Gold nanoparticle based NSET for monitoring Mg2+ dependent RNA folding

Principles and Applications of Resonance Energy Transfer Involving Noble Metallic Nanoparticles

Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection.

Nanoscopic optical rulers beyond the FRET distance limit: fundamentals and applications

In the last few decades, Förster resonance energy transfer (FRET) based spectroscopy rulers have served as a key tool for the understanding of chemical and biochemical processes, even at the single molecule level. Since the FRET process originates from dipole-dipole interactions, the length scale of a FRET ruler is limited to a maximum of 10 nm. Recently, scientists have reported a nanomaterial based long-range optical ruler, where one can overcome the FRET optical ruler distance dependence limit, and which can be very useful for monitoring biological processes that occur across a greater distance than the 10 nm scale. Advancement of nanoscopic long range optical rulers in the last ten years indicate that, in addition to their long-range capability, their brightness, long lifetime, lack of blinking, and chemical stability make nanoparticle based rulers a good choice for long range optical probes. The current review discusses the basic concepts and unique light-focusing properties of plasmonic nanoparticles which are useful in the development of long range one dimensional to three dimensional optical rulers. In addition, to provide the readers with an overview of the exciting opportunities within this field, this review discusses the applications of long range rulers for monitoring biological and chemical processes. At the end, we conclude by speculating on the role of long range optical rulers in future scientific research and discuss possible problems, outlooks and future needs in the use of optical rulers for technological applications.

Development of a long-range surface-enhanced Raman spectroscopy ruler

Optical-ruler-based distance measurements are essential for tracking biomolecular processes in a wide range of analytical biochemical applications. The normally used Förster resonance energy transfer (FRET) ruler is not useful for investigating distance-dependent properties when distances are more than 10 nm. Driven by this limitation, we have developed a long-range surface-enhanced Raman spectroscopy (SERS) optical ruler using oval-shaped gold nanoparticles and Rh6G dye-modified rigid, variable-length double-strand DNAs. The bifunctional rigid dsDNA molecule serves as the SERS-active ruler. Our experimental results show that one can tune the length of the SERS ruler between 8 and ∼18 nm by choosing the size of the oval-shaped gold nanoparticles. A possible mechanism for our observed distance-dependent SERS phenomenon is discussed using the Gersten and Nitzan model. Ultimately, our long-range SERS molecular rulers can be an important step toward understanding distance-dependent biological processes.

Exploiting the light–metal interaction for biomolecular sensing and imaging

The ability of metal surfaces and nanostructures to localize and enhance optical fields is the primary reason for their application in biosensing and imaging. Local field enhancement boosts the signal-to-noise ratio in measurements and provides the possibility of imaging with resolutions significantly better than the diffraction limit. In fluorescence imaging, local field enhancement leads to improved brightness of molecular emission and to higher detection sensitivity and better discrimination. We review the principles of plasmonic fluorescence enhancement and discuss applications ranging from biosensing to bioimaging.

Affinity analysis of DNA aptamer-peptide interactions using gold nanoparticles

Gold nanoparticles (AuNPs) were used as colorimetric probe and fluorescence quencher for affinity analysis of DNA aptamers toward their target mucin 1 (MUC1) peptide. Single-stranded DNA (ssDNA) aptamer-coated AuNPs showed increased stability (i.e., more resistant to aggregation induced by NaCl) in the presence of their target peptide due to the increase in steric protection conferred by the ssDNA-peptide complexes formed on the AuNPs. Based on changes in the UV-vis extinction spectrum of AuNPs (a measure of AuNPs aggregation) and fluorescence restoration of CY5-ssDNA upon ssDNA-peptide complex formation, the formation of the complexes and ssDNA sequence-dependent dissociation constant (K(d)) were determined. Besides the UV-vis and fluorescence measurements, the hydrodynamic diameters, zeta potential measurements, and transmission electron microscopy (TEM) images of AuNPs after various coatings supported the assay principle. The methodology presented herein provides a rapid and sensitive alternative solution for the identification of high affinity binders from systematic evolution of ligands by exponential enrichment (SELEX).

Long-range nanoparticle surface-energy-transfer ruler for monitoring photothermal therapy response

A recent gold nanotechnology-driven approach opens up a new possibility for the destruction of cancer cells through photothermal therapy. Ultimately, photothermal therapy may enter into clinical therapy and, as a result, there is an urgent need for techniques to monitor the tumor response to therapy. Driven by this need, a nanoparticle surface-energy-transfer (NSET) approach to monitor the photothermal therapy process by measuring a simple fluorescence intensity change is reported. The fluorescence intensity change is due to the light-controlled photothermal release of single-stranded DNA/RNA via dehybridization during the therapy process. Time-dependent results show that just by measuring the fluorescence intensity change, the photothermal therapy response during the therapy process can be monitored. The possible mechanism and operating principle of the NSET assay are discussed. Ultimately, this NSET assay could have enormous potential applications in rapid, on-site monitoring of the photothermal therapy process, which is critical to providing effective treatment of cancer and multidrug-resistant bacterial infections.

Gold nano-popcorn attached SWCNT hybrid nanomaterial for targeted diagnosis and photothermal therapy of human breast cancer cells

Breast cancer presents greatest challenge in health care in today's world. The key to ultimately successful treatment of breast cancer disease is an early and accurate diagnosis. Current breast cancer treatments are often associated with severe side effects. Driven by the need, we report the design of novel hybrid nanomaterial using gold nano popcorn-attached single wall carbon nanotube for targeted diagnosis and selective photothermal treatment. Targeted SK-BR-3 human breast cancer cell sensing have been performed in 10 cancer cells/mL level, using surface enhanced Raman scattering of single walls carbon nanotube's D and G bands. Our data show that S6 aptamer attached hybrid nanomaterial based SERS assay is highly sensitive to targeted human breast cancer SK-BR-3 cell line and it will be able to distinguish it from other non targeted MDA-MB breast cancer cell line and HaCaT normal skin cell line. Our results also show that 10 min of photothermal therapy treatment by 1.5 W/cm(2) power, 785 nm laser is enough to kill cancer cells very effectively using S6 aptamer attached hybrid nanomaterials. Possible mechanisms for targeted sensing and operating principle for highly efficient photothermal therapy have been discussed. Our experimental results reported here open up a new possibility for using aptamers modified hybrid nanomaterial for reliable diagnosis and targeted therapy of cancer cell lines quickly.

