Bioanalysis And Detection Based On The Fluorescence Enhancement Effect Of Photonic Crystal

Photonic crystal（PC）is a kind of artificial periodic structure with photonic band gap.Recently,PCs are attracting increasing interest in a wide variety of research fields due to their unique optical properties and structures.Particularly,PCs with controlled micro/nanostructures have emerged as promising materials for a range of bioanalytical applications.Photonic crystals have a special tuning effect on light thus resulting in the fluorescence enhancement effect.Photons with wavelengths near the stop band of PCs propagate at lower speed owing to resonant Bragg scattering,which enhances optical gain,leading to stimulated emission,as well as amplifying the excitation of incident light.On the basis of the fluorescence enhancement effect,PCs have been used to improve the sensitivity for different kinds of fluorescent biological analysis.Herein,two forms of test devices and methods are designed based on the fluorescence enhancement effect of PCs.In the first work we report a method for the fabrication of opal capillary with multiple hetero structures for aptamer-based assays.The method is inspired by plant transpiration.During the fabrication,monodisperse SiO₂ nanoparticles（NPs）self-assemble in a glass capillary,with the solvent gradually evaporating from the top end of the capillary.By a simple change of the colloid solution that wicks through the capillary,multiple hetero structures can be easily prepared inside the capillary.On the surface of the SiO₂ NPs,poly dopamine is coated for immobilization of aminomethyl-modified aptamers.The aptamers are used for fluorescent detection of adenosine triphosphate（ATP）and thrombin.Owing to fluorescence enhancement effect of the photonic hetero structures,the fluorescent signal for detection is amplified up to40-fold.The limit of detection is 32μM for ATP and 8.1 nM for thrombin.Therefore,we believe this method is promising for the fabrication of analytical capillary devices for point-of-care testing.In the second work,we report a method for the fabrication of nitrocellulose（NC）membrane with photonic crystal（PC）pattern for bio-detection.The membrane is prepared by imprinting the corresponding PC pattern into it through thermal Nano-imprint method.Aptamer beacon marked with fluorescein is used for detection of target molecules.One droplet（1-2μl）containing the aptamer-target complexes is dripped onto the nitrocellulose membrane.After evaporation（15-20 min）,the droplet is completely dried and the complexes form a coffee ring on the membrane.The ring keeps growing with the increase of complexes concentration.As the aptamer beacon is marked with fluorescein and PC pattern has a fluorescence enhancement effect,the fluorescent signal on the coffee ring for detection is considerable improved.Fluorescent detection of adenosine triphosphate（ATP）is used for testing the application of this method.Owing to fluorescence enhancement effect of PC,the fluorescent signal for detection is improved and the limit of detection is 80.2μM for ATP.Therefore,we believe this method is promising for the fabrication of patterned photonic nitrocellulose membrane for bio-detection and point-of-care testing.Both of the methods improve the sensitivity of biological detection with the introduction of PCs thus offering an efficient and rapid platform for the detection and diagnosis of diseases.