Responsive Hydrogel-based Photonic Nanochains for Microenvironment Sensing and Imaging in Real Time and High Resolution

Abstract

Microenvironment sensing and imaging are of importance in microscale zones like microreactors, microfluidic systems, and biological cells. But they are so far implemented only based on chemical colors from dyes or quantum dots, which suffered either from photobleaching, quenching, or photoblinking behaviors, or from limited color gamut. In contrast, structural colors from hydrogel-based photonic crystals (PCs) may be stable and tunable in the whole visible spectrum by diffraction peak shift, facilitating the visual detection with high accuracy. However, the current hydrogel-based PCs are all inappropriate for microscale detection due to the bulk size. Here we demonstrate the smallest hydrogel-based PCs, responsive hydrogel-based photonic nanochains with high-resolution and real-time response, by developing a general hydrogen bond-guided template polymerization method. A variety of mechanically separated stimuli-responsive hydrogel-based photonic nanochains have been obtained in a large scale including those responding to pH, solvent, and temperature. Each of them has a submicrometer diameter and is composed of individual one-dimensional periodic structure of magnetic particles locked by a tens-of-nanometer-thick peapod-like responsive hydrogel shell. Taking the pH-responsive hydrogel-based photonic nanochains, for example, pH-induced hydrogel volume change notably alters the nanochain length, resulting in a significant variation of the structural color. The submicrometer size endows the nanochains with improved resolution and response time by 2-3 orders of magnitude than the previous counterparts. Our results for the first time validate the feasibility of using structural colors for microenvironment sensing and imaging and may further promote the applications of responsive PCs, such as in displays and printing.

Self‐Adaptive Magnetic Photonic Nanochain Cilia Arrays

“…Similar to the dispersed responsive hydrogel‐based photonic nanochains, [ 39 ] the printed SMPNCAs also have periodic arrangement of Fe 3 O 4 @PVP CNCs immobilized by only a tens‐of‐nanometer‐thick peapod‐like poly(AA‐ co ‐HEMA) hydrogel shell with a response to pH, and can in real time change their diffracted color in visible spectrum with the external pH stimuli obeying to Bragg's law: where m represents the diffraction order, λ is the wavelength of incident light, n indicates the mean refractive index, d is the lattice constant corresponding to the interparticle distance, and θ is the glancing angle. [ 24 ] Specifically, with the increasing pH in aqueous medium, the hydrogel will swell owing to the enhanced ionization of carboxyl groups and the increased solubility of generated carboxylates, resulting in the increment of d and red shift of diffracted color of SMPNCAs when observed under a vertical H (θ = 90°).…”

“…Observing the Diffracted Color: First, the PBS with pH 6.2, 5.6, 5.1, 4.8, 4.6, and 4.3 were prepared according to previous study. [39] When testing, a pH solution was continuously injected in SMPNCAs. The diffracted color of SMPNCAs was collected when it was uniform and stable.…”

“…Similar to the dispersed responsive hydrogel-based photonic nanochains, [39] the printed SMPNCAs also have periodic arrangement of Fe 3 O 4 @PVP CNCs immobilized by only a tensof-nanometer-thick peapod-like poly(AA-co-HEMA) hydrogel shell with a response to pH, and can in real time change their diffracted color in visible spectrum with the external pH stimuli obeying to Bragg's law:…”

Thermal Responsive Photonic Crystal Achieved through the Control of Light Path Guided by Phase Transition

“…[ 9–11 ] Based on Bragg's law, the change of lattice parameter can cause the change of structural color, which leads to the development of responsive photonic crystals. [ 12–14 ]…”

3D‐Printed Microrobots with Integrated Structural Color for Identification and Tracking

“…Some interesting advanced functional capabilities have been associated with 3D photonic crystals, ranging from advanced label‐free sensors to multilevel security applications. By correlating the color shifts to a specific physical (e.g., temperature, strain, electric fields) or chemical stimuli (e.g., organic molecules, metabolites), low cost and simple colourimetric sensors with high sensitivity have been developed . They have been implemented in both point‐of‐care diagnostics and environmental applications, generally targeting label‐free detection and involve the integration of stimuli‐responsive materials.…”