Optical methods to manipulate and detect nanoscale objects are highly desired in both nanomaterials and molecular biology fields. Optical tweezers have been used to manipulate objects that range in size from a few hundred nanometres to several micrometres. The emergence of near-field methods that overcome the diffraction limit has enabled the manipulation of objects below 100 nm. A highly free manipulation with signal-enhanced real-time detection, however, remains a challenge for single sub-100-nm nanoparticles or biomolecules. Here we show an approach that uses a photonic nanojet to perform the manipulation and detection of single sub-100-nm objects. With the photonic nanojet generated by a dielectric microlens bound to an optical fibre probe, three-dimensional manipulations were achieved for a single 85-nm fluorescent polystyrene nanoparticle as well as for a plasmid DNA molecule. Backscattering and fluorescent signals were detected with the enhancement factors up to ∼10³ and ∼30, respectively. The demonstrated approach provides a potentially powerful tool for nanostructure assembly, biosensing and single-biomolecule studies.

Optical manipulation and detection of nanoscale biospecimen, such as organic nanoparticles, biomolecules, bacterial viruses, and subcellular nanostructures, is crucial in numerous biomedical and biological applications. Traditional lens-based free-space techniques for optical manipulation and detection are limited by their bulky systems and the inherent diffraction limit of light. Micro/nano optical fibers are promising candidates to overcome these issues because of their compact structure, flexibility, high sensitivity, and sub-diffraction-limit confinement. In this review, we focused on recent advances in nanoscale manipulation and biological detection using optical fibers, ranging from the fundamentals to applications for biological exploration, such as nanoparticle delivery and detection, single-molecule trapping and sensing, and single-cell manipulation and analysis. Different kinds of optical fibers were discussed in this review, including tapered fibers, plasmonic fibers, microlens-based fibers, nanofibers, and hollow fibers. We aim for this review to highlight current trends and future direction for applications of optical fibers for nanomanipulation and biodetection.

Using a single biological element as a photonic component with well-defined features has become a new intriguing paradigm in biophotonics. Here we show that endogenous lipid droplets in the mature adipose cells can behave as fully biocompatible microlenses to strengthen the ability of microscopic imaging as well as detecting intra- and extracellular signals. By the assistance of biolenses made of the lipid droplets, enhanced fluorescence imaging of cytoskeleton, lysosomes, and adenoviruses has been achieved. At the same time, we demonstrated that the required excitation power can be reduced by up to 73%. The lipidic microlenses are finely manipulated by optical tweezers in order to address targets and perform their real-time imaging inside the cells. An efficient detecting of fluorescence signal of cancer cells in extracellular fluid was accomplished due to the focusing effect of incident light by the lipid droplets. The lipid droplets acting as endogenous intracellular microlenses open the intriguing route for a multifunctional biocompatible optics tool for biosensing, endoscopic imaging, and single-cell diagnosis.