Label-Free Fluorescent Nanofilm Sensor Based on Surface Plasmon Coupled Emission: In Situ Monitoring the Growth of Metal-Organic Frameworks.

We have proposed a universal label-free fluorescent nanofilm sensor based on surface plasmon coupled emission (SPCE). A metal-dye-dielectric (MDD) structure was fabricated to mediate the label-free monitoring based on SPCE. The nonfluorescent dielectric film smartly borrowed the fluorescence signal from the bottom dye layer and led to a new SPCE response through the adjacent metal film. The fluorescence emission angle and polarization strongly depended on the thickness of the nonfluorescent dielectric film on the MDD structure. As a demonstration, the growth of a two-dimensional zeolitic imidazolate framework film (ZIF-L) was in situ monitored in the liquid phase by MDD-SPCE for the first time. The label-free fluorescent sensors are facilely prepared by a spin coating technique, with the potential to be widely spread for in situ studies, especially toward nanomaterial growth processes.

Label-free aptasensor based on ultrathin-linker-mediated hot-spot assembly to induce strong directional fluorescence.

We have demonstrated the proof-of-concept of a label-free biosensor based on emission induced by an extreme hot-spot plasmonic assembly. In this work, an ultrathin linking layer composed of cationic polymers and aptamers was fabricated to mediate the assembly of a silver nanoparticles (AgNPs)-dyes-gold film with a strongly coupled architecture through sensing a target protein. Generation of directional surface plasmon coupled emission (SPCE) was thus stimulated as a means of reporting biorecognition. Both the biomolecules and the nanoparticles were totally free of labeling, thereby ensuring the activity of biomolecules and allowing the use of freshly prepared metallic nanoparticles with large dimensions. This sensor smartly prevents the plasmonic assembly in the absence of targets, thus maintaining no signal through quenching fluorophores loaded onto a gold film. In the presence of targets, the ultrathin layer is activated to link NPs-film junctions. The small gap of the junction (no greater than 2 nm) and the large diameter of the nanoparticles (~100 nm) ensure that ultrastrong coupling is achieved to generate intense SPCE. A >500-fold enhancement of the signal was observed in the biosensing. This strategy provides a simple, reliable, and effective way to apply plasmonic nanostructures in the development of biosensing.

Prism-based surface plasmon coupled emission imaging.

A prism-based surface plasmon coupled emission (SPCE) imaging apparatus with a reverse Kretschmann (RK) configuration was developed and applied to dye-doped polymer films. Highly polarized, directional and enhanced fluorescence images were obtained. The angular distribution of the SPCE images was in accordance with the validated theoretical calculation performed using Fresnel equation. Prism-based SPCE imaging combined with microarray technology appears to be a promising platform for rapid and high-throughput analysis, especially for high-density arrays. We believe that prism-based SPCE imaging has potential applications in biochemical research.

Surface Plasmon Coupled Fluorescence-Enhanced Interfacial "Molecular Beacon" To Probe Biorecognition Switching: An Efficient, Versatile, and Facile Signaling Biochip.

Integrating probes and a substrate together, a fluorescence-enhanced interfacial "molecular beacon" (FEIMB) is demonstrated, based on directional surface plasmon coupled emission. Through this simple yet efficient interfacial modulation engineering to create an interfacial quencher (graphene oxide)-enhancer (gold nanofilm) pair, the quenching-to-enhancing region of FEIMB can be actively tuned. Therefore, it provides a spatial match between signal transduction and interface-mediated biorecognition switching. Via combination of strong quenching and efficient plasmonic coupling, a synergistically amplified signal-to-background ratio of >1000-fold has been achieved. FEIMBs have been employed in protein and DNA detection, creating a high-performance and universal chip-based plasmon-mediated fluorescence sensing platform.

In Situ Monitoring of Fluorescent Polymer Brushes by Angle-Scanning Based Surface Plasmon Coupled Emission.

