Improved detection limits of protein optical fiber biosensors coated with gold nanoparticles
ABSTRACT The study presented herein investigates a novel arrangement of fiber-optic biosensors based on a tilted fiber Bragg grating (TFBG) coated with noble metal nanoparticles, either gold nanocages (AuNC) or gold nanospheres (AuNS). The biosensors constructed for this study demonstrated increased specificity and lowered detection limits for the target protein than a reference sensor without gold nanoparticles. The sensing film was fabricated by a series of thin-film and monolayer depositions to attach the gold nanoparticles to the surface of the TFBG using only covalent bonds. Though the gold nanoparticle integration had not yet been optimized for the most efficient coverage with minimum number of nanoparticles, binding AuNS and AuNC to the TFBG biosensor decreased the minimum detected target concentrations from 90nM for the reference sensor, to 11pM and 8pM respectively. This improvement of minimum detection is the result of a reduced non-specific absorption onto the gold nanoparticles (by functionalization of the external surface of the gold nanoparticles), and of an optical field enhancement due to coupling between the photonic modes of the optical fiber and the localized surface plasmon resonances (LSPR) of the gold nanoparticles. This coupling also increased the sensitivity of the TFBG biosensor to changes in its local environment. The dissociation constant (Kd) of the target protein was also characterized with our sensing platform and found to be in good agreement with that of previous studies.
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ABSTRACT: Near-field scanning optical microscopy was used in collection mode to examine the optical field distribution on the surface of tilted fiber Bragg gratings (TFBGs) coated with a layer of randomly spaced silver nanocubes. The nanocubes disturb the periodic pattern of the near field visible light distribution arising from counterpropagating cladding modes excited by the TFBG. Spots with more than two orders of magnitude enhancement of the near field light intensity were observed around the nanocubes, as well as an average enhancement over the whole surface of about an order of magnitude relative to uncoated fibers. The near field speckle pattern associated with nanocubes showed a 180-degree periodicity with respect to the linear polarization of the input excitation light launched in the fiber core. The observed phenomena are explained in terms of the plasmonic properties of silver nanocubes. The enhancement factors measured here explain previously observed improvements in the performance of metal nanoparticle coated TFBG devices in sensing and as sources of light for surface-enhanced spectroscopy.RSC Advances 01/2014; 4(38-38):19725. DOI:10.1039/c4ra02770a · 3.84 Impact Factor
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ABSTRACT: Abstract Compounds routinely used to increase the quality of life and combat disease undergo stringent potency and biosafety tests before approval. However, based on the outcome of ongoing research, new norms need to be effected to ensure that the compounds conform to biosafety at all target levels of activity. Whereas in vitro tests used to assess biosafety lack the potency and the translational attribute of a whole animal, mammalian preclinical models are expensive and time exhaustive. Zebrafish (Danio rerio) has emerged as an attractive alternative for biosafety studies due to its small size, genetics, breeding capabilities, and most importantly, similarity at the molecular and physiological levels with humans. It has been used extensively for testing various forms of toxicity, including developmental toxicity, cardiotoxicity, nephrotoxicity, and hepatotoxicity. We review here the utility of zebrafish as a powerful, sensitive, quantitative, noninvasive, and high-throughput whole-animal assay to screen for toxicity. Different forms of toxicity will be discussed briefly before we highlight the present state of genotoxicity study in zebrafish. This review, a first in this research area, will serve as a comprehensive introduction to the field of genotoxicity assay using zebrafish, a nascent but promising field that assays compounds for DNA damage. We also discuss possible approaches that could potentially be pursued to overcome some of the shortcomings in current genotoxic studies.Zebrafish 01/2014; 11(2). DOI:10.1089/zeb.2013.0924 · 1.95 Impact Factor
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ABSTRACT: This paper reports on the application of an optical fiber biosensor for real-time analysis of cellular behavior. Our findings illustrate that a fiber sensor fabricated from a traditional telecommunication fiber can be integrated into conventional cell culture equipment and used for real-time and label-free monitoring of cellular responses to chemical stimuli. The sensing mechanism used for the measurement of cellular responses is based on the excitation of surface plasmon resonance (SPR) on the surface of the optical fiber. In this proof of concept study, the sensor was utilized to investigate the influence of a number of different stimuli on cells-we tested the effects of trypsin, serum and sodium azide. These stimuli induced detachment of cells from the sensor surface, uptake of serum and inhibition of cellular metabolism, accordingly. The effects of different stimuli were confirmed with alamar blue assay, phase contrast and fluorescence microscopy. The results indicated that the fiber biosensor can be successfully utilized for real-time and label-free monitoring of cellular response in the first 30min following the introduction of a stimulus. Furthermore, we demonstrated that the optical fiber biosensors can be easily regenerated for repeated use, proving this platform as a versatile and cost-effective sensing tool.Biosensors & Bioelectronics 01/2014; 56C:359-367. DOI:10.1016/j.bios.2014.01.018 · 6.41 Impact Factor