Protein Assays on Organic Electronics: Rational Device and Material Designs for Organic Transistor-Based Sensors

Artificial receptor-based protein assays have various attractive features such as a long-term stability, a low-cost production process, and the ease of tuning the target specificity. However, such protein sensors are still immature compared with conventional immunoassays. To enhance the application potential of synthetic sensing materials, organic field-effect transistors (OFETs) are some of the suitable platforms for protein assays because of their solution processability, durability, and compact integration. Importantly, OFETs enable the electrical readout of the protein recognition phenomena of artificial receptors on sensing electrodes. Thus, we believe that OFETs functionalized with artificial protein receptors will be a powerful tool for the on-site analyses of target proteins. In this Minireview, we summarize the recent progress of the OFET-based protein assays including the rational design strategies for devices and sensing materials.

Indirect Microcontact Printing to Create Functional Patterns of Physisorbed Antibodies

Microcontact printing (µCP) is a practical and versatile approach to create nanostructured patterns of biomolecular probes, but it involves conformational changes on the patterned bioreceptors that often lead to a loss on the biological activity of the resulting structures. Herein we introduce indirect µCP to create functional patterns of bioreceptors on solid substrates. This is a simple strategy that relies on physisorbing biomolecular probes of interest in the nanostructured gaps that result after patterning backfilling agents by standard µCP. This study presents the approach, assesses bovine serum albumin as backfilling agent for indirect µCP on different materials, reports the limitations of standard µCP on the functionality of patterned antibodies, and demonstrates the capabilities of indirect µCP to solve this issue. Bioreceptors were herein structured as diffractive gratings and used to measure biorecognition events in label-free conditions. Besides, as a preliminary approach towards sensing biomarkers, this work also reports the implementation of indirect µCP in an immunoassay to detect human immunoglobulin E.

Cytokeratins Biosensing Using Tilted Fiber Gratings

Optical fiber gratings have widely proven their applicability in biosensing, especially when they are coupled with antibodies for specific antigen recognition. While this is customarily done with fibers coated by a thin metal film to benefit from plasmonic enhancement, in this paper, we propose to study their intrinsic properties, developing a label-free sensor for the detection of biomarkers in real-time without metal coatings for surface plasmon resonances. We focus on the inner properties of our modal sensor by immobilizing receptors directly on the silica surface, and reporting the sensitivity of bare tilted fiber Bragg gratings (TFBGs) used at near infrared wavelengths. We test different strategies to build our sensing surface against cytokeratins and show that the most reliable functionalization method is the electrostatic adsorption of antibodies on the fiber, allowing a limit of detection reaching 14 pM by following the guided cladding modes near the cut-off area. These results present the biodetection performance that TFBGs bring through their modal properties for different functionalizations and data processing strategies.

Quantification of immobilized protein in pharmaceutical production by bio-assisted potentiometric multisensor system

Quantification of proteins is a key biochemical assay in molecular biology, biotechnology, medicine and pharmacology. Protein quantification protocols can be based on spectrophotometry, enzyme-linked immunosorbent assay, mass spectrometry or quantitative immunoblotting depending on analyte. In case of immobilized protein these methods require suitable sample preparation. Thus, sophisticated analysis becomes even more complex, expensive and time-consuming. Such drawbacks are highly undesirable in industry. In this study we propose a new approach for evaluation of immobilized protein concentration based on application of bio-assisted potentiometric multisensor system. Surface-immobilized recombinant protein A from Staphylococcus aureus (SpA, expressed in Escherichia coli), which is commonly used as affinity ligand immobilized to stationary phase (сhromatography media) for monoclonal antibody purification was employed as the model object. Chromatography media samples containing different amounts of immobilized SpA were analyzed. Proteinase K from Tritirachium album was employed as a bio-transducer. We demonstrated that the suggested approach provides information about immobilized SpA concentration with 0.8mg/ml accuracy in the range 1-6.7mg/ml and within just 16min. Moreover, the proposed procedure requires no expensive materials and equipment and no bio-transducer immobilization. This method has potential of application for fast monitoring of other immobilized proteins in different tasks.

Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the 'footprint' of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

Development of quantitative radioactive methodologies on paper to determine important lateral-flow immunoassay parameters

The lateral-flow immunoassay (LFA) is a well-established diagnostic technology that has recently seen significant advancements due in part to the rapidly expanding fields of paper diagnostics and paper-fluidics. As LFA-based diagnostics become more complex, it becomes increasingly important to quantitatively determine important parameters during the design and evaluation process. However, current experimental methods for determining these parameters have certain limitations when applied to LFA systems. In this work, we describe our novel methods of combining paper and radioactive measurements to determine nanoprobe molarity, the number of antibodies per nanoprobe, and the forward and reverse rate constants for nanoprobe binding to immobilized target on the LFA test line. Using a model LFA system that detects for the presence of the protein transferrin (Tf), we demonstrate the application of our methods, which involve quantitative experimentation and mathematical modeling. We also compare the results of our rate constant experiments with traditional experiments to demonstrate how our methods more appropriately capture the influence of the LFA environment on the binding interaction. Our novel experimental approaches can therefore more efficiently guide the research process for LFA design, leading to more rapid advancement of the field of paper-based diagnostics.

A Bioorthogonal Approach for the Preparation of a Titanium-Binding Insulin-like Growth-Factor-1 Derivative by Using Tyrosinase

The generation of metal surfaces with biological properties, such as cell-growth-enhancing and differentiation-inducing abilities, could be potentially exciting for the development of functional materials for use in humans, including artificial dental implants and joint replacements. However, currently the immobilization of proteins on the surfaces of the metals are limited. In this study, we have used a mussel-inspired bioorthogonal approach to design a 3,4-hydroxyphenalyalanine-containing recombinant insulin-like growth-factor-1 using a combination of recombinant DNA technology and tyrosinase treatment for the surface modification of titanium. The modified growth factor prepared in this study exhibited strong binding affinity to titanium, and significantly enhanced the growth of NIH3T3 cells on the surface of titanium.

An Experimental Study on Guided Bone Regeneration Using a Polylactide-co-glycolide Membrane-Immobilized Conditioned Medium

PURPOSE

To investigate whether bone regeneration can be accelerated by using a conditioned medium (CM) and guided bone regeneration (GBR) technique.

MATERIALS AND METHODS

CM was harvested from rat bone marrow stromal cells (BMSCs). The components of CM were immobilized using a polylactide-co-glycolide (PLGA) membrane treated with and without 0.5 mol/L sodium hydroxide (NaOH) to elevate the hydrophilicity. Four experimental groups were prepared: PLGA membrane treated with (1) phosphate-buffered saline (PBS; PBS-M), (2) PBS and 0.5 mol/L NaOH (hydrophilic treatment; PBS-HM), (3) CM (CM-M), and (4) CM and 0.5 mol/L NaOH (CM-HM). These experimental membranes were observed using scanning electron microscopy. Proteins derived from BMSCs immobilized on the PLGA membrane were detected with liquid chromatography-tandem mass spectrometry (LC/MS/MS). Cell proliferation and alkaline phosphatase (ALP) activity were measured to analyze the effect of CM on the BMSCs. Experimental membranes were transplanted into a rat calvarial bone defect model. Microcomputed tomography and histologic analyses were performed 4 and 8 weeks after transplantation.

RESULTS

The CM derived from BMSCs can be immobilized on the PLGA membrane. Hydrophilic treatment of the PLGA membrane enhanced the amount of CM immobilization. LC/MS/MS analysis showed that the immobilized proteins on the surface of PLGA membrane were extracellular matrix, such as collagen, decorin, and fibronectin. The proteins in the CM, which were released from the PLGA membrane, enhanced cell proliferation and ALP activity in rat BMSCs. Newly formed bone area at the bone defects that had been treated with CM-HM was significantly high compared with those at bone defects treated with the other membranes.

CONCLUSION

The PLGA membrane treated with 0.5 mol/L NaOH and CM promoted bone regeneration in this rat calvarial defect model.

Podosome Formation and Development in Monocytes Restricted by the Nanoscale Spatial Distribution of ICAM1

We studied podosome formation and development in activated monocytes (THP1) at ICAM1 (intercellular adhesion molecule 1) nanopatterns of circular and ring-shaped domains and show that cellular binding to a preclustered ICAM1 nanopattern requires ligand patches of at least 200 nm (corresponding to 14 or more integrins). Podosome-like adhesion formation depends on the structure of the ligand pattern under the developing podosome with larger single domains promoting adhesion in a single patch and multiple smaller domains allowing podosome formation by integration of at least 2 smaller domains on either side of the podosome core. Maturation to rosette structures and recruitment of proteases were only observed with macroscopic ICAM1 presentation.

