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Nayeri F, Aili D, Nayeri T, Xu J, Almer S, Lundström I, Åkerlind B, Liedberg B. Hepatocyte growth factor (HGF) in fecal samples: rapid detection by surface plasmon resonance. BMC Gastroenterol 2005; 5:13. [PMID: 15826299 PMCID: PMC1090571 DOI: 10.1186/1471-230x-5-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2004] [Accepted: 04/12/2005] [Indexed: 11/10/2022] Open
Abstract
Background The development of biosensors, based on surface plasmon resonance (SPR) technology, enables monitoring of a variety of biospecific interactions without the need for chemical-, biological- or radiological-labelled reagents. Method We utilised SPR to detect hepatocyte growth factor (HGF) in reconstituted faecal samples and studied samples from patients with infectious gastroenteritis (n = 20) and normal controls (n = 10). Mouse anti-human HGF monoclonal antibodies and recombinant human HGF receptor (c-Met)/Fc chimera were immobilised in flow cells of a CM5 biosensor chip. Results We found that infectious gastroenteritis produced a higher signal response compared to controls, due to binding of HGF to monoclonal anti-HGF antibody as well as binding of HGF to c-Met receptor (p < 0.01). The SPR signal response correlated with results from ELISA (r = 72%, p > 0.001). The signal response decreased significantly (p < 0.05) when samples were diluted with dextran, because of reduction in both specific as well as unspecific binding of HGF to dextran. The decrease in the specific response might imply that the dextran- binding site for HGF overlaps with the antibody binding epitope, or that dextran binding induces a conformational change of the HGF molecule. Bands corresponding to HGF were found by gel electrophoresis of purified faeces in an affinity chromatography column immobilised by HGF ligands. Conclusion Determination of HGF by SPR might be beneficial in diagnosis of acute situations that present with symptoms of gastroenteritis and may, possibly, guide appropriate medical treatments. This is to our knowledge the first report on the use of SPR for detection of HGF in faeces samples.
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Enander K, Aili D, Baltzer L, Lundström I, Liedberg B. Alpha-helix-inducing dimerization of synthetic polypeptide scaffolds on gold. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:2480-2487. [PMID: 15752043 DOI: 10.1021/la048029u] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Designed, synthetic polypeptides that assemble into four-helix bundles upon dimerization in solution were studied with respect to folding on planar gold surfaces. A model system with controllable dimerization properties was employed, consisting of negatively and positively charged peptides. Circular dichroism spectroscopy and surface plasmon resonance based measurements showed that at neutral pH, the peptides were able to form heterodimers in solution, but unfavorable electrostatic interactions prevented the formation of homodimers. The dimerization propensity was found to be both pH- and buffer-dependent. A series of infrared absorption-reflection spectroscopy experiments of the polypeptides attached to planar gold surfaces revealed that if the negatively charged peptide was immobilized from a loading solution where it was folded, its structure was retained on the surface provided it had a cysteine residue available for anchoring to gold. If it was immobilized as random coil, it remained unstructured on the surface but was able to fold through heterodimerization if subsequently exposed to a positively charged polypeptide. When the positively charged peptide was immobilized as random coil, heterodimerization could not be induced, probably because of high-affinity interactions between the charged primary amine groups and the gold surface. These observations are intended to pave the way for future engineering of functional surfaces based on polypeptide scaffolds where folding is known to be crucial for function.
