Short CommunicationNanoscale mapping of refractive index by using scattering-type scanning near-field optical microscopy
Graphical Abstract
The experimental s-SNOM results (Amplitude and Phase images) are correlated to the theoretical model of oscillating point-dipole. Together they lead to a 4D visual representation with nanoscale resolution of the sample (red blood cells). The topography is represented in three spatial dimensions, while the refractive index is coded using a colormap.
Section snippets
Method
Control erythrocytes (sample A) were prepared by smearing human peripheral blood drops on glass slides. Sample A was used for testing the s-SNOM measurements of erythrocytes' RI by comparing the results to those reported in the literature.10, 11, 12, 13, 14 Sample B was prepared by mixing equal volumes of peripheral blood and isotonic saline solution and smearing the resulting mixture on glass slide. Both samples were imaged immediately after drying at room temperature.
The cover-slips (Zeiss,
Results
The algorithm described in the Methods is run on s-SNOM images acquired from both samples. Figure 1 shows the AFM images (Figure 1, A and D) and the resulting real (Figure 1, B and E) and imaginary (Figure 1, C and F) parts of the RI maps computed using the s-SNOM images corresponding to the two samples. To clearly visualize the results, in Figure 1 RI data corresponding to the glass substrate was removed and only the data for the erythrocytes is displayed. The rectangle area delimited in
Conclusions
Optical data collected with s-SNOM has an optical resolution lying well beyond the diffraction barrier (~35 nm) and is collected in tandem with topography information. The RI mapping based on s-SNOM allows for precise optical investigations at nanoscale which permits local detailed representation of this optical property. Limitations of this method are same as in any scanning‐probe imaging approach and mainly refer to the probe's tip (which limits the resolution to its size) and the sample's
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2022, Advanced Drug Delivery ReviewsCitation Excerpt :s-SNOM imaging was demonstrated on a single RBC in 2016 (Fig. 2f) [78]. Later, Tranca et al. obtained nanoscale complex refractive indices of human erythrocytes based on s-SNOM imaging and a dipole model [86]. Moreover, a systematic spectroscopic analysis of isolated and intact RBC membranes was carried out by Blat et al. [87].
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2022, TrAC - Trends in Analytical ChemistryCitation Excerpt :Other researchers used SNOM to detect distribution of the protein complement receptor 1 (CR1/CD35) and quantitatively measure its clusters in RBC membrane [319]. Furthermore, previous studies have shown application possibilities of the s-SNOM to create high-resolution refractive index (RI) map of the erythrocyte, what can serve as a potential disease biomarker [320]. On the other hand, cytochalasin penetration into the RBC plasma membrane has been demonstrated by the a-SNOM measurements in tapping mode [307].
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2020, Applied Surface ScienceCitation Excerpt :Furthermore, in recent work, we have shown that s-SNOM represents also a very useful tool for quantitatively characterizing optical surface properties of various samples, ranging from dielectrics, semiconductors, metals to biologic tissues by determining their complex dielectric function, and hence other intrinsic optical properties such as the complex refractive index [23,34,35]. This feature is of great benefit for material engineering and characterization [36,37], optical waveguides engineering [35,38,39], biology [23,40] and more. In this article we demonstrate that s-SNOM’s potential for surface characterization can be augmented by employing the phasor representation to represent typical s-SNOM data (in the form of amplitude and phase images) in an alternative way.
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Funding Sources: This work has received support from the European Community's Seventh Framework Programme (FP7/2012-2015) under grant agreement no. 280804 (LANIR, www.lanir.eu) and no. 212533 (BioElectricSurface, www.bioelectricsurface.eu). This communication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. The presented work has been supported as well by the Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding through the research grants PN-II-PT-PCCA-2011-3.2-1162 (NANOLASCAN) and PN-II-RU-TE-2014-4-1803 (MICRONANO).
No competing interests are present.