Optical tweezers have enabled a number of microscale processes such as single cell handling, flow-cytometry, directed assembly, and optical chromatography. To extend this functionality to the nanoscale, a number of near-field approaches have been developed that yield much higher optical forces by confining light to subwavelength volumes. At present, these techniques are limited in both the complexity and precision with which handling can be performed. Here, we present a new class of nanoscale optical trap exploiting optical resonance in one-dimensional silicon photonic crystals. The trapping of 48 nm and 62 nm dielectric nanoparticles is demonstrated along with the ability to transport, trap, and manipulate larger nanoparticles by simultaneously exploiting the propagating nature of the light in a coupling waveguide and its stationary nature within the resonator. Field amplification within the resonator is shown to produce a trap several orders of magnitude stronger than conventional tweezers and an order of magnitude stiffer than other near-field techniques. Our approach lays the groundwork for a new class of optical trapping platforms that could eventually enable complex all-optical single molecule manipulation and directed assembly of nanoscale material.

Optical techniques have proven to be well suited for in situ biomolecular sensing because they enable high fidelity measurements in aqueous environments, are minimally affected by background solution pH or ionic strength, and facilitate label-free detection. Recently, there has been significant interest in developing new classes of optically resonant biosensors possessing very high quality-factors. This high quality-factor enables them to resolve the presence of very small amounts of bound mass and leads to very low limits of detection. A drawback of these devices is that the majority of the resonant electromagnetic energy is confined within the solid light-guiding structure thus limiting the degree to which it overlaps with the bound matter. This in turn lowers the ultimate device sensitivity, or the change in output signal in response to changes in bound mass. Here we present a novel optofluidic biosensor platform that incorporates a unique one-dimensional photonic crystal resonator array which enables significantly stronger light-matter interaction. We show here how this, coupled with the ability of planar photonic crystals to spatially localize the optical field to mode volumes on the order of a wavelength cubed, enables a limit of detection on the order of 63 ag total bound mass (estimated using a polyelectrolyte growth model) and a device sensitivity an order of magnitude better than similar devices. The multiplexing capabilities of our sensor are demonstrated by the individual and concurrent detection of interleukins 4, 6 and 8 using a sandwich assay.

In this article we review the use of near-field photonics for trapping, transport and handling of nanomaterials. While the advantages of traditional optical tweezing are well known at the microscale, direct application of these techniques to the handling of nanoscale materials has proven difficult due to unfavourable scaling of the fundamental physics. Recently a number of research groups have demonstrated how the evanescent fields surrounding photonic structures like photonic waveguides, optical resonators, and plasmonic nanoparticles can be used to greatly enhance optical forces. Here, we introduce some of the most common implementations of these techniques, focusing on those which have relevance to microfluidic or optofluidic applications. Since the field is still relatively nascent, we spend much of the article laying out the fundamental and practical advantages that near field optical manipulation offers over both traditional optical tweezing and other particle handling techniques. In addition we highlight three application areas where these techniques namely could be of interest to the lab-on-a-chip community, namely: single molecule analysis, nanoassembly, and optical chromatography.

Next generation biosensor platforms will require significant improvements in sensitivity, specificity and parallelity in order to meet the future needs of a variety of fields ranging from in vitro medical diagnostics, pharmaceutical discovery and pathogen detection. Nano-biosensors, which exploit some fundamental nanoscopic effect in order to detect a specific biomolecular interaction, have now been developed to a point where it is possible to determine in what cases their inherent advantages over traditional techniques (such as nucleic acid microarrays) more than offset the added complexity and cost involved constructing and assembling the devices. In this paper we will review the state of the art in nanoscale biosensor technologies, focusing primarily on optofluidic type devices but also covering those which exploit fundamental mechanical and electrical transduction mechanisms. A detailed overview of next generation requirements is presented yielding a series of metrics (namely limit of detection, multiplexibility, measurement limitations, and ease of fabrication/assembly) against which the various technologies are evaluated. Concluding remarks regarding the likely technological impact of some of the promising technologies are also provided.

In this paper we introduce Nanoscale Optofluidic Sensor Arrays (NOSAs), which are an optofluidic architecture for performing highly parallel, label free detection of biomolecular interactions in aqueous environments. The architecture is based on the use of arrays of 1D photonic crystal resonators which are evanescently coupled to a single bus waveguide. Each resonator has a slightly different cavity spacing and is shown to independently shift its resonant peak in response to changes in refractive index in the region surrounding its cavity. We demonstrate through numerical simulation that by confining biomolecular binding to this region, limits of detection on the order of tens of attograms (ag) are possible. Experimental results demonstrate a refractive index (RI) detection limit of 7 x 10(-5) for this device. While other techniques such as SPR possess a equivalent RI detection limit, the advantage of this architecture lies in its potential for low mass limit of detection which is enabled by confining the size of the probed surface area.