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Riepl M, Ostblom M, Lundström I, Svensson SCT, Denier van der Gon AW, Schäferling M, Liedberg B. Molecular gradients: an efficient approach for optimizing the surface properties of biomaterials and biochips. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:1042-1050. [PMID: 15667187 DOI: 10.1021/la048358m] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A variety of molecular gradients of alkanethiols with the structure HS-(CH(2))(m)-X (m = 15; X = COOH, CH(2)NH(2), or CH(3)) and oligo(ethylene glycol)-terminated alkanethiols with the structures HS-(CH(2))(15)-CO-NH-Eg(n) (n = 2, 4, or 6), HS-(CH(2))(15)-CO-NH-Eg(2)-(CH(2))(2)-NH-CO-(CH(2))(4)-biotin, and HS-(CH(2))(15)-CO-NH-Eg(6)-CH(2)-COOH were prepared on polycrystalline gold films. These gradients were designed to serve as model surfaces for fundamental studies of protein adsorption and immobilization phenomena. Ellipsometry, infrared spectroscopy, and X-ray photoelectron spectroscopy, operating in scanning mode, were used to monitor the layer composition, gradient profiles, tail group conformation, and overall structural quality of the gradient assemblies. The gradient profiles were found to be 4-10 mm wide, and they increased in width with increasing difference in molecular complexity between the thiols used to form the gradient. The oligo(ethylene glycol) thiols are particularly interesting because they can be used to prepare so-called conformational gradients, that is, gradients that display a variation in oligo(ethylene glycol) chain conformation from all trans on the extreme Eg(2,4) sides, via an amorphous-like phase in the mixing regimes, to helical at the extreme Eg(6) sides. We demonstrate herein a series of experiments where the above gradients are used to evaluate nonspecific binding of the plasma protein fibrinogen, and in agreement with previous studies, the highest amounts of nonspecifically bound fibrinogen were observed on all-trans monolayers, that is, on the extreme Eg(2,4) sides. Moreover, gradients between Eg(2) and a biotinylated analogue have been prepared to optimize the conditions for the immobilization of streptavidin. Ellipsometry and infrared spectroscopy reveal high levels of immobilization over a fairly broad range of compositions in the gradient regime, with a maximum between 50 and 60% of the biotinylated analogue in the monolayer. A pI gradient composed of (NH(3)(+)/COO(-))-terminated thiols was also prepared and evaluated with respect to its ability to separate differently charged proteins, pepsin, and lysozyme, on a solid surface.
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Carlsson J, Mecklenburg M, Lundström I, Danielsson B, Winquist F. Investigation of sera from various species by using lectin affinity arrays and scanning ellipsometry. Anal Chim Acta 2005. [DOI: 10.1016/j.aca.2004.09.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Ivarsson P, Krantz-Rülcker C, Winquist F, Lundström I. A Voltammetric Electronic Tongue. Chem Senses 2005; 30 Suppl 1:i258-9. [PMID: 15738145 DOI: 10.1093/chemse/bjh213] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Aifa S, Aydin J, Nordvall G, Lundström I, Svensson SPS, Hermanson O. A basic peptide within the juxtamembrane region is required for EGF receptor dimerization. Exp Cell Res 2005; 302:108-14. [PMID: 15541730 DOI: 10.1016/j.yexcr.2004.08.032] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Revised: 08/09/2004] [Indexed: 10/26/2022]
Abstract
The epidermal growth factor receptor (EGFR) is fundamental for normal cell growth and organ development, but has also been implicated in various pathologies, notably tumors of epithelial origin. We have previously shown that the initial 13 amino acids (P13) within the intracellular juxtamembrane region (R645-R657) are involved in the interaction with calmodulin, thus indicating an important role for this region in EGFR function. Here we show that P13 is required for proper dimerization of the receptor. We expressed either the intracellular domain of EGFR (TKJM) or the intracellular domain lacking P13 (DeltaTKJM) in COS-7 cells that express endogenous EGFR. Only TKJM was immunoprecipitated with an antibody directed against the extracellular part of EGFR, and only TKJM was tyrosine phosphorylated by endogenous EGFR. Using SK-N-MC cells, which do not express endogenous EGFR, that were stably transfected with either wild-type EGFR or recombinant full-length EGFR lacking P13 demonstrated that P13 is required for appropriate receptor dimerization. Furthermore, mutant EGFR lacking P13 failed to be autophosphorylated. P13 is rich in basic amino acids and in silico modeling of the EGFR in conjunction with our results suggests a novel role for the juxtamembrane domain (JM) of EGFR in mediating intracellular dimerization and thus receptor kinase activation and function.