Gold nano-popcorn-based targeted diagnosis, nanotherapy treatment, and in situ monitoring of photothermal therapy response of prostate cancer cells using surface-enhanced Raman spectroscopy

Prostate cancer is the second leading cause of cancer-related death among the American male population, and the cost of treating prostate cancer patients is about $10 billion/year in the United States. Current treatments are mostly ineffective against advanced-stage prostate cancer and are often associated with severe side effects. Driven by these factors, we report a multifunctional, nanotechnology-driven, gold nano-popcorn-based surface-enhanced Raman scattering (SERS) assay for targeted sensing, nanotherapy treatment, and in situ monitoring of photothermal nanotherapy response during the therapy process. Our experimental data show that, in the presence of LNCaP human prostate cancer cells, multifunctional popcorn-shaped gold nanoparticles form several hot spots and provide a significant enhancement of the Raman signal intensity by several orders of magnitude (2.5 × 10(9)). As a result, it can recognize human prostate cancer cells at the 50-cells level. Our results indicate that the localized heating that occurs during near-infrared irradiation can cause irreparable cellular damage to the prostate cancer cells. Our in situ time-dependent results demonstrate for the first time that, by monitoring SERS intensity changes, one can monitor photothermal nanotherapy response during the therapy process. Possible mechanisms and operating principles of our SERS assay are discussed. Ultimately, this nanotechnology-driven assay could have enormous potential applications in rapid, on-site targeted sensing, nanotherapy treatment, and monitoring of the nanotherapy process, which are critical to providing effective treatment of cancer.

A surface energy transfer nanoruler for measuring binding site distances on live cell surfaces

Measuring distances at molecular length scales in living systems is a significant challenge. Methods like Förster resonance energy transfer (FRET) have limitations due to short detection distances and strict orientations. Recently, surface energy transfer (SET) has been used in bulk solutions; however, it cannot be applied to living systems. Here, we have developed an SET nanoruler, using aptamer-gold nanoparticle conjugates with different diameters, to monitor the distance between binding sites of a receptor on living cells. The nanoruler can measure separation distances well beyond the detection limit of FRET. Thus, for the first time, we have developed an effective SET nanoruler for live cells with long distance, easy construction, fast detection, and low background. This is also the first time that the distance between the aptamer and antibody binding sites in the membrane protein PTK7 was measured accurately. The SET nanoruler represents the next leap forward to monitor structural components within living cell membranes.

Involvement of the LSPR spectral overlap for energy transfer between a dye and Au nanoparticle

Nanometal surface energy transfer (NSET) is a molecular ruler technique that has been utilized to optically probe long distances in biomolecular structures. We investigate the useful spectral range of donor dyes and the importance of overlap between the localized surface plasmon resonance (LSPR) and the donor photoluminescence (520-780 nm) and provide a comprehensive study of the R(0) values for the NSET processes from dyes to 2 nm Au NP (gold nanoparticle). The distance-dependent quenching results provide experimental evidence that the efficiency curve slope, R(0) value, and distance of quenching is best modeled as a surface-mediated NSET process analogous to the predictions of Persson-Lang and Chance-Prock-Silbey (CPS). The results show that the LSPR plays a very important role in the observed quenching of excited-state donors at the surface of the nanometal, and the correlation to the NSET model allows a compilation of the necessary biophysical constants for application within the toolbox of biophysics.

Tracking spatial disorder in an optical ruler by time-resolved NSET

For biomolecular applications, potential interactions between newly developed dye molecules and the biomolecule of interest can dramatically influence the accuracy of optical ruler techniques. By utilizing nanometal surface energy transfer (NSET), an optical technique is developed that allows the nature of interactions between dyes and a biomolecule, namely DNA, to be directly assessed. To demonstrate the method, interactions between well-known molecular dyes based on carboxyfluorescein (FAM, noninteracting) and Cy5 (known intercalator) with DNA is probed. The results demonstrate that FAM exhibits no interactions with the DNA backbone and is adequately represented as a solvent exposed dye, while the commonly used near-IR dye Cy5 exhibits two discrete interactions that depend on the site of appendage and the length of the linker arm. The exact population and nature of Cy5 interaction with the DNA indicates a 37% ratio of intercalation for the internal C(6), a 42% ratio for an internal C(3) spacer length, and no evidence of interaction for terminal labeling. The results allow quantitative assignment of the site occupation of donors to be analyzed providing a powerful set of information for use of dyes in FRET based optical ruler technologies without the need of single molecule methods or the assumption of an averaged site occupation for the donor.

Toxicity and environmental risks of nanomaterials: challenges and future needs

Nanotechnology has gained a great deal of public interest because of the needs and applications of nanomaterials in many areas of human endeavors including industry, agriculture, business, medicine, and public health. Environmental exposure to nanomaterials is inevitable as nanomaterials become part of our daily life, and, as a result, nanotoxicity research is gaining attention. This review presents a summary of recent research efforts on fate, behavior, and toxicity of different classes of nanomaterials in the environment. A critical evaluation of challenges and future needs for the safe environmental nanotechnology are discussed.