Surface enhanced Raman spectroscopy detection of biomolecules using EBL fabricated nanostructured substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

Microchip ELISA coupled with cell phone to detect ovarian cancer HE4 biomarker in urine

Ovarian cancer is a leading cause of death from gynecologic cancers in the USA, and early diagnosis can potentially increase 5-year survival rate. Detection of biomarkers derived from hyperplasia of epithelial tissue by enzyme-linked immunosorbent assay (ELISA) proves to be a practical way of early diagnosis of ovarian cancer. However, ELISA is commonly performed in a laboratory setting, and it cannot be used in a clinical setting for on-site consultation. We have shown a microchip ELISA that detects HE4, an ovarian cancer biomarker, from urine using a cell phone integrated with a mobile application for imaging and data analysis. In microchip ELISA, HE4 from urine was first absorbed on the surface; the primary and secondary antibodies were subsequently anchored on the surface via immuno-reaction; and addition of substrate led to color development because of enzymatic labeling. The microchip after color development was imaged using a cell phone, and the color intensity was analyzed by an integrated mobile application. By comparing with an ELISA standard curve, the concentration of HE4 was reported on the cell phone screen. The presented microchip ELISA coupled with a cell phone is portable as opposed to traditional ELISA, and this method can facilitate the detection of ovarian cancer at the point-of-care (POC).

Microfluidic barcode assay for antibody-based confirmatory diagnostics

Confirmatory diagnostics offer high clinical sensitivity and specificity typically by assaying multiple disease biomarkers. Employed in clinical laboratory settings, such assays confirm a positive screening diagnostic result. These important multiplexed confirmatory assays require hours to complete. To address this performance gap, we introduce a simple 'single inlet, single outlet' microchannel architecture with multiplexed analyte detection capability. A streptavidin-functionalized, channel-filling polyacrylamide gel in a straight glass microchannel operates as a 3D scaffold for a purely electrophoretic yet heterogeneous immunoassay. Biotin and biotinylated capture reagents are patterned in discrete regions along the axis of the microchannel resulting in a barcode-like pattern of reagents and spacers. To characterize barcode fabrication, an empirical study of patterning behaviour was conducted across a range of electromigration and binding reaction timescales. We apply the heterogeneous barcode immunoassay to detection of human antibodies against hepatitis C virus and human immunodeficiency virus antigens. Serum was electrophoresed through the barcode patterned gel, allowing capture of antibody targets. We assess assay performance across a range of Damkohler numbers. Compared to clinical immunoblots that require 4-10 h long sample incubation steps with concomitant 8-20 h total assay durations; directed electromigration and reaction in the microfluidic barcode assay leads to a 10 min sample incubation step and a 30 min total assay duration. Further, the barcode assay reports clinically relevant sensitivity (25 ng ml(-1) in 2% human sera) comparable to standard HCV confirmatory diagnostics. Given the low voltage, low power and automated operation, we see the streamlined microfluidic barcode assay as a step towards rapid confirmatory diagnostics for a low-resource clinical laboratory setting.

Development of a paper-based carbon nanotube sensing microfluidic device for biological detection

Carbon nanotube (CNT) has been utilized for the biological detection due to its extremely sensitive to biological molecules. A paper-based CNT sensing microfluidic device has been developed for the detection of protein, i.e., biotin-avidin, binding. We have developed a fabrication method that allows controlled deposition of bundled CNTs with well-defined dimensions to form sensors on paper. Then, polydimethyl siloxane (PDMS) was used to pattern the hydrophobic boundary on paper to form the reaction sites. The proposed fabrication method is based on vacuum filtration process with a metal mask covering on a filter paper for the definition of the dimension of sensor. The length, width, and thickness of the CNT-based sensors are readily controlled by the metal mask and the weight of the CNT powder used during the filtration process, respectively. Homogeneous deposition of CNTs with well-defined dimensions can be achieved. The CNT-based sensor on paper has been demonstrated on the detection of the protein binding. Biotin was first immobilized on the CNT's sidewall and avidin suspended solution was applied to the site. The result of the biotin-avidin binding was measured by the resistance change of the sensor, which is a label-free detection method. It showed the CNT is sensitive to the biological molecules and the proposed paper-based CNT sensing device is a possible candidate for point-of-care biosensors. Thus, electrical bio-assays on paper-based microfluidics can be realized to develop low cost, sensitive, and specific diagnostic devices.

