Metal clad waveguide (MCWG) based imaging using a high numerical aperture microscope objective

Abstract

Evanescent-field based methods such as surface plasmon resonance (SPR) have been used very effectively for label-free imaging of microscopic biological material in close proximity to a sensing surface. However, the shallow probing depth of SPR (typically less than ~200 nm) can be problematic when imaging relatively thick biological objects such as cells or bacteria. In this paper, we demonstrate how metal-clad waveguides (MCWG) can be used to achieve deeper probing depth compared to SPR while maintaining good imaging spatial resolution. Comparative numerical simulations of imaging spatial resolution versus probing depth are shown for a number of common SPR, long-range SPR, and MCWG configurations, demonstrating that MCWG offer the best compromise between resolution and depth for imaging thick biological objects. Experimental results of synthetic target and live cell imaging are shown that validate the numerical simulations and demonstrate the capabilities of the method.

Nanoplasmonics-enhanced label-free imaging of endothelial cell monolayer integrity

“…The imaging system setup presented in Fig. 1A is based on a high numerical aperture microscope objective and has previously been described (Söllradl et al, 2017). The excitation light (LED filtered at 830 nm, FWHM of 10 nm) is focused on the back focal plane of the objective (NA = 1.46), reflected by the sensor chip placed atop the objective, and imaged by a CMOS camera.…”

“…However, while being highly specific techniques, the use of labelling may impact the cells (Progatzky et al, 2013), which is not the case for non-invasive labelfree methods (Bourassa et al, 2015;Bousse, 1996;Chabot et al, 2009;Fang, 2011;Pancrazio et al, 1999). Cell activity has been successfully monitored using several label-free biosensing methods, in particular by electrochemical impedance spectroscopy (Giaever and Keese, 1993;McGuiness, 2007), resonant Waveguide Grating (Fang et al, 2006;Ferrie et al, 2010), surface plasmon resonance (Chabot et al, 2013(Chabot et al, , 2012(Chabot et al, , 2009Giebel et al, 1999;Maltais et al, 2012;Peterson et al, 2009;Wang et al, 2012) and metal-clad waveguides (Söllradl et al, 2018b(Söllradl et al, , 2018a(Söllradl et al, , 2017. Evanescent-field based methods such as surface plasmon resonance (SPR) and metal-clad waveguides (MCWG) are highly sensitive to small variations in refractive index at the sensor surface (hundred of nanometers).…”

Monitoring individual cell-signaling activity using combined metal-clad waveguide and surface-enhanced fluorescence imaging

“…Cell-based assays using a variety of label-free transduction methods such as diffraction gratings, 3 electrical impedance, 4 and surface plasmon resonance [5][6][7][8][9][10][11] have been proposed to study cellsignaling with no need for exogenous markers. Recently, a more flexible type of evanescent field transduction based on metal clad waveguides (MCWG) has been used in sensing applications with cells and bacteria to probe deeper into the cell body 12,13 than is possible with SPR (typically 200 nm or less for visible and near-IR systems). Using appropriate optics, SPR and MCWG can be used for imaging where advanced systems are capable of resolving intracellular structures.…”

High-resolution-scanning waveguide microscopy: spatial refractive index and topography quantification

“…Interference between the guided wave with its reflections on the border of a finite size index step can smear the guided wave outside the step [7] and deteriorate the resolution and image contrast, requiring further image processing [8]. Söllradl et al [9] proposed to couple the guided wave with a high numerical aperture microscope objective lens; however, the lateral resolution (along the x axis) of their wide field microscope remained limited by the lateral decay propa gation length of the MCWG (several microns). Scanning surface plasmon microscopy (SSPM) uses a strongly focused incident beam to reach the diffraction limit [10 13].…”

“…Actually compared to the method proposed in Ref. [9], no focusing of the resonance angle is needed. A complete study of the whis pering gallery mode imaging with SSPM in the ring and the disk will be reported in a forthcoming paper.…”