The way graphene (GDs) and carbon dots (CDs) are synthesized and combined with TiO2 determine their photoelectrochemical efficiency upon UV and visible LED lights. GDs and CDs are obtained by relatively unexplored top-down methods and conventional bottom-up methods, respectively. Top-down methods consist in the seedless growth of ZnO nanoparticles on the surface of graphene and the electrochemical cleavage of graphene grown on Ni foam. These carbon nanoparticles are later combined with TiO2 by different approaches such as solution mixing, adsorption via APTES linkers, and drop-casting on an already formed TiO2 film. Once the films are formed, they are placed into a photoelectrochemical Zahner cell and irradiated with LED lights at 450 and 360 nm. It is determined that CDs and GDs perform as efficient photosensitizers as demonstrated by an increase of similar to 19- and 20-fold net photocurrent density when irradiated with UV and visible LED lights, respectively. We encountered that CDs are more sensitive upon visible light, whereas GDs promptly respond to UV light due to their difference in size-dependent band gap. Importantly, GDs obtained from seedless growth of ZnO are sensitive to both: UV and Vis LED irradiation. The combination of both nanocarbons would expand the absorption range and may be potentially used as cosensitizers toward the construction of more effective and advanced photoanodes.

The growth of surface-attached single-stranded deoxyribonucleic acid (ssDNA) chains is monitored in situ using an evanescent wave optical biosensor that combines surface plasmon resonance (SPR) and optical waveguide spectroscopy (OWS). The "grafting-from" growth of ssDNA chains is facilitated by rolling circle amplification (RCA), and the gradual prolongation of ssDNA chains anchored to a gold sensor surface is optically tracked in time. At a sufficient density of the polymer chains, the ssDNA takes on a brush architecture with a thickness exceeding 10 μm, supporting a spectrum of guided optical waves traveling along the metallic sensor surface. The simultaneous probing of this interface with the confined optical field of surface plasmons and additional more delocalized dielectric optical waveguide modes enables accurate in situ measurement of the ssDNA brush thickness, polymer volume content, and density gradients. We report for the first time on the utilization of the SPR/OWS technique for the measurement of the RCA speed on a solid surface that can be compared to that in bulk solutions. In addition, the control of ssDNA brush properties by changing the grafting density and ionic strength and post-modification via affinity reaction with complementary short ssDNA staples is discussed. These observations may provide important leads for tailoring RCA toward sensitive and rapid assays in affinity-based biosensors.

One of the main confirmatory metabolites of diabetes mellitus is known as glycosylated hemoglobin (HbA1c), a hemoglobin modified with cis-diol sugars. This work presents an optical detection of this metabolite via the preparation and characterization of glass surfaces coated with gold nanoparticles (AuNPs) and subsequently modified with boronic acid to enhance specificity. Through the localized surface plasmon resonance intrinsic to the AuNPs an absorbance enhancement (82 x) of the Sorel band was obtained due to local electric field enhancement. As a consequence, determination of HbA1c can be performed by absorption spectroscopy in the UV-vis range by monitoring the Sorel band, at 409 nm. The analytical performance of the label-free, nanostructured sensor is studied using univariate and multivariate calibration. The absorbance dependence of the Sorer band as a function of HbAlc concentration showed a linear regression in the clinically relevant range of 0.09-2.35 g/L with a detection limit of 0.03 g/L. The method matches up well analytically when compared to other standard tests and has the advantage of simplicity (sample analysis and signal readout), low cost and fast detection (time of assay completion on the order of 10 s of minutes).

Fluorescence readout is uniquely powerful for biological assays and imaging because it combines the detection of specific biotargets with high spatial and temporal resolution. Recently, several strategies for the modulation in time of fluorescence emission have been proven useful to separate the target signal from constant background contributions. Here, we investigate the emission modulation of organic fluorophores located in the nanometric vicinity of plasmonically heated gold nanorods and apply it to a novel, all-optical homogeneous biosensing scheme. The combination of plasmonic heating and temperature sensitive molecular fluorescence enables the robust quantification of surface reactions.

Herein,we demonstrate stable optical trapping and accurate 3D manipulation of a single dielectric nanoparticle with a scanning optical near field probe.