Label-free, real-time interaction and adsorption analysis 1: surface plasmon resonance

A key requirement for the development of proteins for use in nanotechnology is an understanding of how individual proteins bind to other molecules as they assemble into larger structures. The introduction of labels to enable the detection of biomolecules brings the inherent risk that the labels themselves will influence the nature of biomolecular interactions. Thus, there is a need for label-free interaction and adsorption analysis. In this and the following chapter, two biosensor techniques are reviewed: surface plasmon resonance (SPR) and the quartz crystal microbalance (QCM). Both allow real-time analysis of biomolecular interactions and both are label-free. The first of these, SPR, is an optical technique that is highly sensitive to the changes in refractive index that occur with protein (or other molecule) accumulation near an illuminated gold surface. Unlike QCM ( Chapter 18 ) SPR is not affected by the water that may be associated with the adsorbed layer nor by conformational changes in the adsorbed species. SPR thus provides unique information about the interaction of a protein with its binding partners.

Large-scale femtoliter droplet array for digital counting of single biomolecules

We present a novel device employing one million femtoliter droplets immobilized on a substrate for the quantitative detection of extremely low concentrations of biomolecules in a sample. Surface-modified polystyrene beads carrying either zero or a single biomolecule-reporter enzyme complex are efficiently isolated into femtoliter droplets formed on hydrophilic-in-hydrophobic surfaces. Using a conventional micropipette, this is achieved by sequential injection first with an aqueous solution containing beads, and then with fluorinated oil. The concentration of target biomolecules is estimated from the ratio of the number of signal-emitting droplets to the total number of trapped beads (digital counting). The performance of our digital counting device was demonstrated by detecting a streptavidin-β-galactosidase conjugate with a limit of detection (LOD) of 10 zM. The sensitivity of our device was >20-fold higher than that noted in previous studies where a smaller number of reactors (fifty thousand reactors) were used. Such a low LOD was achieved because of the large number of droplets in an array, allowing simultaneous examination of a large number of beads. When combined with bead-based enzyme-linked immunosorbent assay (digital ELISA), the LOD for the detection of prostate specific antigen reached 2 aM. This value, again, was improved over that noted in a previous study, because of the decreased coefficient of variance of the background measurement determined by the Poisson noise. Our digital counting device using one million droplets has great potential as a highly sensitive, portable immunoassay device that could be used to diagnose diseases.

Single-molecule detection using continuous wave excitation of two-photon fluorescence

Two-photon fluorescence (TPF) is one of the most important discoveries for biological imaging. Although a cw laser is known to excite TPF, its application in TPF imaging has been very limited due to the perceived low efficiency of excitation. Here we directly excited fluorophores with an IR cw laser used for optical trapping and achieved single-molecule fluorescence sensitivity: discrete stepwise photobleaching of enhanced green fluorescent proteins was observed. The single-molecule fluorescence intensity analysis and on-time distribution strongly indicate that a cw laser can generate TPF detectable at the single-molecule level, and thus opens the door to single-molecule TPF imaging using cw lasers.

Microfluidic biosensor for beta-amyloid(1-42) detection using cyclic voltammetry

Numerous studies have identified beta-amyloid(1-42) protein (Abeta42) in the cerebrospinal fluid as a potential biomarker of Alzheimer's disease. It is of particular interest to establish the diagnosis before reaching the stage of clinical severity. The current methods for studying amyloid detection, however, is often time-consuming, expensive, and labor intensive, making the analytical process very slow. Thus, a critical need exists for an analytical system that would enable the rapid investigation of amyloid formation with a very small amount of amyloidogenic peptides and reagents. In our present work, we report a simple microfluidic biosensor to analyze very small quantities of Abeta42 peptide on gold surface that were modified with Au nano-particles onto the thiol groups of self-assembled 1,6-hexandithiol cross-linkers. The vital advantage of this method includes retaining the bioactivity and environment similar to nature for protein immobilization while using minimal amounts of reagents and highly sensitive detection.

