Distance Dependent Resonance Energy Transfer Between Molecular Machine and Plasmonic Nanostructure

poster abstractPhotoswitchable molecules (molecular machines) have attracted a great deal of attention over the past few years for the design of molecular sensors. Among photoswitchable molecules, azobenzene is widely studied due to its trans-cis photoisomerization, which produces a simple structure and optical and Raman spectra, and is photo and electrochemically active, and can be utilized for optical storage and other applications. Localized surface plasmon resonance (LSPR) properties of the metal nanostructures in conjunction with the photoswitching properties of the azobenzene molecules allow the nanoscale environment to be more controlled and to ultimately improve the sensing abilities of the metallic nanostructure. Herein, we develop an ultrasensitive molecular sensor by functionalizing the gold nanoprism with a selfassembled monolayer of alkanethiols containing azobenzenes. This is the first study where light-induced reversible switching of azobenzenes to cis and trans conformations was detected by monitoring the LSPR of gold nanoprisms-based sensing platforms. It was found that the LSPR red shift was observed as the light exposure was switched from UV to blue light due to the cis to trans isomerization of the azobenzene. This shift is consistent with the increase in thickness of the local dielectric environment (0.6 nm) surrounding the nanoprisms with perhaps a contribution from electronic interaction between the nanoprisms and azobenzene. We hypothesize that this electronic interaction is the nearfield resonance energy transfer (NF-RET). Changing the alkanethiol chain length altered the distance between the nanoprisms’ surface to the azobenzene. The LSPR red shift decreases as the distance between azobenzenes and nanoprisms increases due to the decrease in NF-RET. The LSPR shift was found to be reversible as the light source was switched back and forth several times from UV to blue light. The effects of the azobenzene conformational change and its photoreversibility were also probed through surface enhanced Raman spectroscopy (SERS) demonstrating that the NF-RET between the nanoprisms and bound azobenzenes in their cis conformation significantly enhances the intensity of the Raman bands of the azobenzenes and is highly dependent on the distance of azobenzene from the surface of the nanoprisms. The SERS data suggested that the isomerization was controlled by first-order kinetics with a rate constant of 1.0 x 10−4 s−1. Our demonstration of light-induced photoreversibility of this type of molecular machine is the first step toward eliminating current limitations on detection of molecular motion in solid-state devices using LSPR spectroscopy with nanoprisms. Modulating the LSPR position and controlling energy transfer across the nanostructure organic molecule interface are very important for the fabrication of plasmonic-based nanoscale devices

Designing of Gold Nanoprism-Based Reversible and Ultra-sensitive Molecular Sensors

poster abstractPhotoswitchable molecules have attracted a great deal of attention over the past few years in designing molecular machines. Among photoswitchable molecules, azobenzene is widely studied due to its transcis photoisomeration, which produces a simple structure and spectra, and is photo and electrochemically active. The localized surface plasmon resonance (LSPR) properties of the metal nanostructures in conjunction with the photswitching properties of the azobenzene molecules allow the nanoscale environment to be more controlled and to ultimately improve the sensing abilities of the metallic nanostructures. We have developed a method of constructing a self-assembled monolayer (SAM) of azobenzene-containing alkanethiol molecules on the surface of chemically synthesized gold nanoprisms as molecular sensor. The reversible photoswiching properties of azobenzene were studied by monitoring the LSPR peak shift of gold nanoprisms by absorption spectroscopy. It was found that the substratebound gold nanoprisms functionalized with azobenzene alkanethiol molecules resulted in a ~30 nm LSPR peak red shift. The photoswitching behavior of the azobenzene molecules attached to the prisms was monitored after cycling exposure to UV and visible light. A ~12 nm LSPR blue shift was observed as the light exposure was switched from visible to UV light due to the trans to cis isomeration of the azobenze. The LSPR peak shift was found to be reversible as the light source was switched back and forth several times from UV to visible light. The reversible photoswitching of azobenzene-functionalized gold nanoprisms demonstrates their potential as ultra-sensitive molecular sensors for a broad range of applications from nanoelectrochemical systems to medicine

Nanoplasmonic sensor for the detection of cardiac Troponin

poster abstractThe Isoform of troponin I is uniquely produce in the adult human myocardium and it overexpress at myocardial injury. Accordingly, Iso troponin 1 level in plasma and other biological fluids can serve as diagnostic and prognostic disease biomarkers. Our study focus on the design of a label free ultrasensitive nanoplasmonic sensor by utilizing unique localized surface Plasmon resonance (LSPR) property of highly sensitive gold nanoprisms. Herein our study reveals that chemically synthesized nanoprisms with 42 nm average edge lengths can be used in nanoplasmonic sensor fabrication for the troponin detection. The limit of detection has been found to be sub-picomolar concentrations in PBS buffer and we will explore this sensing mechanism to detect Troponin I of myocardial infarction patient’s samples

