Recent Advances in Sensing Applications of Molecularly Imprinted Photonic Crystals

Photonic crystals (PhCs) with a brightly colored structure are novel materials and are widely used in chemical and biological sensing. Combining PhCs with molecular imprinting technology (MIT), the molecularly imprinted PhC (MIPC) sensors are fabricated, which can specifically recognize the target molecules. Aside from high sensitivity and selectivity, the MIPC sensors could recognize the naked eye detection because of its optical properties. In this review, an overview of recent advances in sensing applications of MIPC sensors including the responsive mechanisms, application in environmental monitoring, and the application to human health were illustrated. The MIPC sensors all responded to the analytes specifically and also showed high sensitivity in real samples, which provided a method to realize the rapid, convenient, naked eye, and real-time detection. Furthermore, the current limitations and potential future directions of MIPC sensors were also discussed.

Angle-Sensitive Photonic Crystals for Simultaneous Detection and Photocatalytic Degradation of Hazardous Diazo Compounds

Congo Red (CR) and Amido Black 10B (AB-10B) are anionic diazo dyes, which are metabolized to produce a bioaccumulative and persistent carcinogen, benzidine. In this regard, an angle sensitive sensor composed of photonic crystal supported photocatalyst was fabricated for the simultaneous detection and photocatalytic degradation of diazo dyes from aqueous solutions. Reflectance spectroscopy was used in the detection of CR and AB-10B, which was based on the emergence of the incident angle dependent reflection peaks from the TiO2 coated two-dimensional photonic crystal (2D-PhC) surfaces and their subsequent quenching due to the presence of dye molecules whose absorbance peak intensity overlapped the reflection peak intensity of TiO2 at the respective angle. Interestingly, ultraviolet (UV) mediated photocatalytic degradation of CR and AB-10B was achieved using the same TiO2 coated 2D-PhC surfaces. 2D-PhC underneath the TiO2 layer was able to confine and localize the light on the TiO2 coated 2D-PhC surface, which enhanced the light absorption by dye molecules on the TiO2 surface and the photocatalytic efficiency in the degradation of CR and AB-10B. Finally, this proof-of-concept study demonstrated the fabrication of copolymer film based photonic crystal supported photocatalytic device, which can be used for developing miniaturized sensors competent in on-field detection and degradation of pollutants.

Convenient and Efficient Fabrication of Colloidal Crystals Based on Solidification-Induced Colloidal Assembly

The simple yet efficient and versatile fabrication of colloidal crystals was investigated based on the solidification-induced colloidal crystallization process with particle/water suspension as precursor. The resulting colloidal crystals were constituted by crystal grains with sizes ranging from several tens of micrometers to a few millimeters. Each of the grains had a close-hexagonal array of colloids, which endowed the bulk colloidal crystal powders with some specific optical properties. The freezing of water was shown as the major driving force to form colloidal crystal grains, which supersaturated the solution with nanoparticles and thus induced the formation and growth of colloidal crystal seeds. This process is intrinsically different from those conventional methods based on shearing force, surface tension, columbic interaction or magnetic interaction, revealing a new strategy to fabricate colloidal crystals in a convenient and efficient way.