Enhanced Colorimetric Detection of Volatile Organic Compounds Using a Dye-Incorporated Photonic Crystal-Based Sensor Array.

Chemoresponsive dyes offer the potential to selectively detect volatile organic compounds (VOCs) unique to certain disease states. Among different VOC sensing techniques, colorimetric sensing offers the advantage of facile recognition. However, it is often challenging to discern the color changes by the naked eye. Here, highly sensitive colorimetric VOC sensor arrays from dye-incorporated colloidal photonic crystals (dye-cPhCs) are reported. cPhCs are scalably fabricated on a 4-inch wafer by spin-coating of silica nanoparticles (NPs) dispersed in a photo-cross-linkable monomer, where the gradient shear flow along the film thickness creates densely-packed square arrays of NPs in the top layers, whereas the bulk is quasi-amorphous with larger periodicities. The broadened reflection peak allows for augmented dye absorption originating from the overlap between the photonic bandgap edge of the cPhC and the dye absorption peak, leading to a more noticeable color change upon exposure to VOCs. The sensor array generates distinct color difference maps for acetaldehyde, acetone, and acetic acid, respectively, without any data amplification. The limit of detection for acetaldehyde, acetone, and acetic acid is 1, 0.1, and 0.02 ppm, respectively. Moreover, VOC can be diagonalized by visually intuitive pattern recognition, and principal component analysis at reduced dimensionality is demonstrated.

A Highly Sensitive and Specific Photonic Crystal-Based Opioid Sensor with Rapid Regeneration.

Opioid misuse and overdose have caused devastating public health challenges and economic burdens, calling for the need of rapid, accurate sensitive opioid sensors. Here, we report a photonic crystal-based opioid sensor in the total internal reflection configuration, providing label-free, rapid, quantitative measurements through change of the refractive index. The one-dimensional photonic crystal with a defect layer that is immobilized with opioid antibodies acts as a resonator with an open microcavity. The highly accessible structure responds to analytes within a minute after the aqueous opioid solution is introduced, achieving the highest sensitivity of 5688.8 nm/refractive index unit (RIU) at the incident angle of 63.03°. Our sensor shows a limit of detection (LOD) of 7 ng/mL for morphine in phosphate-buffered saline (PBS, pH 7.4) solutions, well below the required clinical detection limit, and an LOD of 6 ng/mL for fentanyl in PBS, close to the clinical requirement. The sensor can selectively detect fentanyl from a mixture of morphine and fentanyl and be regenerated in 2 min with up to 93.66% recovery rate after five cycles. The efficacy of our sensor is further validated in artificial interstitial fluid and human urine samples.

Switching Chirality in Arrays of Shape-Reconfigurable Spindle Microparticles.

The giant circular photo-galvanic effect is realized in chiral metals when illuminated by circularly polarized light. However, the structure itself is not switchable nor is the crystal chirality in the adjacent chiral domains. Here spindle-shaped liquid crystalline elastomer microparticles that can switch from prolate to spherical to oblate reversibly upon heating above the nematic to isotropic transition temperature are synthesized. When arranged in a honeycomb lattice, the continuous shape change of the microparticles leads to lattice reconfiguration, from a right-handed chiral state to an achiral one, then to a left-handed chiral state, without breaking the translational symmetry. Accordingly, the sign of rotation of the polarized light passing through the lattices changes as measured by time-domain terahertz spectroscopy. Further, it can locally alter the chirality in the adjacent domains using near-infrared light illumination. The reconfigurable chiral microarrays will allow us to explore non-trivial symmetry-protected transport modes of topological lattices at the light-matter interface. Specifically, the ability to controllably create chiral states at the boundary of the achiral/chiral domains will lead to rich structures emerging from the interplay of symmetry and topology.

Janus Microdroplets with Tunable Self-Recoverable and Switchable Reflective Structural Colors.

Microdroplets made from chiral liquid crystals (CLCs) can display reflective structural colors. However, the small area of reflection and their isotropic shape limit their performance. Here, Janus microdroplets are synthesized through phase separation between CLCs and silicone oil. The as-synthesized Janus microdroplets show primary structural colors with ≈14 times larger area compared to their spherical counterparts at a specific orientation; the orientation and thus the colored/transparent states can be switched by applying a magnetic field. The color of the Janus microdroplets can be tuned ranging from red to violet by varying the concentration of the chiral dopant in the CLC phase. Due to the density difference between the two phases, the Janus microdroplets prefer to orientate the silicone oil side up vertically, enabling the self-recoverable structural color after distortion. The Janus microdroplets can be dispersed in aqueous media to track the configuration and speed of magnetic objects. They can also be patterned as multiplexed labels for data encryption. The magnetic field-responsive Janus CLC microdroplets presented here offer new insights to generate and switch reflective colors with high color saturation. It also paves the way for broader applications of CLCs, including anti-counterfeiting, data encryption, display, and untethered speed sensors.