In advanced nanoscience, there is a strong desire to trap and detect nanoscale objects with high-throughput, single-nanoparticle resolution and high selectivity. Although emerging optical methods have enabled the selective trapping and detection of multiple micrometer-sized objects, it remains a great challenge to extend this functionality to the nanoscale. Here, we report an approach to trap and detect nanoparticles and subwavelength cells at low optical power using a parallel photonic nanojet array produced by assembling microlenses on an optical fiber probe. Benefiting from the subwavelength confinement of the photonic nanojets, tens to hundreds of nanotraps were formed in three dimensions. Backscattering signals were detected in real time with single-nanoparticle resolution and enhancement factors of 10(3)-10(4). Selective trapping of nanoparticles and cells from a particle mixture or human blood solution was demonstrated using the nanojet array. The developed nanojet array is potentially a powerful tool for nanoparticle assembly, biosensing, single-cell analysis, and optical sorting.

Due to their low‐symmetry lattice characteristics and intrinsic in‐plane anisotropy, 2D pentagonal materials, a new class of 2D materials composed entirely of pentagonal atomic rings, are attracting increasing research attention. However, the existence of these 2D materials has not been proven experimentally until the recent discovery of PdSe2. Herein, penta‐PdPSe, a new 2D pentagonal material with a novel low‐symmetry puckered pentagonal structure, is introduced to the 2D family. Interestingly, a peculiar polyanion of [SePPSe]4− is discovered in this material, which is the biggest polyanion in 2D materials yet discovered. Strong intrinsic in‐plane anisotropic behavior endows penta‐PdPSe with highly anisotropic optical, electronic, and optoelectronic properties. Impressively, few‐layer penta‐PdPSe‐based phototransistor not only achieves excellent electronic performances, a moderate electron mobility of 21.37 cm2 V−1 s−1 and a high on/off ratio of up to 108, but it also has a high photoresponsivity of ≈5.07 × 103 A W−1 at 635 nm, which is ascribed to the photogating effect. More importantly, penta‐PdPSe also exhibits a large anisotropic conductance (σmax/σmax = 3.85) and responsivity (Rmax/Rmin = 6.17 at 808 nm), superior to most 2D anisotropic materials. These findings make penta‐PdPSe an ideal material for the design of next‐generation anisotropic devices.

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.

Upconversion fluorescence has triggered extensive efforts in the past decade because of its superior physicochemical features and great potential in biomedical and biophotonic studies. However, practical applications of upconversion fluorescence are often hindered by its relatively low luminescence efficiency (<1%). Here, we employ a living yeast or human cell as a natural bio-microlens to enhance the upconversion fluorescence. The natural bio-microlens, which was stably trapped on a fiber probe, could concentrate the excitation light into a subwavelength region so that the upconversion fluorescence of core-shell NaYF:Yb/Tm nanoparticles was enhanced by 2 orders of magnitude. As a benefit of the fluorescence enhancement, single-cell imaging and real-time detection of the labeled pathogenic bacteria, such as Escherichia coli and Staphylococcus aureus, were successfully achieved in the dark fields. This biocompatible, sensitive, and miniature approach could provide a promising powerful tool for biological imaging, biophotonic sensing, and single-cell analysis.

Optical nanoprobes, designed to emit or collect light in the close proximity of a sample, have been extensively used to sense and image at nanometer resolution. However, the available nanoprobes, constructed from artificial materials, are incompatible and invasive when interfacing with biological systems. In this work, we report a fully biocompatible nanoprobe for subwavelength probing of localized fluorescence from leukemia single-cells in human blood. The bioprobe is built on a tapered fiber tip apex by optical trapping of a yeast cell (1.4 μm radius) and a chain of Lactobacillus acidophilus cells (2 μm length and 200 nm radius), which act as a high-aspect-ratio nanospear. Light propagating along the bionanospear can be focused into a spot with a full width at half-maximum (fwhm) of 190 nm on the surface of single cells. Fluorescence signals are detected in real time at subwavelength spatial resolution. These noninvasive and biocompatible optical probes will find applications in imaging and manipulation of biospecimens.