Target molecule imaging on tissue specimens by fluorescent metal nanoprobes

GLAD Based Advanced Nanostructures for Diversified Biosensing Applications: Recent Progress

Glancing angle deposition (GLAD) is a technique for the fabrication of sculpted micro- and nanostructures under the conditions of oblique vapor flux incident and limited adatom diffusion. GLAD-based nanostructures are emerging platforms with broad sensing applications due to their high sensitivity, enhanced optical and catalytic properties, periodicity, and controlled morphology. GLAD-fabricated nanochips and substrates for chemical and biosensing applications are replacing conventionally used nanomaterials due to their broad scope, ease of fabrication, controlled growth parameters, and hence, sensing abilities. This review focuses on recent advances in the diverse nanostructures fabricated via GLAD and their applications in the biomedical field. The effects of morphology and deposition conditions on GLAD structures, their biosensing capability, and the use of these nanostructures for various biosensing applications such as surface plasmon resonance (SPR), fluorescence, surface-enhanced Raman spectroscopy (SERS), and colorimetric- and wettability-based bio-detection will be discussed in detail. GLAD has also found diverse applications in the case of molecular imaging techniques such as fluorescence, super-resolution, and photoacoustic imaging. In addition, some in vivo applications, such as drug delivery, have been discussed. Furthermore, we will also provide an overview of the status of GLAD technology as well as future challenges associated with GLAD-based nanostructures in the mentioned areas.

Energy transfer-based biodetection using optical nanomaterials

This review focuses on recent progress in the development of FRET probes and the applications of FRET-based sensing systems.

Fluorescent nanoprobes for sensing and imaging of metal ions: recent advances and future perspectives

Recent advances in nanoscale science and technology have generated nanomaterials with unique optical properties. Over the past decade, numerous fluorescent nanoprobes have been developed for highly sensitive and selective sensing and imaging of metal ions, both in vitro and in vivo. In this review, we provide an overview of the recent development of the design and optical properties of the different classes of fluorescent nanoprobes based on noble metal nanomaterials, upconversion nanoparticles, semiconductor quantum dots, and carbon-based nanomaterials. We further detail their application in the detection and quantification of metal ions for environmental monitoring, food safety, medical diagnostics, as well as their use in biomedical imaging in living cells and animals.

Radiative decay engineering 7: Tamm state-coupled emission using a hybrid plasmonic-photonic structure

There is a continuing need to increase the brightness and photostability of fluorophores for use in biotechnology, medical diagnostics, and cell imaging. One approach developed during the past decade is to use metallic surfaces and nanostructures. It is now known that excited state fluorophores display interactions with surface plasmons, which can increase the radiative decay rates, modify the spatial distribution of emission, and result in directional emission. One important example is surface plasmon-coupled emission (SPCE). In this phenomenon, the fluorophores at close distances from a thin metal film, typically silver, display emission over a small range of angles into the substrate. A disadvantage of SPCE is that the emission occurs at large angles relative to the surface normal and at angles that are larger than the critical angle for the glass substrate. The large angles make it difficult to collect all of the coupled emission and have prevented the use of SPCE with high-throughput and/or array applications. In the current article, we describe a simple multilayer metal-dielectric structure that allows excitation with light that is perpendicular (normal) to the plane and provides emission within a narrow angular distribution that is normal to the plane. This structure consists of a thin silver film on top of a multilayer dielectric Bragg grating, with no nanoscale features except for the metal or dielectric layer thicknesses. Our structure is designed to support optical Tamm states, which are trapped electromagnetic modes between the metal film and the underlying Bragg grating. We used simulations with the transfer matrix method to understand the optical properties of Tamm states and localization of the modes or electric fields in the structure. Tamm states can exist with zero in-plane wavevector components and can be created without the use of a coupling prism. We show that fluorophores on top of the metal film can interact with the Tamm state under the metal film and display Tamm state-coupled emission (TSCE). In contrast to SPCE, the Tamm states can display either S or P polarization. The TSCE angle is highly sensitive to wavelength, which suggests the use of Tamm structures to provide both directional emission and wavelength dispersion. Metallic structures can modify fluorophore decay rates but also have high losses. Photonic crystals have low losses but may lack the enhanced light-induced fields near metals. The combination of plasmonic and photonic structures offers the opportunity for radiative decay engineering to design new formats for clinical testing and other fluorescence-based applications.

Fluorescence Intensity and Lifetime Cell Imaging with Luminescent Gold Nanoclusters

In this article, luminescent properties of gold nanoclusters (AuNCs) were studied at the single nanoparticle level and also used as novel imaging agents in cell media. Two types of water-soluble AuNCs which were stabilized with a monolayer composed of either mercaptosuccinic acid (MSA) or tiopronin thiolate ligands were synthesized by a chemical reduction reaction. These AuNCs were determined to have an average core diameter of less than 2 nm. On a time-resolved confocal microscope, the emission signals from the single AuNCs were distinctly recordable. The quantum yields of these AuNCs were measured to be ca. 5%. The lifetime of these AuNCs is also much longer than the lifetime of cellular autofluorescence in lifetime cell imaging as well as the lifetime of organic dye Alexa Fluor 488. After being derivatized with polyethylene glycol (PEG) moieties, the AuNCs were uploaded efficiently in the HeLa cells. Fluorescence intensity and lifetime cell images were recorded on the time-resolved confocal microscope in which the emission from the AuNCs was readily differentiated from the cellular autofluorescence background because of their relatively stronger emission intensities and longer lifetimes. These loaded nanoclusters in the cells were observed to widely distribute throughout the cells and especially densely loaded near the cell nucleuses. The AuNCs in the cells were also tested to have a better photostability relative to the organic fluorophores under the same conditions. We thus conclude that the AuNCs have a great potential as novel nanoparticle imaging agents, especially as lifetime imaging agents, in fluorescence imaging applications. We also prospect much broader applications of these AuNCs after further improvements of their luminescence quantum yields.

Plasmonic approach to enhanced fluorescence for applications in biotechnology and the life sciences

One of the most rapidly growing areas of physics and nanotechnology is concerned with plasmonic effects on the nanometer scale; these have applications in sensing and imaging technologies. Nanoplasmonic colloids such as Ag and Au have been attracting active interest, and there has been a recent explosion in the use of these metallic nanostructures to modify the spectral properties of fluorophores favorably and to enhance the fluorescence emission intensity. In this feature article, we summarize our work over a range of nanoplasmonics-assisted biological applications such as flow cytometry, immunoassays, cell imaging and bioassays where we use custom-designed plasmonic nanostructures (Ag and Au) to enhance fluorescence signatures. This fluorophore-metal effect offers unique advantages in providing improved photostability and enhanced fluorescence signals. We discuss the plasmonic enhancement of lanthanide fluorophores whose long and microsecond lifetimes offer the advantage of background-free fluorescence detection, but low photon cycling rates lead to poor brightness. We also show that plasmonic colloids are capable of enhancing the emission of fluorescent nanoparticles, including upconverting nanocrystals and lanthanide nanocomposites.