Fluorescent polymers have attracted interest in many fields such as sensing, diagnostics, imaging, and organic electronic devices. Real-time techniques to monitor and understand the polymerization process are important for obtaining controllable fluorescence polymers. We present a new technique to in situ monitor the growth process of fluorescent polymer brushes by using angle-scanning based surface plasmon coupled emission (AS-SPCE) approach during electrochemically mediated atom-transfer radical polymerization. The polymer thickness was determined by modeling the location of SPCE emission angle(s) with theoretical calculation. The advantages of unique angle distribution patterns, thickness dependence and effective background rejection of AS-SPCE guarantee the success in the real-time investigation for controllable fabrication of fluorescent polymers.

siRNA Knockdown of RRM2 Effectively Suppressed Pancreatic Tumor Growth Alone or Synergistically with Doxorubicin.

Pancreatic cancer is currently one of the deadliest of the solid malignancies, whose incidence and death rates are increasing consistently during the past 30 years. Ribonucleotide reductase (RR) is a rate-limiting enzyme that catalyzes the formation of deoxyribonucleotides from ribonucleotides, which are essential for DNA synthesis and replication. In this study, 23 small interfering RNAs (siRNAs) against RRM2, the second subunit of RR, were designed and screened, and one of them (termed siRRM2), with high potency and good RNase-resistant capability, was selected. Transfection of siRRM2 into PANC-1, a pancreatic cell line, dramatically repressed the formation of cell colonies by inducing remarkable cell-cycle arrest at S-phase. When combining with doxorubicin (DOX), siRRM2 improved the efficacy 4 times more than applying DOX alone, suggesting a synergistic effect of siRRM2 and DOX. Moreover, the combined application of siRRM2-loaded lipid nanoparticle and DOX significantly suppressed the tumor growth on the PANC-1 xenografted murine model. The inhibition efficiency revealed by tumor weight at the endpoint of the treatment reached more than 40%. Hence, siRRM2 effectively suppressed pancreatic tumor growth alone or synergistically with DOX. This study provides a feasible target gene, a drug-viable siRNA, and a promising therapeutic potential for the treatment of pancreatic cancer.

Nanomicelle-Assisted Targeted Ocular Delivery with Enhanced Antiinflammatory Efficacy In Vivo.

Ocular inflammations are common diseases that may lead to serious vision-threatening obstacles. Eye drops for antiinflammation therapy need to be administered multiple times daily at a high dosage due to the rapid precorneal removal and low bioavailability of drugs. To overcome these problems, a cRGD-functionalized DSPE-PEG2000 nanomicelle (DSPE-PEG2000-cRGD) encapsulated with flurbiprofen is proposed. The tailored nanomicelles trigger specific binding to integrin receptors on the ocular surface, which leads to rapid and robust mucoadhesion, superior ocular surface retention, and transcorneal penetration behaviors of nanomicelles. Due to the enhanced drug delivery on ocular surface and in aqueous humor, the functionalized nanoformulation significantly improves ocular antiinflammation efficacy at a low dosage by blocking the synthesis of inflammatory mediators and cytokines. The present study demonstrates a promising strategy that uses a functional peptide combined with nanomicelles for targeted delivery to the eye in ophthalmologic applications.

Optical modulator based on propagating surface plasmon coupled fluorescent thin film: proof-of-concept studies.

We demonstrate that the propagating surface plasmon coupled fluorescent thin film can be utilized as a fluorescence modulator to mimic multiple representative Boolean logic operations. Surface plasmon mediated fluorescence presents characteristic properties including directional and polarized emission, which hold the feasibility in creating a universal optical modulator. In this work, through constructing the thin layer with the specific thickness, surface plasmon mediated fluorescence can be modulated with an ON-OFF ratio by more than 5-fold, under a series of coupling configurations.

High performance dual-mode surface plasmon coupled emission imaging apparatus integrating Kretschmann and reverse Kretschmann configurations for flexible measurements.

