Moreover, we are able estimate the concentration of BSA by simply counting the number of bright LC dot sections. This microscopic protein sensor has potential applications in the real-time detection and quantification of proteins in aqueous solutions. This detection method is advantageous because protein labeling and complex instrumentation are not required.

Recently, liquid crystal (LC) droplets in aqueous solutions have become a new platform for chemical and biological sensing applications. In this work, we present a two-step method to generate monodisperse LC droplets in aqueous solutions for sensing applications. In the first step, we exploit inkjet printing to dispense uniform LC droplets on a solid surface. Uniform LC droplets, ranging from 35 to 136 μm in diameter, can be prepared by printing multiple times on the same spot. In the second step, we flush the LC droplets with a stream of aqueous solution in an open rectangular channel. Factors that determine the polydispersity of the LC droplets include flow rates and surface wettability. Under appropriate experimental conditions (i.e., when the surface is glass and the flow rate is sufficiently high), the LC droplets can be lifted off completely and carried away by the solution, forming free LC droplets (15-62 μm in diameter). These free LC droplets can respond to a chemical reaction and change their optical textures uniformly.

The fabrication of micropatterned structures on PDMS is a critical step in soft lithography, microfluidics, and many other PDMS-based applications. To substitute traditional mold-casting methods, we develop a simple method to create micropatterned nanostructures on PDMS in one step. After exposing a flat PDMS surface to a UV pen lamp through a photomask (such as a TEM grid), micropatterned nanostructures can be formed readily on the PDMS surface. We also demonstrate that fabricated PDMS can be used for the microcontact printing of protein immunoglobulin (IgG) on solid surfaces. This method is probably the simplest method of creating micropatterned nanostructures on PDMS reported so far because it does not need casting, surface coating, or chemical reagents. Only a UV pen lamp and a photomask are required, and this method can be performed under ambient conditions without vacuum. We expect that this method will greatly benefit researchers who use PDMS regularly in various applications such as soft lithography and microfluidics.

In this paper, we report an immunoassay in which probe proteins are immobilized on the surface of liquid crystal (LC) droplets rather than on solid surfaces. The advantage of this immunoassay is that the binding of antibodies to the probe proteins can be transduced by the LC droplets directly without the need for additional steps. For example, when we incubate the LC droplets decorated with immunoglobulin G (IgG) in a solution containing anti-IgG (AIgG), these droplets change their orientations from radial to bipolar configuration. In contrast, when we incubate the IgG-LC droplets in a solution containing anti-human serum albumin (AHSA), no changes are observed. The change of orientational configuration indicates the formation of the antigen-antibody immunocomplex on the surface of the LC droplets. Using LC droplet immunoassays, we successfully detect antibody concentrations as low as 0.01 μg/mL for AIgG and 0.02 μg/mL for AHSA. Because the immunoassay using LC droplets is label-free and gives a unique optical response, it has the potential to be further developed as a portable and low-cost immunoassay., (© 2011 American Chemical Society)

Polybrominated diphenyl ethers (PBDEs) are widespread global contaminants due to their extensive usage as flame retardants. Among the 209 PBDE congeners, tetra-brominated diphenyl ether (tetra-BDE) (congener 47) and penta-BDEs (congeners 99 and 100) are the most abundant, toxic, and bioaccumulative congeners in the environment. However, little is known about microorganisms that carry out debromination of these congeners under anaerobic conditions. In this study, we describe a coculture GY2 consisting of Dehalococcoides and Desulfovibrio spp., which is capable of debrominating ∼1180 nM of congeners 47, 99, and 100 (88-100% removal) to the nonbrominated diphenyl ether at an average rate of 36.9, 19.8, and 21.9 nM day(-1), respectively. Ortho bromines are preferentially removed during the debromination process. The growth of Dehalococcoides links tightly with PBDE debromination, with an estimated growth yield of 1.99 × 10(14) cells per mole of bromide released, while the growth of Desulfovibrio could be independent of PBDEs. The growth-coupled debromination suggests that Dehalococcoides cells in the coculture GY2 are able to respire on PBDEs. Given the ubiquity and recalcitrance of the tetra- and penta-BDEs, complete debromination of these congeners to less toxic end products (e.g. diphenyl ether) is important for the restoration of PBDE-contaminated environments.