A BioDVD media with multilayered structure is suitable for analyzing biomolecular interactions

A biomolecular interactive analysis with antibody-antigen and aptamer-protein was evaluated on Au-over layers deposited on the BioDVD surface. BioDVD consists of multilayered structures with Au layer on the top and it detects analytes by monitoring the changes in reflected light intensity due to analyte adsorption to the sensor surface, on which functional biomolecules are immobilized to bind specifically to the analytes. The BioDVD sensing instrument is based on a commercial digital versatile disc system, which allows the instrument to be small and inexpensive. The BioDVD platform can be fabricated utilizing mass production techniques with additional functional phase change layers that can serve both to enhance sensitivity by optimization of the interferometric cavity optical properties and also as a possible medium for the storage of test related information.

Quantification of protein immobilization on substrates for cellular microarray applications

Cellular microarray developments and its applications are the next step after DNA and protein microarrays. The choice of the surface chemistry of the substrates used for the implementation of this technique, that must favor proper protein immobilization while avoiding cell adhesion on the nonspotted areas, presents a complex challenge. This is a key issue since usually the best nonfouling surfaces are also the ones that retain immobilized the smallest amounts of printed protein. To quantitatively assess the amount of protein immobilization, in this study several combinations of fluorescently labeled fibronectin (Fn*) and streptavidin (SA*) were microspotted, with and without glycerol addition in the printing buffer, on several substrates suitable for cellular microarrays. The substrates assayed included chemically activated surfaces as well as Poly ethylene oxide (PEO) films that are nonfouling in solution but accept adhesion of proteins in dry conditions. The results showed that the spotted Fn* was retained by all the surfaces, although the PEO surface did show smaller amounts of immobilization. The SA*, on the other hand, was only retained by the chemically activated surfaces. The inclusion of glycerol in the printing buffer significantly reduced the immobilization of both proteins. The results presented in this article provide quantitative evidence of the convenience of using a chemically activated surface to immobilize proteins relevant for cellular microarray applications, particularly when ECM proteins are cospotted with smaller factors which are more difficult to be retained by the surfaces.

Selective capture of phosphopeptides by zirconium phosphonate-magnetic nanoparticles

Immobilized metal affinity chromatography is a widely used method for the enrichment of phosphopeptides from proteolytic digests prior to mass spectrometric analysis. Here, we describe the selective enrichment of phosphopeptides from tryptic digests of proteins (α- and β-caseins) by zirconium phosphonate-magnetic Fe(3)O(4)/SiO(2) (core/shell) nanoparticles for phosphoproteome analysis with MALDI-TOF mass spectrometry.

Immobilized metal affinity chromatography/reversed-phase enrichment of phosphopeptides and analysis by CID/ETD tandem mass spectrometry

Major difficulties in phosphoprotein analysis relate to the presence of a huge number of nonphosphorylated proteins and to the wide concentration dynamic range among them. In order to overcome the analysis complexity, specific clean-up and highly efficient enrichment procedures are mandatory prior to the -chromatographic separation and identification by tandem mass spectrometry. In this chapter, a procedure based on immobilized metal affinity chromatography (IMAC)/reversed-phase phosphopeptide purification and analysis by nanoHPLC-ESI-MS/MS with ion trap is described in detail. CID (collision-induced -dissociation) and ETD (electron-transfer dissociation) fragmentation techniques are used in combination to specifically determine phosphorylation sites inside the peptide sequences, through the analysis of MS/MS spectra.

Application of surface plasmon resonance spectroscopy to study G-protein coupled receptor signalling

The G-protein coupled receptor rhodopsin is a classical example of a seven transmembrane helix receptor; it is photoexcited and transmits this light signal to a G-protein mediated cascade. Many components of this receptor-triggered cascade can be purified in their native forms from natural sources making this system most suitable for biophysical studies. A central aspect of cellular signal transduction routes is to understand protein-protein interactions in a quantitative way. Surface plasmon resonance (SPR) spectroscopy is a biosensor-based technique that allows investigating molecular interactions by determining kinetic parameters. We here show how dark-adapted rhodopsin can be immobilized on the sensor chip surface. A laser device implemented in the SPR system allowed us to trigger light-induced conformational changes in rhodopsin and to monitor light-dependent binding of the photoreceptor cell G-protein transducin to rhodopsin. The sensor chip surface can be regenerated and used for several rounds of interaction analysis. Furthermore, illuminated rhodopsin can be regenerated by applying 9-cis-retinal on the sensor chip surface.