Investigating the Effects of Size and Shape of Anisotropic Nanostructures on the Molecular Sensor Response

The photoreversiblity of molecular machine-attached onto anisotropic nanostructures have been studied using optical spectroscopy. For the first time, we have observed an unprecedented 21-nm shift of localized surface plasmon resonance (LSPR) peak of gold nanoprism upon cis to trans isomerization of azobenzenes. The observed shift was a combined effect of energy transfer across the nanostructure and azobenzene molecule and increase in the dielectric environment of the nanostructure. Furthermore, we also investigated the geometrical effects of plasmonic nanostructures by fine-tuning their size and shape on sensitivity of molecular sensors and determined the mechanism underlying LSPR peak shifts. Understanding such mechanism will aid in designing highly efficient sensing platforms for future optoelectronic device fabrication

Highly specific plasmonic biosensors for ultrasensitive microRNA detection in plasma from pancreatic cancer patients

MicroRNAs (miRs) are small noncoding RNAs that regulate mRNA stability and/or translation. Because of their release into the circulation and their remarkable stability, miR levels in plasma and other biological fluids can serve as diagnostic and prognostic disease biomarkers. However, quantifying miRs in the circulation is challenging due to issues with sensitivity and specificity. This Letter describes for the first time the design and characterization of a regenerative, solid-state localized surface plasmon resonance (LSPR) sensor based on highly sensitive nanostructures (gold nanoprisms) that obviates the need for labels or amplification of the miRs. Our direct hybridization approach has enabled the detection of subfemtomolar concentration of miR-X (X = 21 and 10b) in human plasma in pancreatic cancer patients. Our LSPR-based measurements showed that the miR levels measured directly in patient plasma were at least 2-fold higher than following RNA extraction and quantification by reverse transcriptase-polymerase chain reaction. Through LSPR-based measurements we have shown nearly 4-fold higher concentrations of miR-10b than miR-21 in plasma of pancreatic cancer patients. We propose that our highly sensitive and selective detection approach for assaying miRs in plasma can be applied to many cancer types and disease states and should allow a rational approach for testing the utility of miRs as markers for early disease diagnosis and prognosis, which could allow for the design of effective individualized therapeutic approaches

DESIGNING EFFICIENT LOCALIZED SURFACE PLASMON RESONANCE-BASED SENSING PLATFORMS: OPTIMIZATION OF SENSOR RESPONSE BY CON-TROLLING THE EDGE LENGTH OF GOLD NANOPRISMS

poster abstractOver the last few years, the unique localized surface plasmon resonance (LSPR) properties of plasmonic nanostructures have been used to design la-bel-free biosensors. In this research, we demonstrate that it is the difference in edge length of gold nanoprisms that significantly influences their bulk re-fractive index sensitivity and local sensing efficiency. Nanoprisms with edge lengths in the range of 28-51 nm were synthesized by the chemical-reduction method and sensing platforms were fabricated by chemisorptions of these nanoprisms onto silanized glass substrates. The plasmonic nanosensors prepared from 28 nm edge length nanoprisms exhibited the largest sensitivity to change in bulk refractive index with a value of 647 nm/RIU. The refractive index sensitivity decreased with increasing edge length, with nanoprisms of 51 nm edge lengths displaying a sensitivity of 384 nm/RIU. In contrast, we found that the biosensing efficiency of sensing platforms modified with biotin increased with increasing edge length, and the sensing platforms fabricated from 51 nm edge length nanoprisms displaying the highest local sensing efficiency. The lowest concentration of streptavidin that could be measured reliably was 1.0 pM and the limit of detection for the sensing platforms fabricated from 51 nm edge length nanoprisms was 0.5 pM, which is much lower than found with gold bipyramids, nanostars, and nanorods

Label-Free Nanoplasmonic-Based Short Noncoding RNA Sensing at Attomolar Concentrations Allows for Quantitative and Highly Specific Assay of MicroRNA-10b in Biological Fluids and Circulating Exosomes

MicroRNAs are short noncoding RNAs consisting of 18-25 nucleotides that target specific mRNA moieties for translational repression or degradation, thereby modulating numerous biological processes. Although microRNAs have the ability to behave like oncogenes or tumor suppressors in a cell-autonomous manner, their exact roles following release into the circulation are only now being unraveled and it is important to establish sensitive assays to measure their levels in different compartments in the circulation. Here, an ultrasensitive localized surface plasmon resonance (LSPR)-based microRNA sensor with single nucleotide specificity was developed using chemically synthesized gold nanoprisms attached onto a solid substrate with unprecedented long-term stability and reversibility. The sensor was used to specifically detect microRNA-10b at the attomolar (10(-18) M) concentration in pancreatic cancer cell lines, derived tissue culture media, human plasma, and media and plasma exosomes. In addition, for the first time, our label-free and nondestructive sensing technique was used to quantify microRNA-10b in highly purified exosomes isolated from patients with pancreatic cancer or chronic pancreatitis, and from normal controls. We show that microRNA-10b levels were significantly higher in plasma-derived exosomes from pancreatic ductal adenocarcinoma patients when compared with patients with chronic pancreatitis or normal controls. Our findings suggest that this unique technique can be used to design novel diagnostic strategies for pancreatic and other cancers based on the direct quantitative measurement of plasma and exosome microRNAs, and can be readily extended to other diseases with identifiable microRNA signatures