In this paper, we report the role of surfactants in minimizing nonspecific protein adsorption in liquid crystal (LC)-based immunoassays in which LC is used as a readout system. Among all surfactants tested, only nonionic surfactant such as Tween 20 can effectively reduce the nonspecific protein adsorption, while maintaining the selectivity of the LC-based immunoassay. We also show that to minimize nonspecific protein adsorption, Tween 20 can be added directly into the antibody solution to a final concentration of 0.8 mM. After the addition of Tween 20, better correlations between the antibody concentrations and the interference colors of LCs can therefore be obtained. For example, when Cy3 antibiotin was used, black, yellow, red, and green interference colors correspond to a concentration of 5, 25, 50, and 100 μg/mL, respectively. This feature gives LC immunoassay a unique advantage over the fluorescence-based immunoassay.

In this paper, we report a method of detecting DNA targets hybridized to a solid surface by using liquid crystals (LC). The detection principle is based on different interference colors of LC supported on surfaces decorated with single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA). However, the contrast between the ssDNA and dsDNA is not obvious, unless DNA-streptavidin complexes are introduced to the dsDNA to increase the surface mass density. Two different approaches of introducing streptavidin to the system are studied and compared. We find that by premixing the biotin-labeled DNA targets with streptavidin prior to the DNA hybridization, branched-streptavidin complexes are formed and clear LC signal can be observed. This LC-based DNA detection principle represents an important step toward the development of a simple, instrument- and fluorophore-free DNA detection method.

In this paper, we report a study of using cholesteric liquid crystals (CLCs) doped with dodecylamine for detecting aldehyde vapors. CLCs doped with dodecylamine show color change from red to yellow-green upon exposure to 300 ppmv pentyl aldehyde within 60 s. In contrast, no colorimetric response is observed when pure CLCs are used. Characterization by using FT-IR shows that the possible mechanism responsible for the colorimetric response is the formation of an imine bond between dodecylamine and pentyl aldehyde. A new C=N peak at 1670 cm(-1) appears in the spectrum after the exposure to aldehyde vapors. The CLCs doped with dodecylamine show good selectivity for pentyl aldehyde; they do not respond to 200 ppmv pentyl alcohol, pentylamine, acetone, ethanol, and water vapor. This study demonstrates the potential applications of doped CLCs as low-cost and portable gas sensors.

DNA microarrays have been used as powerful tools in genomics studies and single nucleotide polymorphisms analysis. However, the fluorescence detection used in most conventional DNA microarrays is still limited by its sensitivity. The aim of this study is to use a cationic surfactant, cetyl trimethylammonium bromide (CTAB), to enhance the fluorescence intensity of 6-carboxy-fluorescene (FAM)-labeled DNA probes immobilized on a DNA microarray. We show that in the presence of CTAB the immobilized FAM-labeled DNA probes is 11-fold brighter than that without exposure to CTAB. Similarly, when we hybridize FAM-labeled DNA targets to a DNA microarray and treat the surface with CTAB solution, the fluorescence intensity shows a 26-fold increase for perfect-match DNA targets. More importantly, the contrast between perfect-match and 1-mismatch DNA is also increased from 1.3-fold to 15-fold. This method offers a simple and efficient technique to enhance the detection limit of DNA microarrays.

Affinity contact printing (αCP) is a technique that allows the selective capture of a target protein from solutions to a polymeric stamp decorated with an antibody, and then the target protein is printed onto a solid surface. The success of αCP critically relies on the precise control of protein-surface interactions. Here, we report a study on the effect of UV on the protein-surface interactions between protein and polydimethylsiloxane stamps and between protein and glass slides decorated with N,N-dimethyl-n-octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP). Our results show that UV-modified surfaces can be used to improve the transfer efficiency and selectivity of proteins during αCP. For example, the protein transfer efficiency of human IgG onto a DMOAP-coated slide increases from 7.2% to 45.1% after the UV treatment. On the basis of these results, UV-modified surfaces were employed to develop a αCP system for protein detection. The detection limit of anti-IgG in this system is around 10 ng/mL, and the dynamic range is 4 orders of magnitude.

We report a simple method of creating well-defined micropatterns on the surface of a flat PDMS stamp, making it suitable for microcontact printing of proteins. This method only requires a UV lamp (254 nm) and a TEM grid (as a photomask) to modify the surface of PDMS for creating desired micropatterns. By using the UV-modified stamp, a printed protein micropattern that resembles the original TEM grid can be obtained. Surprisingly, unlike the oxygen-plasma-treated PDMS, the UV-modified flat stamp is also long-lasting (>1 week). The method reported herein is very economical for microcontact printing applications because expensive silicon masters and microstructured PDMS are no longer required.

