Data from: Systematic study of the surface plasmon resonance signals generated by cells for sensors with different characteristic lengths

The objectives of this study were to establish an in-depth understanding of the signals induced by mammalian cells in surface plasmon resonance (SPR) sensing. To this end, two plasmonic structures with different propagation and penetration distances were used: conventional surface plasmon resonance and long-range surface plasmon resonance. Long-range SPR showed a lesser sensitivity to the absolute number of round cells but a greater resolution due to its very narrow spectral dip. The effect of cell spreading was also investigated and the resonance angle of long-range SPR was mostly insensitive unlike in the conventional SPR counterpart. Experimental data was compared with suitable models used in the SPR literature. Although these simple averaging models could be used to describe some of the experimental data, important deviations were observed which could be related to the fact that they do not take into consideration critical parameters such as plasmon scattering losses, which is particularly crucial in the case of long-range SPR structures. The comparison between conventional and long-range SPR for cellular schemes revealed important fundamental differences in their responses to the presence of cells, opening new horizons for SPR-based cell assays. From this study, long-range SPR is expected to be more sensitive towards both the detection of intracellular events resulting from biological stimulation and the detection of microorganisms captured from complex biological samples

Experimental setup.

<p>(a) Scheme of the instrument set for angular interrogation of SPR sensors utilizing the attenuated total internal reflection method. Two different SPR structures with different characteristic propagation and penetration lengths were used in this study: (b) cSPR is composed of a layer of gold comprised between the glass substrate (prism) and the cover medium (PBS or DMEM plus cells) and (c) LRSPR is composed of a layer of Cytop polymer deposited on the glass substrate, onto which a thin layer of gold is sputtered, creating a RI symmetry supporting long range plasmon waves.</p

all data - from micrographs to spectra

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Experimental spectra recorded for cSPR sensors and LRSPR sensors at different cell coverage values.

<p>(a) cSPR spectra and (b) LRSPR spectra. The arrows indicate the evolution of the spectra. (c) Micrographs of three different cell coverage values of round 3T3 cells. Scale bar is 100 µm.</p

Comparison of cSPR and LRSPR spectra parameters for the two experimental schemes.

<p>Dependence of <i>θ</i>_res (a) and <i>R</i>_min (b) with respect to the cell coverage (round cells). The inset in (a) represents Δ<i>θ</i>_res/<i>HWHM</i>, the slope of which is the figure of merit of the sensor. It was found that <i>FOM</i> = 1.30%⁻¹ and <i>FOM</i> = 7.39%⁻¹ for cSPR and LRSPR, respectively, yielding a 5.7-fold enhancement in the case of LRSPR. Dependence of Δ<i>θ</i>_res (c), and <i>R</i>_min (d) with respect to the cell spreading. The error bars represent the standard errors.</p

Typical reflectivity spectra of cSPR and LRSPR upon cellular spreading.

<p>(a) cSPR spectra and (b) LRSPR spectra. The cell seeding density was of 150 cells/mm². The arrows show the evolution of the spectra. The insets show a close-up of the minimum of intensity. The coverage values were inferred from the curve in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107978#pone.0107978.s002" target="_blank">Figure S2</a>.</p

Comparison of cSPR parameters from experimental studies to those predicted by the averaged-intensity cSPR model.

<p>Dependence of <i>θ</i>_res (a) and <i>R</i>_min (b) with respect to the cell coverage. Dependence of <i>θ</i>_res (c), and <i>R</i>_min (d) with respect to the spreading of cells. The simulations are plotted in dashed curves (<i>n</i>_cell = 1.35: diamond, <i>n</i>_cell = 1.36: squares, <i>n</i>_cell = 1.37: triangles). Fitting the linear parts in (a) yielded <i>n</i>_cell = 1.3483 (by quadratic extrapolation of the slopes). Error bars represent the standard errors.</p