Theoretical understanding of the SPR sensor response on the protein adsorption

Transcription

1 Proc. 4th Int. Conf. on Global Reearch and Education, Inter-Academia 05 JJAP Conf. Proc. 4 (06) The Japan Society of Applied Phyic Theoretical undertanding of the SPR enor repone on the protein adorption Olga Lopatynka *, Andrii Lopatynkyi, Volodymyr Chegel, Leonid Poperenko Tara Shevchenko Kyiv National Univerity, Kyiv, Ukraine V.E. Lahkaryov Intitute of Semiconductor Phyic, National Academy of Science of Ukraine, Kyiv, Ukraine olga_lopatynka@ukr.net (Received September 6, 05) Thi reearch deal with conideration of the SPR enor repone in the framework of the cattering matrix approach with the modeling of biomolecular layer uing Green function formalim and ective medium theorie. It wa found out that modeling of the SPR enor repone uing abovementioned approache in the denely packed monolayer approximation gave not enough agreement with the experiment. The reaon wa that real molecular layer are rarely denely packed. They uually can be characterized by molecular urface concentration or monolayer filling factor. Approximation of thee parameter allow obtaining their value, which correpond to real biomolecular layer, and give better agreement with the experiment.. Introduction Surface plamon reonance (SPR) i a highly enitive modern technique which ha many application, epecially with invetigation of biological object [-5]. For example, thi technique can be ued to tudy the protein adorption [6-8]. In fact, ometime the problem of reult interpretation appear. The SPR enor repone i uually modeled in the framework of the cattering matrix formalim [9-]. However, the reult of uch modeling often do not conform well to the experiment, becaue thi approach doe not conider the internal tructure of the biomolecular layer. So, we extended thi approach by uing the ective medium theorie [3] and Green function formalim [4,5] for biomolecular layer modeling. The advantage of the Green function approach were conidered in detail in the work [5]. Uing thi method to proce the SPR experimental data, the author have calculated the urface concentration and the component of the molecular permittivity tenor of the biomolecular layer intead of refractive index and thickne of the biomolecular layer. It wa hown that SPR repone depend on the hape and orientation of adorbed molecule with repect to the SPR enor urface. The ective medium theorie are uually ued for the conideration of multicomponent media uch a rough urface [6], nanoparticle in dielectric matrice [7,8], nanoparticle thin film [9], iland film [0] etc. We have applied the ective medium theory approach to biomolecular layer on olid urface, which can be alo conidered a a two-phae multicomponent ytem coniting of biomolecule and buffer olution. Therefore, the main aim of the preent reearch i to compare the reult of SPR repone modeling by abovementioned approache with the SPR experimental data obtained for the protein adorption.. Experimental Commercially available optoelectronic SPR bioenor NanoSPR-3 wa ued in the preent 050-

2 JJAP Conf. Proc. 4 (06) reearch. The TF gla SPR lide with thermally evaporated 45 nm gold film and 5 nm chromium adheion ublayer were exploited a plamon ocillation carrier. The reflected light intenity veru the angle of incidence (SPR curve) wa meaured. At the angle, which i called reonant, the urface plamon reonance occur that caue harp decreae of reflected light intenity. The preence of the biomolecular layer on the enor urface reult in SPR minimum angular poition hift toward larger value. Phophate buffered aline (PBS) olution of trypin (4 kda, globular protein with ize 5 nm) and bovine erum albumin (BSA, kda, ellipoidal protein with ize nm) with concentration of 50 μg/ml were exploited during the experiment. 3. Theory SPR enor repone on biomolecular adorption wa modeled in the framework of the cattering matrix formalim to characterize the multilayer ytem (gla-cr-au-biomolecular layer-buffer olution) with additional conideration of the biomolecular layer uing Green function approach and ective medium theorie. In the Green function approach [] for pherical molecule, the biomolecular layer i characterized by molecular urface concentration N and molecular polarizability A m. Then the reflectance coicient of p-polarized light by the ytem will be [4]: ( Am gxx Am f zz )( R0p ) ( Am gxx Am f zz ) R0p Rp R0 p, ( A ag )( A af ) a( A g A f ) R m xx m zz m xx m zz 0 p where R 0 p i the reflectance coicient of p-polarized light by the ytem without biomolecular layer, 3M n Am 4 Na n i the polarizability of the pherical molecule, 4Am, a N, n are ome combination of the wave vector, xx k /, zz nx g x n f k k0n in, x n k0 k, k0, c n i the refractive index of the protein molecule, n i the refractive index of the urrounding medium, M i the molecular weight of the protein molecule, i the protein denity, N a i the Avogadro number. If the protein molecule i not pherical, then abovementioned equation are ubtituted with repective formula [4]. In the ective medium approach, the biomolecular layer i characterized by the ective refractive index of the biomolecular layer n and filling factor f. Depending on the topology of heteroytem, different ective medium theorie can be ued [3]. For example, for Lorentz-Lorenz ective medium theory the refractive index of the biomolecular layer can be derived from the equation [3] n n n f ( f ), n n n where n i the refractive index of the urrounding medium, n i the refractive index of the