Conventional DNA detection is often accomplished by using UV-vis or fluorescence spectrometry, which requires at least 1 microL of DNA solution. Herein, we report a label-free, liquid-crystal (LC)-based DNA quantification method that is suitable for characterizing DNA solution volumes of <1 microL. The detection principle of this method is based on the disruption of the orientations of LCs by surface-immobilized DNA, which leads to distinct optical textures of LCs visible to the naked eye. However, this method is successful only when the buffer contains divalent cations such as calcium or magnesium. The limit of detection of this method is approximately 4 microg/mL DNA, and only 10 nL of DNA solution is required, which means that as little as 40 pg of DNA can be detected by using this method. This LC-based detection method is also simple to apply and has the potential to be integrated with lab-on-a-chip devices for DNA analysis.

In this paper, we report a new label-free method for the imaging of immobilized oligonucleotide probes on DNA microarrays. The imaging principle is based on the disruption of orientations of nematic liquid crystals (LCs), 4-cyano-4'-pentylbiphenyl (5CB), by the immobilized oligonucleotides on a surface. Because LCs are birefringent materials, disruption of their orientations by the immobilized oligonucleotides can manifest as optical signals visible to the naked eye. LC cells with two homeotropic boundary conditions, which align 5CB perpendicularly to both surfaces, were developed to deliver a distinct contrast between a dark background and a bright image caused by the immobilized oligonucleotides. This design also allows the quantification of immobilized oligonucleotide concentrations through the interference colors of LCs. The LC-based imaging method has a good signal-to-noise ratio and a clear distinction between positive and negative results and is nondestructive to the immobilized oligonucleotides. These advantages make it a promising means of assessing the quality of DNA microarrays.

Chemically micropatterned surfaces have broad applications in many fields. In this paper, we report a new method for preparing chemically micropatterned surfaces by controlling and manipulating supported phospholipid monolayers as soft resist layers with molecular-level precision. First, we introduce self-assembled supported phospholipid monolayers on solid surfaces and use a microcontact lift-up process to create micropatterned phospholipid monolayers (with micrometer resolution) on the surface. Next, the micropatterned phospholipid monolayers can function as "soft" resist layers to protect underlying solid substrates and create either positive or negative chemically micropatterned surfaces during subsequent treatments. Unlike traditional "hard" resist layers which can only be removed by using harsh chemical treatments, this novel soft resist layer only comprises a single layer of compact phospholipid; therefore, it can be easily removed by water rinsing after the preparation of micropatterns. This method is also versatile. It can be applied to prepare a protein microarray or silver patterns on solid substrates.

This letter reports a strategy of using N-terminal cysteine labels for controlling the immobilization of oligopeptides on aldehyde-terminated surfaces through the formation of stable thiazolidine rings. We also study the effect of cysteine position (either N-terminal or C-terminal) and lysine residue on the immobilization of oligopeptides. On the basis of our ellipsometry and quartz crystal microbalance (QCM) results, we conclude that the proposed immobilization strategy is highly site-specific. It works only when cysteine is in the N-terminal position, and the formation of thiazolidine is much faster than the formation of imines between lysine residues and aldehydes, even in the presence of a reducing agent such as NaBH(3)CN. By labeling an oligopeptide CSNKTRIDEANNKATKML with an N-terminal cysteine, we immobilize this oligopeptide on an aldehyde-terminated surface and investigate the enzymatic activity of trypsin acting on the oligopeptide. It is found that trypsin is able to cleave the immobilized oligopeptide having a single anchoring point at the N-terminal cysteine. No cleavage is observed when the oligopeptide is immobilized through multiple anchoring points at lysine residues.

Protein assays are critical analytical tools performed in various biochemical laboratories to quantify the concentration of proteins. In this study, we report the optical responses of a thin layer of liquid crystals supported on glass slides decorated with proteins and the utility of this phenomenon as a new "all-or-nothing" type of protein assay. It was found that the orientations of liquid crystals are very sensitive to the concentration of protein solution applied to the surface. When the protein concentration exceeds a critical value (IgG 5.0 microg/mL, BSA 6.0 microg/mL, FTIC-anti-biotin 0.40 microg/mL, and FITC-anti-IgG 0.37 microg/mL), the thin layer of liquid crystals gives a very sharp dark-to-bright optical response within a small concentration range. This characteristic is not observed in any traditional protein assays, which are based on the adsorption of UV or visible light. The optical response is also very precise and reproducible. It is not affected by the thickness of the liquid crystal cell or the amount of organosilanes coated on the glass slides. The liquid crystal-based protein assay may be very useful for screening purposes, especially when a simple positive or negative answer is desired.

