Gold (Au) nanoparticles, particularly nanorods, are actively employed as imaging probes because of their special nonblinking and nonbleaching absorption, scattering, and emitting properties that arise from the excitation of surface plasmons. Herein, we report a novel sensing method that detects feature orientation at the nanoscale via the defocused imaging of individual Au nanorods (AuNRs) with an ordinary wide-field optical microscope. By simultaneously recording defocused images and two-photon luminescence intensities for a large number of individual AuNRs, we correlate their defocused images with their three-dimensional spatial orientations. The spatial orientation of many individual AuNRs can be monitored in situ and in real-time within a single frame, enabling its use as a technique for high-throughput sensing. The probe size can be as small as several nanometers, which is highly desirable for minimization of any potential interference from the probe itself. Furthermore, the sensing property is insensitive to the excitation polarization and the distribution of the probe aspect ratio, which allows AuNRs of any length within a proper regime to be used as orientation sensors without changing the laser frequency and polarization. These unique features make the orientation probes proposed here outstanding candidates for optical imaging and sensing in materials science and biological applications.

Fluorescent gold nanoparticles with high quantum yield are highly desirable for optical imaging in the fields of biology and materials science. We investigate the one-photon photoluminescence (PL) properties of individual gold nanobipyramids (GNBs) and find they are analogous to those of the extensively studied gold nanorods (GNRs). By combining PL and atomic force microscopy (AFM) measurements with discrete dipole approximation (DDA) simulations, we obtain the PL quantum yield of single GNRs and GNBs. Compared to GNRs in the similar surface plasmon resonance range, the PL quantum yield of GNBs is found to be doubled. The stronger field intensity around GNBs can explain their higher PL quantum yields. Our research would provide deeper understanding of the mechanism of PL from gold nanoparticles as well as be beneficial for finding out optical imaging labels with high contrast.

We demonstrate an approach for easy fabrication of two-dimensional (2D) hexagonal and three-dimensional (3D) face-centered-cubic (fcc)-type photonic crystal (PhC) microstructures in a photosensitive polymer by applying a simple single refracting prism. This prism enables the splitting and recombining of a single incoming laser beam to form multiple-beam interference pattern simultaneously. Thus, antivibration equipment and complicated optical alignment system are not required, leading to a much more simple optical setup than previously reported laser holographic lithography techniques. Large-scale (over 1cm2) 2D hexagonal and 3D fcc-type PhCs have been produced. Reflection/transmission measurements performed on the fabricated 3D fcc-type PhC structures agree well with the corresponding band structure calculation.

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