Ultrasensitive Photoreversible Molecular Sensors of Azobenzene-Functionalized Plasmonic Nanoantennas

Abstract

This Letter describes an unprecedentedly large and photoreversible localized surface plasmon resonance (LSPR) wavelength shift caused by photoisomerization of azobenzenes attached to gold nanoprisms that act as nanoantennas. The blue light-induced cis to trans azobenzene conformational change occurs in the solid state and controls the optical properties of the nanoprisms shifting their LSPR peak up to 21 nm toward longer wavelengths. This shift is consistent with the increase in thickness of the local dielectric environment (0.6 nm) surrounding the nanoprism and perhaps a contribution from plasmonic energy transfer between the nanoprism and azobenzenes. The effects of the azobenzene conformational change and its photoreversibility were also probed through surface-enhanced Raman spectroscopy (SERS) showing that the electronic interaction between the nanoprisms and bound azobenzenes in their cis conformation significantly enhances the intensity of the Raman bands of the azobenzenes. The SERS data suggests that the isomerization is controlled by first-order kinetics with a rate constant of 1.0 × 10(-4) s(-1). Our demonstration of light-induced photoreversibility of this type of molecular machine is the first-step toward removing present limitations on detection of molecular motion in solid-state devices using LSPR spectroscopy with nanoprisms. Modulating the LSPR peak position and controlling energy transfer across the nanostructure-organic molecule interface are very important for the fabrication of plasmonic-based nanoscale devices.

Achieving biosensing at attomolar concentrations of cardiac troponin T in human biofluids by developing a label-free nanoplasmonic analytical assay

“…Based on our published work, these Au TNPs are found to be nearly same (± 1.5 nm) thickness. [44][45][46][47] A representative atomic force microscopy image is shown in Fig. 2D.…”

Active molecular plasmonics: tuning surface plasmon resonances by exploiting molecular dimensions

“…Furthermore, the SAM matrices offer the well-defined nanoenvironments for both single-molecule analysis and functional control of the molecular switches. The performance-enhanced AMP has been demonstrated with 0D azobenzene-based molecular switches [116]. Azobenzene exhibits the reversible photoisomerization between trans and cis isomers upon its alternative exposure to UV and visible light.…”

“…However, SAMs of azobenzene exhibit low isomerization efficiency due to the physical hindrance from the large contour changes of trans-cis isomerization, which has rarely been applied to AMP. By creating 0D azobenzene isolated within the domains of SAMs of alkanethiols on Au nanoprisms, Joshi et al demonstrated a 21 nm peak shift in the LSPRs of the nanoprisms upon the photoisomerization of azobenzene despite the low concentration of the molecular switches ( Figure 6A) [116]. To achieve the maximal peak shift, the concentration of 0D azobenzene in SAMs was optimized to reach a balance between the isomerization efficiency and the density of azobenzene on nanoprisms.…”

Electromechanically Tunable Suspended Optical Nanoantenna

“…More details can be found in Ref. 21. In brief, a collimated white light beam was focused onto the sample surface from below with grazing angle incidence.…”

“…[3][4][5][6][7][8][9] While the plasmonic resonances of nanoantennas can be tailored by changing their size, shape and composition, it is particularly appealing to be able to dynamically control or modulate such resonances, thereby tuning their resonance wavelengths, scattering efficiencies, and emission characteristics. So far, tuning mechanisms have involved (electro)mechanical methods, [10][11][12] modulation of liquid crystals, [13][14][15][16][17] responsive molecules, [18][19][20][21] phase change materials, [22][23][24] and electrical modulation of graphene. [25][26][27] In this letter, we demonstrate a new type of reconfigurable optical nano-antenna operating in the visible spectral range.…”