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Filippini D, Lundström I. Spectroscopic information retained in screen photo-assisted techniques. Anal Chim Acta 2004. [DOI: 10.1016/j.aca.2004.05.081] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Filippini D, Andersson TPM, Svensson SPS, Lundström I. Microplate based biosensing with a computer screen aided technique. Biosens Bioelectron 2004; 19:35-41. [PMID: 14558996 DOI: 10.1016/s0956-5663(03)00132-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Melanophores, dark pigment cells from the frog Xenopus laevis, have the ability to change light absorbance upon stimulation by different biological agents. Hormone exposure (e.g. melatonin or alpha-melanocyte stimulating hormone) has been used here as a reversible stimulus to test a new compact microplate reading platform. As an application, the detection of the asthma drug formoterol in blood plasma samples is demonstrated. The present system utilizes a computer screen as a (programmable) large area light source, and a standard web camera as recording media enabling even kinetic microplate reading with a versatile and broadly available platform, which suffices to evaluate numerous bioassays. Especially in the context of point of care testing or self testing applications these possibilities become advantageous compared with highly dedicated comparatively expensive commercial systems.
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Enander K, Dolphin GT, Liedberg B, Lundström I, Baltzer L. A versatile polypeptide platform for integrated recognition and reporting: affinity arrays for protein-ligand interaction analysis. Chemistry 2004; 10:2375-85. [PMID: 15146511 DOI: 10.1002/chem.200305391] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A molecular platform for protein detection and quantification is reported in which recognition has been integrated with direct monitoring of target-protein binding. The platform is based on a versatile 42-residue helix-loop-helix polypeptide that dimerizes to form four-helix bundles and allows site-selective modification with recognition and reporter elements on the side chains of individually addressable lysine residues. The well-characterized interaction between the model target-protein carbonic anhydrase and its inhibitor benzenesulfonamide was used for a proof-of-concept demonstration. An affinity array was designed where benzenesulfonamide derivatives with aliphatic or oligoglycine spacers and a fluorescent dansyl reporter group were introduced into the scaffold. The affinities of the array members for human carbonic anhydrase II (HCAII) were determined by titration with the target protein and were found to be highly affected by the properties of the spacers (dissociation constant Kd=0.02-3 microM). The affinity of HCAII for acetazolamide (Kd=4 nM) was determined in a competition experiment with one of the benzenesulfonamide array members to address the possibility of screening substance libraries for new target-protein binders. Also, successful affinity discrimination between different carbonic anhydrase isozymes highlighted the possibility of performing future isoform-expression profiling. Our platform is predicted to become a flexible tool for a variety of biosensor and protein-microarray applications within biochemistry, diagnostics and pharmaceutical chemistry.
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Manzano J, Filippini D, Lundström I. Principal component analysis of sample response to RGB light. Analyst 2004. [DOI: 10.1039/b310965h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Karlsson LM, Tengvall P, Lundström I, Arwin H. Penetration and loading of human serum albumin in porous silicon layers with different pore sizes and thicknesses. J Colloid Interface Sci 2003; 266:40-7. [PMID: 12957580 DOI: 10.1016/s0021-9797(03)00595-2] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Human serum albumin was adsorbed into porous silicon layers with thickness up to 3 microm and with different mean pore radius in the range 4.5-10 nm. The adsorbed amount of protein was quantified by I(125) radioactive labeling techniques and ellipsometry. The results show that albumin penetrated into the pores when the mean pore radius was larger than 5.5 nm, but could not totally occupy the available surface area when the layer thickness was larger than 1 microm. Loading of albumin both into porous layers and onto plane silicon as a function of albumin concentration was also investigated. These measurements show that loading of protein increased with protein concentration at least up to 10 mg/ml for porous silicon and up to 1 mg/ml for plane silicon. The maximum deposition into the type of porous layers used here was 28 microg/cm(2), compared to 0.36 microg/cm(2) for plane silicon.
