Antenna-Based Optical Imaging of Single Ca²⁺ Transmembrane Proteins in Liquids

Abstract

Understanding the diversity of biological processes requires methods that can address single proteins in their natural environment and provide insights into structural and functional properties, as well as the local distribution of each individual protein. We use an optical antenna in the form of a single gold nanoparticle to localize incident laser radiation to 50 nm, significantly smaller than the diffraction limit of light. Our approach enables us to optically resolve individual plasma-membrane-bound Ca 2+ pumps (PMCA4) immersed in aqueous environments and to determine the distribution of interprotein distances. We are able to correlate the protein maps with local topology. Improved antenna geometries will make it possible to resolve, identify, and probe single membrane proteins in live cells with true protein resolution of 5−10 nm.

Review of near-field optics and superlenses for sub-diffraction-limited nano-imaging

“…Other geometries include a small metallic particle situated on a dielectric tip. [127][128][129][130][131][132] Also, a microscope was demonstrated where a small metallic particle was trapped and positioned by optical forces. 133 Very recently, a novel corrugated probe geometry has been proposed.…”

Performing tip‐enhanced Raman spectroscopy in liquids

“…In order to overcome these drawbacks, antenna-based apertureless near-field fluorescence imaging has been proposed and demonstrated successfully in the imaging of single Ca 2+ transmembrane proteins in red blood cell membranes. [2] The main drawback of fluorescence approaches is the need for labeling, which always represents an interference with the biological system under study. Thus, errors resulting from changed behavior of the labeled molecules, unspecific staining, or toxic effects often cannot be totally ruled out.…”

Antenna Design for Directivity-Enhanced Raman Spectroscopy

“…Considering the numerical aperture of our microscope Raman system, the nanoantenna presented has near-perfect excitation and collection of the electromagnetic energy. This work is also exciting for related applications, for example, photovoltaics, light-emitting applications, microscopy, sensing, and singlemolecule detection [29,31,36].…”

“…Directing the emission from optical emitters is highly desired for efficient detection and, by reciprocity, efficient excitation as well. Typical applications include light-emitting devices [21,22], photovoltaics [23][24][25][26][27], sensing [28,29], spectroscopy [30][31][32], single-photon sources [33,34], and microscopy [3,35,36].…”