3 JJAP Conf. Proc. 4 (06) protein molecule. Similarly, for the Maxwell-Garnett theory the ective refractive index can be found from the formula n n n n f ; n n n n for the Bruggeman nonymmetrical and ymmetrical theorie the ective refractive indice are the olution of equation and 3 3 n n n n n f n f n n n n f ( ) 0, n n n n repectively. The following value were ued for the calculation of the multilayer tructure parameter: the refractive index of the gla lide wa n =.6, chromium complex refractive index n = 3.66 g і [], refractive index of protein molecule n =.46 [3], the approximate thicknee of adorbed trypin and BSA layer were d tr = 5.0 nm and d BSA = 4.0 nm (BSA long axi i parallel to the urface), repectively [4]. Gold complex refractive index wa fitted for the curve correponding to the initial PBS flow, with n Au = і [5] choen a a gue value for the fitting. Cr 4. Reult and dicuion The kinetic dependence of SPR curve minimum (SPR enogram) for trypin and BSA adorption were experimentally obtained (Fig., ) PBS SPR curve minimum, PBS Trypin Time, min Fig.. The kinetic dependence of SPR curve minimum for trypin adorption. SPR enogram repreent the following procee at the SPR enor urface. The firt horizontal

4 JJAP Conf. Proc. 4 (06) region correpond to the tabilization of the gold-liquid interface after filling the meaurement cell with buffer olution. The next tage with increaing SPR curve minimum poition correpond to the protein adorption proce and the lat region with the decreaing of the SPR curve minimum i connected with the removal of the non-adorbed protein due to rining with buffer olution SPR curve minimum, PBS PBS BSA Time, min Fig.. The kinetic dependence of SPR curve minimum for BSA adorption. The final angular poition of SPR curve minimum exp, which correpond to the formed biomolecular layer on the SPR enor urface, were compared with the imilar value, calculated uing the abovementioned theoretical approach in the denely packed monolayer approximation. Biomolecule filling factor (for ective medium theorie) wa equal to 0.54 and urface concentration (for Green function formalim) of the trypin and BSA layer were m - and m -, repectively (Table I). Table I. Comparion of the experimental and calculated (Green function and ective medium theorie) SPR curve minimum value. exp, Green, LL, MG, Br. nonym., Br. ym., Trypin BSA A one can ee, the calculated value of SPR curve minimum are cloe but not equal to the experimental one. The reaon i that real molecular layer can t be conidered a denely packed. They are characterized by ome molecular urface concentration N (for Green function formalim) or filling factor f (for ective medium theorie). If we change the filling factor (or urface concentration for Green function formalim) among all poible value and calculate the repective poition of the SPR curve minimum, we hall be able to chooe uch value of filling

5 JJAP Conf. Proc. 4 (06) factor (urface concentration) which will correpond to experimental poition of the SPR curve minimum. Therefore, approximation of the abovementioned parameter allow obtaining better agreement with the experiment. It hould be noted that different ective medium theorie gave almot the ame reult which i rather unexpected. Thi can be explained by the fact that the filling factor for the calculation wa 0.54 and thi value i ituated at the limit of ome theorie application. So, further we hall apply only one ective medium theory, namely, Bruggeman ective medium theory becaue it i applicable not only for mall filling factor a, for example, Maxwell-Garnett theory. The reult of the calculation in the framework of parely packed layer are preented in Table II. Table II. Experimentally obtained value of SPR curve minimum and calculated molecular urface concentration, filling factor and ective refractive indice of trypin and BSA layer. exp, N, f 0 6 m - N. Br. Trypin BSA Evidently, Table II demontrate the approximated molecular urface concentration N and filling factor f value that we have obtained which more correctly characterize the real biomolecular layer and give better agreement with the experiment. 5. Concluion The cattering matrix approach for conideration of SPR experiment reult of biomolecular adorption tudy wa extended uing theoretical model decribing parely packed molecular layer. A a reult, it wa found that modeling of the SPR enor repone uing Green function formalim and ective medium theorie allow more correct explanation of the experimental reult taking into account parely packed tructure of biomolecular layer. Propoed approach allow etimating the urface molecular concentration and filling factor, which are important parameter decribing the biomolecular layer. Reference [] A. Olaru, C. Bala, N. Jaffrezic-Renault, and H. Y. Aboul-Enein, Crit. Rev. Anal. Chem. 45, 97 (05). [] P. P. Vachali, B. Li, A. Bartchi, and P. S. Berntein, Arch. Biochem. Biophy. 57, 66 (05). [3] R. Méjard, H. J. Grieer, and B. Thierry, TrAC Trend. Anal. Chem. 53, 78 (04). [4] X. Guo, J. Biophotonic 5, 483 (0). [5] J. Homola, Surface Plamon Reonance Baed Senor, Springer Serie on Chemical Senor and Bioenor Vol. 4 (Springer-Verlag, Berlin Heidelberg, 006), Part III, p. 55. [6] K. A. Wilon, C. A. Finch, P. Anderon, F. Vollmer, and J. J. Hickman, Biomaterial 38, 86 (05). [7] J. Breault-Turcot, P. Chaurand, and J.-F. Maon, Anal. Chem. 86, 96 (04). [8] T. Date, Y. Ueda, H. Atarahi, T. Sawada, H. Matuzawa, K. Tanaka, and T. Serizawa, J. Nanoci. Nanotechnol. 4, 306 (04). [9] Y. M. Bae, B.-K. Oh, W. Lee, W. H. Lee, and J.-W. Choi, Bioen. Bioelectron., 03 (005). [0] G. V. Beketov, Yu. M. Shirhov, O. V. Shynkarenko, and V. I. Chegel, Senor. Actuat. B-Chem. 48,

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