X-ray and MR contrast bearing nanoparticles enhance the therapeutic response of image-guided radiation therapy for oral cancer

INTRODUCTION: Radiation therapy for head and neck squamous cell carcinoma is constrained by radiotoxicity to normal tissue. We demonstrate 100 nm theranostic nanoparticles for image-guided radiation therapy planning and enhancement in rat head and neck squamous cell carcinoma models. METHODS: PEG conjugated theranostic nanoparticles comprising of Au nanorods coated with Gadolinium oxide layers were tested for radiation therapy enhancement in 2D cultures of OSC-19-GFP-luc cells, and orthotopic tongue xenografts in male immunocompromised Salt sensitive or SS rats via both intratumoral and intravenous delivery. The radiation therapy enhancement mechanism was investigated. RESULTS: Theranostic nanoparticles demonstrated both X-ray/magnetic resonance contrast in a dose-dependent manner. Magnetic resonance images depicted optimal tumor-to-background uptake at 4 h post injection. Theranostic nanoparticle + Radiation treated rats experienced reduced tumor growth compared to controls, and reduction in lung metastasis. CONCLUSIONS: Theranostic nanoparticles enable preprocedure radiotherapy planning, as well as enhance radiation treatment efficacy for head and neck tumors

Pedagogical memory and the space of the postcolonial classroom : reading Dangarembga's Nervous Conditions

This article addresses issues of the mnemonic space of the literature classroom by interrogating a classic text of African women’s writing, Tsitsi Dangaremnga’s Nervous Conditions (1988) for the ways it speaks about education in 1960s and 1970s late-colonial Rhodesia. The article suggests that the novel reviews and critiques a number of memorial strategies that were crucial to the colonial educational system, thereby facilitating a reflexive application of the novel’s concerns to the contexts in which it is often taught, that of today’s postcolonial classrooms. The article seeks to place Dangarembga’s novel in the context of its present moment, contemporary South Africa – that of the present critic’s site of practice, both pedagogical and scholarly, and that of many of this article’s readers. This present moment, in turn, is made up the many sites, successive and simultaneous, in which the novel’s work of memory is being re-activated in the minds of students as readers and writers. Via a dialogue between the textual past and the pedagogical present, one which is often subject to critical amnesia, the article seeks to inaugurate a debate on the nature of pedagogical memory in the space of the postcolonial university or high school literature classroom.http://www.informaworld.com/RSCRhb2013gv201

Temperature-Controlled Reversible Localized Surface Plasmon Resonance Response of Polymer-Functionalized Gold Nanoprisms in the Solid State

Solid-state temperature responsive localized surface plasmon resonance (LSPR)-based nanosensors were constructed by functionalizing the glass substrate-attached gold nanoprisms with the thermoresponsive polymer poly­(allylamine hydrochloride)-<i>co</i>-poly­(<i>N</i>-isopropylacrylamide). The robustness of the sensor was enhanced by chemically attaching polymer to the nanoprism surface through an amide coupling reaction versus simple physisorption of polymer onto nanoprism. The highest sensitivity of this kind of solid sensing platform was obtained by employing chemically synthesized gold nanoprisms for fabrication. The surface ligand chemistry significantly influenced the swelling and shrinking transition of the polymer during the temperature variation, which resulted in the alteration of the local dielectric environment of the nanoprisms, modulation of their LSPR properties, and enhancement of sensing efficiency of the nanosensors. Importantly, we have shown for the first time that the dimension of the nanostructure plays an important role in achieving the highest sensitivity for these types of sensors. For example, the edge length of the nanoprisms plays a critical role in the temperature sensitivity of the nanosensors where nanoprisms with ∼28 and ∼40 nm edge lengths displayed ∼10.9 and ∼18.2 nm LSPR dipole peak red-shift, respectively, as the solution temperature increased from 18 to 56 °C. We believe the higher temperature sensitivity for larger edge-length nanoprisms was achieved due to their larger sensing volume. The nanosensors were found to be very stable and displayed high reversibility, which suggests that our temperature-dependent nanosensors can potentially be used as a reversible thermal switch