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Karlsson LM, Tengvall P, Lundström I, Arwin H. Adsorption of human serum albumin in porous silicon gradients. ACTA ACUST UNITED AC 2003. [DOI: 10.1002/pssa.200306518] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Immerstrand C, Jager EWH, Magnusson KE, Sundqvist T, Lundström I, Inganäs O, Peterson KH. Altered impedance during pigment aggregation in Xenopus laevis melanophores. Med Biol Eng Comput 2003; 41:357-64. [PMID: 12803303 DOI: 10.1007/bf02348443] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Melanophores are dark-brown pigment cells located in the skin of amphibia, fish and many invertebrates. The skin colour of these organisms is regulated by the translocation of pigment organelles, and the pigment distribution can be altered by external stimuli. The ability to change colour in response to stimuli makes these cells of interest for biosensing applications. It was investigated whether pigment aggregation in Xenopus laevis melanophores can be detected by impedance measurements performed in transparent microvials. The results show that cell attachment, cell spreading and pigment aggregation all resulted in impedance changes, seen particularly at the highest frequency tested (10 kHz). The mechanisms behind the impedance changes were investigated by the addition of latrunculin or melatonin, both of which cause pigment aggregation. The latrunculin-induced aggregation was associated with cell area decrease and filamentous actin (F-actin) breakdown, processes that can influence the impedance. Lack of F-actin breakdown and an increase in cell area during melatonin-induced aggregation suggest that some other intracellular process also contributes to the impedance decrease seen for melatonin. It was shown that impedance measurements reflect not only cell attachment and cell spreading, but also intracellular events.
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Filippini D, Svensson SPS, Lundström I. Computer screen as a programmable light source for visible absorption characterization of (bio)chemical assays. Chem Commun (Camb) 2003:240-1. [PMID: 12585410 DOI: 10.1039/b210677a] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Visible absorption features suitable for color recognition and micro-plate reading of a standard bioassay are performed by the combination of a computer screen used as a programmable light source and a web camera as detector. The method provides in this way a highly available platform for 'home tests' or 'self-tests', where the requirement is to monitor well defined assays and the use of economical instrumentation is advantageous.
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Winquist F, Krantz-Rülcker C, Lundström I. Electronic Tongues and Combinations of Artificial Senses. ACTA ACUST UNITED AC 2002. [DOI: 10.1002/seup.200211107] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Aifa S, Johansen K, Nilsson UK, Liedberg B, Lundström I, Svensson SPS. Interactions between the juxtamembrane domain of the EGFR and calmodulin measured by surface plasmon resonance. Cell Signal 2002; 14:1005-13. [PMID: 12359306 DOI: 10.1016/s0898-6568(02)00034-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
One early response to epidermal growth factor receptor (EGFR) activation is an increase in intracellular calcium. We have used surface plasmon resonance (SPR) to study real-time interactions between the intracellular juxtamembrane (JM) region of EGFR and calmodulin. The EGFR-JM (Met(644)-Phe(688)) was expressed as a GST fusion protein and immobilised on a sensor chip surface. Calmodulin specifically interacts with EGFR-JM in a calcium-dependent manner with a high on and high off rate. Chemical modification of EGFR-JM by using arginine-selective phenylglyoxal or deletion of the basic segment Arg(645)-Arg(657) inhibits the interaction. Phosphorylation of EGFR-JM by protein kinase C (PKC) or glutamate substitution of Thr(654) inhibits the interaction, suggesting that PKC phosphorylation electrostatically interferes with calmodulin binding to basic arginine residues. Calmodulin binding was also inhibited by suramin. Our results suggest that EGFR-JM is essential for epidermal growth factor (EGF)-mediated calcium-calmodulin signalling and for signal integration between other signalling pathways.
