Subwavelength imaging and detection using adjustable and movable droplet microlenses

Abstract

We developed adjustable and movable droplet microlenses consisting of a liquid with a high refractive index. The microlenses were prepared via ultrasonic shaking in deionized water, and the diameter of the microlenses ranged from 1 to 50 μm. By stretching the microlenses, the focal length can be adjusted from 13 to 25 μm. With the assistance of an optical tweezer, controllable assembly and movement of microlens arrays were also realized. The results showed that an imaging system combined with droplet microlenses could image 80 nm beads under white light illumination. Using the droplet microlenses, fluorescence emission at 550 nm from CdSe@ZnS quantum dots was efficiently excited and collected. Moreover, Raman scattering signals from a silicon wafer were enhanced by ∼ 19 times. The presented droplet microlenses may offer new opportunities for flexible liquid devices in subwavelength imaging and detection.

Optical Trapping, Sensing, and Imaging by Photonic Nanojets

“…In addition, a self-assembled high refractive index droplet microlens can enhance the Raman signal of Si wafers [115]. For bare silicon wafers or wafer regions without droplet microlenses, the detected Raman signal was very weak.…”

“…The microlenses can also be manipulated in three dimensions by the light force generated by the optical tweezers. In 2020, using an optical tweezers system, Chen et al moved C 10 H 7 Br microlenses of different diameters above the CdSe@ZnS quantum dots with an emission wavelength of 550 nm [115]. The quantum dots were excited by the light of a mercury lamp filter.…”

“…Moreover, the fiber probe can also act as a cantilever to improve the flexibility of imaging, using fiber tweezers to trap cells and scan the characters etched on the silicon substrate at a rate of ~20 µm/s [79], as shown in Figure 7f. Additionally, a 2 × 2 C 10 H 7 Br droplet microlens array was assembled using optical tweezers [115] and the assembled droplet microlens was transferred to the polystyrene nanoparticle surface of the stack, where the contour of the nanoparticle became apparent in the field of view of the microscope (Figure 7g). Allen et al [137] used high refractive index (n = 2) BaTiO 3 microspheres embedded in PDMS films to achieve large area imaging of 60 nm Au dimer spacing and 15 nm butterfly junction arrays.…”

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

“…Despite the promise held by all the above-discussed approaches, reliable and precise control of a dielectric microsphere’s morphology and refractive index profile can be challenging. This has spurred the search for microparticles with different shapes for tailored nanojet formation, including solid immersion lens [ 50 , 51 ], ellipsoids [ 52 , 53 ], disks [ 54 , 55 ], toroids [ 56 ], cuboids [ 57 , 58 ], axicons [ 59 , 60 ], and even customized optical fiber tips [ 61 , 62 ]. Among them, microcuboids offer ease of fabrication and enable nanojets with tuned properties by simply selecting the cube size [ 63 ].…”

Large-scale microlens arrays on flexible substrate with improved numerical aperture for curved integral imaging 3D display

“…MLAs have been widely used as key components in lots of optical systems 12 – 14 , such as integral imaging 15 , 16 , optical communications 17 , digital display 18 , detection 19 and far field imaging 20 . In particular, MLAs with good converging performance, great uniformity of focusing and good repeatability of geometry parameters in large-scale is of great important for the prototype and industrialization of integral image 3D display.…”