Short oligopeptides that complex with metal ions with high affinity and high specificity are of interest to the design of chemical sensors. In this study, we compare the complexation properties of two copper-selective tripeptides, Gly-Gly-His and His-Gly-Gly, either in aqueous solutions or immobilized on solid surfaces. Our results show that the copper complex formed by Gly-Gly-His is more stable than the complex formed by His-Gly-Gly in aqueous solutions, because the position of histidine (His) in the Gly-Gly-His permits the formation of a tetragonal copper complex with a high stability. However, when the tripeptides are immobilized on aldehyde-decorated silicon wafer surfaces under a reaction condition that gives rise to near maximum surface densities of tripeptides, both immobilized Gly-Gly-His and His-Gly-Gly experience strong steric hindrance on the over-crowded surfaces. The surface crowding effect causes less complexation with copper ions than that in aqueous solutions. To ensure a proper surface density on the surface for complexation with copper ions, a so-called two-dimensional (2D) metal-ion imprinting technique is employed to avoid the surface crowdedness. By immobilizing Gly-Gly-His in the presence of copper ions, we create a tripeptide-functionalized surface that exhibits high complexation capability for copper ions. We attribute the higher copper complexation capability to the proper intermolecular distances obtained from the ion-imprinting procedure that gives the copper-tripeptide complex a preferential tetragonal geometry. Our results show that the amounts of copper complexed to a copper-imprinted surface functionalized with Gly-Gly-His are 62% higher than those of a nonimprinted surface.

In this paper, we report a method of transferring complementary target DNA from an aqueous solution onto a solid surface by using affinity microcontact printing. In this approach, the probe DNA is first immobilized on the surface of an aminated poly(dimethylsiloxane) (PDMS) stamp. After a complementary target DNA hybridizes with the probe DNA on the stamp surface, the PDMS stamp is printed on an aminated glass slide. By using fluorescent microscopy, we show that only complementary target DNA, but not noncomplementary DNA, can be captured onto the surface of the stamp and then transferred to the aminated glass slide. The transfer of DNA can be attributed to the stronger electrostatic attraction between DNA and amine groups compared to the hydrogen bonds between the hybridized DNA molecules. We also investigate several factors that may influence the transfer of DNA, such as the surface density of amine groups, hybridization conditions, and contamination from unreacted PDMS monomers.

We report a new procedure for modifying the surface of silica gels with glycine, diglycine, and triglycine in the presence of copper ions to create a new type of copper-imprinted sorbent, which exhibits a high adsorption capacity and selectivity for copper ions. Our results show that copper adsorbed onto the copper-imprinted silica gel is 50% higher than that on nonimprinted silica gel at pH 4.5. The high adsorption capacity observed for the copper-imprinted silica gel is attributed to the stable copper complexes formed with two adjacent glycine, diglycine, or triglycine molecules with proper intermolecular distances obtained from the ion-imprinting procedure. Another possible reason for the high adsorption capacity is that the ion-imprinting procedure prevents the surface from being overcrowded; therefore, copper ions can form very stable 1:1 complexes with immobilized diglycine or triglycine. Interestingly, the imprinting effect is even more pronounced when the adsorption experiments are conducted in the presence of competing metal ions such as magnesium and calcium. The copper-imprinted silica gel exhibits a higher adsorption capacity than does the nonimprinted silica gel for all pH values, even when the concentrations of magnesium and calcium are 50 and 76 times higher than the concentration of copper.

In this paper we present a study of using oxygen plasma for chemically modifying inert hydrocarbon self-assembled monolayers of octadecyltrichlorosilane (OTS-SAMs) and rendering active surfaces for protein immobilization. Detailed surface modification and protein immobilization were characterized by using ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared-attenuated total reflectance spectroscopy, and fluorescence microscopy. Our XPS results showed that the surface reaction between OTS-SAMs and oxygen plasma can generate new surface functional groups such as alcohol (C-O), aldehyde (C=O), and carboxylic acid (O-C=O), and their compositions can be controlled by using different treatment times and powers. A short treatment time ( approximately 1 s) and high power (10 W) can lead to a higher density of aldehyde groups, which can serve as linker groups for protein immobilization through the formation of Schiff bases with the amine groups of proteins. By using the fluorescence immunostaining method, we confirmed that human immunoglobulin (IgG) can be immobilized on a glass slide, only if the surface was decorated with OTS-SAMs and if the OTS-SAMs were pretreated with oxygen plasma. The protein immobilized on the oxygen-plasma-treated surface can only be recognized by using a highly specific antibody, FITC-anti-IgG, but not FITC-anti-biotin.