Recent advances in nanotechnologies have prompted the need for tools to accurately and non-invasively manipulate individual nano-objects1. Among the possible strategies, optical forces have been predicted to provide researchers with nano-optical tweezers capable of trapping a specimen and moving it in three dimensions2,3,4. In practice, however, the combination of weak optical forces and photothermal issues has thus far prevented their experimental realization. Here, we demonstrate the first three-dimensional optical manipulation of single 50 nm dielectric objects with near-field nanotweezers. The nano-optical trap is built by engineering a bowtie plasmonic aperture at the extremity of a tapered metal-coated optical fibre. Both the trapping operation and monitoring are performed through the optical fibre, making these nanotweezers totally autonomous and free of bulky optical elements. The achieved trapping performances allow for the trapped specimen to be moved over tens of micrometres over a period of several minutes with very low in-trap intensities. This non-invasive approach is foreseen to open new horizons in nanosciences by offering an unprecedented level of control of nanosized objects, including heat-sensitive biospecimens. Objects as small as 50 nm can be manipulated in three dimensions with near-field-based optical tweezers.

Label-free biosensing based on metallic nanoparticles supporting localized surface plasmon resonances (LSPR) has recently received growing interest (Anker, J. N., et al. Nat. Mater. 2008, 7, 442-453). Besides its competitive sensitivity (Yonzon, C. R., et al. J. Am. Chem. Soc. 2004, 126, 12669-12676; Svendendahl, M., et al. Nano Lett. 2009, 9, 4428-4433) when compared to the surface plasmon resonance (SPR) approach based on extended metal films, LSPR biosensing features a high-end miniaturization potential and a significant reduction of the interrogation device bulkiness, positioning itself as a promising candidate for point-of-care diagnostic and field applications. Here, we present the first, paralleled LSPR lab-on-a-chip realization that goes well beyond the state-of-the-art, by uniting the latest advances in plasmonics, nanofabrication, microfluidics, and surface chemistry. Our system offers parallel, real-time inspection of 32 sensing sites distributed across 8 independent microfluidic channels with very high reproducibility/repeatability. This enables us to test various sensing strategies for the detection of biomolecules. In particular we demonstrate the fast detection of relevant cancer biomarkers (human alpha-feto-protein and prostate specific antigen) down to concentrations of 500 pg/mL in a complex matrix consisting of 50% human serum.

Fully exploiting the capability of nano-optics to enhance light. matter interaction on the nanoscale is conditioned by bringing the nano-object to interrogate within the minuscule volume where the field is concentrated. There currently exists several approaches to control the immobilization of nano-objects but they all involve a cumbersome delivery step and require prior knowledge of the "hot spot" location.(1-6) Herein, we present a novel technique in which the enhanced local field in the hot spot is the driving mechanism that triggers the binding of proteins via three-photon absorption. This way, we demonstrate exclusive immobilization of nanoscale amounts of bovine serum albumin molecules into the nanometer-sized gap of plasmonic dimers. The immobilized proteins can then act as a scaffold to subsequently attach an additional nanoscale object such as a molecule or a nanocrystal. This universal technique is envisioned to benefit a wide range of nano-Optical functionalities including biosensing,(7-12) enhanced spectroscopy like surface-enhanced Raman spectroscopy(13,14) or surface-enhanced infrared absorption spectroscopy,(15) as well as quantum optics.(1,2,6)

We report the use of green fluorescent protein (GFP) as a thermal nanoprobe suited for intracellular temperature mapping. Temperature probing is achieved by monitoring the fluorescence polarization anisotropy of GFP. The method is tested on GFP-transfected cancer cell lines enabling a spatial resolution of 300 nm and a temperature accuracy of 0.4°C [1]. The technique has recently been extended to measure intracellular temperature in an in vivo model of transfected C Elegans.

Multipolar transitions other than electric dipoles are generally too weak to be observed at optical frequencies in single quantum emitters. For example, fluorescent molecules and quantum dots have dimensions much smaller than the wavelength of light and therefore emit predominantly as electric dipoles. Here we demonstrate controlled emission of a quantum dot into multipolar radiation through selective coupling to a linear nanowire antenna. The antenna resonance tailors the interaction of the quantum dot with light, effectively creating a hybrid nanoscale source beyond the simple Hertz dipole. Our findings establish a basis for the controlled driving of fundamental modes in nanoantennas and metamaterials, for the understanding of the coupling of quantum emitters to nanophotonic devices such as waveguides and nanolasers, and for the development of innovative quantum nano-optics components with properties not found in nature.