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Winquist F, Rydberg E, Holmin S, Krantz-Rülcker C, Lundström I. Flow injection analysis applied to a voltammetric electronic tongue. Anal Chim Acta 2002. [DOI: 10.1016/s0003-2670(02)00923-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Hansson KM, Tengvall P, Lundström I, Rånby M, Lindahl TL. Comparative studies with surface plasmon resonance and free oscillation rheometry on the inhibition of platelets with cytochalasin E and monoclonal antibodies towards GPIIb/IIIa. Biosens Bioelectron 2002; 17:761-71. [PMID: 12191924 DOI: 10.1016/s0956-5663(02)00049-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In the haemostatic system a multitude of processes are intertwined in fine-tuned interactions that arrest bleeding, keep the circulatory system open, and the blood flowing. The occurrence of both surface and bulk interactions adds an additional dimension of complexity. These insights have led to the belief that global overall procedures can inform on the likely behaviour of the system in health and disease. Two sensing procedures: surface plasmon resonance (SPR), which senses surface interactions, and free oscillation rheometry (FOR), which senses interactions within the bulk, have been combined and evaluated. The contribution of blood cells, mainly platelets, to the SPR and FOR signals was explored by simultaneous SPR and FOR measurement during native whole blood coagulation, accelerated via the platelets through addition of SFLLRN peptide and inhibition of platelet aggregation with abciximab (ReoPro) and of shape change with cytochalasin E. The SPR technique was found to be sensitive to inhibition of blood cell functions such as adhesion to and spreading on surfaces, as well as platelet aggregation. SPR seemed not to be directly sensitive to fibrin polymerisation in coagulating whole blood. The FOR technique detected the coagulation as a bulk phenomenon, i.e. the gelation of the blood due to fibrin formation was detected. The combination of SPR and FOR may therefore be suitable for studies on blood cell functions during coagulation.
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Hansson KM, Tengvall P, Lundström I, Rånby M, Lindahl TL. Surface plasmon resonance and free oscillation rheometry in combination: a useful approach for studies on haemostasis and interactions between whole blood and artificial surfaces. Biosens Bioelectron 2002; 17:747-59. [PMID: 12191923 DOI: 10.1016/s0956-5663(02)00048-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In haemostatic and biomaterial research biological processes at surfaces and in the bulk phase of the surface-contacting medium are important. The present work demonstrates the usefulness of the combination of surface plasmon resonance (SPR), sensitive to changes in refractive index at surfaces, and free oscillation rheometry (FOR), sensitive to rheological properties of the bulk, for simultaneous real-time measurements on coagulation and fibrinolysis of blood plasma and coagulation of whole blood. SFLLRN stimulated coagulation of native whole blood presented a higher SPR signal with different appearance than plasma coagulation, while the FOR signals corresponding to plasma and whole blood coagulation were similar. This indicated that the SPR technique was more sensitive to cell-surface interactions than to fibrin formation in whole blood during coagulation, while the FOR technique were equally sensitive to coagulation in whole blood and plasma. Spontaneous coagulation of native whole blood in contact with methyl- and hydroxyl-terminated self-assembled monolayers (SAM) on gold and gold surfaces regenerated after coagulation were also studied. The regenerated gold surfaces displayed the shortest coagulation times, although the contact-activation of blood coagulation for these surfaces was low. The methylated and hydroxylated surfaces were comparable in terms of coagulation activation, while the hydroxylated surfaces presented FOR signals that indicated detaching of the coagulum from the surface. The combination of SPR and FOR is well suited for studies of cell- and protein-surface interactions and simultaneous bulk processes. Possible applications are investigations of blood cell defects in patients and monitoring of native whole blood interactions with artificial surfaces.
