Optically active chiral photonic crystals exhibiting enhanced fluorescence and circularly polarized luminescence

Photonic crystals with advanced, unique and well-defined functional nanostructures demonstrate exquisite controllable modulation in light harvesting and emission for unrivalled optical performance. Herein, through ingeniously integrating aggregation-induced emission (AIE) luminogens and chiral helical media into ordered periodic structures, the resulting optically active photonic crystal films exhibit an enhanced photoluminescence (PL) characteristic (increased to 2.2 times the original value) and distinctive emerging circular dichroism (CD) responses near the photonic bandgap (PBG) of the photonic crystal. The modulation of the PL intensity and CD signal peak position is precisely achieved by regulating the PBG by facilely tuning the size of the colloidal nanoparticles. Such an interesting phenomenon is mainly the consequence of the PBG edge enhancement effect (including the slow photon effect) and bandgap separation arising from chirality. Remarkably, the boosted fluorescence facilitates the synergistic effect of valid chirality transfer among achiral AIEgens and chiroptical media in a photonic matrix, which effectively contributes to the enhanced circularly polarized luminescence (CPL) activity, thereby expanding the potential applications of CPL-based optically active photonic materials in circularly polarizing emitting devices.

Photonic Inks with Dual-Layer Security Features by Encapsulation of Color Tunable Fluorescent Dyes in PMMA Colloidal Microspheres

To counter economic terrorism by preventing counterfeit currency, documents and high-value commercial products, new-generation security inks with multiple safety features are required. Herein, color-tunable pyrylium and pyridinium dye-encapsulated polymethyl methacrylate (PMMA) colloidal microspheres are reported to exhibiting brilliant emission and photonic properties. A combination of the PMMA colloidal photonic ink having structural color variation and the dye-encapsulated colloidal photonic ink with fluorescence modulation is used for security labeling. The angle-dependent structural color variations, a remarkable 250-fold fluorescence enhancement, non-toxicity, and the rare earth-free formulation have made the ink novel and suitable for dual-layer high-security printing. Covert security patterns and labels are made overt under 365 nm UV light, while also exhibiting angle-dependent structural color. The increased level of security with developed photonic colloidal inks is demonstrated with dual-layer screen-printed images and patterns on flexible substrates.

Fluorescence-enhanced supra-amphiphiles based on pillar[5]arene: construction, controllable self-assembly and application in cell imaging

Fluorescence-enhanced supra-amphiphiles based on (WP5)2⊃ENDTn were constructed successfully. When n = 9, they can self-assemble into uniform micelles with an average diameter of about 90 nm and be further applied in cell imaging.

Colloidal Photonic Crystal-Enhanced Fluorescence of Gold Nanoclusters: A Highly Sensitive Solid-state Fluorescent Probe for Creatinine

Gold nanoclusters (AuNCs) are an intensely pursued class of fluorophores with excellent biocompatibility, high water solubility, and ease of further conjugation. However, their low quantum yield limits their applications, such as ultra-sensitive chemical or molecular sensing. To address this problem, various strategies have been adopted for augmenting their fluorescence intensity. Herein, we report a facile and scalable approach for the fluorescence enhancement of bovine serum albumin (BSA) capped AuNCs (BSA-AuNCs) using periodic, close-packed polystyrene colloidal photonic crystals (CPCs). The slow photon effect at the bandgap edges is utilized for the increased light-matter interactions and thereby enhancing the fluorescence intensity of the BSA-AuNCs. Compared to the planar polystyrene control sample, the CPC film yielded a 14-fold enhancement in fluorescence intensity. Further, we demonstrated the as-prepared BSA-AuNCs-CPC as a solid-state platform for the highly sensitive and selective fluorescence turn-off detection of creatinine at nanomolar level.

Orhan O, Daly S, O’Regan DD, Rodriguez BJ, Casey E, Rice JH. Electric Field Tunability of Photoluminescence from a Hybrid Peptide-Plasmonic Metal Microfabricated Chip

Enhancement of fluorescence through the application of plasmonic metal nanostructures has gained substantial research attention due to the widespread use of fluorescence-based measurements and devices. Using a microfabricated plasmonic silver nanoparticle-organic semiconductor platform, we show experimentally the enhancement of fluorescence intensity achieved through electro-optical synergy. Fluorophores located sufficiently near silver nanoparticles are combined with diphenylalanine nanotubes (FFNTs) and subjected to a DC electric field. It is proposed that the enhancement of the fluorescence signal arises from the application of the electric field along the length of the FFNTs, which stimulates the pairing of low-energy electrons in the FFNTs with the silver nanoparticles, enabling charge transport across the metal-semiconductor template that enhances the electromagnetic field of the plasmonic nanoparticles. Many-body perturbation theory calculations indicate that, furthermore, the charging of silver may enhance its plasmonic performance intrinsically at particular wavelengths, through band-structure effects. These studies demonstrate for the first time that field-activated plasmonic hybrid platforms can improve fluorescence-based detection beyond using plasmonic nanoparticles alone. In order to widen the use of this hybrid platform, we have applied it to enhance fluorescence from bovine serum albumin and Pseudomonas fluorescens. Significant enhancement in fluorescence intensity was observed from both. The results obtained can provide a reference to be used in the development of biochemical sensors based on surface-enhanced fluorescence.

Fabrication of SiO2/PEGDA Inverse Opal Photonic Crystal with Fluorescence Enhancement Effects

The present paper reports the fabrication of inverse opal photonic crystals (IOPCs) by using SiO₂ spherical particles with a diameter of 300 nm as an opal photonic crystal template and poly(ethylene glycol) diacrylate (PEGDA) as an inverse opal material. Characteristics and fluorescence properties of the fabricated IOPCs were investigated by using the Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), reflection spectroscopy, and fluorescence microscopy. The results clearly showed that the IOPCs were formed comprising of air spheres with a diameter of ∼270 nm. The decrease in size led to a decrease in the average refractive indexes from 1.40 to 1.12, and a remarkable stopband blue shift for the IOPCs was thus achieved. In addition, the obtained results also showed a fluorescence enhancement over 7.7-fold for the Fluor® 488 dye infiltrated onto the IOPCs sample in comparison with onto the control sample.

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.