Enhancing the optical response and biosensing capabilities of bioinspired peptide micro‐waveguides exploiting chromatic aberration

Abstract

Bioinspired peptide waveguides of mesoscopic length scales have established a new paradigm in photonics with possible applications in precision bioimaging, sensing, and diagnostics. Here, we improve the efficiency of coupling various constituent colors of a white light source into single self‐assembled microtube‐shaped passive peptide waveguides by employing chromatic aberration. Thus, we use a chromatically aberrated microscope objective lens to couple light into peptide waveguides. Using both numerical simulation and experiments, we show that the waveguide response displays higher quality factor, wavelength selectivity, and axial coupling range compared to a chromatically corrected standard plan‐fluoritic objective lens. We also demonstrate absorption and refractive index‐based sensing by studying the changes in the optical responses of the peptide tubes in the presence of a wide concentration range of the absorptive Congo red, and the nonabsorptive Coumarin dyes. The former understandably display a much higher response than the latter due to the low finesse of the waveguides. We obtain a detection limit of around 10 nM for Congo red, and 10 mM for Coumarin. Our study opens up possibilities for deploying such peptide microtubes for various biosensing applications utilizing spectral and waveguide characteristics.

Fabry–Perot Cavity by a Bio-Inspired Hollow Tetragonal Waveguide: Toward Femtomolar Detection

“…31 However, most of the reported work is waveguiding using the transverse EM modes, coupled into the waveguides by the evanescent coupling of light exploiting the momentum-matching condition. 20 However, in the present case, because our rods are hollow and filled with air, which has an RI of almost 1, there is no physically allowed angle (θ) that will allow the evanescent coupling of light from the lower surface of the urea-based rods (RI around 1.48) into the rod interior (because numerical aperture NA = sin θ = (n 1 2 − n 0 2 ) 1/2 , where n 1 is the RI of the higher index medium, while n 0 is that of the lower index medium). However, we are able to excite longitudinal or FP modes inside the rods due to the refraction and diffraction of light into them.…”

“…Previously, we have demonstrated the formation of tubular waveguides by the self-assembly of Boc-FF 19 (Figure 1a,b) and FF. 20 The Boc-FF microtube (Figure 1b) can be employed as a waveguide, when excited by white light and a 671 nm laser (Figure 1c). 19 However, we observed only transverse EM modes from such tubular waveguides (Figure 1a).…”

“…19 However, we observed only transverse EM modes from such tubular waveguides (Figure 1a). 19,20 In this Article, we develop a new design where we fabricate hollow tetragonal waveguides with closed ends (Figure 1d−f). The closed ends lead to very interesting consequences when we couple light from a supercontinuum laser; because these waveguides are hollow (air inside), we obtain only longitudinal (Fabry−Perot or FP) modes, due to both the long (length) and the short (width) sides of the waveguides.…”

Processable soft conducting fibers of self-assembled (2,5-diphenyl-2H-1,2,3-triazole-4-carbonyl)-l-phenylalaninate

“…Previously, we demonstrated tubular waveguide formation by self-assembling Boc-FF 20 and FF. 21 The Boc-FF microtube can be employed as a waveguide when excited by white light and a 671 nm laser. 20 In this paper, we have developed nanowires by solvent-induced self-assembly of a phenylalanine derivative.…”