A Kretschmann (KR) and reverse Kretschmann (RK) dual-mode surface plasmon coupled emission (SPCE) imaging apparatus based on prism coupling was built up. Highly directional and polarized fluorescence images for both RK and KR configurations were obtained. Besides, surface plasmon field-enhanced fluorescence and free space imaging can also be measured conveniently from this apparatus. Combining the high sensitivity of KR mode and the simplicity of RK mode, the multifunctional imaging system is flexible to provide different configurations for imaging applications. Compared to the free space imaging, SPCE imaging provides enhanced fluorescence, especially large enhancement up to about 50 fold in KR configuration. Additionally, the degree of evanescent field enhancement effect was easily estimated experimentally using the apparatus to compare the different imaging configurations. We believed that the dual-mode SPCE imaging apparatus will be useful in fundamental study of plasmon-controlled fluorescence and be a powerful tool for optical imaging, especially for microarray and biological applications.

Surface plasmon coupled emission in micrometer-scale cells: a leap from interface to bulk targets.

Surface plasmon coupled emission (SPCE) technique has attracted increasing attention in biomolecular interaction analysis and cell imaging because of its high sensitivity, low detection volume and low fluorescence background. Typically, the working range of SPCE is limited at nanometers to an interface. For micrometer-scale samples, new SPCE properties are expected because of complex coupling modes. In this work, cells with different subregions labeled were studied using a SPCE spectroscopy system. Angular and p-polarized emission was observed for cell membrane, cytoplasm, and nucleus labeled with DiI, Nile Red, and propidium iodide, respectively. The SPCE signals were always partially p-polarized, and the maximum emission angle did not shift, regardless of variations in emission wavelength, fluorophore distribution and stained layer thickness. Additionally, increased polarization and a broader angle distribution were also observed with an increase in sample thickness. We also investigated the impact of metallic substrates on the SPCE properties of cells. Compared with Au and Ni substrates, Al substrates presented better polarization and angle distribution. Moreover, the real-time detection of the cell labeling process was achieved by monitoring SPCE intensity. These findings expand SPCE from a surface technique to a 3D method for investigating bulk targets beyond the nanoscale interfaces, providing a basis to apply this technique to study cell membrane fluidity and biomolecule interactions inside the cell and to distinguish between cell subregions.

Plasmon-mediated fluorescence with distance independence: from model to a biosensing application.

In this article, plasmon-mediated fluorescence biosensing is reported to be distance independent through a full-coupling strategy that effectively activates the entire plasmon coupling region. This concept is demonstrated through collecting the directional surface plasmon-coupled emission (SPCE) signal from fluorescent silica nanoparticles with a size that matches the entire coupling region. Based on this design, the spatial distribution of the fluorophores is confined by the dimension of the nanoparticle. Therefore, these encapsulated fluorophores occupy the maximum coupling dominant region and optimally utilize the coupling effect. Being different from the conventional plasmon-mediated fluorescence, the enhanced fluorescence response becomes nearly independent of distance changes on a wide dynamic range from 0nm to 30nm between the fluorescent nanoparticles and metal structure. Full-coupling SPCE appropriately enlarges the distribution of fluorophores, ensuring that the coupling dominant region is filled with enough fluorophores at varying distances to create a stable and detectable signal. This scale of distances is well suited for many biorecognition events. Full-coupling SPCE solves signal deviation challenges originating from the susceptible and unpredictable orientation and conformation of biomolecules on the nanoscale. Immunoassays and DNA detection are shown with high and reliable signals, demonstrating the advantages of distance-independent full coupling. Without the need of a complicated and rigorous architecture for precise distance control, full-coupling SPCE offers great promise for a general platform of chip-based biosensing and bioanalysis.

Turning on fluorescence by plasmonic assembly with large tunable spacing: a new observation and its biosensing application.

Assembling nanoparticle-film metallic junctions with a spacing of up to tens of nanometers efficiently turned on fluorophores attached to the film from the quenching status to an intense surface plasmon-coupled emission. Benefiting from this new finding, a fluorescence biosensor was created based on the use of a biomolecule-linked plasmonic assembly as the trigger.