The resonance change of plasmonic nanostructures to a small variation of the shallow refractive index as induced by the binding of molecules to the metal surface determines the sensitivity of plasmonic sensors. The magnitude of this change is strongly determined by a number of factors including dielectric constant of the metal at the working wavelength, refractive indices of analyte, and surroundings [J Phys Chem B 109:21556-21565, 2005], but also the spatial overlap between the region of local refractive index change and the plasmon mode. In this chapter we discuss how the plasmon modes of lithographically prepared plasmonic nanostructures can be accurately engineered to design bio-chemical sensors with improved sensitivities.We first describe how metal nanostructures can be designed to control the confinement of light modes down to the nanometer scale. Using 3D calculations based on the finite element method, we then discuss the influence on the sensitivity of the nanostructure geometry and location of the sensed molecule. Finally, we present experimental results that demonstrate this enhanced sensitivity to the detection of small molecules in arrays of gold dimers.

Plasmonic antennas are key elements to control the luminescence of quantum emitters. However, the antenna's influence is often hidden by quenching losses. Here, the luminescence of a quantum dot coupled to a gold dimer antenna is investigated. Detailed analysis of the multiply excited states quantifies the antenna's influence on the excitation intensity and the luminescence quantum yield separately.

Nanoscale single-photon emitters behave generally as dipoles. Here, we demonstrate multipolar and unidirectional emission of a quantum dot by near-field coupling to optical nanowire and Yagi-Uda antennas, that determine its angular radiation pattern and polarization.

Heat is of fundamental importance in many cellular processes such as cell metabolism, cell division and gene expression.(1-3) Accurate and noninvasive monitoring of temperature changes in individual cells could thus help clarify intricate cellular processes and develop new applications in biology and medicine. Here we report the use of green fluorescent proteins (GFP) as thermal nanoprobes suited for intracellular temperature mapping. Temperature probing is achieved by monitoring the fluorescence polarization anisotropy of GFP. The method is tested on GFP-transfected HeLa and U-87 MG cancer cell lines where we monitored the heat delivery by photothermal heating of gold nanorods surrounding the cells. A spatial resolution of 300 nm and a temperature accuracy of about 0.4 °C are achieved. Benefiting from its full compatibility with widely used GFP-transfected cells, this approach provides a noninvasive tool for fundamental and applied research in areas ranging from molecular biology to therapeutic and diagnostic studies.

We show unidirectional emission of a single Q-dot by coupling to a nanofabricated Yagi-Uda antenna. The Q-dot drives the resonant feed element and 82% of the Q-dot emission is emitted in a 12° HWHM angle.

This chapter presents as a proof of concept the development of a nanosensor based on the localized surface plasmon resonance for the analysis of biomolecules. The method presented take advantage of the plasmon generated in the surrounding of gold nanoparticles (i.e., 100 nm) for the specific interaction between antigen and antibody. The procedure for the optimization of an assay for the determination of biomolecules consisted mainly of four steps. First, the immobilization of gold nanoparticles over the glass surface using the appropriate ratio, concentration and time-contact of amino-sylilating agent, and nonreactive sylilating agent. Next, the suitable concentration of coating antigen in order to obtain the maximum signal LSPR. Following this step, the interaction between antigen and antibody (specific antibody) is evaluated by measuring the signal LSPR. Finally, a calibration curve was obtained for the detection of a small organic molecule such as stanozolol using this nanobiosensor. As a proof of concept, the use of a model is performed that in this case is for the detection of an anabolic androgenic steroid, such as stanozolol which is banned for the European Commission (EC) as a growth promoter and for the World Anti-Doping Agency (WADA) as a doping agent. The nanosensor developed demonstrates its feasibility for screening purposes due to the limit of detection achieved (0.7 mu g/L) is under the MRPL required for both organizations (10 mu g/L). A protocol such as that presented here may be generally applied for the analysis of other pollutant such as pesticides or antibiotics, or for biomedical applications for the analysis of biomarkers using the LSPR principle using gold nanoparticles (i.e., 30-120 nm).

ys of metallic nanostructures allow chiral biomolecules to be detected and characterized with increased sensitivity.

Nanoscale quantum emitters are key elements in quantum optics and sensing. However, efficient optical excitation and detection of such emitters involves large solid angles because their interaction with freely propagating light is omnidirectional. Here, we present unidirectional emission of a single emitter by coupling to a nanofabricated Yagi-Uda antenna. A quantum dot is placed in the near field of the antenna so that it drives the resonant feed element of the antenna. The resulting quantum-dot luminescence is strongly polarized and highly directed into a narrow forward angular cone. The directionality of the quantum dot can be controlled by tuning the antenna dimensions. Our results show the potential of optical antennas to communicate energy to, from, and between nano-emitters.