Incorporation of a transmembrane protein into a supported 3D-matrix of liposomes for SPR studies

Surface analytical tools as surface plasmon resonance (SPR) have become increasingly important in biomedical research since they offer high detection sensitivity compared to traditional biomedical methods. For the use of SPR as a biomedical research tool there is a need to immobilize the reactants to a solid sensor surface. It is nowadays fairly straightforward to immobilize various reactants and hydrophilic proteins to a solid sensor surface and SPR has successfully been used in several applications using such proteins when studying various protein interactions. When using SPR for the analysis of transmembrane proteins the immobilization onto the solid surface becomes more difficult. Transmembrane proteins are more sensitive to the surroundings and need to be incorporated into a structure where it can reside in a natural environment. Supported liposomes offer such environment. In this chapter a new method is presented where multilayers of such supported liposomes are used to immobilize transmembrane proteins onto a solid sensor surface which is suitable for use in SPR detection.

Highly sensitive optical detection of specific protein in breast cancer cells using microstructured fiber in extremely low sample volume

A simple optical method using hollow-core photonic crystal fiber for protein detection has been described. In this study, estrogen receptor (ER) from a MCF-7 breast carcinoma cell lysates immobilized inside a hollow-core photonic crystal fiber was detected using anti-ER primary antibody with either Alexa Fluor 488 (green fluorescent dye) or 555 (red Fluorescent dye) labeled Goat anti-rabbit IgG as the secondary antibody. The fluorescence fingerprints of the ERalpha protein were observed under fluorescence microscope, and its optical characteristics were analyzed. The ERalpha protein detection by this proposed method is based on immuno binding from sample volume as low as 50 nL. This method is expected to offer great potential as a biosensor for medical diagnostics and therapeutics applications.

Facile method for selective immobilization of biomolecules on plastic surfaces

A key aspect of biochip and biosensor preparation is optimizing surface attachment of biomolecules. Here, we report a facile approach for selectively immobilizing biomolecules on amphiphilic polymer-coated plastic surfaces with anti-biofouling properties. To modify plastic surfaces, we synthesized two types of random copolymers by radical polymerization, which consisted of three parts: an anchoring group; a PEG component, which acted as a repellent of nonspecific biomolecules; and a functional group, to which biomolecules were conjugated. Dodecyl- and benzyl-based copolymers were highly soluble in water, presumably due to the presence of multiple PEG groups, and could easily coat the model plastic surface (polystyrene) in an aqueous environment. The antibiofouling property of each polymer-coated plastic surface was examined by measuring the extent of nonspecific protein adsorption using bovine serum albumin (BSA). Both polymer-coated plastic surfaces showed a very low level of BSA adsorption relative to that of an uncoated plastic surface (control). Finally, we showed that streptavidin and antibodies, as representative biomolecules, could be selectively immobilized on the polymer-coated plastic surfaces imprinted with biotin and protein A, respectively, by microcontact printing, exhibiting an intense signal with low background.

[Use of soybean trypsin inhibitor for modification of gold surface of the sensor chips in surface plasmon resonance spectrometer]

Kunitz soybean trypsin inhibitor (STI) and glutaraldehyde are used to create an interlayer for proteins immobilization on the gold surface of the sensor chips of surface plasmon resonance spectrometer. Human serum albumin (HSA), goat Ig G and bovine eye lens alpha-crystallin are immobilized via the proposed interlayer. We studied the effects of the duration of storage of the sensor chips before use and pre-treatment by "piranha" solution on the STI adsorption by the gold surface. The influence of STI surface concentration, as well as the effect of the duration of storage of STI-modified sensor chips on the HSA immobilization are investigated. The binding of specific antibodies to the immobilized proteins and non-specific binding to the modified surfaces are studied. HSA immobilization on the bare gold surface is compared to that on the surfaces, modified by different methods.