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Enander K, Dolphin GT, Andersson LK, Liedberg B, Lundström I, Baltzer L. Designed, folded polypeptide scaffolds that combine key biosensing events of recognition and reporting. J Org Chem 2002; 67:3120-3. [PMID: 11975577 DOI: 10.1021/jo010954n] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Ekeroth J, Konradsson P, Björefors F, Lundström I, Liedberg B. Monitoring the interfacial capacitance at self-assembled phosphate monolayers on gold electrodes upon interaction with calcium and magnesium. Anal Chem 2002; 74:1979-85. [PMID: 12033295 DOI: 10.1021/ac015635a] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Electrochemical impedance spectroscopy has been used to evaluate the change in interfacial capacitance upon calcium and magnesium coordination to a phosphate-modified electrode. The phosphate electrode was prepared via immobilization of phosphorylated, thiol-containing, serine analogues onto gold. Upon subjection to calcium and magnesium, a substantial drop in capacitance was observed. Magnesium displayed the largest influence on the capacitance: a 27% capacitance drop was observed upon introduction of a 1 mM solution of magnesium ions. The lowered capacitance is a result of a change in the potential and charge distribution at the film/electrolyte interface as the cations coordinate to the phosphate groups. Moreover, the relationship between electrode potential and capacitance has been investigated and reveals a significant difference between monovalent and divalent cations. As complementary information, infrared reflection absorption spectra of the phosphorylated monolayer having different counterions are presented. The results reported in this paper indicate that the phosphorylated amino acid analogue monolayers could be used in investigations of the biochemically important coordination of calcium and magnesium to phosphates and phosphorylated amino acids.
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Mecklenburg M, Svitel J, Winquist F, Gang J, Ornstein K, Dey E, Bin X, Hedborg E, Norrby R, Arwin H, Lundström I, Danielsson B. Differentiation of human serum samples by surface plasmon resonance monitoring of the integral glycoprotein interaction with a lectin panel. Anal Chim Acta 2002. [DOI: 10.1016/s0003-2670(02)00101-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Danermark B, Antonson S, Lundström I. Social inclusion and career development--transition from upper secondary school to work or post-secondary education among hard of hearing students. SCANDINAVIAN AUDIOLOGY. SUPPLEMENTUM 2002:120-8. [PMID: 11409771 DOI: 10.1080/010503901750166880] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The aim of this study was to investigate the decision process and to analyse the mechanisms involved in the transition from upper secondary education to post-secondary education or the labour market. Sixteen students with sensorioneural hearing loss were selected. Among these eight of the students continued to university and eight did not. Twenty-five per cent of the students were women and the average age was 28 years. The investigation was conducted about 5 years after graduation from the upper secondary school. Both quantitative and qualitative methods were used. The results showed that none of the students came from a family where any or both of the parents had a university or comparable education. The differences in choice between the two groups cannot be explained in terms of social inheritance. Our study indicates that given normal intellectual capacity the level of the hearing loss seems to have no predictive value regarding future educational performance and academic career. The conclusion is that it is of great importance that a hearing impaired pupil with normal intellectual capacity is encouraged and guided to choose an upper secondary educational programme which is orientated towards post-secondary education (instead of a narrow vocational programme). Additional to their hearing impairment and related educational problems, hard of hearing students have much more difficulty than normal hearing peers in coping with changes in intentions and goals regarding their educational career during their upper secondary education.
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Jager EW, Immerstrand C, Peterson KH, Magnusson K, Lundström I, Inganäs O. Biomed Microdevices 2002; 4:177-187. [DOI: 10.1023/a:1016092228965] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Testorf MF, Karlsson AM, Svensson SP, Oberg PA, Lundström I. A model for switch-like phenomena in biological systems. Biophys Chem 2001; 94:1-9. [PMID: 11744185 DOI: 10.1016/s0301-4622(01)00231-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We present a model for the activity of protein clusters based on a simultaneous desorption of an activator (agonist, substrate molecule, etc.) and an inactivator (antagonist, inhibitor, etc.) caused by the collision or interaction between two effector molecules (e.g. receptors, enzymes). This model gives rise to switch-like dose-response curves, which are difficult to explain by ordinary co-operativity. It fits with recent experimental results obtained on single cells. Some other interesting aspects of the model are also pointed out. The model is similar to the model used to explain steep 'dose-response curves' in heterogeneous catalysis, caused by the reaction between two different molecules or atoms on the surface of the catalyst.
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